would be 12.5 o'clock, but for few second only), so I'm not sure I will ever want to listen to movies at such a high SPL level. I usually listen to music with knob position somewhere between 11 and 12 o'clock (an absolute max. The amplifier used here was an Yamaha A-S701 that has about 185W/channel on 4 Ohms speakers, so enough "juice" to rich the THX goal, so while playing -20dB from above (with over-the-ear closed headphones, to protect my hearing) I was able to get a 85dB SPL reading from REW with volume potentiometer at 1 o'clock position. To protect our hearing, the audio files used for such test are usually -20dB instead of 0dB, so we will need to measure a listening level of 85dB SPL, which is much safe for our hearing than 105dB SPL. If you have a calibrated SPL meter it might be more simple worth notice that apps like DecibelX might not be perfect for use here, because I noticed a 10dB higher reading than my ECM999/Focusrite with pink noise, although with 440Hz sine was identical readings.Īudio files to do the measurements are -20dB and were grabbed from (also attached here) and I had them "checked" with foobar and its Peak-meter visualization and these are indeed -20dB files. Same setup was used to measure speaker's output too. Using REW to measure room's acoustics could be read here. I've used a Superlux ECM999 connected to Focusrite Solo Gen3 and measured my room's background noise and I found about 26-27dB SPL. Of course, for balanced amplifiers a 4V RMS balanced DAC would be required and for those with built-in DAC in your home-theater system you will probably don't need to care much about the inside DAC's level. I used a fixed-output 2V RMS DAC, but if using a volume controlled DAC a true-RMS multimeter or a scope can be used to accurately measure the output level for 2V RMS and mark the correct volume knob position. Stereo speakers used are CANTON GLE496 with a sensitivity of about 90dB/. Then, I moved in my living room where room size is more generous (25m2) and the two SB1000 can hit 115dB SPL for sure. I tried to rich the THX Reference Level in my bedroom (15m2), but my Mackie subwoofer can't get to 115dB SPL, although my active monitors can get to the required 105dB but the level of distortions coming from both speakers and furniture, when playing -20dB pink noise, was rather high, so I gave up. Given an in-home silence of 25-30dB SPL, that means a dynamic of about 75-80dB for the full-range speakers and up to 90dB for the low-end bass. However, the desired reference level for watching/listening movies is 105dB SPL for full-range speakers and 115dB SPL for the low-end octaves, so for subwoofers. The idea behind finding the THX Reference Level for our home-use audio equipment is to ensure a good dynamic for watching movies, well.at least this is how the THX guys think that it should be, so I'm sure they're right, at least for cinemas. A very good read would be Techniques-for-establishing-and-maintaining-audio-loudness.pdf and cinema_calibration_tech_report.pdf, both attached to this post. A very good article about the THX Reference Level would be. I've seen several threads on Internet forums about measuring THX Reference Level on our domestic audio equipment from home.
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