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Old 22nd July 2010, 11:18 PM   #21
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Hiya Graham,

I say you need an lcd monitor then get that center speaker directly under the television.

What are the dimensions of your center channel ?

Stuffing ? Bracing ?

Norman
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Old 23rd July 2010, 01:34 AM   #22
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I estimate for a sealed .707 qtc would need .22ft3 for a fsb = f3 = 100hz.

Maybe a box 10.5" wide x 13.5" tall x 6.5" deep (.32ft3).
Real ply, not the 3/4" 5 layer oak stuff from home depot.
That would take advantage of the 300hz - 500hz bump.

Norman
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Old 23rd July 2010, 12:16 PM   #23
goneill is offline goneill  New Zealand
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Hi Norman,

The cabinet's external size is 31cm wide, 24.5cm high and between 27cm and 30cm deep, made of 2cm MDF. I don't think there is any bracing as it's too small to need any, but I think Mark put a bit of foam lining in. That makes it just over 17L (less the foam and driver itself) which I think is nearly twice the .32ft3 you calculated.

The driver is tilted up to allow for the distance below the monitor, which is already an LCD, but at 47" would be too high with a speaker under it.

Graham
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Old 23rd July 2010, 05:58 PM   #24
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Hmm. OK, call it 205mm x 270mm x 245mm (internal HxWxD), giving a Vb of just over 13.5 litres. Accounting for damping, that should be ~critically damped 0.5 Qtc.
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Old 23rd July 2010, 11:16 PM   #25
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Ah, ok.


Norman
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Old 28th July 2010, 04:32 AM   #26
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Mark has OKed these drawings and has asked me to post them. URLs below. Visualization of Twin A7 tower:

Click the image to open in full size.

dave

Twin A7 Tower
Twin A7 Centre
A12 Centre
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Old 28th July 2010, 09:36 AM   #27
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Thanks Dave and Mark...I'm building these bad boys!
And the plans for the alpair 12's pictured?

Last edited by aptquark; 28th July 2010 at 09:47 AM.
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Old 28th July 2010, 09:48 AM   #28
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Quote:
Originally Posted by norman bates View Post
I estimate for a sealed .707 qtc would need .22ft3 for a fsb = f3 = 100hz.

Maybe a box 10.5" wide x 13.5" tall x 6.5" deep (.32ft3).
Real ply, not the 3/4" 5 layer oak stuff from home depot.
That would take advantage of the 300hz - 500hz bump.

Norman
What other type of ply Norman? I cant get BB here.
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Old 28th July 2010, 11:27 AM   #29
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I'm not sure............

But my guy who builds boxes for me used oak ply with more layers than the 5 one from Home Depot, but he has a wood place nearby and can get 1/4" cherry (damn pretty).

I thought I'd come across 13 ply 3/4" appleply 5 or so years back at a local medium sized hardware store called Menards.

The dual alpair 7's work for surrounds in Graham's system because they are much closer to your ears than the 3 alpair 12's across the front. The a7 has about 39 cm2, so 2 of them have a squeek more than half of the area of an alpair 12 (149cm2). The dual a7 looks like a mltl, while the pencil with its large slot works more like an open baffle providing a boost below the drivers hump, awesome idea there. The a12's +5db hump falls 300-500hz, close to the textbook -3db point for baffle step for a baffle 10.5", then the box hump fills in from 100-300hz (+6db Feq like open baffle) by using the rear wave (where baffle step would be 6db down, at least in my setup backing up to large windows).

I believe 1 larger driver is better than 2 smaller drivers because the ceiling reflection is smoother than the multiple suckouts you get when standing above / below a dual driver setup (or off axis of an mtm or a dual full range driver setup). Otherwise the sound seems like it is coming at you from a tunnel in front of you, similar to what I hear when listening to a d'appolito mtm, but much different from someone speaking in the room. A single driver feels more like a point source than my dual 4" does, hard to put your finger on exactly why.

I'd rather run A12 pencils all the way around. That way you can easily swap them if damaged, blown, etc. It would be hard to make a center channel pencil for the 12, but I think it is possible, assuming you can have a seperate large shelf for a maybe squarish 2' x 2' box (I could) .....

Norman

Stereo Clarity (my markaudio supplier)
Welcome to Nick Ozanich Custom Home Theaters! (my builder)

Last edited by norman bates; 28th July 2010 at 11:29 AM.
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Old 28th July 2010, 04:28 PM   #30
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Quote:
Originally Posted by aptquark View Post
And the plans for the alpair 12's pictured?
The Pensil12s?

planet_10 hifi

If you check back in a few days there is a more comprehensive document going up that includes the superPensil12

dave
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