# Assymetry versus on-axis?



## John Simpson (May 10, 2007)

Hi all,

When placing subwoofers (in this case, IB-manifolds) does anyone know if it will sound better if the drivers are set off-axis to the room. Here's a diagram of what I mean:










I've received advice that solution B is best, but I'm not certain why. Especially since the main speakers are all on-axis to the room.

Advice very welcome!


----------



## Sonnie (Apr 11, 2006)

What was the reasoning behind the advise given for solution B? I'm curious.

With sub-bass it has always been my understanding that location is all about where you get the best natural response for your listening position. Once you get the wall built where the drivers will be located... and before you cut any holes... you may do what I did to determine the best location for my IB drivers (although I never actually built the IB system). I placed a sub in the main listening position and then measured the response at several locations on the wall/ceiling where I might install a driver.


----------



## John Simpson (May 10, 2007)

Yeah, it is curious. The technician said placing the subs "on-axis" would increase the "boom" effect... which I read to mean additive soundwaves creating nodes along the centre of the room. Considering no one actually sits with their head in the exact centre of the room, I'm not sure it's such an issue.

Then again, nodes can popup anywhere, particularly if two low-frequency emitters are working in tandem on the same plane. No matter how much absorption is in the room, there's not much you can do about them (they're not, after all, caused by reflection!).


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

Not sure I follow. On-axis or off-axis in relation to what? Or do you really mean symmetrical vs. asymmetrical?

In any event, my understanding is the same as Sonnie’s: If you have location options (many people don’t), put your current sub at the listening position and take REW measurements at your prospective locations, to see where you get the best response. That “boom,” if it is an issue, should be obvious. After all, a “boom” is nothing more than a response peak.

Regards,
Wayne


----------



## Ethan Winer (Jul 21, 2006)

John Simpson said:


> I've received advice that solution B is best, but I'm not certain why.


The _only_ way to know for sure which sub placements are best (flattest response) is to measure the response at the main listening position while you move them around and experiment. Anything less is just guessing.

--Ethan


----------



## Bob_99 (May 8, 2006)

Assuming that everything is truly symmetrical in the room, it's my thought that symmetrically the two subs simply enhance each other while assymetrically they should (if placed correctly) minimize peaks and dips of the FR in the room which is what the benefit of a second sub should be.


Bob


----------



## Anthony (Oct 5, 2006)

My understanding was always the same as Bob's. 

If you use two subs, they should be slightly "off" in order to excite modes the other does not and not to reinforce existing modes.

That being said, I have not set up any multi sub systems (always been one or full range speakers + sub).


----------

