Equal-Loudness-Curves / Fletcher-Munson / ISO 226 / etc. - WHY do we care?

[smellygas]

This might seem like a silly question, but the equal-loudness contours (originally the Fletcher-Munson curves), and now the ISO 226 standard, all basically show the actual SPL (dB) loudness of a frequency that sounds just as loud as another frequency. It also shows that this varies based on the actual listening volume. But WHO CARES? - is what I want to know.

I mean, it's been very well established that a perfectly flat SPL vs. frequency curve, measured in an anechoic chamber, is what sounds best to listeners. So when we would we care about these equal-loudness curves, or for that matter, when would we want to equalize to conform to one of them?

SG

[454Casull]

In normal listening applications, you wouldn't want to equalize with respect to those curves.

They are useful for certain types of testing. Also for "rules of thumb" when it comes to determining which order of distortion is the most audible.

[pedroskova]

So when we would we care about these equal-loudness curves, or for that matter, when would we want to equalize to conform to one of them?

When you're measuring distortion at low frequencies and the harmonics fall in areas of the curve in which our hearing is much more acute. No amount of EQ'ing will help this.

[gedlee]

Basically you are right, they aren't very useful for audio playback. Some bass boost might be implied at low levels, this much is obviuos just from listening, but nothing more.

[LineSource]

Originally posted by smellygas
So when we would we care about these equal-loudness curves, or for that matter, when would we want to equalize to conform to one of them?

SG

If the recording microphones received a 100db SPL concert and you want to listen at 72db in your home, a db_record vs. db_play calibrated ISO 226 loudness coutour circuit adds dynamics that makes the music sound much more realistic. If you sat in the back of a live performance where the SPL was 72db much of the dynamics would also be lost. You want the dynamics and frequency SPL balance of stage mics at normal home listening levels.

It would sound best to just play the recording at 100db SPL in a dedicated room, and this is great a few hours each week, but just not normal daily home life.

[smellygas]

Hey, these are all very interesting replies. I was thinking along the same lines, but I wasn't 100% positive.

What kind of confuses me is why this guy:
http://web.mac.com/jon_whitledge/Whi...art1_jun08.pdf
equalizes his system to follow the inverse of a B-weighted curve. (i.e. 24dB boost at 20Hz and 11dB boost at 20kHz). Is there any merit to this? He references a JAES article from 1992. If this is an optimal equalization, I guess I'll pay $5 for the article.

SG

[chrisb]

Originally posted by smellygas
Hey, these are all very interesting replies. I was thinking along the same lines, but I wasn't 100% positive.

What kind of confuses me is why this guy:
http://web.mac.com/jon_whitledge/Whi...art1_jun08.pdf
equalizes his system to follow the inverse of a B-weighted curve. (i.e. 24dB boost at 20Hz and 11dB boost at 20kHz). Is there any merit to this? He references a JAES article from 1992. If this is an optimal equalization, I guess I'll pay $5 for the article.

SG

This was a "competition grade" car audio system, built into a Dodge Sprinter van - does that relate to the application or environment most of us would be considering for a home system?

[sreten]

Originally posted by smellygas


I mean, it's been very well established that a perfectly flat SPL vs. frequency
curve, measured in an anechoic chamber, is what sounds best to listeners.
SG

Hi,

The above statement needs serious qualification to be accurate.

/sreten.

[gedlee]

Originally posted by sreten
The above statement needs serious qualification to be accurate.

In what way? It seems accurate to me given the limited scope of the statement. There is far more to the situation - like polar response - but the above is still certainly true.

[MaVo]

Originally posted by smellygas
I mean, it's been very well established that a perfectly flat SPL vs. frequency curve, measured in an anechoic chamber, is what sounds best to listeners.

At high volumes, yes. At low volumes, a little bass boost makes the sound better. This is what those curves imply.