Audio Science Review of Expert 200.

[Confused]

Is there something more suitable?  Maybe analogue is better?  Are there issues with multi-meters presenting a resistance of their own?  There is a whole topic here I think.

Multimeters are unsuitable for making AC measurements at high frequencies, they are mainly designed for making AC measurements at 50 or 60 Hz. You are quite lucky you did no damage to your speakers by attempting to make high frequency measurements at potentially such high power levels.

If I understand the level control on the Devialet correctly, if for example you were using a 2 volt input signal into one of the analogue line inputs, and the maximum level for the line input was set to 2 volts on the Devialet, with the volume set at 0dB then the amplifier should be outputting a signal at full rated power.

If that was the case you would surely not be able to be in the same room with the power at that level!

The only way to achieve a meaningful measurement would be to replace the speaker with an 8 ohm resistive dummy load rated at at least one kilowatt. You could then measure the peak to peak sine wave AC waveform with an oscilloscope across the terminals of the dummy load.


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I tend to agree with your points here.  However, I think I may not have been clear enough myself regarding what I was actually trying to achieve with my earlier measurements.  I mentioned in my earlier post that I wanted to make some "real world" measurements to improve my own understanding of this HF power issue.  To be clearer, what I did NOT want to do is to try to attempt a "full power" test.  You mention I was lucky not to do any damage and that I would not be able to be in the room during a full power test.  In fact, the approach was to start at a very low gain, I was not only using a volt meter but I also had a SPL meter.  I was creeping the gain up slowly to see the influence on both volume and SPL.  I would have stopped the test before I got to very high SPL's.  There might be a degree of bravery in doing tests like this, but fear of damaging the kit kept me very much on the cautious side of things.  For the record, the 10kHz tone ran to about 95dB @ 1m, no more, which was subjectively a little uncomfortable, but I kept it at this level for only a little over a second or so.  Plus, in terms of my own bravery in testing, this was far enough for me to quit, and had the test tone been at a higher level, I would certainly have quit at about -20dB on the Devialet's gain, as I said, I was just trying to get a feel for real world power levels, I was not attempting a full power test.

Or to put this another way, if someone were to try a test as you describe, with a one kilowatt resistor and a 2V analogue input, we know what the end result would be, the amp would shut down.  Which I guess takes us full circle to one of the key points of this thread, why do Devialets shut down during HF testing at relatively low power levels?

Thinking about my own results a little more, I got to just under 6 watts with SPL's in the mid 90's, at 0dB gain.  Not that loud or that much power.  Considering the 10kHz tone was at about -18dB, these numbers actually look about right.  Certainly not super accurate, but in the right ball park.  So in theory, if the gain is then increased to +18, or a full 0dB test tone is used, then mathematically this would need about 380 watts to produce the tone at 113dB.  So maybe digital mutli-meters are not suitable for high frequency measurements, but in this case I suspect the results are not actually that far out, they look reasonable at least.

A few comments in this thread mentioning that digital multi-meters are no good for HF measurements, but does anyone know any details?  Do they overread, under read, or are they just "inaccurate".  Plus, what types of multi-meter are good for the job?  I noted earlier that Archimago seemed happy with a similar use of a digital multi-meter, but I also not he is suggesting using a 220Hz tone, somewhat lower than 10kHz.  So, are digital multi-meters maybe OK up to 300Hz, then inaccurate beyond?  Or is Archimago wrong to suggest a digital multi-meter for even 220Hz?  Does anyone have any decent information with regard to this?  I did a bit of searching on line, the information I found is not great, but it does look like some digital multi-meters will struggle at about 10kHz, but should be reasonably good below that.  From what little I have found, it looks like Archimago's 220 Hz test should be OK, but over 1000Hz it depends on the specific meter design.  As I said, the information I can find is not that good, if anyone has some decent information, I would be interested.

Anyway, no tests are planned today - Time for some music …..