Technical Survey Paper -- Need Some Help!

[Johan Potgieter]

Thanks, Jeb-D,

That was exactly the point.

..... perhaps of language I've missed the point.

Yes, possibly my language usage (not a good excuse but Engresh is only my second language!)

Johan mentions; quote <Those figures were indicative of what was required in good designs to make distortion inaudible, and were applied with the necessary stability margins without eroding open loop gain to well within the audible range>

To rephrase:
Those figures were indicative of what was required in good designs to make distortion inaudible, and without the need to apply stability margins such that the networks had to curtail open loop gain into the audible frequency range (as is common nowadays).

 

[Johan Potgieter]

I question that assumption. Back in those days, speaker design was very much a "black art". The early designs may have required quite a bit of damping to tame squirrelly impedance v. frequency characteristics. Since the advent of the "Thiel Method" of speaker design, this is no longer the case. Modern speeks don't seem to have that need. I find that too much gNFB makes for a "solid statey" sound. When I tried ~20db(v) of gNFB the result was truly horrendous.

Mmmm ... not sure what you are questioning, Miles. But where you introduce damping (I did not); the prime use of nfb is not to effect damping in the first place, but to reduce distortion. Damping comes as a bonus, and is usually more than sufficient after the necessary nfb to achieve 'inaudible' distortion has been applied. In fact, using nfb primarily to create a high damping factor can have disasterous results if other necessary factors are not in order. The unfair anti-nfb chorus is often as a result of this.

I am not a loudspeaker expert, but I cannot see that any design protocol can obviate the factor of loudspeaker damping (more accurately, Rgen). It is part of Qe, thus as much a factor as Vas etc.

As for your experiences, I respect that - I was not there to be able to criticise! Only, how many other factors played a role? 'Solid-statey' sound is a totally separate ball-game ... but we are somewhat off-topic; enough then.