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Author Topic: Adding delayed out of phase subs to decrease room modes  (Read 10272 times)

Herman Chigrin

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Modeling the room modes
« Reply #10 on: March 21, 2011, 03:17:30 pm »

It's been quite a while, but I believe the white paper refered to in the earlier post was published by an engineer with JBL and is availabe from their website.  If I remember correctly, one of the interesting (and somewhat intuitive) points made was that the multiple subs should not be positioned symetrically in the room.  For example, you don't want to have a left and right sub both equally spaced on the floor at the front wall.

Is there software or any other feasible way to model the room modes for the subwoofer frequencies, so that I can figure out placement and quantity of subwoofers?

Thanks,
Herman
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Ivan Beaver

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Re: Adding delayed out of phase subs to decrease room modes
« Reply #11 on: March 22, 2011, 07:40:11 am »

  If I remember correctly, one of the interesting (and somewhat intuitive) points made was that the multiple subs should not be positioned symetrically in the room.  For example, you don't want to have a left and right sub both equally spaced on the floor at the front wall.
That is exaclty the point I was talking about in my last post here.  In a small rooms this can work well for "energizing the room modes".  It DOES NOT work in large rooms, where this technique will just case all sorts of new problems.
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Ivan Beaver

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Re: Modeling the room modes
« Reply #12 on: March 22, 2011, 07:42:34 am »

Is there software or any other feasible way to model the room modes for the subwoofer frequencies, so that I can figure out placement and quantity of subwoofers?

Thanks,
Herman
Most of the models out there that do sub freq are only in 2D.  I am not aware of any that do 3D.  And that really starts to change things.

What is a hobby of many guys in small rooms is constantly moving the subs around untill they get what they like.  And that can be very opinion driven.  Do you want impact or depth for example?  What is more important?
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Herman Chigrin

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Re: Modeling the room modes
« Reply #13 on: March 22, 2011, 03:14:14 pm »

Most of the models out there that do sub freq are only in 2D.  I am not aware of any that do 3D.  And that really starts to change things.

What is a hobby of many guys in small rooms is constantly moving the subs around untill they get what they like.  And that can be very opinion driven.  Do you want impact or depth for example?  What is more important?

I would say that impact is more important. As far as depth -- flat down to 30hz is good enough. The upper range of subwoofer coverage is 90 to 100Hz, with 18 db/octave crossover. But I am thinking to try a 12db/octave as well. So the subs will play into the midbass range, I presume.
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Chris Carpenter

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Re: Modeling the room modes
« Reply #14 on: March 22, 2011, 04:54:34 pm »

flat down to 30hz is good enough
...
So the subs will play into the midbass range, I presume.

 ???
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Ivan Beaver

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Re: Modeling the room modes
« Reply #15 on: March 22, 2011, 06:28:52 pm »

I would say that impact is more important. As far as depth -- flat down to 30hz is good enough. The upper range of subwoofer coverage is 90 to 100Hz, with 18 db/octave crossover. But I am thinking to try a 12db/octave as well. So the subs will play into the midbass range, I presume.
And what about music that has notes below 30Hz?

Are you saying that the musician has no purpose in putting them in there?

If the notes are in the music, then they deserve to be heard as the artist intended.

Just curious, why do you say 18dB/octave for the low pass?  Maybe that is what works for you, but people with different subs and full range cabinets may need very different crossover freq or slopes.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Randall Hyde

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Re: Adding delayed out of phase subs to decrease room modes
« Reply #16 on: March 22, 2011, 06:29:41 pm »

Your idea, 80Hz

Now put walls behind those two subs...
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Kevin Unger

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Re: Modeling the room modes
« Reply #17 on: March 22, 2011, 09:47:40 pm »

Stick the sub in the center of the room.

Do a walk around, and see where the bass "sits" and sounds the best.

Place subs around the room in those areas.




You'll usually end up in corners, of coarse. I've done this in small rooms a few times with great success.
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Herman Chigrin

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types of subs
« Reply #18 on: March 23, 2011, 12:42:37 am »

To clarify, I meant that the subs will cover the range below 80Hz. This is sort of a given because my midbass straight horns have a cutoff at 80Hz. I do want to hear any music material below 30Hz, to answer the question, I was just trying to make a point that for me personally, impact is more important than depth. If it is possible to get BOTH, I would love to hear the recommended approach. Also, as far as low pass crossover SLOPES, I am open to experimentation and I am in no way trying impose my opinion.

So far I can make a guess of how the subs shall be located, based on suggestions and the "CEDIA audio guide": in two or four corners, vertical arrays floor to ceiling. Plainly stated, two or four bass columns in corners, facing into room.

The question remains, what type subs provide both impact and good depth? Sealed, ported, tapped horns, bandpass?
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Ivan Beaver

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Re: types of subs
« Reply #19 on: March 23, 2011, 07:58:05 am »

To clarify, I meant that the subs will cover the range below 80Hz. This is sort of a given because my midbass straight horns have a cutoff at 80Hz. I do want to hear any music material below 30Hz, to answer the question, I was just trying to make a point that for me personally, impact is more important than depth. If it is possible to get BOTH, I would love to hear the recommended approach. Also, as far as low pass crossover SLOPES, I am open to experimentation and I am in no way trying impose my opinion.

So far I can make a guess of how the subs shall be located, based on suggestions and the "CEDIA audio guide": in two or four corners, vertical arrays floor to ceiling. Plainly stated, two or four bass columns in corners, facing into room.

The question remains, what type subs provide both impact and good depth? Sealed, ported, tapped horns, bandpass?
As usual there is more to it than just the type of sub.  What size and price are you willing to tolerate?

If you want a horn to go down low-it is going to have to be LARGE.  A ported box will go lower and be smaller.  HNOWEVER, it will not get as loud as the properly sized horn.

How loud do you need it to be? 

It is not just a simple question with a simple answer.  There are a lot of variables that have to be considered.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!
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