Using a RS SPL meter


What is the proper way to use a RS SPL meter in order to measure the room response. What I have done is set the meter to "C" weighting, "fast response". In particular, I wanted to see what was happening in my room from 200 Hz down (my room is 14'5" wide x 19' long with coffered ceiling).
This is the part I'm not sure I did correctly. Using a Sterophile Test CD, I played 200Hz track, and adjusted the volume of my preamp in my room until the RS SPL measured 90 db. I then played each of the following tracks (with lower freqs), and recorded the db reading from the SPL. I put the RS SPL on a tripod, at ear level, from my listening position, and pointed the meter directly forward (aimed between the two speakers).
Wow, the response dropped significantly below 60 Hz? I'm talking about a drop of 18db by the time i got down to 25 Hz. (My speakers are Acoustic Zen Crescendos, which are full range). I understand (from another thread here on A'gon) that the RS SPL is deficient in the lower frequencies, and that I need to add db's to the reading I get (however, even after db's to the response, the response below 50 would still be down over 12 db).
So,
#1 Am I using the meter correctly?
#2 If not, what is the correct way to measure room response using the RS SPL meter?
#3. Any thing else you want, to add or need to know?
In advance, thanks!
Louis
louisl
90 db is pretty loud for constant listening. I hope you do not ruin your hearing or listen for long periods at that level. Although if your in room response is as bad as the measurements say..... your real levels may be quite a bit lower.
I think the microphone is designed to be pointed up rather than directed at the sound source. Slow trajectory is commonly used to get a steadier reading. Measurement with sine waves might be fraught with artifacts.

db
While the meter can be of some use, since it is not in most cases correctly calibrated, the readings can be very misleading. Its mike, and some freestanding mikes also, can have a wide error rate, best to look to rent a calibrated mike and use some of the free computer programs to do a better test.
Iirc I used to set the meter to 0 dB for the average sound level in the room. Then when you move around the room you can see the peaks and the dips in dB relative to the average level.
Good advice from Geoffkait and Tom 6897 (an ear is a terrible thing to waste). But also you should read the J. Gordon Holt article in the Stereophile archives on flat frequency response and consider that along w the impact of the measures you take to achieve it.