Horn Loaded Subwoofers

[StephenM]

Having been on this board more than a week now, I've seen the regular suggestions of horn loaded subs. To satisfy my curiosity, I did peruse some measurements of a couple models, one DIY, and the other the vaunted Danley DTS-10. While the output was most impressive for both models, I did note an interesting anomaly:

The DIY horn sub:

http://www.data-bass.com/images/measurements/42/E%20gjallerhorn%20waterfall.jpg

The Danley DTS-10

http://www.data-bass.com/images/measurements/29/E%20dts10%20waterfall.jpg

That's some pretty significant resonant activity. Here's a couple more conventional subs for reference:

SVS PB13U, 20Hz mode

http://www.data-bass.com/images/measurements/53/B%20svs%20pb13%20ultra%2020hz%20waterfall.jpg

SVS PB13U, Sealed mode

http://www.data-bass.com/images/measurements/57/B%20pb13%20sealed%20waterfall.jpg

Velo DD18+

http://www.data-bass.com/images/measurements/68/B%20dd18%2B%20servo%20gain%208%20waterfall.jpg

Is this a recognized drawback of horn loaded subs? What causes this behavior?

[CECAA850]

I didn't recognize the DIY sub. Was it tapped or front loaded?

[StephenM]

It is tapped.

http://www.data-bass.com/data?page=system&id=45

[CECAA850]

It may be a product of the tapped design (back wave front wave interaction??). I'd be curious to see a waterfall of a FL horn to see if it has one hump or no humps. A classic case of measures bad, sounds great.

I have read on a couple occasions that some of the horn designs don't really measure all that well but everyone who hears them raves over their SQ.

[Chris A]

Is this a recognized drawback of horn loaded subs? What causes this behavior?

This is a drawback of tapped horn subs that are very small relative to the size of a conventional horn size. The apparent resonances are a function of reflection paths due to acoustic impedance mismatch at the horn's mouth with the room. If the mouth was many times larger, these effects would be non-issues.

Note that a tapped horn sub is a fairly complex device in that it behaves like a horn with two drivers: one at the throat to provide the main acoustic output of the horn, and one driver close to the mouth to cancel resonances and fill nulls in the horn's complex response due to its severely undersized horn mouth.

It's actually a pretty neat trick that Tom Danley patented the same driver cone(s) driver to do this. There are also other patents on tapped-horn like designs that represent prior art and I believe invalidate the Danley patent, but I believe that we should acknowledge his contribution of the tapped horn design.

Having said that, one should be aware of the limitations of the tapped horn designs in terms of usable bandwidth: I use steep 40 Hz crossover filters on my SPUDs and Jub bass bins. The tapped horns' response complements Jub bass bins response to handle the bottom octave below the 31 Hz -3dB point of the corner-loaded Jub bass bins.

TANSTAAFL [] Everything works great in my setup but I wouldn't use SPUD TH subs crossed at a higher frequency than ~40 Hz. Same advice applies to the DTS-10 and the DIY TH design.

If you are thinking about using direct-radiating subwoofers instead, understand that they suffer from driver compression and greatly increased IMD (about 20-25 dB higher- in fact), which is non-harmonic distortion. I don't know about you, but I prefer to have uneven FR which I can handle with EQ over non-harmonic distortion of direct radiators.

Chris

[StephenM]

Thanks for the explanation!