Measurement Test

[Sonnie]

Okay... it's a holiday here and I was somewhat bored... so I decided to do a measurement test.

I often wondered when we do our measurement testing for our subs and we place the mic at the location that we believe is center of our ears is really accurate enough. After all, our body is not there and our head is not in the way. What our left and right ears hear are bloced by the rest of our head. When we factor in the fact that our body is missing and the mic is not really placed at our left and right ears... are we getting the most accurate response... or is the response we are getting accurate enough.

So... I decided to test it and see for myself.

Using my ECM8000 mic I placed in on my tripod as I normally do and took a quick measurement just like I normally would... centered about where my ears would be. Then I took the tripod away, sat down in my main listening position, placed the tip of the mic at the bottom of my left ear opening and measured. Then the same for my right ear. Below are the response measurements.

Centered mic response:




Left ear response:




Right ear response:




Left and right ear response comparison:




All three measured responses compared:




I was actually surprised to learn that the body does not have that much effect on the response... (and I'm no small chump here - 6' 225lbs).... plus their is somewhere between 6-8" distance between my ears (although not much filling the gap ) and the difference in location of mic when measuring from each ear, but only half that when comparing from the original centered mic location.

I suppose this suggest we are okay measuring the way we've always measured. Some of you probably already knew this, but I wanted to prove it for myself and for others who may have been curious at one time or another.

[brucek]

somewhere between 6-8" distance between my ears (although not much filling the gap)

Yeah, I completely agree.

Whoops, that's not the the quote I meant to agree with - sorry

I suppose this suggests we are okay measuring the way we've always measured.

Yeah, I completely agree. After I've done a measurement and set my filters up, I have in the past gone around the room with my meter and done several sweeps to determine if the prime position where I set my filters was the only good one. Not so in my room anyway. Most of the room is still pretty good and the BFD has tamed the resonant hump throughout the whole room.

Your response is quite good sonnie. It's of course no where near as good as mine.

brucek

[Sonnie]

I guess I had it coming huh?

[Ayreonaut]

From what I observed, the low frequencies aren't affected that much by the proximity of a body. I felt confident that my results were accurate simply holding my RS meter at arm's length while I sat in the seat next to the primary position. In my room, neither moving the meter a foot nor changing the orientation of the meter affected the reading, so even a steady hand wasn't critical.

I did it the old fashioned way with the test tones, RS meter a and a pencil. I think that the results were accurate enough that hooking up a sound card and doing frequency sweeps might not yeild different filter settings. A filter setting 1 db this way or that sounds practically identical.