Measurements to show an amplifier's 'lack of juice' for specific speakers?

[whazzup]

Upon reading Amir's recent review of LS50 meta and its ~3 ohm impedance, this question popped up in my mind again. Can an amp's lack of juice to drive a speaker show up in sonic measurements? Do transient peaks get affected? Or do they manifest as overheating in the amp, or shutting down? Way higher distortion at high SPLs? Inadequate volume output?

Expensive high wattage amps are frequently marketed to people who 'fear' about an amplifier that cannot drive speakers properly, will be cool to see actual examples, to separate facts from myths.

 

[Plcamp]

It would be interesting to see how amps react to lowering load impedance, when it starts to misbehave, what does that look like?

Trying to run attached in a parallel pair I perceived an inability to handle the bass at elevated volumes using a Yamaha RXA3030 receiver, while a power amp off the preouts I perceived no problem. (No I did not blind test etc, I just tried it)

Anyway, it would be nice to know, when amps are tested at ASR, at what minimum impedance the amp misbehaves…a figure of merit?

 

[nemanja_t]

Some magazines do, for example german Stereoplay

 

[whazzup]

It would be interesting to see how amps react to lowering load impedance, when it starts to misbehave, what does that look like?

Trying to run attached in a parallel pair I perceived an inability to handle the bass at elevated volumes using a Yamaha RXA3030 receiver, while a power amp off the preouts I perceived no problem. (No I did not blind test etc, I just tried it)

Anyway, it would be nice to know, when amps are tested at ASR, at what minimum impedance the amp misbehaves…a figure of merit?

Me, I just do not have the fortune (or misfortune) of testing really low impedance speakers, so can't really imagine how an 'incompatible' amplifier - speaker combo sounds likes / measures. Yes, will be cool to see such negative examples in action.

 

[whazzup]

Some magazines do, for example german StereoplayView attachment 146526

Sorry don't quite understand the graphs. The first doesn't seem to show any difference between 8/4/2 ohms, while the second shows rising 'distortion' with higher frequencies?

 

[abdo123]

You need an osciiloscope.

 

[Beave]

The "power cube" measurements that were done for/by the magazine "The Audio Critic" would show how much power an amp could provide to different complex loads (different magnitudes and phases) before clipping.

https://www.audiograph.se/wp-content/uploads/2018/10/PowerCube_12p_brochure_complete.pdf

 

[LTig]

The "power cube" measurements that were done for/by the magazine "The Audio Critic" would show how much power an amp could provide to different complex loads (different magnitudes and phases) before clipping.

https://www.audiograph.se/wp-content/uploads/2018/10/PowerCube_12p_brochure_complete.pdf

This! AFAIR there was a discussion quite some time ago whether @amirm might try to get one but it was too expensive.

 

[whazzup]

Is there a specific phenomenon that we can point to and say with certainty 'Hah! So your amp has insufficient power for your speakers!'

 

[nemanja_t]

Sorry don't quite understand the graphs. The first doesn't seem to show any difference between 8/4/2 ohms, while the second shows rising 'distortion' with higher frequencies?

It is on “Kompatibilitätsdiagramm“ (easy german word), where they say in comment that it is very powerful and can drive speakers with a low impedance.

 

[kschmit2]

German magazine AUDIO also uses the power cube or rather stability diagram. And they have developed a metric that allows you to determine whether a loudspeaker/amplifier combo matches or not.

I have added three files with translated articles explaining what they do. Maybe @amirm can chime in on this too.

 

[abdo123]

Is there a specific phenomenon that we can point to and say with certainty 'Hah! So your amp has insufficient power for your speakers!'

yes, it's when the waveform looks distorted on a oscilloscope, otherwise you just have to rely on your ears and tea leaf reading of the often lacking amplifier specifications of the manufacturer.

 

[nemanja_t]

German magazine AUDIO also uses the power cube or rather stability diagram. And they have developed a metric that allows you to determine whether a loudspeaker/amplifier combo matches or not.

I have added three files with translated articles explaining what they do.

It looks like this:

 

[kschmit2]

It looks like this:
View attachment 146639

Thanks for attaching this, as it also shows the distortion factor in the right column. They are referred to in one of my files, but I forgot to include the graphs.

 

[Plcamp]

I like from the article this kind of plot…seems informative. Looks to me this could differentiate amps for anyone needing to drive complex low impedance loads.

 

[solderdude]

Indeed the electrical phase (differs from acoustical one) is also of importance.
Would have liked to have seen +/- 90 degrees for the current opposite the output voltage.

 

[abdo123]

Indeed the electrical phase (differs from acoustical one) is also of importance.

from the few graphs i've seen it doesn't seem to be doing anything 4 Ohm and above, what's the difference between electrical and acoustical phase?

 

[solderdude]

Here you can see electrical phase issues explained graphically.
There is a difference between capacitive and inductive loads.

Inductive load:
At 90 degree angle between voltage and current the amp supplies a voltage but no current. 90 degrees later the amplifier does not supply a voltage but the amp has to provide the maximum current. 45 degrees later, as an example the output voltage is negative but the current is still positive.

For capacitive loads a similar thing happens but in the other 'direction'.

Acoustical phase rotates many times depending on distance from woofer and tweeter to the ear, distance etc.

 

[Plcamp]

Indeed the electrical phase (differs from acoustical one) is also of importance.
Would have liked to have seen +/- 90 degrees for the current opposite the output voltage.

sixty degrees should cover the bases…ninety would imitate powering a speaker with its drivers short circuited!
Then again, it would also be a feature of merit to survive output short circuits…if it were not dangerous to try it, amps really should withstand dead shorts.

 

[solderdude]

Not really as with a short the current and voltage would have the same value.
The phase can rotate 90 degrees but the current would still be limited by the ohmic part of the speakers.
But sure... most speakers will not go +/-90 degrees but remain below +/- 60 degrees electrically but when testing amps why not see how they handle this ?