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Author Topic: Rear canceling subwoofer  (Read 1044 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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Ivan Beaver

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Re: Rear canceling subwoofer
« Reply #10 on: June 10, 2018, 12:13:20 pm »



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
That is a very often overlooked/misunderstood issue with directional subs.

They need area behind them to work.

I often see "directional subs" that are placed a couple of feet from a wall.

That destroys anything the array is meant to accomplish, and makes the overall sound worse.

But-sadly-many people do directional arrays just to be "different or cool", so they can talk to their friends as if they actually knew what is going on------.

They understand the "marketing concept" behind the idea, but don't understand the workings.

And the "workings" is what is important to understand whether or not you should do it, or just face them all forward.

The ONLY times I do directional subs is when the directivity is more important than the sound quality.

You don't get both.
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Paul G. OBrien

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Re: Rear canceling subwoofer
« Reply #11 on: June 10, 2018, 05:09:26 pm »

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.

The easy solution here is to simply set yourself up somewhere else like off to the side of the speaker stack, you probably wouldn't have to move too far away to get yourself into a bass null or at least out of the power alley where bass is the heaviest.
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Lance Hallmark

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Re: Rear canceling subwoofer
« Reply #12 on: June 11, 2018, 01:17:49 pm »

Not a resolution per se but if you are not using a personal monitor consider setting one up. It will make the sound at your booth more balanced & tolerable, rather than just the muffled bass hitting you. I have subs set up right in front of the DJ table often and doing this makes it much more enjoyable for me, even if I don't need the monitor for beat mixing.
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Mark Wilkinson

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Re: Rear canceling subwoofer
« Reply #13 on: June 11, 2018, 05:10:27 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

Thank you Art, 
magic indeed  ;)

Your link was spot on.
You know, it almost seems like what he is doing with passive cardioid, is really old school stuff revisited.
I mean it's just a different port placement/structure, right ?

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Art Welter

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Re: Rear canceling subwoofer
« Reply #14 on: June 13, 2018, 11:47:33 am »

Thank you Art, 
magic indeed  ;)

Your link was spot on.
You know, it almost seems like what he is doing with passive cardioid, is really old school stuff revisited.
I mean it's just a different port placement/structure, right ?
More than just placement, -the devil is in those "structural" details.
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