# Bipole or Multiple Direct Radiating Surrounds?



## Chris in Dallas (Apr 4, 2007)

I'm building a fully active HT system, and am planning to use identical speakers all around. They would be bookshelf-size, with response down to about 60 Hz, crossed into a pair of sonosubs around 70 Hz. I have plenty of amplifier channels, so that is not an issue at all. The room will be roughly 14x20, oriented the long way. Ceiling height will vary from about 9' at the center (across the short span) to about 6'4" at the front and back. Currently planning on two permanent rows of seating (with room for more temporary seating, such as pillows on the floor in front).

My question is this: Should I go with multiple identical direct-radiating side surrounds, or with single (or multiple) bipole side surrounds? What about in the back? I can also use direct radiating speakers, but wire them out of phase with each other to create bipole speakers in separate cabinets, effectively.

In commercial theaters, they use multiple identical direct radiating surrounds to create a diffuse effect. Can I, should I, go for the same thing? I find the idea of 9 or 11 identical speakers appealing, and it sure would make building easy.


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## fbov (Aug 28, 2008)

Chris,
Go with a single direct-radiating, full range side surround for _each channel_ of surround source material from your pre/pro. (i.e. 2 surrounds for 5.1, 4 for 7.1) Wire all in phase and let the pre-/pro do it's job, which is crating the diffuse effect. Multiple drivers producing the same signal will interfere with one another causing frequency-dependent peak-and-null patterns in the listening area. 

Commercial theaters use many surrounds, initially with a single channel source, but with appropriate delays to prevent interference patterns from appearing. Use whatever your pre/pro can provide, but only 1 speaker per unique program channel.

Have fun,
Frank


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## Kmott (Mar 29, 2009)

Chris,

Based on my understanding:

Dipoles will provide the most diffuse soundfield and required for THX setups.

Bipoles provide better imaging and are recommended for Dolby Digital and DTS.

Identical full range speakers are for high resolution multi-channel music such as SACD and DVD-Audio. They will also provide the most even timbre matching and are ideal if size and expense are not an issue.

Hope this helps


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## Anthony (Oct 5, 2006)

If you are only going to have two surround speakers on the sides, go with a dipole setup. That will create the best diffuse soundfield for the rears at multiple listening positions.

If you are going to have just two speakers on the back wall, then direct radiating would most likely be better, but not necessarily as diffuse (i.e. you can localize the point source).

If you can go with four speakers, you can put dipoles on the side walls and direct radiating in the rear for a 7.1 setup.

As for the "real theater" setup. They have much larger volumes to fill and the speakers are farther away from the listening positions. This gives more time/space for all the speakers to integrate in your brain and make them sound diffuse. It also lessens the likelihood of being exactly halfway between two speakers and getting a weird interference pattern. In a much smaller room with only a few speakers lining the walls, you stand a good chance of being in a weird peak/null between two speakers.

Of course, this all being said, I have seen each of the arrangements I just mentioned in actual houses and they all sounded pretty good. I definitely prefer the dipole rear sound over the others, though.


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## tued (Mar 5, 2008)

take a listen to the Real HT Info Poddcast #46 they discuss this issue. Their conclusion is either go with the dipole solution or the multiple rear-speaker setup.


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## Owen Bartley (Oct 18, 2006)

I think it will also depend on how you're positioning the speakers relative to the seating. I built a dipole rear centre surround (for 6.1) and because it is placed some distance from the rear wall, the side firing tweeters don't have the impact that they would have in another setup. In that case I probably would have been better off with direct radiating. However, if all of the speakers will be mounted on or near walls, I think dipole could sound great for all 4 channels, giving you a very diffuse surround field.


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## tonyvdb (Sep 5, 2007)

For a room your size going with more than 7 speakers will be not only overkill but will cause issues with cancellation and imaging problems. Go with the standard THX recommended setup and you will be very happy.


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## Chris in Dallas (Apr 4, 2007)

tued said:


> take a listen to the Real HT Info Poddcast #46 they discuss this issue. Their conclusion is either go with the dipole solution or the multiple rear-speaker setup.


I am 37, going on 38, I think, therefore, that I am forgiven for not ever having really figured out what the hey a "podcast" is. I assume it is something I can play on my computer(?)


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