Music_ Noise and Hearing Damage

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					 1912                                          SA     MEDIESE        TVD     KRIF                          6 No ember 1976

                            Music, Noise and Hearing Damage
                                                     JUNE SCHNEIDER

                         SUMMARY                                   nature of risks which music and industrial noise at high
                                                                   levels constitute.
    This article sets out the issues involved in the considera-
                                                                      Excessive noise can lead to a shift in the hearing
    tion of noise-induced hearing damage. Exposure to noise
                                                                   threshold, resulting in hearing loss. One's ears become ac-
    can lead to a shift in the hearing threshold, resulting in
                                                                   customed to continual loud noise or high ambient
    loss of hearing. This shift may be either temporary or
                                                                   sound, attenuating that noise, with a concomitant lessen-
    permanent. When it is permanent it is usually irreversible
                                                                   ing of sensitivity, or deafening to soft sounds. When the
    and not all persons can be helped by hearing aids. Per-
                                                                   exposure to loud noise or the duration of the noise it-
    manent shifting of the hearing threshold may be caused
                                                                   self is brief, the shift in the hearing threshold will be
    by exposure to high sound levels. Ratios between lengths
                                                                   brief. This temporary shift is often referred to as 'hearing
   of exposure and frequency levels are given. The mea-
                                                                   fatigue' (Hallowell Davis' term). If, however, exposure
   surement of sound levels and assessment of acoustic
                                                                   continues day after day, year after year, the threshold
   hazards are presently related to non-fluctuating sounds.
   Music fluctuates too much to be measured in these terms.
                                                                   shift will become permanent. Continual excessive pressure
   Means have now been worked out to correlate the pres-
                                                                   on the ear's sensitive hair cells will cause physical damage
   sure of fluctuating sound (like music) with that of non-
                                                                   (sensorineural damage) and result in loss of hearing.
   fluctuating sound (like industrial noise) and thus to           Hearing damage thus depends on the pressure and intensity
   equate statistics governing noise as an acoustic hazard         of sound, and on the length of exposure to sound.
   with ,the hazard constituted by music. Table I shows the
   ambient sound levels which sllould be considered as             Loss of Hearing Acuity with Regard to Speech
   unsafe per number of hours' exposure. I plead for better
   acoustic design in environmental planning and stress               A permanent shift in the hearing threshold usually
   that people exposed to loud noise or music should under-         occurs slowly, but it is irreversible. Because hearing loss
   go hearing tests regularly as the main preventive mea-          occurs slowly and is usually superimposed upon a charac-
   sure.                                                           teristic ageing process, it is often not detected for years.
                                                                   A shift of 25 decibels (dB) in the threshold of hearing
  S. AII'. med. 1., 50, 1912 (1976).                               would result in slight difficulty in the hearing of every-
                                                                   day speech. (The American Academy of Ophthalmology
 An editorial, 'Hazards of music and nOIse', In the SAMJ]          and Otolaryngology regards a hearing loss of 25 dB as
  raised some important issues which deserve serious atten-        the beginning of impairment of understanding spoken
 tion. The question is more complicated than the approach          English.') A shift of 30 dB would cause obviously apparent
 adopted in the editorial would lead one to believe. State-        loss of hearing. Such hearing damage could not be material-
 ments such as                                                     ly helped by the use of a hearing aid. Most hearing aids
     'The danger of loss of hearing acuity in people exposed       amplify sounds to reach higher hearing thresholds, but
     to 'pop music' and other noises has recently been em-        since loss of hearing acuity i often more than a 'straight'
     phasised'                                                    shift in the hearing threshold, with the upper frequencies
 or the report by Chad wick referred to, which asked               usually being more affected than the lower frequencies
 '''Is Tchaikovsky's 1812 Overture really safe for human          (one of the reasons why speech, in particular, becomes
ears to withstand?'" quoting an assurance that                     unrecognisable and therefore unintelligible), the hearing
    '''even fortissimo passages for a full orchestra were         aid's over-all amplification does not remedy the condition
    well below the acoustic trauma hazard strata'"                significantly. Many hearing aids attempt to cope with the
are far too vague to be helpful.                                  situation by amplifying sounds in the upper-frequency
    It is not only 'loudness' of music or noise (relative or      zones more than those in the lower-frequency zones, and
accurately measured), but also the duration and frequency         more recent hearing aids (such as the           orelco' ew
of exposure to high ambient sound levels, and the type of         Life' hearing aid) boost frequencies over I 000 Hz only,
the sound pressures, which are at issue when noise-induced        intending thus to overcome the problem of 'lost conso-
hearing damage is under consideration.                            nants'.
    The question centres around regular and irregular sound          The problem, however, is rather more complicated, and
pressure and intensity. exposure to high sound levels and         the boosting of the upper frequencies and 'lost conso-
the relationships between such exposure and the types             nants' via a hearing aid does not always render speech
of high sound pressure and inten ity. and finally the             immediately intelligible. The person whose hearing acuity
                                                                  has gradually diminished, has usually made adjustments to
                                                                  cope with his gradual loss of hearing. He does this by
                                                                  changing the mode by which he interprets the 'code'
                                                                  which language represents. The hearing aid restores the
                                                                  original language code now unfamiliar to, or unlearned
6    ovember 1976                                  SA      MEDICAL          JOUR      AL                                          1913

by the patient over many years. To overcome the resul-                         TABLE I. MAXIMUM ALLOWABLE EXPOSURE TO
tant confusion, many persons require a proper hearing                                    DIFFERENT SOUND LEVELS
training when they get their hearing aid.
                                                                               Exposure duration            Maximum sound level
   Loud noise and loud music have long been thought to
                                                                                  (hours/day)                     (dB (A) )
constitute a risk to hearing acuity, and only fairly recently
serious attention has been focused upon this, with attempts                           8                              90
to investigate the subject scientifically. The first major,                           4                              93
and from many points of view still definitive, research                               2                              96
project was conducted in 1970 by Burns and Robinson'                                   1                             99
in the UK. Their report, together with the subsequent                                 V2                             102
'Code of Practice for Reducing the Exposure of Employed                               1f4                            105
Persons to N oise as well as results from the Second
British Conference on Audiology (1975)*, are now stan-                   factories or workshops (average level ± 90 dB) will be
dard references.                                                         safe for up to 8 hours a day exposure, the 'loud' disco-
                                                                         theque (> 100 dB) should be considered unsafe for periods
The Acoustic Environment                                                 longer than about 30 minutes. Accurate in theory, this
                                                                         may in fact not be true in practice, where another impor-
   The normal thresho~d of human hearing makes the                       tant aspect must be taken into consideration, i.e. the
frequency level 0 dB (A) only just audible. Normal                       fluctuation of sound pressure. This is an aspect of con-
listening levels are around 60 dB (A); the sound level in                siderable confusion, uncertainty and even subjectivity,
a noisy factory or workshop would probably be around                     for it centres around the controversial i sue of the rela-
90 dB (A); discotheques usually play music at levels over                tion between music (or sound) and noise. Burns and
 100 dB (A); and a jet aircraft, some 90 m away, will                    Robinson' do not regard sound as 'continuous', as
register around 120 dB (A) which is only ± 15 dB lower                   quantifiable ambient sound which can be measured in
than the level at which the human ear suffers instanta-                  decibels and related to exposure periods, unless it fluc-
neous, permanent damage (± 135 dB (A».                                   tuates by less than 8 dB. It is unlikely that any music
   Human vocal sounds cannot constitute a risk to human                  contains so little fluctuation. Even the most monotonous,
hearing: the human voice raised to its loudest level (±                  'mechanistic' 'pop music' has dynamic levels fluctuating
75 dB) cannot, at any reasonable proximity, exceed the                   more than this. It seems, therefore, that the sound levels
safe tolerance of the human ear (± 85 dB). Town-plan-                    of music can never be equated with continuous, indus-
ning, and with it acoustic design, or what one might                     trial noise in this context, and that findings concerning
call the acoustic ecology, was at one time governed by                   hearing hazards due to exposure to noise are not directly
this. For example, the size of a city was once determined                applicable when that 'noise' is music.
by the audibility of a single human voice raising an alarm,                  Nevertheless, even if it cannot be defined or measured
and many cities were for a time actually prohibited to                   in the same terms as non-fluctuating noise, hearing damage
exceed that size. Mozart's Vienna was 'quiet enough' to                  due to loud music does constitute a real risk. In Leeds,
enable fire signals to be 'given by the shouts of a scout                Fearn 6 conducted extensive testing on the hearing of
mounted atop St Stephen's Cathedral'.'                                   regular 'pop music'-listeners and concert-goers, comparing
   In contrast with the past, human sounds are currently                 them with a control group who did not listen to music.
being overwhelmed by technological sound, and such 'non-                 Hearing diminishment among those who regularly listened
human' sounds far exceed the safe acoustic tolerance of                  to music was sufficiently significant to apply Burns' and
the human ear (85 dB). Most car hooters, for example,                    Robinson's' criteria for industrial noise to loud music
register ± 88 dB at a distance of 14 m under calm condi-                 (although Fearn 6 suggests that different people manifest
tions, while the sirens of police cars measure ± 96 dB.                  differing sensitivity to damage). Burns and Robinson'
A new American 'yelping' siren measures as much as 128                   and the 'Code of Practice for Reducing the Exposure of
dB at a distance of ± 2,5 m.'                                            Employed Persons to Noise>! offer a useful formula for
   The Burns and Robinson' report maintains that only                    eq uating fluctuating dynamic levels with continuous noise,
ambient sound levels of less than 85 dB can be regarded as               and therefore to music: they offer the measurement of
safe levels for ambient working sound, and classifies hear-              'quivalent continuous sound' levels (called Le.,). Le. -
ing as being at 'long-term risk' if the ear is exposed to con-           e:j uivalent continuous sound, is defined by the equation
tinuous sound levels greater than 90 dB for 8 hours·a day.
                                                                                                     T (PA (t»' dt
Each diminishing of the 8-hour duration by half, ren-                                           t
ders an additional 3 dB 'safe'.
                                                                               Le.,    10 log
                                                                                                    r0    Po'
   Hope' tabulated the maximum continuous exposure                                     equivalent continuous sound normalised to
time at different noise levels which is allowable (Table 1).                           an 8-hour exposure
                                                                               T        total working period in hours
Noise and Music                                                                PA      instantaneous A-weighted sound pressure
                                                                                        in N/m'
  With calculations based upon Table I and the figures
                                                                                Po     reference rms sound pressure
quoted earlier, one could conclude that while the 'loud'
                                                                               t       time.
'This research has been added to by wo,k from SpoendJin in Zurich, and   This gives the sound level in fluctuating sound that will
Kuzniarz, Swieczynski and Lipowzan in Katowice, Poland.
  1914                                            SA     MEDIESE             TYDSKRIF                                    6 [ ovember 1976

  produce sound pressure accurately comparable to a non-                creating risk situations can be recognised and handled ac-
 fluctuating, continuous sound of the same numeric value                cordingly. Acoustic design should become part of indus-
 (in decibels). As indicated, a conventional decibel level              trial design, and consideration of tbe ound environment
 meter is only helpful in the context of this inquiry for the           sbould become part of environmental planning. Above all,
  mea urement of continuou sound level. Sound level                     from the point of view of the medical profession, it
 meters which can measure equivalent continuous sound                    hould be made common practice that people habitually
 levels, are, however presently being made.                             or frequently exposed to loud noise or loud music sbould
    Research into the question of noise-induced hearing                 have tbeir hearing checked regularly, so tbat shifts in the
 damage thus reveals definite hazard to workers in par-                 hearing threshold might be detected before tbey become
 ticularly loud working environments, sound-engineers,                  irreversible.
 musicians, music-listeners and inhabitants of our noise-                                               REFERE 'CES
 poUuted cities alike, though obviously in differing degrees.
                                                                         I. Editorial (1975): S. Afr.  med. J. 49, 2111.
 The re ults of ucb research provide information which                  2.   Hope. A. (1975): St"dio Sound, 17, 49.
 could lead to effective preventive measures. Existing                  3.   Burns. W. and Robinson, D. W. (Department of Health and Social
                                                                             Secur~{y) (1970): Report on Hearing and Noise in Industry. London:
 legislation to protect workers from acoustic trauma is                      HMSO.
                                                                        4.   Code of Practice for Reducing the Exposure of Employed Persons to
 neither really efficiently comprehensive, nor does its terms                Noise (1972): London: HMSO.
 cover all those whose hearing is at risk. More extensive use           5.   Murray Schafer, R. (1973): The MlIsic of the Ellvironment. London:
                                                                             Universal Editions.
 should be made of sound meters to measure ambient noise                6.   Feam, R. W., Reports 'os A571/1, A572/1.        niversity of Leeds:
                                                                             Department of Architecture.
 in working and recreational environments. so that levels               7.   Fearn, R. W. (1976): Archimedes, 18, I

 Histol'y 01 Meclidne

                                    Country Practice
                                                                              ID     the 1920s
                                                           R. SCHAFFER

                          SUMMARY                                       was a set of Record syringes in a spirit-proof case and I
                                                                        had numerous hypodermic tablets and ampoules of pituitrin
  Experiences in a country practice in the Easte.rn Cape and            and camphor in oil with ether. Among the hypodermic
  later in small town practice during the 1920s are described.          tablets were morphine, scopolamine, strychnine, atropine,
  Economic circumstances compelled me to become a                       ergotine, heroin and digitalin. The bag also had a special
  general practitioner. I had regrets in 1924, but not since            compartment for a chloroform drop bottle and there were
  then. General practice has been a rewarding experience.               a mouth gag, a tongue forceps and, of course, a Schimmel-
                                                                        busch mask.
  S. A/I'. med. l., 50, 1914 (1976).                                      I also possessed a varied collection of surgical instru-
                                                                        ments, most of which had been given to me by friends.
I arrived in Sterkstroom in April 1924 with a recently-                 My most useful and most frequently used instruments were
acquired MB diploma and unlimited confidence in my                      my dental forceps, my catheters and my metal urethral
ability to deal with all major and minor medical, surgical              dilators. The possession of which I was most proud was
and obstetric problems.                                                 my second-hand open two-seater Ford. The car had a
   I had bought a Rotunda Hospital midwifery bag equip-                 brass radiator shell, no self-starter, no detachable rims,
ped with a combined douche can and steriliser. axis trac-               and electric lights which worked only when the engine was
tion midwifery forceps. pubiotomy needle, a Gigli's saw                 running.
and a perforator. There were metal-covered bottles for                    I arranged accommodation at a local hotel for £5 per
Lysol, tincture of iodine and liquid extract of ergot. There            month, hired suitable rooms for use as surgery and dis-
                                                                        pensary for £2.10.0 per month and engaged a surgery boy
Qucenstown, CP                                                          for £1.10.0 a month. Some people thought that the boy
R. SCHAFFER,       "-LB. B.CH., M.D.
                                                                        was overpaid. There was no telephone, except at the local
                                                                        post office, I could not afford a receptionist and I most
Paper presenled al the Jubilee Congress of the Medical Association of
  ulh Africa, Johannesburg, 14 - 1 July 1975.                           certainly did not need a bookkeeper.