Down With Flat!
Although we like to think of audio as high-tech and up-to-the-minute, it, like virtually everything else, is hidebound by rituals, mental sets, and assumptions that have no better basis than simple tradition. One of these is flat frequency response.
The reason flat frequency response has become an audio tradition is because it seems to make so much sense. The obverse of GIGO (footnote 1), the FFR view is that, if you present to the human ear the same frequency response as existed in the concert hail, the result will be a spectral balance which the ears perceive as identical to the original sound. What could be more self-evident? Nothing, except that this traditional approach to audio component design doesn't always work very well.
There are, however, many cases where it does. Microphones, phono cartridges, and audio electronics almost invariably sound pretty much the way their measured frequency responses suggest they would. (At least, they do if that response curve doesn't come packed in the box with a Japanese phono cartridge.)
But loudspeakers? Well, Sir, something is very much amiss in the world of loudspeakers.
Just about every manufacturer of high-end speaker systems brags about how flat their frequency response is because, of course, flatness is considered one of the prime objectives of any audio-component design. Unfortunately, in a loudspeaker, the flat frequency response doesn't seem to work.
Many times in past years I have been impressed by the incredible flatness of the measured high-end response of some speakers: almost like the proverbial straight edge out to 15kHz, and sometimes beyond. In every such case, I have been equally amazed at how positively awful those loudspeakers sounded—so tipped-up at the high end that could not enjoy listening to them. (They aroused a deep nostalgia for the days when preamps all had tone controls.)
Nor am I the first to have observed that an objectively flat high end sounds tipped up. Ever since acoustical engineers started using equalizers to "voice" recording studios and monitor systems, they have observed this marked disparity between what measures flat at the top and what sounds flat. They were all ultimately reduced to pulling down the whole high end and—Heaven forbid!— adjusting it by ear. No one seems to know why this is so, but the important thing right now is that it is.
That flat/rising high end has become an even greater liability for loudspeakers since Compact Disc came along, because CD players and discs are not subject to the HF and detailing losses we all grew so accustomed to and comfortable with (tradition) from analog discs. If a "flat" speaker needs a 2dB pull-down at 10kHz with analog sources, it usually needs about 4dB with CDs.
Similarly, audiophile loudspeakers that measure flat through the lower middle range seem to have a penchant for sounding sucked-out and gutless through that region.
Footnote 1: For those who aren't into computing, GIGO stands for Garbage In, Garbage Out: ie you feed a computer misinformation or wrong instructions, and it is guaranteed to hand you back a perfectly logical wrong answer. Our nation's president, whomever he may be at the time, should keep on his desk a plaque bearing this acronym.—JGH