Two sets of surrounds-can this be done? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 02-27-2000, 03:17 PM - Thread Starter
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I have two rows of seating in my H.T. and the surrounds are slightly in front of the second row. This really does a number on the sound field. I have a B&K receiver with pre-outs and I was wondering about adding a second set of speakers. Is this feasable?

How would I go about deciding on the mounting position for the second set? Will this improve or ruin the effects for my main seating row? I have also wondered whether a dipole design would help with only one set utilized.

Dave


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post #2 of 9 Old 02-28-2000, 12:56 AM
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Dave, do you have direct radiators (monopoles) now?

What you could do is buy dipoles and mount them to the sides of the listening position. You could also mount bipoles on the rear wall if this is feasible. What I have done is have two pairs of direct radiators that face perpendicular to each other. If you have direct radiators now, you could face them toward a wall to make the soundfield less localizable. Another idea may be to point them towards the ceiling but if they have ports on the rear baffle, this idea would take some ingenuity.

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post #3 of 9 Old 02-28-2000, 06:19 AM
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While theaters do have more than one set of side speakers (and rears), they also have specialized electronics and delays for this to work properly. Also, consider that these are much larger spaces and the speakers are considerably further away from the listener (and higher fromt the floor).

Monopoles will create exactly the problem you have noticed. Most surround processors have been designed on the presumption the sides will be dipole. Meridian is an exception; but, then again, Meridian wrote their own software while most others buy their software from one of two chip suppliers.

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post #4 of 9 Old 02-29-2000, 06:33 PM
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I'm using two sets of surround speakers and it works just fine.
I have Atlantic Tech. direct radiating
speakers on the side and A.Tech.
dipoles behind.I've experimented alot
and I prefer all four on. The side
speakers give cues when needed.If a
dragon is flying around the speakers,
for example,you want a cue that he's
side left.The back speakers sort of
flood the listening area with ambient
sounds. I think if you,re going to
have two or more sets of surrounds
you could have all direct radiators,
and forget bipoles,dipoles,ect.

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post #5 of 9 Old 03-01-2000, 02:42 PM
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Dennis is on the right track from a psycho-accoustic point of view. Tomlinson Holman did an exhaustingly thorough paper on the placement of surround speakers in the reverberant field (big theaters) and the near field (our homes). I forget the title, but at one time it was available from the THX division at Lucasfilm. It was the science behind the decsion to make Home THX surround speakers dipoles. Multiple surround speakers, even in theaters, suffer from some psycho-accoustic annomaly that I will leave to Mr. Holman to explain.

If you can get the dipoles above and away from your two rows by a little, dipoles will serve you very well.

Good luck.

Randal F.
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post #6 of 9 Old 03-01-2000, 08:56 PM
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Randal,In a big room you could have
four diples,couldn't you? If two
are good,couldn't four be better?

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post #7 of 9 Old 03-01-2000, 11:05 PM
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Ms. B:

Maybe. It might depend on how big the room is and how far away your side walls are, and the dispersion characteristics of the transducers in your surrounds. The problem may be that some listeners may be out of the null for some of the dipole surrounds. In other words they would radiate directly to the listeners. If that where so, then their unique effect of not being able to be localized would be diminished or compromised.

The not-so-good psycho-accoustic effect that Mr. Holman documents in his paper when multiple direct-radiating speakers are used to create a surround field is a hollow, kind of tin can-sounding character. It has something to do with how all these speakers react together in the accoustic environment.

They apparently decided dipoles can't be used in the large theater because the seating area is so big. Dipoles couldn't possibly cover the entire listening area without becoming direct radiators for some as I mentioned above. Instead they opt to use a multiple speaker array to provide complete, uniform coverage of the theater, and try to minimize the problem of the hollowness with placement and room EQ. His paper goes into great scientific detail on how precise placement of surround speakers provide the most uniform coverage in the theater. This includes the number, spacing, and precise tilt down toward the audience.

A new twist to this, though, is the arrival of Dolby EX. I understand that THX is going to recommend two dipole surrounds on the rear wall of home theaters for this. It seems to me that one would do the trick, again depending on a number of factors. I plan to try one.

Anyone considering whether two dipoles placed even with and well above the listening area would be effective, should install them and use the Video Essentials DVD test that sends the voice or noise to all the channels. If you have used dipoles that are from the same family as the front speakers, I think you will be quite amazed at the impressive quality of the effect.

Enjoy.

Randal
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post #8 of 9 Old 03-01-2000, 11:17 PM
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Ms. B:

After this robust pontification, I would say that if you can position your multiple diploles such that their null is always pointed toward the listening area, then I'm sure they would sound great. The only reason, though, that you would see a designer do this would probably be in a room where two dipoles could not achieve enough spl. Two high quality dipoles can handle the coverage with adequate amplification and sound terrific.

Enjoy.

Randal

[This message has been edited by Cam Man (edited March 02, 2000).]
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post #9 of 9 Old 03-02-2000, 05:52 AM
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Among the reasons for dipoles (in the home) is as a result of the way we perceive the direction of sound. You cannot put two monopoles directly to the side of the listener and get a side image. We actually perceive the sound to be about 20 degrees in front of us.

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