Subwoofer phase
tmartin2 -- Mon, 02/20/2006 - 09:27
Normally subs are placed behind main speakers, I suppose for aethetic purposes. That implies that sound from the subs is delayed. If you adjust phase, by definition you can't advance phase, you can only delay. So, to get the sub and the main speaker to be in phase, you delay the sub a cycle? Is this delay audible?
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Tom,
I'm not sure if the one cycle delay is audible, but I do think having the sub significantly out of phase with the main speakers (or L/C/R speakers) is audible. However, I've found a workaround that seems to help with many--though not all--subwoofers.
The workaround: Try experimenting with the subwoofer distance settings on your A/V controller or AVR (and also, of course, on your DVD-Audio/SACD player). My experience has been that you can often find a specific distance setting where bass timbres, textures, and transients will audibly "snap" into sharp focus.
Note: The setting that works best may turn out to be substantially different from the actual, physical distance between the subwoofer and your listening position.
Why does this unorthodox approach work? My thought is that while a simple phase adjustment knob cannot, as you point out, advance phase, the distance setting function can and does adjust the relative "launch times" of signals to each channel. Given a broad enough range of adjustment, you can usually find a setting that aligns the sub with the main speakers.
The catch: Some subwoofers exhibit a significant amount of phase shift over their operating frequency ranges. Where this is the case, I've gotten the best overall results by trying to optimize phase alignment in the frequency region of the main-to-sub crossover point.
Best,
Chris Martens
Audio Editor, The Perfect Vision
Chris Martens
Editor, Avguide.com/Playback/The Perfect Vision
There's a sure-fire technique for getting a subwoofer in phase with the main speakers. First, reverse the red and black speaker leads going to your left and right speakers. Play a test tone at the crossover frequency (you can find tones on most test CDs) and have someone sit while you adjust the phase control. Turn the phase control until the person in the seat hears the least amount of bass. Return the speaker leads to their correct polarity and the sub is perfectly dialed-in.
By reversing the red and black leads on your speaker, you are putting them out of phase with the sub. When you hear the least bass, the main speakers and the sub are maximally out of phase. When you return the speaker leads to their correct position, the sub and main speakers are maximally in-phase.
It is much easier to dial-in a maximum null than a maximum peak.
Robert Harley
Hi Robert,
When you said play a test tone @the crossover frequency do you mean the subwoofer crossover or the speaker's crossover? can you explain this procedure in more detail I'm very interested in this technique I have a dual subwoofer setup and the phase controllers are variable.
Thanks
The test tone should be the frequency of the crossover between the subwoofer and main speakers. For example, many speakers crossover over to a subwoofer at 80Hz (which is also the THX standard). At this frequency, the signal is being reproduced by the main speakers as well as the subwoofer. Substantially below 80Hz, the entire signal is reproduced by the subwoofer. Substantially above this frequency the entire signal is being reproduced by the main speakers. The test tone must be at the crossover frequency so that it is reproduced by both the main speakers and the subwoofer. The technique works only when the main speakers and subwoofer are both reproducing the test tone.
You can verify that the main speakers and sub are reproducing the tone by looking at the drivers and seeing excursion on the sub's cone as well as the main speaker's woofer.
Does this explanation answer your question?
Hi Robert
I just wanted to say thanks for this info - I'm new to home theater and I found this really helpful :-)
Hi Robert,
Thank you for the explanation and I'm sorry for the delay response. Yes this really helped me understand the concept of the technique and I have tried it and it worked beautifully, now I can hear a much better response on the bass and the sound has improved enormously. Thanks again for the help.
Respectfully,
Arthur
Thanks for the note, Arthur. I'm glad it worked. It is such a simple and effective technique.
If the Subs are behind the mains thenb you have to delay the mains BACK to the subs. There is no way of delaying the subs to match mains that are in front of them. Unless you know of a processor that can tell the future and emit sound before it is actually played.
If the subwoofer is behind the main speakers, you can delay the signal sent to the subwoofer so that it is in-phase with the signal from the main speakers, but one wavelength behind. The woofers in the main speakers and the woofer in the subwoofer move forward and backward together and are thus in-phase.
How does this apply to Quad Electrostatics with a REL sub?
The technique should apply equally well to Quads with a REL subwoofer.
can this technique be applied to car audio system? thanks in advance.