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Author Topic: Rear canceling subwoofer  (Read 715 times)

William Abel

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Rear canceling subwoofer
« on: June 09, 2018, 12:49:45 pm »

Hi All,

I have LABhorns, TH118's, and in the past direct radiating 18" subwoofers.

My question is; Is their a subwoofer similar to the size if a TH118 that has less sound radiating from the back like the LABhorns?

 I'm currently a wedding and school dance DJ, and usually set up in a corner, right behind the sound system. The bass from the 2) TH118's usually beats the crap out of me when the dance gets going. For bigger events I have used a couple LABhorns, laying down with their mouths together, much quieter behind the sound system.

Does a push-pull, or other type help this?

Thanks,
Bill


   
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Art Welter

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Re: Rear canceling subwoofer
« Reply #1 on: June 09, 2018, 01:36:49 pm »


1)My question is; Is their a subwoofer similar to the size if a TH118 that has less sound radiating from the back like the LABhorns?

2)I'm currently a wedding and school dance DJ, and usually set up in a corner, right behind the sound system. The bass from the 2) TH118's usually beats the crap out of me when the dance gets going. For bigger events I have used a couple LABhorns, laying down with their mouths together, much quieter behind the sound system.

3)Does a push-pull, or other type help this?
Bill,

1)Fulcrum Acoustics makes several "Subcardioid" subs with as much as 10dB of rear rejection from a single amp channel, the CS118, CSP118,  CS121, CSP121, all of which are not much larger than a TH-118.
2) Probably most of the difference is due to the larger mouth area and increased depth of the LABSubs, as well as "bigger events" would imply a larger distance from the enclosures.
Setting yourself in a corner will concentrate the LF gain, better to put the subs there, and yourself somewhere else.
3) The larger the frontal area, the less rear wrap. Large horns do have some degree of pattern control in the upper pass band compared to a front loaded speaker, and the plenum on either push-pull or push-push can also impart some upper directivity, though the LF wrap will be roughly the same given the same frontal dimensions.

With two subs, two amp channels, and  two channels of processing you can run a cardioid or end-fire array and reduce level behind the subs, though backed into a corner that approach is useless.

Art
« Last Edit: June 09, 2018, 03:52:19 pm by Art Welter »
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Mark Wilkinson

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Re: Rear canceling subwoofer
« Reply #2 on: June 09, 2018, 02:45:29 pm »

Hi All,

I have LABhorns, TH118's, and in the past direct radiating 18" subwoofers.

My question is; Is their a subwoofer similar to the size if a TH118 that has less sound radiating from the back like the LABhorns?

 I'm currently a wedding and school dance DJ, and usually set up in a corner, right behind the sound system. The bass from the 2) TH118's usually beats the crap out of me when the dance gets going. For bigger events I have used a couple LABhorns, laying down with their mouths together, much quieter behind the sound system.

Does a push-pull, or other type help this?

Thanks,
Bill


 

Hi Bill,
I have labs and orbit-shifters which I think are fairly close to a TH-118. 
My labs have less rearward energy in comparison also, especially when coupled.

I've recently built a pair of plenum loaded double 18"s than can be used either push-pull or push-push.
I don't know if it's the plenum or their size, or most likely a combo of both, but they have a surprising amount of rearward reduction, even used singly. I need to measure...
But the thing is, they are about as big as labhorns.....the plenum takes up a good bit of volume.

The Fulcrum boxes that Art posted look interesting...
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Mark Wilkinson

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Re: Rear canceling subwoofer
« Reply #3 on: June 09, 2018, 02:47:05 pm »


1)Fulcrum Acoustics makes several "Subcardioid" subs with as much as 10dB of rear rejection from a single amp channel, the CS118, CSP118,  CS121, CSP121, all of which are not much larger than a TH-118.

Art

Hi Art,
any idea what Fulcrum is doing to get the rear attenuation ?
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Dave Garoutte

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Re: Rear canceling subwoofer
« Reply #4 on: June 09, 2018, 03:17:43 pm »

Do you have space to do an end fire config with your TH118s?
Or would that look weird.
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Art Welter

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Re: Rear canceling subwoofer
« Reply #5 on: June 09, 2018, 03:59:58 pm »

Hi Art,
any idea what Fulcrum is doing to get the rear attenuation ?
Yes, it's magic ;^).

https://soundforums.net/community/threads/cardioid-using-aperiodic-ports-a-la-fulcrum-acoustics.207180/

The position of the ports and the acoustical resistance of some "stuff" act like a second order LP phase shift in addition to the port's "phase inversion"...

The little Fulcrum line array using the passive cardioid is really cool too- it would take a huge horn to get that kind of a pattern.

Art
« Last Edit: June 09, 2018, 04:10:22 pm by Art Welter »
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William Abel

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Re: Rear canceling subwoofer
« Reply #6 on: June 09, 2018, 08:07:53 pm »

Yes, it's magic ;^).

https://soundforums.net/community/threads/cardioid-using-aperiodic-ports-a-la-fulcrum-acoustics.207180/

The position of the ports and the acoustical resistance of some "stuff" act like a second order LP phase shift in addition to the port's "phase inversion"...

The little Fulcrum line array using the passive cardioid is really cool too- it would take a huge horn to get that kind of a pattern.

Art

Interesting,
Bill
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William Abel

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Re: Rear canceling subwoofer
« Reply #7 on: June 09, 2018, 08:09:24 pm »

Hi Bill,
I have labs and orbit-shifters which I think are fairly close to a TH-118. 
My labs have less rearward energy in comparison also, especially when coupled.

I've recently built a pair of plenum loaded double 18"s than can be used either push-pull or push-push.
I don't know if it's the plenum or their size, or most likely a combo of both, but they have a surprising amount of rearward reduction, even used singly. I need to measure...
But the thing is, they are about as big as labhorns.....the plenum takes up a good bit of volume.

The Fulcrum boxes that Art posted look interesting...

I'd be interested in the measurements.
Bill
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David Sturzenbecher

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Re: Rear canceling subwoofer
« Reply #8 on: June 09, 2018, 11:06:51 pm »

I'd be interested in the measurements.
Bill

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Jason Raboin

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Re: Rear canceling subwoofer
« Reply #9 on: June 10, 2018, 06:45:21 am »

We have 4 CSP118 as well as some FL283.  It's the real deal, especially on Linea Research amps.  This fall I'll be using 12 a side FL283 and 2 a side CSP118 for two shows at The Wang in Boston and a show at The Kimmel Center on Philadelphia.  Oh, and the Palace in New Haven as well.
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