By Federico Miyara, María Victoria Gómez,
María Susana Flores, Lorena Lorenzo
At the present time, technology provides increasingly better solutions for the emission of unwanted sound that characterizes many devices, vehicles, and commercial, recreational, and industrial premises. However at the same time, several reports point out that environmental noise is gradually increasing, particularly in urban areas or near highways and airports.
Two possible causes of this situation are the fact that noise control techniques involve higher financial costs (which neither industry nor consumers easily accept), and the exponential growth of the number of noise sources. There is, however, another hidden reason which is at least equally important as the aforementioned ones: the almost complete lack of information regarding the noise issue (including knowledge of its causes, its detrimental effects on humans and the environment, and its solutions) which prevails in our society. This leads to a negligent social behavior with regard to the care of the acoustic environment; individuals not only allow themselves to produce high-level noise, but they accept without complaint, and even willingly, noise from both individuals and society.
Throughout history, the most popular approach in the fight against noise has been to regulate noisy activities, punishing noise violators with fines or closures depending on the different types and degrees of offenses. Very seldom, however, do regulations create adequate conditions for the spontaneous and voluntary observance of what the law prescribes.
One of the most effective means of creating those conditions is, in our opinion, education. Through education, it is possible to give individuals hard facts regarding noise, as well as to inculcate in them principles and habits of environmental care, including care for the acoustic environment.
There are two basic types of education: systematic education, imparted at school as an integral part of the curriculum of formal studies, and asystematic education, usually conducted outside the school environment. Asystematic education takes advantage, for instance, of the mass media. In the present paper, we focus on systematic education, leaving for a later study the analysis of the asystematic approach for environmental education.
Several studies have unequivocally pointed out that noise (i.e., unwanted sound) negatively affects the intellectual, physical, and recreational activity of human beings, as well as our sleeping and resting activities. This is true even when noise is not too loud. In addition to simple annoyance (which in the long run can lead to states of stress), noise causes digestive disorders, hypertension, tachycardia, sleep alterations, abnormal hormonal secretion, immunologic disorders, interference with several kinds of activity, reduced intelligibility of speech, etc. (Berglund et al., 1995). When the average occupational sound level exceeds 80 dBA, the risk of hypoacusis (permanent hearing impairment) becomes statistically significant (ISO 1999 : 1990 E). In the case of children and youngsters, not only is the risk larger, but it extends to the cognitive and learning areas. Indeed, several reports have shown that the school performance of children exposed to high noise levels is, both in the short and the long term, worse than that of children attending more quiet schools or classrooms (Moch, 1986). Noise may also negatively affect the development of children’s personality, stimulating a tendency towards violent behavior (Navarra, 1997).
According to the 1994 Amendment of the Argentina National Constitution, all people have the right to enjoy a balanced and healthy environment (Constitución de la Nación Argentina, art. 41, 1994), and this includes, of course, the acoustic environment. According to the Children's Rights Convention (United Nations, New York, 1989, arts. 24-2-e and 29-1-e), children (including teenagers under this designation) not only have this right, but they also should be educated on issues pertaining to environmental hygiene. This means that principles such as respect for the natural environment should be inculcated in them from the beginning of their education. Because this Convention has constitutional rank since the 1994 Amendment, the National State is responsible not only for providing such a healthy environment, but also for providing the environmental education requisite in order to ensure that society has the know-how to protect and take care of the environment. In other words, education regarding environmental hygiene and the prevention of environmental problems is key to sustaining a healthy environment. This project articulates this premise.
For children, the first step towards sound hygiene is to begin to pay attention to sound itself; that is, sound as a sensory stimulus rather than as a communication tool. Throughout almost all of their previous experience, sound has been just a means of information exchange, an intermediary element in order to connect themselves with their surroundings and other people. It is thus necessary to stimulate children to discover that there are many more environmental sounds than the ones which are often consciously perceived. The human brain has the noteworthy ability of classifying and filtering out irrelevant auditory information. When we examine sound as a sensory stimulus, we intentionally try to "deactivate" that filter, listening carefully to each one of the sounds constituting the soundscape.
The activity suggested in order to fulfill this objective is to perform “active listening,” first in the classroom, then elsewhere in school, and finally during walks or outings, especially ones that are concurrent with other activities. The watchword will be to keep silent and pay attention to as many different sounds as possible (such as those generated or produced by vehicles, people and their activities, animals, music, musical instruments, machines, wind, etc.). Children also should make an oral or written account of the noises, depending on their ability level. Then, the lists should be compared and a single list including should be made combining all the sounds. This activity should be considered as a game. Silence shouldn't be imposed in a compulsory fashion. If some of the kids can't help talking or making noise, their sounds should simply be considered as additional sounds to include in the list.
Another relevant aspect to work on with children is the ability to classify sounds according to various features, such as pitch or loudness. It should be developed with two objectives: first, to be able to detect or identify potentially hazardous sounds; and second, to improve the perception of sound itself. Emphasis should be put on those qualities or properties of sound that happen to be more readily identifiable, such as pitch (bass/treble), intensity (loud/soft), duration (long/short/impulsive), and some timbric features (brilliant/opaque, percussive/not percussive, harsh/smooth). Often one finds some feature which can be classified according to more than one criterion. This gives rise to interesting comments and discussions in classroom.
Conceptualizations are useful at all levels (in appropriate amounts), because they help to arrange empirical facts into knowledge. We can conceptualize in the fields of anatomy, physics, perception, and pathology, among others. For the sake of clarity, we will discuss each category separately. In practice, however, it is often convenient to treat related concepts simultaneously.
In the case of young children (Kindergartners), it is a good idea to make anatomical observations of the visible parts of the auditory apparatus: the (external) ear or pinna, the ear canal, the tragus and the lobe, and to learn their names and location. It is also useful to compare the sense of hearing with other senses such as sight and touch, and to look for differences and similarities. An important difference between hearing and seeing that should be stressed is that it is virtually impossible to stop hearing. There are no effective means of "closing" the ear completely, which makes it rather vulnerable. This is an important fact regarding sound hygiene to teach children.
Older children will easily understand the existence of the eardrum (tympanic membrane). In those schools which have medical services, it would be very interesting and most instructive if children paid a visit to the doctor and made direct observations of the eardrum with an otoscope (an optical instrument that enables the observation of the ear canal).
Later on, the complete auditory system should be described. There are beautiful and large color plates depicting the anatomy of the ear in great detail which may be used to illustrate hearing to the class. (Such materials are usually available from stores specializing in hearing aids or laboratories which manufacture otological medicines.) Pupils should be made aware that though the pictures show a big ear with big and seemingly robust parts, the real size is very tiny, which makes the ear a rather delicate organ.
Briefly, the ear is made of three parts: outer ear (pinna and ear canal), middle ear (eardrum and three minute bones called ossicles), and inner ear (cochlea and labyrinth). The first two stages carry out the conduction of sound coming into the ear towards the inner ear. Much in the same way as a lever, they convert the high-amplitude and low-pressure vibrations of airborne sound present at the outer ear into low-amplitude and high-pressure vibrations needed for waterborne transmission in the inner ear. The cochlea, a snail-shaped organ buried in the temporal bone, contains the hair cells (so called because they are terminated by hair-like structures) which perform the conversion of sound waves into nervous impulses. These impulses, in turn, make their way into the brain cortex, where the actual sensation of sound is evoked and the auditory signal decoded. Hair cells are most delicate, since they are extremely small (thousands of them would fit in one centimeter). They are thus easily damaged, and once destroyed they do not reproduce themselves.
Physical conceptualization is a rather abstract field, usually reserved for kids in the final two years of basic instruction. Here it is interesting to view sound as a wave phenomenon that is generated by the vibration of an object. The vibrating object transmits its vibration to the air, which in turn communicates its own vibration to the ear. These vibrations, wherever they take place, constitute a phenomenon which repeats again and again with a certain cadence (i.e., with a characteristic number of cycles per second, called frequency). High-pitched sounds (treble) have a high frequency, and low-pitched ones (bass), a low frequency. Frequency is measured in Hertz (Hz). Human beings can hear sounds from 20 Hz through (hopefully) 20,000 Hz (also abbreviated 20 kHz). Actually, very few people can perceive frequencies as high as 20 kHz; most individuals will not hear much above 16 kHz.
Sounds may be classified according to their frequency contents or spectrum. Most real-life sounds contain more than one frequency. Single-frequency sounds are called "pure tones" or simply "tones," and are very seldom found in nature; an exception are whistles. Voiced sounds, such as the vowels and many musical sounds in which a pitch can be perceived, contain several frequencies, all of which are multiples of the lowest frequency (i.e., the fundamental frequency). Other sounds, usually called "noises" (such as environmental noise, the noise of the sea or of the wind), contain many unrelated frequencies. Voiced sounds, especially the high-pitched ones, are potentially more hazardous than unpitched sounds.
The concept of sound level is essential in sound hygiene. It is the magnitude representing how loud a given sound is. It is measured in A-weighted decibels (abbreviated dBA). Sound level is measured with an electronic instrument called sound level meter. The following table contains the sound level for several sound sources and typical environments. It should be stressed that sound level depends not only on the source, but also on the acoustic environment in which the source is located, as well as the distance and location of the listener or meter.
|
Description |
Sound Level (dBA) |
| Pain threshold | 120 |
| Discotheque, full volume | 110 |
| Pneumatic drill at two meters | 105 |
| Noisy industrial environment | 90 |
| Piano at one meter, medium strength | 80 |
| Quiet car passing by at two meters | 70 |
| Normal conversation | 60 |
| Nighttime urban noise | 50 |
| Inside room (daytime) | 40 |
| Inside room (nighttime) | 30 |
| Recording studio | 20 |
| Soundproof room | 10 |
| Hearing threshold at one kHz | 0 |
The next conceptualization regards psychoacoustics, i.e., how sound is perceived. Although there are many interesting phenomena in this field, there is one which cannot be skipped over: masking. Masking arises when a sound that can normally be heard becomes inaudible in the presence of another sound (usually a louder one). We refer to these sounds as the masked and the masking sound respectively. It is not just that the masked sound seems to be softer than the masking one when compared to it. It simply cannot be heard any longer. This has important consequences for the understanding of speech in the presence of noise. Since consonants are usually comparatively weak phonemes, they are easily masked by ambient noise, particularly if it is intense. Unfortunately, most of the acoustic information of speech is conveyed by the consonants, hence the reduced intelligibility of speech with intense ambient noise.
Hearing may be reduced as a result of several causes. In the first place, there are conductive disorders, i.e., any alteration of the sound path between the external ear and the cochlea. This may be the consequence of something as trivial as a wax obstruction of the ear canal, of a perforation of the eardrum, or of any one of several diseases of the middle ear (such as an otitis or an ossicle sclerosis). These troubles are usually reversible. Nowadays it is even possible to replace one of the ossicles with a prosthesis through surgery.
There are also perceptual diseases, i.e., those affecting one or more parts of the inner ear, such as the hair cells or the auditory nerve. Since neither of them can be replaced, this kind of disease is mostly irreversible, and so is the resulting hypoacusis.
The mechanism of destruction of the hair cells involves changes in hair cells’ metabolism, induced by noise through blood flow alterations, which may damage proteins. In addition, hair cells can experience mechanical rupture due to excessive stresses (Berglund et. al., 1995). In the latter case, the destruction may occur suddenly (an acoustic trauma) as in the case of auditory accidents (the exposure to extremely loud noises from blasts or explosions, for instance), or gradually, due to recurrent exposure to loud sounds for several years.
Hypoacusis involves an upward hearing threshold shift (meaning that a louder sound is required in order to be heard), and it also may involve the presence of tinnitus, i.e., different kinds of subjective sounds such as whistle- or cricket-like sounds. Tinnitus may become severely upsetting, especially when it is permanent. Often, after a relatively short exposure to a very high sound level, tinnitus appear as a temporary effect. This should be considered as a warning and should not be ignored.
A single exposure to noise of about 90 dBA for a time interval ranging from several minutes to a few hours usually results in a temporary increase of the hearing threshold, which might be accompanied by tinnitus. After several hours of hearing rest, the temporary hearing loss usually disappears. If, on the other hand, the rest period does not last long enough, a new acoustic assault happens before the effects of the previous one have had time to recede, making matters worse.
There is some connection between an individual's susceptibility to noise-induced hearing impairment and the extent of his or her temporary deafening. This provides a rather simple criterion to assess one’s own potential for noise-induced hearing loss if one is recurrently exposed to a given noise. The criterion involves paying attention to the temporary effects of a particular kind of noise. It is very likely that such temporary effects will become permanent after an exposure of several years.
In order to ensure a better acquisition of knowledge, conceptualizations should be complemented by or even derived from experience. Experiments create an agreeable and productive working climate, so the teacher should use this technique whenever possible. Most of the experiments detailed below may be done using discarded or readily available and cheap materials.
Aim: That children acquire the concepts of pitch and loudness.
Materials: A large cardboard box, a stick, a musical triangle or a little bell.
Procedure: Children are asked to strike the box and the triangle or bell with the stick, paying attention to the differences in pitch. Then they vary the strength of the strokes, so as to appreciate the differences in loudness.
Aim: That children discover experimentally the masking phenomenon and its effect on the intelligibility of speech.
Materials: Any cardboard box, a stick or a pencil, and two or three clean empty cans loaded with a few stones or pebbles.
Procedure: Ask a child to slide the stick continuously over the box as if drawing circles. The sound is clearly perceived. Then, while the first child keeps sliding the stick, ask other children to shake the cans so as to produce a rather loud noise. The sound of the stick is now almost inaudible. Repeat the experiment, replacing the stick noise with a child speaking very softly or whispering.
Aim: That children discover that sound propagates not only through the air but also through solid objects.
Materials: Two clean empty yogurt pots, a middle-sized nail and a piece of thread or thin rope 10 or 20 meters long, depending on available room.
Procedure: Use the nail to punch a small hole in the bottom of each pot. Put the ends of the thread through the holes and tie a knot inside each pot. When the thread is pulled tight, the device works as a sort of "telephone." The children should talk and listen by pairs. One child should speak into one pot and the other should listen from the other. In order to reduce the leakage of airborne sound, the first one should not speak loud. This experiment works best in an open space.
Aim: That children learn that very loud sounds cause temporary deafening.
Materials: Some clean empty cans loaded with several stones or pebbles, and some medium-sized cardboard boxes.
Procedure: The group of children should be divided into two teams. One of them should protect their ears by pressing the tragus strongly against the opening of the ear canal, in order to "close" it. The second team should shake the cans and hit the boxes for two or three minutes. Then everybody should be quiet and try to write down the words the teacher will dictate to them with very soft voice (almost whispering). The children belonging to the ear-protected team will in general make fewer mistakes than the unprotected ones. In order for the experiment to be successful, there should be no significant performance differences between both teams when tested in equal conditions, and the teacher should dictate simple words with unequivocal orthography. It must be clear for both groups that the activity is not competitive in nature, but a co-operative experiment.
NOTE: Because of its short duration this experiment does not cause any risk for the children. However, the teacher should be attentive, in case any unusually sensitive child exhibits a strong negative attitude towards loud noise. If this is the case, the experiment should be suspended.
Aim: That children learn there is a natural involuntary tendency to raise the voice in the presence of loud sounds.
Materials: A Walkman or a portable radio with headphones, and any text to read.
Procedure: One student should be asked to listen to the Walkman or radio through the headphones. The other children should keep quiet. Starting with the music at a low volume, the student should read the text to the others. Then the teacher should gradually raise the volume. After awhile, the student will start to raise his or her voice. When the volume is deemed high enough, the teacher should turn the music off. The child will find himself or herself shouting, and will consequently lower his or her voice.
NOTE: The same comments already made regarding individual sensitivity apply here. It is perhaps a good idea to do this experiment with a child who is used to listening to music on a Walkman.
Aim: That children verify that large vibrating surfaces increase the sound level.
Materials: A paperclip, a rubber band, a medium- or large-sized cardboard box.
Procedure: Unbend one side of the paperclip in order to form a "P," and bend the straight part into an "L." Cut the rubber band and fasten one end to the round part of the clip. In the first part of the experiment, one child should stretch the rubber band and another child should play the string as he or she would do with a guitar. A weak sound will be produced. For the second part, pin the free leg of the L to one side of the box. One child should hold the box firmly on the table, while a second child should stretch the rubber band by pulling the free end and playing it. In this case the sound is much louder because the surface of the box reinforces the sound.
The ISO 1999 (1990) International Standard specifies a method to calculate the expected auditory effect of noise on people. This, in turn, allows us to obtain the percentage of the population at risk of suffering a hearing handicap, that is, a reduced ability to understand speech. These figures can be obtained as a function of the average sound level and the exposure time in years. Although this standard is mainly oriented to measure occupational exposure to noise, it may be applied with minor changes to other cases, such as exposure to recreational sounds. As an example, consider the case of a disc-jockey who has worked for 10 hours a week between the ages of 15 and 25 at an average sound level of 105 dBA. Application of hearing handicap criteria along with the ISO 1999 Standard leads to the conclusion that this disc-jockey may suffer hypoacusis with a probability of 30%. In other words, almost one out of three individuals in similar conditions will have difficulties understanding normal speech. In a similar fashion, one out of five individuals listening music three hours a day with a Walkman at a level of 95 dBA will experience similar difficulties after 20 years (Miyara, F., 1997a).
These examples show that the systematic exposure to very high sound levels is extremely dangerous. It is important to warn children of this as often as possible at school, lest we have a complete generation of precociously hearing-handicapped people. Thus, hygienic habits related to hearing should start to be imparted at school as early as the Kindergarten level, much as teeth brushing is taught.
First of all, infants and young children should be stimulated to develop a natural rejection of very loud sounds or noises. The silent walks described in Section 4 may help not only to improve sound awareness and perception but also to develop the appreciation for natural sounds, for which the human ear is best adapted. As children have a social tendency to speak too loudly, it also would be convenient if they learned to talk just at the necessary voice level. Informal contests awarding those children capable of expressing themselves (without mimics) with the lowest voice level could be organized.
Children should also learn how to protect their ears. A walk along a busy avenue may be a good pretext to exercise hearing protection. Bear in mind that the protection obtained by simply covering the ears with the hands is not as effective as closing the ear canal pressing the tragus with the forefinger. Since children's hands are usually dirty, it is not recommended that they introduce their fingers into the ear canal (to avoid infection hazards). The classic "ear plugs" made out of a piece of cotton wool are another resource to try, especially in those activities requiring free hands. In order to avoid infections or contagion, plugs should not be exchanged, and they should be discarded if dropped. Professional hearing protectors are available from pharmacies and hardware stores. Their use is recommended in very noisy environments.
Older children and teenagers should be warned about the dangers of loud music. It is very important to realize that the most beautiful music may cause the same damage that an equally loud noise can cause. The brain cortex is able to discriminate one sound from the other, but the ear, which ultimately becomes injured, does not. As we have already mentioned, the Walkman is a potentially noxious device. Since it is carried everywhere, and often listened to in noisy environments, the user tends to raise the volume in order to mask the ambient noise. Indeed, music's sound level is on average set about 20 decibels above ambient noise. If, for instance, the Walkman is used while walking along a downtown street where the noise level is 75 dBA, the listener will adjust the volume in order to get 95 dBA of music at his or her eardrums.
Shooting and fireworks detonation are two activities which involve a high hearing risk. At short distances or, even worse, in closed or semi-closed places such as rooms, patios, or courtyards, the sound level at the instant of the explosion is extremely high, and thus potentially very hazardous. Indeed, severe irreversible damage may take place at once. These kind of activities should be discouraged, and if for any reason they should happen to be unavoidable, it is highly necessary to wear hearing protectors during the exposure.
Paying a visit to a school or institute for deaf children might illustrate in a clear fashion the real nature of the risk of exposure to acoustic aggressions on a regular basis. Such a visit should be programmed very carefully, with emphasis on other educational objectives such as minority groups integration, solidarity, etc. This kind of activity should never be given an exhibitionist character or used in order to arouse unfounded fears.
Protecting hearing health shall consider not only the individual but also social or communal protection. This is an important element to take into account while designing field work practice for courses with civics contents (usually at senior levels). The detection of community noise pollution sources is a relatively simple matter even without the aid of acoustical measurement equipment. Students could be assigned the task of looking up information on applicable (local and national) regulations as to noise control, interviewing enforcement officers, making literature searches, collecting newspaper articles, jurisprudential precedents, occupational statistics, etc. Noise pollution also could be compared with other sorts of environmental pollution. This research work not only should motivate students (teenagers are naturally willing to carry out activities which help to pinpoint societal problems), but also help make them aware of the noxious effects of noise.
Some of the preceding proposals were put into practice in three educational establishments of Rosario (Argentina): the Provincial School of Dance Nigelia Soria (PSDNS), the Provincial School No. 773 Pablo Pizzurno (PSPP), and the Center of Studies on Art Technology (CETeAr).
In the first case (PSDNS), the experience was carried out in the music class. Since this is a secondary school, specific information on hearing and on the effects of loud sounds, as well as on sound hygiene, was given. Active group listening was carried out in the school's courtyard, where the sound level was low enough to be able to listen to some natural sounds. Students took note of the different kinds of noise. Noise levels were measured with the aid of a sound level meter. This instrument captured the interest of the students, since through it they could grasp the real meaning of the concept of "decibel," which is most often employed in an informal and imprecise way. Sound levels in the courtyard and in the street were compared. The impact of these activities on the students has been deemed positive. They became aware of the nature of the problem, and were able to transfer the new concepts to practical situations, such as recreational noise from discotheques and other dancing places.
In the case of the PSPP, the experience was performed with two different groups of children in the fourth year of the elementary school. First, walks around the neighborhood were organized in order to carry out active listening. Children were able to identify many different sounds. When asked to classify them, at the beginning they exhibited some confusion with regard to the categories of loud/soft or treble/bass. This is evidence that outside school they have received little or no previous stimulus on sound and its properties. The experiment on masking came up spontaneously during the stroll. They noted that at the center of a square they were able to talk to each other even from a distance of several meters, whereas at the sidewalk of a busy (and hence noisy) avenue they were not. (In connection with this, it was observed that some children strayed a bit from the group in order to avoid the interference of their own friends.) Then the children were asked to describe the sounds that made them feel better: (walking on dried-up leaves, birds' chirps, quietness, steps on the grass); and which ones made them feel worse (a parrot's cry, the screech of a rusty pulley, the ambulance's siren, a ball-point pen scraping against a glass, a piece of glass shattering). By simple intuition the children identified non-aggressive sounds (soft and not very treble sounds) as pleasing ones, whereas the aggressive ones (i.e., high-pitched or very loud sounds) were deemed unpleasant. In other words, they intuitively rejected potentially hazardous sounds. When a train happened to pass near the group of children blowing its horn, one girl who lived near the train tracks commented that "in the nighttime the horn sounds louder." The kids thus started to meditate on sound and its properties. Some of them discovered on their own that the soprano recorder is higher pitched than the contralto recorder because of its smaller size.
The construction of different percussion instruments in the classroom was another pretext to investigate sound while at a playful activity. Then a percussion piece was collectively extemporized (it should be pointed out that this particular school doesn’t have a music teacher). Interestingly, when the sound level happened to increase, some children would feel uncomfortable, particularly those who love singing and listening to music.
Other programmed activities included showing the children a sound level meter and measuring the sound level of different kinds of noise, as well as visiting the municipal library (Biblioteca Argentina) in search of textbooks and other references in the field of acoustics and noise pollution.
Finally, we have the experience at the CETeAr. The students are late teenagers and adults who study to get a degree as sound technicians. Many of them are already working either as disc-jockeys or as sound reinforcement assistants. Here the emphasis was placed on the auditory risk of individuals exposed to an occupational noise such as that found at discotheques or at a live rock concert. Students were particularly interested, and some of them were eager to get more information on the subject. Many students made comments about several temporary effects they experienced after several hours of work, ranging from temporary hearing reduction to the appearance of different sorts of tinnitus. They admitted that the usual sound level of pop music is very high.
The experience at different educational establishments shows that individuals in general, and especially in the case of young children, tend to reject those sounds which are aggressive for the human ear. Older children get used to those sounds, most often for social reasons (Miyara, 1997b), accepting and even requiring large sound power. This confirms the idea that it is necessary to develop an interest and a critical point of view with regard to the environmental noise issue when children are still very young. We can also conclude that this subject happens to be attractive for most students regardless of their level and particular interests. This in turn encourages us to go on and spread this experience.
Berglund, Birgitta - Lindvall, Thomas (Eds.) "Community Noise. Document prepared for the World Health Organization." Archives of the Center for Sensory Research, Stockholm University and Karolinska Institute, Volume 2, Issue 1, 1995.
Constitución de la Nación Argentina. Compañía Europea de Comunicación e Información S.A., Colección Documentos, Página 12, Buenos Aires, Argentina, 1994.
Convención de los Derechos del Niño. Organización de las Naciones Unidas, New York, EEUU, 20 de noviembre de 1989 (reproduced in the already cited edition of the Constitución dela Nación Argentina and passed by National Law Nro 23.849).
ISO. "Acoustics. Determination of occupational noise exposure and estimation of noise-induced hearing impairment." International Organization for Standardization, International Standard ISO 1999:1990(E), Geneva, Suisse, 1990.
Miyara, Federico. "How Much Noise is too Much Noise?" Article available at the Right to Quiet Society's web-site. (See links at the Noise Pollution Clearinghouse web-site).
Miyara, Federico. "Ceremonia de Iniciaciónal Ruido." Diario La Capital. Rosario, Argentina, 23 June, 1997. (There is an English translation on the Noise Pollution Clearinghouse web-site).
Moch, Annie. "Los efectos nocivos del ruido." Colección Nueva Paideia, Editorial Planeta, Barcelona, 1986.
Navarra, Gabriela. "Por qué somos violentos." Suplemento Salud del Diario La Capital. Rosario, Argentina, 20 August, 1997 (with simultaneous appearance in other newspapers, such as La Nación, Bs. As., Argentina).
Federico Miyara is the Director-Coordinator of the Acoustics and Electroacoustics Laboratory and Professor of Acoustics, Noise Control and Linear Electronics at the School of Electronic Engineering, both of the National University of Rosario, Argentina.
María Victoria Gómez is Professor of Music at the Provincial School of Dance "Nigelia Soria" (Rosario, Argentina) and of Flute and Recorder at the Municipal School of Music of Rosario, Argentina.
María Susana Flores and Lorena Lorenzo are Professors of General Basic Education at the Provincial School No 773 "Pablo Pizzurno."