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I'm converting audio speaker to run on batteries. the speaker is Stagg SMS 8p - RMS 90W, peak power consumption 200W which is consistent with 1A fuse for 220V.

Say I go with 12V battery - peak current would be under 17A. If I choose reasonably priced 20C Li(Fe)Po modules -> I can get this current from relatively small 1Ah battery.

My question is -- if I set the volume to maximum non-distorted level -- how much time would I get playing 'typical' music. Preferably advise a software to which I can feed my playlist and get peak-to-average power ratio.

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  • \$\begingroup\$ Have you included losses for the inverter? \$\endgroup\$ – Solar Mike May 24 '18 at 13:37
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    \$\begingroup\$ For badly compressed music the average power will be about 5 dB lower than the peak power so if peak power is 200 watts then 5 dB down on this is about 60 watts. For the more discerning listener of jazz and classical you might be 20 dB lower at 2 watts average. \$\endgroup\$ – Andy aka May 24 '18 at 14:18
  • \$\begingroup\$ @Andy: That may be correct for typical power represented by music. However, it should be noted that amplifier power output is not necessarily directly proportional to the RMS level of the signal. \$\endgroup\$ – Olin Lathrop May 24 '18 at 15:35
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Your real question is apparently how much power does your amplifier and speaker combination draw at normal listening levels, when it is known to draw 200 W peak.

The best answer is simply to measure a few representative cases. It is really hard to guess how much below the 200 W peak the average consumption is.

This will depend on the volume of the output sound, which is a function of the volume of the input signal and the volume control setting. How sharply volume effects the power consumption has to do with the architecture of the amplifier. If it is a efficient class D, then power consumption will be some minimum bias plus a large component proportional to volume. If it's a class A, then the bias level will be much higher with a smaller remainder that goes up with volume.

Again, you have to measure it.

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  • \$\begingroup\$ It's a class D amplifier, I doubt there's Class A amplifier in any device industrially produced in last 30 years. \$\endgroup\$ – Gleb May 25 '18 at 9:57
  • \$\begingroup\$ How do I measure? Ampermeter on the power line wouldn't help me much. \$\endgroup\$ – Gleb May 25 '18 at 9:59
  • \$\begingroup\$ @Gleb: Class D certainly makes sense today, but audiophool gear often doesn't make sense. If you know the power voltage, then all you need to measure is the current. It seems like a ammeter on the power line is exactly what you want. \$\endgroup\$ – Olin Lathrop May 25 '18 at 10:51
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12V at 1Ah means about 12Wh. If you have 90W average consumption then you get about 12Wh/90W = 0.1333h = 8 minutes of music.

This is not accounting for any transformation losses (which can be easily 80% per stage).

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