WAF Subwoofer vs Front Loaded Horn - diyAudio
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Old 26th February 2014, 12:56 AM   #1
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Patrick Bateman's Avatar
Join Date: Oct 2006
Location: San Diego
Default WAF Subwoofer vs Front Loaded Horn

Over on DIYMA* we've been having an interesting discussion about horn subs versus conventional subs. And one of the participants suggest that I should do the following:

1) Measure my ported subwoofer
2) then EQ my front loaded horn so that the response is the same

Kudos to Hanatsu*, this made for an interesting comparison.

But first, here's some pics of our subs.

Click the image to open in full size.

The sub with "wife acceptance factor" is a Kef C4. This is a ported subwoofer with an 8" driver. It takes up 1.25 cubic feet. It's basically a cube with sides that are about 33cm each.

The horn sub is something I call a 'Depth Charge.' It's a front loaded horn that I crammed into a 20" Sonotube. Both subs are tuned to a similar frequency, about 38hz, give or take a couple of hertz. The Depth Charge is a horn, and it is significantly larger. Nearly five times as large, at six cubic feet.

Click the image to open in full size.
Here's the frequency response and the phase response of the two subwoofer. Theoretically, the larger sub should be more efficient. Theoretically, the phase response of a horn should lag by about 90 degrees, due to the quarter wave resonance, and the phase response of a vented box should lag by about 180 degrees, because it's radiating from the back of the cone. In the real world, this is a lot more complex, because of the length of the port, the length of the horn and the efficiency of each. (IE, if you have a ported box with a crummy port, as the SPL gets louder and louder the box starts to behave like a sealed box, because the port can't generate much output, and that makes the phase look more and more like a sealed box.)

In this measurement I see a few things:
1) The horn (blue) has an output advantage over the ported box. At the tuning frequency, it's particularly noticeable, where the horn is about eight decibels louder than the ported box. Of course, this is just Hoffman's Iron Law; if we used five ported boxes we'd have close to eight decibels more output. When it comes to subs, bigger is better.
2) Theoretically a horn has about half of the phase lag as a ported box. And these measurements seem to reflect that; at the tuning frequency the horn has about 50% less phase lag than the ported box.

* original discussion is here: http://www.diymobileaudio.com/forum/...2-post121.html
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Old 26th February 2014, 05:12 AM   #2
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Patrick Bateman's Avatar
Join Date: Oct 2006
Location: San Diego
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

^^ Here's the predicted phase response of the 'Depth Charge' horn, the predicted SPL response (unfiltered), the frequency response (filtered with a 2nd order lowpass at 140hz), and the measured response (with a 2nd order lowpass at 140hz, built into my subwoofer's amplifier.)

Note that the simulations may be off by a bit, because this is an unusual horn; all the bends are 180 degrees and it's been crammed into a Sonotube.

Last edited by Patrick Bateman; 26th February 2014 at 05:19 AM.
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Old 28th February 2014, 06:07 PM   #3
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Join Date: Sep 2008
Do you have the measurements without gating? They are not really valid below 80Hz with it for the pink trace.

Do the excess phase (or GD) differ between them?
Otherwise the phase is only the product of changes in the frequency plot (more or less). So a shallower slope means less phase shift.
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