Time to buy a class D amp?

IMO it is possible to overdamp loudspeakers and thus truncate the bass notes

This statement gives a wrong impression for amplifiers output impedance. That should really be.
There are a small minority of speakers that are "overdamped" by bad design or being purposely overdamped designed, and it's the speaker manufacturer problem to get the "Q" correct. Not because the amp is over-damped or underdamped.
And amps are also supposed to measure as flat as possible regardless of load impedance they see. 

From the Speaker design bible
.707 is said to be the correct "Q" with respect to damping. A higher Q indicates a woofer that is underdamped (loose) while a number lower than .707 indicates an overly damped woofer.

There is no such thing as too low for an amps output impedance. They even build speakers with "driver servo control circuits" to control the bass driver excursions even more and faster than the amps can do.

A classic example of trying to corner the amp/speaker market was the Linn/Naim scam of the 80's when a "purposely overdamped speaker" was mated with a "purposely under damped amp", when together they were a match and sounded good.
When either were substituted for something else and there was either, no bass because of being too tight, or too much soft woolly bass.
When a Krell was substituted for the amp, there was very little bass, (what!!! a Krell with no bass!!) that raised the eyebrows.
Needless to say this idea was Linn/Naim was exposed eventually and they did stopped doing it probably through fear of being called cheats, great marketing idea though if you have no conscience.

Cheers George     

Servo controlled woofer is much different from a low output impedance amplifier connected to a woofer that will keep moving after the amplifier signal goes to 0. A servo controlled woofer can be designed to smoothly stop a woofer without any ringing if so desired.


"Damped" and damping factor are of course not the same thing. Damping factor is a simple output impedance  / 8 Ohm calc.  "Damped" refers to how or the characteristic of how a system will respond to a step response.


Speakers are designed to be driven typically by constant voltage sources. Dynamic drivers on the other hand can behave better, i.e. lower distortion with constant current sources.  To that end, all speakers are the product of trade-offs, and designing for 0 output impedance forces other trade offs a particular designer may not want to make. The amplifier is part of the circuit that governs how the speaker will behave. We can talk about a "perfect" world, but dynamic drivers are already imperfect. So better to discuss which imperfections you want to live with.

Servo controlled woofer is much different from a low output impedance amplifier

I didn’t say it was the same, I said it controls even better the cone movement than the amps damping factor alone can.
I’ve asked you three times now, go away please, and stop stalking my posts.

This is a public forum. I will respond to the content of your posts if I please. That is how public forums work. You didn't start this thread. Lose the attitude.

An amplifier with a high damping factor may limit the total error energy in the woofer cone movement, which could be one measurement of "better", but there is no guarantee that will sound better, because the energy may be concentrated over a narrow frequency range (ringing) that is audible, compared to what happens with an amplifier with a lower damping factor. This is not a new concept, and is explored in the item linked by Nelson Pass, and has been discussed on/off since the 70's.


This is much different from a servo controlled woofer movement where the actual physical position is directly controlled, not an indirect via the coil wires (and through the cross-over).

In theory the "signal" stops and starts as recorded so that is accurate. The problem is the woofer does not stop right away. In a lower damping factor amp the output resistance will help dissipate the energy in the woofer which can give it a more controlled stop.

This is of course the theory but in practice (IOW the real world) is not a thing. The woofer never 'stops'; its always in motion; there is no recording where the woofer 'stops'. The only way for it to 'stop' as often described abover is if a DC pulse is being reproduced, which is something that neither the amp or speaker will ever have to do. On this account I've often viewed this as a red herring.


More to the point, the idea is that the woofer will continue to oscillate after the initial pulse. But in reality after the woofer moves the first way, the audio signal directs it in the opposite way; it never gets the signal removed and so can't ring. This is why amps with a low damping factor can do quite well in the bass. The real problem isn't ringing or distortion, but getting too much bass if the amp fails to reduce power into impedance peaks of the woofer's impedance curve. This isn't a control issue (which is also a problematic idea), its simply that an amp with insufficient low impedance will simply make too much power.