REW SPL Data Logger to Cal AVR Speaker Levels - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 4 Old 02-01-18, 06:01 PM Thread Starter
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REW SPL Data Logger to Cal AVR Speaker Levels

Well, Iím deep in the process of trying to integrate 2 different subwoofers with an existing 7.2 home theater system using a miniDSP 2x4 DSP for the subs. However, thatís not what this post is about. During this process I decided to do baseline measurements of the existing speaker settings. One of the first things to check is the volume balance of each of the speakers. I have in the past used a Radio Shack analog SPL meter both hand held and on a tripod. However, I really didnít think that it was easy or an accurate method. The AVRís pink noise signal causes variations on the meter readings. Also, you have to be close enough to be in viewing distance of the meter face to read it, but not in the way of the sound. I really think this close proximity affects the direct or the reflected SPL meter readings.

While exploring and learning some of the vast array of capabilities of the REW software, I came across the Logger button on the SPL Meter window. I tried clicking on it several times with no specific intent to see what it would do. Then, it finally hit me! Why not use this to log the AVR speaker level calibration output with the measurement Mic used for frequency response or other more typical REW uses.

So, after thinking a little bit, I decided to test my existing calibrated speaker levels by setting up the AVR to the Speaker Level Calibration Menu and cycle through the speaker outputs with the Mic in the main Listening Position. I could change the AVR speaker level setting (with the IR Remote) from out of the way and then wait as long as I wanted on each speaker to get a real time averaged plot of its level. I really didnít even care if the Mic and/or SPL Meter were calibrated. All I wanted to do was watch and match the levels coming out of each speaker and the subwoofers. So, I ran through the baseline data log for all the speakers. When I changed to the next speaker, there was a convenient sharp drop in level that the logger picked up to mark the event. So, after the first run through of all the speakers, I looked at the chart data and decided to go back and change the AVR speaker level setting for the speakers that needed either more or less gain. I found for my situation this was the easiest method because of the location of my PC that was running REW and the viewing angle of my AVR and its display.

Well, to my surprise and after 3 attempts (see pictures below). I finally got all speakersí level matched within +/- 0.5db with verifiable data to prove its accuracy (within the limits of the Mic and AVR settings capabilities). This method for my AVR (that only allows 1db level changes) was much better than when I started. I also feel that this calibration method would result in a more accurate and repeatable settings with less side effects like meter reading variations and not being physically near the measurement Mic!

I would be interested in hearing whether anyone else has done this or have I just reinvented the wheel! Anyway, I would really like to hear about other ways to use REW that may be lesser known but useful.
Attached Thumbnails
REW SPL Data Logger to Cal AVR Speaker Levels-hts-01-avr-spkr-cal-levels-lf-subs.jpg  

REW SPL Data Logger to Cal AVR Speaker Levels-hts-02-avr-spkr-cal-levels-lf-subs-adjust-01.jpg  

REW SPL Data Logger to Cal AVR Speaker Levels-hts-03-avr-spkr-cal-levels-lf-subs-adjust-02.jpg  

REW SPL Data Logger to Cal AVR Speaker Levels-hts-04-avr-spkr-cal-levels-lf-subs-adjust-03.jpg  

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post #2 of 4 Old 02-02-18, 08:20 AM Thread Starter
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Summary of AVR Speaker Level Calibration Method Data

I just wanted to summarize the results that I achieved with this AVR Speaker Level Calibration Method. The first Log Chart shows the baseline level measurement accuracy of a previously done careful adjustment with the analog Radio Shack SPL meter. Itís +2.5db to -5db from an arbitrary 60db reference. Thatís a 7.5db variation in loudness between all the speakers. The most error seems to be the subwoofers SPL at -5db. This may be the inaccuracy of the RS SPL meter at low frequencies or the difficulty in interpreting the variations of level with pink noise test signal or both. The first try adjusts speaker levels to a reduced spread of 3db from the original 7.5db. The 2nd try further improved the variation max/min SPL variation to 1.5db. Finally, after the 3rd try of changing speaker level settings I had approximately 1db (or +/-0.5db) of variations - the lower limit of my AVR level adjustment capability at 1db increments.

If you try this method, I would be interested in hearing whether your previously set levels were right on or as bad as mine were when I started.
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post #3 of 4 Old 02-03-18, 06:57 PM
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Re: REW SPL Data Logger to Cal AVR Speaker Levels

Pretty clever – yes, you may indeed have re-invented the wheel!

Personally I don’t have any problems using a meter with the receiver test tones. If the meter fluctuates, I just use the highest figure it registers for all speakers (or the lowest, whatever I’m in the mood for). Even without the meter, I would certainly be able hear a 2 dB difference...

Regards,
Wayne



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post #4 of 4 Old 02-04-18, 12:03 PM Thread Starter
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AVR Speaker Level Setting Technic

Quote:
Wayne A. Pflughaupt wrote: View Post
Pretty clever - ...
I’ll take that comment to mean you have not seen this particular use for the SPL Data Logger function. I too in the past have exclusively used the Radio Shack analog SPL meter for gain matching my 7.2 HT System. However, I always questioned the accuracy of the settings because of measurement fluctuations and proximity to the measurement mic of the meter.

An observation to note is the Subwoofer (the last measurement slot at about 2:00 [min:sec]) SPL variations are definitely larger (maybe +/-2db or 4db total) than the main, center or all surround speakers. In addition the low frequency accuracy for the RS SPL meter may require a 3-6db correction factor.

I do know that gain settings can be critical to getting a good L/R balance or a solid centered sound image. Also small gain changes can be the differences between subjective evaluations. I do know that after trying this Speaker Level Matching technic, I now feel confident that I have all speakers matched as close as I can set or measure. I don’t have a pair of “golden ears” that I trust. I do like the more absolute and verifiable results that the REW SPL Data Logger can give me.

I would suggest that if you are going through the trouble of doing REW measurements for whatever your reason that you first start with this Speaker Gain Level Check and/or Adjustment so you know exactly where you stand. Then after all your system changes and adjustments to ensure that nothing has affected those baseline Gain Level settings.

I have a feeling you may be surprised, as I was, that this is not as easy to do accurately as you originally thought!
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avr , cal , data , levels , logger , rew , speaker , spl

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