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Measuring Symmetry in Small Rooms Utility Software
Old 23rd December 2010
  #1
Gear Nut
 

Measuring Symmetry in Small Rooms

What acoustic measurements with what interpretations will give me an idea of acceptable symmetry for a small mixing room?

The room is 10 x 12 ft. However, there is no way, with any acceptable speaker positioning, that it will be naturally symmetrical. The back wall has an offset entry (about 2.5 ft. into the room), left side has floor to ceiling book shelves, the right side is all closets with folding doors (4), outside window at the front between the two speakers. I have FuzzMeasure Pro and calibrated mic.

This post is not about acoustic treatments or ignoring listening tests, its about what quantitive measurements to make and how to interpret them with regard only to acceptable symmetry and the resulting stereo image. Acceptable means what measurements would a pro expect in an average or slightly below average treated mixing room. I know there is more to room treatment than symmetry, but I have not yet found any quantitive analysis of symmetry. These measurements will of course be balanced with subjective listening tests as the room is treated.
Old 23rd December 2010
  #2
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johndykstra's Avatar
 

symmetry is more crucial in the front half of the room. depending on the desired room model and appropriate response as viewed on an ETC, the symmetry of the back half can be viewed as very important (rfz) to much less so (non-environment).

in terms of what a pro might expect in terms of measurement, we really must look at the cubic space available, and set yourself up for a reasonable amount of expectations. typically, a pro probably wouldn't expect too much from 120 sq. ft.

Given a 12' length of a room, a RFZ with a 20msec ISD termination would be quite difficult to achieve. Lots of redirection going on, and a lot of work. Even then, the 20msec goal post will likely need to be shortened. Conversely, while a non-environment room has no appreciable ISD termination, it's design calls for a very short, even decay of frequencies. With a 120 sq. ft. alotment, you're going to have a hard time getting the low end to decay as quickly as the highend... tuned traps behind absorbent are likely your option here. And soffit mounted mains with a reflective front wall would still need to be addressed.
Old 24th December 2010
  #3
Gear Nut
 

Quote:
Originally Posted by johndykstra View Post
in terms of what a pro might expect in terms of measurement, we really must look at the cubic space available, and set yourself up for a reasonable amount of expectations. typically, a pro probably wouldn't expect too much from 120 sq. ft.
Excellent, thanks. I was not implying that I was expecting to achieve acceptable results, but more how and what do I measure to see how far off the room is from acceptable.

So if I get this right, then as long as the first reflection points are treated well, the next problem as far as stereo image is going to be low frequency decay and not the fact that my side and back walls may not be symmetrical. Which is pretty standard treatment sequence anyway.
Old 24th December 2010
  #4
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johndykstra's Avatar
 

Let's not get too down... "acceptable"... totally achievable in my mind. I've heard of rooms with a +/-1db response variance... with flat decay time. THis is what I meant by what a pro may expect, and how I viewed this as "not probable" for a room of your size. "Acceptable" is well within reach.

Don't start with permanently placing 1st reflection treatments. You are going to want to do a good round of experiments with your and the speaker's positions in the room, done in an non treated environment for the time being.

I just posted this "order of operations" in another thread:

https://www.gearslutz.com/board/6142416-post4.html

I go on later in that thread to suggest a read by SAC, to really get a grasp of the concept.

Consider some measurements with the door into the room open to gain some more bass space.

One thing I forgot to mention in the link above... when you get to ETC testing, make sure to perform multiple measurements all around the "mix spot" as you will likely be moving your head a bit when you mix, your test mic should as well.
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