A different question on wattage.



Audioholics Five-0
2,999 18 1
But that's not the reality. I can play an orchestra without disabling the state's power grid.
So I'm missing something... but I'm not sure what.
Look it at another way. You can listen to an orchestra live without blowing out your ear drums, in spite of the myriad of frequencies involved at any given moment in time, meaning the actual total SPL involved isn't that high. When that sound is recorded by a mic, pressure variations caused by the sound are converted into a correspondingly finite electrical signal, capturing the complex waveform of the sound.


Audioholic Overlord
5,081 7 1
Within some limits; but not entirely.

I know that power requirements don't spiral towards infinity; but I don't know if the SPL is constant or changed, nor how power requirements change.
Yes, the spl will change if you don't keep the input voltage to the speaker constant. I think I know what you may be looking for now, let me try the following.

1. You are right about the instantaneous moment by moment spl of say two sine waves, say a 1 kHz and a 2 kHz will be different, the peaks won't be 2X as such because they won't peak together, but at some points they will have the "constructive interference" effects, see @Irvrobinson link article in an earlier post.

2. In reality you don't necessary get a ton of spl and power draw because:

a) While the instantaneous peak spl could be louder or much louder but they would be of very short duration typically, in terms of RMS, the +ve and -ve effects of the multiple waves may not change by very much, I think it is the music composers (Bach, Beethoven etc.) and song writer's job to make sure the vocal and instruments all play nice to each other. By the way, that's why some music has >20 dB dynamics, and you are right in that sense about what you have been saying all along, but again, the average spl should not change anywhere near as much as the peaks do due to the effects of multiple frequencies being play together. The speaker and the amp do see the peaks though for sure.

b) Again, sorry for repeating, when the lab, say Gene's AH, or Sounstage.com, Stereophile, S&V measure a speaker's FR, they apply a constant voltage of 2.83 V. The ideal speaker will show flat response full band. If they were to use not just a 1kHz sine wave, but mix it with 1.5, 2, 2.5,....10kHz etc., that waveform will become a complex waveform, but if they would keep the same voltage of 2.83 Vrms, the average spl output would remain roughly the same, but the peak will no longer be just 3 dB higher (for the one sine wave). In the the speaker scenario, you get louder spl and more power draw simply because you now have two amplifier channel and two speakers doing the work and sucking juice, each suck the same. You can even use one amplifier to feed two speakers if the two have the exact same sensitivity and FR as the one under test, but with double the impedance (to compensate for the parallel effect).

So to summarize, the key points for your puzzle are:

- RMS (for voltage consideration) vs Average (for power consideration) Vs instantaneous (for both voltage, power and SPL consideration).

- Speaker's spl output depends on the voltage, if you limit the voltage to 2.83 V rms measured at the speaker's terminal, the average power draw will be double when playing a complex signal with two sine waves vs one.

- You are correct about the +ve and -ve effects of having multiple signals, but how much louder peaks and power draw depends on how they all come together. Hence one reason why the average draw for some music may be 1 watt average, but the peak could be over 1000 Watt if the music has a peak to average ratio of 30 dB.

Here is a cool site, where you can vary the amplitude and wavelength (i.g. frequency) and see that exact effect of the resultant one. You don't need to know Fourier:D, unless you want to create those things, such as pink noise yourself.


How does this play out when a passive breaks apart a signal?

Assuming all drivers are involved, can I multiply the number of channels on the crossover by the voltage? Or is the voltage reduced by the crossover when splitting (let's assume, for argument, all drivers in the speaker are equally efficient and no deliberate inefficiency is added by the crossover).

It can't just halve the voltage (as that would reduce the volume of an individual wave). But if it maintains the voltage to (say) 2 drivers (separated by a crossover),isn't that functionally the same as two separate speakers?
Have to go to my partner's shop now to continue on my diy speaker project now, will get back to you later, hours later..

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