Crossover active vs. passive question

[roll - gybe]

Hey guys, I just added a new sub to my secondary setup, which is an HT setup. Already it sounds pretty darn good.

Here is something a little weird though. My receiver, a lower end Yamaha 5490, crosses over to the sub channel at 90hz. My fronts are full range towers that roll off at 38hz. Set to main=small, LFE = sub

So, I set the subwoofer (LFM-1 EX) to active low-pass at 90hz. Sounded good. Then I set the low-pass to bypass, b/c the receiver should be doing the separation. However, with that change, a lot more of the range started to go through the sub. I can even hear the very bottom end of vocals through the sub with this setting.

I would have thought the 90hz active LPF would have produced the same sound as the bypass since the receiver is supposedly directing the LFE channel.

Any thoughts on this?

 

[markw]

Subs don't offer a "brick wall" type of crossover. Frequencies above the crossover frequency frequency are still passed to the sub, although they graduality fade out as the frequencies increase.

When you use two crossovers, the resulting slope may be steeper then either crossover alone provides.

It sounds to me like when you used the two crossovers (in the receiver AND the sub), it resulted in a (combined) steeper slope than when you used only the crossover in the receiver, which may be more gradual than you would like.

 

[roll - gybe]

That is interesting. I never thought that the rolloff might be sloped.

The fact that I am getting some of the dialouge lows out of the sub with the receiver's crossover bothers me.

Seems like male voices shouldn't go below 90hz. Maybe I am wrong.

Also, if the voice is supposed to be directional, and I have some of it coming from the sub in a non-direction format, will this be sub-optimal?

 

[markw]

That is interesting. I never thought that the rolloff might be sloped.

The fact that I am getting some of the dialouge lows out of the sub with the receiver's crossover bothers me.

Seems like male voices shouldn't go below 90hz. Maybe I am wrong.

Also, if the voice is supposed to be directional, and I have some of it coming from the sub in a non-direction format, will this be sub-optimal?

It's not that male voices go much below 90 hz, but more so that the AVR's crossover still sends frequencies above 90 hz to the sub.

Assume a 12 db/octave low pass filter set for 90 hz. This means that a frequency of 180 hz will still be sent to the sub, albiet at a level 12 db lower than the original 90 hz. Frequencies in between will be sent to the sub, although the lower the frequency, the louder they will be.

Although not the last word in any subject, this site can provide some pretty good rule-of-thumb info: http://en.wikipedia.org/wiki/Voice_frequency

If you'll notice, the male range seems to be right in that one octave range.

The sub seems decent enough. It's crossover is speced for 24 db/octave wich is pretty steep and is probably why you don't have this problem when it's in the circuit. It seems that it's the crossover/slope in the AVR that's in question here.

If you want to minimisze thie effect, you might want to position the sub in the same plane as the front speakers, perhaps near the center.

 

[roll - gybe]

ok, so I used an SPL meter and test tones today. My speakers are fairly linear from about 40hz with a node around 125hz.
Then when I add the sub, I get a huge node around the x-over point. So, I put it back on active low pass, and it seems a lot more linear. I think I will leave it there for now.

I get it a pretty even +10db up to the x-over point, then 0db.

Does the delta of 10db have to do with how the LFE signal is handled?