When Measuring a Woofer's Response, Where Do You Place the Mic?
I've been designing a set of speakers/crossovers and have been dealing with the woofer's response.
The woofers (10" JBL 2251J) are in ~1/2 cu ft ported cabinets. These are to be used as midrange speakers with an 18" for the woofer and a Heil AMT for the tweeter
I can set the crossover values to get the 2251s to better than +- 3 dBA from ~120 Hz - 4K, in my room, when the mic is placed <1" of the woofer dome, within the "confines of the cone" itself.
However, if I pull the mic back, even just a couple inches, it's a totally different story where the bass end fall off like a stone. And of course, the further back you measure, the more the room influences the results.
I wish I had an anechoic chamber, but that won't happen. I may be able to take it outside and lie it on its back raised a bit so the port would be open in the back.
But even then, how close should the mic be to the cone and where/how did JBL take the measurement???
http://www.audiokarma.org/forums/sty...s/scratch2.gif
Thanks
How to do it, from D.B. Keele
From D.B. Keele's website:
6. "Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement," J. Audio Eng. Soc., (April 1974).
A loudspeaker test technique is described which depends on nearfield pressure measurements
made in a nonanechoic environment. The technique allows extremely simple
measurements to be made of frequency response, power response, distortion, and
electroacoustical efficiency.
Ruediger