Measurement microphones

[cameronthorne]

I would like the ability to do some basic measurements and plots of my system. I want to be able to do nearfield speaker frequency response measurement, and subwoofer (even below 20Hz) measurement. I would also like to be able to look for room modes and nulls at the listening position. It would be neat to look at waterfall plots of decay time as well to see how lively my room is. If possible, I would also like to be able to create spectrum plots from sound files on the computer, but this isn't a priority. I realize that not one single software package will do all this.

I currently have: a Radio Shack SPL meter and Room EQ wizard. I haven't used REW out yet because I haven't finished building the speakers, thus nothing to test. If I wanted to step up to something a little better, what should I consider?

I see a bunch of inexpensive DIY measurement mic plans online based on the Panasonic electret capsules. Are any of these a better value than simply getting a $50 Behringer ECM 8000? What other budget measurement mics are worth considering?

Either way, I will need a mic preamp. My only PC in the house is a Dell laptop, with a less than spectacular sound card, so I am assuming better ADC would behoove me as well, so now I am looking at the $150 M-Audio MobilePre USB. Is there anything else that would get me a quality mic pre-amp and USB computer interface for less money?

Then I'm sure there is better software out there. TrueRTA is $40-100, ETF/R+D is $150-300. I'm not currently looking for driver measurement software like Praxis or CLIO, but I'm aware that there is plenty of high dollar software out there. I'm just looking at the budget stuff.

So what capabilities does spending an extra $200-500 afford me above REW and my Radio Shack SPL meter?

Any other recommendations? Thanks.

-- Cameron

[joecarrow]

It depends on what your time is worth. The Behringer has great build quality, is very consistent, and is basically a sure thing. The Panasonic electret capsules are supposed to be at least as good as the Behringer, but their durability and consistency is based on any supporting materials you build.

Any CSD you do is going to look pretty bad when your room is included- probably so bad as to be meaningless. I've only seen people look at those when the drivers are close miced, and only above a cutoff frequency in the hundreds of hertz.

You'll probably be better suited with an external soundcard, but not necessarily. I used a patch cable to check the distortion and noise of my Thinkpad laptop, and it turns out that it is just barely borderline for driver testing. I'd be able to tell good drivers from bad, but I wouldn't be able to tell good drivers from excellent drivers.

Get ARTA software (for free), and a patch cable ($5 most places), and see how bad your sound card really is. Speaker Workshop is also free, and can do some useful things.

Of course, if you go for the Behringer, you'll need XLR and phantom power- so you'll need some kind of pre-amp. I use a Behringer 4-channel mixer that I bought when I was doing more live sound work. You can probably get better and cheaper these days.

Just getting a good mic will get you far better accuracy than the SPL meter. The RS SPL meters just don't have even frequency responses.