Don Keele on Constant Beam Transducer (CBT) Speakers and then some

Apr 3, 2010
16,022
0
0
Seattle, WA
#1
Don is one of those very down to earth people that is lovely to listen to, pun intended :). He was the one that discovered navy research for sonars in building transducers with unified patterns and applied it home and commercial speaker systems. CBT as it is called, has incredible benefits which he explains yet they are deceptively simple to build. It is one of those "cheat the laws" of physics kind of things.

Even though this presentation is about CBTs, he contrasts them frequently with how traditional speakers work including some really nice animations. Unfortunately everything is in short-hand so you may have to pay close attention. Topics covered are speaker lobing, effects of floor reflections, line arrays (what they are and aren't), horns, directivity, etc.

The videos are all HTML 5 so you can speed them up (I suggest doing that for the first video):

 
Apr 3, 2010
16,022
0
0
Seattle, WA
#3
I have of course. It is a remarkable experience. Imagine being in massive room and said speaker playing. You walk towards it yet unlikely any normal speaker, the volume hardly gets louder! It is a superb solution for outdoor events where the levels of very high yet you don't want to make the listener that is sitting close deaf. They also come in very handy for the surround sounds in home theater because invariably people are sitting too close to one or more of those speakers.
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,089
63
48
Manila, Philippines
#6
I'm very interested in acoustic shading (amplitude and phase) for individual drivers in an array. When the VR-111 Towers arrive which have individual amps w adjustability for each of the four sub drivers per column, it will be interesting to see what shading can do. Given the very long wavelengths at the XO frequencies differences in distance from each driver shouldn't be much of a problem especially since below 40 Hz the drivers are mostly reproducing sustains and decays as the leading edge transients are handled up top. One just has to be careful with the transitions so the bass doesn't curl. That you can use the floor as a mirror essentially doubling up an array is most intriguing. If this works we can drop gain by a significant amount for less distortion/more "ease".

I'll report on the experiments when the time comes. This won't be easily described in words so I'll likely just snapshot from a Phonic PAA6.
 

zztop7

Member Sponsor
Dec 12, 2012
750
0
0
Edmonds, WA
#7
To JackD201 [post #6] & dallasjustice [because of your extensive excellent posts on integrating low frequencies].
Please note part 5 starting @ 2:20 of Don Keele's presentation.
Here are some Quotes [maybe a little rough]:
"there is a frequency in which down with [?width?] the frequency blows-up"
"comparable to size of array"
"maintain beam width down-to at least 200HZ.
zz.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,090
0
0
Dallas, Texas
#8
To JackD201 [post #6] & dallasjustice [because of your extensive excellent posts on integrating low frequencies].
Please note part 5 starting @ 2:20 of Don Keele's presentation.
Here are some Quotes [maybe a little rough]:
"there is a frequency in which down with [?width?] the frequency blows-up"
"comparable to size of array"
"maintain beam width down-to at least 200HZ.
zz.
That makes sense to me. Below those frequencies, its all omnidirectional and dominated by the room, rather than the speaker.

I looked over the promotional literature. It looks good as far as FR. But I didn't see any mention about the time domain. I wonder whether DSP would really be needed for the crossovers in speakers like these. I just can't get my mind around using a passive crossover and still maintaining a time coherent wavefront. It seems impossible.
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,089
63
48
Manila, Philippines
#9
I can think of a few passive speakers that have electronic time alignment in their crossovers although most companies use mechanical time alignment.
 

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