HEARING IMPAIRMENT DUE TO NOISE AND LOUD SOUND REPRODUCTION

 

SOME NEW POINTS OF VIEW AND SOME HYPOTHESES FOR FURTHER

RESEARCH

1983 The Anstendig Institute

Fine music, at normal to soft volume levels, is capable of physically calming and refining the -listener's body while producing internal physical experiences of an emotional nature that can range from exquisite to frightening. But music is also capable of strongly stimulating the body to movement and of determining the character of the movements, in which case, the louder the music, the stronger the effect. This, of course, is what people are after when they go to dance at discos where music is played at nearly ear-splitting volume levels. There are certain very real experiences to be had from loud volume listening, but loud volume levels also present very real dangers to one's hearing.

I. SOUND IS A STRONG, MEASURABLE PHYSICAL FORCE

It is generally wrongly assumed that the experience of hearing is principally a non-physical matter of conscious experience and that the accompanying emotions also occur in the non-physical realm of consciousness. But, hearing is primarily a physical phenomenon: up until the very last stage, in which the physical, material phenomena of vibrations are somehow transformed into the non-physical, immaterial phenomenon of consciousness, all stages of hearing are physical in nature. (The mental processing of what one hears is no longer part of the act of hearing, but necessarily a process that follows it.) It is seldom realized that sound waves themselves are strong physical forces. But consider the fact that, in many microphones, the pickup element would be demolished by volume levels that are still within the tolerances of human hearing and that special microphones have to be built to withstand the force of much loud rock music. Clearly, sound waves have considerable force. The physical force of sound, coupled with our deeply ingrained psychological reactions to it, make sound probably the most powerful influence on us. To understand this, think of your reactions to a car's screeching brakes, to a policeman's siren, to an explosion, to someone crying, etc. Only intense pain might cause stronger, but not faster, reactions.

II. THERE IS REASON TO BELIEVE THE LOUDNESS OF SOUND IS NOT THE ONLY FACTOR THAT LEADS TO HEARING LOSS

The problem of hearing loss due to noise or due to listening to music is generally considered to be exclusively a matter of how loud the sounds are, the assumption being that soft sounds are less dangerous and loud sounds more dangerous. In fact, many articles on the problem of hearing loss describe fixed volume levels beyond or within which any sounds will cause hearing impairment, and these limits are not very loud (one well-publicized claim is that exposure to sounds of 70 to 80 do for long periods of time will result in hearing damage, and the ranges of 90 to 110 do are described as dangerous even for short periods). While The Anstendig Institute does not doubt these findings, it has reason to believe that, at such comparatively moderate volume levels, the loudness of the sounds per se is not the main reason for hearing loss. The evidence we cite is that:

1) in The Anstendig Institute's own test-situations, we have been able to observe just the opposite result, i.e., greater hearing sensitivity after long sessions of listening to music that was within the stated volume ranges;

2) we know of other situations that produce the same effect of greater hearing sensitivity after people are subjected to even louder volume levels. For example: orchestras routinely use rehearsal rooms that are just big enough to house their 100 or so members, and we have never heard of anyone suffering hearing impairment from a good rehearsal. In fact, a phenomenon often happens whereby everyone is hearing MORE acutely after a first-class rehearsal. This is noticeable in the fact that, beforehand, when everyone has arrived and taken his seat, the ambient noises in the room are not noticed. But afterwards, and even during pauses later in the rehearsal, the ambient noise is annoyingly apparent. Suddenly everyone notices every little sound, most of which were present before the rehearsal. Obviously the hearing of those in the room has changed so that everyone is hearing louder due to the physical relaxation and acute concentration necessary in order to play their instruments. A heightened state of sensitivity has resulted and not a hearing loss, even though, under these conditions, sound pressure levels of well over 100 dB are common. I spent many summers rehearsing daily in orchestras and bands numbering well over 200 players in the Interlochen Bowl of the National Music Camp, Interlochen, Michigan. In spite of the enormous sound-pressure-levels, many of those musicians have grown up to be among the finest in the world, with excellent hearing.

Long before the present public awareness of the dangers of loud volume listening, The Anstendig Institute conducted test sessions in which long tapes of music having the same equalization characteristics were played. The listening was begun at a moderate volume level and the music was correctly equalized to sound natural at that level. The volume was then slowly increased until sound pressure levels of 100 dB to 115 dB occurred momentarily at climaxes. Each successive increase in volume was carefully re-equalized to retain the same natural sounding quality. At the end of these sessions, everyone present was invariably hearing louder and more perceptively. Room sounds, like the hum of the amplifier's power supply, the residual noise coming through the speakers, street noises, every tiniest movement by anyone in the room, were suddenly disturbingly loud whereas, before the session, no one noticed them. One could literally hear a pin drop. It was obvious to everyone that this was due the deeper state of relaxation of muscle-tensions their bodies had relaxed into while listening. That became clear when we disturbed the physical state we were in by getting up and doing other things that demanded the tensions of our usual bodily movements and reactions: some of the acuity of our hearing had been lost when we then returned to listening, but everyone noticed that they were still hearing louder than before we listened to the loud music.

Incidentally, we have observed that the above improvements in sensitivity in hearing will usually be accompanied by an added sensitivity in the other senses, i.e., one tastes more intensely, one smells more intensely, etc. The Anstendig Institute strongly recommends that the medical-research community investigate this interrelation of all sensory perception by accompanying tests of hearing loss with tests of other sensory perceptions. It would be interesting to test whether loud sounds and music which cause damage to people's hearing also cause a diminished sensitivity in other areas of sensory perception.

The above examples should not be misunderstood as claiming that the dangers of loud music and loud noise have been exaggerated. The hearing losses that have been observed are very real and scientifically well documented, and there is no reason to doubt the audiologists' warning that the problem is reaching epidemic proportions. The above examples merely indicate that there is much more to the problem than currently indicated and that, at volume levels that are within known human tolerances (up to short term peaks of 110 dB to 115 dB--the threshold of pain is 140 dB) not ALL loud sounds are damaging. Some can, under the right conditions, be beneficial. But most people cannot adequately differentiate between dangerous and not-dangerous sounds, so it must be emphasized that one should, as a rule, avoid all unnecessarily loud sounds.

Obviously, music played by an orchestra in a rehearsal and the music used in The Anstendig Institute's tests differ greatly from the usual sounds that we are bombarded with in our everyday lives. Musical sounds are not merely noise. They are, in the case of the rehearsal room, relatively refined sounds produced live by those present in the room, whose bodies are vibrating in the same vibrational flow of the music they are playing. The recorded music used by the Institute has been screened by Mr. Anstendig, a trained orchestra conductor. Only music played in the most refined manner possible, both in its expressiveness and in its rhythmic flow, is used. Of utmost importance is the fact that the music is equalized by Mr. Anstendig so that it sounds natural and that the equalization is readjusted for every change in the overall volume level.

Our tests indicate that one can be hearing louder and more sensitively after relaxed listening at louder volume levels (85 to 100 dB, with momentary peaks above 100 dB) IF THE PERFORMANCE IS OF HIGHEST QUALITY, IF THE SOUND REPRODUCTION HAS BEEN CAREFULLY EQUALIZED WHILE LISTENING, AND IF THE LISTENER REMAINS RELAXED AFTERWARDS. This phenomenon is not, however, limited only to listening at loud volume levels. The same phenomenon of increased sensitivity can occur when listening to music at moderate levels. The Anstendig Institute also observes this in its more typical test sessions during which the music remains mostly within 60 to 80 dB volume levels, with peaks of about 90 to 95 dB.

The conclusion is that being subjected to 70-80 dB of noise is probably dangerous only because of the ERRATIC quality of the noise, not because of the volume level. Finest music at those volume levels would have the opposite effect.

III. THE QUALITY OF SOUNDS PLAYS A GREAT ROLE IN THEIR EFFECT ON US

The music that we listen to can affect us in a positive or negative manner depending on the quality of the music and, more particularly, the quality of the performance. The composers of most classical masterpieces have carefully considered their intended expressive content in relation to the technical possibilities of instruments or the voice. These masterpieces "sit" well, i.e., are comfortable to play, only when played in the manner presupposed by the composer, which means with the intended expressive content. In wrongly interpreted, or just plain badly played, performances, there is an added factor of unease and discomfort for the players. The performances do not flow naturally, the rhythmic quality suffers, becoming especially erratic at every awkward-to-play passage, and the uneasiness of the players becomes part of the expressive content, usually dominating it. The playing either becomes nervously keyed up, usually when the music is difficult to play, or it becomes lethargic, bored, and enervated when the players have no technical difficulty but the performance is not "happening" expressively. The Anstendig Institute is aware of recordings by highly respected musicians that key listeners up and make them nervous and physically uncomfortable, to the point of causing hyperactive physical effects such as diarrhea in very sensitive subjects. Similarly, we have had experience with recordings of music that create just the opposite state in the listener--one of lethargy, diffuse concentration, and ennui. We have not documented the effect of these performances on one's hearing, because they are either stopped as soon as we become aware of their effect, or they are played for relatively short periods of time, either to corroborate our observations or to demonstrate them. But because of the effect produced on our bodies, we strongly suspect that these types of less-than-impeccably performed recordings play the greatest role in hearing loss from listening to recordings, especially when the volume level stays below 100 dB. This supposition strongly supports our conclusion that, with low volume-level noise, it is the ERRATIC quality of the noise that is responsible for hearing damage.

Many of the negative effects on people that are attributed to noise pollution could very well be due to the erratic nature of the other vibrational influences around them. This is especially likely when negative effects are apparently due to noise levels as low as 70 to 80 dB, as have been reported. Most noise of the 70 to 80 dB level comes from sources that also produce other vibrations besides sound vibrations. At that relatively low sound-pressure level, the effects of other erratic vibrations, especially in one's immediate surroundings, could easily have more effect on a person than the sounds. A very possible effect is that the sounds and the other (usually mechanical) vibrations could be vibrating at rhythmic dissonance to each other, thereby causing ill-effects on one's hearing mechanism. For example, our paper Hearing Loss From Listening with Headphones suggests that the bodies of people listening with headphones are often out of synchronization with the program they are listening to due to erratic or otherwise coarser vibrational influences around them. This dissonance between their bodies and the listening program can amount to a physical irritation. Parts of the structure of the ear are so delicate that this irritation could be causing subtle damage, especially to the most delicately vibrating sections of the inner ear that have to simulate the very highest and lowest frequencies that are more difficult to produce because of the fast speed in the one case and the slow speed and the magnitude of the wave-length in the other. Since the person listening with headphones is distracted by what is being listened to and since this damage would affect frequencies that are usually not the fundamental sounds, he would not necessarily notice either the irritation due to the erratic influences around him or their effects. He would experience both as part of the listening experience in the same way that the listener does not notice the effects of overly loud volume levels while he is listening to them. We refer the reader to our papers on the quality and the effects on us of the vibrational influences around us.

IV. EQUALIZATION CAN REDUCE THE DANGERS OF LOUD RECORDINGS

Since some people will insist on playing recordings loudly, measures should be taken to minimize the chance of damage. We are more sensitive to some frequencies than others and this characteristic of our hearing worsens at loud volume levels. Also, in amplified live music and in sound-reproduction there are exaggerated peaks in volume at approximately the same frequency range to which we are most sensitive. Much of the damage done by loud-volume listening is due to the peaks in volume in those frequency ranges. But all amplified sound reproduction has to be equalized in order for it to sound natural. Those frequencies that have to be reduced the most in volume in order for sound-reproduction to sound natural at loud volume levels are exactly the frequencies to which we are most sensitive. Therefore, when music is properly equalized, it can be played at substantially louder volume levels--loud enough to satisfy most loud-music fans-with greatly reduced danger of hearing damage.

It should be emphasized that the program-equalization under discussion is different from the type of equalization sometimes used in the audio industry. Usually the audio-industry uses equalizers to smooth out the frequency response of a sound-system in a given room with the help of measuring instruments. That type of equalization is called room-equalization. What The Anstendig Institute means by PROGRAM-equalization is the equalization by ear of the program material while it is playing so that it sounds natural to the listener. Essentially, this amounts to using an equalizer as an elaborate tone-control. When done correctly (with a little practice) this type of equalization will automatically compensate for the greater sensitivities of the listeners in the most dangerous frequency ranges.

The instruments mostly used for measuring volume levels of sound are called Sound-Pressure-Level-Meters. These meters give a reading that reflects an average of the volume of all the frequencies. But sounds are never equally loud in all frequencies, and in fact, are usually of highly uneven loudness, with certain frequencies often many times louder than others (these are called peaks). Thus, one should not rely on sound-pressure-level-meters to set a limit to the volume of sounds as their readings do not give any indication of the volume of these frequency peaks which could easily be 20 dB or more louder than the reading on the meter. This fact makes reference to "tolerable" sound-pressure-levels a highly inaccurate designation.

Our research shows that our hearing is not a fixed entity, but changes in sensitivity over relatively short periods of time, particularly in relation to our physical states of tension and relaxation.2 The greatest amount of change in the shortest period of time has been observed during concentrated music-listening as the subject's body relaxes into and is affected by the flow of the music. We also found that the degree of change in sensitivity is not equal in all frequency ranges. The frequencies where the most change occurs are in the regions where much hearing loss occurs. This fact makes the testing of a person's hearing very similar to attempts to study the brain in relation to consciousness. In order to study it, one has to disturb or destroy it: one cannot get inside and look at the brain without destroying it and even external means of studying it disturb or destroy the phenomena of consciousness that one wants to study. For example, one can never study the brain's functioning during an exquisite artistic experience because the means of studying it, no matter how sophisticated, can never be as delicate as the experience and would have to coarsen, if not destroy, it. Similarly, testing a person's hearing when the person is anything less than totally comfortable in his/her most characteristic listening attitude in sympathetic surroundings can never duplicate that person's actual hearing acuity. Even the weight of wearing headphones or visual distractions can disturb a person's natural potential for auditory perceptions. The subject must be given time to relax and become comfortable in his/her surroundings and the testing must be done in situations that do not entail distractions or physically uncomfortable apparatus.

The observations and suggestions in this paper may seem too subtle to be factors in tangible damage to one's hearing. But one must remember that, along with sight, hearing is the most complicated and most delicate process known to man. The whole being plays a role in the hearing experience since it involves the whole body-- not just the hearing apparatus centered around our ears--and all capacities of mind. We do not hear the source of a sound; we hear the vibrations of our own bodies after they are caused to vibrate by the sound-waves from the source. Sound vibrations have to be recreated by our bodies before we experience them. Sound waves are small to begin with, and the reproduction of them by the body takes place in miniature, particularly in the tiny, innermost parts of the ear. The enormous effects on us that hearing sounds, even quiet ones, can have indicates that these tiny components of the hearing mechanism are interconnected with all of the networks of the body that cause our reactions. Most hearing impairment is not an equal reduction in volume of all frequencies, but rather involves specific frequencies that are physically difficult for our bodies to reproduce such as the low bass or the high frequencies. In view of the extreme delicacy of most of the hearing process and the fact that the body has to be able to reproduce the vibrations in all their nuances in order for us to hear and experience them, it becomes easy to understand that the slightest imbalances, unnecessary tensions, irritations, and even conflicting vibrations can derange the hearing mechanism enough to limit one's ability to physically reproduce, and thus to hear and experience, some of the finer frequency ranges and expressive nuances. Hearing consists in hearing sounds and in perceiving the characteristics of and the nuances in the flow of the sounds. When hearing, the body is much like a phonograph needle in a record groove in that it must trace and recreate all the vibrations, nuances, and qualities of vibrations around it. Nuance is as important as loudness in a complete listening experience, and The Anstendig Institute recommends including tests of sensitivity to nuance in auditory testing.

 

1 Related papers of The Anstendig Institute point out that we are affected physically by the quality of all external vibrational influences around us. The reasons for this are explained in the paper The Body as a Machine.

2 See our paper Sound Equalization In Relation To How We Perceive Sound.

 

  

The Anstendig Institute is a non-profit, tax-exempt, research institute that was founded to investigate the vibrational influences in our lives and to pursue research in the fields of sight and sound; to provide material designed to help the public become aware of and understand vibrational influences; to instruct the public in how to improve the quality of those influences in their lives; and to provide the research and explanations that are necessary for an understanding of how we see and hear.