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Old 24th August 2005, 11:41 AM   #1
maxw is offline maxw  United Kingdom
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Question power distrobution in a multi-way system

I am just wondering how power is shared by each drive in for example a 3 way system, Woofer-Mid-Tweeter.
I'm guessing from the weight of the cone and the amount of movement the woofer will use the most but is there a formula?

The main reason I ask is when reading power measurements for tweeters they say "nominal power = 80W" so does that mean if you arranged it with a woofer the combo can handle 80w (as long as the woofer is up to it too) ?? or is that like 80 Watts of treble? or am I looking at this the wrong way?

any help would be much appreciated....
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Old 24th August 2005, 11:57 AM   #2
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In my estimation, if the drivers all have the same sensitivity, with demanding classical music the bass range 20-200 requires about double the midrange (200-2k) power and the treble about half the midrange. So if you have a 200 watt woofer amp in a triamp system you should have at least 100 watts in the midrange and 50 watts in the treble to maintain the same max spl levels. As far as a passive three way you can say pretty much the same about the power handling ratio of the drivers provided the crossover is working properly - IE if the treble driver is crossed too low or with too shallow of a slope it may not handle anywhere near it's rated power. This is basing the power requirements on the power of the recorded music content rather then weight of the cone, or the amount of cone movement ect -

So if used properly an 80 watt treble driver should be OK with a 320 watt amplifier if the system's drivers/network is well matched - hardly the norm but a good estimate IMHO
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Old 24th August 2005, 11:58 AM   #3
Salas is offline Salas  Greece
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Roughly -3dB per octave doubling. Like in Pink Noise.
Then you sometimes get special kinds of music with uneven distribution.
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Old 24th August 2005, 12:09 PM   #4
maxw is offline maxw  United Kingdom
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Quote:
Originally posted by Magnetar
In my estimation, if the drivers all have the same sensitivity, with demanding classical music the bass range 20-200 requires about double the midrange (200-2k) power and the treble about half the midrange. So if you have a 200 watt woofer amp in a triamp system you should have at least 100 watts in the midrange and 50 watts in the treble to maintain the same max spl levels. As far as a passive three way you can say pretty much the same about the power handling ratio of the drivers provided the crossover is working properly - IE if the treble driver is crossed too low or with too shallow of a slope it may not handle anywhere near it's rated power. This is basing the power requirements on the power of the recorded music content rather then weight of the cone, or the amount of cone movement ect -

So if used properly an 80 watt treble driver should be OK with a 320 watt amplifier if the system's drivers/network is well matched - hardly the norm but a good estimate IMHO
That makes some sense, cheers!


Quote:
Originally posted by salas
Roughly -3dB per octave doubling. Like in Pink Noise.
Then you sometimes get special kinds of music with uneven distribution.
OK, so then suppose you have a 200W Woofer crossed at 200Hz, then you are at only 12.5W at around 3200 Hz.....isn't that a bit low?
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Old 24th August 2005, 12:23 PM   #5
Salas is offline Salas  Greece
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Sounds low but it isnt. You can fry the average 1 inch dome tweeter with a 3kHz 20W RMS sinewave within minutes.
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Old 24th August 2005, 01:22 PM   #6
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Rod Elliot suggests here: http://sound.westhost.com/bi-amp.htm that there is roughly equal power on either side of 300 Hz. Of course this will vary with your choice of music, but that is probably close enough.

If your bottom end needs equalization, be sure to add that much power to the botom end. For example, my subs need 6 dB (4 x power) of boost at 24 Hz for flat response. To keep up with 150W on the mains I'd need 600W if the sensitivity was the same.

If you look closely at tweeter specs you'll see that usually the maximum system power is usually specified with some sort of high pass filter. A Focal TC120-TD5 is rated at 150 W system power and 15W nominal - they don't really expect it to receive over 15W in a 150 W system, since it needs a >2500 Hz 2nd order high pass filter.

So, to more direclty answer your question, you can use as little as 15W for your tweeter if the XO is >2500 Hz or so. A good place to try a class A amp without heating your living room too much.
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Old 24th August 2005, 01:30 PM   #7
maxw is offline maxw  United Kingdom
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Quote:
Originally posted by BobEllis
Rod Elliot suggests here: http://sound.westhost.com/bi-amp.htm that there is roughly equal power on either side of 300 Hz. Of course this will vary with your choice of music, but that is probably close enough.
Ahh, this is interesting. Thanks.

Quote:
Originally posted by BobEllis

If you look closely at tweeter specs you'll see that usually the maximum system power is usually specified with some sort of high pass filter. A Focal TC120-TD5 is rated at 150 W system power and 15W nominal - they don't really expect it to receive over 15W in a 150 W system, since it needs a >2500 Hz 2nd order high pass filter.
Well that is exactly what prompted me to ask this question. Most tweeter/mid specs dont say this!

Quote:
Originally posted by BobEllis
So, to more direclty answer your question, you can use as little as 15W for your tweeter if the XO is >2500 Hz or so. A good place to try a class A amp without heating your living room too much.
hehe
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Old 24th August 2005, 02:18 PM   #8
forr is offline forr  France
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The following data helped me a lot, they were published in a french audio magazine by Pierre Etienne Sirder about twenty five years ago. They are based on Harwood's works at the BBC. For a maximum power of 55 W, the power distribution in bands is:

Band (Hz) -> Power (W)

32 - 63 -> 4.4 W
63 - 125 -> 8.8 W
crossover at 125 Hz, total bass = 13.2 W

125 - 250 -> 10 W
250 - 500 -> 10 W
500 - 750 -> 7 W
750 - 1000 -> 5 W
1000 - 1500 -> 3.5 W
1500 - 2000 -> 2.5 W
crossover at 1500 Hz, total medium = 35.5 W

2000 - 3000 -> 1.75 W
3000 - 4000 -> 0.875 W
4000 - 6000 -> 0.44 W
6000 - 8000 -> 0.22 W
8000 - 12000 -> 0.11 W
cross over at 1500 Hz, total tweeter = 5.9 W

If your crossover is at 125 Hz and 1500 Hz, then the electric power reaching each unit is the sum of the powers in the band 32 - 125 Hz (bass), 125 - 1500 Hz (medium), 1500 - 12000 Hz (tweeter).

By scaling to your maximum power and your crossvoer frequencies, you can estimate the power requirements of your amplifier and speakers.

~~~~~~~ Forr

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Old 24th August 2005, 02:39 PM   #9
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Interesting stuff. I suspect that todays recordings have more bass content than those of 25 years ago, though. Especially when you look at HT. I think this due to the combination of better recording capabilities and the ability of many consumer systems to reproduce the bottom octaves.
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Old 24th August 2005, 03:06 PM   #10
synergy is offline synergy  United Kingdom
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from the eminence speaker book -
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