How much LF sound is sent to surround channel?

[mpompey]

I was looking at the freq specs of the surround speakers I'm thinking about purchasing,
Axiom QS8s. The specs from the Axiom sites post a +/-3 dB freq response from 95 Hz to 20 KHz.

So here's my question, do I need to change my crossover setting on my receiver to match (100Hz)?
How much low freq info (sub 95 Hz) is sent to the surround channel? Do I need to consider other speakers?

 

[majorloser]

I know this may not help.

THX certified speakers are designed for the crossover to be set for 80 Hz, the high pass filter to be set at 12 dB slope and the low pass filter set at 24 dB slope.

That being said, very little information at or below 80 Hz should reach any of the speakers if you have them configured in the receiver's setup as "small" or "THX". It should be sent to the subwoofer.

 

[j_garcia]

With current codecs, the surrounds are full range technically. When configured to small, they will still receive sound below the x-over, but it will be much reduced, so no need to worry really. I'd try it with both 100 and 80 and see which sounds best.

 

[mpompey]

My fear is that I get the surrounds and since my receiver is set for 80Hz, audio freq between 80 and 100 gets dropped out, since the speaker can't produce the sounds in that in-between range.

 

[MDS]

My fear is that I get the surrounds and since my receiver is set for 80Hz, audio freq between 80 and 100 gets dropped out, since the speaker can't produce the sounds in that in-between range.

No fear necessary, it doesn't quite work that way. A crossover has a slope that defines how quickly the signal is reduced. As majorloser said already, the high pass is typically 12 dB per octave (an octave is a doubling or halving of frequency) and the low pass is 24 dB/octave.

The high pass xover will start attenuating the frequency 1 octave below 80 Hz (40 Hz) by 12 dB and less so for the frequencies between 40 and 80. The idea is that the amplitude of the frequency at 80 will be roughly unchanged. So there will still be some content below 80 Hz sent to the speakers but it will be greatly reduced. The content between 80 and 95 (the speakers stated low frequency extension) will be unchanged but of course the speaker itself will not play it at its original amplitude because it can't.

Likewise, there will still be 160 Hz (1 octave above the xover) sent to the sub, but it will be reduced by 24 dB by the low pass xover.

If the stated low frequency response is 95 Hz, then a 100 Hz xover may be more appropriate however as the frequencies below 100 Hz will only be slightly attenuated.

 

[mpompey]

Okay, I think I got it. Set my receiver to 100Hz and see how that sounds with those speakers.