is two full range drivers in one baffle a problem?

[planet10]

Originally posted by janneman
why isn't there cancellation with a single driver from signals from different parts of the cone? Or is there, what they call beaming?

There is cancellation resulting in beaming and roll-off. One of the reasons why a well designed phase plug can do so much good.

dave

[kelticwizard]

Originally posted by janneman
I always thought that if you have two drivers close together and feed them with the same signal, you can consider them as one driver with a double area.

For the bass and much of the mids, you can. It is only in the upper frequencies that you run into these problems.

Originally posted by janneman
If there is cancellation, why isn't there cancellation with a single driver from signals from different parts of the cone? Or is there, what they call beaming?

I haven't done any research on this, but I would bet that if you could make two speakers with completely square diaphragms and surrounds, and placed them one atop the other, you probably would not have these problems. If you put two circles one atop the other though, you can see that the sound will tend to come from two sources. With square speakers, I would think the behavior would be very similar to a single diaphragm, (if they're square, I'm not sure you can call them "cones" ).

[kelticwizard]

Here is the frequency response of thirteen 4 inch speakers in a line source array. The authors eventually got smoother-but not flat response, from a combo of glass fiber wedges in front of the speakers. Flat response to 2,000 Hz was achieved with a simple equalizer circuit.

This is from an article, Constant Directional Characteristics From A Line Source Array by David Klepper and Douglas Steele, which was published in the Journal of The Audio Engineering Society in July, 1963.

Since it was a small graph, I had t fill in some blotchy parts around 500 Hz with MSPaint. But not much.

[kelticwizard]

Question:

Originally posted by bbaker6212
Any way to remove or reduce this problem? Stagger the drivers with their centers not virtically alligned? Place them side-by-side?
Firing at different slightly different angles?

Answer:

Originally posted by Planet 10
You can mount them co-axially (quite difficult in 3-space ) or at an angle of at least 90 degrees (and if you are going that far you might as well do it 180 degrees and take advantage of push-push.

The question was about just two drivers, and the answer is correct.

However, for a line array, at least one company tried bbaker's approach. How successfully it worked out, I don't know. From the article above in the Journal of The Audio Engineering Society, here is all the info the article contains on this configuration.

Just thought I would throw this in for fun.

PS: This is a snippet from the article. The Barber Pole enclosure is not the authors' enclosure. They include it in the article just as a quick survey of work already done on Line Arrays. In case it is not clear, the Barber Pole enclosure does not contain any fiberglass wedges in front of the speakers. The authors' enclosure, which they go on to describe, has them. The Barber Pole does not.

[planet10]

Originally posted by kelticwizard
I haven't done any research on this, but I would bet that if you could make two speakers with completely square diaphragms and surrounds, and placed them one atop the other, you probably would not have these problems. If you put two circles one atop the other though, you can see that the sound will tend to come from two sources. With square speakers, I would think the behavior would be very similar to a single diaphragm, (if they're square, I'm not sure you can call them "cones" ).

If you change square to rectangle, then consider that people are doing this with "ribbon" tweeters. You could also consider ESLs.

dave

[kelticwizard]

Ribbons and electrostatics-didn't think of that. Yes, they are usually arrays too, now that you point it out.

That first chart in the thread-reposted below-shows the response for thirteen 4 inch speakers mounted in a vertical array. I noticed something surprising.

The off-axis response at 40 degrees off-axis is a shocking 17 dB below the on-axis response at 2,000 Hz! A single 4 inch speaker does much much better than that. With off-axis response like that, one of the best features that you would think an array gives you-horizontal off-axis response similar to a single driver of it's diameter but cone excursion much, much less-would appear to be imaginary. There are 10 inchers around which give better off-axis response than that!!

Does anybody have any idea why this would be?

[kelticwizard]

Here is the response graph, both on and off axis, for the 10" Peerless CSX 10" woofer, 850146. The cone area is 7 times as large as a 4" speakers, yet note the vastly superior off-axis response. Look at the 2,000 Hz line. At 60 degrees off axis, (red line), the Peerless 10" has significantly better response than the 4" line array does at only 40 degree off axis!

For the sake of Line Array fans, I can only hope that this is not the usual thing. If it is, why build a Line Array?

[ryoshu]

Originally posted by kelticwizard
For the sake of Line Array fans, I can only hope that this is not the usual thing. If it is, why build a Line Array?

Why not? You never know until you try, and for some of us, trying is what matters

(my case of drivers arrived today and construction starts tomorrow (today?))

[planet10]

Originally posted by kelticwizard
That first chart in the thread-reposted below-shows the response for thirteen 4 inch speakers mounted in a vertical array.

What was the spacing on the 4"?

Peter, this paper you will probably find interesting.

Line-Source paper by P Taylor [888 kB]

dave

[Bose(o)]

Barber pole is a way out...slight change in the direction. Saw bose 802s on the same pole and was wondering why they all we were at a slight change of angle. This would be the reason.