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Old 19th July 2004, 07:44 PM   #1
tiroth is offline tiroth  United States
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Default Surround speakers: mono/di/bi/tripolar?

Perhaps because this forum is mostly dedicated to 2-channel audio there has not been much discussion about designs for surround speakers. The easiest choice of course is direct-radiating speakers to match the mains, but I'm interested in exploring alternatives because of the tendency to localize the ambient sounds to the surround speakers. An old solution is to roll off the HF but I think this is not applicable when we speak of discrete surround formats (5.1,6.1,7.1 channel).

Click the image to open in full size.

Perusing the home theater discussion groups it seems that there is a lot of appreciation for dipole loudspeakers which, unlike dipole mains, place the listener in the dipole null. The rationale is that for the more localizable higher frequencies, most of the sound reaching the listener will be reflected, giving a larger sense of space. Some of these designs are also switchable to bipole mode, which supposedly sounds better with (most?) multichannel music formats.

The best shoot-out I've found online is the link below; it is an interesting article but the test methodology is a bit bizzare and renders the conclusions a bit suspect in my mind.
http://www.hometheatermag.com/loudsp.../25/index.html

To throw more fuel on the fire, there seems to be little agreement in the marketplace on how to arrange the "bipole" drivers--there are a host of designs which place the drivers at less than 90 degrees with respect to the lister. I am guessing this is a hedge--less null, but still less directional than a direct radiator.

There are also newer "tripole" speakers which are basically a direct radiator mated with a bipole, with the direct radiator covering some of the lower bass (probably to avoid bipole canceling) but also featuring a direct-radiating tweeter. I suspect, both in theory and from looking at the FR plots in tripole mode versus direct mode, that these speakers are a real mess in the HF due to interactions from the dipoles, reflections, and the direct tweeter. But maybe the monopole bass driver is a good idea.
http://www.hometheaterhifi.com/volum...rs-7-2000.html

I intend to experiment with some of these configurations but I certainly don't have the desire to build two (or more) of everything. The designs which look most appealing to me are the basic or angled dipole as well as dipole mated with a monopole woofer (<100, 150Hz?)--a hedge perhaps between dipole and tripole.

Any thoughts from the forum? I've seen some theoretical comments by planet10 in favor of angled bipole for this application, but I've also seen the sentiment expressed that bipole speakers have no place in discrete surround sound--for those who have tried some of these setups, what did you think?
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Old 19th July 2004, 09:10 PM   #2
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I very recently created 180 degree dipolar surround speakers out of Wayne J's Dayton Home Theater design which I am now using in my home theater. You can see a few pictures on my website (sig, in the current theater pics link) and a full write-up on them will be posted shortly (almost done with it). They are positioned so that their center is about 7 1/2 feet off of the ground and the listener's ear is perpedicular to the poles. I enjoy the sound very much, it does allow for a greater degree of ambience.
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Old 19th July 2004, 09:30 PM   #3
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For me (personally) I prefer dipoles - I use the angled kef tdm34ds for side and rear duties. Angled with a forwards firing 'bass' unit (they're thx speaks so designed to cross at 80Hz)

I've tried a fair amount of monopole rears over the last 8 years in 4 different rooms, and just prefer the 'diffuse' feel of the dipoles.

I'd imagine you couild diy a decent version using tang-band full-range type drivers iso the kef uni-q's, and an 8" bass unit. I ~believe~ the xo points are around 300Hz and 2,500Hz. You'd need a bass unit with a -3dB around 80Hz sealed though. (I was going to do this but felt my passive xo skills weren't up to it...)

This is for film though - I've never tried surround music through dipole and have heard that monopole is champion there. ie you want localised sound in music..

Hth a bit.

Rob
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Old 19th July 2004, 10:14 PM   #4
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Default Something completely different...

Quote:
Originally posted by tiroth
comments by planet10
Here is a pic of my latest surround experiment ... these will hang from the ceiling just behind and a bit to the sides of the listening area. They have a 6" FR w whizzer (costing only labour and some ductseal, these are very much Frugal-phile (tm) material.

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Old 19th July 2004, 10:17 PM   #5
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Default Re: Something completely different...

Quote:
Originally posted by planet10


Here is a pic of my latest surround experiment ... these will hang from the ceiling just behind and a bit to the sides of the listening area. They have a 6" FR w whizzer (costing only labour and some ductseal, these are very much Frugal-phile (tm) material.

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Old 19th July 2004, 10:21 PM   #6
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Default Re: Something completely different...

Quote:
Originally posted by planet10
these will hang from the ceiling just behind and a bit to the sides of the listening area.
Seriously? Ouch on the SAF....

The "whizzer" looks like it is mounted to the enclosure and not the cone. (?)
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Old 19th July 2004, 10:27 PM   #7
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Default Re: Re: Something completely different...

Quote:
Originally posted by leadbelly


Seriously? Ouch on the SAF....

The "whizzer" looks like it is mounted to the enclosure and not the cone. (?)
Compared to the dirty great projector I've got hanging off my ceiling they look positively cute

Rob
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Old 19th July 2004, 10:50 PM   #8
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Default Re: Re: Something completely different...

Quote:
Originally posted by leadbelly
Seriously? Ouch on the SAF....

The "whizzer" looks like it is mounted to the enclosure and not the cone. (?)
Seriously... the wife like the way they look (they originally came with a cylinder enclosing everything. They are small (about 7" in diameter ... that isn't the whizzer, it is the deflector. The driver fires up into the delector, giving a 360 degree radiation pattern.

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Old 20th July 2004, 04:03 AM   #9
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Old 20th July 2004, 12:22 PM   #10
tiroth is offline tiroth  United States
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Dave,

As usual, weighing in with something interesting and esoteric.

Thanks to everyone for their thoughts.
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