Crossover power effect

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NoahH

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Crossover power effect
« on: 13 Sep 2021, 09:06 pm »
Hi all,
I was hoping someone more educated in EE could help me (and keep me from emailing Danny more).

I am trying to understand what the filters in a crossover do with filtered signal power.

Specifically, if I put a high pass filter on a speaker because a sub will take those lower frequencies, I understand the lower signals will not make it to the driver, but does it take the filtered signal and dissipate it as heat or instead cause something 'different' to happen in the circuit with the amp.

The pragmatic reason I am asking is understanding exactly how it affects the demands on the amp. I.e. did it lighten the load on the amp allowing low wattage amps to drive the frequencies that made it past the filter to greater levels, or is the power wasted?

Danny guided me to do the filtering before the amp leading me to assume it is the 'heat' option but I don't want to bug him with follow ups just to educate myself.

Thanks all!

FullRangeMan

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Re: Crossover power effect
« Reply #1 on: 13 Sep 2021, 09:35 pm »
This is a apparently simple matter if one uses a xover without worrying about what it does or how the parts behave and interact with the amp, but if one wants learn in detail the behavior of an xover is a complex subject.

In the lasts years of US Audio mag they published a reactance/inductance/impedance graphic when testing a speaker that allowed the reader see some speakers are not a sweet peach to driver even being rated easy to drive by the manufacturer.

The fact is that xovers consume low level musical signal/energy (mV/uV) to work, unfortunately this energy is lost as heat.

Specifically, if I put a high pass filter on a speaker because a sub will take those lower frequencies, I understand the lower signals will not make it to the driver, but does it take the filtered signal and dissipate it as heat or instead cause something 'different' to happen in the circuit with the amp.
A capacitor mods impedance.
A air core inductor att the freq 6dB/octave, the most destructive inductors of the musical signal are the iron cores, but they are cheap and attenuate 18dB/octave if I remember correctly.
The pragmatic reason I am asking is understanding exactly how it affects the demands on the amp. I.e. did it lighten the load on the amp allowing low wattage amps to drive the frequencies that made it past the filter to greater levels, or is the power wasted?
I dont see how the load to the amp would be relieved, the xover parts add an additional load to the amp drive and lower the sensitivity of the speaker in question, the lightest load an amp can have is to drive the speaker directly, without xover IMO. This is a multi-faceted subject that allows one to have multiple point of views, your questions are very wide broad which exceeds my little knowledge.
« Last Edit: 14 Sep 2021, 12:12 am by FullRangeMan »

mlundy57

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Re: Crossover power effect
« Reply #2 on: 13 Sep 2021, 11:14 pm »
Putting the high pass filter to roll off the lows usually requires a high value. If you are using  separate preamp and power amp, or an integrated amp that uses external connections between the preamp and power amp sections, like some NAD models, you can use a cap to keep the low frequencies from getting to the power amp. This not only keeps the speakers from having to deal with the bass energy, it also relieves the power amp from having to deal with it. This method makes it easiest for flea watt amps.

HAL

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Re: Crossover power effect
« Reply #3 on: 14 Sep 2021, 02:03 am »
This is a greatly simplified explanation.

If you are using a standard high pass or low pass filter on the drivers of a speaker, out of the frequency pass bands of the filter, the impedance of the circuit becomes high, so little power from the amp is dissipated by that circuit.  In the areas outside of the frequency pass band you can think of the crossover and driver as a high value resistor and very little load for the amp. 

Hope that helps.

Cheytak.408

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Re: Crossover power effect
« Reply #4 on: 14 Sep 2021, 05:03 am »

A(n) air core inductor att the freq 6dB/octave, the most destructive inductors of the musical signal are the iron cores, but they are cheap and attenuate 18dB/octave if I remember correctly

You memory failed you.  A single inductor - be it air, ferrite, nano-crystalline, iron or plutonium core attenuates @ 6dB/ octave.

NoahH

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Re: Crossover power effect
« Reply #5 on: 14 Sep 2021, 12:25 pm »
I appreciate the info from folks above. Thank you for the detailed responses!

DannyBadorine

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Re: Crossover power effect
« Reply #6 on: 14 Sep 2021, 02:57 pm »
Hi all,
I was hoping someone more educated in EE could help me (and keep me from emailing Danny more).

I am trying to understand what the filters in a crossover do with filtered signal power.

Specifically, if I put a high pass filter on a speaker because a sub will take those lower frequencies, I understand the lower signals will not make it to the driver, but does it take the filtered signal and dissipate it as heat or instead cause something 'different' to happen in the circuit with the amp.

The pragmatic reason I am asking is understanding exactly how it affects the demands on the amp. I.e. did it lighten the load on the amp allowing low wattage amps to drive the frequencies that made it past the filter to greater levels, or is the power wasted?

Danny guided me to do the filtering before the amp leading me to assume it is the 'heat' option but I don't want to bug him with follow ups just to educate myself.

Thanks all!


I'm no expert here but putting the filter before the amplifier is much different than after the amplifier.  If you put a high pass filter before the amplifier then the amplifier never receives the low frequency information and will be much more efficient.  I don't think that it dissipates as "heat", but rather the low frequency information is never made by the amplifier.  I'm assuming that you are referring to some sort of active crossover (DSP or analog circuit).  If you put the filter after the amplifier then the amplifier is still reproducing the low frequency information and the capacitor (plus other passive crossover parts) will be releasing that information as heat.  I think the reason that Danny is recommending that you do it before the amplifier is that it will be more efficient for the relationship between the amplifier and speaker.  There will be less resistance between the amplifier and speaker.  Additionally, low frequency information takes more power so filtering before the amplifier makes the amplifier more efficient.

Danny Richie

Re: Crossover power effect
« Reply #7 on: 15 Sep 2021, 02:17 pm »
I just shot a new video on this subject. It will be out shortly.

NoahH

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Re: Crossover power effect
« Reply #8 on: 15 Sep 2021, 09:38 pm »
I just shot a new video on this subject. It will be out shortly.

Awesome! Much appreciated.