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Speaker level adjustment
My amplifier has two outputs. One is switched, and used for the
speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. |
Speaker level adjustment
"Chris J Dixon" wrote in message ... My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. If the dining room application is for background music during meals, then it should work fine by attenuating the 'speakers relative to the others. Unless you know how many dBs you need to attenuate, and can then calculate the series resistance value, you'll be better off getting a loudspeaker volume control as is used in Pubs and Restaurants for just such an application. They're not expensive and it does allow you to make changes easily. This will do it. http://cpc.farnell.com/_/bt936/louds...all/dp/AV01580 It's a transformer-based design (presumably a variable auto-transformer, like a Variac). A bit more expensive than a couple of 5-10 watt resistors, but the extra flexibility is worth-while. S. -- http://audiopages.googlepages.com |
Speaker level adjustment
"Serge Auckland" wrote in message ... "Chris J Dixon" wrote in message ... My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. If the dining room application is for background music during meals, then it should work fine by attenuating the 'speakers relative to the others. Unless you know how many dBs you need to attenuate, and can then calculate the series resistance value, you'll be better off getting a loudspeaker volume control as is used in Pubs and Restaurants for just such an application. They're not expensive and it does allow you to make changes easily. This will do it. http://cpc.farnell.com/_/bt936/louds...all/dp/AV01580 It's a transformer-based design (presumably a variable auto-transformer, like a Variac). A bit more expensive than a couple of 5-10 watt resistors, but the extra flexibility is worth-while. S. -- http://audiopages.googlepages.com There is something odd about that part - a pair of audio transformers rated 60W with 20Hz to 20kHz response in package 140mm x 85mm x 45mm - and variable as well - and for £20. Don't expect it to sound very good. Michael Kellett |
Speaker level adjustment
"MK" wrote in message ... "Serge Auckland" wrote in message ... "Chris J Dixon" wrote in message ... My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. If the dining room application is for background music during meals, then it should work fine by attenuating the 'speakers relative to the others. Unless you know how many dBs you need to attenuate, and can then calculate the series resistance value, you'll be better off getting a loudspeaker volume control as is used in Pubs and Restaurants for just such an application. They're not expensive and it does allow you to make changes easily. This will do it. http://cpc.farnell.com/_/bt936/louds...all/dp/AV01580 It's a transformer-based design (presumably a variable auto-transformer, like a Variac). A bit more expensive than a couple of 5-10 watt resistors, but the extra flexibility is worth-while. S. -- http://audiopages.googlepages.com There is something odd about that part - a pair of audio transformers rated 60W with 20Hz to 20kHz response in package 140mm x 85mm x 45mm - and variable as well - and for £20. Don't expect it to sound very good. Michael Kellett Yes, but they are most likely auto transformers, and I wouldn't believe the response....they don't quote dB limits or distortion. Remember it's for background music, not listening, so it will be adequate for the job it was designed for. If the OP needs high quality, he will be better off with a pair of active 'speakers and a multi-room system, but that's neither cheap nor simple. S. -- http://audiopages.googlepages.com |
Speaker level adjustment
"MK" wrote in message
http://audiopages.googlepages.com There is something odd about that part - a pair of audio transformers rated 60W with 20Hz to 20kHz response in package 140mm x 85mm x 45mm - and variable as well - and for £20. Don't expect it to sound very good. They never actually have to pass the entire 60 watts, only a fraction of it. And, they have a reputation for not being perfectly flat over the entire range. Face it, with typical extension speakers response down to 80 Hz would probably suffice. |
Speaker level adjustment
"Brian Gaff" wrote in message om... I was just thinking this. I keep thinking saturated core for some reason. Are we sure its not just two wirewound pots as I have in an old QED device? They tend to be noisy when you move them though. Brian -- Brian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: __________________________________________________ __________________________________________________ __________ They could be, but the CPC site says they are transformer based, so I have assumed they use a tapped autotransformer, like a Variac. S. |
Speaker level adjustment
"Serge Auckland" wrote in
message "Brian Gaff" wrote in message om... I was just thinking this. I keep thinking saturated core for some reason. Are we sure its not just two wirewound pots as I have in an old QED device? They tend to be noisy when you move them though. Brian -- Brian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: __________________________________________________ __________________________________________________ __________ They could be, but the CPC site says they are transformer based, so I have assumed they use a tapped autotransformer, like a Variac. Right. The transformer is designed to present twice the nominal impedance of the speakers to the amplifer, and uses boot/buck winding configurations to minimize the actual power the transformer needs to handle. |
Speaker level adjustment
"Serge Auckland" This will do it. http://cpc.farnell.com/_/bt936/louds...all/dp/AV01580 It's a transformer-based design (presumably a variable auto-transformer, like a Variac). A bit more expensive than a couple of 5-10 watt resistors, but the extra flexibility is worth-while. ** Do NOT under any circumstances use this device. It is a 100%, guaranteed amplifier DESTROYER ! Attenuators used with solid state hi-fi amplifiers must not be of the auto-transformer type. Seen the damage using them does, many times. Think low frequency core saturation, very low DC resistance. Bad news !!! ...... Phil |
Speaker level adjustment
"Serge Auckland" They could be, but the CPC site says they are transformer based, so I have assumed they use a tapped autotransformer, like a Variac. ** Do NOT under any circumstances use such devices. They are 100%, guaranteed amplifier DESTROYERS ! Attenuators used with solid state hi-fi amplifiers must not be of the auto-transformer type. Seen the damage using them does, many times. Think low frequency core saturation, very low DC resistance. Bad news !!! ...... Phil |
Speaker level adjustment
"Arny Krueger" The transformer is designed to present twice the nominal impedance of the speakers to the amplifer, and uses boot/buck winding configurations to minimize the actual power the transformer needs to handle. ** Purest gobbledegook. ...... Phil |
Speaker level adjustment
"MK" This will do it. http://cpc.farnell.com/_/bt936/louds...all/dp/AV01580 It's a transformer-based design (presumably a variable auto-transformer, like a Variac). A bit more expensive than a couple of 5-10 watt resistors, but the extra flexibility is worth-while. There is something odd about that part - a pair of audio transformers rated 60W with 20Hz to 20kHz response in package 140mm x 85mm x 45mm - and variable as well - and for £20. Don't expect it to sound very good. ** Expect it to blow your amplifier. Here is a nice pic of the insides: http://www.avstorm.co.uk/Switch_boxe...36_17 63.html Consists only of a multi-position switch and 2 tiny auto-transformers. ...... Phil |
Speaker level adjustment
Serge Auckland wrote:
"Chris J Dixon" wrote My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. If the dining room application is for background music during meals, then it should work fine by attenuating the 'speakers relative to the others. Unless you know how many dBs you need to attenuate, and can then calculate the series resistance value, It is hard to say exactly, my ear isn't calibrated ;-) I reckon that if I picked a figure out of thin air, then bought two resistors for each speaker totaling that figure, ( say 1R & 2R2) by experimenting with using them singly or series/ parallel, I would get quite a range. If I wanted, for example, 3 dB attenuation, what resistor would you calculate? Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. |
Speaker level adjustment
In article , Chris J Dixon
wrote: Serge Auckland wrote: If the dining room application is for background music during meals, then it should work fine by attenuating the 'speakers relative to the others. Unless you know how many dBs you need to attenuate, and can then calculate the series resistance value, It is hard to say exactly, my ear isn't calibrated ;-) I reckon that if I picked a figure out of thin air, then bought two resistors for each speaker totaling that figure, ( say 1R & 2R2) by experimenting with using them singly or series/ parallel, I would get quite a range. For an 8Ohm speaker using those in series would give 1dB and 2dB. Chances are that you'd hardly notice the change in volume. If I wanted, for example, 3 dB attenuation, what resistor would you calculate? The answer will vary with the spectrum of the music and the impedance-frequency variations of your speakers. Unless your speakers have the same impedance at all audio frequencies... which seems unusual. Slainte, 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 |
Speaker level adjustment
"Chris J Dixon" wrote in message ... Serge Auckland wrote: "Chris J Dixon" wrote My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. If the dining room application is for background music during meals, then it should work fine by attenuating the 'speakers relative to the others. Unless you know how many dBs you need to attenuate, and can then calculate the series resistance value, It is hard to say exactly, my ear isn't calibrated ;-) I reckon that if I picked a figure out of thin air, then bought two resistors for each speaker totaling that figure, ( say 1R & 2R2) by experimenting with using them singly or series/ parallel, I would get quite a range. If I wanted, for example, 3 dB attenuation, what resistor would you calculate? Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. For a 3dB attenuation on an 8 ohm 'speaker you need a series resistance of 3.27 ohms. For 6 dB you need 8 ohms. But note that this assumes a nominal 8 ohm load, and loudspeakers are not pure 8 ohm loads. Also, by putting such a series resistance in the loudspeaker lead you will change the frequency response of the loudspeaker considerably. However, as this seems to be for background music rather than critical listening, it will probably be perfectly acceptable. I suggest you use 10 watt resistors. Alternatively again, a 20 ohm 10 watt wire wound pot wired in series will allow you to make adjustments. S. -- http://audiopages.googlepages.com |
Speaker level adjustment
"Chris J Dixon" wrote in message ... My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. Hi Chris, have a look at the Wilmslow Audio site - they used to do a high-power L-pad that might be useful for padding down one of the outputs. Kind regards Mike |
Speaker level adjustment
fredbloggstwo wrote:
have a look at the Wilmslow Audio site - they used to do a high-power L-pad that might be useful for padding down one of the outputs. Thanks for that, all I needed was the right terminology. Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. |
Speaker level adjustment
fredbloggstwo wrote:
"Chris J Dixon" wrote in message .. . My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. Originally, the relative sound levels in all three rooms were reasonably matched. However, during a kitchen refit, I had to get rid of the conventional speakers, and fitted a pair of small KEF in-ceiling units. These have a rather lower output level. If I deselect the dining room pair, the kitchen is well enough matched to the living room. As a least cost work-around, it strikes me that I might be able to improve the situation by inserting series resistors in the feed to the dining room. Would this work? Living in a semi, I don't run at particularly high sound levels. have a look at the Wilmslow Audio site - they used to do a high-power L-pad that might be useful for padding down one of the outputs. I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. I am now wondering about a completely different approach. I could have totally separate control using something like http://www.ebay.co.uk/itm/New-Mini-TA2020-Stereo-Audio-Amplifier-Power-Adapter-for-Car-MP3-iPod-Motor-/111246826219?pt=UK_AudioTVElectronics_HomeAudioHiF i_Amplifiers&hash=item19e6d3daeb Fed from the phono socket tape output of my main amplifier. I understand that quality may not be great, and I would always have two volume controls to adjust, but these are tiny ceiling speakers, so it will probably be fine. Any better ideas? Chris -- Chris J Dixon Nottingham UK Plant amazing Acers. |
Speaker level adjustment
On 27/01/2014 16:41, Chris J Dixon wrote:
I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. I find that odd, as if it's wired correctly, an L-pad should give an adjustment range from 0- 100% of full power. Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. -- Tciao for Now! John. |
Speaker level adjustment
John Williamson wrote:
On 27/01/2014 16:41, Chris J Dixon wrote: I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. I find that odd, as if it's wired correctly, an L-pad should give an adjustment range from 0- 100% of full power. Well, AFAUK I have done it right, but I suppose that is a bit of a circular argument. ;-) Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. So, significant expense, compare with my proposal which you snipped. Just for the record, what would its advantages be? Chris -- Chris J Dixon Nottingham UK Plant amazing Acers. |
Speaker level adjustment
On 28/01/2014 10:24, Chris J Dixon wrote:
John Williamson wrote: On 27/01/2014 16:41, Chris J Dixon wrote: I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. I find that odd, as if it's wired correctly, an L-pad should give an adjustment range from 0- 100% of full power. Well, AFAUK I have done it right, but I suppose that is a bit of a circular argument. ;-) Indeed. Obviously, you'd not deliberately or knowingly do it incorrectly. :-) Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. So, significant expense, compare with my proposal which you snipped. Just for the record, what would its advantages be? Completely independent control of levels on all speakers. Only one amplifier to go wrong, and 100 volt line amplifiers tend to be designed and built to last for ever even when abused. The downside is that the transformers can degrade the sound quality slightly, which may obviously be an issue. -- Tciao for Now! John. |
Speaker level adjustment
In article ,
John Williamson wrote: Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. I've used a 100 v line transformer I had lying around to adjust the level of a speaker fed from a normal low impedance amp. It worked rather better than a pad. It had five level taps on it - but it would be a bit of luck if it gave the amount of attenuation wanted. Pads always seem to upset the bass end - even on speakers which aren't exactly Hi-Fi. -- *Procrastination is the art of keeping up with yesterday. Dave Plowman London SW To e-mail, change noise into sound. |
Speaker level adjustment
On 28/01/2014 10:24, Chris J Dixon wrote:
John Williamson wrote: On 27/01/2014 16:41, Chris J Dixon wrote: I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. I find that odd, as if it's wired correctly, an L-pad should give an adjustment range from 0- 100% of full power. Well, AFAUK I have done it right, but I suppose that is a bit of a circular argument. ;-) There are only three terminals on a potentiometer. The amplifier should go to the outer pair and see 8R load. The speaker should go to the centre tap and one end (the low end). If you choose the correct end then you will get a logarithmic adjustment and if you choose the wrong end you will get a sort of all or nothing behaviour. Rotation 0 1 2 3 4 5 r (correct) 0 0.5 1 2 4 8 (correct) r'(wrong) 0 4 6 7 7.5 8 Swap the end you connect the speaker to and you might be surprised. You still lose some bass damping this way but it may not bother you. -- Regards, Martin Brown |
Speaker level adjustment
On 28/01/14 10:51, John Williamson wrote:
On 28/01/2014 10:24, Chris J Dixon wrote: John Williamson wrote: On 27/01/2014 16:41, Chris J Dixon wrote: I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. I find that odd, as if it's wired correctly, an L-pad should give an adjustment range from 0- 100% of full power. Well, AFAUK I have done it right, but I suppose that is a bit of a circular argument. ;-) Indeed. Obviously, you'd not deliberately or knowingly do it incorrectly. :-) Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. So, significant expense, compare with my proposal which you snipped. Just for the record, what would its advantages be? Completely independent control of levels on all speakers. Only one amplifier to go wrong, and 100 volt line amplifiers tend to be designed and built to last for ever even when abused. The downside is that the transformers can degrade the sound quality slightly, which may obviously be an issue. as can ANY form of passive attenuation to a loudspeaker designed to be driven from a 0.1 ohm source. 100V line or not. 100V line is merely a way to transmit audio POWER over long distances using less than arm sized cabling. The fact that it is in general more robust is not inherent in the 100V-ness of it, but more because such systems tend to be deployed out doors or in large buildings where the integrity of cabling and its immunity from lightning strikes or induced surges or shorts cannot be guaranteed, and into professional applications where a lack of robustness is not tolerable either. A better way in domestic situations is to deploy active loudspeakers fed from e.g a 1V line source, preferably balanced 600 ohm., and possibly with power being fed to them via the wires, and then attenuate that and feed it to a local low output impedance amplifier. In short pretty much what a pair of 'computer speakers' already does. -- Ineptocracy (in-ep-toc’-ra-cy) – a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers. |
Speaker level adjustment
On 28/01/14 10:56, Dave Plowman (News) wrote:
In article , John Williamson wrote: Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. I've used a 100 v line transformer I had lying around to adjust the level of a speaker fed from a normal low impedance amp. It worked rather better than a pad. It had five level taps on it - but it would be a bit of luck if it gave the amount of attenuation wanted. Pads always seem to upset the bass end - even on speakers which aren't exactly Hi-Fi. +1 You can use a transformer to adjust power output via taps without upsetting the impedance - but resistive pads are not good for bass units. As part of my essays into reproducing 'valve sound' for guitar amplifiers, artificially raising the output impedance of the power amplifier was routine. The good old Vox A30 amplifier has an output impedance of some 80 ohms. Driving an 8ohm pair of loudspeakers, the effects are dramatic. Massive bass resonance, about the bottom A on a guitar, plus overall treble boost as the rising impedance of the speaker voice coil (a lot of leakage inductance in a voice coil) is no longer a significant effect in reducing treble output. Boom an chink we used to call it. Also all other resonances in the paper cones and cabinets are much less well damped, so the sound comes 'alive' with the sound of - well wood and paper! The amplifier loudspeaker and cabinet are the 'sound box' of an electric guitar and give it an interest and colour it otherwise lacks. Hifi it aint. But it isn't intended to be, either. -- Ineptocracy (in-ep-toc’-ra-cy) – a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers. |
Speaker level adjustment
On Tue, 28 Jan 2014 10:56:29 +0000 (GMT), "Dave Plowman (News)"
wrote: In article , John Williamson wrote: Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. I've used a 100 v line transformer I had lying around to adjust the level of a speaker fed from a normal low impedance amp. It worked rather better than a pad. It had five level taps on it - but it would be a bit of luck if it gave the amount of attenuation wanted. Pads always seem to upset the bass end - even on speakers which aren't exactly Hi-Fi. I'm not familiar with the design of attenuator pads used in 100v and 70v line driver setups but presumably it must be raising the 'source' impedance as seen by the speaker. I suppose the reduction of "Damping Factor"[1] is allowing the bass cone resonance to more prominently dominate the frequency response. [1] Forty years ago, "Damping Factor" was an oft quoted figure of merit for amplifiers which was derived from the output impedance (ideally, zero ohms) of the amplifier versus the impedance of the speaker loads it was designed to drive. Figures of 400:1 for 8 ohm loads being not uncommon (implying an output Z of 0.02 ohms). Since over 90% of the typical bass driver's "Voice Coil Impedance" was made up of its ohmic resistance, the actual "Damping Factor" was more like 1:1 using such an amplifier (the voice coil resistance being effectively in series with the amplifier's output impedance). In practice, the damping effect was only of importance at the resonant frequency of the drive unit which is reflected as an increase of impedance which, for an 8 ohm driver, could climb to as high a value as 30 or more ohms. In the case of a 32 ohm impedance at resonance, the actual damping factor applied by our "400:1 Damping Factor" amplifier would actually be a mere 4:1, just 1% of the claimed 'figure of merit' implied. It's been a good 30 years or more since I last looked at such Hi Fi advertising 'blurb' so I don't know whether this misleading practice has stopped and the more useful "Output Impedance" figures are being quoted instead (e.g. "Output Z = 20 milli ohms", rather than "DF=400:1 for 8 ohm loads"). Quite frankly, the difference between 500 milli ohms and 20 milli ohms output impedance would be barely measurable let alone audible. -- Regards, J B Good |
Speaker level adjustment
And QED used to make resistive speaker controls with wirewound pots. OK
they could get a bit warm and crackly, but the seemed to work. Brian -- From the Sofa of Brian Gaff Reply address is active "Johny B Good" wrote in message ... On Tue, 28 Jan 2014 10:56:29 +0000 (GMT), "Dave Plowman (News)" wrote: In article , John Williamson wrote: Another alternative would be to install a 100 volt speaker system with independent volume controls in each room, but that would mean buying a new amplifier,and some matching transformers and volume controls. I've used a 100 v line transformer I had lying around to adjust the level of a speaker fed from a normal low impedance amp. It worked rather better than a pad. It had five level taps on it - but it would be a bit of luck if it gave the amount of attenuation wanted. Pads always seem to upset the bass end - even on speakers which aren't exactly Hi-Fi. I'm not familiar with the design of attenuator pads used in 100v and 70v line driver setups but presumably it must be raising the 'source' impedance as seen by the speaker. I suppose the reduction of "Damping Factor"[1] is allowing the bass cone resonance to more prominently dominate the frequency response. [1] Forty years ago, "Damping Factor" was an oft quoted figure of merit for amplifiers which was derived from the output impedance (ideally, zero ohms) of the amplifier versus the impedance of the speaker loads it was designed to drive. Figures of 400:1 for 8 ohm loads being not uncommon (implying an output Z of 0.02 ohms). Since over 90% of the typical bass driver's "Voice Coil Impedance" was made up of its ohmic resistance, the actual "Damping Factor" was more like 1:1 using such an amplifier (the voice coil resistance being effectively in series with the amplifier's output impedance). In practice, the damping effect was only of importance at the resonant frequency of the drive unit which is reflected as an increase of impedance which, for an 8 ohm driver, could climb to as high a value as 30 or more ohms. In the case of a 32 ohm impedance at resonance, the actual damping factor applied by our "400:1 Damping Factor" amplifier would actually be a mere 4:1, just 1% of the claimed 'figure of merit' implied. It's been a good 30 years or more since I last looked at such Hi Fi advertising 'blurb' so I don't know whether this misleading practice has stopped and the more useful "Output Impedance" figures are being quoted instead (e.g. "Output Z = 20 milli ohms", rather than "DF=400:1 for 8 ohm loads"). Quite frankly, the difference between 500 milli ohms and 20 milli ohms output impedance would be barely measurable let alone audible. -- Regards, J B Good |
Speaker level adjustment
John Williamson wrote:
On 28/01/2014 10:24, Chris J Dixon wrote: John Williamson wrote: On 27/01/2014 16:41, Chris J Dixon wrote: I boxed up an L-pad http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544 and installed it a while ago, but it doesn't really seem to have sufficient adjustment. Actually, that isn't quite correct, see below, I had forgotten what I actually did. I find that odd, as if it's wired correctly, an L-pad should give an adjustment range from 0- 100% of full power. Well, AFAUK I have done it right, but I suppose that is a bit of a circular argument. ;-) Indeed. Obviously, you'd not deliberately or knowingly do it incorrectly. :-) Looking again at what I have done, if you remember my original problem: [My amplifier has two outputs. One is switched, and used for the speakers in the living room. The other is taken via a separate switch box to speakers in the dining room and kitchen. The kitchen is too quiet.] I used the L-pad to reduce the volume in the dining room, which closer examination shows is actually working. However, to get the kitchen loud enough, the living room would be too loud, and I don't really want to mess with that output, since that is the best set of speakers. Chris -- Chris J Dixon Nottingham UK Plant amazing Acers. |
Speaker level adjustment
"The Natural Philosopher" You can use a transformer to adjust power output via taps without upsetting the impedance ** Very dodgy connecting a matching transformer to any old SS amp. Many output stages cannot cope with the very low primary resistance and propensity to core saturation at low frequencies. - but resistive pads are not good for bass units. ** Perfectly OK for the purpose of an extension speaker. As part of my essays into reproducing 'valve sound' for guitar amplifiers, artificially raising the output impedance of the power amplifier was routine. ** By adding a 0.1ohm 5W resistor to the ground in the feedback loop and returning the speaker to it - right ? The good old Vox A30 amplifier has an output impedance of some 80 ohms. Driving an 8ohm pair of loudspeakers, the effects are dramatic. ** The speakers in an AC30 are series connected, giving a nominal 16 ohms. At bass resonance, that will rise to about 60 ohms - so the amp's output will rise by 4 times giving a 12dB peak at about 75Hz. Massive bass resonance, about the bottom A on a guitar, plus overall treble boost as the rising impedance of the speaker voice coil (a lot of leakage inductance in a voice coil) is no longer a significant effect in reducing treble output. Boom an chink we used to call it. ** That is the sound of an AC30 - despite the amp testing almost flat with a dummy load. Lotsa valve guitar amps use PP output pentodes with little or no NFB, just like the AC30. ..... Phil |
Speaker level adjustment
"The Natural Philosopher" Phil Allison wrote: You can use a transformer to adjust power output via taps without upsetting the impedance ** Very dodgy connecting a matching transformer to any old SS amp. Many output stages cannot cope with the very low primary resistance and propensity to core saturation at low frequencies. Never had any problems with any of my designs attaching 100V transformers to em. ** ROTFL - so ****ing what ? LF response is pre tail;rerd to get rid of serious 'rumble' on most amps anyway ** Saturation may easily well ocurr at 50Hz or higher. You have no clue - do you ? and SOAR protection mens teh worst that can happen is serious distortion if you end up wit DC bias.. ** You have even less than no clue. FYI: A great many hi-fi amps have no or useless SOA limiting and a mere switch on thump will cause instant output stage destruction if a transformer is connected to the output. - but resistive pads are not good for bass units. ** Perfectly OK for the purpose of an extension speaker. No not perfectly good. Acceptable. Barely. ** Yawnnnnnnnnnnn... You a professional bull**** artist or what ? The good old Vox A30 amplifier has an output impedance of some 80 ohms. Driving an 8ohm pair of loudspeakers, the effects are dramatic. ** The speakers in an AC30 are series connected, giving a nominal 16 ohms. At bass resonance, that will rise to about 60 ohms - so the amp's output will rise by 4 times giving a 12dB peak at about 75Hz. Are they? Been too long..but your figures are as I recall from tests in terms of ferquency and gain.. ** I overestimated the boost, with 80 ohms driving 60 ohms max boost is more like 8dB. Lotsa valve guitar amps use PP output pentodes with little or no NFB, just like the AC30. Actually you would be surprised. ** No I wouldn't. I make my living repairing valve guitar amps - among others. Since 1973. They do NOT. Only the AC 30 (EL84) was in any way seriously high impedance. ** Oh, there are lots of others with impedances in the 50 to 200 ohms range. All those with pentodes and no feedback. Most EL34 naps had some feedback - Marshalls come out around 8 ohms and the US amps (tetrodes) were much more 'hi fi' at less than an ohm. ** Nonsense. Only one maker of valve "guitar amps" had such low output impedances - Dynachord. I concluded that Fender, being an ex radio engineer, designed decent amplifiers. ** Fender amps vary a lot, but most have output impedances over 4 ohms even with a 4 ohm nominal load rating. 1950s models ( SE and PP) had no NFB at all. Whoever did the Vox was a post war penny pinching scoundrel, ** Huh ?? The main reason Vox used no NFB was that being class A, it was simply not needed to reduce crossover distortion - as was the case with all Fender's class AB designs. and Jim Marshall was a carpenter, ** Fact he was a drummer and music shop owner who employed techs to do his amp building. They just copied a popular Fender design at first - then stuffed it up. IN short the British 'valve' sound was entirely due to a serendipitous coincidence of parsimony and incompetence. ** Describes Marshall to a T. Swapping Fender's 5881s and 6L6s for EL34s was a master stroke of incompetence. Then of course both Jim Marshall and the Vox boys were chasing decibels at low cost, so both employed ultra lightweight speaker cones that had vile coloration and zero stiffness. But louder. One imagines Celestion were glad to unload these at any price. ** ROTFLMAO !! Celestion made their guitar ( and radio ) speakers to be as efficient as possible plus suitable for open back enclosures. Low cone mass and fairly high resonant frequencies are the name of the game, plus limited VC excursion for safety. Rest of your tripe snipped. ..... Phil |
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