"The paper you just referenced specifically referred to using pink noise for low precision 1/3 octave measurements and the paper stated that to get accurate measurements, you need to average measurements over a time period due to the random structure of the signal. I referred to these issues in my previous reply. Such low precision measurements are useless for analysis of a room in order to find and correct many low frequency problems." - WmAx
I think the problem was that the THX/Rane manual is aiming for:
"Remember that we are trying to achieve a response in the LCR channels of ±1 to 2 dB from 100 Hz to 1 kHZ without drastic EQ shifts."
and -
"When equalizing the Subwoofer Channel, you should concentrate on reducing the serious peaks. You may find that because of the depth of the room modes a ruler flat response is not within the range of the equalizer. This not a major concern since a response within ± 3 or 4 dB is very acceptable."
Perhaps then the use of pink noise is done with the knowledge that accurate low frequency equalisation is not required. Considering the accuracy and performance of most domestic subwoofers, this is probably a perfectly fair thing to do.
The book I referred to earlier does make the point that a flat response is not necessarily desirable in a normal domestic, or even professional, set up. This is because rooms with low reverberation times in the mid-range and treble aren't very pleasant to work in. Therefore the bass increase which is normally present in normal living rooms is in some ways a good thing, as it helps to hide treble/mid-range reverberation. In a real musical performance however, at a good venue, the sound field would be diffuse at all frequencies. It does go on to say that many professional studios do take measures to make reduce large peaks in low frequency reverberation.
As for the psychoacoustics of pink noise, mentioned earlier:
"Research done a decade earlier by C.P. and C.R. Boner defined a need for a "house curve". They based this on the fact that a flat electro-acoustic frequency response in a large room sounds too bright on well-balanced program material. Or in simpler phrase, we perceive sound in a large room to have more treble."
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http://www.hometheaterhifi.com/volume_9_2/feature-article-curves-6-2002.html
This is with regard to the 'x-curve' used in cinemas.
"The measurement of EQ is done using wideband pink noise excitation through the speaker. The larger the room, the longer and greater the reverberation buildup over time, resulting from this steady-state signal. If we measure EQ on a fixed bandwidth basis, like full octaves or third octaves, the reverb which tends to be stronger at low frequencies will tend to make the SPL read louder there than at the higher frequencies where it is better absorbed. By knowing how much the meter reading is influenced by this effect, a curve can be used to compensate."
Maybe this is why the THX/Rane manual says -
"Because of this perception of flat tonal balance, pink noise is a very useful tool when using a spectrum analyzer with 1/3 octave or octave measurement intervals, and when comparing loudspeakers for spectral similarity by ear".
As Chris said earlier, the key thing here with perceived tonal balance is only useful for loudspeaker comparision by ear. It's all a bit confusing really and not very important.
