Vented rear chamber horn subwoofer

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shrub0
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Vented rear chamber horn subwoofer

#1 Post by shrub0 » Tue Jan 14, 2020 12:58 pm

A year or so ago I was playing with hornresp and my approximation of a t18.
I figured out I could get better low end extension by porting the rear chamber.
Frequency response looked good but I noticed the impulse response went to hell.

There's a sub design on youtube and avsforum called the devastator that is getting alot of buzz it's a quasi horn bandpass enclosure with a rear port.
So let me know your thought if you have tried a rear ported horn or think it'd be worth trying.

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Bill Fitzmaurice
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Re: Vented rear chamber horn subwoofer

#2 Post by Bill Fitzmaurice » Tue Jan 14, 2020 5:41 pm

The DR, Wedgehorn and Jack series are all ported chamber horns. Port rear chambers work fine with horns down to about 80Hz, but below that not so much. That's why I don't use them with horn loaded subs.

Bruce Weldy
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Re: Vented rear chamber horn subwoofer

#3 Post by Bruce Weldy » Tue Jan 14, 2020 6:29 pm

Bill Fitzmaurice wrote:
Tue Jan 14, 2020 5:41 pm
The DR, Wedgehorn and Jack series are all ported chamber horns. Port rear chambers work fine with horns down to about 80Hz, but below that not so much. That's why I don't use them with horn loaded subs.
Would this include the OTops also with their ports on the side?

6 - T39 4-25" 2-22" 3012LF
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Bill Fitzmaurice
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Re: Vented rear chamber horn subwoofer

#4 Post by Bill Fitzmaurice » Tue Jan 14, 2020 9:38 pm

Yes, forgot about them.

shrub0
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Re: Vented rear chamber horn subwoofer

#5 Post by shrub0 » Wed Jan 15, 2020 7:56 am

What was the reason it didn’t work for low bass?

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Bill Fitzmaurice
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Re: Vented rear chamber horn subwoofer

#6 Post by Bill Fitzmaurice » Wed Jan 15, 2020 8:32 am

Sensitivity of the port output is too low. I get around that with the midbass horns by tuning the rear chamber high, which realizes greater port output sensitivity at the expense of low end response. That technique doesn't work with a bass horn.

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Re: Vented rear chamber horn subwoofer

#7 Post by shrub0 » Wed Jan 15, 2020 2:26 pm

I see, thanks Bill.

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jimbo7
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Re: Vented rear chamber horn subwoofer

#8 Post by jimbo7 » Sun Jan 19, 2020 12:23 pm

To continue the ported horn topic....so what would this thing be? https://shop.gsgad.com/collections/horn ... ingle-unit Looks like a 6th-order bandpass to me.

Came across it on youtube https://www.youtube.com/watch?v=DgtVxjg06to
Last edited by jimbo7 on Sun Jan 19, 2020 12:35 pm, edited 1 time in total.
BFM builds:
XF212
T24 BP102 24"
2x SLA's 6-5" mids, 9- gt-302's
2x AT 14" MCM 55-2421
TrT 5" MCM 55-2421
AT 18" JBL GTO804
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Simplex 10 BP102

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Bill Fitzmaurice
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Re: Vented rear chamber horn subwoofer

#9 Post by Bill Fitzmaurice » Sun Jan 19, 2020 12:34 pm

By all appearances it's a band pass reflex, but I'd need to see actual plans to be sure. I don't see anything that qualifies as a horn.

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jimbo7
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Re: Vented rear chamber horn subwoofer

#10 Post by jimbo7 » Sun Jan 19, 2020 12:42 pm

Bill Fitzmaurice wrote:
Sun Jan 19, 2020 12:34 pm
I'd need to see actual plans to be sure
It says the bass quality is "excellent" and the mid-bass rating is "supreme". What else could you want? https://shop.gsgad.com/pages/performanc ... ison-table
BFM builds:
XF212
T24 BP102 24"
2x SLA's 6-5" mids, 9- gt-302's
2x AT 14" MCM 55-2421
TrT 5" MCM 55-2421
AT 18" JBL GTO804
2x OT12 flat array
2x SLA Pro 2-Alpha 6's 2-Goldwoods
2x T39 24" 3012lf
Simplex 10 BP102

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Re: Vented rear chamber horn subwoofer

#11 Post by Bill Fitzmaurice » Sun Jan 19, 2020 3:03 pm

"These are subjective ratings independent of the output level."

There are things where subjectivity matters, like 'which is better, Coke or Pepsi?' But with anything that involves spending more than a couple of bucks I want to see some objectivity as well.

GSG does not provide a “frequency response” for each subwoofer because a simple frequency response provides virtually no information about the capabilities of the subwoofer.

Translation: They don't have frequency response charts. That's OK, most sources don't. But if you're going to claim to have made a better mouse trap I want to see some dead mice. :?

shrub0
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Re: Vented rear chamber horn subwoofer

#12 Post by shrub0 » Thu Feb 06, 2020 10:43 pm

To me that devastator might make alot of spl for movies but I don't think music would sound good.

Take for example the phase response of the devastator nano from the hornresponse model. At 60 hz the phase is at -165 and at 120 hz the phase is 151 degrees.

Let say we have a kick drum with a fundamental at 60 hz and a harmonic at 120hz. In the devastator the harmonic has a phase change of 316 degrees. If I'm thinking about this right the harmonic will be delayed 7.3 ms

Btw from my approximate of the table tuba in hornresponse I see a phase change of 26 degrees for the difference between 60hz and 120hz.

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Re: Vented rear chamber horn subwoofer

#13 Post by caddylackn » Wed Mar 18, 2020 10:40 pm

The Devastator website lists it as a 5th order Bandpass box.
It requires a subsonic filter at 12 dB Butterworth at 17-20 Hz and needs 2,000 to 5,000 watts.

The maximum output is listed as >133 dB at 80 Hz.

I think the minimum cost "cheap" pro sound 21" driver recommended for it is $500.
This is really professional sound equipment modified for home theater use.
16.5" AT w/ 860w
TLAHs w/ 9 mids & 16 tweets
17" THTLP w/ Dayton RSS315HF-4
16" TAT w/1060w
18" TT w/ Dayton DCS-205-4
5.5" TrT w/ DCS-205-4
T-18 w/ DCS-205-4
33" THT w/ Dayton Titantic 1200
Building--DR200s

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Bill Fitzmaurice
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Re: Vented rear chamber horn subwoofer

#14 Post by Bill Fitzmaurice » Thu Mar 19, 2020 7:20 am

There is no 5th order band pass alignment. Band passes are always even order. https://en.wikipedia.org/wiki/Loudspeak ... _band-pass

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