BackstageAn Engineer's Perspective

Whisper XD…Electrostatics “An Open Mind to Open Sound”

The goal with Whisper XD is to provide all the positive attributes of the best electrostatic dipoles without any of the drawbacks. I grew up loving the openness  of the Sound Labs and the open baffle Dahlquist DQ-10s back in the '70s.  If I thought Focus SE offered every last degree of openness, there would not have been a Whisper XD.  

So, why doesn't Legacy offer an electrostatic design?

-Though the simplest and earliest form of loudspeakers, the best electrostatics are still limited by the efficiency/dynamic range trade-off.  Move the diaphragm closer to the stators to improve sensitivity and you'll scorch a diaphragm the thickness of sandwich wrap with thousands of volts.  Move the diaphragm farther from the stators and potential dynamic range increases - but the sound intensity produced drops off exponentially with the distance.
-Electrostatics are prone to be affected by humidity, insects and diaphragm stretching.  Roger West has implemented faceted panels and a copper charge-diffusion ring to minimize some of these effects.
-Electrostatics are quite placement sensitive relative to rear walls.
-Electrostatics roll-off 6 dB per octave below the frequency with a wavelength 4 times the baffle width.  For example, a two foot wide baffle cancels its own bass output below 140 Hz.
-Electrostatics project 50% of their energy diffusely.  Therefore the soundstage they generate is always largely a function of the room, not the recording.  This creates a 'they are here' experience. Convincing, but not quite right on many recordings.
We all love the sound of open baffle designs, but to image consistently they must diminish linearly in radiating surface as the wavelength get smaller. But how many do?  Violins and female vocals can sound six feet wide.


Whisper XD creates a 'you are there experience'.  Outdoor concert recordings sound outdoors.   Small chamber orchestras and jazz clubs sound like a smaller more intimate venue.  Big recordings sound big like the big electrostatics, but with more dynamics and more realistic in-room settling time, which is perceived as greater quickness.

Play the drum track on the Legacy test CD for example.   Listen to the air squeeze out of the high-hat.  Listen to the oscillating roll of the ride. Note the impact of the kick drum.  No way the electrostatics can do that as well as the Whisper XDs. While the midrange timbre is very natural on both speakers,  Legacy does it with 4 push-pull pistons that radiate an oval pattern to control the directivity precisely.  Each of the 7" mids has a magnet in front and back.  The magnet in the front is a neodymium disc located under the phase plug. From there the radiating surface progressively shrinks to the 4" AMT and then the 1" AMT.

Recording engineer James Thompson recently documented a demonstration of Whisper XD's accuracy.  Not only did they measure ruler flat, but they correlated with an imaging index of 10.
TEN.  Most good loudspeakers have an in room index of 5 to 6.

Oh yeah, I almost forgot, Whisper XD comes with a room correction processor and 4 channels of 500 watts which you might find handy.

Bill Dudleston
Chief Designer
Legacy Audio


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