Measuring speakers

Does anyone know how to measure speakers' frequency response like they do in magazines? I'd like to confirm my speakers' lo frequency specifications to adjust with a subwoofer.
You would need some sophisticated equipment and a suitible environment to replicate testing as done in the mag's.

As a pratical matter even if you could it wouldn't make much difference in actual use since the room and speaker placement makes a huge difference.

Buy a test disc and a Radio Shack sound level meter and use it to set up the sub's and integrate their response with the main speakers. Easier than doing it by ear.
Newbee is right, but the closest that you can come is to measure the speaker in a quiet, outdoor environment lifted well off of the ground. Use a CD with test tones, such as those inexpensively available from Stereophile or a tone generator and a sound level meter, the Radio Shack model mentioned is very inexpensive and should work nicely.

Buy a test disc...

Or make one on your computer (if you have one). Freeware is available for both Mac and PC. Save your file to AIFF (Mac) or WAV (PC). Then burn your file to a CDR. You can make a disc not only for your sub to main crossover, but for testing your whole system as well. (or if you do not want to go through the motions, just buy one!)

I prefer to make my own because I can pinpoint any frequency I choose.
there is also SW that dive you greater control than CD test discs (this may be what Jamscience is refering to to make discs). I have 2 packages, one freeware called "Multigen" is a frequency generator that generates simply sine waves - it has continuously variable frequency. It also allows more complex harmonics contruction. The other is AQT (Audio Quick Test) - it's more sophisticated and costs $. The entry version is $30. I'm only a user of these, not afilaited with either company. I have them loaded on a laptop that I connect to a pre-in for testing in room setup. I us the RS meter for amplitude measurements, but as has been said, this is highly imprecise. Finally, Jamscience's suggestion to burn a cd is a great idea for more quick testing. It's much easier to load up a cd, than to connect up a laptop, boot up, etc, if all you want to do is run a quick scan.
The Behringer DEQ2496 has a spectrum analyser function, and is cheap enough to be bought simply for this feature. (About $350 including microphone). Much easier to use than the RS meter and test CDs.

Furthermore, after you see your in-room frequency response, and recover from the shock, you can go about fixing it using the automatic equalization feature.
When I test my speakers, I use a Rolls MO2020 signal generator and my RS sound meter. I find it to be very effective.
I use the DEQ 2496 as well. Wouldn't you still need a test cd as well? If I am wrong please fill me in, but I believe the unit only has a pink noise generator. I am not questioning your knowledge, but you got me questioning mine. I could be missing out on some very useful features of this EQ.

Nuguy...For frequency response measurement and correction all you need is the internally generated noise signal. However, a test CD, such as the one put out by Denon, includes other tracks that I have found useful.
Check out ETF acoustic It is very sophisticated stuff and pretty affordable. You will spend many hours playing with this program.