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Dxvideo 15th May 2007 07:54 AM

Another stupid question!
If I make two way active speaker system with LM4780 and give him +/-35v power (that enough to drive 60W for 8 ohm loadfs)
That system will give 120W or 60W in total. So I can call it a 120W active speaker or 60W?

Thanks in advance..

tade 15th May 2007 08:05 AM

because the crossover's job is to split power at a certain frequency, you cannot add the power, however you will see a benefit because both amps will share the load. The system will never take more than sixty watts.

Dxvideo 15th May 2007 08:07 AM

Ok tade, thanks a lot.
This is what I exactly needed.

AndrewT 19th May 2007 01:10 PM

your active 60+60W speaker will sound louder than a 60W passive speaker.
It may sound as loud as a 100W amp driving a passive crossover using the same drivers.
It may even sound louder than 120W into those passively crossed drivers.
At these very high levels the active version will sound cleaner due to the lack of (or reduced) clipping in the respective amplifiers.

Dxvideo 19th May 2007 01:49 PM

So the total power will be 60W theory is wrong?
I am confused! I agree with your "clear sound" theorem. However if we filter the signals by hi and low frequencies then;
If total signal is at level x,
If we pick up some frequencies (y) from inside that x,
If we pick up the other frequencies (z) from inside also that x
The total x will never changed. And y+z will always gives x. So our final signal will be equal to x.
So if you split or not split the signal; the result will never changed. You can take it like bi-wiring. When you connect your speakers as biwired then the total rms output will change or not?
This is my opinion. May be I am mistaken.

AndrewT 19th May 2007 05:32 PM

you will have an

active 60+60W speaker
Beyond that is guesswork when trying to compare it to passive speakers.

But let's examine a few bits of guesswork.

Assume one frequency passing from source to your ears.
Let's put out 60W @ 200Hz. Send this to the active speaker and you get the SPL due to 60W. Send the same 60W to a passive crossover, the SPL (from the same driver) will be marginally lower due to the crossover components and the longer cables.
Similarly a high frequency signal @ 1kHz will be marginally louder from the active driver than from the passive driver.

Now consider two frequencies in the signal, one frequency passing to each driver. Let's suppose they are equal in magnitude. That 60W signal passing to bass speaker will produce the same SPL as the single frequency case. Similarly that high frequency signal will be the same as the single frequency case. The resulting output from the two speakers will be the sum of two 60W SPLs arriving at your ears.

Now consider what happens to the passive system with two frequencies each split by the crossover and sent to their respective drivers.
The 60W signal is a 31Vpk signal. Each frequency is of equal magnitude and so each frequency is half of that voltage. This means that 15.5Vpk from each of the two frequencies forming the total signal just reaches the clipping voltage of the 60W amplifier.
The resulting signal coming from the passive crossover is 15W less the losses in the crossover. It appears that each signal is 6db down from the active case. They then add again in the air to arrive at your ear still 6db (+ a bit) down from the active case.

This a somewhat simplistic analysis but it does show that active speakers can, when processing complex signals, sound a lot louder than passive speakers using the same drivers. The first thing to realise in this simple analysis is that each of the drivers cannot take the same power as when combined into a passive system. In a two way, the bass/mid may take 50W and the treble just 5W but when combined with a crossover could be (correctly) specified as a 60W speaker. But the active system is more likely to be a 50W + 20W active system. Even this will play complex signals louder than the 60W system. And it has the benefit of double the voltage drive into the treble speaker to avoid clipping in the treble amp. The active 50W+20W will play single frequencies at about the same SPL as the passive system.

davidlzimmer 20th May 2007 04:39 PM

BUT!!! The Watt police will not come and get you if you tell your friends you have 120W per channel! :D

Hartono 20th May 2007 04:46 PM

2 x 60 watt amplifier per speaker (60W for tweeter+60W for woofer)
total 120 watt amplification per speaker.

I think above is suitable for sale documentation.

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