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cyclometh · Posted: Thu Aug 19, 2010 1:59 pm Post subject: Taking room measurements

I'm trying to get an idea of the characteristics of my studio using a tool called "Room EQ Wizard". It's ostensibly for doing acoustic measurements for home theaters, but can generate measurement graphs and waterfalls quite nicely.

The question is (and this may be painfully obvious) where is the best place to locate the speakers I'm using to generate the test tones? I normally don't use monitor speakers, just headphones, and I don't use this space for listening to music, etc.

What are some suggested parameters for measurements to take (start/end frequency, # of sweeps, etc?)

Thanks for any assistance as I try to get a handle on what the space "looks" like. Smile

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cyclometh · Posted: Thu Aug 19, 2010 2:24 pm Post subject:

If it helps:

Room is 10'2" (122 inches) W x 11'3" (135 inches) L x 7'6" (90 inches) H.

Floor is carpet over cement with underlayment of some type- it's not hard to walk on, but you can tell it's not wood underneath. Walls and ceiling are textured plaster over sheetrock.

Very crude layout drawing:

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Mike Sommer · Posted: Thu Aug 19, 2010 3:49 pm Post subject:

That will work. And reverse that set up so you can get a idea of what your listening position looks like. Them randomly take different measurements around the room. (Printout your diagram and mark the positions of where your took the measurements.)

What you'll end up with is a general picture of what your room looks like.

A bit of advice, put a heavy blanket on your desk to eliminate the resonance of the desk when testing in that area.

Good luck.
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Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

cyclometh · Posted: Thu Aug 19, 2010 3:53 pm Post subject:

Where should I locate the speakers used for the test tones? I'm running an amplifier to some relatively small PC-quality speakers at the moment, I have a single larger speaker also.

What I'm not clear on is where the best location for the sound source is when running the tests.

Also, tangentially-related: Is it more optimal to use the SPL meter's line output or my usual recording microphone for running the tests?

Is 0 to 20Khz, 4 sweeps going to get good data?

Thanks muchly!

(the boxy thing under the desk on the diagram is a chair- did you think that was where I had the speakers? If so, no trouble, I can do that easy)
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Mike Sommer · Posted: Thu Aug 19, 2010 4:16 pm Post subject:

cyclometh · Posted: Thu Aug 19, 2010 5:54 pm Post subject:

OK, I updated the graphic and took some measurements. Each position is numbered, and each has an SPL graph and a waterfall. To avoid spamming up the thread with ZOMGLOTSOFGRAPHS I've only posted the first 2 inline, the others are links. Smile

Except for Position 1 B (speaker facing away from Mic) all measurements were taken with the speaker facing the recording position, specifically sitting on the chair in the picture, pointing forward.

All tests were done from 0 to 20 kilohertz, using a single Infinity SM-82 speaker driven by a Kenwood amplifier. I followed the calibration instructions for the software to the letter and used a Radio Shack 33-4050 analog SPL meter mounted in a shockmount on a mic stand, using the line out of the SPL meter as the mic source.

cyclometh · Posted: Thu Aug 19, 2010 6:05 pm Post subject:

Looking at the numbers, I find myself wondering if I did it right, though. The values don't seem to correspond to the levels I would expect...
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Mike Sommer · Posted: Fri Aug 20, 2010 12:24 am Post subject:

Like I said the room is a bit of a mess. And this is typical of a small symmetrical room.

You have a deep Null at about 80Hz , and lost of comb filtering in the mids.

So now let's just focus on the area you will be doing your recording at, I can only assume this will be at your desk.

Set the mic at the 38% position of your room, which is about 51 inches off the wall; at the height of where your mouth would be. Set the speaker on the desk about 2 or 3 feet away from the mic, with the tweeter pointing at the mic.

I would like to see two full frequency test with no smoothing and with 1/32 smoothing.

I'd also like to see if you can get a low frequency test, with water falls as well. See if you can dial in these settings into your software:
Offset 45 ms
Duration 500 ms
Min Frequency 30 Hz
Max Frequency 300 Hz
Min Magnitude -40 dB
No smoothing

Let's see what you can get.
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The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

cyclometh · Posted: Fri Aug 20, 2010 12:56 am Post subject:

Will do, I'll take those measurements tomorrow when my family's not sleeping. Laugh

As to the parameters, the test parameter options are Start/End Freq, Level, Length (currently 256k), and Sweeps. I'm not sure how or if I can dial the other settings you mentioned into this software but I'll poke around and see what I can figure out.
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cyclometh · Posted: Fri Aug 20, 2010 7:17 pm Post subject:

As promised, I've taken the measurements as you requested- as closely as I could match the settings you wanted me to dial in to the software, in any case. For example, 1/32 smoothing was not available as an option, so I chose 1/48. I hope that is acceptable.

I believe I was incorrectly measuring with the first set I did yesterday,; I did not have the levels calibrated properly and there may have been some significant issues with the signal returned from the SPL meter due to cabling problems, which I've resolved with a trip to my music store for new cables. If you'd like I can take a new set of measurements in the various positions now that I have those issues sorted.

Anyway, I have 8 new graphs for you. I took 4 sets of measurements, all with the SPL Meter/Mic at 38% position, specifically 51 inches from the wall, at head height, in a shockmounted mic stand, with the mic oriented at the tweeter on an Infinity SM-82 speaker sitting on the desk almost exactly 2 feet away. Sound levels were calibrated to 75db in all tests.

* 0 to 20KHz, 4 Passes, 1/48 Smoothing
* 30 to 300Hz, 4 Passes, 1/48 Smoothing
* 0 to 20KHz, 4 Passes, No Smoothing
* 30 to 300Hz, 4 Passes, No Smoothing

For each test I generated an SPL graph and a waterfall. I'm posting them below as links.

0-20KHz, 1/48 Octave Smooothing:

SPL:
http://yafh.com/image/a2a82a49-test1.jpg
Waterfall:
http://yafh.com/image/21c1e633-test1_wf.jpg

30-300Hz, 1/48 Octave Smoothing:

SPL:
http://yafh.com/image/f1292ad0-test2.jpg
Waterfall:
http://yafh.com/image/93fc4021-test2_wf.jpg

0-20KHz, No Smoothing:

SPL:
http://yafh.com/image/8556c377-test4.jpg
Waterfall:
http://yafh.com/image/1819242a-test4_wf.jpg

30-300Hz, No Smoothing:

SPL:
http://yafh.com/image/e3ce8480-test3.jpg
Waterfall:
http://yafh.com/image/050e1c0b-test3_wf.jpg

P.S.
Thank you sincerely for your time and energy in helping out with all of this. It is sincerely appreciated.
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Mike Sommer · Posted: Fri Aug 20, 2010 8:16 pm Post subject:

This new round of test are a little better and with the no smoothing shows what's really going on. The low end is not really behaving as it was before. but these are good enough to move forward.

If you test again and move the mic position 4 or 5 inches you should get some different readings. If you don't mind I'd like to see what happens.

What these are telling me is that your are going to need a lot of bass trapping. and some very thick Broadband panels on the on the walls, including a cloud above the recording area.

As you proceed with treatment, you should take more measurements to see how the room improves.
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The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

cyclometh · Posted: Fri Aug 20, 2010 8:38 pm Post subject:

Will do. As I said, I believe that the new set of measurements are MUCH more accurate, as I had bad cabling in the first round- I discovered that when I listened to the actual signal from the SPL meter with my headphones it sounded like it was coming from the bottom of a cave that had water flowing in it. >.<

I'll post those tomorrow and move the mic a bit further away from the speakers.

Thanks again for the assistance.
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