Mic distance for driver measurements

[ted4412wilt]

How far should I place my ECM8000 from a driver using STEPS for minimal problems from measurement room reflections? I assume this should change with frequency. I am using a Xenex 802. What level to measure without overdriving the mic or mixer? Advice for measurement techniques would be greatly appreciated. I will be measuring a North D25 tweeter to compare with the factory measurement paper to calibrate my mic. Also will be measuring drivers from 4" to 10". Thanks,
Ted

[SY]

It depends on what you're measuring. If it's a woofer, you want that mike nearly touching the driver. That will get you information good to a few hundred Hertz. For midrange and treble measurements, the mike should be backed off a meter or so. You'll then start picking up reflections, but those can be windowed out (with a concomitant loss of information in the lower frequencies).

If you're going to do measurements, you'll find that Joe d'Appolito's book "Testing Loudspeakers" will be the best expenditure you could make. There's a lot of subtlety to the simple view I just gave you, and modern measurement methods will allow you to collect tons of incorrect data very efficiently if you're not aware of the basics.

[tvrgeek]

Found out the hard way chasing weird distortions you can't near-field a tweeter. I find about half a meter to be a good compromise between ambient noise and level. (tweeter mounted in a meter square baffle.) One meter, as SY says, is probably wise for a mid. Full systems I only test outside. I have never had much luck with the ground plane method Joe recommends. Do get and read his book.

Not sure about the overload capability of our 8000's, but my little Audio Buddy preamp drives me crazy. I have to set the gain to below the "signal detected" LED to keep it from breaking up. I need a much better mic preamp. VU meters would be nice.

You can not calibrate your mic. Send it off and have it done by a pro. Only about $50 bucks. It is not that far off to start with. You can calibrate your electrical path.

[Joachim Gerhard]

unfortunately the beringer is not accurate and has big variety. i bought 5 and non of them worked to any precission. that would not be a problem if they delivered a correction file that could be implemented in modern soundcard measurement systems. i measure in 1m on tweeter axis 15° off outdours at good weather or in a big hall for best result. keep the speakers at least 2m from all surfaces. i recommend the Girardin Mic from Liberty instruments. i have 4 that work just fine since 4 years and they come with a correction file that makes them a clone of the AOC paciffic condenser.

[planet10]

Neither the Beringer or the similar Dayton are very flat. Paying someone like Cross Spectrum to calibrate it is well worth the cost.

dave

[tvrgeek]

They are not THAT bad. Better than a home brew Panasonic capsule even with Sigfried's mod. They are dirt cheap. "Real" instrumentation mics cost 10 to 100 times as much and still need calibration. But absolutely, pay a lab to calibrate them.

PS. Makes you wonder how the cheap AVR auto calibration works with 50 cent mics, now doesn't it? Might explain why they don't work!