# Speaker crossover question



## Doctor X (Apr 3, 2007)

Hi,

I was having a discussion with a friend about crossovers in a speaker and in an amplifier and my friend insists the crossover in an amplifier can cascade with the speakers crossover.

I said they shouldn't interact, but he was saying that the passive crossovers in the main speakers do not magically disappear and any home theatre receiver will have a highpass of 12db/oct and lowpass of 24db/oct because the assumption is that most hifi passives are 12db/oct, thus creating a sum total of 24db/oct, thus keeping the phase in-line.

What is he saying? Is there any truth in the matter or is it ?


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## robbo266317 (Sep 22, 2008)

Doctor X said:


> Hi,
> 
> I was having a discussion with a friend about crossovers in a speaker and in an amplifier and my friend insists the crossover in an amplifier can cascade with the speakers crossover.


This should not happen if you have set everything up properly.



Doctor X said:


> I said they shouldn't interact, but he was saying that the passive crossovers in the main speakers do not magically disappear and any home theatre receiver will have a highpass of 12db/oct and lowpass of 24db/oct because the assumption is that most hifi passives are 12db/oct, thus creating a sum total of 24db/oct, thus keeping the phase in-line.
> 
> What is he saying? Is there any truth in the matter or is it ?


I do not believe this is true. My mains crossover to their mids at 600 Hz, this is well outside the range the receiver is crossing between the mains and the sub ie 80Hz. 

You need to find out what equipment is being used and what frequency range they believe is the issue so we can give better examples.


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## Doctor X (Apr 3, 2007)

So you are saying that the internal crossovers in a speaker are so outside the operating range of an amplifiers low-pass filter that it couldn't possibly interact? Correct me if I'm wrong?

My friend made a general comment and said any crossover being used would cascade with the speakers crossover. So he is making a general claim. 

If I had a 2-way bookshelf speaker, not sure how low the woofers are crossed over. But if I used a 100 Hz crossover, there is no way it can cascade or interact with the speakers passive crossover?


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## PT800 (Feb 19, 2008)

The XO points between the drivers in any speaker has nothing to do with an AVR's BM XO point.
Lets say you have a 3-way with XO points @ 800 htz, 3000 htz. Those points have nothing to do with the AVR's BM XO @ 80 htz to the subwoofer. In this case, the 8" mid-bass driver starts its rolloff around 80 htz, which is an acoustical rolloff and the AVR's 80 htz XO is just keeping that 8" driver from producing sound below 80 htz, sending everything below to the sub.


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## ironglen (Mar 4, 2009)

PT800 said:


> The XO points between the drivers in any speaker has nothing to do with an AVR's BM XO point.
> Lets say you have a 3-way with XO points @ 800 htz, 3000 htz. Those points have nothing to do with the AVR's BM XO @ 80 htz to the subwoofer. In this case, the 8" mid-bass driver starts its rolloff around 80 htz, which is an acoustical rolloff and the AVR's 80 htz XO is just keeping that 8" driver from producing sound below 80 htz, sending everything below to the sub.


Right on.

IF however, your avr crosses up to 100-150hz (I have an old one around that does this) as well as some serious mains that have a three-way that cross mids really low, say 100-300hz range, then yes they will interact in the slope region.


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## PT800 (Feb 19, 2008)

ironglen said:


> Right on.
> 
> IF however, your avr crosses up to 100-150hz (I have an old one around that does this) as well as some serious mains that have a three-way that cross mids really low, say 100-300hz range, then yes they will interact in the slope region.


Well, the obvious solution to that problem, is a new AVR that gives you a multitude of XO points.
Any AVR that does a fixed BM @ 150 is meant to be used with really small Bose size speakers. 
Not some fairly large 3-ways.


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## robbo266317 (Sep 22, 2008)

Doctor X said:


> If I had a 2-way bookshelf speaker, not sure how low the woofers are crossed over. But if I used a 100 Hz crossover, there is no way it can cascade or interact with the speakers passive crossover?


Correct. The crossover point for a bookshelf 's drivers is going to be up around 2 kHz.


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## ironglen (Mar 4, 2009)

PT800 said:


> Well, the obvious solution to that problem, is a new AVR that gives you a multitude of XO points.
> Any AVR that does a fixed BM @ 150 is meant to be used with really small Bose size speakers.
> Not some fairly large 3-ways.


I never stated I had a problem :bigsmile:

Early generation receivers had this, even my Pioneer, and 100-150hz isn't really that much higher for a competent sub to handle. Plus, many bookshelves can perform flatly until 100hz, possibly 80hz at measly volumes with no low end equalization, but then, I don't run mine at measly volumes, so by crossing higher I have much more headroom :dumbcrazy:


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## PT800 (Feb 19, 2008)

ironglen said:


> I never stated I had a problem :bigsmile:
> 
> Early generation receivers had this, even my Pioneer, and 100-150hz isn't really that much higher for a competent sub to handle. Plus, many bookshelves can perform flatly until 100hz, possibly 80hz at measly volumes with no low end equalization, but then, I don't run mine at measly volumes, so by crossing higher I have much more headroom :dumbcrazy:


But you did state a possible problem, you just did not specify if it was your problem.

I am quite aware of the older AVR's XO points. Both a Sony and Marantz AVRs I had in the '90s had fixed 100 htz settings. And that certainly works for larger speakers. But when you get up to 150 htz then not so good. And for either of those XO points, the subs need to be up front between the mains so as not to be able to localize the subs.
Thus the THX 80 htz standard so the subs can be placed for max output.


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## Doctor X (Apr 3, 2007)

Even modern AVRs allow for variable crossover options from 40 Hz- 150 Hz and sometimes even 200 Hz.


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## PT800 (Feb 19, 2008)

Doctor X said:


> Even modern AVRs allow for variable crossover options from 40 Hz- 150 Hz and sometimes even 200 Hz.


Yes, but the two I referenced to, Sony and Marantz 880 had _fixed_ 100 htz XO. And a fixed 150 would be even worse.
That is a huge disadvantage compared to an AVR that has 40~150 htz XO, when it comes to matching up speakers.


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