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Old 17th April 2014, 08:32 AM   #11
SAC is offline SAC  United Kingdom
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No surprises this is a bit controversial then. It certainly does well as a whole speaker reviews/comments wise - sponsored or not. It was good enough for Steve Hoffman's recording studios which is no small thing I expect.

The speaker itself warranted a serious effort at cloning as shown in the link, but interest in the woofer design is not evident on the internet. Is it simply not worth the financial cost of doubling woofers for what must be a subtle if not room dependent gain?
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Old 17th April 2014, 08:57 PM   #12
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Celestion did this a very long time ago, with their dipole subwoofer for the SL600 speaker.
It used two bass driver, one behind the other. This technique allows for more swept volume without increasing overall baffle size, so keeping the profile very compact.
Although the relative phase responses can be adjusted to vary the response between dipole and some cardiod variant, I don't know id this was actually done.
There should be a paper from Graham Bank floating around somewhere that describes what he did.

Andrew
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Old 17th April 2014, 10:16 PM   #13
Scott L is offline Scott L  United States
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Default Gradient ?

Quote:
Originally Posted by AndrewJ View Post
Celestion did this a very long time ago, with their dipole subwoofer for the SL600 speaker.
It used two bass driver, one behind the other. This technique allows for more swept volume without increasing overall baffle size, so keeping the profile very compact.
Although the relative phase responses can be adjusted to vary the response between dipole and some cardiod variant, I don't know id this was actually done.
There should be a paper from Graham Bank floating around somewhere that describes what he did.

Andrew
Was there not (in addition to what you have described) some sort of offering
specificaly made to fit under the Quad Electrostatic ?

p.s. I met Bill at Axpona/Atlanta and asked about the Whisper's woofers.
His answer was that they were "differential". Still to this day, I do not know what he meant.
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Old 17th April 2014, 10:22 PM   #14
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Looks to me the whisper has added drivers to bring up the sensitivity, that's about the only way to do it other then bigger motors (that have higher rolloff) so to fit them on the board the goofballs just stuck them on the back panel. It's pretty funny what some people will actually pay for
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Old 17th April 2014, 11:06 PM   #15
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Yes, Gradient produce a dipole subwoofer to go with the Quads.
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Old 18th April 2014, 09:03 AM   #16
Toaster is offline Toaster  United Kingdom
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I think Linkwitz also used compound drivers in N-frames for one or more of the Audio Artistry designs. Nothing wrong with the principle if both Bank and Linkwitz have used it.
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Old 18th April 2014, 11:36 PM   #17
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Quote:
Originally Posted by Scott L View Post
p.s. I met Bill at Axpona/Atlanta and asked about the Whisper's woofers.
His answer was that they were "differential". Still to this day, I do not know what he meant.
A quote from one of their earlier brochures:

“Differential technology:
Whisper’s compound alignment is rooted in Harry Olsen’s early papers more than twenty-five years ago. (Olsen is legendary for his mathematical and acoustic modeling of microphones). Olsen suggested such an alignment as a way to effectively steer low frequencies. Whisper is the first broadband realization of this differential technique…

The low frequency drivers operate in phase with each other and combine acoustically as a pair of figure- of-eights, one behind the other. The result: a compound null formed at the sides of the enclosure, which minimizes resonances and room reflections.”


From there, internet searches for “differential microphones” or “gradient microphones” will help explain.
Basically Olson developed microphones that used difference in phase between several elements to provide directional control of the pickup pattern at low frequencies. That is where the word “differential” comes from. The attached pic from one of his patents shows how the directivity could be increased with additional elements. Figure 1a/2a/3a are for a monopole. Figure 1b/2b/3b are for a dipole(notice the familiar cosine directivity function). Figure 1c/2c/3c are for a compound dipole where the directivity is increased to cosine^2)

Olson also developed directional loudspeaker arrays using these same techniques.
https://secure.aes.org/forum/pubs/journal/?elib=2006

However, the Whisper drives its compound woofers in phase(different from Olson) so the directivity pattern will be the same as for a single dipole woofer at low frequencies. Linkwitz has analyzed this configuration and also seemed at a loss as to what advantages there might be.
Electro-acoustic models

The most obvious advantage has already been mentioned, increased output with no increase in baffle size. When experimenting with this setup many years ago, there were two other advantages I noted. For the same output, the compound dipole will have its dipole peak and null an octave higher in frequency. Also, for the same output, the compound dipole will lack any cavity resonance when compared to an H frame or similar dipole woofer. Both of these would be important in the Whisper as the compound woofers are not being used just as subwoofers, but need to operate cleanly up to(past) the 300Hz crossover point with the mids. The reason for this high crossover point is to keep the directivity controlled below 300 hz where the size of midrange array is starting to look acoustically small.

Quote:
Originally Posted by AndrewJ View Post
Celestion did this a very long time ago, with their dipole subwoofer for the SL600 speaker.
It used two bass driver, one behind the other. This technique allows for more swept volume without increasing overall baffle size, so keeping the profile very compact.
Although the relative phase responses can be adjusted to vary the response between dipole and some cardiod variant, I don't know id this was actually done.
There should be a paper from Graham Bank floating around somewhere that describes what he did.
Not sure if this is the paper you were talking about, but attached is an old white paper on the Celestion System 6000 I’ve had in my files for quite some time. Discussion of the subwoofer begins on page 3. One interesting thing I noted was that they intended for the left and right channel subwoofer arrays to be rotated or oriented independently from the satellites to adjust the excitation of the different room modes for smoothest bass response.
Attached Images
File Type: png Olson_gradient_Patent.png (25.2 KB, 213 views)
File Type: gif compound-dpl-Linkwitz.gif (23.1 KB, 211 views)
Attached Files
File Type: pdf Celestion_System6000_White_Paper.pdf (275.6 KB, 18 views)

Last edited by bolserst; 18th April 2014 at 11:42 PM. Reason: Added pic of Linkwitz Analysis in case it is removed from his site.
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Old 19th April 2014, 12:48 AM   #18
SAC is offline SAC  United Kingdom
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Very interesting feedback. Helps me in ruling out this config really. Since I use a low crossover there is no significant benefit to my build it seems, though lack of cavity resonance is welcome.

Thanks to all for comments.
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Old 20th April 2014, 01:31 AM   #19
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in one of his whitepapers Duddleston said each additional 15" provided +3db of output. A one point he built a jig that allowed stacking of 8 drivers. Interesting but not too practical
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Old 20th April 2014, 06:41 AM   #20
puppet is offline puppet  United States
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SAC ... if you do a ripple tank simulation of the bass drivers connected out of phase the resulting nulls at 90* are very pronounced with a close enough approximation of 90* fore and aft.

Same distance between drivers in the ripple sim .. connected in phase .. produces four or more nulls including the on axis position. As one would use digital delay, increasing the spacing between the drivers (connected in phase) does increase forward radiation but not at the intensity level of the drivers wired out of phase.

All of this does seem to be at the mercy of frequency. Some ranges offer very nice patterns ... some don't. I wonder if the electronics developed by Mr. Duddleston formulates a time/frequency curve to maintain the desired directivity in the bass operating range.
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