What matters about SINAD measurements

[DonH56]

In the midrange, hand-waving:

• 1 dB change in volume is about as small as we can distinguish when listening to music (or whatever). This is not the criteria for comparisons (that's more like 0.1 dB) but the smallest step we can detect (just noticeable difference, JND).
• 3 dB is about the step most of us will tweak the volume (or the sound board) when someone asks us to make it "just a little" louder or softer. That also takes twice the power.
• 10 dB is twice as loud (or half the volume for -10 dB) and takes ten times the power.
• 20 dB is four times as loud (or one-quarter the volume for -20 dB) and takes 100 times the power.

Takeaways might be that, if you really need more amplifier, you probably need a lot more; and, the sales guy describing the benefits of going from 110 W to 125 W (a recent experience) is probably full of it or something else is causing the difference.

FWIWFM - Don

 

[birkbott]

View attachment 25226

Hi QAMatt. I was generalizing, based on typical SINAD v. power curves such as the one shown for a Denon AVR-X3300W. The "knee" is the "onset" of clipping, above which distortion rises rapidly (we don't want to listen there), and at which is calculated the lowest percentage, here about 0.015%. So marketing today usually uses this "best" figure, although it is valid only for instantaneous peaks. Properly sized for speaker sensitivity and room acoustics, most of the time, this amplifier output would be less than 1w, where SINAD is closer to 0.1% - but you won't see that advertised.

I have trouble squaring measurements with advertised specs often. This is the measurement for the Schiit Vidar as published on their website (8 ohm load)

The knee looks like it's at about 25-26 watts and yet they rate this amp like this: THD: <0.01%, 20Hz-20KHz, at 100W RMS into 8 ohms

How is that possible? I don't even see 100 watts on this graph. Or maybe I'm reading it wrong?

 

[NTK]

... How is that possible? I don't even see 100 watts on this graph. Or maybe I'm reading it wrong?

You have confused voltage with power. The horizontal axis is RMS voltage. Power is the square of Vrms divided by load resistance. In this case, the onset of clipping is about 28 Vrms, the load resistance is 8Ω, the power is 28*28/8 = 98 W. Since it is typical to report maximum power at 1% THD (the green horizontal line in the graph), this amp just passed its advertised spec.

 

[birkbott]

You have confused voltage with power. The horizontal axis is RMS voltage. Power is the square of Vrms divided by load resistance. In this case, the onset of clipping is about 28 Vrms, the load resistance is 8Ω, the power is 28*28/8 = 98 W. Since it is typical to report maximum power at 1% THD (the green horizontal line in the graph), this amp just passed its advertised spec.

Thank you for clearing that up, I knew something had to be off.