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Old 25th February 2005, 02:36 PM   #21
Few is offline Few  United States
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You can roughly gauge fs by looking at the low frequency limit of the speaker. If it's intended to run full range, it's likely to be in the tens of hertz range (~20-50 Hz). My panels are supplemented by dynamic woofers so their resonance frequency was designed to be closer to 100 Hz. This implies higher diaphragm tension, all else being equal, which allows a higher bias voltage to be applied.

The total Q is often quite high unless something is done to damp it. It'll almost certainly be over 1 and I wouldn't be surprised by a Q of 5 or 10. If the panel is damped by a layer of fabric, for example, the Q will drop considerably but my guess there would be even worse than the ones I've provided already.

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Old 25th February 2005, 03:30 PM   #22
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The high Q of the ESL bass response is often put to work to counteract the bass cancellation that occurs in dipoles. It is only a partial and inexact compensation, but it works pretty well for Quads and other full-range ESLs. If you arrange the high Q bass bump to occur near the frequency where dipole cancellation causes its roll-off, you can compensate for it, to some degree, over a narrow range. The same applies to dipole cone woofers of course. As Few says, some designers, such as Peter Walker, have put a layer of silk-like material inside the stator to provide some resistance to air flow, which damps (lowers) the Q to whatever it needs to be for the best approximate dipole cancellation.

Just like a cone, if you measure Fs in an ESL panel that is placed in an infinite baffle (or in free space which may be a close approximation), and then put the driver into a sealed box with known interior volume, you can measure the rise in resonance frequency and Q and then calculate Vas. With either driver type you have a “spring-mass” second order system.
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