Power loss through speaker crossovers

June 27, 2021
 by Paul McGowan

7 comments on “Power loss through speaker crossovers”

  1. All designers of active speakers I met always wondered about the high values of minimum requirements for amp power given from the manufacturers of passive loudspeakers. However I think the biggest losses concerning sound quality aren’t found in the more or less huge power losses but in the inherent inter-driver phase shifts and delays of multi-way passive speaker designs. Simply compare your passive loudspeaker with a good pair of single driver headphones focusing on speed, detail and resolution. The solution: active speakers or speakers with an active crossover and DSP equalizer.

    1. I agree. You said it in other words but the biggest advantage of active crossovers is the amps only see the reactance of a voice coil and not the often crazy reactance of many passive crossovers and then the amp is happier and ‘sounds’ better.

  2. This is an interesting question that highlights the difference between efficiency and sensitivity. A crossover constructed solely from ideal inductors and capacitors does not dissipate any power, and so has 100% efficiency, even when stopping low frequencies from reaching the tweeter and stopping high frequencies from reaching the woofer. Most capacitors are ideal in this sense, but inductors might have a significant series resistance if constructed from thinner wire.

    One interesting case is the BBC LS3/5a. The overall sensitivity is really quite low, and the T27 tweeter has much higher sensitivity than needed in this design. Most designers would use resistors to attenuate the signal to the T27, but the BBC used an autotransformer. Consequently, the feed to the T27 is matched to the overall sensitivity, but still efficient. This is achieved by presenting a high impedance to the amplifier.

  3. I’ve seen over the years, 2-way speakers that didn’t have the coil in series with the woofers.
    Yay thoe, the capacitors were there on the tweeters.
    But today, I am seeing something that doesn’t quite make a lot of sense to me.
    Avantone Pro, has come out with an active pare of monitors that they call the CLA10A.
    But their passive mottles, can only handle 60 watts RMS, and 120 watts max all in to an 8 ohm load.
    But their active mottles, have 200 watt amplifiers built in to them.
    If the max is 120, wouldn’t 200 watts blow those speakers up?

    1. The quick answer is yes, if you abuse the CL10A speakers, the 200 W amplifiers are easily capable of destroying the drivers. We have to ask how the passive CL10 speakers are specified. They are rated at 60 W program. I assume this means a music signal with a long term average of 60 W. That’s actually quite a big signal. The so-called crest factor of a music signal (the ratio between the peak level and the long term average) is normally in the range 10 dB to 20 dB. At 10 dB crest factor, if the 200 W amplifier in the CL10A is used to the limit without clipping, it will deliver 20 W into the speaker drivers, well within the 60 W limit.

  4. usually no coil on the woofer means direct coupling the woofer to the amp(no woofer low pass) and letting the woofer roll off on it’s own. Usually that’s a compromise in that drivers rarely behave nicely at the top of their range(though a few do).

    Speaker power ratings are nominal and most of the time only a few watts are driving them even when they’re loud. Transients can be way higher in power but last usually only for a few milliseconds so huge transients usually are safe. But long term(even a few seconds) of very high power can blow a driver, especially tweeters(fortunately the power of most music is not in the tweeter range).

    1. Good morning Hahax!
      I must tell you, that both you and Mark hit on some strong points there. But looking at Avantone Pro’s passive mottles of the CLA10A which are, the CLA-10, they also have two different power amps you could pare up to them.
      But if you were to go to their website:
      https://www.avantonepro.com
      and read about them, they suggest that you pare the CLA-10 monitors to their CLA-200 power amp.
      I haven’t thought about doing this as of yet, but I do own their CLA-100 power amp.
      I think that if I were to put the CLA-10 monitors on that amp, I’m 20 watts under the max power handling.
      But also, at the same time, I have a pare of passive 3-way second order crossovers that I ordered from Parts Express a little more then 6 years ago. Except for my tube amps, the rest of my amps don’t like those crossovers.
      They run my amps in to a dead short.
      But looking at the crossovers, they have four capacitors, and four coils on them.
      Two of those coils, have farad poles in them.
      While the other two coils don’t.
      But where the woofers are to be connected, there is an electrolytic capacitor wired across the coils that have the farad poles in them.
      One coil is plus, the other coil is minus.
      But I don’t understand why these crossovers try to short my amps out.

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