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Old 21st March 2012, 12:40 AM   #3881
DF96 is offline DF96  England
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Quote:
Originally Posted by benb
Are speakers usually designed with the assumption they'll be driven only by an amplifier with a high damping factor?
Mostly, yes.

Given the voice coil resistance will be several ohms, a few tenths in the cable will have only a small effect. The main effect is to prove that really high amplifier DFs are pointless, although in themselves harmless.

A current mode amplifier would need to be used with speakers designed for it (i.e. more mechanical damping), unless you like to listen to the bass resonance.
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Old 21st March 2012, 01:07 AM   #3882
bcarso is offline bcarso  United States
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Quote:
Originally Posted by benb View Post
I'd think they should be tested with a range of driving impedances, if for no other reason than to find out what happens.
John Atkinson does measure loudspeaker impedances. And he measures amplifiers with resistive loads and simulated loudspeaker loads. So between those one can get an idea about the loudspeaker/amplifier interactions.

Last edited by bcarso; 21st March 2012 at 01:24 AM. Reason: blunder in recollection
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Old 21st March 2012, 01:37 AM   #3883
tvrgeek is offline tvrgeek  United States
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At least in the simulation of th e120, the key to distortion, particularly even, is the value ratio of the gate stoppers. As much as 20dB between the calculated recommended values and what can be done by playing around.

This makes sense to think about it. It also means that decent performance is a matter of hand selecting in-circuit. The recommended values of 470 and 330 are not balanced. 440 and 400 sim to null all even harmonics. It did not like higher values. This was masking everything else I was playing with on the input as those changes were below the outputs distortion by a lot.
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Old 21st March 2012, 02:28 AM   #3884
godfrey is offline godfrey  South Africa
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Quote:
Originally Posted by gk7 View Post
...but when I insert a 0.46 Ohm resistor
between my amp and speaker (thus lowering the damping factor from
something > 50 to something about 17)...
That would typically cause frequency response variations of 1/2 a decibel or so, depending on the speakers. Whether that's audible and/or objectionable would depend on the listener and the speakers IMHO.
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Old 21st March 2012, 03:34 AM   #3885
bcarso is offline bcarso  United States
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Quote:
Originally Posted by godfrey View Post
That would typically cause frequency response variations of 1/2 a decibel or so, depending on the speakers. Whether that's audible and/or objectionable would depend on the listener and the speakers IMHO.
Broad (i.e., low-Q) variations are durable (i.e., survive the passage to "double-blind") in subjective evaluations. Even at that rather remarkably low level. It helps to have trained listeners, indeed.
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Old 21st March 2012, 04:54 AM   #3886
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I love low-Q resonances, they are easy to equalize electrically.
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Old 21st March 2012, 05:26 AM   #3887
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by gk7 View Post
I have no reason not to believe you, but when I insert a 0.46 Ohm resistor between my amp and speaker (thus lowering the damping factor from something > 50 to something about 17) the difference in the bass region is _very_ clearly audible. How can this be the case if its never more than 2 ?
You need to separate two things here.

One is the actual damping (electrical) of the voice coils movement by the source. The other is frequency response. Unless your Speaker is a pure full range driver with no crossover, flat impedance and well controlled LF Peaks you can expect changes in frequency response that are quiet wide ranging. Also, you will alter (lower) the distortions in the speaker by adding series resistance

However, this has nothing to do with electrical damping.

This brings us back to the "system" part. I for example design my speakers such that reasonable levels of source impedance do not cause frequency response shifts (in other words with a flat impedance).

The bottom line is that any given speaker system needs to be designed with a view to what source impedance will be present. While "Zero ohm" is a common convention, in fact many speakers do not work well under these conditions.

Ciao T
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Old 21st March 2012, 05:32 AM   #3888
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by wahab View Post
A low NFB amp will have higher but less variable output impedance, so for the case above of 2R output Z , it may well vary from about one to five ohms in function of frequency , audio band wise.
Alas I posted earlier on an Amplifier schematic that would probably fit "low NFB" (only 14dB NFB looped around the output stage). This Amplifier is expected to have around 0.15 Ohm open loop output impedance with 0.03 Ohm closed loop output Impedance.

I will probably fit an additional circuit to synthetically increase the output impedance to 3 Ohm, which is the target source impedance for all of my personal speakers, as otherwise this solid state Amplifier would be put too much at a disadvantage regarding sound quality.

Ciao T
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Old 21st March 2012, 06:39 AM   #3889
gk7 is offline gk7
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Thiele and Small ?
The added 0.46 Ohm should result in +0.7 dB at 80Hz which is almost
nothing, but it does sound to me like more; will have to measure it
once I have my measurement mic ready.
3.9 Ohm added (for a DF of 2) should give +4.5 dB at 80Hz according to
the resulting TSP change, this should be easily audible, no ?
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Old 21st March 2012, 07:04 AM   #3890
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Hi,

Quote:
Originally Posted by gk7 View Post
Thiele and Small ?
No, voice coil DCR vs. nominal impedance...

Ciao T
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