Cabinets for Altec 515B woofers suggestions

[MrMonster]

Hello Lads,
Can some of you make suggestions for cabinets for the Altec 515B woofer? I have a pair of 256's with Jabo conical horns, and Behringer crossovers running right now, they sound great, but I do need a better Xover.

The point is, the tremendous size of the A5 boxes is eating into the room space.
If they were even a foot less in length and width, it would be a bit more manageable in my front room.

Are there any of the Altec or JBL bass reflex box designs for the 15" woofer that would help deliver an equivalent sound with a smaller footprint?

Thank you,
Donald Bowm

[MrMonster]

Sorry, I meant 828 or 826 cabinets, plus this photo has my 311-60 horns on.

[GM]

Obviously, if you remove the horn, the reflex box can have a smaller footprint and of course it won't sound the same through the mids, but it will sound more tonally balanced over a wider BW once the HF horn is shelved down to match it. To narrow it up to the width of the 311-60 though and keep the same height requires and even deeper cab, so once we start shrinking its depth, its bass response starts leaning out also.

Bottom line, you can make the cab as small as ~3 ft^3, but it won't have any bass output.

GM

[bvn]

See my notes under "my Altec A10" - which uses 515b's
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The theater configurations get their low end from the huge cabinet surface area (AKA "wings") and the distance from the audience. 3 dB down at ~90 Hz isn't that bad. From what I remember from my acoustics classes is that the coupling (with air) roll-off (de-coupling) begins at the wavelength that matches the circumference of the radiator.
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A 15" radiator has a ~4' circumference, which puts the 3 dB down decoupling point in the 200 Hz .. ~250 Hz range. 4 such radiators will drop the de-coupling point an octave - which matches the Thiele-Small prediction quite closely.
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There are 5 ways to increase the radiator size - horns, ports, passive radiators, more, and wings (a form of horn for large diffraction situations - which require at least 1/2 wavelength to fully develop).
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The guiding rules of all engineering are: anything that works is a compromise and Mother Nature is a bitch.

[Panomaniac]

I agree with GM. You could lose the horns in the 828 cabs and save a good bit of space.
Don't remember who much room they use up, but it's substantial.

The 828 box with the back of the horn flare open has a net volume of ~11 ft. You could probably get away with a net volume of about 8 feet with the 515B. That means a box of 40x19x22" (3/4" ply). That should save you a lot of room.

[GM]

Don't recall if any of the 828 series had open horn cavities, but the closed off units are ~9.4 ft^3 net with driver installed. Altec listed the 825 with its open horn cavities at 12.66 ft^3 minus driver, so ~12.33 ft^3 net loaded with a 515B. From memory though, I recall calcing it at ~11.4 ft^3, so YMMV.

Regardless, when it comes to cab net volume (Vb), less is always less bass/tuning flexibility and if the signal's total impedance is high (source + any passive resistance), then at some point in the Vb reduction curve the system will become under-damped unless its tuning is made ~aperiodic in nature.

Also, in retrospect, the 311-60 with driver is ~as deep as the 825/828, so reducing the cab's outside width/depth dims to less than the HF horn's 'footprint' is as small as you can make it unless of course he wants them shorter also.

GM