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Old 19th November 2004, 10:20 PM   #1
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Default Legacy Whisper bass?

Does anyone out there know what Bill Dudleston is doing with the bass alignment of the Whisper? It is a dipole, but what is he achieving with the second woofer behing the first?

Also, his woofers look more like the pro sound type without much excursion capability, but I keep reading on here that one must have high excursion to successfully have an open baffle. I have heard the Wisher twice and really liked the sound in the bass region.

Greg
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Old 20th November 2004, 03:22 PM   #2
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Click the image to open in full size.


Been there, done that.



The Legacy Whispers use an outboard EQ box which controls the bass alignment (boost) and gives some flexibility over the in room response.

The compound woofers acts a bit like an ISO Barik configuration.

This set here was built with some pioneer woofers, sourced for a QTS of 0.6; not all that long a throw, but lots of cone area.

It's swept volume that counts... like a big V8.

~Jon
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Old 22nd November 2004, 12:47 PM   #3
Bill F. is offline Bill F.  United States
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Quote:
It is a dipole, but what is he achieving with the second woofer behing the first?
I've wondered this same thing. The Whisper write-ups I've read are quite coy on this point, saying only something about how they help further narrow bass dispersion.

On relatively narrow baffles like the Whisper's, two in-phase cones would serve to lengthen the the effective front-to-back path length without bringing Fp down into the passband.

I believe their close spacing also serves to raise their Qts, since half the airload damping is effectively removed from each cone.

Just guesses--I'd love to hear Bill D's answer.

Quote:
The compound woofers acts a bit like an ISO Barik configuration.
But the purpose of that alignment is to lower Vas for small boxes--the opposite of what's normally considered ideal for OBs, where the best drivers have the largest Vas.
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Old 15th April 2014, 06:05 PM   #4
SAC is offline SAC  United Kingdom
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I am considering doing this compound woofer thing with some spare alpha 15a drivers I have. Seems ideal for the close sidewall issue such as that I suffer from.

There is a lack of interest in this going by my Google search, this clone attempt being the closest - though lacking in theoretical details (sub delay required, etc) Page Title

In the picture I propped up the spare 15" as an experiment. Will do the woodwork now, unless anyone hates the idea. 0.7 QTS is preferred so the alphas should work being high QTS!?

Bit of theory;
"Bill's goal with the Whisper is to reduce floor, ceiling and side-wall interactions by creating a "null" to the sides at all frequencies across the audio band. The photo above shows the compound woofer-loading technique Dudleston uses for the Whisper. The way the woofers interact creates an acoustical null in the bass on either side of the loudspeaker cabinet. "
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Old 15th April 2014, 10:28 PM   #5
puppet is offline puppet  United States
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This has to be PPSL ... no? ... at least that's how I interpret the quoted description you posted. Nevermind ... found a description of the original Legacy Whisper ... seems that the woofers are wired in phase.

Last edited by puppet; 15th April 2014 at 10:46 PM.
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Old 16th April 2014, 09:31 AM   #6
SAC is offline SAC  United Kingdom
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A good description can be seen here;
"Legacy describes the speaker as an "acoustic gun." This goal is no easy thing to accomplish with low frequencies. A large woofer in a box—any woofer in a box—will behave as an omnidirectional radiator. Dudleston therefore eliminated the woofer box entirely. The two pairs of closely-spaced back-to-front, in-phase 15" woofers behave like the twin diaphragms of some directional microphones; the result is a tight figure-8 directivity pattern with a null at the speaker's sides. (That there's a truly massive null at the speaker's sides can be confirmed easily by ear.) The Step One bass processor, installed between preamp and power amp(s), serves to adjust the Q and level of the woofers to let them couple effectively with the room without compromising their controlled dispersion. "
Legacy Audio Whisper loudspeaker | Stereophile.com

Further specifics here;
"Signals from the two baffles are combined acoustically with time compensation to steer the low frequency wave-launch forward, while creating a progressively reduced acoustic output to the sides until reaching a null at 90 degree off axis. "
Legacy Whisper XD Review


Since I run a Najda DSP unit - 4 (5 option coming) channel crossover - this is within reach for me.
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Old 16th April 2014, 09:33 PM   #7
winslow is offline winslow  United States
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That's a bunch of marketing goobly gook...
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Old 16th April 2014, 09:56 PM   #8
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A bunch of marketing hype? You betcha! All that surface area of the cones flapping about with nowhere to go! Except curl right around the basket edge seeking out the rarafied air!
"like a big V8"....yeah, with pure slick ice on the ground....no traction to put down all that "power"!



__________________________________________________ Rick............
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Old 16th April 2014, 11:25 PM   #9
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"Also, his woofers look more like the pro sound type without much excursion capability,"
that smacks of a negative connotation toward pro audio drivers bud! last time i checked a good many of them have x-max on par or greater than "audiophile"(read snooty, opinionated,class racist)speakers.
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Old 17th April 2014, 03:48 AM   #10
ScottG is offline ScottG  United States
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Quote:
Originally Posted by winslow View Post
That's a bunch of marketing goobly gook...
Actually it's not.. or perhaps it's not entirely.

What's happening with the bass-driver section is rather like achieving a hypercardioid radiation pattern - improving the null off-axis:

https://www.google.com/search?q=hype...w=1228&bih=664


Like a monopol, a dipole, or a cardioid: it still reacts to room modes.. but it usually reacts a bit differently ("shifting" the freq. response for the mode generated nulls and peaks).

Perhaps the most pertinent part relates to some degree of "enhanced" channel separation in the lower midrange/upper bass.


IMO that's actually the best part of the design.

The midrange section is the worst - which requires a far-field listening position.
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