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In the Forum: Horn-Loaded Speakers
In the Thread: My Multi-way Horns

Post Subject: Mid-bass horn observationPosted by jessie.dazzle on: 11/30/2009

Looking at phase 3, one of the first things that pops out is the following:

Skushino wrote:
"...75-240Hz [from a] 12" x-driver [loaded into a] 70Hz [horn with an] 8" throat..."

Because they are a royal PITA to make, you'll want to give yourself every chance of getting your base horns right the first time.

If you're really expecting 75Hz, you'd be better off going with a horn that has a lower cutoff; the sort of standard "rule of thumb" is to dimension the horn such that its cutoff is one octave below the lowest frequency you plan to ask that horn to produce. This, in your case would call for a horn having a cutoff of 37.5Hz (call it 40Hz). Not allowing this margin may result in the dreaded honk, though many do push their bass horns well into this margin, it is, strictly speaking, not kosher... Factor in some reinforcement from walls, ceiling, floor, and you may get away with pushing it (you can apply the same rule to your 142Hz horn, but there you are probably close enough).

If playing by the "book", you are talking about a horn that measures around 10-feet, and that's only back to the driver mounting plane; now add the length of the back chamber and you'll get something like 11 feet total.

Also, the horn will need to have substantial mass; this must be taken into consideration when contemplating ceiling-mounting (not impossible though).

On another subject, looking at your CAD image leads me to recommend that you consider an acoustically transparent screen, allowing you to use a bigger screen, and partially (visually) obscure some of the horns. I'm assuming a pull-down model, which could be retracted when not using a projector.

Best of luck with the project,

jd*

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