Psychoacoustics is the study of the psychological and the physiological responses to sound.
This discussion is mainly about the physiological responses to pitch and loudness of sound.
Sound is a compression wave, and it produces physical force. This is observed by watching the vibrations produced by exposed speakers of any speaker system.
Hig pitch sounds are quantified as high frequency sounds such as the whistling sounds of jetliner engines at takeoff. This high pitch sound is measured at 90 dB at 150 feet away from the aircraft. Decibels measure the intensity of sounds. Loud sounds with an intensity of 180 dB are said to be lethal.
Humans can hear sounds of frequencies (hertz, Hz) between 20 Hz and 20,000 Hz. Dogs hear sounds between 50 Hz and 45,000 Hz, cats hear sounds between 45 Hz and 85,000 Hz, bats can hear up to 120,000 Hz, dolphins up to 200,000 Hz, elephants can hear between 5 Hz and 10,000 Hz, and humans can perceive 4 Hz to 16 Hz sounds with the sense of touch, according to established studies.
Pitch is the sensation of frequency. Pitch is a subjective psychoacoustical attribute of sound. Pitch also depends on the sound pressure level or loudness. Pitch lowers as sound pressure increases. A high pitch is a very rapid oscillation and a low pitch is a slower oscillation. A turboprop propeller rotating at high speed produces a high pitch sound and a slowly rotating wind turbine produces a thumping sound.
Noise is audible, and the adverse effects of noise exposure have been well documented to cause stress, annoynace and aggressive behavior.
Constant thumping sounds produced by the rotation of a wind turbine will produce adverse physiological effects.
Here is an illustration of the psychoacoustic effect, i.e., the adverse psychological and physiological effect of sound.
Some young teenagers like to turn up the volume of their car stereo to maximum, and at traffic stops, the people in the next lane can hear the loud music and “feel” the vibrations of the beats of the bass percussion instruments.
The very loud thumping sounds of the beats of bass percussion instruments make heart beats more pronounced. One not only can feel the thumps but one’s heart beat will also harmonize with the thumps.
High pitch sounds can cause temporary tinnitus or ringing in the ear. Lengthy durations of high pitch sounds will cause permanent tinnitus. Sudden explosions are the most well known causes of both temporary and permanent tinnitus.
The high pitch of a soprano can shatter wine glasses. It is the resonance created in the glass that shatters the glass. It is an implosion. The soprano voice causes an internal resonance (vibration) in the glass.
Extremely high pitch sounds are used in crowd control. Extremely high pitch sound such as ultrasound > 20,000 Hz is used in imaging and it has been shown to stimulate bone healing. This may be the effect of cellular vibration brought on by the ultrasound.
Pitch lowers as sound pressure increases.
Here are some observations about the physiological effects of low pitch sounds.
Low pitch sounds include low decibel humming sounds, audible thumps made by the rotation of wind turbines, and the relatively high decibel and low pitch rhythmic beats made by plucking a cello string and the double bass as well as low pitch whale songs.
Low pitch sounds do not shatter wine glasses, but they produce increased sound pressure, in other words, they produce increased compression wave pressure. Like the visible vibrations of the exposed speakers, the louder the percussion beats or thumps are, the more forceful the speakers vibrate, and sudden bursts of air can be physically seen shooting out from the rear openings of the speaker box.
Low pitch sounds of 4 Hz to 16 Hz below the audible range can be perceived by the sense of touch. In a sense, we are feeling or detecting the pressure of the compression wave at these low frequencies. This low pitch sound pressure is thus able to cause a physical response (feeling of touch) and resonance or vibration in the human body. This physical resonance or vibration affects the brain, and it can cause pounding headaches, nausea, dizziness, as well as annoyance, anxiety, depression and aggression.
The changes or fluctuations in ambient pressure and the vibrations in the air caused by the constant thumping of the wind turbine are thus sensed by our ears, and our sense of touch picks up sound in the inaudible range of 4 Hz to 16 Hz. Our physiological response to these fluctuations and vibrations would bring on the headaches, the nausea, the dizziness as well as other psychological effects such as anxiety.
When pitch lowers, the pressure of the sound as a compression wave increases. Therefore, it is this pressure of low pitch sounds that causes physiological responses in the human body.
The louder the sound, the higher the intensity. The loud sound or high intensity sound combined with low pitch are much more harmful physiologically than loud or high intensity sound combined with high pitch.
Even slight changes in atmospheric pressure that are unrelated to sound can be felt in the ear. One feels a slight deafening in the ear and pressure to the ear when the cabin pressure of the airplane increases during landing. One also feels a slight deafening in the ear and pressure to the ear when one starts descending from 7200 feet above sea level at Immigrant Gap on Highway 80 returning from Reno, Nevada, to Sacramento, California, at sea level.
Sudden high pitch sound bursts do cause relatively high pitch ringing in the ear. Sudden low pitch sound bursts can shatter physical objects and tissue such as eardrums or the tympanic membranes. This can be explained by the fact that high pitch sounds have less compression wave pressure than lower pitch sounds which have stronger compression wave pressure. It is this pressure that brings on headaches.
The physiological effect of sound would then depend on the sound pressure or the pressure of the compression wave upon an object. So physical damage would be the result of this pressure rather than pitch. A sudden high dB sound such as an explosion creates a sudden compression wave that impacts the eardrums. It causes ringing in the ear. But it would be the lower pitch compression wave produced simultaneously by the explosion that carries the impact pressure that shatters the membrane of the eardrums.
Since pitch lowers when sound pressure increases, the lower pitch sounds would be more physically damaging than high pitch sounds. The low pitch sounds carry more physical energy or impact energy than high pitch sounds.
It also seems that lower pitch and higher pressure sounds can bring about
resonance within the physical body more forcefully than higher pitch and lesser pressure sounds. An observation in this regard is that we can physically feel low pitch high pressure sound such as the thumping of the percussion instruments coming out of a speaker at maximum volume. On the other hand, we hear sirens but we do not seem to be able to physically feel the high pitch sound of the siren.
We react immediately to high pitch screeching sounds and sirens but we react more calmly to low pitch sounds. Annoyance to high pitch screeching sounds is immediate but curiosity is our initial reaction to low pitch hums and thumps.
There are several observations here. First, it may be that our hearing and our brain are naturally tuned in to low pitch sound. Second, Low pitch sounds are pleasant whereas screeching sounds are unpleasant and we tend to get annoyed and want to escape. Third, low pitch sounds are more soothing than very high pitch screeching sounds.
So, the physiological damage of sound would result from a combination of sound intensity or loudness and the strength of the pressure of the compression wave of the sound. It would be the low pitch high pressure sound rather than the high pitch low pressure sound that produces resonance within our physical body.
Ultrasound would then produce vibrations at the cellular level whereas low pitch sound would produce resonance.
In the case of dolphin therapy, it may either be the audible clicking sound or the ultra high pitch sound inaudible to humans that may be producing a therapeutic effect. The sounds made by the dolphin may either produce vibrations or resonance in the human body which would then promote healing.
If we follow the premise that ultrasound produces vibrations at the cellular level and low pitch high pressure sound produces resonance, and that humans are tuned in to low pitch sound, then both ultrasound and lower pitch sound such as the sound produced by beating a bunch of wooden sticks on a wooden floor and blowing air into a microphone should be able to produce therapeutic effects. Could this also explain how a tumor inside a patient’s body shrinks when being shouted at in Chinese: “Go away! Get out!”? What would happen if we shouted at an internal tumor “to go away, get lost!” in English?
Psychoacoustic effect of Buddhist chants
The psychoacoustic effects of Buddhist chants depend on pitch, tonality, and the chanting speed. Here are some observations:
Low pitch monotone slow speed chanting produces a soothing effect. The low pitch monotone slow speed chanting of Om Mani Padme Hum in low male voices of Tibetan monks is soothing. It affects the brain waves by bringing them down to a restive state. Higher pitch fast singing of Om Mani Padme Hum by other choruses do not bring on a restive state of the brain.
Many Buddhist masters have said that when reciting and chanting the names of the Buddha, the slower the chanting speed, the lower the pitch of the chant and the more monotone the chant, the more prolonged the enunciation, the more effective the chant will be.
Some Buddhist monks from Taiwan often conduct chanting sessions that would last for hours by reciting entire Buddhist sutras and scriptures very rapidly but with a monotone voice and low pitch.
The different styles of chanting produce different psychoacoustic effects. In slow chanting, one feels relaxed and unrushed. In rapid recitations, often times one feels rushed, and there is a strong sense of needing to catch up with the pace of the lead reciter.
As a result, a slow chant creates a sense of calm. One feels relaxed and refreshed after finishing the slow chanting session. A rapid recitation does not produce a sense of calm and one does not feel relaxed, rested and refreshed after the recitation session.
Psychoacoustic effect of listening and mental singing
We all know that listening to different types of music provokes different emotions. Some make us want to stomp our feet, clap our hands, sing along, others make us sad and cry.
Mental singing and humming a tune produce a calming effect.
In learning a foreign language, repetitive mental recitation of a foreign vocabulary word enhances memory of that word. This exercise also familiarizes our listening acuity and reduces our initial unfamiliarity towards the foreign language we are attempting to learn. It is an internalization of the sounds of that foreign language and is only one of the prerequisites to enunciating and pronouncing words correctly in that foreign language. The hearing impaired has difficulty producing correct enunciations. This is because of a lack of full and normal hearing. However, people who have lost their hearing later on in life can still enunciate correctly. This is because they can still remember the correct enunciation and they can still reproduce it vocally. This is the ability of the mind to remember sounds.
The prerequisites to fluency in speaking a foreign language thus involve memorization of the particular sounds of that foreign language and a process of internalization of foreign enunciations. This internalization is not memory per se. It is the internalization of bits of sound or “sound bites” (not in the journalistic sense, but in the linguistic and acoustic sense). Thus, the ability to read and write a foreign vocabulary word comes out of memory whereas the ability to say that word and to speak fluently in a foreign language depend on the mind’s learned ability to manipulate the “sound bites” associated with that foreign word or the “sound bites” of foreign words one uses to speak that foreign language.
People who speak a foreign language with a heavy accent also go through this internalization of the sounds of that foreign language. The memory of the enunciations is there but when the memorized enunciations are vocalized, the accent of the mother tongue of the speaker distorts the vocalized enunciation. This distortion does not impede fluency in any way.
The heavy accent is a physiological effect of the mother tongue on the enunciation of speech.
Psychoacoustic effect on autistics
When I was teaching an 11-year-old autistic girl, I tried to play some classical music of Mozart to see if the music can induce some behavioral modification in the child. The child did not reject the music. However, the child was fascinated by African drum beats. She would sit in a corner of a room listening to the African drum beats for hours on end. This fascination with African drum beats was also witnessed by a caretaker of a young male autistic adult.
The African drum beats seem to be able to regulate brain waves to produce a calming effect and a tranquilizing effect on the autistic child as well as on the young male autistic adult.
The autistic child would be totally immersed in listening and would not respond to any interruption. When there was too much interruption, the child gets angry and goes into a tantrum.
It seems that the interruption disturbs the mental calmness produced or induced by the African drum beats.
The African drum beats seem to produce a psycho-physiological response.
Ear wax serves at least four functions. First, it dulls the sound that enters the ear. Second, it protects the eardrums from the wave pressure of sound. Third, it protects the ear by preventing insects from entering the ear canal. Fourth, it keeps water from getting into the deep inner ear but it also seals moisture inside the ear. Often one can hear sloshing inside the ear when one presses the area just below the triangular protuberance in front of the outer ear canal.
One way to remove ear wax is to place a drop or two of hydrogen peroxide in the ear and then remove it with the dropper to suck the moisened and loosened ear wax out. Over accumulation of ear wax can cause temporary deafness.