Sorry, I meant 828 or 826 cabinets, plus this photo has my 311-60 horns on.
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
Sorry, I meant 828 or 826 cabinets, plus this photo has my 311-60 horns on.
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
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
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.
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.
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
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Hello Lads, and thanks for the response.
I don't know if I made myself clear. The HF horns are not in the cabinet, I have them mounted on top of the box.
So now, I have just the 515B woofer loaded in the box, with a full open bottom port.
They sound very good now, with good clean Bass, and I was hoping to mount the LF 515B in a smaller footprint box and hopefully keep the same performance.
IS there a list somewhere of cabinets that Altec mounted the 515B only, or with a smaller HF horn?
Thank you,
Donald Bowman
We understand, we are referring to getting rid of the 515B's horn, i.e. put it in a simple ported box.
I don't recall 515s being spec'd in anything but horn cabs, though that doesn't mean they don't perform well in vented or sealed alignments if properly tuned and EQ'd for the app, i.e. the room and source impedance. Don't recall it being spec'd with any horn smaller than the 511 either, though it could be interchanged with any 803B/416 series cab design and EQ'd to suit.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Yeah GM, about 11ft seems right to me.
I had done a quick sim on the 515B in an 11ft vs 8ft box and it looked pretty good. Group delay was better in the smaller box, if that matters. Tuning in the mid 30s for both boxes. Didn't look at damping.
So Mr. Monster you should be able to go with a smaller box and still sound nice. In a simple box you lose the A7 style bass flare which does take up some room. Would my 40x22x19 box fit your needs?
If you are running your cabs with wide open vents now, you really aren't getting much bass. What you may be getting is a nice hump circa 60Hz. A better tuned reflex box will give you lower, cleaner bass. I know, been there, done that! =)
The thing about GD isn't how much, as how low, it peaks, especially since it increases with decreasing Fb, so if you tune low enough that it decays away before our hearing acuity improves enough for it to be an issue........... and why I always recommend a low tuning for best overall vented alignment performance.
Many folks prefer higher tunings though, so from this we can infer that either GD isn't the 'bad thing' that the ported 'bashers' maintain and/or many folk's LF hearing acuity is nowhere near as good as they believe it is and judging by the overwhelming commercial success of a certain consumer brand combined with the perceived high SQ of highly resonant tapped horns, I'm going with the latter.
Again, the horn's rather large dims sets the smallest practical footprint, so your width/depth appears to be a little small based on its published drawings.
Hmm, IIRC the cab's Fb is up around 80 Hz with no baffle boards, making it a crude BLH which yields enough of a broadband tuning peak to extend the LF horn's gain BW down to around its 110 Hz flare frequency, so for deep, bass shy, music it's an acceptable tuning choice, though I imagine it ideally needs a bit more damping around the driver to quell excessive mids emanating from its mouth. A good tuning if XO'd to a suitably 'fast'/efficient sub system also now that digital EQ/delay down into the single digits is available at a reasonable price.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
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