Try going to www.headphone.com and click "reading stuff" and scroll down to "revenge of the giant toilet paper tubes" and read all information. Than go to www.cardasaudio.com and click "insights" and scroll to speaker setup and read all info. This should give you some info to flatten those BUMPS. |
Hi Njonker; first, it amazes me that you could import and show this graph here on Agon. 2nd, the graph itself is very interesting, and may well give me enough incentive to try doing what you did, as I have both the STPH CD 2 and a Rat Shack SPL meter. Rather than doing the 1st logical step as you have, ie the measurements, I bought five ASC tube traps, 11" dia. X 4 ft., and 3 panel traps, 15" X 4 Ft., and just tuned my 14 X 22 room by ear using these ASC products. There is also other furniture in the carpeted room, such as drapes, bookcases, CD storage etc. You obviously have sonic peaks in the mid-bass, mid-range, and low treble. Using the ASC products and ordinary furniture, it's my guess that you could significantly reduce those peaks. Thankyou for the excellent information. Craig. |
like garfish, i'm really impressed with the fact that your post is like none i've ever seen. will you kindly share with us how you imported the graph? |
The graph is actually pretty simple to do. You put it on a web server, then include a link in your post. The link is done by a simple html tag.
Using square brackets in stead of smaller than / greater than signs, the tag looks like this: [img src="http://www.myhome.org/pics/roomresp.gif"]. You would of course use greater than in stead of [ and less than in stead of ].
Niels. |
You need to take into account that the RS meter is not REAL accurate in the first place. There is a list of corrections that need to be factored in before you start "gutting" your room, buying room treatments, moving your speakers, etc... I can't seem to find the website that posted this info nor the sheet that i printed out with the specific corrections. Once i can locate either one of them, i will post it here unless someone beats me to it. Sean
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I'm also impressed with the graph. I don't have a web server at my disposal--so I doubt I'll try this at home. As to the problem. A couple of things, the meter should be on slow response. I've done it both ways, it doesn't seem to make much of a difference so I believe your graph is close to accurate, with the exceptions of Sean's post (which I'm very interested in the website). Mikec's post points out some very good areas for info. However, I'll bet you have a little over an 11 foot span between walls, or that's your ceiling height (or close 10.5 feet). Room tuning works very well about 125Hz. It does work at lower frequencies, but not nearly as effective. That bump at 50 Hz will be difficult to correct without electical correction. Most people, including myself, consider equalizers a measure of last resort--but if there is no other way--it will make a big improvement. Infinity has a single notch filter on their new speakers to accomplish exactly this. Tact has been making digital correction systems for sometime. Perpetual technologies also has a digital domain correction engine (but this only works if you ONLY listen to digital sources throught the Perpetual technologies P-1A). It seems to me there is a market for a very low noise low frequency addustable notch filter. This is such a common problem. McIntosh made room correction equalizers. They are very good--but something simplier with less noise would be prefered. Looks like an opportunity for someone or some company. |
To really understand your graph you should describe the dimensions of your room, the position of the speakers and the position of your measuring SPM. If the graph is the speaker response at your normal listening position, then your have a fairly flat system response. IT IS NORMAL TO HAVE IN ROOM RESPONSE MEASUREMENTS SIMILAR TO YOUR GRAPH. The dip at 200Hz is probably a floor reflection phase problem. Try experimenting with speaker toe-in to address the peak at 4KHz. As a reference, perform the same measurement 1 meter directly in front each speaker. They should measure much flatter. |
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. |
Paolo not bad for a fellow Italian from Italy. Now do you want to rewrite that in Italian. Good Advice |
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. |
I have a similar question to Njonker's. I have plotted a graph using the test tones from Stereophile test cd 3. I used a Radio Shack spl from the listening position. My results are much flatter than Njonker's, staying within +-4 db of 80db at 1 kHz, with the exception of a 10 db spike at 6000-8000 kHz. What room characteristic would cause this? how does this compare to others who have tried this? Njonkers, I think you may have started something with your graphs. You have inspired me to get up to speed with my computer skills. |
The methods described so far really only give rough approximations to the actual response at the sweet spot. This is because of the multitude of reinforcements and nulls that are caused by the multiple reflections. Your actual response is actually much worse than the curves shown. Impluse methods, such as MLSSA or those used by Sigtech, or specialized sweep tones should be used for room tuning. The asc tube trap site has an extensive explaination on their MATT test page (http://www.tubetrap.com/. I use both ASC tubtraps and a Sigtech DSP to tune my room. They make a huge difference and my room is good to begin with. |
I think I may have missed the thrust of this discussion, and I'm a month late to boot, but here's some related info:
It looks as though the analog RS SPL meter is capable of providing data sufficiently accurate to be useful in addressing speaker/room frequency response. By applying the published correction values you are "calibrating" your $35 test instrument! The overall response of the meter is far from flat, but apparently pretty consistent from unit to unit, so the corrections should apply to your meter as well as mine. The analog version is preferred over the digital version for its superior high frequency response, and it is the one the corrections were established with and for. If you are so inclined, you can modify the meter with some capacitor changes and a better electret mic capsule (cheap and obtainable from Digi-Key) and improve the meter's response so that the corrections are no longer needed. Running repeated tests and charting the results is mighty tedious, and I'd recommend wearing earplugs to protect your hearing and preserve your sanity. Considering the HUGE frequency response deviations exhibited by virtually all speakers/rooms, the testing is worth the effort if you are able to make constructive changes based on the measurements. But, if there's nothing you can do about a mountain-range response, you might be happier not having it staring you in the face! Personally, I think that correcting (or at least minimizing) these gross frequency response errors caused by speaker-to-room interactions yields a more significant improvement to a system than most of the stuff we spend our time and money on.
Here are some sites/pages to check out:
(Sorry, but I don't even know how to make these active links, much less generate and post beautiful graphics! I guess you'll have to cut and paste...)
1) http://216.150.71.139/audioinnovation/rsmeter.html
2) http://www.hometheaterforum.com/uub/Archives/Archive-000001/HTML/19990806-17-000048.html
3) http://www.audiophilia.com/hardware/spl.htm
4) http://www.smr-archive.com/forum_3/messages/1220.shtml
5) http://www.gti.net/wallin/audio/audio.html |
Jaycee, thanks for the response.
I ended up buying a different instrument to test with, after some people had pointed out the flaws in the methodology I was using here, and using different test methods. Some of the things seen in the graphs above were artifacts from the RS meter used, but not all.
Using my Terrasonde The Audio Toolbox 2, a handheld, calibrated SPL meter, tone generater, and real time spectrum analyser, I did the tests again with pink noise and slow C weighting. I found that I had a high-frequency and a bass problem. The high frequency problem was mainly caused by reflections from the walls it seems; hanging a rug about 2.5" from my back wall solved most of that. Right now, my in-room response abve about 400Hz is within +/- .5dB! The difference is amazing... Imaging improved incredibly, and the system sounds 'calm' now.
As for the bass problems, I tried building some traps using the mthods found in an article on headphone.com, but I made some calculation mistakes, so they did more harm than good. Then I found the ASC website, they sell accoustical products to deal with room acoustics, and offer a free consulting service. I have provided them with room and frequency response information, and they are working up a solution for the bass problem. We shall see what comes out of it...
Niels. |
Njonker, is it possible for you to show the graph of your room before treatment with the toolbox. I've been intrigued by this product, and was wondering just how different the results were. |
Niels,
The correction for the Radioshake meter are as follows. Replot the response by ADDING the correction values to measure values and then seee where you stand.
Freq correction
20 6.2
25 4.4
31.5 3
40 2
50 1.3
63 0.8
80 0.5
100 0.3
125 0.2
160 0.1
200 0
250 0
315 0
400 0
500 0
630 0
800 0
1000 0
1250 0
1600 0.1
2000 0.2
2500 0.3
3150 0.5
4000 0.8
5000 1.3
6300 2
8000 3
10000 4.4
12500 6.2
16000 8.5
20000 11.2 |
