by Marek Roland-Mieszkowski, M.Sc., Ph.D., Digital Recordings
This paper has been recommended by Digital
Recordings as suggested reading for their AUDIO-CD
Copyright 1989-2010, Digital Recordings. All Rights Reserved.
PDF version (17 kB)
General Misconceptions about Sound and Hearing
- o Loud sound is not dangerous, as long as you don't
feel any pain in your ears.
Our threshold for pain is at about
120 - 140 dB SPL but sound begins to damage our
hearing when it is above 85 dB SPL (for a 8 hour
- o Hearing loss after sound exposure is temporary.
Some of the hearing loss will be
permanent. Indication of damage is ringing and
noise in the ears (called tinnitus) after sound
exposure. This is a clear indication that sound
exposure took place. Another indication of that is
the difficulty to communicate on the phone and in
the noisy restaurant or cafeteria.
o If you have a hearing loss already, you don't have
to protect your hearing any more.
Hearing loss accumulates. More
exposure to loud sounds leads to more hearing loss.
- o Hearing loss is mostly caused by aging.
Research shows that accumulative
exposure to loud sounds, not age, is the major
cause of hearing loss.
- o Hearing loss can be repaired by medicine, surgery
or hearing aids.
- Although certain improvements can be
obtained by the use of hearing aids. In the case of
hearing losses inflicted due to the noise exposure,
the resulting quality of hearing will be far from
normal. So far no drugs or therapy can correct noise
induced hearing loss. This could affect your
professional performance as a musician, sound
engineer, medical doctor, air traffic controller,
telephone operator, pilot and driver or in any other
profession where performance depends on good
hearing. Also, your enjoyment of music would
- o Loud sound only damages your hearing.
- Loud sound can change your heart rate,
vision and reaction time. It may make you more
aggressive and in general, negatively affect you.
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Common Misconceptions about "Sound Engineers" and Sound Reinforcement
- o They know what they are doing, when adjusting
Most of so-called "sound engineers"
(about 99%) have no formal training in acoustics
and sound reinforcement. The operation of sound
systems does not require any licence or qualifying
exam, yet the operators are in control of a
potentially very damaging form of energy.
- o They adjust sound to safe levels.
Most (about 99%) don't use sound
level meters to measure intensity. Instead they
judge the sound level "by ear",an inexact
procedure even if we assumed they had no
hearing loss. Research in Halifax night spots
showed in 1986 that a risk of hearing loss for
patrons was present in 64% of all tested locales
during 1 hour of exposure and in 95% during 4 or
more hours of exposure (a typical evening at a
night club lasts 4 hours).
- o Equalization and adjustments of sound
parameters are properly done.
Many of the so-called "sound
engineers" have significant hearing losses.Sound
adjusted to their liking may be far from well-
balanced sound. This could further increase the
danger of exposure to harmful sound levels.
- o Sound systems have built-in safety features.
Most sound systems are tremendously
powerful and are capable of producing sounds
much louder than adjusted levels. However, these
systems have no built-in protection against surges
in sound due to feedback or accidents.
- o There is a law to protect the public against unsafe
In Canada, no law exists to protect
patrons who frequent entertainment premises
(such as: clubs, concerts, school dances etc.)
from harmful sound exposure, which could result
in permanent hearing loss. Although there is a law
governing the safety of workers, it appears not to
be enforced in the entertainment industry.
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Common Misconceptions about "What People Like" and People's Rights
- o Most people like their music loud.
Although some people like loud music,
especially if they already have a hearing loss, most
audiences note little perceptible difference between
sound levels of 85 dB SPL and 100 dB SPL.
However, 100 dB is much more dangerous than 85
dB sound, having 32 times more destructive power
(115 dB sound found in many clubs has 1000 times
more destructive power than 85 dB sound).
- o Most patrons of night clubs enjoy being immersed
in loud music.
Most of the patrons attend night clubs
for the social interaction. They are not interested
in music performed so loudly that they are unable
to carry on a conversation. In many environments
which were tested during our "Sound Survey",
normal conversation was impossible. People were
shouting in each others ears, further increasing the
danger of receiving a significant hearing loss. I
would strongly suggest that bars cash in on "safety
zone" advertising (no more than 85 dBA sound
- o Everyone has a right to decide what sound level to
It could be argued that patrons who
choose to attend night clubs, especially young
adults, are unaware of the potential danger. On
the other hand, those who knowingly expose
themselves to overly loud sounds are creating
future medical problems for themselves. In my
opinion, this burden should not be put on the
In the range of safe sound levels (let's say up to
85 dBA for a 8 hour exposure) adjustment should not
be restricted. However, levels above 85 dBA are
dangerous and can cause permanent hearing
damage. Given the choice, most sensible people
would not knowingly choose to put themselves in
an environment that was considered hazardous to
their health. However, many patrons are unaware
of the potential danger of sustaining permanent
hearing loss and are also unaware of the fact that
noise levels over 85 dBA are dangerous.
An informed public, coupled with rational behavior,
are key ingredients in the protection of individuals
from both hearing loss and extra health costs.
Unfortunately, existing legislation does not require
informing patrons of potential health hazards that
could harm them, thereby eliminating the concept
of "informed consent". Enforcement of existing
work place laws should protect nightclub
employees, patrons, teachers, musicians, D.J's or
any other individual who may be exposed to
dangerous noise levels that could pose a potential
health hazard. Regretfully, such laws are very
seldom implemented or enforced.
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Facts about Sound and Hearing
o Frequency range: With normal hearing, one can
hear frequencies from 20 Hz to 20,000 Hz. ( 20
cycles/sec to 20,000 cycles/sec ).
o Intensity range: With normal hearing, one can
hear intensities from 0 dB to 140 dB. This
corresponds to power ratio (defined as ratio of the
highest audible intensity to the lowest audible
intensity) equal to 100,000,000,000,000.
o Recommended maximum allowable
(by Nova Scotia Department of Labour) are:
16 hours for 80 dBA sound
8 hours for 85 dBA sound
4 hours for 90 dBA sound
2 hours for 95 dBA sound
1 hour for 100 dBA sound
30 min for 105 dBA sound
15 min for 110 dBA sound
7.5 min for 115 dBA sound
0 min for above 115 dBA sound (there should
be no exposure at
o Number of channels:
We often characterize sound
systems by number of channels. Mono means 1 -
channel system, stereo means 2 - channel system,
quadro means 4 -channel system. We have two
ears, so one can think,that auditory system is
stereo (2 channel), but as a matter of fact sound
in each ear is divided into 24 discrete channels
called critical bands. Therefore auditory system
(hearing system) acts as 48 - channel system.
o Critical bands allow discrimination of different
sounds simultaneously. Also they allow to hear
sounds in noisy situations (for example
conversation during party or in the cafeteria).
Hearing loss is often accompanied by damage to
the critical bands, which in some situations can
profoundly change ear's selectivity. Hearing aids
(HA's) act like 1-channel devices since they can't
feed signals directly to separate critical bands.
Therefore they do not compensate for this
o Illustration of hearing loss (intensity): Let's
assume that a single bird sitting far away in the
tree produces a sound level 0 dB (barely audible). A
person with hearing loss (after going to "bad clubs")
requires a minimum sound level of 40 dB in order
to hear the sound. How many birds have to sit in
the tree in order for this person to hear them ?
Answer: 10,000. For the person with 50 dB loss it
will take 100,000 birds and with 60 dB loss it will
take 1,000,000 birds.
o Potential dangers: Hunting and target shooting,
power tools, noisy vehicles, loud music (concert,
club, walkman, stereo system at home or in the
car). Please wear hearing protection in the
situations like that.
WWW Hearing Test
the first comprehensive and entirely web-based hearing test
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Use Digital Recording's inexpensive
semi-professional coupler DR1-R
with a Radio Shack Sound Level Meter
to calibrate headphones, earphones, microphones or other SLM's.
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