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Re: Your claims/responses here and elsewhere.

"The anthropomorphisation of circuit elements and currents, claiming they have a predilection for going in a certain direction, have intentions and objectives, know where they are coming from and are going to etc. etc. is a dangeroud thing!"

I did nothing of the sort. I merely stated that the back signal will take the path of least resistance and you know what, I was right! How do I know this, Otala et al. that's how. I now have AES papers from 1978 and 1980 that show that he phenomenon is real and potentially quite stongly affecting the sound. Shall I quote their findings to you?
Here is the abstract:

"The possibility of dynamic intermodulation distortion at the amplifier-loudspeaker interface is discussed. THis distortion is produced in amplifiers using high values of negative feedback, and having moderate or high open-loop output impedance in comparison with the loudspeaker impedance. The mechanism is intermodulation between the signal and its delayed versions, generated by the loudspeaker and propagated in the feedback loop. Experimental measurements showing the probability of considerable distortion are described."

Here is the Summary:
"The analysis and the measurements show that:

at its various mechanical resonant frequencies, the loudspeaker may feed back to the amplifier much of the energy it received.

The loudspeaker may also act as a signal generator due to mechanical excitation of its voice coil by cone break-up, sustained oscillation of moving parts, delayed responses, etc.

provided that the power amplifier has an OPEN-LOOP output impedance in excess of a few ohms, and simultaneously substantial overall feedback, these backward energies are not subject to intrinsic damping at the amplifier output, but a corresponding feedback signal is generated within the amplifier, in trying to counteract the loudspeaker-generated signal and keep the output voltage constant.

The signal in the forward path of the amplifier thus consists of two components, the original input signal and the loudspeaker reaction signal, both of the same order of magnitude.

These two signals my interact in the nonlinearities of the amplifier, generating intermodulation products between the two. Loudspeaker nonlinearity is here to be considered equivalent to any open-loop nonlinearity of the amplifier, since it will effectively be situated inside the feedback loop, unless the open-loop output impedance of the amplifier is considerably lower than the specified load impedance.

this distortion, here termed interface intermodulation, IIM, will be most prominent at low frequencies wehre the loudspeaker-generated signal is at its greatest.

The susceptibility of the amplifier to IIM distortion can be measured bz using a modified difference-tone method, where on of the signals is injected to the input, and one to the output of the amplifier. Maximally, the latter signal should equal in power tthe maximum output power of the amplifier, to create a conservative worst-case fr this effect."

So, I am not making this stuff up as you can see.

Here is the conclusions from the 1980 paper:

"It has been demonstrated that the loudspeaker can considerably alter the nature and composition fo the internal singals of an amplifier. Porvided internal nonlinearities of any kind exist within the amplifier (my note: all amps are somewhat nonlinear so this is a give), the loudspeaker thus has a capability to change the amplifier distortion properties. The effect is strongest at the low frequencies, where the loudspeaker reactive properties are most outspoken.

The susceptibility of an amplifier to this loudspeaker effect is different for different amplifier topologies. The most important parameter in this respect is the amplifier open-loop impedance Zol. A low value of Zol prevents the loudspeaker to have any remarkable effects, but if Zol by virtue of the circuit topology is large, the loudspeaker generated reaction signal inside the amplifier may be of the same order as teh original input signal.

The effect described does not normally increase the amplifier distortion considerably. Instead, it has the capability to change the amplifier spectra, and its audible character."

So I guess I am not making things up in my own fantasy world afterall, Cliff. I got the research of Otala to back me up on this one.


"As is believing that audio circuits are somehow "special", delicate and subject to their own laws (?) of physics that no-one but the initiated inner circle are blessed to understand."

Who said anything about that? However, if feedback is involved it is clear that the OPEN LOOP output impedcance of the amp has a strong effect on how much back EMF goes through the feedback loop (as does the amount of feedback used) and thus how much effect there is on the sound. So in that sense the topology IS very important.

Just because I bother to read this stuff and you don't doesn't give you the right to call me a troll I am nothing of the sort.

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  Michael Percy Audio  

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