Discussion of the "Pano" method for estimating amplifier power requirements

[restorer-john]

Edit: Wait... the level has been set before the test tone come into play. So a good amplifier will put out the same voltage with a test tone regardless of frequency. So why would the value measured by the voltmeter change if the meter reads true RMS over that range?

Some of Fluke's meters will give you accurate AC True RMS readings up to 20KHz on continuous waveforms. Most meters top out a a few KHz regardless of whether they are true RMS or not.

 

[PeteL]

Alright. One more attempt to explain.

I think there is some misunderstanding of what crest factor is. It is not the same as dynamic range. It comes about when we have multitone signals. Below is an illustration.

View attachment 77659

Here we have a summation of 8 sine waves of different frequencies and phase (the solid black curve at the top is the sum). All of the individual sine waves have V_peak = 1 V, and they are all steady signals. In this case, the CF of the summation signal rose to 11.2 dB. (Phase of the individual signals were calculated to maximize the CF to make this a worst case.) We can see that a multitone signal made up of pure sine waves can have CF far greater than that of the original sine waves.

Assuming an 8 ohm load, the average power of each of the individual tones is 0.0625 W, and the combined average power is 0.5 W (as indicated by the 2 V rms). Now the V_peak of our signal is 7.24 V. If I have an amp rated for 0.5 W with a single frequency sine wave, a V_peak of 2.83 V will be good enough to meet the power rating, but way insufficient to reproduce our signal of 0.5 W average power.

All this is in addition to dynamic range of the program. That's why, if one wants to play music at an average power of 1 W, one may want an amp rated at 100 W (10 dB for the crest factor consideration, plus 10 dB for program peaks) to avoid clipping.

Also, what confuse the matter more is that in times of Internet streaming, where music comes from anywhere, mastering software suites came up with the "DR score" of a recording to help retrieve some sense out of the loudness war architects, but this DR score is in fact the crest factor of the recording. And then came the LUFS, which are nothing else than a negative value of the rms value compare to full scale. So no wonder no one knows what is what.

 

[garbulky]

86 dB sensitivity is on the low side, but not too unusual. For example: Revel M126Be
[Edit] Yes. Bookshelves usually have low sensitivity.

I actually listened to that at a friends place. It sounds quite nice, not worth the price though