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Clarifying “target EQ” in my mind.

rdenney

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I read where people are using the downward spectral tilt of the expected in-room measurement as a target for automated DSP room correction.

But I’m missing something. I understand from Toole that the tilt is not a target, which I interpret to mean an objective to be attained, but rather an outcome of other attributes.

Toole tells us that equalizing to force a speaker to overcome room issues (in the region above ~400 Hz) is a fool’s errand, because people hear through those room resonances naturally, and forcing it electronically may make a good speaker bad. He insists that EQ should only be applied to correct anechoic frequency response, not in-room response, except in the bass region.

As I read it, downward tilt is an outcome of a speaker’s tendency to have reduced high frequencies off-axis. Flat on-axis response mixes with treble-shy off-axis response to create something in between. If the mixed tilt is too steep, the speaker may have poor high-frequency dispersion or the first reflections may be too dominant. Toole tells us this cannot be repaired with electronics, and we need to damp first reflections or get better speakers.

He likens it to adding another layer of the circle of confusion. He concludes we should only equalize to flatten the on-exis anechoic response, particular for good speakers that have similar frequency response shapes off-axis.

Therefore, the downward tilt simply can’t be a target for automated room processing. At best, it’s a validation of room treatments, speaker selection and placement. But it seems to me that a speaker with infinite directivity might have little or no downward tilt in the room and still be ideal.

The bass region is a whole other topic, of course.

Do I have that right?

Rick “worshipping at the Floyd Toole altar at present” Denney
 

NTK

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I'm copying here Dr Toole's explanation in a post in AVS Forum (with my emphasis):
https://www.avsforum.com/threads/of...theater-thread.2515137/page-168#post-57820394

Some thoughts on room EQ and the "Harman" curve
This discussion illustrates some fundamental issues with respect to room equalization. I spend many pages in my book discussing this in detail, but here are some simplified thoughts.​
As the "creator" of the "new Harman target curve" I can clear up some misunderstandings. Those who have the 3rd edition of my book can see where the curve came from - Figure 12.4. It is nothing more than the steady-state room curve that results from measuring any of several forward-firing loudspeakers that have been awarded very high ratings in double-blind listening tests. These steady-state room curves are substantially predictable from the "early reflections" curve in the spinoramas, as is illustrated.​
Now, if you measure such a curve or something very close to it, and your speakers are conventional forward firing designs, it means that you probably have chosen well. Small tilt-like deviations may be seen and broadband tone-control-like adjustments can be made to achieve a satisfactory overall spectral balance. No small detail adjustments should be made because it is highly likely that they are acoustical interference (non-minimum-phase) phenomena that two ears and a brain interpret as innocent spaciousness - room sound. "Correcting" these is likely to degrade the audible performance of truly good loudspeakers - unfortunately this behavior is not uncommon in auto-EQ algorithms created by companies that do not make loudspeakers. Their marketing philosophy is that their magic can make any loudspeaker in any room into a perfect system. Sorry, but a small omni mic and an analyzer are not the equivalent of two ears and a brain. It is not uncommon to be forced to override auto EQ with manual adjustments to restore the inherent sound quality of excellent loudspeakers. In some cases the "off" icon is the preferred solution.​
The simple fact is that a steady-state room curve is not accurately descriptive of sound quality - comprehensive anechoic data are remarkably capable, but such data are rare.​
The Harman curve is not a "target" in the sense that any flawed loudspeaker can be equalized to match it and superb sound will be the reward. The most common flaws in loudspeakers are resonances (which frequently are not visible in room curves) and irregular directivity (which cannot be corrected by equalization). The only solution to both problems is better loudspeakers, the evidence of which is in comprehensive anechoic data.​
Remember, the Harman curve relates to conventional forward-firing loudspeaker designs. Legitimate reasons for differences are different loudspeaker directivities - omni, dipoles, etc. - or rooms that are elaborately acoustically treated, or both.
If a "target' curve has been achieved, and the sound quality is not satisfactory, the suggestion is often to go into the menu, find the manual adjustment routine, and play around with the shape of the curve until you or your customer like the sound. This is not a calibration. This is a subjective exercise in manipulating an elaborate tone control. Once set it is fixed, and in it will be reflected timbral features of the music being listened to at the time. In other words, the circle of confusion is now included in the system setup. By all means do it, but do not think that the exercise has been a "calibration". Old fashioned bass & treble tone controls and modern "tilt" controls are the answer and they can be changed at will to compensate for personal taste and excesses or deficiencies in recordings. Sadly, many "high end" products do not have tone controls - dumb. It is assumed that recordings are universally "perfect" - wrong!​
All that said, equalization of steady-state room curves at low frequencies is almost mandatory in small rooms. Multiple subwoofers can reduce seat-to-seat variations so that the EQ works for more than one listener - Chapter 8.​
Those wanting to dig deeper can read my book or look at this open-access paper:​
Toole, F. E. (2015). “The Measurement and Calibration of Sound Reproducing Systems”, J. Audio Eng. Soc., vol. 63, pp.512-541. This is an open-access paper available to non-members at www.aes.org
 

MZKM

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If I understand correctly, you mainly should correct peaks/dips.
If a speaker runs too hot, maybe apply a shelf filter.

However, the slope of the in-room curve is not representative of bright/dull sounding, as that’s based off dispersion.
 
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