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Re: Critique this list of "rules of thumb" for SET/Speaker Interface

24.18.240.124

Posted by Paul Joppa on December 28, 2006 at 18:14:41

In Reply to: Critique this list of "rules of thumb" for SET/Speaker Interface posted by RioTubes on December 28, 2006 at 09:44:18:

Obviously I agree with #1! :^)

Many of these are often but not always true. That's because they may be symptoms rather than a root cause. I'd like to expand on a few of them - consider this my two cents worth:

#3, 5, and 11 basically say to avoid mechanical damping. But it's really only a problem when it's significantly nonlinear. Linear mechanical damping, specifically of the surround, will reduce cone resonances and coloration, and is a good thing. But many surrounds and spiders may have anonlinear damping, specifically a hysteresis behavior which can be fairly unpleasant - like poor capacitors in the electronics.

These same points, plus #2 in part, also caution against wild impedance swings which can cause response variations with amps of different damping factor. If a speaker is voiced for SET amps with typical damping factors, then that is not a problem. By far the largest problem is speaker systems which have a minimum impedance below, say 75% of the nominal impedance. Impedance peaks cause less of a problem.

#2, 6, and 12 are also related. I don't think the nominal impedance is important, as long as the amp has a suitable impedance tap on the output. SET amps usually have a damping factor of 2 to 4, meaning the output impedance is 1/4 to 1/2 the nominal. Four ohm speakers work fine on a four ohm tap, but they hurt on an 8 ohm tap and really suck with a 16 ohm tap.

#4, QT matters, not QE, and fs/QT has to do with the bass cutoff, at least for direct radiator speakers. QE is relevant for horns because a good horn will add considerable mechanical (radiation) damping, swamping out the speaker's mechanical damping.

#7, 8, and 10 basically say that the speaker should be efficient. To get efficiency, some combination of powerful motor, light moving mass, and large radiating area is needed. But none of these parameters by itself is critical. All of them also make for poor bass extension. What really matters is efficiency and bass extension, which rep[resents a tradeoff among these parameters and the system requirements.

#9 - yes, alnico and neodymium do often sound good. A major reason is that they are conductive, which ceramic is not, so these magnets effectively have shorting rings built in to reduce distortion. But ceramic magnet systems with shorting rings have the same virtue, and should not automatically be rejected.

I am a great admirer of Eduardo de Lima’s work and would encourage anyone to read his papers if you are thinking of making an integrated speaker/amplifier system.

This post is made possible by the generous support of people like you and our sponsors:

Schiit Audio

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