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For the longest time, I wanted to measure the frequency characteristics of my listening room. Using the Stereophile Test CD2 (tracks 16,17 and 18) and Radio Shack SPL meter, I measured the frequency response of my listening room recently. My Thiel 3.6 speakers were driven by Audio Research 100.2 amp.SPL-(dB)-76--75--74--73--72--71--70--69--68--67--66
16.0-kHz------------------------------------------*
12.5----------------------------------------------*
10.0--------------------------------------*--------
-8.0----------*------------------------------------
-6.3----------*------------------------------------
-5.0------------------*----------------------------
-4.0--------------------------*--------------------
-3.15---------------------*------------------------
-2.50---------------------*------------------------
-2.00---------------------*------------------------
-1.60---------------------*------------------------
-1.25-------------------------*--------------------
-1.00-----------------------------*----------------
800-Hz----------------------------*----------------
630-------------------------------*----------------
500---------------------------------------*--------
400---------------------------------------*--------
315-------------------------------*----------------
250-----------*------------------------------------
200-----------*------------------------------------
160-----------*------------------------------------
125---------------*--------------------------------
100---------------*--------------------------------
-80-----------*------------------------------------Volume level was setup so that SPL reading was 70dB at 1kHz. As you can see, there is a 72dB (2dB gain difference) plateau between 1.6-3.15kHz. This could be responsible for slightly bright sound I hear every now and then although I almost always blame my speakers. Further, 6.3-8kHz is at 75dB level (5dB gain difference) and this too also contribute to my problems.
Is there a way to reduce these humps in the above frequency response WITHOUT using an equilizer?? Room treatments are what I have in mind. However, these room modes are problamatic and I may have to live with it until I change my room. Moving the speakers and the changing listening chair position are another options. What are your experiences? What would be the most effective?? Like to hear from you.
Thanks
Priyap.s. All values in the above figure are POSITIVE
Follow Ups:
If you are not familiar with the following site, you might want to check it out:http://www.geocities.com/jonrisch/a.htm
First off you "only" have a about a 10db range. Not bad actually!Next I've read that the RS SPL meter is inaccurate above 10khz so you may want to take those readings with a grain of salt.
Finally, the dip a 500 follwed by a rise ast 250 is classic "suck out" or "Alison effect". An equalizer won't help. If certain waves lengths are being cancelled by reflections, trying to boost them just results in frustration. (You can't amplify somethin' you ain't got.)
The classic solution is to buy Alison speakers! This may not be something you care for. Two other approaches: 1- the simplest is to experiment with moving your speakers a couple of inches at a time, however, the optimal position may be impractical (and besides this often just relocates the dips and peaks to other parts of the spectrum) 2- room treatment, specifically absorbant material behind the speakers is the most likely prescription since that is probably the source of the reflections that cause cancellation. With luck this can be done with ordinary decor. Otherwise there are folk more than willing to take you money on sound-absorbant panels.
Sam-
Glad to hear I am within +/- 10dB range. Brad suggested that I calibrate these using a calibration curve (see his post below). After calibration, the frequencies between 315Hz-8.0kHz now falls within 68-73dB! A range of 5dB. That is quite encouraging.As I told Bruce (see below), I may have to cover the sidewalls and the front wall behind the speakers as they are reflective. If I have to guess, these walls may have a reflective coefficient of 50-60%. That cannot be good.
Sometime back, I wanted to buy a room treatment package. They wanted about $1200. This package included a bass trap, side, front and back wall treament. I just walked away. May be I should seriously consider it. First I'll try to experiment with bedsheets, drapes, etc. If it works, I'll be $1200 poor (LOL).
Priya
There folks who would die to have room max-min room response of 5db! I suspect any room treatment will be audible more in stereo image improvement than coloration.
I wouldn't worry about anything less than an indicated 4 db. A couple of ideas come to mind. First, the Thiels are tilted back, so the tweeter may generate some ceiling reflections. If there's a tasteful way to limit those, it might help. Other than that, keeping the speakers away from sidewalls or putting absorbent materials on sidewalls adjacent to the speaker might bring this down. You might also try adjusting toe-in.I assume you made these measurements at the listening position, equidistant from the speakers.
The problems you are complaining about are not room resonances. They are either the product of excess speaker radiation or excess reflection of certain frequencies back to the listening position. Looks like you have some room gain working in the bass, though.
Bruce-
Thanks for the explanation. You guessed it correctly. My speakers are barely toed-in. That pobably is the main problem. As a result, I may be getting that excess high frequencies reflected back to my listening position. Yes, I did measure these at my listening position.Also the side wall and front wall behind the speakers are reflective. I'll experiment by covering these area and see if I can reduce that hump around 1.6-3.15kHz.
All of my CD cabinets have glass doors!! I covered these with a bedsheet and got about 1-1.5 dB improvement. However, this may fall within the margin of error of the instrument and am not all that sure. Pushing the listening chair back is another option, but I don't want to get too close to the back wall!
Room gain in the bass can be solved by moving my furniture (couch, love seat, etc). When I move these around, low end of the spectrum change. At the moment, lowend sound sound ok. Although the speakers roll-off around 30Hz, my room can handle only down to 35Hz. The room gain in the bass, therefore, may be due to what I call, a "subwoofer effect."
These things never seems easy and I still keep trying (LOL).
Thanks
Priya
Hi Priya,There is a calibration file for the Radio Shack meter. If you haven't, you need to look at the following post that Nemo did a while back.
Have a great day,
Brad
Hi Brad,
I tried the website http://www.gti.net/wallin/rsmeterd.htm, but that has been either deleted or moved. Can you please check?Thanks
Priya
Hi Priya,Some of them work. Try the below one. I just tried it.
Brad
Hi Brad,
I read the alternative one. It says meter reading is not reliable outside 10kHz and 35Hz. My plot in the original post falls within that area. Hence, I am bit confused as what I have to do next. Are you suggesting that I do all the mods recommende on that page? This is begining to drain me a bit.I agree that I need to calibrate the meter outside those ranges, but if I am within, do I stiil have to do it? Also, the post was for the analog meter. I have the digital version. Do you remember if the ranges were the same?? Sorry to pounce you with these questions (LOL).
Priya
The adjustments are for the analog meter only. No one has published a correction curve for the digital one.
{B^}
Hi Priya,No, all you have to do is add or subtract from the number you took. If something says that at 30hz the meter is +2db, then you should subtract 2db from that reading.
I know that meter readings can drive a person crazy for a while. For one thing, it takes too long to get good readings across the board. Another thing, is you aren't getting small enough increments, to see how bad your room modes are. With my Tact RCS 2.2X, the increments are down to the 1/2 hz area and taken fully with subwoofers within 5 minutes. I can look at the results, move my speakers and try again. Once I try again, I can overlay one graph over the other and see if any improvements. This allows you to move speakers around to multiple locations and help find the best placement.
If you look under the FAQ section, there are some good papers written on speaker placement. That's a good place to start.
Some people might say, "let your ears be your guide", however it is almost impossible to compare 2 different locations from memory. Also, you might gain improvements in the bass and suffer in the midrange. You might perceive this as an improvement and not miss the loss in midrange until later. Very complicated subject.
Hope this helps some,
Brad
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