How much comparable power do we need for different frequencies?

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#24
In my experience you need more power the lower you go in frequency. By the time you're in subwoofer range, you may need 10 to 30 times as much power as you would send to your tweeters.

In my system every driver gets its own amplifier channels. It's a 4-way, so that equals 8 amplifiers.

Each side looks like this:

18" Subwoofer: 20-85 Hz: 600 watts
Dual 8" Woofers: 85-400 Hz: 200 watts
Dual 4" Midrange: 400 - 2000 Hz: 75 watts
Single Planar Tweeter: 2000 - 20,000 Hz: 35 watts


Even with 600 watts for the sub, it still goes into clipping and distortion before I can hear it happen in the mids and highs.

I don't think it's a simple function because at low frequencies the output doesn't beam and must fill up a volume much larger than the mids and highs do. This is why many frequency response graphs don't show below a few hundred Hz because in an anechoic situation the output measured drops off like a rock. Of course, inside a space such as a room the results are different.
 
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#25
Yes, aggree with the result, but is it really the power that is needed.
To avoid clipping it is normally the max current and the max voltage you depend on.
But almost never at the same time.
So in comes crest factor and power factor.
So the amp almost never uses its full power. (Max voltage and Max current) even if the voltage is near clipping
 
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#26
tmuikku said:
Yeah, SPL is ultimately about volume displacement, simplified it means cone area * excursion. To maintain same SPL octave lower in frequency, the volume displacement needs to quadruble. So, since any woofer or tweeter has static size, as it stays ~the same size no matter what frequency it tries to reproduce, it means higher frequencies need way less excursion than lows to maintain flat SPL. This means highs can get away with way less power to move smaller cone less, than at same SPL at some lower frequency bigger cone needs to move way more.

Two octaves down volume displacement is 16x already, so either the cone area must have gone up or the excursion, which would need more power in general. Sensitivity is often the voltage sensitivity, how much SPL is measured at 1m at standard 2.83V or 1V or what ever input. For highs this is very low, compared to lows. For example, if you have 90db at 100Hz, and count 7 octaves up it's 12800Hz which needs 4^7 = 16384 times less volume displacement to reach 90db. Typical 15" driver has about 850cm^2 cone area, while a 1" tweeter dome is roughly 5cm^2, this is difference of 170. 16384 / 170 is roughly 100, so the woofer still needs to have about 100x excursion of the tweeter even though it's much larger, to product same SPL at 100Hz as the tweeter does at 12800Hz.

Consequently 12800Hz wavelength is roughly 2,7cm, so almost equals diameter of the tweeter. Wavelength of 100Hz is 3.4m, so if you wanted a woofer to be have as little excursion at 100Hz as tweeter has at 12800Hz, the woofer would need to be roughly 3.2m in diameter!🙂 15" is way less, like 10x, hense much more excursion required.

Well, these numbers seem so outrageous I might have error, so please welcome anyone to double check 🙂 But it's along the lines, lows are very tough to reproduce due to very very long wavelenght.
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Tmuikku, this was the first reasonable answer 👍and maybe a good start for a formula. Thank you. 😎

If you invent a calculation tool, you will be a legend,😎 since there is no way to learn it anywhere else.

I asked this questions several times in many years in different forums and nobody couldn't answer it.

Maybe you make a formula with changable parameters such as frequency, cone diameter, xmax etc. ?

Unfortunetly, my mathematical skills are not as strong as yours.
 
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#29
The calculations of tmuikku is important physical properties, but does not give the full picture. The standard modell for one driver is the lumped model. As you se ZL is frequency dependent.
So also the magnet, stiffnes of suspension, moving mass and others plays a huge part of the efficiency of the speaker. And that again tells us how much power is needed at a frequency to get a certain SPL or sound power level

1730463075655.png
 
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