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Center Channel; Horizontal or Vertical?

post #1 of 17
8/24/06 at 4:24am
Thread Starter 
In another thread, the highly respected Sanjay Durani makes the following comments, (re-quoted here so as not to hi-jack that thread):
Quote:
Originally Posted by sdurani View Post

The thing about lining up drivers in a speaker is that the sound cancels in the direction they're lined up in but remains unrestricted in the opposite direction. Follow:

If you were to place the centre speaker with the drivers lined up horizontally, they would cancel in the direction of the drivers (listeners on the left and right of the sweet spot would not get good sound) and be unrestricted vertically (giving you reflections off the ceiling and floor, which would muddy dialogue clarity). Talk about a lose-lose situation.

Compare that to rotating the speaker so that the drivers lined up vertically. Sound would cancel in the vertical direction, for less bounce off the ceiling and floor, but sound consistent horizontally, so all the listeners on the couch hear the dialogue clearly. In short, everything you would want from a centre speaker.

Sanjay,

Could you go into a little more detail about this? What is it about lining the speakers up in a cabinet that causes the effect you're describing. Is it diffraction off the cabinet or interaction between the speakers? Also, is there anything a speaker designer can do to overcome this phenomenon, such as playing with the polar radiation pattern, or some phase relationship in the crossover, etc.?

Here is another possiblity: my CC has what Klipsch calls a tapered-array crossover where one of the woofers is crossed at 550 Hz and the other at 1950. From the Klipsch website:

Quote:


The RC-7 center channel features Klipsch's version of 2.5-way crossover technology, called tapered-array. With tapered-array, the two Cerametallic woofers work together to deliver high impact bass with one driver transitioning out at the mid-range frequencies. This provides more consistent coverage across the listening field, less tonal error and improved dialogue intelligibility.

The high quality crossover networks of the RC-7 are carefully designed for an improved blend between the lower midrange and upper bass frequencies.

If I wanted to measure my CC to see if it has the effect you describe, could I take my SPL meter and move it around the speaker in the different planes while playing pink noise? Then reorient the speaker vertically and repeat the measurement?

Thanks for your always insightful help.

Craig
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post #2 of 17
8/24/06 at 7:48am
Quote:
Originally Posted by craig john View Post

Could you go into a little more detail about this? What is it about lining the speakers up in a cabinet that causes the effect you're describing. Is it diffraction off the cabinet or interaction between the speakers?

The latter.

Quote:


Also, is there anything a speaker designer can do to overcome this phenomenon, such as playing with the polar radiation pattern, or some phase relationship in the crossover, etc.?

The only sure way is to have the crossover low enough so that driver spacing is much less than 1/2 the wavelength at crossover.

Quote:


Here is another possiblity: my CC has what Klipsch calls a tapered-array crossover where one of the woofers is crossed at 550 Hz and the other at 1950.

A small help in terms of woofer-woofer interaction but not woofer-tweeter interaction, of course.

Quote:


If I wanted to measure my CC to see if it has the effect you describe, could I take my SPL meter and move it around the speaker in the different planes while playing pink noise? Then reorient the speaker vertically and repeat the measurement?

Pink noise is too wide-band and the effects will be masked. You need to use an audio RTA to see the spectral change with position or try to use a sine-wave or warble-tone at the crossover frequency.

Kal
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post #3 of 17
8/24/06 at 8:16am
Quote:
Originally Posted by craig john View Post

Could you go into a little more detail about this?

I oversimplified for the other thread, but here's a detailed version:

http://www.birotechnology.com/articles/VSTWLA.html
Quote:


If I wanted to measure my CC to see if it has the effect you describe, could I take my SPL meter and move it around the speaker in the different planes while playing pink noise? Then reorient the speaker vertically and repeat the measurement?

Probably, though a RTA and sweep tones would allow you to measure the lobing more easily. Even without measuring, try doing some listening tests with your centre speaker oriented both ways and you sitting off-axis. I think you'll hear why L/R speakers designed for music listening never have horiziontally arrayed drivers.

Sanjay
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post #4 of 17
8/24/06 at 8:24am
and to minimise that effect there are some manufactures that have come up with tweaks to the typical center design, like Energy's Reference Connoisseur line
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post #5 of 17
8/24/06 at 10:24am
Quote:
Originally Posted by laststarfighter View Post

and to minimise that effect there are some manufactures that have come up with tweaks to the typical center design, like Energy's Reference Connoisseur line

That oblique arrangement will assure sub-optimal radiation with either vertical or horizontal orientation.

The best compromise is when you can rotate the mid-tweeter array so that it is vertical when the speaker cabinet is vertically or horizontally mounted (as long as the mid-woofer crossover frequency is low enough).

Kal
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post #6 of 17
8/24/06 at 12:28pm
agreed
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post #7 of 17
8/24/06 at 1:29pm
Quote:
Originally Posted by sdurani View Post

I oversimplified for the other thread, but here's a detailed version:

http://www.birotechnology.com/articles/VSTWLA.html
Sanjay


I think I prefered your simplified version.
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post #8 of 17
8/24/06 at 1:38pm
Quote:
Originally Posted by laststarfighter View Post

and to minimise that effect there are some manufactures that have come up with tweaks to the typical center design...

Indeed. There are some horizontal centre speakers which have three tweeters or tweeter+midrange arranged vertically inbetween the flanking woofers. Not optimal, but helps a little in the vocal range. It also shows that some manufacturers recognize the problem with horizontally arrayed drivers and are doing their best to address it within the constraints of aesthetics.

Sanjay
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post #9 of 17
8/24/06 at 1:43pm
Quote:
Originally Posted by ericgl View Post

I think I prefered your simplified version.

Yeah, some of that math made my eyes glaze over. But the article was interesting because it not only talked about the problems with horizontally arranged drivers, but also pointed out that not all the problems magically disappear when the drivers are stacked vertically. And that last part is rarely talked about.

Sanjay
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post #10 of 17
8/24/06 at 1:54pm
Sanjay,

Just a quick question in general about driver arrangements. I use M&K 150s which have three vertically aligned tweeters next to two vertically aligned 5.25" woofers. The front field is seamless to me having three identical speakers. However, I'm curious as to what would be the compromises with this setup?
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post #11 of 17
8/24/06 at 2:04pm
There are two issues. One is that stacked drivers (3 tweeters or 2 woofers) will have narrowed and less uniform vertical dispersion than a single driver covering the same band. This is not necessarily a problem if the vertical window of uniform FR is at the listener's ear level.

The second is that having the tweeters lateral to the woofers will do the same in the horizontal plane. It seems that such an asymmetric arrangement must result in anomalies although with multiples the interaction will be complex

I do not feel competent to pass judgement on this complex design which may work well. I do wish to mention that the vast majority of successful speakers share a similar geometry which affords them wide, controlled and uniform dispersion for domestic setups.

Kal
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post #12 of 17
8/24/06 at 2:09pm
Quote:
Originally Posted by sdurani View Post

Indeed. There are some horizontal centre speakers which have three tweeters or tweeter+midrange arranged vertically inbetween the flanking woofers. Not optimal, but helps a little in the vocal range. It also shows that some manufacturers recognize the problem with horizontally arrayed drivers and are doing their best to address it within the constraints of aesthetics.

Sanjay

I was going to also post a picture of a speaker like this one:


but thought the first one got my point across, that there are other center speakers with horizontal form factors with different driver layouts.
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post #13 of 17
8/24/06 at 2:16pm
Quote:
Originally Posted by laststarfighter View Post

I was going to also post a picture of a speaker like this one:
but thought the first one got my point across, that there are other center speakers with horizontal form factors with different driver layouts.

A distinctive effort to address the problem which may or may not be successful. There are still laterally placed drivers (a consequence of any horizontal design) and success depends on their spacing and frequency ranges.

Kal
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post #14 of 17
8/24/06 at 2:20pm
Quote:
Originally Posted by Kal Rubinson View Post

There are two issues. One is that stacked drivers (3 tweeters or 2 woofers) will have narrowed and less uniform vertical dispersion than a single driver covering the same band. This is not necessarily a problem if the vertical window of uniform FR is at the listener's ear level.

Yes, they do say it is critical that these speakers be at ear level to the extent that they even sell a laser pen to support this issue. In addition, they are THX certified which in part I assume means that they are also trying to limit the vertical dispersion.
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post #15 of 17
8/24/06 at 3:15pm
Quote:
Originally Posted by smithb View Post

I'm curious as to what would be the compromises with this setup?

What Kal said. Plus, without seeing measurements (especially off-axis) for those speakers, it's hard to tell what the compromises would be and how severe. The fact that they are THX certified at least indicates that they have wide horizontal dispersion and controlled vertical dispersion.

Sanjay
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post #16 of 17
1/7/07 at 8:01pm
One of the few things Bose did right with the VSC-10, angle drivers to compinsate for loss of horizontal dispersion charateristics. Now if they would only use appropriate drivers, they would have something there, for $50 more.
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post #17 of 17
1/8/07 at 6:15pm
Great thread. I tried some real world examples to see if I understand this.

I have one center speaker with 2 horizontally aligned low frequency drivers and a vertically aligned midrange and tweeter in between. The mid/woofer crossover frequency is at 1000 Hz, 1/2 the wavelength at the crossover = 6.78 inches.

The spacing between the two large drivers (edge of cone) is slightly less than 5 inches, which should be good in terms of reducing the effects of cancellation. Correct?

I have another center speaker with two low frequency drivers, and tweeter in between. The crossover is 3000 Hz, 1/2 the wavelength at the crossover = 2.26 inches. Spacing between the drivers is 4 inches, so cancellation is a problem.
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