Inexpensive Double Mic Setup For Low Frequency BR, TL Measurement

[kelticwizard]

Okay, here's my idea.

I finally decided to get some Panasonic WM61A capsules and set them up like Linkwitz says. Also to learn SpeakerWorkshop.

What I would like to do, though, is to connect one mic capsule, as set up according to Linkwitx, into each of the separate channels in my soundcard-an old Soundblaster, by the way. That way I can measure the output of the port and woofer at the same time, and have things summed for phase, etc.

Since the port is likely to be a different size than the woofer cone, (much smaller in a Bass Reflex, possibly larger in a TL), the mixer settings will have to be adjusted. The smaller radiator, such as the Bass Reflex' port compared to the driver's piston, will need to be lowered to compensate for the fact that each square inch of port will be radiating higher SPL than if the port were the same size as the piston. The sound card should also adjust for phase, etc, so a reading of the cone/port should be attainable by the nearfield method with one Panasonic WM61A capsule, as set up by Linkwitx, in front of each radiator, (port and cone).

The inspiration for this idea is from an article in the Journal of The Audio Engineering Society by D.B. Keele. It is entitled Low Frequency Looudspeaker Assessment by Nearfield Sound-Pressure Measurement.

By the way , I have scanned this article and will happily send it to anyone who Emails me.

My question is-do you think this idea will work in Speaker Workshop? How about some other freeware/cheapware program?

[pinkmouse]

SW can only measure on one channel at once, it uses the other for calibration, I'm not sure about other software. I would be interested in reading the article though.

[claudio]

Hi,
SW, as well as other software based measurements programs, doesn't know how well your sound card performs, so they use one channel to compensate for you card frequency response (reference channel). If you use just 1 channel (the data channel) your measurement response will be the sum of:

1) your sound card
2) your amplifier
3) the DUT
4) your mic
5) your mic preamplifier

Using the reference channel will exclude item 1+2; using a calibrated mic will exclude item 4; using a flat response mic-pre will exclude item 5.

regards,
Claudio

[Ron E]

You can read many of Keele's articles online, he now has a website.

http://www.dbkeele.com/

[kelticwizard]

Thanks for the link, Ron. That makes it easier for everybody.

The article is article number 6 on Ron's link.

Wish I knew that before I scanned the article.