When to Put Sub Out of Phase?

[Bing Fung]

I have moved my sub to the back of the listening room as I don't have enough room up front. Should I be placing my sub out of phase for this position?

I have switch back and forth in phase, but don't seem to notice a difference. If there was I would give the slight edge to the sub in phase.

What should the distance be set to if it's right beside my couch... 0 - 2 feet? The distance to the front wall and back (15 feet)?

[ThomasW]

Here's my suggestion......

Set the distance the same as you would if the sub were in the normal position.

Now try playing with the phase. What your listening for with the phase is if the bass becomes louder.

If there's no difference change the distance are repeat the process.

Not really scientific but the best idea I have....

[Bing Fung]

THanks Thomas, I wil try that :T

[Bam!]

Bing!

Put that sub right up to sofa....

It will rock your world! It's what I call Dynamic Slam!

Also....technically speaking it should be set to 180 when it is in front of the mains .....

[brucek]

Bing,

It's generally accepted that locating your sub in a corner is best. You'll excite every reasonance in the room and the acoustic coupling will be the greatest. That said, I don't think anyone can make any meaningful prediction about the optimum phase setting for your sub. The interaction of the room itself combined with the wavelength distances of the sub from the listener and mains speakers will all contribute to a difficult unpredictability that mathematics can't really solve on its own.

Phase shift becomes a problem when two sources are mixed, whether electrically on a wire or in the air as sound pressure. If you have two signals 180 degrees (worse case) out of phase, you will have complete cancellation at that point. This is the reason it's fairly important to ensure your mains speaker connections are 'in-phase', because there's a very good chance that they'll be producing the same signal, and if it's 180 degrees out of phase, there will be cancellation problems.

With regard to a sub when using bass management, the phase is only significant around the crossover where the mains and sub are producing the 'same' frequencies. You don't want them out of phase and acoustically cancelling each other at that point. Certainly when the sub is acting alone in mono (for example, an octave below crossover), the phase control has no effect on what you hear.

My feeling is that the only accurate method to set the phase control is by trial and error with a frequency response test while sitting in your usual listening position driving the sub and mains in concert. If you have a phase switch, simply try it in both positions and see which is more favourable once the response is graphed. If your phase control is variable, try several settings and use the one with the best response around the crossover.

I'm sure you already know this since you have a BFD, but for those who don't, you can do a response check from 16Hz to 160Hz at 1/6 octaves, at about a level of 85dB to 90dB SPL taken with a Radio Shack SPL meter at your normal prime listening position using a source of a CD playing 5 second sine wave tones .. (Be sure to use the correction constants for the Radio Shack meter for 1/6 octaves).

There is good information and an Excel graphing tool on Sonnie Parkers site (listed below) which has the graphs all pre-done including compensation correction for the SPL meter: The site is dedicated to a BFD equalizer, but the information is still very useful if you're doing a response on your system.

http://www.snapbug.ws/bfd.htm

Myself, I use the tone generator below to make my 5 second tones...

FREE tone generator listed below - save the tones in five second files and burn them on a CDR.

http://www.nch.com.au/action/index.html ....scroll down to audio software / NCH Tone Generator

but you can also use the tones on Sonnies site at http://www.snapbug.ws/sinewaves.

Once you've done a response of your system and graphed it, you'll be able to tell what's happening with the different phase settings a lot better than relying on your ears and playing music.......

brucek

[Bing Fung]

Excellent information Bruce... :T

Its amazing all these simple tools a person has at his disposal and how soon we (I) forget how to use them :roll: I will start getting that set up... I don't have a useable corner at this time, however I may try to rearrange the furniture to see if I can grab a corner. If I could get one, it would still be opposite of the mains.

Thanks for the links.

Bam, sort of like a cheap tactile transducer huh? :W

[Bam!]

Bam, sort of like a cheap tactile transducer huh? :W

:yesnod: :roflmao: