Tony_R:
TNTTNT: .....so I got the meter out last night and did my own mental plots and curves. I found a huge room spike at 42hz, followed by an enormous trough at 65hz climbing back to 0db at 78hz. The spike at 42hz sent the needle off the meter. What ever was causing the suck out at 65hz was pretty severe, because even the sub hardly affected this, even at moderate gain.
As a matter of interest, how are you calibrating your measuring equipment? Does the microphone / transducer you're using have a uniform response at these frequencies?
Or are you just using it as a rough guide to a 'relative' response?
It seems that you need some quite expensive sophisticated equipment to get a truly accurate response measurement..
http://www.paradigm.com/en/paradigm/r_and_d/anechoic_accuracy.php
Hi, I am using the radioshack analogue meter and desktop, with a dedicated audio soundcard (Terratec).
With the PC, I feed one of the PC line outs to a PC line in, to form a feedback loop to calibrate the soundcard, which my software allows me to do. The software gave me the facility to load a calibration adjustment file for my make of soundmeter, which I downloaded and fed in.
I have checked up on my meter, and one made by Galaxy is much more accurate, but also 3x the price. I did some further research, and my meter has a reputation for being pretty accurate in the low bass end of the range. It isn't deemed very good for the midrange and higher. It quotes error of +- 2db.
Looking at the calibration file, it seems to gradually add 1db between 40hz to 60hz, but otherwise is flat as a pancake.
The problem with using just a measurement approach is that it treats all the range with equal importance. If I had to ruin the 30hz region to get a flatter response above this, I would. This is based on the fact that the 30hz frequency may not be active very often with music.
The metering has given me an idea of how my room behaves and it has been interesting and useful. I rang PMC about something, and we chatted a bit. I told the gentleman what I was up to. He said "I bet you get a huge suckout at 100hz". I was gobsmacked, because he was right. He said it was the interaction between the floor and ceiling. I have found sites which, after fed with room dimensions, have predicted huge blowouts in the 40hz area, so again I found this quite interesting.
So far the community have given me some good ideas for test track, as I have been astounded by how the mixing and recording quality of some of my CDs vary (adversely a lot of the time). I don't have many CDs where I trust the quality of the bass, and again the community have helped.