I am new to this forum. i have some new rooms that i would like to have professionally analyzed to see the frequency response. i have done some preliminary stuff but would like to consult with someone who does this every day. can you point me in the right direction ?
But there are probably others closer to you. Maybe someone else will have some suggestions. I have always done this myself, and it's not that difficult if you have just a few tools. Here's the classic procedure, though I believe there may be more modern methods using TEF analysis and other techniques.
Set up a high quality small diaphragm omnidirectional condensor mike at ear level where you sit while mixing. It must be an omni mike, not carioid. Play pink noise in mono through both of your loudspeakers, loudly enough to drown out all ambient noise by at least 20 dB. That is, the difference in record level should be at least 20 dB. [more is better] between playing the noise and not playing the noise. Record at least ten seconds of the noise from the mike onto a high quality medium like a DAT or a computer. 16 bits at 44.1 is fine.
Now load the file into SoundForge or some other audo editor that offers a spectrum analyzer, and view the results at the highest resolution offered. You might also record the noise with the mike at other locations in the room. If you have an expensive mike it probably came with a custom printed frequency response curve. You can add/subtract that curve from your measurements to remove the mike's contribution to the results.
Okay that's one test. The other test uses plain sine waves, which more closely reflects real music such as a bass player sustaining a note on a slow ballad. Use the same measurement technique of playing, recording, and analyzing to see what you have. While you're fooling around with sine waves, also walk around the room and listen for places where the tones get louder and softer. In most rooms if you play a single frequency tone the difference between loud and soft is 15 dB. or more, and complete cancellations are not uncommon.
if anyone knows anybody closer than CT, yes please keep'em coming. i'm in Long Island, New York.
after reading about your classic procedure, i will definitely start analyzing. is a certain mic you would recommend ? the gold-line website is great and i will call them tomorrow. there windows software kit with TEF analysis looks interesting. i wonder what it costs and what the advantages are? i am curious why they use a cardioid mic ? An omni seems more logical. again, thank you for your time and info.
Any small diaphragm omnidirectional condenser mike that is high quality and has a reasonably flat response will work. If the mike has a calibration sheet that shows the response of that particular mike, all the better because you can account for the mike's deviation in your measurements. I have an AKG C451, and I bought a CK22 omni capsule to use for room measurements.
> i wonder what it costs and what the advantages are? <
I believe the Goldline system is very expensive to buy, anyway, because it's a combination of hardware and software. So it's probably a lot cheaper to have someone come by your place and do the measuring.
I have no idea why TEF or other more modern methods are supposed to be better than the good ol' pink noise and sine waves tests.
Here is an informative link - these guys' software is $150, demo is free. I haven't set up the demo yet, but it looks kinda cool.
Ethan, one of the advantages of using the computer to do the test, is that it can do a pulsed noise test and plot RT-60 across the band. It also does a waterfall plot so you can see how much effect your step-by-step treatments have had.
The cool thing about this particular software, is that it's optimised for cheesy soundblaster type cards and the Radio Shack SPL meter as a mic. It actually profiles your hardware and corrects for it.
With that setup, you can do lower freq modal tests, but for complete room treatment involving higher freqs, you would need a better mic, etc - They offer a small condenser and preamp for a reasonable price, as well as other modules for the software.
> one of the advantages of using the computer to do the test, is that it can do a pulsed noise test and plot RT-60 across the band. <
Yes, I am aware of that, and was half-kidding about not knowing why TEF et. al are supposed to be better. I know the impulse tests can take into account reflections and other time-based factors, which yields more knowledge than just seeing comb filtering and not being sure what caused it.
> It actually profiles your hardware and corrects for it. <
Cool!
> With that setup, you can do lower freq modal tests, but for complete room treatment involving higher freqs, you would need a better mic <
Most problems that are fixable are at the lower frequencies. The best way to correct mid/high frequency issues is to buy better loudspeakers! Again, I'm half-kidding...
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