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Old 16th March 2004, 09:53 PM   #1
Wizard of Kelts
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Default Calling Dr. Fletcher! Dr. Munson! Apparent 20 dB Discrepancy!

It will take two posts to ask this question.

Below is a Fletcher-Munson Curve from the following website:
http://www.allchurchsound.com/ACS/edart/fmelc.html

In this curve, a tone that is approx. 102 dB at 30 Hz is only 80 dB at 1,000 Hz.
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Old 16th March 2004, 09:57 PM   #2
Wizard of Kelts
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Yet the allegedly same Fletcher-Munson curve from a different website seems to show a 30 Hz at 102 dB is equal to a 1,000 Hz tone at 100 dB, or thereabouts.

http://www2.sfu.ca/sonic-studio/hand..._Contours.html

Does anyone have an explanation?
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Old 16th March 2004, 10:11 PM   #3
sreten is online now sreten  United Kingdom
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Well your second set of curves seems to indicate that :

100phon = 100db linear from 40Hz to 1Khz - I wish !

The bass end of the curves is so different its untrue.

I'd like to know which is the most "modern"
updated and accurate set of curves.

I think we'd all like it to be the second !

This was the set of curves I used a reference
for quite a while from one of my hi-fi books.

sreten.
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Old 16th March 2004, 10:30 PM   #4
sreten is online now sreten  United Kingdom
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Quote:
The ear is not equally sensitive to all frequencies, particularly in the low and high FREQUENCY ranges. The RESPONSE to frequencies over the entire AUDIO range has been charted, originally by Fletcher and Munson in 1933, with later revisions by other authors, as a set of curves showing the SOUND PRESSURE LEVELs of PURE TONEs that are perceived as being equally loud. The curves are plotted for each 10 dB rise in level with the reference tone being at 1 kHz. Also called loudness level contours and the Fletcher-Munson curves.
If the first set are the 1933 curves then perhaps the
later set are due to revisions by later authors.

As I've said I was initially familiar with the second set of
curves which I am sure are used to balance relative
levels of EQ for studio monitoring at different average
SPL levels, i.e. from normal to very high SPL (85dB to 105dB)
(According to the studio literature 20 years ago)

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Old 16th March 2004, 10:39 PM   #5
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I am glad someone else saw the difference too. I thought I had read something wrong.

From my own experience, I am inclined to believe the first chart is the true one.

I wonder if revisions made by later authors would still be called the Fletcher-Munson curves. Could it be that Fletcher and Munson have become generic for loudness curves, like kleenex for nose tissues or scotch tape for clear tape?
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Old 16th March 2004, 11:16 PM   #6
GM is online now GM  United States
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>I wonder if revisions made by later authors would still be called the Fletcher-Munson curves. Could it be that Fletcher and Munson have become generic for loudness curves, like kleenex for nose tissues or scotch tape for clear tape?

====

Probably so among folks who aren't all that familiar with human hearing research. The '56 Robinson-Dadson curves are the ones I see referenced in books, various papers. They are plotted near the end of this: http://www.dilettantesdictionary.com/pdf/e.pdf

GM
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Old 17th March 2004, 12:29 AM   #7
Ron E is offline Ron E  United States
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The Fletcher-Munson curves were done with headphones.

The Robinson-Dadson curves were done with loudspeakers.

The difference is mainly in the bass and has to do with the increased sensitivity of the body (rather than the ears alone) to vibration at low frequencies.

Typically the F-M curves have a 0dB reference level at the bottom and the R-D have a bottom curve called "minimum audible field", or M.A.F.

F-M
http://physics.nku.edu/asg/docpics/fletcher_munson.gif

R-D
http://www.music.miami.edu/programs/..._3/fig_3_6.gif
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Old 16th November 2004, 08:22 AM   #8
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i came across this thread while reading about rob dad / fletch muns this evening.

i hope i'm reading this forum correctly, and this hasn't been pointed out yet, but

these curves:

http://www.allchurchsound.com/ACS/edart/fmelc.html

are not the fletcher munson curves at all, they are the Robinson Dadson curves

these curves:

http://www2.sfu.ca/sonic-studio/hand..._Contours.html

are the Fletcher Munson curves.

This mistake - presenting Robinson Dadson and calling it Fletcher Munson is wildly common on the web, it seems.

a nice file for quick reference

http://www.sengpielaudio.com/Fletche...son-Dadson.pdf

it's not in english but it outlines the correct curves - there used to be an english version of that file, but it's nary to be found on google this eve.

take care,

Brian
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Old 16th November 2004, 10:23 PM   #9
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The first set of curves are indeed the Robinson and Dadson free field curves. They are not the curves derrived by Fletcher and Munson, which the second set are. They are more accurately refered to as 'Equal Loudness Curves'. Besides the set derived by Fletcher-Munson and Robinson-Dadson, there are also the Churcher-King set, and the random noise contours by Pollack. Although there are differences in the contours by each set of researchers, they all agree for the most part. They show the loudness level (in phons) required for various frequencies to sound 'equal', at different reference levels. The reference level frequency was 1kHz.
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Old 18th November 2004, 11:24 AM   #10
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Quote:
Originally posted by Hornlover
Although there are differences in the contours by each set of researchers, they all agree for the most part. They show the loudness level (in phons) required for various frequencies to sound 'equal', at different reference levels.
Taking the 100 dB @ 1KHz level in the graphs of the first two posts, there is a 15 dB or so difference at 30 Hz. That is quite a difference between the two graphs.

Moving away from the deep bass region, yes, there does seem to be pretty good agreement between them.
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