How do you use it to help with speaker placement? Speaker performance? Room acoustics? Etc, etc. etc.
Yes, I use one, several in fact. My favs are the Radio Shack's analog version and a B&K instrumentation model.
You measure speaker output levels with it. There are many test discs with test tones available. Obviously for stereo the right and left channels should match. If they don't you've got trouble.
I suggest perusing a good book on acoustics and high-end audio, such as Robert Harley's Guide, to learn how you can use measurements to improve your system's sound, as this is a subject that can't be adequately covered in a response to a general forum question.
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
Great way is to do it by ear. Get Stereophile test CD 2 and play track 19. Listen over headphones first. That is what you are hoping to hear in the room. Now sit down and play it again in the room. Now you know the seriousness of your problem, because you can hear your room stumble around instead of being a fast room. This test is called MATT, Musical Articulation Test Tones.
You can watch the needle of your analog radioshack meter. Anytime the needle is not swinging wildly, and kinda just shivers in one spot, that’s your problem to fix. Go to http://www.acousticsciences.com/matt.htm to get a free download of the test, and a free training session about how it works and what rooms sound like, bare and with conditioning. Also how to figure the problem frequency using sound meter and stop watch.
Generally, you want to play the room symmetrically so both speakers feel the same space around them and have the same sound. You do not want your speaker to be on the diagonal out from the corner. It’s best to locate the woofer part of your speakers at the “mode free” injection points. These are 29% or 42 % of the distance between the parallel surfaces they are between. Front back, left right and up down. Your head likes to be at some combination of those dimensions, except that it stays on the centerline between and perpendicular to the speakers.
It’s fun to lay out the geometry of the room and then add in the 29 and 42% lines. Where ever they intersect is a good place to locate your speakers and your head. There will be some combination of intersection points that makes for a good listening foot print.
.For smaller low budget rooms, use diagonal sound panels across all the corners, the 4 vertical and 4 horizontal at the ceiling corners. DIY or BUY, either way they work good. Foam I cheapest, fiberglass works octaves below foam but costs more. No free lunch… Once bass is under control, get some absorbing panels or curved thin diffusion panels for reflection points on each side wall, behind you and between the speakers on front wall. Your system should start sounding pretty amazing. Get a used Persian carpet from Goodwill for the space between the speakers and the listener. No matter what kind of carpet you think you have, guaranteed, it sounds awful.
Inventor of the TubeTrap and President of Acoustic Sciences Corp