Health and Safety

  • The human ear can safely tolerate the softest audible sound, called “0” dB sound pressure level (SPL), while loudest sound tolerable is usually considered to be 120 dB SPL.  Interestingly, older treatments call 120 dB SPL the threshold of pain, whereas because some stadium concerts and raves can operate even higher levels, such levels are nowadays called the threshold of tickle in the ear; 140 dB SPL is now considered the threshold of pain, but it is also the point at which permanent damage may occur even for brief exposure.
  • The frequency range for sound perceived by humans is from about 20 Hz to 20 KHz (20,000 Hz), although these numbers are taken as averages of large numbers of listeners, and some young of people can hear out to as high a frequency as  24KHz. At the other end of this spectrum, sounds below 20Hz are not usually heard but felt, if strong enough.  Various devices deliver more or less of the frequency range.  A telephone delivers a narrow frequency range, from about 300 Hz to 3 KHz, so lacks deep bass and high treble.  This is why the letters “s” and “f” pronounced by a talker are easily confused over a telephone.  The “s” sound lies principally at a higher frequency than the “f” sound, and the telephone cuts off the higher frequencies, sometimes making the two indistinguishable.
  • A level of 85 dB SPL, about twice as loud as normal speech in a movie theater, is tolerable for 8 hours per day without long term consequences to hearing, but louder sounds are tolerable for shorter times.The world has become a combat zone for one of your most precious possessions: your ability to hear.  During everyday activities, you are in constantly in close proximity with audio sources with the potential to permanently impair your future ability to hear.As for protecting your ability to hear clearly, one of the most common and sensory damaging dangers is distortion.  This is not the same as volume.  Your ears can handle a considerable amount of clearly produced volume; however, if the audio source is filled with distortion, the human ears soon fatigues and starts to degenerate.
  • A common source of distortion is the device known as the “boom box”.  Car radios are another source of overdriven audio sources, played through under-qualified amplifiers and reproduced by speakers setting up a much higher distortion noise to clear signal ratio, which begins to break down the sensitivity of your audio sensors.
  • In other scenario, you attend a rock concert.  After a few minutes, you start to feel buzzing or tingling in your ears.  This is the first sign that your ears have become overloaded and are in danger of suffering permanent and irreparable damage.
  • The audio signal in question does not have to be loud, however. Many television engineers and craftspeople who works in close proximity to a bank of television monitors for long periods of time discover that they have either lost or are losing their high-end sensitivity.  Many of these individuals cannot hear higher than 10 KHz.