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Room compensation (frequency flattening), good or bad?

All normal livingrooms have resonances. Some frequencies are amplified by the room. So you donīt get the flat frequency response your music equipment hopefully has if your musik is played through loudspeakers. There are lots of peaks in the frequency spectrum in a normal room
Therefore, some hifi enthusiasts try to counteract the fluctuations electronically.
In principle you connect a frequency generator to an amplifier (or there is one built-in), and do a sweep over the audio spectrum (20-20 000 Hz). Then you measure the sound preassure with a microphone, and compensate the input frequency response so that it compensates for the room frequencies. When the process is done, the microphone "hears" a flat response, the room resonances have been cancelled out.
This might seem to be good, but is it really? Not if you want the music to sound as if the musicians were playing right there in your room.. Why?

Your ears are not microphones connected to a flat response amplifier.
Instead, your perception of sound is strongly controlled by your brain.
If you read this in a "normal" room, are you constantly irritated by room resonances and echo? Probably not, unless you sit in an empty cellar. Does that mean that your room is virtually resonance free?
Not at all. A typical livingroom has a lot of resonances, between floor and ceiling, between parallell walls, tables to ceiling, underside of tables to floor, and between other hard surfaces in the room that reflect sound.

Our livingroom is pretty well damped. The sofa and armchairs are covered by velvet almost all the way down to the floor, the walls have bookshelves filled with books, and the Wilton carpet on the floor also dampens resonances. Still, when making a 100 - 1000 Hz sweep with less than 2 dB sound preassure variance close to the loudspeakers we measured a full 16 dB (!!!) peak (and a lot of 6 - 10 dB peaks at other frequencies) about 2½ meters (8 ft) from the loudspeakers (where we and our guests usually sit when listening to music).
And still, everyone who listens to music in our livingroom give us thumbs up for the perfect sound. No complaints about resonances ever. How can that be?

The brain.
If you come from a perfectly acoustically damped room directly into a normal livingroom you will be astonished by how much echoes and resonances there are in the livingroom. But not many seconds later they are gone.
Well, they are not gone, of course, but your brain has adjusted your hearing to the acoustics of the room. So if you play music in the room, your brain will "flatten the curve", and it sounds just as good as your music equipments allows.
But do a microphone recording of the music a few meters from the loudspeakers, go to a well damped room and listen to the recording through identical loudspeakers, and it will probably sound awful. Because now, when you are in another room your brain has re-adjusted your hearing, and you hear the resonances of the other room from the recording. Because the brain always adjusts for the room where you are. (As much as possible, but in an empty cellar or a parking garage there is simply too much echo and resonances for it to succeed.)

Because your brain keeps adjusting to room resonances, trying to equal out those resonances electronically, so a microphone will detect a flat frequency response, while the room is as it was before, will make the sound unnatural.

A practical illustration:
Letīs say someone is playing the piano in your livingroom. It will sound natural. (Of course, because it is person playing a real piano.)
Now you make a recording while he/she is playing, with the microphone as close to the piano as possible (so you record only the piano, with no interference from the room).
Then you replace the piano by a perfect sound source, a perfect amplifier and perfect loudspeakers placed where the piano was before. No frequency compensation, just a perfectly flat frequency response and no distortion.
What will happen? Well, as the sound from the loudspeakers is identical to the sound from the piano there will be no difference. It will sound exactly as if the person was playing on the real piano. It will sound perfectly natural.

However... If you had done a room compensation to the frequency curve of the amplifier it would not sound natural. Your brain would still adjust your hearingīs frequency response and flatten the resonance peaks of the room.
Letīs say there was a 10 dB peak at 500 Hz in your room. After a few seconds in that room your brain has lowered its sensitivity to this frequency by 10 dB, so you are not irritated by the 10 dB peak.
But your sound equipment has been "calibrated" so that 500 Hz is lowered by 10 dB to achieve a flat response measured by the test microphone...
Then you perceive a 10 dB dip! Because your brain had already compensated by 10 dB and now the electronics reduces the signal by another 10 dB at 500 Hz to make the microphone "hear" a flat frequency response.
The microphone will detect a perfect compensation, but your ears hear a 10 dB dip.

What most "experts" or "nerds" donīt take into consideration is how our hearing really works.
Our hearing is not a brainless microphone and amplifier combination. It is a highly sofisticated system that makes life easier and more pleasant. If the brain could not do room compensation, playing music and even listening to a person talking indoors would be a pain because of resonances and echo. But now the brain does an excellent job in calibrating your hearing for different room acoustics.

So... Is it good to use electronic room compensation to get a flat frequency response in a normal room?
Will electronic room compensation make the sound more natural?
NO, it will do the opposite.

If you want the impression of the musicians playing live in your room (and that is what Hi-Fi is really all about, isnīt it?), the sound equipment should have a flat response without any dips or peaks. Then, the sound from the loudspeakers will be affected by the room identically to how the sound from real live artists playing in the room would be. And that, I think, is real Hi-Fi. When you cannot hear if there is a living artist playing or a recording.