Which would you go for? (with response curves) - diyAudio
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Old 6th March 2008, 06:52 PM   #1
pdq2 is offline pdq2  United States
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Default Which would you go for? (with response curves)

I'm working on a large horn-loaded subwoofer project which needs to fit in a particular space, and after playing around forever with different drivers and designs in HornResp I've come down to a couple favorites. Both are the same driver (B&C 12PLB76).

This will be mostly for HT, but some music too. The room is 16 feet square, and even though it isn't "sealed" I'm anticipating a bit of a room resonance around 35 Hz (half wavelength~16 ft).

Plan A is pretty simple, with only two 90 degree turns, and the response (left, below) is pretty flat, rolling off below 40. I might use an equalizer to boost @20 Hz, and might get _a bit_ of room gain (although I'm not counting on it) to improve the very-low end response.

Plan B adds another corner (this one bends ~ 150 degrees) for more length, and gets better low end extension, but adds some ripples in both the response and impedance. (The dip at 35 Hz is actually intentional, to try to diminish the expected room resonance @ 35Hz I mentioned above.)

I've been going back and forth- I'd like to go for that last octave, but not if it means distortion or funky resonances, perhaps even beyond what HornResp shows, since it models these horns as straight shots, which this is not.

I can (and will) give you more details on this project later, but for now, which general direction would you take?
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Old 6th March 2008, 08:53 PM   #2
pdq2 is offline pdq2  United States
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Default Here are those response curves-

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Old 7th March 2008, 12:40 PM   #3
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Is it a corner horn or where does it sits in the room? If you want to place it under a desk or table, you can extend the horn path a bit further using that desk/table. Simulate it as an extra conical segment in Hornresp. This could give you the extra LF you want, as I would advise against using boost to get to 20Hz, especially with horns.
Check out the displacement curve in hornresp to see if there is any room below your horn cutoff to boost.

That said, the second one with the tiny dip seems the most interresting. If you check out the small 40Hz horn sub Cowanaudio made, you'll see that when you radiate closely into a corner, the space confinement in a room is more than 1/8th space so this should lessen the dip. You can also get a lower cutoff becouse of the >1/8th space loading. (I remember he got flat till 29Hz out of his predicted 40Hz horn when pushed into a corner.)
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Old 7th March 2008, 05:51 PM   #4
pdq2 is offline pdq2  United States
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Default Thanks, Cordraconis-

For some more details, my intent is to entirely hide this horn in the triangular space behind some cabinetry we're having built-in that cuts across a corner of the room. A pure exponential horn will run up the wall behind this cabinetry, then turn 90 degrees, using the top of this cabinetry, the ceiling, and adjacent walls as a (conical) extension to the horn. The mouth is then ~12000 sq cm, the simplest horn length is around 350 cm, and the whole thing is invisible to the wife!

In HornResp, the schematic looks like this:


Click the image to open in full size.

...so that even though the final segment is conical (actually it's rectangular, but the expansion is conical, not exponential), it matches up pretty well with the longer exponential first part.

The second design, with the dip, adds some (folded) horn length at the base, up to around a total length of ~450 cm.

My intent was twofold- when we decided to build in this cabinetry, I saw an opportunity to use the space behind for a really big subwoofer, which is something I've always wanted to build. My secondary intent is to make this as wife-and-decor-acceptable as possible.

So thinking about it more last night, I'm leaning toward the simpler design, since I really don't want the end result to be "boomy" at all (at 35 Hz or below in this room), just really clean (yet fairly deep) bass.
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Old 9th March 2008, 04:06 AM   #5
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If you don't need >100Hz, have a look at some of the tapped horn designs in the big TH thread if you haven't already. Erik's Eminence 15" design (with a 3015LF - circa post 666) looks like a beast, and a lot simpler to build than a conventional horn. By the sound of it, should fit into a similar space too.

Of the two you posted, the one on the left.
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Old 12th March 2008, 03:59 PM   #6
jol50 is offline jol50  United States
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I'm more into car subs, but would you really want a HT sub that died after 40Hz? I would want lower than a car and I shoot for minimum 30 before it drops off for SQ. Even if you EQ it back up you lose db and suck power and with that steep a curve it may not work well at all. I don't know all of your constraints with a horn, but I'd think the chart on the left would miss most of what a HT sub is for. I would want to be touching 20Hz for sure in a HT sub of any size, if possible. Unless you are worried about waking up the people next door/vibration/you just can't go that big/etc. Just my $.02.
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Old 15th March 2008, 02:45 PM   #7
pdq2 is offline pdq2  United States
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Default Thanks for the replies

I'm going with the one on the left. Max SPL at 20 Hz (by HornResp- that is, without any room gain) is still over 105 dB which is only about 5 dB less than the design on the right.

I'll post photos of the project later.
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Old 15th March 2008, 02:51 PM   #8
jol50 is offline jol50  United States
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Let us know how it works out, looks like a cool project.
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