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

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

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

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

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

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

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.

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.

"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

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.