Varying X-over points?

daniel_paul_

A few things I have read here have got me thinking. For 5.1 sould I set the X-over for the sub on the reciever to a higher # like 120hz. I have my RTi8's at 60. The theory being that it will play more of the 0.1 channel's F.R.

But with 2 Channel should I match the crossovers at 60 so the same base is not getting duplicated between 60-120 hz?

This sounds right and I have the ability to set different X-overs for different sources. Tell me what you think.

curved

daniel_paul_ wrote: »

A few things I have read here have got me thinking. For 5.1 sould I set the X-over for the sub on the reciever to a higher # like 120hz. I have my RTi8's at 60. The theory being that it will play more of the 0.1 channel's F.R.

But with 2 Channel should I match the crossovers at 60 so the same base is not getting duplicated between 60-120 hz?

This sounds right and I have the ability to set different X-overs for different sources. Tell me what you think.

I would keep that down towards 60 - should match what the sub is at.....mine is at 60hz for AVR RTi8's. The sub is set at ~65hz. It's ok to overlap a little, I just don't like the sound of subs when it plays upwards to 120hz. To me that's what the 6.5" drivers are for (and are much better at).

zingo

I agree with curved, but I have set mine at 80Hz in the past. I would try between 60-80Hz for both and see what sounds best.

daniel_paul_

The note that got me thinking was that there are sounds in the 0.1 channel that go up to +/- 150hz. My sub goes up to 150 -3db. I will not go above 120 though.

I think the test will be my Red Hot Chilly Pepers concert DVD in DTS. It always sounded as if there was no bass line. I am going to run it both ways and see what happens.

zingo

daniel_paul_ wrote: »

The note that got me thinking was that there are sounds in the 0.1 channel that go up to +/- 150hz. My sub goes up to 150 -3db. I will not go above 120 though.

But consider this, the signal to your mains is full range, but most people cross them above the frequency that they are capable of. Is it a bad thing that you could be playing 50Hz through your mains and your not? Definitely not. You high pass your mains for a reason, and for the same reason you would low pass your sub.

Just because you can, doesn't mean you should.

kuntasensei

How you set your system depends on the receiver. If you can assign a different crossover point for each channel, you're golden. If, however, you have an older AVR that lets you set one global crossover, 95% of them filter the LFE channel at that point as well. Additionally, most AVRs that just have LARGE/SMALL filter the LFE channel around 80Hz if any speaker is set to small. AVRs with independently adjustable crossovers, however, usually do not filter the output after summing all the channels - they do it before the summing occurs, meaning that even if you have all your channels set to 80Hz, the LFE channel should still be passed through up to its 120Hz point. This is why many receivers now also include a LPF (low pass filter) of LFE adjustment, especially in THX receivers where this setting defaults to the THX conceit of 80Hz. I set this to 120Hz so the full LFE channel is reproduced. You'll see arguments that little is in the LFE channel above 80Hz. While mixers do strive to keep anything above 80Hz in the LFE channel, there are harmonics above 80Hz that give the low frequencies their perceived tone and are very important to how the sound is reproduced.

The LFE channel (the .1) is brickwall filtered at 120Hz and shouldn't contain any information above 120Hz by design. For proper playback of the LFE channel, the crossover on your subwoofer itself should be turned to its highest point or defeated completely if possible. This is not only so the entire LFE channel passes to the sub unaltered, it's to minimize the chance of active crossovers creating a delay that will throw off proper distance/delay of the subwoofer. If you have a system that measures acoustic distance (such as products with Audyssey), it will take delays in the signal chain into account and set the distance correctly, even if it differs slightly from the actual physical distance.

Zingo's correct that most people set crossovers above the frequency the speakers are capable of. Why? BECAUSE YOU'RE SUPPOSED TO. Crossovers are not a sudden transition from one speaker to the other, but a gradual slope where the crossover point is roughly the mid-point (i.e. the point where sound is reproduced equally by both drivers). A common misconception is that if you set your mains to 60Hz, you aren't sending anything below 60Hz to that speaker. WRONG. The speaker is still playing that information, just at an attenuated level, whereas the subwoofer gradually picks up the duty as the speaker hands it off.

Speakers are usually spec'd to the point where they naturally roll off by 3dB. Now, let's say you set your system crossover to the actual -3dB point of the speaker, 40Hz in the case of your RTi8s. The transition of the crossover will then interact with the natural rolloff of the speaker, creating a dip in the frequency range around 40Hz because the subwoofer has not yet begun to take on all of the sound reproduction duties. A good guideline to avoid this is to set system crossovers 1/2 octave above the -3dB point so you get a good smooth transition (assuming ideal acoustics with no phase cancellation issues). In the case of your RTi8s, 60Hz is an excellent setting (40Hz -3dB point x 1.5 = 60Hz, giving you 1/2 octave higher than the speaker's rolloff point).

Another good reason to set your subwoofer's crossover to its maximum is to ensure that you don't cascade that crossover's slope with that of the AVRs per-channel crossovers. For instance, if your subwoofer's crossover is set to 80Hz and your channels are also set to 80Hz, you're doing two bad things:
1) You're filtering the 80-120Hz content out of the LFE channel with digital surround tracks, with some content attenuated down below 70Hz.
2) You're creating a dip at 80Hz caused by the two crossovers interacting and attenuating sound in the crossover range.

If you set your subwoofer's crossover to 120Hz and your mains to 60Hz, the crossover has a steep enough slope that your subwoofer is not going to be playing anything significant near 120Hz and should not be localizable in any way. However, with Curved's example of setting the subwoofer's crossover to 65Hz with the mains at 60Hz, you ARE attenuating bass in that region because of the overlap. That's only 1/12th of an octave above the digital crossover's midpoint, which means you'll create a handy dip in frequency response from roughly 55-70Hz in an ideal room.

Having said all of that, it's YOUR SYSTEM. If it sounds good to you, all the advice in the world means diddly squat. But if you're asking what you should do in theory, I hope the above clarified things a bit. In my opinion, you shouldn't low pass your subwoofer. The signal to it is already being low passed by the crossover on the receiver and using any low pass filter on the subwoofer itself risks cascading with the low pass from the crossovers for each channel. If your goal is accurate reproduction, get the crossover on the subwoofer out of the way and let the AVR's crossovers do what they're designed to do.

daniel_paul_

I had to read that twice.;) I definately have the sub X-over turned all the way up. Thanks for the info. You confirmed my fear of loosing some of the LEF channel by having my sub match the fronts at 60hz. I will be away this weekend but will test at 60,80,100 & 120hz X-over points next week.

daniel_paul_

zingo wrote: »

But consider this, the signal to your mains is full range, but most people cross them above the frequency that they are capable of. Is it a bad thing that you could be playing 50Hz through your mains and your not? Definitely not. You high pass your mains for a reason, and for the same reason you would low pass your sub.

Just because you can, doesn't mean you should.

Since it seams the theory is sound. I am going to mess around and see what works. I know what you are saying though. 120hz may be a little high. For instance the HSU's upper limit is 90hz. I, however, have the PSW10. I'll let you know what I find.

curved

daniel_paul_ wrote: »

I had to read that twice.;) I definately have the sub X-over turned all the way up. Thanks for the info. You confirmed my fear of loosing some of the LEF channel by having my sub match the fronts at 60hz. I will be away this weekend but will test at 60,80,100 & 120hz X-over points next week.

I've tried it again after reading that. To me it sounds like the sub is trying to play too high up. I actually adjusted mine to 80 which sounds the best to me.

curved

Correction from the last post - I adjusted it a hair over 80hz on the sub and left it at 60hz on the AVR