Here was my methodology.
1. Set the trim in the AVR equal to zero for the left, center, right and sub channels as a starting point.
2. Set all speakers to cross over at 80Hz. Set sub LPF to 120Hz. Shut off sub.
3. Launched REW and opened the REW SPL tool so I could measure sound output using the calibrated UMIK-1.
4. Placed the UMIK-1 in the MLP at ear height, pointed at the ceiling.
5. Set my AVR to "stereo" mode.
6. Played the internal AVR pink noise for L. This disables my volume control. I adjusted the gain on the L monitor so that it was reading as close to 75dB as possible (73.6dB) using the small gain dial.
7. I then adjusted my iPhone SPL meter to also read 73.6dB, slow C weighted.
8. I turn off the L monitor, turn on the sub and play the AVR pink noise for the sub.
9. I adjusted the sub volume knob to read as close to 73.6dB as I could via the REW SPL meter. I had a choice of either 75.5dB, or 72.4dB. I chose the former (and later test with the later).
10. The iPhone app at this point reads 64.5dB for the sub. Well worth that $4.
Can we agree that at this point, my sub should
be level matched (within a few dB) to my L channel? At least according to the AVR?
Now to compare to REW.
11. Opened the REW signal generator, selected Pink Noise, "Full Range" output, and set the dB FS output to -20.
12. Set output to Channel 1 & Channel 2. Turned off the sub, turned on L channel.
13. Played the full range pink noise tone and raised the AVR main volume until REW SPL was showing 75dB.
14. Verified the AVR was seeing 2 channel PCM and set to "stereo".
15. Turned off the L speaker and turned on the sub.
16. Played the full range pink noise tone again and found the sub was reading 79dB in REW, and 64.4 on the iPhone.
Burned a CD containing two FS pink noise tones, one from the realtraps test tone Cd
, and the other from the Blue Sky test tone CD
(which I know was recorded at -20dB FS).
Played them through my oppo 970HD, adjusting main volume of the left to be 73.6dB and then comparing to what the sub read.
Found a discrepancy again.
Don't trust my oppo as I've never really found it's audio setup to be very user friendly.
17. Switched out to my Sony Blu-ray, which outputs raw PCM for CDs.
18. Verified that is what the AVR was seeing.
19. Adjusted volume on the AVR so that L was reading 73.6dB for the blue skies tone. AVR volume was then -8.5.
20. Sub then read 78.9dB and iPhone read 64dB.
21. Tried the real traps tone and set L to read 73.6dB in REW.
22. AVR volume was then -14.5.
23. Sub read 80dB and iPhone read 64.5dB.
AVR and test tone CD do not agree.
So here we have the following
AVR sets L at 73.6dB and Sub at 75.5dB.
Cross referenced with REW L is 73.6dB and Sub is 79dB (+3.5
Cross referenced with Realtraps L is 73.6dB and Sub is 80dB (+4.5
Cross referenced with Blue Skies L is 73.6dB and Sub is 78.9dB (+3.4
In all these cases the sub is high, so I redid the initial AVR setting and chose 72.4 (next volume notch down) and repeated this procedure with REW, omitting the test tone CD as it agrees quite closely with REW. This is what I found:
AVR sets L at 73.6dB and Sub at 72.4dB.
Cross referenced with REW L is 73.6dB and Sub is 76.4dB (+4.0
This mirror's quite closely the smoothed response I posted earlier between my AVR and REWs settings, which I was eyeballing as a 5dB difference.
Which is more likely in this scenario? I am screwing up something in what I have listed above, or my AVR does not output an accurate sub pink noise signal? I'm leaning toward the later.
I tried the RTA method and it had me land up exactly where REW's full range pink noise signal had me set the subwoofer level.