• 01-14-2005, 09:40 AM
    Stu-r
    "Best" subwoofer crossover frequency
    Just thought I'd share this. I've been listening to stereo music and home-theater for about 50 years. I've always set the subwoofer crossover based on the other speaker low-frequency cutoffs or the "recommended" crossovers (90hz for Yamaha receivers, I understand Noussaine recommends 120-130hz, etc). But lately, the sound I've been getting has been irritating.

    I finally found the problem and corrected it. Because of room limitations, my subwoofer is located next to one of my mains, which means it must be set in phase with that main. My center is about six feet from that main. There seems to lie the key. At 80-90hz (a commonly used crossover frequency), the sub is 1/2 wavelength from the center. 180 degrees out of phase, and uncorrectable at that frequency because of the need to maintain phase with the mains. The solution was to choose a crossover equating to one full wavelength at the distance from the center speaker.

    Although the crosover frequency doesn't look intuitively good, the interference effects are gone and everything (classical, vocals, and HT) now sounds great. If you want to try this, divide 1100 by the distance in feet between your center and subwoofer. That will give you the frequency equal to one full wavelength at the distance between them. If you don't select a lower crossover frequency, the interference effects between them will be minimized. In my case, the ideal is 173hz. The closest I can get to 173hz crossover on my HT receiver is 150hz. But that's close enough. You may also have to recalibrate the subwoofer level if the sub isn't particularly flat at its room location.
  • 01-14-2005, 10:26 AM
    kexodusc
    Uhh, not sure I follow you here...but if your sub is STILL 6 feet away from your center channel speaker, it is STILL 1/2 wavelenght from the center at a 90 Hz frequency, regardless of what "Crossover" point you select....me thinks you've confused something here.
    Don't think crossover point and phase are related in the way you are implying...
  • 01-14-2005, 11:21 AM
    Stu-r
    Quote:

    Originally Posted by kexodusc
    Uhh, not sure I follow you here...but if your sub is STILL 6 feet away from your center channel speaker, it is STILL 1/2 wavelenght from the center at a 90 Hz frequency, regardless of what "Crossover" point you select....me thinks you've confused something here.
    Don't think crossover point and phase are related in the way you are implying...

    Crossover point and phase *at the crossover frequency* are absolutely related as long as the distance between the sub and center are constant. The phase relationship between the sub and center change with frequency. Check your basic physics.

    At 173hz, 6ft is not 1/2 wavelength, but a full wavelength. In this case, the objective is to reduce/cut off the center speaker *before* it gets down to a frequency that is 1/2 wavelength at the distance it is from the subwoofer (a half wavelength of 6ft = 80-90hz; a full wavelength of 6ft = 173hz). Think about it.
  • 01-14-2005, 11:36 AM
    kexodusc
    Yeah, yeah, love the jab about basic physics...much appreciated.

    In keeping with basic physics, you do of course realize that you now have a multi-channel system emitting directional cues from a mono system (your subwoofer)...So left, right, andcenter channel signals (and rears if applicable), that are directional in nature (ie: above 80 Hz) will now be emitted from the subwoofer.

    So much for soundstaging and imaging....how's that basic physics for ya!
  • 01-14-2005, 11:51 AM
    Stu-r
    Quote:

    Originally Posted by kexodusc
    Yeah, yeah, love the jab about basic physics...much appreciated.

    In keeping with basic physics, you do of course realize that you now have a multi-channel system emitting directional cues from a mono system (your subwoofer)...So left, right, andcenter channel signals (and rears if applicable), that are directional in nature (ie: above 80 Hz) will now be emitted from the subwoofer.

    So much for soundstaging and imaging....how's that basic physics for ya!

    Ha! Ha! Good riposte! Some of the literature has long stated that approximately 200hz is the boundary for directionality. If you include audible time of arrival effects, it's lower. But the audible improvement across the board is undeniable without the cancellation effects of the two speakers operating out of phase. As a matter of fact, I find directional and surround effects are *much* improved with the change.
  • 01-14-2005, 12:11 PM
    kexodusc
    What you are implying is interesting, to the say the least...in my room, a 90Hz crossover is very directional at times...the sub gives itself away...not sure if this is a flaw of the sub or what, the speakers don't do it as much, but I suspect that's because they are working in stereo creating an image. Don't really know, don't care. It's pretty well documented directional cuess extend below 100 Hz now, some argue below 70Hz, I can't hear that, but maybe some can.

    I have enough room acoustic issues crossed over at 40-60 Hz to worry about before I go doubling or tripling that. And my subwoofer doesn't do nearly as good a job above 80 Hz as my main speakers do together to justify the decrease in performance just to phase align the center channel.
    Still, I'll toy with your suggestions...we'll call it the Stuey method.

    Cheers!
  • 01-14-2005, 03:12 PM
    Stu-r
    Quote:

    Originally Posted by kexodusc
    What you are implying is interesting, to the say the least...in my room, a 90Hz crossover is very directional at times...the sub gives itself away...not sure if this is a flaw of the sub or what, the speakers don't do it as much, but I suspect that's because they are working in stereo creating an image. Don't really know, don't care. It's pretty well documented directional cuess extend below 100 Hz now, some argue below 70Hz, I can't hear that, but maybe some can.

    I have enough room acoustic issues crossed over at 40-60 Hz to worry about before I go doubling or tripling that. And my subwoofer doesn't do nearly as good a job above 80 Hz as my main speakers do together to justify the decrease in performance just to phase align the center channel.
    Still, I'll toy with your suggestions...we'll call it the Stuey method.

    Cheers!

    That's surprising. If the distance settings for the sub are not correct on the AV receiver, it can cause that kind of separation, or possibly if the sub is a considerable distance from both of the mains. I haven't noticed that spatial disconnect, even with cannon-fire, where it should be most noticeable. Every foot is equal to about a milliseceond. The ear is supposed to be able to resove to about 6 microseconds (I just read on another page). So it can resolve the difference. So any difference between the actual sub distance from the listener and the setting value will do it. A long decay time from the sub's location (reflection) will also do it (acts like another source). Cheers.
  • 01-16-2005, 11:30 AM
    Richard Greene
    A crossover frequency makes the subwoofer down -24dB or more at 150-160Hz. is good
    24dB/octave -- use turnover frequency up to 80Hz.
    18dB/octave -- up to 60Hz.
    12db/octave -- up to 40Hz.

    The goal is to hear no male voices through the subwoofer with the other
    speakers turned off. If that happens your subwoofer is very likely to be
    sonically invisible.

    Your analysis about bass cancellations places too much attention on a minor issue. Quarter wavelength cancellations happen at dozens and dozens of frequencies related to room geometry and dimensions. Using lots of bass traps reduces them by absorbing the reflections (out-of-phase reflections cause cancellations). In a typical room, the bass frequency response at the listening position is worse than +/- 10db measured using a very slow sine wave sweep that excites room resonances (standing waves).

    Quarter wavelength cancellations are severe only if there are three cancellations at the same frequency. Example: Woofer located 3 ft. from side wall, 3 feet from floor and 6 feet from another woofer playing exactly the same bass = three cancellations at the same frequency .

    In general, all front speakers and subwoofers should be located the same distance from your ears and hooked up in-phase because frequencies at and near the crossover frequency are usually reproduced by all of these speakers.



    Quote:

    Originally Posted by Stu-r
    Just thought I'd share this. I've been listening to stereo music and home-theater for about 50 years. I've always set the subwoofer crossover based on the other speaker low-frequency cutoffs or the "recommended" crossovers (90hz for Yamaha receivers, I understand Noussaine recommends 120-130hz, etc). But lately, the sound I've been getting has been irritating.

    I finally found the problem and corrected it. Because of room limitations, my subwoofer is located next to one of my mains, which means it must be set in phase with that main. My center is about six feet from that main. There seems to lie the key. At 80-90hz (a commonly used crossover frequency), the sub is 1/2 wavelength from the center. 180 degrees out of phase, and uncorrectable at that frequency because of the need to maintain phase with the mains. The solution was to choose a crossover equating to one full wavelength at the distance from the center speaker.

    Although the crosover frequency doesn't look intuitively good, the interference effects are gone and everything (classical, vocals, and HT) now sounds great. If you want to try this, divide 1100 by the distance in feet between your center and subwoofer. That will give you the frequency equal to one full wavelength at the distance between them. If you don't select a lower crossover frequency, the interference effects between them will be minimized. In my case, the ideal is 173hz. The closest I can get to 173hz crossover on my HT receiver is 150hz. But that's close enough. You may also have to recalibrate the subwoofer level if the sub isn't particularly flat at its room location.