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Amplifier frequency responce depending on loudspeaker impedance - measurements and test?

hakanfw

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Hi
To my experience the gain of an amplifier depends on the loudspeaker impedance...
Noooo... I do not have a gazillion$ measurement system, and a trackrecord of 100 amplifier/speaker combinations
BUT, I detect an increase in output sine voltage depending on impedance of the loudspeaker, most obvious around impedance peaks. It would be in the order of a few dB...
I search the web and all I find are these simple "calculators" where you compare "8 ohm" speakers with "4 ohm"...

Does anyone here know of measurements of amplifier frequency responce over fex a "dummy load" emulating a complex loudspeaker impedance?
I know the Swedish "Audio Engineering Society" use a dummy load to test amplifiers if they are "transparent" "before-after-test".

But... measurement results of frequency responce over a dummy load?

BR Håkan
 

Vladimir Filevski

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Higher amplifier output impedance - higher frequency deviations from flat, when the load is real speaker.
Stereophile magazine always use simulated loudspeaker impedance for measuring amplifiers:
https://www.stereophile.com/content/vac-sigma-170i-iq-integrated-amplifier-measurements
Black graph is the result of very high output impedance (8.8 ohms!):
321VAC170fig01.jpg
 
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hakanfw

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THAT's what i mean :)

However...
This was a tube amp and some 8 ohms internal impedance and in the order of the loudspeaker impedance... explaining voltage dividing and the amount of "frequency response bumpiness".
I get a swing in the order of "a couple of" dB on a solid state amplifier (Denon POA-800) when measuring separate loudspeaker units. The voltage dividing principle would call for an internal impedance of "2" ohm... and with a damping factor of "a lot" that sound weird o_O
Something ELSE is happening... :mad:

Interesting though since a bumpiness of a few decibels will show up as irregularities on the speaker when it is not to blame...
Different amplifiers will perform differently and with a audible variation even though the listed frequency response over a pure resistor i almost perfect.

Wellwell - anyone else that has a similar link but perhaps from a solid state amplifier?

BR Håkan

PS. Something tells me that class-D amplifiers could be better at this???
 

Wes

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class-D amplifiers could be better than what other designs?
 

Vladimir Filevski

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I get a swing in the order of "a couple of" dB on a solid state amplifier (Denon POA-800) when measuring separate loudspeaker units. The voltage dividing principle would call for an internal impedance of "2" ohm... and with a damping factor of "a lot" that sound weird o_O
Something ELSE is happening... :mad:
Without presenting relevant measurements it is impossible to determine what is happening, but definitely your case is very rare and unusual. If you still have the same amplifier and loudspeaker, please post here measured loudspeaker impedance and amplifier frequency response. Anyway, conventional solid state amplifier (like Denon POA-800) usually has very low output impedance, so frequency variation is very low. Here is example from Stereophile review of solid state amplifier:
https://www.stereophile.com/content/cambridge-audio-cxa81-integrated-amplifier-measurements
Black graph is amplifier frequency response on simulated loudspeaker impedance - very flat!
1220CXA81fig01.jpg
 

DonH56

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