Sub connection question

tcrossma

I have a Paradigm Ultracube 10 sub, which has but a single RCA line-level input. The sub has a variable low-pass filter in the range of 40-160, I think.

The receiver is a Yamaha RX-V2500. I'm currently using the LFE pre-out on the receiver to connect to the sub.

I keep reading that it's not a good idea to double-filter the signal going to the sub. Is there a different/better way I could be connecting my particular sub?

Thanks,

tim

phuz

You're doing it right. Just turn off the filtering on the receiver. If you can't turn it off, set it as high as you can on the receiver or the sub, but not both.

tcrossma

I currently have the receiver set to 80hz, and the sub dial turned all the way up to 160. But that's still two filtering processes.

I can't raise the crossover on the receiver otherwise my fronts won't get any signal below that value.

My receiver doesn't appear to have an unfiltered LFE out, so I think my only other option is to connect the sub using the front L/R pre-outs and bypass the receivers filtering.

Does anyone else go through this trouble to try and get to only 1 filtering process, or is it a waste of time?

thanks.

phuz

People really do go through that trouble.

tcrossma

Ok, so last night I hooked up the sub using the front L/R pre-outs of the receiver, set the receiver to "no subwoofer", front speakers as Large, and an 80hz crossover. I set the low-pass filter dial on the sub to what I think is approx. 80mhz. I then recalibrated the levels using the receivers test tones and my SPL meter.

I tested a few music CD's and a concert DVD. There's definitely more bass being pushed out than when I had it connected using the sub pre-out. But i'm wondering if it's accurate or not.

Since the fronts are set to large, they are receiving the entire frequency range. My speakers are rated with the -3db point at 48hz. The subwoofer is set to low-pass at 80hz. So, between 48hz and 80hz isn't there going to be an artifical boosting of bass since it's doubled between both the fronts and the sub?

The way i've hooked it up might not be correct, but I tried following the "polk way" as described on Polk's website somewhere in the FAQ. I've done it before using a subwoofer that has speaker-level inputs and just connected it all through the sub, but my sub only has a single line-level input. The "polk way" seems to indicate (assuming i've read it right) that the way i've hooked it up would work, but i'm just not sure.

Maybe I should set the sub low-pass lower, to try and match the speakers better? That makes some sense, except that then i'm using the speakers for bass from 48hz on up and taking it away from the sub -- which kind of defeats the purpose of having a sub.

Anyone have any thoughts on all this?

phuz

An overlap of 10-20hz is not abnormal. Most likely the crossover in the sub cuts over a 12db range. So if it's set for 80hz, then it will play 80hz at -12db, and 68db at full force. Volume between 80 and 68hz increases as it goes lower.

Also, try setting your fronts to "small" and use the crossover at 80 or 70hz.

If you have both set at 80db, and both have a 12db curve, then they should match up well and not "double up" in the crossover range. This all depends on your equipment though. I haven't read the manual or specs on the sub or receiver so I could be wrong, but setting things that way is relatively common in home theater, car audio, and 2 channel audio.

Finding out the specs and playing with it until you feel that it's blending nicely is part of the fun.

John K.

Tim, my thoughts are that it appears you're unduly concerned about the "double filtering" issue, since it's easily avoidable with your UC10. This would only be an issue when both filters are acting in the crossover area(e.g. 80Hz) where both the speakers and the sub are making a significant output. Setting your 2500's crossover to 80Hz, with the speakers set "small" also rolls off the UC10 at 24dB/octave above 80Hz when you use the single sub input on the UC10. So, if you set the UC10 filter to the top(actually 150Hz)this moves it out of the way of the 80Hz crossover that the 2500 is doing and at 150Hz there's no significant interference issue.

Yes, if you allow the speakers to run full-range this results in louder bass where they and the sub are overlapping, but as you suggest, this isn't as accurate as making full use of the bass management on the 2500 by setting the mains "small". It's your money of course, so if you really prefer the sound that way you should use those settings, but a more precise division of duties between your speakers and sub at 80Hz results when you let the 2500 do it.

danger boy

use the LFE output on your receiver and be done with it. if it isn't giving you good results.. then you have some setting(s) wrong in your Yamaha receiver.

start over..

what are your front speakers, large or small?

maybe your subwoofer isn't in the right place, move it to another place in your room if you can of course.

tcrossma

Thanks everyone.

I've gone back to using the sub pre-out and will not concern myself with the "double filtering" issue.

It sounds good enough and everything, but mainly lacking is music (movies has plenty of bass). I had been concerned that my receiver wasn't sending enough bass to the sub pre-out when playing a CD. I was just trying to rule out that possibility by running through the front L/R.

But, I think really i'm just trying to squeeze water out of a stone and probably can't get the quality I want out of my equipment. An upgrade is in the near future anyway, so i'll just try and stop myself from tweaking until then

tim