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Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Chaps,
Just wondering if anyone has any experience. Given I have some days off I might do this. Have a couple of 4" bass units and a tweeter kicking around the garage and the desire that _anything_ must be better as a centre speaker than a horrid injection molded plastic speaker that came with the (oldish TV). Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. Pete |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
Peter Chant wrote:
Chaps, Just wondering if anyone has any experience. Given I have some days off I might do this. Have a couple of 4" bass units and a tweeter kicking around the garage and the desire that _anything_ must be better as a centre speaker than a horrid injection molded plastic speaker that came with the (oldish TV). Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. Pete I would be more concerned with the crossover. Is it going to br MTM ? I made a center design over 15 years ago. It worked well, and I got my desired pattern. I didn't use it as a bass though. They were a bit smaller than 4 inch. I used a common enclosure, sealed, with plenty of interior damping, and front panel antidefraction. Greg |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
"Peter Chant" wrote in message
... Chaps, Just wondering if anyone has any experience. Given I have some days off I might do this. Have a couple of 4" bass units and a tweeter kicking around the garage and the desire that _anything_ must be better as a centre speaker than a horrid injection molded plastic speaker that came with the (oldish TV). Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. Are you trying to achieve bass or just better/louder audio? If you are wanting bass (and TV sound is as good - some say better - than FM radio) then you might want to consider using signal level filtering and then driving both speakers with one amp in one enclosure. If you are wanting to achieve better audio quality in stereo the two enclosures physically separated and driven is a better choice. Remember that ultimately it is all about moving air and up to around 120Hz (some say 150Hz) there is little directionality so a common so-called sub-bass unit is a good option in this situation as each driver will only have to do half the work. One thing not to overlook: how will adjust volume levels? If your TV has the option of feeding audio out at line level that is volume controlled then you don't have a problem - although you say it is an older TV so this is unlikely as it is only a feature that has come in over the last maybe five years or so with the larger takeup of home cinema. If this is the case then you have to use the TV headphone output with all its attendant noise and distortion which begs the question of whether it is worth doing in the first place. Assuming you have a LCD/Plasma TV even if it is old, have you considered fitting deflectors under the (usually) downward facing speakers to direct the sound to you viewing position? You'd be surprised how much difference such a small change can make. -- Woody harrogate three at ntlworld dot com |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Peter Chant wrote:
Just wondering if anyone has any experience. Given I have some days off I might do this. Have a couple of 4" bass units and a tweeter kicking around the garage and the desire that _anything_ must be better as a centre speaker than a horrid injection molded plastic speaker that came with the (oldish TV). Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. ** Long as the 4 inch drivers are closely similar, using a common enclosure and one port is the way to go. The Bose 802 ( pro audio version of the 901 ) used 8 x 4 inch drivers and two ports - not that it is any shining example of design. Seriously, one large port IS better than two smaller ones - less losses and wind noise ie chuffing. If you have the basic TS parameters for the drivers ( Vas,Fs and Qs) and pop them into WinISD Beta you can easily see how altering the box volume and port frequency changes things. .... Phil |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/09/2014 07:08 AM, gregz wrote:
I would be more concerned with the crossover. Is it going to br MTM ? I made a center design over 15 years ago. It worked well, and I got my desired pattern. I didn't use it as a bass though. They were a bit smaller than 4 inch. I used a common enclosure, sealed, with plenty of interior damping, and front panel antidefraction. Likely MTM - unless there is a brighter idea. Got a large CRT TV at present. Will likely look at size suitable to stand a likely LCD on it for the day when the CRT breaks. Of course acoustic parameters are a prime driver for box size as well. Crossover Mk1 will be some caps I have in the garage and some wire likely wound around a cardboard former. However, in future I can have a play with active, actually designing it properly etc. My thinking for the future would be that a plan might be to run the two bass speakers as one up until they hit a frequency where their distance apart might become problematic, then roll one off. Small is good for this case. Bass/Tweeter as normal. I have a 2 channel power-amp spare - but 3 would be ideal if active! antidefraction? Do you mean round the edges and stand the grill off of the front baffle? Pete |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/09/2014 07:53 AM, Woody wrote:
Are you trying to achieve bass or just better/louder audio? Probably should have explained the situation a little more. Currently have CRT TV. DVD player / laptop (if worth using) feeding into a cheap 5.1 decoder. Don't us it much, but nice on the odd occasion. Fronts are the two floor-standers in my hifi. Rears are a pair of home-made bookshelf speakers (largish) that seem surprisingly good given the lack of design that when into making them. Centre speaker is a horrid 1 way piece of plastic injection moulding with likely the cheapest speaker they could fit in. In comparison to anything else in the room it sounds compressed, narrowband and generally awful. This arrangement is ad-hoc, lacks ergonomics, but apart from the cheap surround decoder it consists of things I already own. Replacing the centre will make a large difference. Not looking for perfection, but a large improvement is easy. I could ebay a centre I or I could use the drivers lying around the garage. If you are wanting bass (and TV sound is as good - some say better - than FM radio) then you might want to consider using signal level filtering and then driving both speakers with one amp in one enclosure. If you are wanting to achieve better audio quality in stereo the two enclosures physically separated and driven is a better choice. Floor-standers on the fronts. I seriously need to move into a detached house, away from neighbours before I think about more bass. Remember that ultimately it is all about moving air and up to around 120Hz (some say 150Hz) there is little directionality so a common so-called sub-bass unit is a good option in this situation as each driver will only have to do half the work. I did wonder whether I should mix the sub channel into the fronts. However, I already have plenty of bass to the extent that I have considered turning it down for movies. One thing not to overlook: how will adjust volume levels? If your TV has the option of feeding audio out at line level that is volume controlled then you don't have a problem - although you say it is an older TV so this is unlikely as it is only a feature that has come in over the last maybe five years or so with the larger takeup of home cinema. If this is the case then you have to use the TV headphone output with all its attendant noise and distortion which begs the question of whether it is worth doing in the first place. Hifi - knob on pre-amp. Rears, knob on integrated amp. Centre knob on gutted home made pre-amp. All from 5.1 decoder. A pain in the arse, but it does work. If keen then Alps six gang pots are going on ebay for 12 quid. Assuming you have a LCD/Plasma TV even if it is old, have you considered fitting deflectors under the (usually) downward facing speakers to direct the sound to you viewing position? You'd be surprised how much difference such a small change can make. Not tried that - not applicable in my situation. If I get chance I'll try that somewhere else. |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Peter Chant wrote:
My thinking for the future would be that a plan might be to run the two bass speakers as one up until they hit a frequency where their distance apart might become problematic, then roll one off. ** If you put the two woofers in series, that will make the impedance 16 ohms and increase effective the amplifier power rating - then put say a 20uF cap across one of them. The impedance will drop towards 8ohms above 1 kHz and the no cap driver gets 6dB more level - just what you need to maintain flat response. ..... Phil |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/09/2014 12:22 PM, Phil Allison wrote:
Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. ** Long as the 4 inch drivers are closely similar, using a common enclosure and one port is the way to go. Two Audax AT100M0 drivers. Found data sheets on-line last night. http://www.audax.com/archives/AT100M...gue%201994.pdf I love the internet, that info would have been harder to get hold of when I bought the drivers. Don't speak French so ringing them up might not have gone well. The Bose 802 ( pro audio version of the 901 ) used 8 x 4 inch drivers and two ports - not that it is any shining example of design. Seriously, one large port IS better than two smaller ones - less losses and wind noise ie chuffing. Less surface area of the port compared to its volume / area - makes sense. Suppose front / back is unimportant. Back is probably neater if I have one port only. If you have the basic TS parameters for the drivers ( Vas,Fs and Qs) and pop them into WinISD Beta you can easily see how altering the box volume and port frequency changes things. Don't run windows if that is a windows program. Probably could run it under wine. There seem to be plenty of on-line calculators. I have a few 'cookbook' type design books as well, so if I have the parameters I could also try them. Given that these two tiny 4in paper drivers are a lot smaller than the twin 6.5in polypropylene ones in my mains and that the centre is running speech not full range I wonder if I ought to try something else? I wonder what happens if build some sealed enclosures which are slightly larger than normal to give a Q of around 1 so there is no rise in the bass before they roll off. Would that avoid boominess that I might get with ported boxes or if I used a Q of 0.7? http://www.diyaudioandvideo.com/Calculator/Box/ I've worked this out* for a _single_ driver. (* got someone else's website to do it for me) Sealed Box Q=1 Vas = 4.41 lts fs = 64 Hz Qts = 0.48 Qtc = 1 Dimensions Vb = 0.05 ft3 = 1.32 lts = L x W x H f3 = 104.82 Hz fb = 133.33 Hz That seems rather With the more normal Q of 0.707 I get: Sealed Box Q=0.707 Vas = 4.41 lts fs = 64 Hz Qts = 0.48 Qtc = 0.707 Dimensions Vb = 0.13 ft3 = 3.77 lts = L x W x H f3 = 94.28 Hz fb = 94.27 Hz Vb: Speaker Box Internal Volume f3: 3dB Cutoff Frequency fb: Enclosure Resonant Frequency Annoyingly I can't find my books. Website recommends a ported enclosure - perhaps I should follow that advice: http://www.diyaudioandvideo.com/Calc.../SealedPorted/ Ported. Guess cone dia at 3.5in. (can't be bothered to find a rule right now) Ported Box Vas = 4.41 lts fs = 64 Hz Qts = 0.48 D = 3.5 in Dimensions Vb = 0.28 ft3 = 7.83 lts = L x W x H f3 = 49.72 Hz fb = 53.57 Hz Dv = 1 in = 2.5 cm Lv = 1.85 in = 4.53 cm Or I could just read the datasheet which gives various box volumes and port sizes underneath a chart showing the various frequency responses... Volume anywhere between 1.7 and 10lt! I suppose the manufacturerintended this to be used in ported boxes. This is of course for a single driver. So I do need to do the sums for a twin driver enclosure - unless I simply make two single driver boxes side by side. Assuming doubling Vas is all I need to do then running that through the last website gives: Ported Box Vas = 8.82 lts fs = 64 Hz Qts = 0.48 D = 3.5 in Dimensions Vb = 0.55 ft3 = 15.65 lts = L x W x H f3 = 49.72 Hz fb = 53.57 Hz Dv = 1 in = 2.5 cm Lv = 0.53 in = 1.26 cm Hmm. Double the size but I do save 1/2p making a shorter port... |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/09/2014 11:06 PM, Phil Allison wrote:
Peter Chant wrote: My thinking for the future would be that a plan might be to run the two bass speakers as one up until they hit a frequency where their distance apart might become problematic, then roll one off. ** If you put the two woofers in series, that will make the impedance 16 ohms and increase effective the amplifier power rating - then put say a 20uF cap across one of them. The impedance will drop towards 8ohms above 1 kHz and the no cap driver gets 6dB more level - just what you need to maintain flat response. Interesting thought. Does that not kill the electrical damping from the amp, as at resonance each speaker sees mainly the impedance of the other speaker rather than the low impedance amp output. Or if using a ported enclosure does that not matter? Just found my copy of the Loudspeaker Design Cookbook. Perhaps I ought to re-read part of it. Hmm, if I don't care about looks I could use a push pull format with the driver facing towards me being the one with the mid frequency roll off. Also, if it is going to be ugly then I can just glue and screw some MDF or ply and do it in a day! More thoughts - once going unsymmetrical why not go isobaric? Do I want to roll off the rear - hidden driver? Given the calcs give a 3.5lt enclosure can I keep a small enough volume between the two drivers for it to not be significant? If I want to stand a TV on it it may be too small. Another design issue has surfaced. Usual practice seems to be to mount the flange of the speaker on the front face of the fron baffle - so the speaker is not recessed. However, the spider is so shallow that 1/2 of ply/ MDF will largely block off the holes in the spider! Pete |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
In article ,
Peter Chant wrote: Likely MTM - unless there is a brighter idea. Got a large CRT TV at present. Will likely look at size suitable to stand a likely LCD on it for the day when the CRT breaks. Of course acoustic parameters are a prime driver for box size as well. You might find it a problem sighting a speaker with a powerful magnet close to a CRT set. -- *Can atheists get insurance for acts of God? * Dave Plowman London SW To e-mail, change noise into sound. |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
Just as a thought, have you considered trying one or both
speakers (series or parallel) on an open baffle to see what they sound like? If you are not wanting bass then a piece of wood maybe a foot or so square might be a starting point? I once tried it with a drawer from an old dresser which had a thicker than might be expected floor panel. Worked surprisingly well. -- Woody harrogate three at ntlworld dot com |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
"Woody" wrote:
"Peter Chant" wrote in message ... Chaps, Just wondering if anyone has any experience. Given I have some days off I might do this. Have a couple of 4" bass units and a tweeter kicking around the garage and the desire that _anything_ must be better as a centre speaker than a horrid injection molded plastic speaker that came with the (oldish TV). Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. Are you trying to achieve bass or just better/louder audio? If you are wanting bass (and TV sound is as good - some say better - than FM radio) then you might want to consider using signal level filtering and then driving both speakers with one amp in one enclosure. If you are wanting to achieve better audio quality in stereo the two enclosures physically separated and driven is a better choice. Remember that ultimately it is all about moving air and up to around 120Hz (some say 150Hz) there is little directionality so a common so-called sub-bass unit is a good option in this situation as each driver will only have to do half the work. One thing not to overlook: how will adjust volume levels? If your TV has the option of feeding audio out at line level that is volume controlled then you don't have a problem - although you say it is an older TV so this is unlikely as it is only a feature that has come in over the last maybe five years or so with the larger takeup of home cinema. If this is the case then you have to use the TV headphone output with all its attendant noise and distortion which begs the question of whether it is worth doing in the first place. Assuming you have a LCD/Plasma TV even if it is old, have you considered fitting deflectors under the (usually) downward facing speakers to direct the sound to you viewing position? You'd be surprised how much difference such a small change can make. Ha, I taped cardboard under my tv to reflect. It works. Greg |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
Peter Chant wrote:
On 12/09/2014 12:22 PM, Phil Allison wrote: Probably making a vented enclosure. Is it better put the drivers in a single enclosure or to make essentially two separate enclosures side by side? Can't really think of any pros and cons except to do the sums and see if the box sizes are realistic. ** Long as the 4 inch drivers are closely similar, using a common enclosure and one port is the way to go. Two Audax AT100M0 drivers. Found data sheets on-line last night. http://www.audax.com/archives/AT100M...gue%201994.pdf I love the internet, that info would have been harder to get hold of when I bought the drivers. Don't speak French so ringing them up might not have gone well. The Bose 802 ( pro audio version of the 901 ) used 8 x 4 inch drivers and two ports - not that it is any shining example of design. Seriously, one large port IS better than two smaller ones - less losses and wind noise ie chuffing. Less surface area of the port compared to its volume / area - makes sense. Suppose front / back is unimportant. Back is probably neater if I have one port only. If you have the basic TS parameters for the drivers ( Vas,Fs and Qs) and pop them into WinISD Beta you can easily see how altering the box volume and port frequency changes things. Don't run windows if that is a windows program. Probably could run it under wine. There seem to be plenty of on-line calculators. I have a few 'cookbook' type design books as well, so if I have the parameters I could also try them. Given that these two tiny 4in paper drivers are a lot smaller than the twin 6.5in polypropylene ones in my mains and that the centre is running speech not full range I wonder if I ought to try something else? I wonder what happens if build some sealed enclosures which are slightly larger than normal to give a Q of around 1 so there is no rise in the bass before they roll off. Would that avoid boominess that I might get with ported boxes or if I used a Q of 0.7? http://www.diyaudioandvideo.com/Calculator/Box/ I've worked this out* for a _single_ driver. (* got someone else's website to do it for me) Sealed Box Q=1 Vas = 4.41 lts fs = 64 Hz Qts = 0.48 Qtc = 1 Dimensions Vb = 0.05 ft3 = 1.32 lts = L x W x H f3 = 104.82 Hz fb = 133.33 Hz That seems rather With the more normal Q of 0.707 I get: Sealed Box Q=0.707 Vas = 4.41 lts fs = 64 Hz Qts = 0.48 Qtc = 0.707 Dimensions Vb = 0.13 ft3 = 3.77 lts = L x W x H f3 = 94.28 Hz fb = 94.27 Hz Vb: Speaker Box Internal Volume f3: 3dB Cutoff Frequency fb: Enclosure Resonant Frequency Annoyingly I can't find my books. Website recommends a ported enclosure - perhaps I should follow that advice: http://www.diyaudioandvideo.com/Calc.../SealedPorted/ Ported. Guess cone dia at 3.5in. (can't be bothered to find a rule right now) Ported Box Vas = 4.41 lts fs = 64 Hz Qts = 0.48 D = 3.5 in Dimensions Vb = 0.28 ft3 = 7.83 lts = L x W x H f3 = 49.72 Hz fb = 53.57 Hz Dv = 1 in = 2.5 cm Lv = 1.85 in = 4.53 cm Or I could just read the datasheet which gives various box volumes and port sizes underneath a chart showing the various frequency responses... Volume anywhere between 1.7 and 10lt! I suppose the manufacturerintended this to be used in ported boxes. This is of course for a single driver. So I do need to do the sums for a twin driver enclosure - unless I simply make two single driver boxes side by side. Assuming doubling Vas is all I need to do then running that through the last website gives: Ported Box Vas = 8.82 lts fs = 64 Hz Qts = 0.48 D = 3.5 in Dimensions Vb = 0.55 ft3 = 15.65 lts = L x W x H f3 = 49.72 Hz fb = 53.57 Hz Dv = 1 in = 2.5 cm Lv = 0.53 in = 1.26 cm Hmm. Double the size but I do save 1/2p making a shorter port... You could try a little series resistance on the woofers to push up the Qts and be more suitable for closed box? This probably will not help you, but here was my quest. 15 years ago ? http://www.pitt.edu/~szekeres/center.htm Greg |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Peter Chant wrote:
** If you put the two woofers in series, that will make the impedance 16 ohms and increase effective the amplifier power rating - then put say a 20uF cap across one of them. The impedance will drop towards 8ohms above 1 kHz and the no cap driver gets 6dB more level - just what you need to maintain flat response. Interesting thought. Does that not kill the electrical damping from the amp, as at resonance each speaker sees mainly the impedance of the other speaker ** Nonsense. The two drivers do not act independently so no such scenario can exist. Just found my copy of the Loudspeaker Design Cookbook. Perhaps I ought to re-read part of it. ** Read it all again if you ****ing like. Won't mean a thing to a narcissistic, know nothing nutter like you. .... Phil |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/10/2014 07:46 AM, gregz wrote:
You could try a little series resistance on the woofers to push up the Qts and be more suitable for closed box? Interesting. This might actually reduce the influence of the amp and cables. I have one book which I cannot find which was obsessed with measuring the amp impedance and matching the speaker to the amp. This probably will not help you, but here was my quest. 15 years ago ? http://www.pitt.edu/~szekeres/center.htm Not far from what I have in mind. Thanks. Might go push-pull as there seems to be pros and the cons are that they are a little ugly. |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/10/2014 06:15 AM, Woody wrote:
Just as a thought, have you considered trying one or both speakers (series or parallel) on an open baffle to see what they sound like? If you are not wanting bass then a piece of wood maybe a foot or so square might be a starting point? No. If I do that I'll have to put a foot on the bottom. Perhaps sides... Actually if I put a foot on the bottom then the speakers are near the screen and effectively the TV is part of the baffle. Apart from making sure it does not fall off the TV there are few reasons not to try this. I once tried it with a drawer from an old dresser which had a thicker than might be expected floor panel. Worked surprisingly well. |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/10/2014 12:44 AM, Dave Plowman (News) wrote:
In article , Peter Chant wrote: Likely MTM - unless there is a brighter idea. Got a large CRT TV at present. Will likely look at size suitable to stand a likely LCD on it for the day when the CRT breaks. Of course acoustic parameters are a prime driver for box size as well. You might find it a problem sighting a speaker with a powerful magnet close to a CRT set. The bass drivers are sheilded. |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
Peter Chant wrote:
On 12/10/2014 07:46 AM, gregz wrote: You could try a little series resistance on the woofers to push up the Qts and be more suitable for closed box? Interesting. This might actually reduce the influence of the amp and cables. I have one book which I cannot find which was obsessed with measuring the amp impedance and matching the speaker to the amp. This probably will not help you, but here was my quest. 15 years ago ? http://www.pitt.edu/~szekeres/center.htm Not far from what I have in mind. Thanks. Might go push-pull as there seems to be pros and the cons are that they are a little ugly. You can probably find programs that you can add series resistance and find output results. I used an old dos program. A little resistance will not change efficiency much but will change low end results. Greg |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
"Peter Chant" wrote in message
... On 12/10/2014 07:46 AM, gregz wrote: You could try a little series resistance on the woofers to push up the Qts and be more suitable for closed box? Interesting. This might actually reduce the influence of the amp and cables. I have one book which I cannot find which was obsessed with measuring the amp impedance and matching the speaker to the amp. I can understand that approach with a valve amp where there is an output transformer involved, but matching with a transistor amp? Eh? The main factor with a transistor amp is having a power supply that could deliver the (often short term) currents needed. JLH proved it could be done easily by having a regulated PSU. In the '80s I built a dual mono power MOSFET amp with regulated supplies a la JLH and tests showed it would do 110W into 8R and 220W into 4R - which is what it is all about. [I would still be using it today save it has developed a dc offset problem on one channel and I have never had the time to sit down and find out why.] I had a pair of the Bailey designed transmission line speakers at the time (rather like the Imhoff TLS80] and that could rattle windows at 10 paces with that amp! A few decades ago there was an obsession with getting the amp output impedance as low as possible to increase the damping factor, until someone - could have been JLH or Doug Self or someone like that - proved that it is easy to over damp a circuit. Indeed the lower the amp output impedance becomes the more effect the resistance of the interconnecting cable has which was why I believe there was a move to direct amping. I believe it was only with increasingly powerful computer modelling that it was discovered that much could be achieved by better driver, cabinet, and particularly crossover design and at the same time more could be made of signal level filtration so bi or tri-amping became popular and to an extent survives today (although very little in the UK from what I read.) As a result of the work on crossovers, in my very limited experience you will often find a small series resistor on the output of the bass section of a crossover. Now I know this will be contentious, but from what I heard years ago the Motional Feedback speaker marketed by Philips did far more to achieve purity of (bass) sound than anything I've ever heard. I remember going to one of the hi-fi shows in Harrogate probably in the '70s. I walked into the ballroom at the Old Swan Hotel (of Agatha Christie fame) as I could hear what I thought was a brass band playing - possibly Grimethorpe - so you can imagine my surprise when all I saw was two MFB loudspeakers. Staggered was not the word. The only reason that I can think they never took off was (a) the price which compared with the price of some so-called hi-fi kit these days would now be seen as cheap and (b) because it was done by Philips who were not perceived to have hi-fi capability. I often wonder what would have become of the technique if the design had been done by someone like an early Linn? -- Woody harrogate three at ntlworld dot com |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
In article , Woody
wrote: "Peter Chant" wrote in message ... On 12/10/2014 07:46 AM, gregz wrote: You could try a little series resistance on the woofers to push up the Qts and be more suitable for closed box? Interesting. This might actually reduce the influence of the amp and cables. I have one book which I cannot find which was obsessed with measuring the amp impedance and matching the speaker to the amp. I can understand that approach with a valve amp where there is an output transformer involved, but matching with a transistor amp? Eh? I'm not clear what "matching" means above. An engineer would probably assume "arrange for the two impedances to be equal". However it may have been used more vaguely, akin to "suit one another" in some other way. The normal view is that the required output pressure-time pattern is defined by the *voltage*-time pattern the amp asserts at the terminal of a speaker system. Then its the job of the ampliier to supply what current the speaker demands for that voltage to be applied. The complications are of course, thing like the difference between speaker units and complete speaker systems and effects of items like crossover newtworks, etc, and how they are taken into account. "Matching" in the "make impedances the same" respect seems odd given how much the impedance of a typical speaker will vary with frequency. Also likely to vary with other factors. I guess this is why people adopted the presumption for "the voltage defines the waveform and you then supply the demanded current". Now I know this will be contentious, but from what I heard years ago the Motional Feedback speaker marketed by Philips did far more to achieve purity of (bass) sound than anything I've ever heard. I remember going to one of the hi-fi shows in Harrogate probably in the '70s. I walked into the ballroom at the Old Swan Hotel (of Agatha Christie fame) as I could hear what I thought was a brass band playing - possibly Grimethorpe - so you can imagine my surprise when all I saw was two MFB loudspeakers. Staggered was not the word. The only reason that I can think they never took off was (a) the price which compared with the price of some so-called hi-fi kit these days would now be seen as cheap and (b) because it was done by Philips who were not perceived to have hi-fi capability. I often wonder what would have become of the technique if the design had been done by someone like an early Linn? A snag which may have held back MFB is the need to buy the speakers and amp as a package deal. This means losing some degree of choice, then and in the future. And how many makers make good speakers *and* good amplifiers? Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
On Thu, 11 Dec 2014 08:11:05 -0000, "Woody"
wrote: "Peter Chant" wrote in message ... On 12/10/2014 07:46 AM, gregz wrote: You could try a little series resistance on the woofers to push up the Qts and be more suitable for closed box? Interesting. This might actually reduce the influence of the amp and cables. I have one book which I cannot find which was obsessed with measuring the amp impedance and matching the speaker to the amp. I can understand that approach with a valve amp where there is an output transformer involved, but matching with a transistor amp? Eh? The main factor with a transistor amp is having a power supply that could deliver the (often short term) currents needed. JLH proved it could be done easily by having a regulated PSU. In the '80s I built a dual mono power MOSFET amp with regulated supplies a la JLH and tests showed it would do 110W into 8R and 220W into 4R - which is what it is all about. [I would still be using it today save it has developed a dc offset problem on one channel and I have never had the time to sit down and find out why.] I had a pair of the Bailey designed transmission line speakers at the time (rather like the Imhoff TLS80] and that could rattle windows at 10 paces with that amp! I was designing and building PA amps back in the 70s which absolutley relied on tight PSU voltage regulation to avoid blowing my chosen output transistors (Motorola 2015s recovered from Gvt surplus acquired analogue Computer PSU fan cooled heatsink assemblies - twenty to a fan cooled heatsink module) which weren't particularly good performers slew rate wise and only had a max Vce of 60 volts. By using a 45v 10A analogue voltage regulated supply for each channel (again, using more of those Motorola 2015s) along with a solid state version of the polyfuse (yet another 2015) of my own invention and using a bridge output amplifier design, I was able to make a 200W RMS per 4 ohm load stereo power amplifier (800W PMPO in the language of cheap hi fi except that it was sustained PMPO as in a total of 400W of 500Hz square wave into 4 ohm resistor loads on each channel). I modified my 'electronic polyfuse' so that its overload point varied according to the signal output voltage so that it only peaked at the ten amp setting when full output voltage was present, effectively turning it into an impedance overload protection system (at zero or low voltage output, the trip current was set for a more modest 2 or 3 amps to avoid a halfway condition that would otherwise be guaranteed to burn out the transistors at low to mid volumes if a short circuit were to develop across the speaker output terminals). You knew without any ambiguity, typical of the "output protection' drive limiting nonsense circuits used on a lot of commercial home hi-fi systems, when the amp had suffered such an overload by the fact that the output would go silent and the peak indicator lamp went to a permanent glow (normally extinguished other than for brief faint flashes if you were driving it to the _actual_ voltage clipping limit on bass peaks). Resetting was just a matter of removing the overload (unplugging the appropriate speaker cable). Now, in spite of the merits of regulated voltage rails for the output stages of a Hi-Fi amplifier, there's also some merit to the use of completely unregulated analogue PSUs, provided the output devices have an ample margin of voltage rating. PMPO ratings have some validity in that real music very rarely contains sustained notes that need to be of higher amplitude than the transient peaks in the rest of the mix. Since transient peaks can easily exceed the maximum peaks of bass notes that can be auditioned at realistically loud levels by some 10 to 20dB, the transient high energy reserve in the analogue PSU's smoothing capacitors can be put to very good use to allow such transient peaks in the music to be reproduced with less clipping distortion, for a PSU with a given sustained maximum power rating. The difference in performance between two amplifiers with the same PMPO rating, one using a regulated PSU where the PMPO can be sustained indefinitely and the other using an unregulated PSU where the PMPO can't be sustained for more than a few milliseconds may be indistinguishable with real music sources, especially so with a lot of orchestral classical works using traditional acoustic instruments (organ recitals, otoh, are a different kettle of fish, more akin to the modern electronic instrumentation of rock and pop music). The amp using a regulated PSU will have a continous rating two or three times that of the unregulated one. Sticking to analogue PSUs, this makes the unregulated PSU option considerably cheaper to manufacture yet still capable of reproducing the maximum sound level peaks of the more expensive amp on most classical music recordings (organ recitals excepted). Incidently, my clip montoring circuit wasn't reliant on using a regulated PSU, it would work equally well with an unregulated supply. This is an important consideration in that all you really need to know about the volume setting is that it sounds loud enough and yet isn't running into clipping (or severe clipping - at very high acoustic power levels, your inner ear could be producing such clipping artifacts indistinguishable from amplifier clipping, in a properly designed amp that responds gracefully to such 'overload conditions'). IMHO, there's no real need to have a fancy VU meter monitoring the amplifier's output voltage. A minimalistic clipping indicator is all that is really required in practice. The only reason I have fitted such an LED meter to the front panel of my miniature 50W per channel stereo amp was to utilise an otherwise unused meter as a decorative bauble to add a little bit of visual interest aside from the simple on/off mains switch and an indicator lamp for which the meter now serves. A few decades ago there was an obsession with getting the amp output impedance as low as possible to increase the damping factor, until someone - could have been JLH or Doug Self or someone like that - proved that it is easy to over damp a circuit. Indeed the lower the amp output impedance becomes the more effect the resistance of the interconnecting cable has which was why I believe there was a move to direct amping. I believe it was only with increasingly powerful computer modelling that it was discovered that much could be achieved by better driver, cabinet, and particularly crossover design and at the same time more could be made of signal level filtration so bi or tri-amping became popular and to an extent survives today (although very little in the UK from what I read.) As a result of the work on crossovers, in my very limited experience you will often find a small series resistor on the output of the bass section of a crossover. I take issue with the quoting of 'Damping Factor' figures expressed as a ratio of speaker impedance to amplifier output impedance, eg DF of 400 on 8 ohm speaker loads, implying an output impedance of just 20milli ohms. It would be better to simply quote this 20 mill ohms figure (the lower the better) than to falsely claim that the amp can dampen the speaker cone movement 50 times better than an amp with a Zo figure of 1 ohm. The whole thing is a nonsense. The marketing droid who came up with this bit of pseudo technobabble rather conveniently forgets the 7.5 ohms or so resistance of the voice coil of an "Eight Ohm" speaker drive unit which is effective in series with the ampfilier's output impedance with respect to any electrical damping effect. Sadly, it would seem that a lot of 'accoustic engineers' have also fallen for this con. When a typical bass driver is tested to determine its free air resonance impedance you see typical values around 4 or 5 times its nominal impedance (around 35 ohms for an 8 ohm voice coil drive unit). What this means is that the actual damping factor is more like 4 to 1 regardless of whether the driving amp impedance is 20milli ohms or half an ohm. Furthermore, it's important to measure the speaker's resonance under damped conditions (ie, detect a dip in current when driven from a low Z source rather than look for a voltage peak when driven from a high Z source) since the damping will effect the resonant frequency. Now I know this will be contentious, but from what I heard years ago the Motional Feedback speaker marketed by Philips did far more to achieve purity of (bass) sound than anything I've ever heard. I remember going to one of the hi-fi shows in Harrogate probably in the '70s. I walked into the ballroom at the Old Swan Hotel (of Agatha Christie fame) as I could hear what I thought was a brass band playing - possibly Grimethorpe - so you can imagine my surprise when all I saw was two MFB loudspeakers. Staggered was not the word. The only reason that I can think they never took off was (a) the price which compared with the price of some so-called hi-fi kit these days would now be seen as cheap and (b) because it was done by Philips who were not perceived to have hi-fi capability. I often wonder what would have become of the technique if the design had been done by someone like an early Linn? The trick with such motion feedback is to eliminate any direct electrical coupling between the two transducers and, more importantly, bandwidth limit the response of the driver amp/feedback loop to avoid negative feedback becoming postive feedback due to phase shift. This technique can be quite effective, as you seem to have witnessed, in cancelling the non-linear effects of air pressure loading on the cone, as well as inherent non-linearities in the magnetic driving forces over the 'throw' of the voice coil's working range. Luckily, these imperfections are far less noticable when dealing with the mid to hi frequency ranges covered by mid range/tweeter drive units. It's fortunate indeed that this technique is a practical reality with bass drive units where it can offer the most benefit. -- J B Good |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/11/2014 09:39 AM, Jim Lesurf wrote:
I can understand that approach with a valve amp where there is an output transformer involved, but matching with a transistor amp? Eh? I'm not clear what "matching" means above. An engineer would probably assume "arrange for the two impedances to be equal". However it may have been used more vaguely, akin to "suit one another" in some other way. I used 'matching' in the more general form not the specific electrical engineering way. In the circumstances I was describing the book was recommending measuring the output resistance of the amp (and presumably cables) so that the exact figure for electrical damping could be used. Now - say I was to build a transmission line... Pete |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/10/2014 10:22 PM, Peter Chant wrote:
On 12/10/2014 06:15 AM, Woody wrote: Just as a thought, have you considered trying one or both speakers (series or parallel) on an open baffle to see what they sound like? If you are not wanting bass then a piece of wood maybe a foot or so square might be a starting point? No. If I do that I'll have to put a foot on the bottom. Perhaps sides... Actually if I put a foot on the bottom then the speakers are near the screen and effectively the TV is part of the baffle. Apart from making sure it does not fall off the TV there are few reasons not to try this. Cheap adjustable hole saw has arrived. It it works it will pay for itself in saved hassle in one use. However, if baffle is a min of a foot wide one wavelength between front and back will be at over 400Hz, so roll off will be quite high. I wonder if I can put the speakers in a scrap piece and temporarily fix a larger sheet so I don't have to drill my nice unsullied sheet of ply! |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
In article , Johny B Good
wrote: I was designing and building PA amps back in the 70s which absolutley relied on tight PSU voltage regulation to avoid blowing my chosen output transistors (Motorola 2015s recovered from Gvt surplus acquired analogue Computer PSU fan cooled heatsink assemblies - twenty to a fan cooled heatsink module) which weren't particularly good performers slew rate wise and only had a max Vce of 60 volts. By using a 45v 10A analogue voltage regulated supply for each channel (again, using more of those Motorola 2015s) along with a solid state version of the polyfuse (yet another 2015) of my own invention and using a bridge output amplifier design, I was able to make a 200W RMS per 4 ohm load stereo power amplifier (800W PMPO in the language of cheap hi fi except that it was sustained PMPO as in a total of 400W of 500Hz square wave into 4 ohm resistor loads on each channel). [snip] Now, in spite of the merits of regulated voltage rails for the output stages of a Hi-Fi amplifier, there's also some merit to the use of completely unregulated analogue PSUs, provided the output devices have an ample margin of voltage rating. Indeed. At the end of the 70s/early 80s I deliberately chose to use unregulated supplies specifically to let the amp deliver transient peaks well about the amplifier's 'continouous' rated power. The drawback is that this can remain hidden when people read adverts or reviews. So doesn't help 'sell' the amp. But does let it deliver more when it comes to music. Lets it play undistorted at much higher levels. IMHO, there's no real need to have a fancy VU meter monitoring the amplifier's output voltage. A minimalistic clipping indicator is all that is really required in practice. Indeed. I stuck a LED on the output of a monostable that triggerred when the difference in voltage across a longtail pair rose when the amp clipped or struggled. So if the LED stayed unlit you knew the output was essentially just a scaled up version of the input with no clipping or limiting. Even very short 'clips' would cause the LED to light for about half a sec so you had time to see the event. [snip] I take issue with the quoting of 'Damping Factor' figures expressed as a ratio of speaker impedance to amplifier output impedance, eg DF of 400 on 8 ohm speaker loads, implying an output impedance of just 20milli ohms. It would be better to simply quote this 20 mill ohms figure (the lower the better) than to falsely claim that the amp can dampen the speaker cone movement 50 times better than an amp with a Zo figure of 1 ohm. The whole thing is a nonsense. Damping Factor made more sense back in the days when power amps were valve and almost all of them had high output impedances. But even then it was a weird term given the details. e.g. Amps having an output impedance that varies with frequency, level, etc, and generally *not* being resistive. And speakers also being nothing much like a resistor. Alas we seem stuck with the term. The amps output impedance can matter, purely due to any effect by interacting with the speaker's impedance variations with frequency or signal level. Not really an issue of 'damping' but of fiddling about the frequency response in a way that mirrors the speaker's impedance-frequency curve. Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Jim Lesurf wrote: The whole thing is a nonsense. Damping Factor made more sense back in the days when power amps were valve and almost all of them had high output impedances. But even then it was a weird term given the details. e.g. Amps having an output impedance that varies with frequency, level, etc, and generally *not* being resistive. And speakers also being nothing much like a resistor. Alas we seem stuck with the term. ** Damping factor has been relegated to a non issue with hi-fi amplifiers for many decades - despite which it still looms large in the minds of most audiophools. Bull**** baffles brains and good marketing gimmicks never die. In another area of amplifier design, damping factors vary enormously from one model to another and yet rates no mention in advertising at all. I am speaking of guitar amps, where the effective DF may be anything from 100 to 0.1 or lower - making for very audible differences. Famous valve amps like Marshall and Fender have DFs of about 1 due to use of modest amounts of NFB. Early VOX amplifiers were class A and used no NFB at all resulting if very low DF numbers like 0.1. When VOX released their first SS models, the DF was even lower than the valve ones - due to using a combination of voltage and current feedback. The same idea is still used in lot of modern SS guitar amps to get DFs of between 0.3 and 2, so mimicking the tonal character of popular valve models. But makers keep it all a big secret. How very odd. ..... Phil |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
On Sat, 13 Dec 2014 01:58:55 -0800 (PST), Phil Allison
wrote: Jim Lesurf wrote: The whole thing is a nonsense. Damping Factor made more sense back in the days when power amps were valve and almost all of them had high output impedances. But even then it was a weird term given the details. e.g. Amps having an output impedance that varies with frequency, level, etc, and generally *not* being resistive. And speakers also being nothing much like a resistor. Alas we seem stuck with the term. ** Damping factor has been relegated to a non issue with hi-fi amplifiers for many decades - despite which it still looms large in the minds of most audiophools. Bull**** baffles brains and good marketing gimmicks never die. In another area of amplifier design, damping factors vary enormously from one model to another and yet rates no mention in advertising at all. I am speaking of guitar amps, where the effective DF may be anything from 100 to 0.1 or lower - making for very audible differences. Famous valve amps like Marshall and Fender have DFs of about 1 due to use of modest amounts of NFB. Early VOX amplifiers were class A and used no NFB at all resulting if very low DF numbers like 0.1. When VOX released their first SS models, the DF was even lower than the valve ones - due to using a combination of voltage and current feedback. The same idea is still used in lot of modern SS guitar amps to get DFs of between 0.3 and 2, so mimicking the tonal character of popular valve models. But makers keep it all a big secret. How very odd. .... Phil Guitar amplifiers are a case apart. The maker does what is necessary to get the sound he wants - fidelity doesn't come into it. He will use low damping factors to encourage speaker resonances, that being part of the overall instrument sound. That is why Celestion - pretty much undisputed rulers of the guitar driver unit world - have so many models with varying, highly resonant responses. There was a lot of early resistance to SS guitar amps for this very reason. Makers didn't really understand what was needed and tried to adapt standard op-amp type circuits with a dominant pole and heavy negative feedback. This was a failure on so many counts, from the over-damped control of the speaker to the disastrously harsh limiting characteristic that stopped people playing at high volume. This resulted in the feeling that solid state watts were smaller than valve watts. In a decent valve guitar amp feedback is pretty much confined to the taming of the wildly varying bias condition of the output valves. The entire rest of the chain will be run open loop to achieve the desired smoothly curving transfer characteristic. d |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Don Pearce wrote:
In another area of amplifier design, damping factors vary enormously from one model to another and yet rates no mention in advertising at all. I am speaking of guitar amps, where the effective DF may be anything from 100 to 0.1 or lower - making for very audible differences. Famous valve amps like Marshall and Fender have DFs of about 1 due to use of modest amounts of NFB. Early VOX amplifiers were class A and used no NFB at all resulting if very low DF numbers like 0.1. When VOX released their first SS models, the DF was even lower than the valve ones - due to using a combination of voltage and current feedback. The same idea is still used in lot of modern SS guitar amps to get DFs of between 0.3 and 2, so mimicking the tonal character of popular valve models. But makers keep it all a big secret. How very odd. Guitar amplifiers are a case apart. ** Sure - where wildly varying damping factors actually have a big effect on sound and makers studiously avoid any mention of it. While the complete opposite occurs with hi-fi amps. .... Phil |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
On Sat, 13 Dec 2014 15:27:20 -0800 (PST), Phil Allison
wrote: Don Pearce wrote: In another area of amplifier design, damping factors vary enormously from one model to another and yet rates no mention in advertising at all. I am speaking of guitar amps, where the effective DF may be anything from 100 to 0.1 or lower - making for very audible differences. Famous valve amps like Marshall and Fender have DFs of about 1 due to use of modest amounts of NFB. Early VOX amplifiers were class A and used no NFB at all resulting if very low DF numbers like 0.1. When VOX released their first SS models, the DF was even lower than the valve ones - due to using a combination of voltage and current feedback. The same idea is still used in lot of modern SS guitar amps to get DFs of between 0.3 and 2, so mimicking the tonal character of popular valve models. But makers keep it all a big secret. How very odd. Guitar amplifiers are a case apart. ** Sure - where wildly varying damping factors actually have a big effect on sound and makers studiously avoid any mention of it. They don't studiously avoid mention of it. The high output impedance is an integral part of the design philosophy. They design to ensure that there is a low enough damping factor to allow the speaker cone to sing properly. And getting the figure right is part of their intellectual property, not a bragging item. d |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Don Pearce wrote:
Guitar amplifiers are a case apart. ** Sure - where wildly varying damping factors actually have a big effect on sound and makers studiously avoid any mention of it. They don't studiously avoid mention of it. ** Yes they do - you bull****ting old fool. The high output impedance is an integral part of the design philosophy. ** Except for all the ones that have low and medium output impedance. They design to ensure that there is a low enough damping factor to allow the speaker cone to sing properly. ** That is utter ********. And getting the figure right is part of their intellectual property, not a bragging item. ** Completely insane crap. Most would say that Don has lost it - but I know he never had a single clue in the first place. ..... Phil |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
On Sun, 14 Dec 2014 00:31:17 -0800 (PST), Phil Allison
wrote: Don Pearce wrote: Guitar amplifiers are a case apart. ** Sure - where wildly varying damping factors actually have a big effect on sound and makers studiously avoid any mention of it. They don't studiously avoid mention of it. ** Yes they do - you bull****ting old fool. The high output impedance is an integral part of the design philosophy. ** Except for all the ones that have low and medium output impedance. They design to ensure that there is a low enough damping factor to allow the speaker cone to sing properly. ** That is utter ********. And getting the figure right is part of their intellectual property, not a bragging item. ** Completely insane crap. Most would say that Don has lost it - but I know he never had a single clue in the first place. .... Phil And normal service has resumed. d |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/11/2014 10:12 PM, Peter Chant wrote:
Cheap adjustable hole saw has arrived. It it works it will pay for itself in saved hassle in one use. However, if baffle is a min of a foot wide one wavelength between front and back will be at over 400Hz, so roll off will be quite high. I wonder if I can put the speakers in a scrap piece and temporarily fix a larger sheet so I don't have to drill my nice unsullied sheet of ply! Speakers installed on an off-cut of kitchen worktop as an open baffle. Surprised how well that works - could even here the low bits in 'LFO'! I have a feeling a some sort of enclosure will make it more space friendly. |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
On 12/10/2014 06:15 AM, Woody wrote:
Just as a thought, have you considered trying one or both speakers (series or parallel) on an open baffle to see what they sound like? If you are not wanting bass then a piece of wood maybe a foot or so square might be a starting point? I once tried it with a drawer from an old dresser which had a thicker than might be expected floor panel. Worked surprisingly well. Have done that. Two bass / mids mounted with tweeter on a piece of kitchen counter top. Mid-woofers in series but with 2x6.8uF cap across one. Somehow it sounds a bit 'boxy'. Mid range seems accentuated. I'll have to wire the drivers in parallel and see what happens. I wonder if this is an effect of the baffle arrangement or a fundamental limitation of the drivers. |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Peter Chant wrote:
Have done that. Two bass / mids mounted with tweeter on a piece of kitchen counter top. Mid-woofers in series but with 2x6.8uF cap across one. ** Wow, so he took my suggestion seriously after all. Somehow it sounds a bit 'boxy'. ** LOL - an open plain baffle can sound a bit "woody" if it is made from ply or pine. Mid range seems accentuated. ** Gee - a lack of low bass will do that ... I'll have to wire the drivers in parallel and see what happens. ** It will be 6dB louder and have even more midrange. I wonder if this is an effect of the baffle arrangement or a fundamental limitation of the drivers. ** Trying to balance and passively equalise a home brew *two way* speaker by ear alone is a near impossible task - I know cos I have tried many times. Since you cannot adjust the mid frequency level independently, you have to be damn lucky with your choice of drivers. However, with a three way design, options for tweaking the response really open up. A couple of years back, I picked up a pair of old AR2axs for A$100. These are a three way design with a really primitive x-over and cheaply made drivers that had deteriorated to the point of useless. The money got me two, nice looking cabinets of about 45 litres volume. I stripped them both out and started again with three Peerless drivers chosen to have similar dB/watts and in sizes to fit the existing baffle cut outs. The chosen woofer's response was modelled in the same volume box using WinISD and it was near perfect. So, I purchased a 10 inch woofer, 4 inch midrange and 1 inch soft dome with a big mounting plate. The new mid got its own 2 litre enclosure, made from a thick cardboard port tube running back to front- which also helped to stiffen the front baffle. The original AR mids were "sealed back" types, just like old fashioned paper cone tweeters - yuck. Much effort and time was spent on the passive x-over which was externally connected to the box until I felt no further improvement was possible. Testing was done first with sine waves and then 1/3 octave pink noise using a Rode calibrated SPL meter. Further testing was done with an AKG CK2 condenser mic and 4 cycle sine wave bursts observed on a scope - a very informative technique for revealing colouration and one which works well inside a room. X-over frequencies ended up at 450Hz and 2.2kHz with 3dB of attenuation for mid and tweeter. I bought a 4 ohm tweeter to make sure it would have enough level to match the woofer cos you sure as heck do not what to have to attenuate that. The tweeter's HP filter is 18dB/octave while the others are all 12dB/octave.. The x-over uses three air cored inductors and five 250VAC rated poly caps plus a couple of big bi-polars for the woofer. The mid enclosure was stuffed tight with damping material and sine wave burst testing showed there were virtually no internal echoes emerging. The new speakers are use mainly for watching DTV and DVD movies - so had to sound natural on speech and they do. FYI: My previous speakers were Quad ESL57s which I had used for over 20 years - they needed major restoration work done by an expert, so I sold them to a guy who was willing to finance getting that done. ..... Phil |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
Just for info I've been having a play with a Behringer Ultracurve Pro
DEQ2496. Basically a dual channel equaliser. It has a built in pink noise generator and mic input, and using those will auto eq a speaker system. Quite remarkable given the low price. -- *My wife has a slight impediment in her speech. She stops to breathe. Dave Plowman London SW To e-mail, change noise into sound. |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
In article ,
Bob Latham wrote: Basically a dual channel equaliser. It has a built in pink noise generator and mic input, and using those will auto eq a speaker system. Quite remarkable given the low price. I've often thought about this kind of digital processing and my understanding of what happens is obviously a bit limited as digital processing AFTER the volume control looks a bit dodgy to me. I'm not saying I'm right, I don't know but it worries me because.... Ideally, for best noise etc results, you'd use it before the volume control. Of course, not all pre-amps have this facility. -- *Indian Driver - Smoke signals only* Dave Plowman London SW To e-mail, change noise into sound. |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
In article , Bob Latham
wrote: In article , Dave Plowman (News) wrote: Just for info I've been having a play with a Behringer Ultracurve Pro DEQ2496. Basically a dual channel equaliser. It has a built in pink noise generator and mic input, and using those will auto eq a speaker system. Quite remarkable given the low price. I've often thought about this kind of digital processing and my understanding of what happens is obviously a bit limited as digital processing AFTER the volume control looks a bit dodgy to me. I'm not saying I'm right, I don't know but it worries me because.... Assuming you set the sensitivity of the DAC input such that the dac *just* does not clip when your playing the loudest recording you have at the loudest you'll ever play it, what happens to the quality of quantisation when you play a quietly recorded piece with volume turned down? Have to give the usual engineering answer "It depends..." :-) e.g. The 851C I use employs a 'digital' volume and balance control. However it converts all inputs to 384k / 24bit. So for most of the digital source material most people will have, a 'good' system of this kind would allow the output quantisation noise level to remain defined by the source material for a modest amount of level scaling downward. I expect some more modern systems will duly use a mix of higher internal rates and either more bits per sample or heavily noise-shaped 'DSD' sic. But the argument comes out much the same from a theoretical POV. But of course in *reality* if you wind down the level more and more, then eventually the signal/noise will start to suffer. Just a question of when that starts to happen. Bear in mind, though, that the chances are that even 24bit audio files you may obtain will be likely to have a background noise or quantisation level that is rather higher than implied by 24 bit range. And such a range is likely to be well beyond what you'd experience in most normal homes. The real problems with digital 'EQ' for room and speaker are more complicated. It depends on the details of what you need to 'correct'. The most obvious example being a room or speaker response that has a narrow and deep dip somewhere. That implies needing to boost any signals at the frequency quite a lot. Which may then clip the DAC... or clip the following amps, etc. Consider the implications of a 20dB 'dip' for example. You'd have to wind down the general volume by 20dB to avoid the clipping problems which could be caused by boosting some components by 20dB before the room and speaker which had a corresponding 20dB drop. And some room/speaker problems are almost unfixable by such means as "measure the frequency response, then 'invert it' to get a flat result". So its reasonable to expect such an EQ to give you some improvements. How much, and at what point you encounter problems, depends entirely on the details of the case. Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Centre, speaker - twin drivers, use one enclosure or two separateenclosures side by side?
Jim Lesurf wrote:
The real problems with digital 'EQ' for room and speaker are more complicated. It depends on the details of what you need to 'correct'. The most obvious example being a room or speaker response that has a narrow and deep dip somewhere. And some room/speaker problems are almost unfixable by such means as "measure the frequency response, then 'invert it' to get a flat result". ** Best thing you can do is to EQ the speakers themselves outdoors in the back garden. Suggest you put the pair side by side and the test mic in the central position, about 2 metres away. ( If you have Quad ESL63s or the like, just forget it, you cannot improve perfection) Nothing an EQ can do will fix a poor listen room but human ears do learn to listen through some of the defects in a room given time - but a reverberant room is a dead loss from the outset. Means a typical room with bare walls & ceilings,large glass windows etc. Polished wood floors are an abomination, sound wise. FYI: Best listening room I or anyone I know ever experienced belonged to a friend of mine living nearby in Sydney. Prompted by suggestions from myself and some telephone advice from an acoustics expert - his 5m x 10m x 3m lounge room was as follows. 1. Timber floor over joists, covered in shag pile carpet and underlay = dead to low, mid and high frequencies. 2. Double brick cavity walls covered in short pile carpet from floor to ceiling on 3 sides, bookshelves full of books on the fourth = dead to mid and high frequencies. 3. Large timber frame covered in carpet and underlay strung 0.3m under the plaster on joist ceiling covering about 50% of the area - hung above the listening position. 4. Heavy curtains covering the two small windows. 5. Listening position was 4 metres away from the rear wall and speakers about 3 metres in front of that. 6. House in a quiet cul-de-sac with tolerant neighbours. Result was nearly anechoic, anyone who spoke facing away from the listener was hard to hear. Hand claps made *no* audible echo. The room had stacked Quad ESL57s and a twin KEF B139 sub - parked against the rear wall. Good recording sounded *spectacular*, with a clarity and the full original ambience you only usually get to hear with electrostatic headphones. In that room, I was able to also audition Yamaha NS1000s and Magnaplaners, not at the same time though. The Yamahas sounded remarkably similar to one pair of ESL57s but could not beat two pairs when played loud. The Quad's sound was then very noticeably cleaner. The Magnaplanars sounded just awful, poor sales dude who brought them over for a demo that evening was reluctant to bring them inside after few minutes spent listening to the stacked Quads. My friend spent about the same money improving his room as he had on one pair of Quad ESL57s - about $1000 in 1979. His only new purchase after what was a Sony CD player in 1983 - after he had a good listening session with my CDP101 of course. The idiotic notion that the CD format was a lemon was rife in those days. .... Phil |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
Phil Allison wrote:
Jim Lesurf wrote: The real problems with digital 'EQ' for room and speaker are more complicated. It depends on the details of what you need to 'correct'. The most obvious example being a room or speaker response that has a narrow and deep dip somewhere. And some room/speaker problems are almost unfixable by such means as "measure the frequency response, then 'invert it' to get a flat result". When the DiAppolito MTM configuration was first thought up, the odd or even order crossover was selected to provide maximum range of dispersion. His was vertically mounted. Then decided it was better to narrow dispersion by changing order of crossover, to minimize ceiling floor bounces. I always went for maximum dispersion, especially in horizontal mounting. I like to move around a bit. The drivers natural phase change must be entered in the crossover order, at selected crossover frequency. Greg ** Best thing you can do is to EQ the speakers themselves outdoors in the back garden. Suggest you put the pair side by side and the test mic in the central position, about 2 metres away. ( If you have Quad ESL63s or the like, just forget it, you cannot improve perfection) Nothing an EQ can do will fix a poor listen room but human ears do learn to listen through some of the defects in a room given time - but a reverberant room is a dead loss from the outset. Means a typical room with bare walls & ceilings,large glass windows etc. Polished wood floors are an abomination, sound wise. FYI: Best listening room I or anyone I know ever experienced belonged to a friend of mine living nearby in Sydney. Prompted by suggestions from myself and some telephone advice from an acoustics expert - his 5m x 10m x 3m lounge room was as follows. 1. Timber floor over joists, covered in shag pile carpet and underlay = dead to low, mid and high frequencies. 2. Double brick cavity walls covered in short pile carpet from floor to ceiling on 3 sides, bookshelves full of books on the fourth = dead to mid and high frequencies. 3. Large timber frame covered in carpet and underlay strung 0.3m under the plaster on joist ceiling covering about 50% of the area - hung above the listening position. 4. Heavy curtains covering the two small windows. 5. Listening position was 4 metres away from the rear wall and speakers about 3 metres in front of that. 6. House in a quiet cul-de-sac with tolerant neighbours. Result was nearly anechoic, anyone who spoke facing away from the listener was hard to hear. Hand claps made *no* audible echo. The room had stacked Quad ESL57s and a twin KEF B139 sub - parked against the rear wall. Good recording sounded *spectacular*, with a clarity and the full original ambience you only usually get to hear with electrostatic headphones. In that room, I was able to also audition Yamaha NS1000s and Magnaplaners, not at the same time though. The Yamahas sounded remarkably similar to one pair of ESL57s but could not beat two pairs when played loud. The Quad's sound was then very noticeably cleaner. The Magnaplanars sounded just awful, poor sales dude who brought them over for a demo that evening was reluctant to bring them inside after few minutes spent listening to the stacked Quads. My friend spent about the same money improving his room as he had on one pair of Quad ESL57s - about $1000 in 1979. His only new purchase after what was a Sony CD player in 1983 - after he had a good listening session with my CDP101 of course. The idiotic notion that the CD format was a lemon was rife in those days. ... Phil |
Centre, speaker - twin drivers, use one enclosure or two separate enclosures side by side?
In article ,
Phil Allison wrote: Nothing an EQ can do will fix a poor listen room but human ears do learn to listen through some of the defects in a room given time - but a reverberant room is a dead loss from the outset. Means a typical room with bare walls & ceilings,large glass windows etc. Polished wood floors are an abomination, sound wise. Crikey. I actually agree 100% with you. Must be Xmas. ;-) -- *Born free - taxed to death * Dave Plowman London SW To e-mail, change noise into sound. |
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