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Bipoles , dipoles or direct speakers


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#1 of 21 Hisham_k

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Posted December 25 2002 - 01:35 AM

To all you guys with a 6.1 setup.
After experiencing with the 6.1 setup for a while now on different movies,what would you rather use for the back surround or back center speaker(s) : Dipoles, Bipoles or Direct radiating .

#2 of 21 Kevin C Brown

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Posted December 25 2002 - 05:39 PM

I "mimicked" the front 3 to the back three for a while:

Def Tech BP-30's and a CLR 2000 up front, and BP-20's and a CLR-1000B in back. All identical 6.5" woofer drivers. (So the rear center was a direct radiator.) People *say* that having a direct radiator back there can make that speaker too localizeable, but I never seemed to notice that (and I did try Posted Image ).

One problem I found with dipoles is, if you look at a freq response curve, it is atrocious. But that's because of how it's designed.

My impression is, and this is after me switching from 5.1 to 6.1 and now I'm in the process of going to 7.1, and getting a lot of feedback from a lot of people (some know what they are talking about, and some don't Posted Image ), as you add more speakers, it is less critical whether they are localizeable or not.

The reason why, is that movie theaters themselves use many, far away, direct radiators. Dipoles were always an attempt to mimic the *effect* of the monopoles in a theater in the home.

So for example for me, even though I had bipoles in the back for surrounds (which I personally feel is a really nice compromise between monopoles and dipoles), when I go to 7.1, my plan is for 4 identical direct radiators in an arc across the back of the room.
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#3 of 21 StephenL

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Posted December 25 2002 - 06:06 PM

I tried direct radiators for the back surround, but the sound sometimes seemed to come from the front center. Dipoles solved that problem.
"It's most disappointing. I shall have to go all-out on some modifications."

#4 of 21 Hisham_k

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Posted December 25 2002 - 06:10 PM

Kevin

Very true. I am using two dipoles in the back center which
I have set to bipoles . Using Bipoles is a step up from dipoles.
But I am leaning towards changing them to direct radiators,
after I auditioned the same set up at a friend of mine who uses direct radiators for the back surrounds.

I believe that from my own experience ( this is a personal opinion) that direct radiating speakers all around is the way to go.

#5 of 21 Tom Brennan

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Posted December 25 2002 - 08:06 PM

Most dipoles and bipoles ARE direct-radiators. I've seen only 2 dipoles that weren't direct-radiators, one an EV compression driver with a horn on each end and a custom di-polar horn system used by one of the guys in our horn club. You can see the rig on our site, it's wild.

Direct-radiating refers to the manner in which the diaphragm couples to the air and not to how many directions or what directions the speaker is sending sound. A diaphragm that acts directly on the air is a direct-radiator, whether this diaphragm is a monopolor cone or a dipolar planar-magnetic doesn't matter. An indirect-radiator is a speaker in which the diaphragm couples to the air through an intermediary device, examples are horns and bandpass boxes. Also the old Dayton-Wright electrostatics that put the diaphragm in a bag of heavier than air gas.

Unfortunately this term direct-radiating, a term with a specific technical meaning going back to the 1930s, has been misused by technically ignorant writers for popular HT mags aimed at an audience of callow young men in their 20s.



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#6 of 21 David Lorenzo

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Posted December 25 2002 - 08:15 PM

Sounds like you have a chip on your shoulder.

Direct-radiator is a common term applied almost universally to a surround speaker whose drivers are aimed at the listening position.

It is a term that is absolutely applicable to be used like this. Words tend to evolve in the English language and can have more than one meaning.

#7 of 21 Tom Brennan

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Posted December 26 2002 - 02:41 AM

David---Words can have more than one meaning, explicit technical terms shouldn't. Such imprecision in language encourages confusion. The fact that language evolves doesn't mean it always evolves in a helpful manner or that one should simply except all error in language.

I doubt very much the term is used universally to mean speakers that direct sound in one direction, I've talked to way too many engineers and designers to buy that. Marketing guys might like the term though.

My having a chip on my shoulder or not has nothing to do with the truth.
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#8 of 21 Brett DiMichele

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Posted December 26 2002 - 03:08 AM

Tom,

For arguments sake...

Direct Radiation and Indirect Radiaton refers to the way
any loud speaker can deliver it's sound to the listener.

For example take a "Passive Radiator" does that mean that
somehow the sound makes it to the listener through some
passive manner of radiation? The piston assebly is motor-
less and is driven indirectly by the internal air of the
box, but the sound it produces is directly radiated to the
listener. So technicaly it should be called a Passive Direct
Radiator.

Dynamic Loudspeaker is the term applied to a traditional
Piston, Suspension and Motor Structure based LoudSpeaker
and Radiation refers to the dispersal of sound from the
point source of the driver, Be it Dynamic, Electrostatic,
Planar or Horn Loaded.

Yes No?
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#9 of 21 Tom Brennan

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Posted December 26 2002 - 03:45 AM

Brett---I've thought about vents and passive radiators before and I think they are examples of indirect radiation.

Any form of loudspeaker; dynamic, electrostat, piezo, armature or singing arc, can be either direct-radiating or horn-loaded.
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#10 of 21 Phil Iturralde

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Posted December 26 2002 - 06:26 AM

FYI: Definitions:

direct radiator: A loudspeaker which does not have a horn between the moving element and the air is called a direct radiator. Most direct radiator-type speakers are for home use, while horn-type speakers are preferred for sound reinforcement applications. Direct radiators generally provide smoother, more uniform response, while horns are much more efficient, providing a greater output level for a given power input. Also, horns have greater directivity, which is desirable in sound reinforcement systems.

dipole: In loudspeaker design, a dipole radiator is a system which radiates forwards and rearwards with equal energy, but with opposite polarity. Examples of dipole radiators are electrostatic loudspeakers and planar speakers. Some cone-type speakers have dipole radiators. For a dipole radiator to have adequate low-frequency response, it must be very large to prevent the rear wave from canceling the front wave. Also, the dipole radiator must not be placed close to and parallel to a wall, working best when not near reflective surfaces.

bipolar: A type of loudspeaker design where the sound emanates from the sides of the monitor, specifically designed to be surround-sound monitors. These type of speakers work well for ambience material, but less well for dialog, soundtrack or main effect sound. This is opposed to a direct radiator speaker which distributes the sound in front, or a tripole design which is a combination of a direct radiator and a bipole.

I use identical direct radiator speakers to anchor my Front R&L and Side Surround R&L (JBL S26) - based on following Dolby Labs official recommendation found in their 5.1-Channel Production Guidelines:
Quote:
3.2.1 Front Speakers (pg. 24)
To promote good imaging, all three should be identical, just as conventional L and R stereo speakers must be matched. If all three cannot be the same model, the center speaker may be a smaller model from the same product line.

3.2.2 Surround Speakers (pg. 25)
Whenever possible, use the same speakers all around to achieve uniformity.

Quote:
... what would you rather use for the back surround or back center speaker(s) : Dipoles, Bipoles or Direct radiating.

With the advent of Dolby Digital EX, Dolby Labs still recommend in their on-line article - "A Listener's Guide to Dolby Digital EX" ...

Quote:
The ideal is to have identical speakers for all the surround channels.


... so if I upgrade to EX, I'll just add another set of JBL S26's. Many have used another identical Center Speaker for their 6.1 setup since the EX encoded INFO is not discrete but provides a matrixed encoded surround back channel imbedded in the regular discrete left and right surround channels.

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#11 of 21 Kevin C Brown

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Posted December 26 2002 - 11:00 AM

Phil- Thanks for the info!

I have personally been trying to decide between. a) 2 bipoles for surrounds and 2 monopoles for rears from 2 different manufacturers. b) all direct radiators from the same manufacturer, but towers for the surrounds and bookshelves for the rears, or, c) 4 identical bookshelf speakers. I had pretty much decided on c, and your info solidifies that. Cheers!
If it's not worth waiting until the last minute to do, then it's not worth doing.

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#12 of 21 David Lorenzo

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Posted December 26 2002 - 01:04 PM

Tom:

I think you mean "accept all error in language"?
I see your point now and agree, but most people wouldn't
know about the prior definition of direct radiator. I didn't until now. So the technically correct word would be "monopole", correct?

#13 of 21 Tom Brennan

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Posted December 26 2002 - 01:26 PM

David---Yes (slapping my head) I meant accept. Yes, the proper term is monopolar.
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#14 of 21 Brett DiMichele

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Posted December 26 2002 - 02:27 PM

LOL

Leave it to Phil to come along and post the BIBLE of info
for us..


MonoPolar... Hmmmm... I like it!
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#15 of 21 Kevin C Brown

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Posted December 26 2002 - 08:29 PM

I don't know. Says "bipolar" right in the manual for the Def Tech speakers I have, so that's what I go with... Posted Image
If it's not worth waiting until the last minute to do, then it's not worth doing.

KevinVision 7.1 ...

#16 of 21 JimC_A

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Posted December 26 2002 - 11:08 PM

How about the Axiom QS8?

#17 of 21 StephenL

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Posted December 28 2002 - 06:36 AM

The best way to determine what type of speaker works best in your room is to listen to audio that uses the surround back channel. Your results may vary depending on room acoustics and distance between listener and back surround. A back surround speaker that images like a front center speaker is worse than no back surround speaker at all. See this thread for more information:
http://www.hometheat....threadid=62230
"It's most disappointing. I shall have to go all-out on some modifications."

#18 of 21 Kevin C Brown

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Posted December 28 2002 - 08:48 AM

Quote:
A back surround speaker that images like a front center speaker is worse than no back surround speaker at all.

Have you tried it? I have, and your statement is not correct. At least in my experience. Posted Image

And, specifically for Logic 7 and THX Ultra2, direct radiators are recommended for the rear speakers. Plus, see the 2nd post in this thread.
If it's not worth waiting until the last minute to do, then it's not worth doing.

KevinVision 7.1 ...

#19 of 21 StephenL

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Posted December 28 2002 - 09:41 AM

Kevin, perhaps you misunderstood my statement. It is possible for a sound directly behind the listener to appear as if it coming from directly in front of the listener. This is unacceptable. I have experienced this and described it in this thread and the thread below:
http://www.hometheat....threadid=62230
"It's most disappointing. I shall have to go all-out on some modifications."

#20 of 21 StephenL

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Posted December 28 2002 - 09:54 AM

Also see this post by Philip Brandes for an excellent description of the phenomenon:
http://www.hometheat....14#post1229414
"It's most disappointing. I shall have to go all-out on some modifications."


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