"Modular" Subwoofer Horns? - diyAudio
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Old 17th June 2015, 08:57 PM   #1
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Default "Modular" Subwoofer Horns?

I've seen a few resources that say multiple basshorns can be used together to provide for the appropriate mouth area/cut-off, for instance:
BASSHORN - Avantgarde Acoustic? Hornloudspeaker GMBH
How do I go about designing multiple horns to combine and operate as one large horn?
What happens to the low frequency output when you combine short horns?

But I can't find any actual literature saying why this is the case (and I've been looking for days ), and I'm a little bit confused on both the design and the acoustics.

In terms of design, there's a paradox between setting a flare rate and setting a length sufficient to support the cut-off. Take, for instance, and exponential horn who's cross-sectional area is defined by the usual S(x)=S_t * e^(m*x).

The size of the mouth/throat determines the efficiency of the horn, while the flare of the horn determines the cutoff. I'm confused what the rationale is here, though, because setting the size of the size of the mouth of an individual horn in a combined system (say, if I wanted to stack four horns next to each other, I'd calculate the needed mouth size for a given cut-off and then divide by four), I'm necessarily also changing the flare rate or the length; if I want to keep the length at 1/4 wavelength, then the flare is going to necessarily be much shallower, if I want to keep the same flare rate then the length is going to be shorter.

For instance, if I hypothetically wanted to create a *single* horn to be operated in the corner of a room (1/2 pi steradians) with a 20 hz cutoff and a driver with an Sd of .1219 m^2 (typical for an 18" driver), I could design a horn with a mouth area "Sm" of

(c^2/(32*pi*Fc^2) = ~3 m^2

My flare constant "m" would be

4*pi*Fc/c ~= 0.73

and my length "l" would be

Log(Sm/St)/m = 4.36298

Now, if I try to build four "modular" horns, each comprising 1/4 of the mouth area "Sm" and being 1/4 wavelength of 20 hz long, my flare rate is going to be truncated.

But if I do the same calculation for a horn that has 1/4 the mouth size (i.e. ~ 3/4 m^2), I can use the proper flare rate, but my length will be shorter (around 2.46 m).

The two parameters contradict each other; either you're truncating the flare rate or length. Which is it meant to be if you're design multiple horns to be used in tandem?
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Old 17th June 2015, 09:56 PM   #2
NEO Dan is offline NEO Dan  United States
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Hornresp has a multiple speakers (cabinet/system) option [CTRL]+K
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Old 17th June 2015, 10:06 PM   #3
wg_ski is offline wg_ski  United States
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This is why you end up with high compression ratios when you try to go deep - you make the throat area smaller too. For tapped horns you usually try to further undersize the mouth, exacerbating the problem. It becomes a 'purple paper eater' - don't try this with your daddy's EVM18B.
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