OK, so it doesn't need to be a truly flat response, but Audyssey says they're trying for smooth, IIRC. If the low frequency dip in the response curve above isn't audible, I'll sell all of my equipment and use an iPod for the rest of my life.
Deep notches are clearly audible, especially when moving through the acoustic space and when a seating location is very close to that mode, it's extremely annoying. Not only do some bass notes disappear, if the person moves to either side, the phase problem will be similar to holding a working woofer that's receiving a signal with the axis perpendicular to the listener. Should we just accept the room modes and think that it's OK?
If the level of the notes isn't even and/or smooth as an instrument is played up and down the scale, how realistic is it? Obviously, an instrument can have "dead" notes, but a good one won't. This will change with distance to the instrument in free space, but when bad acoustics enter the equation, the distance doesn't need to change, only the listener's position.
So, the question exists- we can make it smooth with a "house curve", make it flat AND smooth with some dips and peaks, or tweak it so it sounds good to their test subjects. As a coarse measure, I always liked Yamaha's variable loudness control- the amount of correction needed depends on the SPL, so it makes a lot more sense than just a toggle switch. However, Murphy's Law means that some of the frequencies boosted will be excessively strong.
I also use Dynamic after I got a email from the Audyssey after I asked a question: What are the best Dynamic EQ settings for movies, music and games
" Movies are mixed in rooms calibrated for film reference. To achieve the same reference level in a home theater system each speaker level must be adjusted so that –30 dBFS band-limited (500 Hz – 2000 Hz) pink noise produces 75 dB sound pressure level at the listening position. A home theater system automatically calibrated by Audyssey MultEQ will play at reference level when the master volume control is set to the 0 dB position. At that level you can hear the mix at the same level the mixers heard it.
Audyssey Dynamic EQ is referenced to the standard film mix level. It makes adjustments to maintain the reference response and surround envelopment when the volume is turned down from 0 dB. However, film reference level is not always used in music or other non-film content. The Dynamic EQ Reference Level Offset provides three offsets from the film level reference (5 dB, 10 dB, and 15 dB) that can be selected when the mix level of the content is not within the standard.
0 dB (Film Ref): This is the default setting and should be used when listening to movies.
15 dB: Select this setting for pop/rock music or other program material that is mixed at very high listening levels and has a compressed dynamic range.
10 dB: Select this setting for jazz or other music that has a wider dynamic range. This setting should also be selected for TV content as that is usually mixed at 10 dB below film reference.
5 dB: Select this setting for content that has a very wide dynamic range like classical music."
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FWIW, those level settings should have - ahead of them, since they're showing the attenuation.
I would have to run Audyssey to try that- without running it, I don't think I EVER exceeded -12dB although the room size and surfaces have control over that. Once multiple reverberations become almost as loud as the direct sound, it sounds so bad there's no reason to continue at that SPL.
When I was using my Denon AVR, I didn't run Audyssey, but I did use the manual EQ and Room EQ Wizard to get a smooth response at the listening location, with the roll-off starting in the 1-2KHz range.
There are many reasons to EQ- to make it smooth, to make it easier to listen to, to make it fit someone's hearing deficit(s) or make it flat when that's what someone thinks it needs. However, I haven't seen many people talk about making it sound REAL. Real instruments aren't necessarily what the recording is mixed for and if the sound of the real instrument and the recording were compared via A/B switching, a lot of people would prefer the recording.
There will never be total agreement but if it sounds better, use it. The Harmon speaker test showed that most people preferred the same speakers, but if the test had been designed to find their preferred sound, I think it would have been more valid on an absolute scale. However, Dr Toole said that management went to him to find out why their speakers weren't selling as well as others, so it was purely a marketing test.