Tuning speaker / room response?

As a professional Acoustic consultant, I would give few suggestion about measurement tecnique (even if it is quite hard, with my poor English). First of all, the way you took measurements cannot give reliable results. In my opinion, the best signal to be used is pink noise. If you have a SLM with freq. analysis you can use a full band pink noise. Otherwise, there are CD with pink noise filtered in 1/3 of 1/1 octave bands. If you use a pure tone, the measure will be too much affected by the mic position (standing waves). If you repeat the measure 5 inches away, you could obtain totally different curve. In any case, the measure should be always taken averaging the value on a zone close to listening position, and not in a fixed point. If you have an integrating sound level meter, it will make the average by itself, otherwise you can average by yourself, but always using SLOW time response.
Regarding your curve, the response in low freq. is normal for a typical listening room. But, the high freq. response is usually much more flat, and your curve is probably affected my measurement errors.
As Abstract7 says, it is quite hard to get room correction with passive device at low freq. due to the long wavelength. Any absorbing device is effective if its thikness is at least 1/4 of the wavelength. At low freq. only resonant devices are effective, as Helmoltz resonators, or "vibrating board" resonator (I don't think this is the correct english transation). But, both of them, to have a good effect, requires a lot of surfaces and volume, (and have a very low W.A.F. :-).
For high freq. absorbtion, I suggest to avoid any exotic and expensive devices. Normal carpets and curtains are more than enough.

FYI, if you want to include graphs or pictures here or with your ads, you need only download your images to any of a number of free web servers such as www.honesty.com. Then follow Njonker's advice for getting the image to come up here. If you'd like to learn more, you can purchase a book that teaches you HTML (Hypertext M [something] Language) at any bookstore for around $15. It's simple to learn and makes it easy to spice up your ads.

How ever simple it might be to put this sort of thing on a thread it is still very impressive. Kudos Njonker, maybe more will follow.

OK, take two of the experiment will thus involve pink noise and a spectrum analyser. I have done a bit of research on linear mics, PC Sound Cards et all, and as it turns out, it is not really economical to turn my PC in to a spectrum analyser. (See other thread on PC Spectrum Analyser).

What I found is that using an osciloscope, I got a nice 1kHz sine wave from a test CD to look as such. When my sound card was done with it, looking at the representation on the PC, there were tons of harmonics. So, I have a spectrum analyser coming to do this right.

So let me describe my room, here is a quick picture:


The black boxes are the speakers, they are actually toed in about 50 degrees. The blue box is roughly where I took the meassurements, and where I normally listen. The room (narrow part) is about 14' wide, about 20' long. Ceiling at about 9'.

The left wall is almost exclusively glass, about 90%. Glass is framed in hardwood. The floor is hand-made tile over concrete. Front and rear wall are drywall. Right hand side wall on narrow part is brick. Front part right side wall open to higher level floor. Ceiling is hardwood boards with beams hanging down at 8' and 16' from the front of the room; beams are hardwood, 4" wide, 8" high.

There is a couch against the back wall, two recliners (one where blue square is, one to the left). There are rugs inbetween the speakers and listening spot, from about 1' left of left to about 1' right of right speaker, another rug between recliners and couch.

The plan for this weekend is to repeat the experiment using pink noise and spectrum analyser. I will perform the test at several points in the room to see what results I get.

Finally, I suspect some people are going to suggest changing speaker placement radically. That is not really an option due to the traffic pattern in the room. I am sure it would be better to move the speakers 3' more out of the wall, but it aint gonna happen. *sigh*.

More data later...

Niels.

Neils can you place the sound system on the back wall where the couch and recliners are? I see you realize that where the speakers are placed now, that they should be around 60in off the wall behind your speakers. Looks like you might get better results reversing the setup. If your auctual room size is 14 wide X 20 long, placing the speakers (woofer center to walls and opposite speaker) 42in from side window wall and 82in to opposite speaker and 60in from wall behind speaker and seating position 10ft from same wall. This could be a starting point to take measurments from. This is if you can reverse the room if possibe. Also that little nook at the bottom right, if you can turn that into a continuous wall (closet maybe with a solid door) might help with the reversal. Just for fun try this arrangment and see if there is an improvment. Good-nite, i'll ck in the morning.