等响曲线 五

，每一条曲线代表一个响度水平．如标有

40< /p>

分贝的曲线上各点所代表的声音响度是相同的，

它们的响度水平< /p>

都是

40

分贝

( dB)

。

Equal-loudness contour

From Wikipedia, the free encyclopedia

(Redirected from Equal-loudness contours)

An equal-loudness contour is a measure of sound pressure (dB SPL),

over

the

frequency

spectrum,

for

which

a

listener

perceives

a

constant loudness when presented with pure steady tones. The unit

of measurement for loudness levels is the phon, and is arrived at by

reference to equal-loudness contours. By definition two sine waves,

of

differing

frequencies,

are

said

to

have

equal-loudness

level

measured in phons if they appear equally loud to the average young

person without significant hearing impairment.

Equal-loudness

contours

are

often

referred

to

as

"Fletcher- Munson"'

curves,

after

the

earliest

researchers,

but

those

studies

have

been

superseded

and

incorporated into newer standards. The definitive curves are those

defined in the international standard ISO 226:2003 which are based

on

a

review

of

several

modern

determinations

made

in

various

countries.

Contents [hide]

1 Experimental determination

2

Recent

revision

aimed

at

more

precise

determination

-

ISO

226:2003

3 Side versus frontal presentation

4 Headphones versus loudspeaker testing

5 Relevance to sound level measurement and noise measurement

6 See also

7 Notes

8 References

9 External links

[edit]Experimental determination

The human auditory system is sensitive to frequencies from about

20

Hz

to

a

maximum

of

around

20,000

Hz,

although

the

upper

hearing limit decreases with age. Within this range, the human ear

is most sensitive between 1 and 5 kHz, largely due to the resonance

of

the

ear

canal

and

the

transfer

function

of

the

ossicles

of

the

middle ear.

Equal-loudness

contours

were

first

measured

by

Fletcher

and

Munson

using

headphones

(1933).

In

their

study,

listeners

were

presented

with

pure

tones

at

various

frequencies

and

over

10

dB

increments in stimulus intensity. For each frequency

and intensity,

the listener was also presented with a reference tone at

1000 Hz.

The reference tone was adjusted until it was perceived to be of the

same

loudness

as

the

test

tone.

Loudness,

being

a

psychological

quantity, is difficult to measure, so Fletcher and Munson averaged

their results over many test subjects to derive reasonable averages.

The lowest equal-loudness contour represents the quietest audible

tone

and

is

also

known

as

the

absolute

threshold

of

hearing.

The

highest contour is the threshold of pain.

A

second

determination

was

carried

out

by

Churcher

and

King

in

1937,

but

these

two

investigations

showed

considerable

discrepancies over parts of the auditory diagram.[1]

A

new

experimental

determination

was

made

by

Robinson

and

Dadson (1956) which was believed to be more accurate, and this be

came

the

basis

for

a

standard

(ISO

226)

which was considered definitive until 2003, when the standard was

revised

on

the

basis

of

recent

assessments

by

research

groups

worldwide.

[edit]Recent

revision

aimed

at

more

precise

determination

-

ISO