| |
G8MNY > TECH 12.11.24 07:54z 160 Lines 8847 Bytes #133 (0) @ WW
BID : 19767_GB7CIP
Read: GUEST
Subj: Sound Levels, dBA dBB & dBC
Path: SR1BSZ<IW0QNL<IZ3LSV<I0OJJ<I3XTY<GB7COW<GB7CIP
Sent: 241112/0752Z @:GB7CIP.#32.GBR.EURO #:19767 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
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
Read previous mail | Read next mail
| |