My image was off

[Thoburn]

Hi gang,

I have Lowther DX-4 drivers in a tall-ish Medallion cabinet with Rythmik subs in the base of the cabinet. I drive them with a Stereomour running 2A3 tubes. For as long as I can remember I have been plagued with a lop sided sound stage. Everything seems shifted to the right. Center stage sounds like it is closer to the right speaker than the middle.

My listening room (also our living room) is about 16 feet wide. There is a fire place that is off center. My left speaker is about 28 inches from the left wall. My right speaker is about 5 feet from the right wall. I figure that the off set speaker positioning was the problem. I have considered putting a balance pot in the system, but was not happy with the idea. Today, I figured it out! Using a hand held mirror I located the exact first reflection on the left wall. I built a Quadratic Diffusor using a design off the I-net that is about 28 inches wide and 4 feet tall. I put the diffsusor at the first reflection and WOW. The center stage is now almost centered. Now I have to make the thing pretty so it will pass WAF.

[Doc B.]

Yup, the room is a huge part of the system. Symmetry really matters, and killing first reflections is a big part of getting things balanced and focused. In general, the more asymmetric the room the more treatment you should have in the front of the room. And the closer you sit to the speakers the less adverse affect you will get from the room asymmetries.

[sl-15]

Using a hand held mirror I located the exact first reflection on the left wall. I built a Quadratic Diffusor using a design off the I-net that is about 28 inches wide and 4 feet tall. I put the diffsusor at the first reflection and WOW. The center stage is now almost centered. Now I have to make the thing pretty so it will pass WAF.

could you elaborate on how you found that reflection with your mirror? and maybe could you include a photo if it is not too much trouble. i am curious how that diffusor looks. sounds like it was an easy fix for you. thanks, stefan

[Thoburn]

The center of my speakers is marked with a small black line at the base of our fireplace hearth. While sitting in my listening spot I used a hand held mirror flat against the left wall. When I can see my Lowther driver in the mirror that is the first reflection of sound from the left driver.

The diffusor I built is an ugly thing. It is made from 14 pieces of 1/2 x 6 X 48 inch fiber board. It was an experiment, so I went on the cheap side. The stuff is very heavy which probably is good sonically. Each of these walls is connect to it's neighbor by a ~ 1.75 inch wide piece of said fiberboard with differing depths of 0 to 5.5 inches. The depth of each well was calculated using an app at the following web site:

<http://www.subwoofer-builder.com/qrd.htm>
 
I don't have any pictures yet and I'm out of time. More to come.