Assymetry vs on-axis placement?

[Johnson]

Hi all,

I've received some advice that there will be less room "boom" by placing the two front IB manifolds off-axis to the room. Here's a diagram:



Is solution B the preferred method? I've rarely seen this type of placement in the examples we have here... and it also strikes me as a little odd, considering the main speakers are all perfectly symmetrical.

Opinions welcome...

[chrisbee]

Corner loading gain will be greater with one sub than the other.

My main speakers (in fact my whole system) are arranged at one end of a long room but look across the room rather than along it. This places the left main and left rear speaker close to the walls and corners. The right main and rear speakers are nearly 10 feet from a wall or corner.

Running REW sweeps on each of my main speakers easily proves that the frequency response is complete different between the two.

You will probably have exactly the same "problem" with two subwoofers.

Only testing with a couple of box subs using REW would prove any room mode advantage from your suggested asymmetric layout.

[inm8]

To gain a better understanding of what is going on you should do some research on "two point source interference patterns".

Basically when you have two coherent point sources (ie: your two manifold openings) in a unobstructed environment you get what is commonly referred to as a 2D standing wave pattern. At specific points in the room (or space) you will get constructive and destructive interference. In terms of sound what this means is that there will be areas in the space where output from the IB will seem loud and other areas where the IB's output will appear to be much softer.

Of course, all of the above is theoretical. Among many things, it does not factor in room interaction and the fact that your "space" will contain other objects (i.e.: humans, chairs). Therefore, having an asymmetrical layout is a good thing, in THEORY. However, in the real world it may make little difference, or it may even end up doing more harm than good. There's no real way of knowing without testing the locations before you install, and obviously that isn't an option for you. I'm sure there is a genius physicist out there that could run some computer simulations and give an answer, but I don't know any ;D

Here's a simple way to experiment and understand what is going on:

1. Grab a flat tray or tank (eg: paint tray, bath tub, sink) and fill some water in it.

2. Get two pens (or similar objects) that you can dab in and out of
the water. (these are your point sources, or in practical terms, your "manifolds")

3. Get someone else to push the point sources in and out of the water at the same time while you are watching.

4. Watch the wave motion and keep these two things in mind:

• Constructive interference will occur where two crests or two troughs meet.
  
• Destructive interference will occur where crests and troughs meet.
  

5. For bonus points , put other objects in your tray/tank as "obstructions" and see what effect they have on the wave pattern.

You really need a ripple tank, an overhead light, and a clear white surface underneath to do it properly, but even trying it in a bath tub should be sufficient to gain a basic understanding of what is going on.

[ThomasW]

This is why room model simulation programs exist....

home.comcast.net/~thomasw-2/SubwooferSetupandEQpage12.html