If by 'loudspeaker' you mean the system of a driver in its enclosure, the response in the main resonance region is normally ruled mainly by its acoustic design. It was indicated that the actual damping factor as seen by the loudspeaker is limited to about 1,3. (Again not talking of active or other special designs.)
The damping of cone movement by placing a short over it damps overshoot at whatever frequency the 'short' is active at. Agreed; that does not include cone effects not reflected as forces on the voice coil proper.
Low DF does not necessarily reflect on an amplifier's sound quality - it is more a loudspeaker thing. But not all tube amps have low DFs - there are some urban legends here. A typical p.p. tube amp design of some 20W output with 20dB negative feedback (nfb) can have DFs in the region of 45 - 60 (note classic Williamson and Leak designs, to name only two).
The often perceived high quality of a tube amp, particularly low/zero nfb and/or single-ended types, results from audible second and third harmonic products. [Musically second harmonics are an octave higher than the original. Most music will sound better (the word warmer is a typical perception used) with some such added. About 1% - 2% third harmonics added are reported to make brass and string instruments sound more crisp.] The amplifier is then indeed partly a musical instrument, 'improving' the original.
Also very low DFs as a result of low/zero nfb and pentode output tubes can cause peaky response in loudspeakers, again possibly manifesting as 'pleasantness' depending.
Damping factor is useful when applied at all frequencies of the full audio spectrum (20-20).
...And preferable to be above 100 (8 Ohms) and 50 (4 Ohms), all across the range, in linear fashion. ...I think, I believe.
Amps with a higher damping factor (measured) are my preference. ...Yamaha, Rotel, ...
...And preferable to be above 100 (8 Ohms) and 50 (4 Ohms), all across the range, in linear fashion. ...I think, I believe.
Amps with a higher damping factor (measured) are my preference. ...Yamaha, Rotel, ...
Very well controlled bass is exactly what I'm talking about and Damping Factor doesn't provide it...end of story!
It would be of great help if everybody tries to tell his own point of view, using objective means only, on what defines controlled bass .
I flatter myself by thinking that I know and have enough experience, being involved in the development of a number of well-known subwoofer drivers, to have a fairly comprehensive idea of what constitutes good, solid bass and what doesn't.
Evidently, I was in error and I'll leave to the "armchair experts" to have the definative "final say".
Good Day,
TerryO
Try this: Amp turned off, tap on the woofer cone, then turn the amp on and do the same. For completeness you could also switch in some resistors. The experiment works best with large woofers.
I do not contest anything about your experience. I am just curious of what objective facts you consider as associated to controlled bass.
I am going to add my two pennies worth here damping factor can be important i cannot see here any mention of negative impedance an amplifier can be more than just a short it can actually apply a reverse breaking signal to the moving voice coil
I have measured this effect in the past
any comments on that then ?
I have measured this effect in the past
any comments on that then ?
Negative output impedance is an oscillator waiting to happen - actually a number of oscillator types rely on (locally) negative impedance. It's a neat trick to offset wire resistance under very controlled circumstances, but requires great care in application.
Ideally a loudspeaker should have enough mechanical damping to not require much on the electrical side... but there always is the difference between theory and practice. And there are crossovers, which may make a multi-way speaker far more demanding than a wideband affair by way of turning their impedance response into a rollercoaster ride. Single drivers rarely require more than about a DF of 5-10, stuff with crossovers may be a fair bit more picky. Keeping a particularly mean construction that dips down to 1.5 ohms and goes up to 16 ohms within 0.3 dB across the band mandates that source impedance be no greater than 58 milliohms, or DF ~140 ref. 8 ohms. A well-behaved 4 ohm speaker ranging between 3.2 and 10 ohms would be happy with 168 milliohms, or a DF of 48 ref. 8 ohms (24 ref. 4 ohms).
As to how much DF you need, well, that would depend on the loudspeakers and their respective impedance variation. You can basically use a calculator intended for headphone outputs (shoot for 0.3 dB of response variation if you want to be strict), though that one assumes a purely ohmic output impedance, and speaker power amps typically have an output inductor that results in reduced DF at higher frequencies.
There is no real maximum for DF, but the point of diminishing returns is reached when output impedance becomes negligible vs. a typical run of cable... 1 m of AWG14 twin-lead already contributes 17 milliohms, so DF couldn't be greater than 470 ref. 8 ohms at this point.
Ideally a loudspeaker should have enough mechanical damping to not require much on the electrical side... but there always is the difference between theory and practice. And there are crossovers, which may make a multi-way speaker far more demanding than a wideband affair by way of turning their impedance response into a rollercoaster ride. Single drivers rarely require more than about a DF of 5-10, stuff with crossovers may be a fair bit more picky. Keeping a particularly mean construction that dips down to 1.5 ohms and goes up to 16 ohms within 0.3 dB across the band mandates that source impedance be no greater than 58 milliohms, or DF ~140 ref. 8 ohms. A well-behaved 4 ohm speaker ranging between 3.2 and 10 ohms would be happy with 168 milliohms, or a DF of 48 ref. 8 ohms (24 ref. 4 ohms).
As to how much DF you need, well, that would depend on the loudspeakers and their respective impedance variation. You can basically use a calculator intended for headphone outputs (shoot for 0.3 dB of response variation if you want to be strict), though that one assumes a purely ohmic output impedance, and speaker power amps typically have an output inductor that results in reduced DF at higher frequencies.
There is no real maximum for DF, but the point of diminishing returns is reached when output impedance becomes negligible vs. a typical run of cable... 1 m of AWG14 twin-lead already contributes 17 milliohms, so DF couldn't be greater than 470 ref. 8 ohms at this point.
The main problem with a negative amp output resistance is to tame the resonance of the voice coil inductance, Le, with the capacitive component of the motional impedance, Ces.
The value Le is neither constant with frequency nor with the voice coil displacement in the gap.
sgrossklass, you bring up some interesting points. especially the passive crossover. add that and all bets are off.
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