Setting up crossover in AV receiver and subwoofer ?

[Vaughan Odendaa]

If I have it correct, one only needs to use the crossover in the amp (and not in the subwoofer), correct ?

Can someone explain what happens when, for example, an 80hz crossover is chosen in receiver settings and, at the same time, choosing an 80hz crossover at the back of the sub ?

I just need to understand this right because as far as I know, there is cascading, phase cancellation and other problems, but if someone more knowledgeable can explain to me what is effectively happening, I would really appreciate it.

In fact, one of our installers said that you must use both (and I think that is quite wrong.) . . . ."I've been in the industry for ten years. . .blah, blah". . you know, the type of answer which is actually not an answer at all.

Also, if there are no switches to disable the crossover on the sub, what happens when one takes the crossover control to maximum ? How does that bypass the sub crossover ?

Sorry about all the questions, but I just would like to know in more detail what is happening, crossover-wise. Thanks.

--Sincerely,

 

[mike c]

I don't know why but, you're not supposed to set two crossovers the same OR near each other - cascading.

if there is no bypass, if the receiver is set to 80hz, set the subwoofer crossover to the max - 120+hz or more.

 

[Seth=L]

I don't know why but, you're not supposed to set two crossovers the same OR near each other - cascading.

if there is no bypass, if the receiver is set to 80hz, set the subwoofer crossover to the max - 120+hz or more.

If you set the x-over on the sub at 80hz while the receiver is also set for 80hz the rolloff will be to sudden, yoiu will likely be losing a part of the frequency band or at least have some unecessary dropouts. Since the crossover on each doesn't immediatly cut the frequency off at 80hz you would only want one crossover doing the job, the receiver is the best choice because it directly controls the speakers and the subwoofer.

 

[MDS]

Also, if there are no switches to disable the crossover on the sub, what happens when one takes the crossover control to maximum ? How does that bypass the sub crossover ?

Setting the sub's xover to maximum effectively bypasses it because the receiver's xover will have already attenuated (reduced) the frequencies between the receiver's xover point and the sub's xover point.

Briefly, the xover has a slope - it does not cut off exactly at the chosen xover frequency. The slope is usually 24 dB per octave (an octave is a doubling or halving of frequency). So with an 80 Hz xover setting it will start acting on signals at 160 Hz (one octave above) and they will be reduced by 24 dB. If the sub's xover is set to its max, which is usually higher than 160 Hz, then there will be very little signal for it to act on and thus for all intents and purposes it is out of the way.

 

[Vaughan Odendaa]

Thanks guys for the comments, I really appreciate it. In terms of how crossovers work and why using both causes phase cancellation, would someone here be able to explain the techical reasons behind cascading ?

Thanks again.

--Sincerely,

 

[Vaughan Odendaa]

Hmm, no replies. Oh well.

--Sincerely,

 

[Warpdrv]

I personally can't answer that question, but do check back, as someone likely will be able to... This isn't the most populated forum, so answers aren't always right away...

Good question BTW...

 

[Vaughan Odendaa]

Thanks, Warp. I haven't posted here in awhile and I really do value each comment made. Knowing the 'how' or 'why' behind the answer will make me understand the problem much better (and help others too as well).

Thanks again.

--Sincerely,

 

[Nick250]

I did not know the answer either and I was also curious.

"In physics, phase cancellation is the effect of summing two waves that are out of phase with each other. Since the waves are not in phase, the crests and troughs will not match up, and the end result could be a wave that has less overall amplitude than both of the original waves."

http://en.wikipedia.org/wiki/Phase_cancellation

Nick

 

[Vaughan Odendaa]

I was hoping for an in depth explanation because I know that there are several experts lurking around these parts. Please respond if possible.

Thanks.

--Sincerely,

 

[Vaughan Odendaa]

Please respond.

--Sincerely,