Question on 8182 cabinet modifications

[dhook17322]

I am starting on construction of cabinets for a couple 3182's. The factory dimensions for the 8182 enclosures are very poorly chosen from the standpoint of an investment in plywood, namely 54" tall and 26" deep. Would it hurt performance much to change the size to say 48" x 48" x24"? That would actually increase the volume somewhat and save a lot of scrap.

[cclark65]

I am not positive, but I think you can change the shape of the cabinet and dimensions, but you really should keep the volume the same, unless the original cabinet was designed completely wrong for the speaker. I don't know the width of the 8182 cabinet, but pretend it's 24. Take the 54*26*24 and you get a volume of 33696 cubic inches. You could change the height to 48 and leave the width at 24, but you should make the depth to 29.25 inches. That would keep the volume the same and save plywood. Also take into account any bracing inside the structure, that will reduce internal volume also.

If you change the volume of the cabinet, then it will have different characteristics, some of which could be bad, such as the speaker becoming unloaded at lower frequency and popping the cone out of the frame...you wouldn't want that to happen!

I am sure the original design was specified to fit behind theater screens in the little area behind the curtain.

[dhook17322]

Thanks much. The factory internal dimensions are 52.5"h x 34.5"w x 23.5"d with a 9" port x 12.88" length giving a volume of 42,564 cu.in. or 24.6cu. ft.
I'm aiming for 46.5"h x 22.5"deep x ~40.7w" to keep the volume the same. Allowing for additional bracing, the width might increase to around 42" to keep the same volume.
The drawing doesn't spec any insulation. Any idea on how much to add, all sides or only 3 of 6 sides?

[LICORNE]

Hi,

I plotted your specs with 42" wide internal volume.The simulator tells me to change the port
resonance. At 19 Hz it gives me the same results as the original plan 9" by 12" deep.

As for Insulation 3 sides is better than all sides. It's a ,matter of taste.

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[dhook17322]

Thanks much for the help. The Fs for a 3182 is 18Hz. Is there any choice of resonant frequencies with the port dimensions if the width is increased to ~46"? Can the resonant freq. be lowered a little to 16 or 18Hz. I'm kind of a pipe organ fanatic and it would be good if the sub can go down to 16 Hz if possible.

[LICORNE]

Hi,

The simulator gives a reading AT 46.5 wide a port length of 12.5" Fr 18HZ.
This simulator is very sensitive to box configuration.


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[LICORNE]

Oops port length 12.7 "

[LICORNE]

Hello there,

These cabinets are ported. You will need the tube
lenght that goes into the port hole.

There's a program on the web to calculate port length . You need the speaker displacement parameter of the speaker
to do so. Speaker displacement Ft cube would be XMAX if I'm not mistaking in the THIELE Small Parameters.


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[Russ Farrell]

Hi Dave:
IRT insulation, everything I've read and been told says 3 sides, as Convergence said. I asked Altec why they didn't use any in the 8182. They said that at low subwoofer frequencies the wavelength is so long compared to the insulation thickness and particle size that the insulation has no effect at all. They had run some tests to confirm this. They did say that it is extremely important to be sure there are no air leaks in the cabinet joints.
The 8182/3182 was introduced at an AES Convention in the LA Hilton. The demo room was a typical hotel meeting room; far too small for an ideal demo. I'm quite sure Bob Davis brought most of the demo material. He liked organ music too. Can't remember what the lowest notes were, but under 20 Hz. Dave, I'm confident you will hear, and your stomach will feel, your 16 Hz pipe. We had to leave the room every 15-20 minutes to let our stomachs settle. Don't worry, Dave, you won't be playing it constantly like that (will you?). BTW, I loved it. Enjoy. Russ

[dhook17322]

Thanks much for the great information, just what I hoped for. And the best Independence Day to all!