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G8MNY  > TECHNI   12.02.10 09:01l 160 Lines 8845 Bytes #999 (0) @ WW
BID : 48913_GB7CIP
Read: GUEST
Subj: Sound Levels, dBA dBB & dBC
Path: IZ3LSV<IW0QNL<F4BWT<PI8CDR<ON0BEL<GB7CIP
Sent: 100212/0012Z @:GB7CIP.#32.GBR.EU #:48913 [Caterham] $:48913_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To  : TECH@WW

By G8MNY                                               (updated Jan 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

THE EAR
The human ear has a very wide frequency & level range. From the faint 0dBA that
approximates to the threshold of hearing & represents an ear drum movement in
the order of the width of an atom, to energy levels greater than a million
million times stronger, or greater than a million times that movement. This
huge dynamic range is achieved by an AGC action in the ear that uses muscles to
dampen the movement of the acoustic path to the cochlea. The minimum level
change that can be detected is about 2dB over this range.

Too much sound for short time results in ringing in the ear, some damage
usually has happened if you hear this. Long periods of loud sound actually
breaks off the frequency sensing hairs in the cochlea, resulting in permanent
loss of that frequency!

Frequency resolution is about 2% at most frequencies, e.g. 20Hz @ 1kHz.

NON LINEAR EAR RESPONSE
This chart shows a young human ear response dBP (phons) of equal loudness
measured against Sound Pressure Level, (0dB = 2 dynes/cm2 or 20 uPascals).

  \ Hz 20     50    100    200    500    1k     2k     5k     10k    20k
 SPL\ ÚÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁ¿
140dB ´`-.__                                                        ./ Ã140dB
130dB ´_    ~``---...___     Threshold of Pain      Baby's       _./   Ã130dB
120dB ´ `--..           ~`````--------------..____  Cries? _..-''     .Ã120dB
110dB ´`-._  ``--...___         120dBP            ~`-....-'     __ _./ Ã110dB
100dB ´-.  `-._        ````--.._____..------....____      _..-'~  '    Ã100dB
 90dB ´-.~`-._ ~`Ä-.._          100dBP              ~`--'~    _.._   ./Ã 90dB
 80dB ´-.`-._ `-._    ~``---...._______..----.....___    _..-'    `'~  Ã 80dB
 70dB ´\ `-. `-._ `-..__          80dBP              `--'     _.._   ./Ã 70dB
 60dB ´  \  `-.  `-._   ~``---..._______..----.....___   _..-'    `-'  Ã 60dB
 50dB ´     \  `-._  ~`--..__      60dBP              `-'     _.._   ./Ã 50dB
 40dB ´       \    ~`-..__   ~`--._____.-----.....____   __.-'    `-'  Ã 40dB
 30dB ´         ` ú.      ~`--..__   40dBP            `'~    _.._    ./Ã 30dB
 20dB ´     Threshold` - _   20dBP~`---------.....____  __.-'  _ `--' /Ã 20dB
 10dB ´         Of Hearing ` - . _                    `~     /   \ _ / Ã 10dB
  0dB ´                    0dBP    ~ ` ` ' ' ' ' - . _ . . /           Ã  0dB
      ÀÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÙ
       20     50    100    200    500    1k     2k     5k     10k    20k

You will see that the response is far from flat, & that the bass end is also
very compressed a 20dB change only seems like 10dB.

Frequency range & sensitivity changes with age, from 20Hz-20kHz when young, to
-20dB @ 4kHz when old with some 20 to 40dB reduction in overall sensitivity as
well, but the threshold of pain remains the same.

Here is a large list of typical sound levels taken from a 1963 DAWE Meter H/B
& some from G4WYW's bul. Some sounds may be louder now!

EXAMPLE                       dB Wtg      NOISE       mPa    uBar   Ref Mic
Ear drum ruptures            160 dBC   Damage       2K Pa   20 Bar  damaged
Limit of safe exposure       150 dBC   Some damage  6.3 KPa 6.3 Bar damaged
of body to continuous noise,
Sensations of imbalance &
skin heating.
Military aircraft @ 30m      140 dBC                200 Pa   2 Bar  damaged
Threshold of pain            130 dBC     !!!!!!!     63 Pa  630000  damaged
Jet Aircraft @ 500ft &       120 dBC    Deafening    20 Pa  200000   112mV
Threshold of discomfort.
Pneumatic Drill & Boiler     110 dBC    Deafening    6.3 Pa  63000    35mV
Making Factory & Jet @ 150m
Disco well away from LS.
Powerful mower at 1m
Train whistle at 15m.
Motor Horn                   105 dBC    Deafening    3.5 Pa  35000    20mV
Noisy food blender @ 0.5m    100 dBC    Very Loud    2.0 Pa  20000    12mV
Inside train compartment
when door is slammed &
Lorry in narrow street.
Inside an Old Tube Train      95 dBC    Very Loud    1,125   11000   6.3mV
Busy Street                   93 dBC    Very Loud      893    8.90   5.0mV
Upper limit of daily noise,   90 dBC    Very Loud      630     6.3   3.6mV
Automatic lathe at 1m &
exposure regarded as OK.
Workshop                      88 dBC    Very Loud      502    5.00   2.8mV
Small Car @ 24ft              83 dBB    Very Loud      282    2.80   1.6mV
Noisy Office, Alarm clocks    80 dBB    Very Loud      200    2.0    1.2mV
Noisy Office                  78 dBB    Loud           158    1.60   980uV
Inside Small Car              73 dBB    Loud            89    .89    500uV
Less Busy Street              70 dBB    Loud            63    .63    360mV
Large Shop                    68 dBB    Loud            50    .50    280uV
Radio Set @ Full Volume       65 dBB    Loud            36    .36    200uV
Normal conversation @ 1m      60 dBB    Loud            20     2     120uV
Normal Conversation @ 2m      58 dBB    Moderate        16    .16     98uV
Urban House                   53 dBA    Moderate        9.8   .098    50uV
Quiet Street                  50 dBA    Moderate        6.3   .63     36mV
Quiet Office                  48 dBA    Moderate        5.2   .052    28uV
Rural House                   43 dBA    Moderate        2.8   .028    16uV
Quiet Speech &                40 dBA    Moderate        2.0    .02    12mV
Residential area at night.
Public Library                38 dBA    Faint           1.6   .016     9uV
Quiet Conversation            33 dBA    Faint           0.9   .009     5uV
Ticking of watch              30 dBA    Faint           0.63  .006   3.6uV
Rustle of Paper               28 dBA    Faint           0.5   .005     3uV
Whisper                       23 dBA    Faint           0.3   .003     2uV
Quiet country lane            20 dBA    Faint           0.2   .002   1.2uV
Quiet Church                  18 dBA    Very Faint      0.16           1uV
Still Night in Country        13 dBA    Very Faint      0.1          0.5uV
Blood pulsing & Heartbeat     10 dBA    Very Faint      0.06         0.3uV
Sound Proof Room               5 dBA    Very Faint      0.04         0.2uV
Threshold of Sound             0 dBA    Extremely Faint 0.02         0.1uV

WEIGHTINGS
Frequency weighting filters are used to change the measured level to reflect
the human ear response. It is achieved with gentle filters in the measuring
system, normally manually switched in. The use of the wrong weighting for a
particular sound may affect the measurement when compaired to the apparent
noise level as perceived by the ear or not, depending on the sound frequency
content, so sometimes just dBA is used for all levels!

Gain
0dB´                   _ . , - - . , _     Ã 0dB
-10´            _.- '                   ` -Ã -10  dBA is for sound levels up
-20´         _-'                           Ã -20  to 55dB, it has a response
-30´      _-'    Weighting Curve A         Ã -30  peaking at 2kHz with heavy
-40´   _-'                                 Ã -40  LF cut of -50dB @ 20Hz &
-50´_-'                                    Ã -50  -10dB @ 20kHz.
   ÀÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÙ
     20  50  100 200 500 1k  2k  5k  10k 20k

Gain
0dB´           _ . , - Ä Ä Ä Ä - . , _     Ã 0dB
-10´     _.- '                          ` -Ã -10  dBB is for sound levels
-20´  _-'                                  Ã -20  between 55dB & 85dB, it is
-30´_-           Weighting Curve B         Ã -30  flatter than dBA with only
-40´                                       Ã -40  -24dB @ 20Hz LF roll off &
-50´                                       Ã -50  the same -10dB @ 20kHz.
   ÀÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÙ
     20  50  100 200 500 1k  2k  5k  10k 20k

Gain
0dB´    _ . , - Ä Ä Ä Ä Ä Ä Ä Ä - . , _    Ã 0dB  dBC Weighting is level above
-10´- '                                 ` -Ã -10  85dB, it is quite flat 30Hz
-20´                                       Ã -20  to 10kHz, & only -10dB roll
-30´             Weighting Curve C         Ã -30  off @ 10Hz & 20kHz. It is a
-40´                                       Ã -40  frequency response with the
-50´                                       Ã -50  flattest weighting, almost
   ÀÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÙ      the same as an unweighted
     20  50  100 200 500 1k  2k  5k  10k 20k      Sound Pressure Level (SPL).

N.B. dB"C" is not dB"c" which is dBs with respect to an RF carrier.

HIFI TRICKS
These ear response tonal level changes are the principle behind Loudness
controls on modern audio domestic systems, eg. boost low frequency Bass & top
end Treble when the volume control is set low, as it will sound much louder to
the ear.


Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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