Robbie commented in MMD 2000.01.12.08:

>[ Gunshots and loud tones are quite different sounds.  When I play the
>[ calliope I wear ear protectors designed for use around jet aircraft.

The ear is a wonderful feat of our Creator that without immediate
damage can perceive sound pressure levels from 0 to 130 dB, an
impressing power range of 10^13 times.  [ 10000000000000 times! ]

A central trick to achieve this big range is the Stapedius muscle that
pulls and displaces the smallest bone in your body, Stapes, that
transfers the sound from the eardrum to the inner ear 'microphone'.
When you hear a strong sound this muscle contracts by a reflex to pull
Stapes such that the sound transmission to the inner ear is decreased;
it acts as a protective 'automatic volume control'.

One basic problem is that this muscle contraction takes time, tens
of milliseconds.  That is why gunshots are so dangerous to the ear,
because with such short sounds there is not enough time for this
mechanism to act.  Also, just because the gunshot sound is so short,
you don't perceive it as loud as it really is, and perhaps you neglect
to protect yourself for that reason.

With extended strong sounds Stapedius can do its work, but after
a while it is fatigued and its protective action decreases.  And
correspondingly the auditory nerve system is fatigued and you are
mislead this sound is not as loud as it really is and again you may
neglect protection.

The basic mechanism in hearing damage from overexposure to sound is
that you wear out and crush an increasing number of the delicate hairs
protruding from the (about 30,000) hair cells in the inner ear.  Once
damaged they never recover and you suffer a permanent hearing loss.
The hearing cells for high frequencies are adjacent to the sound input
to the inner ear and these are the first ones to be decimated by
over-exposure.

Another, and a worse, kind of damage is tinnitus, a virtual noise or
beep that goes on forever, originating in your auditory nervous system.
The cause can be infections or tumors in the inner ear, but also an
over-exposure to sound.  Tinnitus can drive people crazy.

Much research has been done on hearing impairment induced by industrial
noise and there are consequent international recommendations for
maximal noise dose to avoid such damage.  This is a set of curves in
a diagram of maximum permitted noise spectral level vs. frequency,
sloping (very) roughly -3 dB per octave.  At 500 Hz you allow 88 dB for
more than 5 hours per day, 93 dB for 2-5 hours, 98 dB for 1-2 hours,
109 dB for less than 20 minutes per day, etc.  If any of these
conditions is exceeded you should wear a noise protector.

More recent investigations on symphony orchestra musicians have shown
that they generally receive less hearing damage than predicted from the
sound levels they are exposed to.  The reason is believed to be
psychological.  Pop musicians using amplification, and their audience,
are usually way up in the dangerous area and protectors are strongly
recommended.  Also, tinnitus cases among these people are much more
frequent than you would like to know.

A typical mid-range organ flue pipe blown at 8 inches water column
and 1 foot distance roughly matches the 1-2 hour per day curve, so you
should be able to voice such pipes without fear.  Calliope and reed
pipes are considerably louder and clearly motivate protectors at close
distance.

The simplest protectors are plugs made from cotton, special fibers,
foam plastic, wax or molded plastic.  Using cotton, fold a flat pad
in two and roll it hard into a cone with its tip at the fold, put it in
your ear with the tip inward.  These plugs attenuate high frequencies
to the order of 20 dB but do very little toward low frequencies.  They
do a good protection job but distort the tonal balance.  While doing my
military service we used empty pistol cartridge shells as earplugs
(hole inwards) while shooting.  Slightly uncomfortable but quite
efficient.

To reach more appreciable low frequency attenuation you will need the
protector type with big cups covering the whole ears and soft cushioned
brims resting against the head.  Lighter variants, perhaps with foam
cushions stay in the 20 dB range.  The better performance is with heavy
cups and liquid filled or heavily encapsulated cushions to insure
weight and tightness; this type attenuates in the 30 dB range.

You cannot get notably higher attenuation than this because of the
bypass sound entering directly through your skull.  For ultimate
requirements like on an aircraft carrier you have to enclose your
entire head in a helmet, like an astronaut.

There also exist fancy protector variants including electronics for
active noise suppression and for communication purposes.

Plug protectors for musicians and other critical listeners
designed for equal attenuation at all frequencies are exemplified at
http://neatnoise.com/products.htm.  A moderately priced standard type
attenuates about 20 dB.  Special high equality types for 15 or 25 dB
cost in the range of $200 and have to be individually tailored at a
hearing clinic.

Examples of ear protectors can be seen at http://arbill.com/leight2.htm
and http://www.soundsafetyproducts.com/ppe/hearing/muffs/qm29.htm.

Thanks to Robbie for finding the links.  (Neither of us corresponded
with the companies).

Johan Liljencrants

 [ Thanks for the fine article, Prof. Johan!  -- Robbie