Originally Posted by Matt Fowler
In regards to this:
"With no subwoofer boost, beyond the original Audyssey calibration, the regular channels should have peaks of up to 105dB and the LFE channel should have peaks of up to 115dB, with the right 5.1 movie content, at a master volume of 0.0. "
Based on the BEQ charts I believe very few movies have peaks at 115db at reference at a single frequency, but if they do they would show up on the graph as -10dbfs. So when I run a sweep in rew at 12dbfs its like a 113db signal were it in a movie track. That is just one frequency though, a scene could be playing multiple frequencies or employing a bass management scenario where the actual peak is a composite of frequencies (say its a blend of 15-18hz content) that combines to goes way over 115db. Maybe I have this concept horribly wrong.
You don't have the concept horribly wrong, but the engineer in you is trying to turn a general principle into a physical actuality. Dolby/THX Reference was designed as a way to set a safe volume level for movies, and as a way to establish uniformity in the movie-making and movie-watching industry. 85dB was established as a normative average volume level for a 5.1 movie, with dynamic peaks allowed of up to 105dB for the regular channels, and 115dB for the LFE channel.
Those commercial cinema standards were then applied to home theater. Where an HT system has been calibrated to Reference, via something like Audyssey, the system should be able to hit peaks of approximately 105dB for the regular channels, and 115dB for the LFE channel, at a master volume level of 0.0. (That's with no subwoofer boost added--just the calibrated trim levels.)
The numbers listed above are approximate because all measurement microphones, including the Audyssey mics used for calibration, have some error factor. With the Audyssey mics, the error factor is +/-3dB, and with your UMIK-1, it is +/- 1.5dB.
But, that's just the audio system, what about the actual movies? Nothing says that a movie has to be recorded at an average volume of 85dB, and most movies aren't. Film mixers don't actually pay any attention to average volume levels for cinematic releases (they have to for some TV movies and programs, depending on the network).
So, the "average" volume levels can be higher or lower than 85dB. And, they may have many peaks, or very few. They may reach 105/115dB repeatedly, or never at all. And, that's not just the difference between a blockbuster and a light romantic comedy. The volume differences apply to action movies and blockbusters, too. They just aren't supposed to exceed
peak volumes of 105/115dB. (Incidentally, all of the above is covered in Section II-A of the Guide.)
If you want to know how loud a particular movie is, with your system, in your room, then you need to measure it. Anything else, including BEQ graphs, may not be reliable for your
calibrated system, at your
volume levels and with your
subwoofer boosts. That's what I mean when I say that you can't go from a general principle, such as Dolby/THX Reference, to a physical actuality for any given movie. The industry established some maximum safe listening and calibration standards, but the actuality varies from room-to-room, and from movie-to-movie.
One additional way that the actuality varies is with respect to the way that we perceive volume in smaller rooms. According to SMPTE RP 200, in rooms below 20,000^3 (which would include all HT's) we perceive loudness differently than we do in a commercial cinema. That's due to room boundary effects for all frequencies. (Think of the difference between singing in the shower, versus in a very large room.) For instance, in your 6,000^3 room, a master volume level of -5 MV would correspond to Reference (0.0 MV) in a commercial cinema.
I remember that you wanted to find a formula to tell you how loudly you should listen, and how much subwoofer boost you should use. In the end though, I think that it has to be a personal decision. I know that when I first got my current subwoofers, I pushed them pretty hard to find out what their ceiling was. But, I gave out before they did.
In the last couple of years, I have been very content just to listen at whatever volume level seems comfortable, or pleasant, or exciting, depending on my mood at that particular time, without caring as much about the actual volume level, or the subwoofer boost. You may or may not reach a similar equilibrium point in time, after you have experimented as much as you care to.
But, in my case, I found that it was a more relaxed way to enjoy my audio, and I think that I am protecting my hearing a little more, now that I am not trying to push the envelope quite as much.
I hope that this discussion helps to clarify things a little more, because I am pretty tapped-out now.