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Quote </td></tr><tr><td id="QUOTE">Please note the article says and I quote "85dB(A)". The "(A)" stands for "A weighting". Again, as I've said before, "A weighting" is much different than the "C weighting" that is used for most SPL measurements with music sources. "C weighting" will also typically register 10dB lower than "A weighting" on average for the same music signal source. In music much of the SPL level in the "C weighting" is due to the bass frequencies which the human ears are not as sensitive to.</td></tr></table>
The reason for this is C-weighting represents flat frequency response for the entire audio band with filtering outside of the bandwidth while A-weighting applies filtering outside of the midrange audio bandwidth.
A vs C weighing
how the human ear perceives loudness as a function of frequency is based on the Fletcher & Munson Curve. In actuality, the most damaging musical content at high listening levels to our ears is in the midrange from about 500Hz to 7kHz where we are most sensitive. There is little difference between A and C weighing at these frequencies thus the graphs that Yamahaluver pointed our are still valid.
Here is a link to the Fletcher & Munson Curve I used in a previous article:
http://audioholics.com/techtip....son.gif
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Quote </td></tr><tr><td id="QUOTE">Just to clarify, the reason THX recommends a 75dB SPL calibration level (not reference level), is because the calibration signal is attenuated by 30dB before it is recorded into the receiver/prepro software or onto a calibration DVD like Video Essentials, AVIA, or Sound & Vision. The HT reference SPL level has always been 105dB, even for THX. Thus when you play a DVD the reference volume will truly be capable of reaching 105dB (not 75dB).</td></tr></table>
Good clarification here Bruce, I agree, and I should have stated this more accurately. However, there is no reason why a good quality amp section in a high performance receiver cannot allow a user to reach this levels in a typical living room with reasonably efficient speakers, which constitutes most home theater speakers these days, with of course the exceptions such as ESL’s.
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My experience with many different systems is that strained sound at reference levels is caused by distortion components from either the amplifier or speaker or both and room reflections from a live room subtly influencing the quality of the sound. </td></tr></table>
I don’t fully understand your last comment as “Room acoustics” can have the most profound impact on the quality of sound for a system. This is an issue IMO many people fail to address in high performance systems.
[Edited: posted incorrect information about the differences between A and C weighing, corrected]</font>