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Can 2 subs be out of phase due to placement?
Old 5th June 2006
  #1
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Can 2 subs be out of phase due to placement?

I don't know if this is a ******** question, but I got into a small argument with a club manager because I wanted to move the clubs subs that were placed 5 feet apart (in depth). I protested that they would be out of phase if left the way they were (which suited the layout of the room). The manager said that it was impossible for them to be out of phase due to the fact that they are omni directional. Am I clueless or was she talking out of her ass? Can 2 subs be out of phase due to placement?
Old 5th June 2006
  #2
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Zwinter's Avatar
 

Quote:
Originally Posted by Jetblack
I don't know if this is a ******** question, but I got into a small argument with a club manager because I wanted to move the clubs subs that were placed 5 feet apart (in depth). I protested that they would be out of phase if left the way they were (which suited the layout of the room). The manager said that it was impossible for them to be out of phase due to the fact that they are omni directional. Am I clueless or was she talking out of her ass? Can 2 subs be out of phase due to placement?
Yes, she is most definitely talking out of her ass. Subs, like any speaker, can be out of phase to another speaker. This is caused by the distance, and time (which are connected by the speed at which sound waves travel), discrepancies between them. Just so you know the wavelength of a 100 Hz tone is approximately 11ft. So if you had one sub 5.5 ft further away from your ear, 100 Hz signal of the two subs would be 180 degrees out of phase (which is bad!!!). In fact, at 5 ft you would be lacking some serious bottom end, which is what every club wants because it gets the girls shaken what there mama gave them.
Old 5th June 2006
  #3
Gear Head
 

Quote:
Originally Posted by Jetblack
I don't know if this is a ******** question, but I got into a small argument with a club manager because I wanted to move the clubs subs that were placed 5 feet apart (in depth). I protested that they would be out of phase if left the way they were (which suited the layout of the room). The manager said that it was impossible for them to be out of phase due to the fact that they are omni directional. Am I clueless or was she talking out of her ass? Can 2 subs be out of phase due to placement?
If you simplify the problem to direct sound, the direct sound can be out of phase, but it doesn't really have to do with the speakers dispersion pattern. Rather their relative distance from the listener. You'd need to separate them pretty far apart and such that one is substantially closer than the other. At the lowest C on the piano the wavelength is ca 10m. For the two subs to cancel each other you'd need one of them half a wavelength or 5m closer than the other. For the next higher C, 2,5m etc. So for 5' you could expect some problems in the next octave, dependiing on where the crossover frequency is. In a real room there are walls and they reflect sound and complicates the picture substantially. Enough to cause similar problems already with a single sub in many rooms.

best regards
Lars
Old 5th June 2006
  #4
Lives for gear
 

Quote:
Originally Posted by Zwinter
because it gets the girls shaken what there mama gave them.
The way I heard it was --
You've got to put the kik in the girls ass... and then...

The girls dance
The boys buy beer
You make more money to buy more gear

Steve
Old 6th June 2006
  #5


Not out of phase, technically. But you get phase cancelation problems like the others have explained.

Best to have them on either side of the main area. That way, they are in phase in the center line walking away. But, then, you can always just lower the x-over poing to where it doesn't matter......



-tINY

Old 6th June 2006
  #6
Mastering
 

Quote:
Originally Posted by Jetblack
I don't know if this is a ******** question, but I got into a small argument with a club manager because I wanted to move the clubs subs that were placed 5 feet apart (in depth). I protested that they would be out of phase if left the way they were (which suited the layout of the room). The manager said that it was impossible for them to be out of phase due to the fact that they are omni directional. Am I clueless or was she talking out of her ass? Can 2 subs be out of phase due to placement?

Timing is important.... phase is time. You start to lose the point source of the wavefront. The relative phase between subs is critical whether or not they are "omnidirectional". Low frequency energy from a sub is fairly omnidirectional, but that's not important... what's important is regardless of the polar pattern, the RELATIVE phase (timing) from the two subs to your ear will definitely vary if you move them around. Only when they are equidistant from the listener or time aligned via delays to the listener will the phase be "pretty correct".

That said, in a club, things are so wacky anyway and there is no single point for listening, that I doubt it's going to hurt any more for the myriads of listeners in the club. You have a different thing going and what you need to design is a good DISTRIBUTED system, which has no imaging whatsoever, but hopefully a fairly uniform frequency response. You don't usually notice the multiple images from the mulitple loudspeakers, but that's what's really happening in a club. It's just a little less critical with the subs than with the higher freqs.

In my mastering room, phase is VERY critical. If I move a sub an inch I have to realign and re-time align the sub and the satellites for a SINGLE point (the listener). The relative phase for any other listening position will not be ideal. And as for the phase between the two subs, if there is no differential time delay, it does help, REGARDLESS OF THEIR POLAR PATTERN. Or you start to get a diffuse image. The only reason it works fairly well off axis is because low frequencies have long wavelengths so the cancellations at low frequencies are not as extreme. But it's audible, and if you have a critical room, don't do it. I don't consider a club with wacky acoustics and multiple mids and tweeters all over the place to be so critical that

BK
Old 6th June 2006
  #7
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Zwinter's Avatar
 

Quote:
Originally Posted by squeegybug
The way I heard it was --
You've got to put the kik in the girls ass... and then...

The girls dance
The boys buy beer
You make more money to buy more gear

Steve
I am sure most guys have to admit that after watching a girl do her thing you need a beer...or two...or, as in my case, I would probably be money ahead to just buy the bar.
Old 6th June 2006
  #8
Gear Maniac
 

Quote:
Originally Posted by bob katz
Timing is important.... phase is time.

..In my mastering room, phase is VERY critical. If I move a sub an inch I have to realign and re-time align the sub and the satellites for a SINGLE point (the listener). The relative phase for any other listening position will not be ideal. And as for the phase between the two subs, if there is no differential time delay, it does help, REGARDLESS OF THEIR POLAR PATTERN....BK
These concepts should branded on the foreheads of sound engineers and anybody who sets up playback systems. Or El Markos work for the pain-intolerant.
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