Axiom Home Page Forums General Discussion Home Theater sub crossover...what gives?

I have a 3802 with a Paradigm ps1000 that I've had for about 7yrs. I have the receiver's x-over set to 80hz using the LFE out and the subs x-over turned all the way up. The deal is I can adjust the subs x-over from 80 to 150hz and clearly hear the change. Shouldn't the receiver clip everything above 80hz. Is there a chance my x-over has degraded and the increase I'm hearing is actually the 80hz signal?

Crossover's don't "clip" at where you set them. It's a gentle slope. If you set it at 80hz, you're sub is still going to be getting a LFE signal below 80hz.

I'ts the above 80hz that I seem to be hearing.

I guess I worded that wrong. You'll still get signal above and below 80hz. That is why it's suggested that you keep the subs crossover set as high as it will go, or if possible defeat it's crossover all together.

Yes, topr, as Craig pointed out, your system is working normally. The subwoofer crossovers are never a "brick-wall" filter either on the high-pass or low-pass side.

And defeating the low-pass crossover on the subwoofer as much as possible is always the "right" starting point when you use the bass management on your receiver. But some people (not me) use the sub's low-pass filter on top of the receiver's crossover in order to further optimize the main/sub transitions and the overall response at around the crossover frequency. For example, if you set the receiver's sub crossover and the sub's low-pass filter both at 80Hz, you will effectively increase the "slope" of the low-pass crossover for the sub. Depending on the room and other conditions, it is quite possible that such settings may actually provide a better results, although I would not recommend them as an initial setting.

If the suggested setup is to turn the the sub's x-over all the way up, shouldn't there be an expectation that the receiver's x-over will maintain the 80hz signal, I'm ok with +/- 8hz or so, but its probably closer to 20hz

Topr, a correctly operating receiver crossover is supposed to roll off the sub at a rate of 24 dB per octave above the selected crossover frequency; as Craig and sushi pointed out, the response isn't suddenly cut off above 80hz. Another good reason to avoid the use of the crossover control on the sub except as a last resort is that they're generally quite inaccurate, both as to range and marked frequency. The "80hz" setting could easily be off by 20hz.

Does the amount of slope vary from receiver to receiver i.e., do some receivers have better cross over circuits than others. If there can be that much variance it just seems strange that turning the subs x-over all the way up is the recommended setting. I understand it for attenuation purposes but the trade off...

The bass management feature on most receivers (and all THX-certified ones) are "digitally accurate" at 24dB/oct on the low-pass side, and 12dB/oct on the high-pass side. The latter is set shallower so that when it combines with the natural acoustic bass roll-off of typical "small" speakers it will mimic a ~24dB/oct cutoff. In fact, THX-certified satellite speakers are consciously designed to give a 12dB/oct roll-off below 80Hz.

Anyway, if you use the digital bass management provided by the receiver, you don't want to have another low-pass filter to further affect these precisely designed roll-offs -- unless, as I said above, you know what you are doing and want to add some exotic tweaks.

Thanks fellas, didn't mean to get to far off the beaten path there. Its just when I put a sound meter on it and got a 6db jump on a 75db test signal when turning that crossover all the way up it made me twitch a little. It's also corner loaded a bit (no other choice) so that doesn't help...Now I don't have any excuse to demo a VTF-2