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How can 100 watt amplifiers can damage your hearing ?
If I had made a mistake in the complicated calculations, please tell me.
The watts, mentioned below, can be greatly reduced, if you use 5 speakers in a "Home Theater".
If your speaker are 3 dB more efficient than a low efficiency speaker (1%)
then the watts, mentioned below, can be halved.
No matter how you look at it,
100 watts into low efficiency speakers (1%) (if your speakers can handle 100 watts !)
in a room, can damage your hearing, within a short period of time.
Have you been to a loud concert or loud night club ?
Do you have trouble hearing people speak , after a loud concert or loud night club ?
Do you get "ringing" in your ear, a few hours after a loud concert or loud night club ?
If the answer is yes, you have damaged your hearing,
which might or might not recover (partially or fully).
Our ears are delicate instruments,
that can be easily damaged.
Our ears have evolved over thousands of years
to listen to very soft sounds and soft human speech.
In the olden days,
a very soft sound could mean
an insect (i.e. food) creeping through the dry leaves on the ground.
The human who can hear the insect, will eat better, and stand a better chance of surviving.
The very soft sound could also mean that a predator is creeping up on the human.
If you cannot hear the predator, you are dead !
The human who can hear soft human speech,
will stand a better chance of surviving.
The humans who can only hear loud human speech,
will attract predators, and get eaten,
or frighten away prey, and starve !
Our ears are VERY DELICATE instruments,
that are designed for very soft sound and soft human speech.
VERY DELICATE instrument are easily damaged.
There is no such thing as a robust delicate instrument !

Things like loud drums are a "new" invention,
and our ears were never designed for loud drums.
Anybody who is stupid enough to put his ear right next to a loud drum,
will damage his hearing, within a short period of time.
Of course, you will say that nobody is that stupid,
but there are Hi Fi Enthusiast will test his new 100 watt amplifier,
by turning up the volume and seeing "how loud can my new amplifier go" ..........humm.........
And that Hi Fi Enthusiast name is not Homer Simpson !
How many Hi Fi reviews of powerful equipment say stupid things like
"I am not sure which gave up first, the amplifier, the room or my ears."
110 dB loud sounds can damage (temporary or permanent or partial recovery)
the Hi Fi Reviewers hearing within 10 minutes !
Page 718 of the 3rd edition of  The Science of Sound by Rossing , Moore and Wheeler 
Mr. Thomas D. Rossing is with the Northern Illinois University.
Mr. F. Richard Moore is with the University of California.
Mr. Paul A. Wheeler is with Utah State University.
Is there any point in reading the reviews done by the above mentioned Hi Fi Reviewers
in next month's Hi Fi magazine ?
Our ears works in the funny way.
Our ears has to hear very soft sound,
and not overload, when there is loud sound.
The only way, our ear can do this,
is to use something like a "Logarithmic" scale.
Translated into English, that means
400 watts do NOT sound 10 times louder than 40 watts.
Our ears do NOT work like that !
Some people have suggested that
400 watts sound twice as loud as 40 watt.
I did say that our ears work in a funny way !
400 watts will damage your hearing within a short period of time !
Page 718 of the 3rd edition of  The Science of Sound by Rossing , Moore and Wheeler
+ a bit of calculations
A man shouting only produces
a pathetic 0.05 acoustic watts
A man shouting at the top of his voice produces 0.05 acoustic watts.
0.05 watt is 20 times less than 1 watt !
If you have low efficient speakers (1%),
you only need 5 watts from your amplifier
to reproduce a man shouting as loudly as possible.
If you have more efficient speakers,
you only need about 1 or 2 watts from your amplifier
to reproduce a man shouting as loudly as possible.
If you have a man shouting as loudly as possible,
in your living room,
how long will it be,
before your neighbour bangs on the wall ?

A man's voice at 10 feet
varies from about 22 dB to 90 dB.
Page 231 of 2nd edition of Music, Physics and Engineering by Mr Harry F. Olson
1 watt into the "typical" modern speaker
will produce about 85 dB to 90 dB (at 1 meter)
How many watts do you think you need ?
Typical average listening level needs a minuscule 0.003 watt ,
which is 333 times less than 1 watt
Page 459 , 460 and 461 of  The Science of Sound , 3rd edition by Rossing , Moore and Wheeler 
Mr. Thomas D. Rossing is with the Northern Illinois University
Mr. F. Richard Moore is with the University of California
Mr. Paul A. Wheeler is with Utah State University
states that :-
The typical average listening level of 65 dB in a room (unspecified size)
requires 0.01 milliwatt to 0.03 milliwatt of acoustic power.
                                        0.03 milliwatt is 33,333 times less than 1 watt
If you use a low efficiency loudspeaker of 1% efficiency,
you only need 0.001 watt to 0.003 watt of power from your amplifier.
                                             0.003 watt is 333 times less than 1 watt.
At an orchestral concert you will hear peaks of 105 dB or more.
If you use a low efficiency loudspeaker of 1% efficiency,
you only need 10 watts to 30 watts of power from your amplifier.
An orchestra playing full blast will produce 110 dB in the front rows of the concert hall.
The Hi Fi Enthusiast will say
I want my amplifier to reproduce 
"an orchestra playing full blast producing 110 dB in the front rows of the concert hall."
That is totally reckless !   He could damage his hearing, within 10 minutes !
(Please read Page 718 of 3rd edition of The Science of Sound by Rossing , Moore and Wheeler)
Are you sure that this Hi Fi Enthusiast's name is not Homer Simpson ?
Mr. Thomas D. Rossing is with the Northern Illinois University
Mr. F. Richard Moore is with the University of California
Mr. Paul A. Wheeler is with Utah State University
Page 718 of the 3rd edition of  The Science of Sound by Rossing , Moore and Wheeler 
estimates that :-
You might lose as much as 34 dB of your hearing,
after exposure to 10 minutes of 110 dB of loud sound.
Your hearing will probably recover from VERY MINOR DAMAGE.
Unfortunately, if the damage is is severe, your hearing will partially recover,
and you would have permanently lost some of your hearing.
Page 459 of the 3rd edition of The Science of Sound by Rossing , Moore and Wheeler 
10 watts to 30 watts
into low efficiency speakers (1%) produces 105 dB in a room. 
105 dB is dangerously close to 110 dB that
can damage your hearing after 10 minutes.
Page 718 of the 3rd edition of The Science of Sound by Rossing , Moore and Wheeler 
The question is
will the hearing loss be permanent or temporary
or a PARTIAL recovery (with some permanent hearing loss) ?
This is not a laughing matter.  This is a real danger.
Do some searches on the Internet, and you will hear sad stories of
Recording Engineers who had to give up work
because they had damaged their hearing,
by listening to their huge Studio Monitors at deafing level.
You might not have to give up work,
but you might not be able to enjoy your Hi Fi set,
after a few years of VERY LOUD music.

Another problem is
a moderately loud sound for many hours
might be as bad as a 
a very loud sound for a few minutes.
"80 db for a day"
is as bad as
"110 dB for 10 minutes"
Page 718 of the 3rd edition of The Science of Sound by Rossing , Moore and Wheeler 
If you use a low efficiency loudspeaker of 1% efficiency,
you only need 0.03 watt to 0.1 watt of power from your amplifier
to get 80 dB in a room.
80 dB for a day can cause 34 dB loss in your hearing.
0.1 watt into low efficient speaker (1%)
is loud enough
to damage your hearing, after a day.
You might get back most of the 34 dB hearing loss, within a short period,
but in extreme cases you could permanently lose some of your hearing sensitivity.
DO YOU REALLY WANT 100 WATT AMPLIFIERS ?
Why do some Studio Engineers and some Hi Fi Reviewers
suggest that you need 100 watt amplifiers ?
Some Studio Engineers and some Hi Fi Reviewers who listen to
VERY VERY LOUD MUSIC for many months / years,
would have damaged insensitive hearing,
so they need more powerful amplifier and louder music for their damaged insensitive hearing,
which will damage their hearing even more ......... and so on ....... and so on .......................
The is a dangerous problem, because it happens over a period of time, 
so the victim does not realize how bad his hearing is becoming.
If some of the Studio Engineers realized what was happening,
they could have turned down the volume,
and prevented further damage to their hearing.
Recommendations of the American
Occupational Safety and Health Administration (OSHA)
Please read page 733 of the 3rd edition of  The Science of Sound
Mr. Thomas D. Rossing is with the Northern Illinois University.
Mr. F. Richard Moore is with the University of California.
Mr. Paul A. Wheeler is with Utah State University.
If you do not believe the 3 eminently qualified persons above,
please read page 733 of their book
and you will find that
The American Occupational Safety and Health Administration ( OSHA )
limits exposure to occupational noise to 110 dB for 30 minutes a day.
The American Occupational Safety and Health Administration ( OSHA )
limits exposure to occupational noise to 90 dB for 8 hours a day.
If you use a low efficiency loudspeaker of 1% efficiency,
you only need 0.3 watt to 1 watt of power from your amplifier
to produce 90 dB in a room.
You should not listen to 0.3 watt to 1 watt from your amplifiers
for more than 8 hours a day !
Turn down the volume !
Doesn't that remind you of the days when Mum and Dad yells
"Turn down the volume.  Are you deaf ?"
"Health and Safety" at home is every bit as important as "Health and Safety" at work.
 
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