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Looking around the internet, there haven't been many answers to this questtion. Here is one which doesn't fully explain it: Power input smaller than output? How can this be?

So I am confused. I know that a transformer (step-up or step-down) can change the voltage and amperage, but without changing the overall power output. So how is it that a speaker (eg Panasonic SC-CMAX5) have a much higher output than input? How can the energy which is put in be less than watt is put out (get it?). The SC-CMAX 5 has a nominal input ("power consumption") of 92W but an output (RMS) of 1000W.

Is it something to do with the RMS or PMPO listed on the spec sheet?

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  • \$\begingroup\$ What they are calling "Normal Use" wouldn't be anywhere near 1000W of sound output, it's probably what it uses playing music with a few watts of power output. \$\endgroup\$
    – PeterJ
    Aug 4, 2015 at 9:28
  • \$\begingroup\$ It's not just a speaker. It's also got a "digital amplifier", and a mains power connection. \$\endgroup\$
    – The Photon
    Aug 4, 2015 at 9:29

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The 92W is an "average" figure while the 1kW is a "maximum". To get a true idea of the maximum input power it could draw, we'd need to look at the information plate on the mains input. There will be capacitors in the power supply for delivering power into peaks. If you actually got it set up and outputting at peak volume it would probably draw >1kW from the mains.

It's not unusual for speaker power outputs to be really misleading, although this is the Panasonic official website and they quote RMS and PMPO. 1kW is quite loud!

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  • \$\begingroup\$ Thank you. That made it somewhat clearer. So if you could graph the input power and output power without any loss, they would be exactly the same at any one instant in time... \$\endgroup\$
    – Adrian
    Aug 4, 2015 at 9:47
  • \$\begingroup\$ @Adrian As long as both power domains are expressed the same way, there will be a very good degree of linearity to it, yes. PMPO versus input RMS would yield a very different kind of graph. Bear in mind though power in watts RMS is still higher than average power consumption by a mathermatical rule, at 1kW RMS output this unit can still only draw an average power of 900W: en.wikipedia.org/wiki/… \$\endgroup\$
    – Asmyldof
    Aug 4, 2015 at 9:55
  • \$\begingroup\$ Yes, although there will be some power loss as heat in the amplifier - not too much in a modern class D, but old tube amps and class A/AB configurations wasted quite a bit. So input power will be higher than output power. Provided you're measuring on the same scale, as @Asmyldof points out. \$\endgroup\$
    – pjc50
    Aug 4, 2015 at 10:06
  • \$\begingroup\$ @Asmyldof: There's no such thing as "watts RMS" \$\endgroup\$
    – EM Fields
    Aug 4, 2015 at 10:07
  • \$\begingroup\$ @EMFields if there is no such thing, why is it quoted everywhere? \$\endgroup\$
    – pjc50
    Aug 4, 2015 at 10:08

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