Hifi critic article 10-12/2013
There's an excellent article from Martin Colloms concerning loudspeaker design wherein he explains problems with reflex/ported loudspeakers in the time domain. He shows the group delay problem this type of speaker exhibits. One of the real world examples he uses is from various studio mixing engineers at different locations. It was shown these engineers were EQing the bass differently for the same program material. It was discovered that these engineers were simply calibrating their in room monitors using steady state test signals to achieve a "flat" FR. Of course, the EQ differences were shown to be caused not by the FR difference but due to the time domain differences with their loudspeaker's group delay. That is, bass may measure flat with a steady state signal but not perceived that way given sufficiently poor time behavior.
Michael123,
You are only seeing one-half of the coin. The other half is in the time domain. The time domain anomalies affect how much of a particular frequency you hear. FR and time domain are interrelated. Interestingly, Colloms makes the case that the group delay problems with bass reflex speakers can be corrected with DSP. In some cases, a correction of up to 10 feet may be necessary.
Modern day DSP shouldn't be thought of as an EQ. The best DSPs correct BOTH FR and time domain. Btw, I don't know anyone that sets a full range target curve to flat. I think Amir has posted the Harmon studies showing the curves that people tend to prefer. Most DSP designers will offer recommended curves. Those are usually backed with many listening tests and can be tailored to personal preference.
Michael.