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#757 - 01/03/02 09:49 PM Surrounds

What are the reasons one would choose to use quadpoles (qs4's for example) as oppossed to directional speakers (such as M3's) for the rear effects channels in a 5.1 setupt?

which speaker type should be used for the rear effect channels in a 7.1 system and for what reasons?

#758 - 01/05/02 06:58 AM Re: Surrounds
Ian Offline

Registered: 03/13/01
Posts: 1155
I asked a very good friend of mine who has done extensive testing on just this question for his input. The following are his answers to your questions. This analysis is right on the money.

The discrete nature of 5.1-channel sound, where individual channels are entirely separated from one another, and mixed in that fashion, would, logically, seem to suggest the use of direct-radiating speakers such as M3's, rather than QS4's, which use a quadpolar radiation pattern. But, based on my listening tests, 'tain't true.

Think about the interior of commercial movie theaters (as well as the way sound waves behave in real life). A movie theater's sidewalls each have three or four surround speakers in addition to at least two on the rear wall of the theater. The point is to produce envelopment of the listener in the sound field as conceived and recorded by the sound
engineer and the movie's director. That's why so many surround speakers are used in a commercial theater--to immerse the audience in a diffuse field that blends with and enhances the on-screen action without diverting the viewer's attention away from the screen.

Your listening room, of course, isn't nearly as large a space as most commercial theaters; nevertheless, envelopment in the sound field is just as important in a home theater. In my experience, a multiple-radiating surround speaker of a bipolar, dipolar or quadpolar
design (such as the QS4's) is more effective at producing a sense of envelopment in domestic living rooms, dens, and dedicated home theater setups than direct-radiating speakers.

And--get this--based on my comparison tests, there is no loss of imaging specificity (i.e. specific rear-mixed directional effects) using a quadpolar radiator, even for music-only programs in DTS, Dolby Digital, DVD-Audio or SACD. If a movie effect is mixed to the right-rear channel, you'll hear it from the right rear direction. And fly-over effects
(Pearl Harbor, for example) will be just as convincing, so the same advice applies to 7.1-channel setups as well. Indeed, in a small room, I would argue that multi-polar surrounds are essential to achieving convincing surround sound. So go with the Axiom QS4's; you can experiment with the M3's on the sidewalls if you wish. If they don't call attention to themselves as sources of sound (this never should occur in a properly arranged home theater setup), then hurray, your installation is a success!

Ian Colquhoun
President & Chief Engineer
Ian Colquhoun
President & Chief Engineer

#759 - 01/05/02 11:18 AM Re: Surrounds

Thanks for your reply Ian.

Let me see if I can now summarize what has just been said.

In an ideal world using any pair of speakers, the object is to create a realistic soundstage with a proper image without being able to determine where the source speakers are located.

With that said, this is easily accomplished using quality front speakers, yet it is much more difficult at the rear locations. I am assumming this is do to the distance that the listener sits from the speakers???

So to accomplish an Ideal 5.1 setup(ignoring the center in this discussion): You would want all 4 speaker to be an equal distance around the listeren to fom a rectangle, where the front speakers are as far apart from each other as they are from the listener and the same would apply to the rears (two equilateral triangles where the listener is the common point between the two trinagles).

Now this would be ideal. Unfortunately the average person doesnt have this kind of real estate to deal with. so what you are saying is that the quadpolar somewhat diffuses the rear signals to make pinpointing the their location during listening more difficult?

#760 - 01/06/02 05:28 PM Re: Surrounds
jkohn Offline
old hand

Registered: 01/06/02
Posts: 96
I see two issues with this logic, though. First, it's my understanding that the reason theaters use an array of speakers to create a diffuse soundstage is because so many of the seats in a theater are in non-optimal positions. IE, if a large theater used direct radiating speakers to create a more accurate soundstage then it would sound great for people sitting in the center of the theater, but really lousy for people who are sitting in the back corner. To me this is different from many home-theaters, where there are not any bad seats. In my home-theater a few of the seating positions might be slightly off center, but I don't have anybody sitting in the back corner. :) So in this case, if I can get a more accurate soundstage with direct-radiating speakers, shouldn't I?

My second issue is more of a question really - how are the soundtracks on DVD's mixed, compared to the soundtracks mixed for the theater? Are they mixed with discrete channels in mind?

I think my living room is better suited to direct-radiating anyway, because I cannot put the surrounds on the side walls; they have to go in the back corners, toed-in towards the seating position. This seams to work pretty well with the direct-radiating speakers that I currently have, but I'm not so sure how dipole/quadpole speakers would work in this situation. I realize this may not be the completely optimal speaker placement, but I'm limited by using my living room - dedicated theater will have to wait until my next house, several years down the road.


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