If you don't watch your sound dosage, you might become hard of hearing. Research now shows that exposure to excessive sound, not aging, makes people lose their hearing.

NOTE: See:


Look for the following symptoms of hearing damage:

  1. PAIN - If you feel pain from the sound, get away from there immediately!
  2. TEARING - If you hear a tearing sound in one or both ears, get away from there immediately!
  3. BUZZING - If the sound makes a buzzing sound in one or both ears, get away from there immediately!
  4. DISTORTION - If the sound as you hear it is distorted get away from there immediately!
  5. MUFFLED SOUND - If the sound is suddenly muffled, get away from there immediately!
  6. RINGING IN EARS - If you have ringing in your ears that lasts longer than one day, you probably have hearing damage.
  7. WRONG DIRECTION - If you hear sounds of visible events coming from the wrong directions, you have damage.
  8. LOSS OF BALANCE - If you have loss of balance and have just listened to loud sounds, you probably have hearing damage.


Making correct measurements

In order for sound exposure to be safe and for sound regulations to be interpreted properly, sound measurement must be correctly made. There are errors in many of the laws, because the laymen who wrote them did not understand acoustics.

The table at right states the correct setting of the sound pressure level (SPL) meter for measuring sound and noise levels at the location of the listener (or at the distance specified in the law), not at the location of the sound source. Many laws incorrectly specify the A weighting when the B, C, or Z weighting is more appropriate. Using the A weighting for loud sounds is appropriate only if the listener is a far enough away from the source that the level at the listener has dropped into the A weighting range, but the measurement is taken a lot closer to the source.

If the reading is being taken for protection of hearing, it should be taken close to the source. The standard distance for close readings is one meter (1 m) from the source. If the reading is being taken for protection of adjacent property owners from sound annoyances, the readings should be taken at the property lines.

In open air, the sound intensity drops by 6 dB each time the distance from the source is doubled from the distance of the last reading.

In an enclosed space, unless there are sound-absorbing materials, the sound intensity is nearly the same everywhere inside that space.


infrasound or < 50 HzZ (reading in dBZ)
above 85 dBC (reading in dBC)
55 dB to 85 dBB (reading in dBB)
below 55 dBA (reading in dBA)

Selecting the correct weighting

It is important to use the correct weighting for the sound levels being measured. Each weighting is valid only inside the specified range. Attempting to use a weighting outside its range gives erroneous readings. Such false readings cause the readings to be higher or lower than the real SPL levels. Use the correct weighting.

If it is available, get a dBZ reading first. Then take a dBC reading. If the dBZ reading is larger than the dBC reading, use dBZ. Otherwise use the dBC reading to choose dBC, dBB, or dBA from the list above.

Appendix A: Understanding the various weightings

Many otologists think the weighting curves should be adjusted to add sounds which are not perceived as loud, but which do cause hearing damage. The new Z weighting satisfies this.

Sounds below 20 Hz are not even represented in the A, B, or C weighting curves, because most ears do not sense them as sounds. But enough acoustical energy in the infrasonic area can cause pain, and can cause hearing loss beginning in the 3 KHz area in some individuals.

Even the Z weighting does not cover infrasound adequately. The level can be estimated if the infrasound is present alone. Use this procedure:

  • Take a Z weighted reading of the sound alone.
  • Add 10 dB to the reading for infrasound.

Many SPL meters do not have a B weighting selection (The ISO stupidly discontinued the standard). If a sound falls within the B weighting range, it can be measured with this procedure:

  • Take an A weighted reading.
  • Take a C weighted reading.
  • Find the arithmetic mean of these readings.

Most SPL meters do not have a Z weighting selection. If a Z weighting us needed, it can be estimated with this procedure:

  • Take a C weighted reading of the sound alone.
  • Add 10 dB to the reading for sound below 25 Hz.
  • Add 30 dB to the reading for infrasound.

The OSHA Regulation

The OSHA (Occupational Safety and Health Administration) guidelines for sound exposure say that workers may be exposed to the following levels of sound pressure (SPL) for the following time periods (but only ONE of these levels in any 24 hour period). In addition, hearing protection is required to be available at any level above 85 dB SPL. Many otologists feel that the OSHA guidelines do not provide enough protection. (See below for the otology-recommended NIOSH scale.)

Use the dBZ scale if available. Otherwise use dBC.

A formula for calculating these times (using an ordinary scientific calculator or a spreadsheet) follows:

OSHA max time (hr):
O_time = 2 ^ ((105 - SPL) / 5)

A formula for calculating the portion of the maximum dose used by a given sound exposure follows:

OSHA dose:
O_dose = time (hr) * 2 ^ ((SPL - 105) / 5)

* is multiplication
/ is division
^ is exponentiation


> 115 dB SPLNONE
115 dB SPL15 minutes
110 dB SPL30 minutes
105 dB SPL1 hour
102 dB SPL1.5 hours
100 dB SPL2 hours
97 dB SPL3 hours
95 dB SPL4 hours
92 dB SPL6 hours
90 dB SPL8 hours
Extension (not in OSHA regs):
87 dB SPL12 hours
85 dB SPL16 hours (protection)
82 dB SPL24 hours (continuous)

OSHA permitted exposure times

The NIOSH-ANSI Recommendation

NIOSH (National Institute for Occupational Safety and Health) and ANSI (American National Standards Institute) have adopted a stricter standard based on equal amounts of energy. Here is their scale of the amount of sound a person may be exposed to in a 24 hour period:

Use the dBZ scale if available. Otherwise use dBC.

A formula for calculating these times follows:

NIOSH max time (hr):
N_time = 2 ^ ((94 - SPL) / 3)

A formula for calculating the portion of the maximum dose used by a given sound exposure follows:

NIOSH dose:
N_dose = time (hr) * 2 ^ ((SPL - 94) / 3)


> 115 dB SPLNONE
115 dB SPL28 seconds
112 dB SPL56 seconds
109 dB SPL1 minute 52 seconds
106 dB SPL3 minutes 45 seconds
103 dB SPL7 minutes 30 seconds
100 dB SPL15 minutes
97 dB SPL30 minutes
94 dB SPL1 hour
91 dB SPL2 hours
88 dB SPL4 hours
85 dB SPL8 hours
82 dB SPL16 hours
80 dB SPL24 hours (continuous)

NIOSH recommended maximum exposure times

The EPA Recommendation

EPA (Environmental Protection Agency) has adopted a yet stricter standard based on equal amounts of energy. But it seems to be based on removing annoyances, rather than hearing protection, since no person in the audience of a concert could hear the music. Here is their scale of the amount of sound a person may be exposed to in a 24 hour period:

Use the dBZ scale if available. Otherwise use dBC, or dBB if the dBC reading is below 85 dB.

A formula for calculating these times follows:

EPA max time (hr):
E_time = 1.5 * 2 ^ ((82 - SPL) / 3)

A formula for calculating the portion of the maximum dose used by a given sound exposure follows:

EPA dose:
E_dose = time (hr) / 1.5 * 2 ^ ((SPL - 82) / 3)


97 dB SPL3 minutes
94 dB SPL6 minutes
91 dB SPL11 minutes 15 seconds
88 dB SPL22 minutes 30 seconds
85 dB SPL45 minutes
82 dB SPL1 hour 30 minutes
79 dB SPL3 hours
76 dB SPL6 hours
73 dB SPL12 hours
70 dB SPL24 hours (continuous)

EPA recommended maximum exposure times


115 dB SPL15 minutes 28 secondsNONE
112 dB SPL22 minutes 45 seconds 56 secondsNONE
109 dB SPL34 minutes 28 seconds 1 minute 52 secondsNONE
106 dB SPL47 minutes 38 seconds 3 minutes 45 secondsNONE
103 dB SPL1 hour 20 minutes 7 minutes 30 secondsNONE
100 dB SPL2 hours 15 minutesNONE
97 dB SPL3 Hours 30 minutes3 minutes
94 dB SPL4 hours 36 minutes 1 hour6 minutes
91 dB SPL7 hours 2 hours11 minutes 15 seconds
88 dB SPL10 hours 30 minutes 4 hours22 minutes 30 seconds
85 dB SPL16 hours (protection) 8 hours45 minutes
82 dB SPL24 hours (continuous) 16 hours1 hour 30 minutes
79 dB SPL24 hours (continuous) 24 hours (continuous)3 hours
76 dB SPL24 hours (continuous) 24 hours (continuous)6 hours
73 dB SPL24 hours (continuous) 24 hours (continuous)12 hours
70 dB SPL24 hours (continuous) 24 hours (continuous)24 hours (continuous)

Comparison between the standards


Now, how do you figure out your exposure if you are exposed to different levels of these sounds for different periods of time?

Here is one way to calculate your total dose to damaging sound (using the NIOSH levels):

Example: You are exposed to:

91 dB SPL - 1 hour
88 dB SPL - 3 hours
85 dB SPL - 4 hours

Is your total dose too large?

A spreadsheet is ideal for figuring these doses. Using the same example:

1SPLHoursDose C formula shown
2911.5 =B2*2^((A2-94)/3)
3883.75 =B3*2^((A3-94)/3)
4854.5 =B4*2^((A4-94)/3)
Sum:1.75 =Sum(C2:C4)


Spreadsheet for figuring NIOSH doses

Manually calculating NIOSH doses:

dose1 = 1 * 2 ^ ((91 - 94) / 3)
dose1 = 1 * 2 ^ (- 3 / 3)
dose1 = 1 * 2 ^ (-1)
dose1 = 1 * .5
dose1 = .5

dose2 = 3 * 2 ^ ((88 - 94) / 3)
dose2 = 3 * 2 ^ (-6 / 3)
dose2 = 3 * 2 ^ (-2)
dose2 = 3 * .25
dose2 = .75

dose3 = 4 * 2 ^ ((85 - 94) / 3)
dose3 = 4 * 2 ^ (-9 / 3)
dose3 = 4 * 2 ^ (-3)
dose3 = 4 * .125
dose3 = .5

Sum the doses:
total_dose = dose1 + dose2 + dose3
total_dose = .5 + .75 + .5
total_dose = 1.75

This is larger than 1, so there is a very large chance of damaging hearing.



Recent research has indicated two new facts about hearing loss:


    Age related hearing loss is now thought to not exist. Instead, what was thought to be age-related hearing loss has now been found to be acquired hearing loss from cumulative exposures to the loud sounds of steam trains, firearms, and factories.


    Extremely low frequency sounds do not follow the tables above, because the weighting curves used for the sound measurements above are based on audibility. But it is now thought that frequencies under 60 Hz, and especially those approaching DC impulse transients, cause hearing damage, even though they are not very audible. This damage begins in the "rock range", starting between 2 KHz and 6 KHz, and expanding in frequency range as exposure continues. So the following precautions should be taken:



Standard sound level meter weightings Several different weighting systems are used for several different purposes.

The chart is repeated so it can be seen without much scrolling.

The following list shows the correct weighting for each use:


Examples of types of hearing loss There are several mechanisms of hearing loss. The curves show the effect on hearing from each one:



The path of the sound from the open air to the brain:

  1. The pinna (earflap, A) changes the amplitude and phase of the sound depending on which direction the sound is coming from. This helps the brain determine the direction the sound came from.
  2. The sound enters the ear canal (B) and heads toward the tympanic membrane (eardrum, C).
  3. The sound vibrates the tympanic membrane (eardrum, C). The tympanic membrane (C) separates the outer ear from the middle ear.
  4. The vibration of the tympanic membrane (C) causes the malleus (hammer, D), a tiny bone (ossicle), to vibrate. This converts the air pressure vibrations in the sound to mechanical vibrations in the bone.
  5. The malleus (D) causes the incus (anvil, E), another tiny bone, to vibrate. Muscles control how much of the motion of the malleus (D) is transferred to the incus (E). Ligaments connect the bones together.
  6. The incus (E) causes the stapes (stirrup, F), yet another tiny bone, to vibrate. Muscles control how much of the motion of the incus (E) is transferred through ligaments to the stapes (F).
  7. The stapes (F) causes the oval window (G) to vibrate. The oval window is a membrane that separates the air-filled middle ear from the fluid-filled inner ear.
  8. The oval window (G) transmits the mechanical vibrations of the stapes (F) to vibrations in the fluid in the vestibular canal (N) of the cochlea (J).
  9. The cochlea (J) sorts the sounds by frequency and stimulates different nerves in the auditory nerve (K) for each frequency. This will be explained in detail below.
  10. Sound passing through the entire cochlea (J) exits through the round window (H) and is absorbed by the air in the middle ear.
  11. The semicircular canals (L) are not used for hearing. They are used for balance, keeping track of any motion of the head. But information about motion of the head is needed to keep motion of the head from being heard as sound through motion of the cochlea as the head moves.
  12. The Eustachian tube (M) goes from the middle ear to the nose. It equalizes pressure between the middle ear and the outside air during a yawn.

How the cochlea sorts sound frequencies:

  1. The vestibular canal (N) carries sound waves in fluid from the oval window (G) to the membrane assembly(R). After the sound vibrates the membrane assembly (R), it returns to the round window (H) through the tympanic canal (P).
  2. The membrane assembly (R) is a group of several membranes and sensory organs. It contains the hair cells that turn sound energy into nerve impulses.
  3. The membrane assembly (R) is tapered, with the narrow end near the base of the cochlea, where the oval and round windows (G & H) are, and the wide end is at the apex, where the helicotrema (S) is. The narrow end is stiff, while the wide end is floppy. These two properties, combined with the distance along the canals from the base, determine which parts of the cochlea are responsive to which frequencies. Each position is resonant to mainly one frequency, and vibrates the most with that frequency.
  4. The highest frequencies (20 KHz) are detected at the base of the cochlea. The lowest frequencies (63 Hz) are detected at the apex. See the frequency diagram at right.
  5. Since the nerves can't pulse faster than about 100 Hz, the frequencies must be sorted and given separate nerves. Nerve pulsing speed encodes loudness, not pitch.
  6. Frequencies between 20 Hz and 60 Hz vibrate the entire membrane assembly (R). The sound is detected, but not given a sensation of pitch (frequency).
  7. Frequencies below 20 Hz normally pass through the helicotrema (S), bypassing the membrane assembly (R). They are not normally detected.
  8. Frequencies above 20 KHz normally can't vibrate the membrane assembly (R), so they are not normally detected.
  9. The brain then reconstructs the nerve impulses into what we actually perceive.
  10. Consonant (pleasant) sets of tones make the membrane assembly (R) vibrate gently with inactive nodes between the vibrating parts.
  11. Dissonant (unpleasant) sets of tones cause the membrane assembly (R) to vibrate harshly, with parts of it that are close together moving in opposite directions.
diagram of human ear
  • A. Pinna (earflap)
  • B. Ear Canal
  • C. Tympanic Membrane (eardrum)
  • D. Malleus (hammer)
  • E. Incus (anvil)
  • F. Stapes (stirrup)
  • G. Oval Window
  • H. Round Window
  • J. Cochlea
  • K. Auditory Nerve
  • L. Semicircular Canals
  • M. Eustachian Tube
  • N. Vestibular Canal
  • P. Tympanic Canal
  • R. Membrane Assembly
  • S. Helicotrema
functional diagram of human ear
frequency diagram of cochlea

The frequency locations are approximate, since various people's cochleas are made differently.

Notes on the structure and function of the ear: