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Atmospheric Disturbance Caused by Cooling Fans
Impact on our home "Salbu" located two kilometres northwest of Eskom's station Apollo

Introduction and Notes

Salbu Experience - Larsen Family


Having experienced the debilitating side effects of the "throbbing" sound caused by a battery of forty eight large cooling fans at the Eskom converter station Apollo it is alarming to learn that the noise spectrum (centred on 33 Hz) being radiated from this battery of fans falls inside the "sensorially sensitive" frequency range of 13 Hz to 40 Hz used by commercially available mind machine "entrainment programmes" optimised for the manipulation of the human brain.

The Apollo Fan Blade Repetition Rate of 33 Hz coincides with the higher end of the human brain's Beta Wave frequency range (13-30 Hz) and is associated alertness and in particular with the human "fight/flight" mode. The frequency of the 'beat note' caused by the bank of Apollo fans coincides with the frequency of the human brain's Delta Waves (1 to 3 Hz) that are strongest in the deepest part of the sleep cycle.

This "unfortunate" combination of frequencies could explain why, the intrusion into our home of the almost silent "Apollo Noise", causes members of our family to be woken from a deep sleep in an alert and "fight/flight" state of mind.

Recent measurements taken at our home by the Laboratory of Vibration and Acoustics, a division of the South African Bureau of Standards (SABS), confirm that, even on a so called quiet night, the 33Hz "throbbing sound" measured at a level of 45 dB exceeded acceptable levels as defined by both the Broner and Leventhall Low Frequency Noise Annoyance Assessment by Low Frequency Noise Rating (LFNR) curves and the more recent RC Mark II rating procedure. RC Mark II is a refined procedure for rating the noise of heating, ventilating and air-conditioning (HVAC) systems in buildings - (Submitted July 1997) - Warren E. Blazier, Jr.)

Low frequency pure tones, just at or above the threshold of hearing, have been found to cause extreme annoyance. (see:- Broner, 1978b: Tempest 1979: Chatterton, 1979: Leventhall, 1980.)

Typical outdoor and indoor SALBU noise profiles, resulting from noise generated at APOLLO, are shown in the adjacent RC diagram. It can be seen that the LF noise from Apollo exceeds the threshold of hearing by a considerable margin.

RC diagrams, recommend by Warren Blazier, are used for the evaluation of the impact of noise caused by air-conditioning (HVAC) systems. The vertical scale shows the level of the noise in dB and the horizontal scale shows the frequency of the noise in Hz.

For "minimum impact" the noise from the (HVAC systems should follow one of the RC curves shown in the adjacent diagram. The RC 25 curve would be suitable for use in quiet office areas. As yet there are NO published RC curves for use on very low noise level environments. The 'red numbered' RC curves in the adjacent diagram have been added for guidance purposes only.

Warren Blazier's report states that, at the present time, there is no consensus a standard for assessing and rating HVAC-related sound containing audible tonal or narrowband components and the RC Mark II method does not address very-low ambient noise conditions typical of performing arts and assembly spaces for worship, or special facilities such as recording studios.

It should be noted that the bedroom area shown in this example has a high degree of sound insulation and has NO external windows or doors. The TV room example, shown in the diagram, would be more typical of the sound attenuation that could be expected for the average bedroom.

It can be clearly seen that, both outdoors and indoors doors, the "33 Hz and 66 Hz low frequency pure tone components of the pulsating noise" from the Apollo DC Fans are the dominant noise signals. Note the VERY LARGE (20 dB) change in level of the low frequency component of the Apollo Noise due to variations atmospheric conditions AND that the low frequency noise from Apollo exceeds Zwicker's low frequency hearing threshold for 10% of the population by a considerable margin.

As expected the lower frequency components of this noise are NOT attenuated by the building and if an attempt were made to 'mask' the low frequency noise by introducing 'shaped' noise in order to MATCH an appropriate Broner and Leventhall LFNR curve, or Warren Blazier's appropriate RC curve, the level of the 'masking noise' INSIDE the bedroom area of the house would have to be at least 40 dBA.

The use of a continuos indoor 'shaped masking' noise in excess of 40 dBA would be unacceptable as the World Health Organisation (WHO) recommends that the average noise level for undisturbed sleep should be less that 30 dBA with a peak night time maximum of 45 dBA. The generally accepted maximum level for OUTDOOR nighttime noise for a residential area is 45 dBA (i.e. Ldn=55 dBA). Typical attenuation figures for a dwelling with open window is 10 dBA and with closed windows is 20 dBA. Sleep disturbance and annoyance occurs at indoor levels of greater than 30 dBA.

Ear plugs offer little or no relief AND we have been advised that to "insulate" our home against very low frequency noise we would have to turn it into an airtight "concrete bunker" with sealed doors and without any windows !

To view a typical indoor (bedroom) Salbu noise profile: Click HERE. The "33 Hz pulsating tonal noise" from the Apollo DC Fans is the dominant noise signal.

As the health and well being of our family is as stake we await a definitive answer to our letter addressed to the Chief Executive of Eskom.

    NOTE: The debilitating Apollo "throbbing" sound, comprised of multiple 33 Hz tonal signals with a "beat" or repetition rate of 1-7 pulses per second, is clearly illustrated by the three-dimensional "waterfall" image with the caption that reads: "A PICTURE IS WORTH A THOUSAND WORDS"

    NOTE: The debilitating effect of the noise is dramatically illustrated by yet another "PICTURE"

Current Situation

We are once again being harassed by an abnormal atmospheric condition caused by a battery of forty eight very large cooling fans at the ESKOM Apollo "DC" converter station. This station is located on the southern border of the Rietvlei Game Reserve about two kilometres south east of our farm Salbu and is becoming operational after being out of service for many years.

The Portuguese government, as owner of Hidro-electrica De Cahora Bassa (HCB), which controls Mozambique's Cahora Bassa hydropower plant recently negotiated a favourable tariff deal with ESKOM to supply electricity to the Republic of South Africa (RSA).

As a result of this new tariff deal ESKOM is refurbishing the Apollo "DC" converter station. Electricity is supplied from the Cahora Bassa hydropower plant in northern Mozambique to South Africa by means of a million volt DC transmission line.

The Apollo converter station changes the direct current (DC) electricity supply from the Cahora Bassa generators into an alternating current (AC) supply suitable for distribution into the ESKOM owned electricity grid.

For further information see Financial Mail - November and December 1997 - articles headed CAHORA BASSA.

Historical Background

A number of years after we had established our home in this area ESKOM purchased a portion of the farm Witkoppies and constructed the station Apollo . Shortly after the commissioning of the Apollo DC converter station we become aware of an incessant "vibration" that could be "felt" rather than heard. A few hours after sunset this "vibration" became audible as a"throbbing sound". The source of this debilitating atmospheric disturbance was traced to " banks" of very large "valve cooling fans" in the DC section of the station Apollo. After conducting an extensive investigation Eskom gave us the undertaking that this "noise" problem would be rectified. Shortly after giving us this undertaking the supply of electricity from Cahora Bassa was discontinued. Many years later, when it was anticipated that the supply from Cahora Bassa would be resumed, Eskom once again assured us that, before the DC section of the station Apollo went back online, this "noise" problem would be rectified. See our recent letter to Eskom for an update and summary.

  • About the Apollo "DC" Valve Cooling Fans
  • There are 48x vertically facing fans - arranged in 6x banks of 8 fans
  • Fan Blade Repetition Rate (BRR) = 33 Hz - see below
  • Each fan is 2.5 meters in diameter
  • Each fan has 6x Blades
  • Each fan is driven with a 37KW 1470 RPM motor
  • Fan pulley ratio 710/160 = 4.43
  • Fan speed 331 RPM, or 5.52 revs per second
  • Base Noise = 6x5.52= 33.1Hz (BRR)
  • Total fan motor power is 1.78 Megawatts
  • Fan cooling capacity in excess of 11 Megawatts

Turbulent "Apollo made" Inversion Layer

Sound waves are deflected away from warm air towards cooler air. Therefore under favourable atmospheric conditions, when the lower air is warm, sound waves are deflected upwards and can pass over a neighbouring property. Conversely under unfavourable conditions, when the upper air is warm, sound waves are deflected downward onto neighbouring properties.

We must assume that the hot air caused by the Megawatts of heat blown upward by the Apollo DC cooling fans spreads out and produces an unfavourable condition in the form of a local "Apollo made" inversion layer.

This "Apollo made" inversion layer, together with a "33 Hz pulsating air stream" from each the forty eight Apollo fans, will cause a local turbulent atmospheric condition that will not only raise the level of noise from other sources, thus increasing the "ambient" noise level on our property, but will "modulate" this ambient noise and cause complex, and disturbing, "intermodulation" products.

Brian Marston (marstonb@wr.com.au) wrote: The spreading of the spherical wavefront spreads the energy over an ever increasing area such that the area increases by the square of the distance from the origin, hence the sound level (for very low frequency noise) decreases by 6dB for every doubling of distance.

Sound Pressure Level = Sound Power Level - 10*log10(4 * pi * radius *radius) Sound Pressure Level = Sound Power Level - 10*log10(4 * pi) -20*log10(radius)

If the wavefront is constrained to spread cylindrically as can occur under atmospheric thermal inversion conditions then the increases in a linear manner and hence the sound level will only decrease for this situation by 3dB per doubling of distance.

Sound Pressure Level = Sound Power Level - 10*log10(4 * pi * radius) Sound Pressure Level = Sound Power Level - 10*log10(4 * pi) - 10*log10(radius)

Normally (for very low frequency noise) in the atmosphere the decrease falls somewhere between 3dB and 6dB per doubling of distance.

Why is this incessant low level "throbbing sound" so debilitating?

We are coming to the conclusion that it is the random beat note (circa 4 Hz per second) - arising out of the multiple (circa 33 Hz) pure tones generated by the battery of large cooling fans - that is causing us distress and that the impact of this noise cannot be simply defined by the level of the tones and/or the spectral balance of the noise. It is the long term nighttime exposure to this incessant "throbbing sound", with an irregular beat, that has caused us to become "sensitised" to this debilitating, low level, "modulated" VLF noise.

Low frequency pure tones, just at or above the threshold of hearing, have been found to cause extreme annoyance. (see:- Broner, 1978b: Tempest 1979: Chatterton, 1979: Leventhall, 1980.)

Why is the freeway noise more acceptable?

Noise from the distant freeway sounds like the sea and, in the absence of the tonal sounds from the banks of Apollo Fans, is acceptable. Some mornings the noise from the freeway reaches a high level at Salbu. The freeway noise is predominately a random noise and any tonal noise from vehicles travelling at freeway speed is typically a few octaves higher in frequency than the Apollo Fan Noise. To view a typical outdoor Salbu noise profile under noisy freeway conditions when the Apollo Fan noise is not present: Click HERE.

Debilitating side effects caused by "Apollo made" Turbulence

Mind Machines - Mind Manipulation Programmes make use of the frequency range 13-40 Hz

The suppliers of "TURBO Mind Machines" claim that "With the proper combination of waveform, frequency and pulse repetition rate, many people experience euphoria, heightened awareness and vivid dreams." There are many suppliers of such equipment and all make similar claims - The suppliers of "mind machines" refer to a number of published papers on the subject. (ref:www.mind-gear.com)

Salbu Experience - Larsen Family

After an extended period of exposure to the "throbbing" of the Apollo DC fans members of our family subscribe to the claims made in the above statement. Family members claim that, after long term exposure, they have become "entrained" and the debilitating "throbbing" sound induces vivid dreams and/or wakes them up. The false feeling of euphoria makes further sleep difficult if not impossible.

Having experienced the serious debilitating side effects of this noise it is frightening to read that most "entrainment" or mind manipulation programmes start out in the beta frequency range (13-40 Hz) and that the Apollo Noise spectrum is inside this range of frequencies.

As the health and well being of our family is as stake we need to have a definitive answer to our recent letter addressed to the Chief Executive of Eskom

Effects of Beta Frequency Binaural-beat Audio Signals

These following reports confirm that the Larsen family has every reason to be concerned about the nature of the Apollo noise

  • Investigation Into the Effect of Beta Frequency Binaural-beat Audio Signals on Four Measures of Human Memory.
    Author: Richard Cauley Kennerly. (http://www.monroeinstitute.org/research/human-memory-kennerly.html)

  • EEG and Subjective Correlates of Alpha Frequency Binaural-Beat Stimulation Combined with Alpha Biofeedback.
    Author: Dale S. Foster, PhD. (http://www.monroeinstitute.org/research/alpha-binaural-beat.html)

  • Binaural Auditory Beats Affect Vigilance Performance and Mood (theta/delta range)
    Duke University Medical Center, Durham (http://www.monroeinstitute.org/research/lanepaper.html)

    NB: Copies of the above papers were given to Eskom and SABS personnel by Salbu staff.

    Entrainment and Mind Manipulation

    Most entrainment programmes start out in the beta frequency range (13-40 Hz.) to match and pace our waking state rhythm and gradually slow (ramp) to the target range. The initial phase may seem so exciting with the vivid colours and kaleidoscopic patterns you see in your "mind's eye" that you may doubt that you will slow down and let go of the mind chatter and tension. This fast, almost psychedelic phase passes quickly as the pulsing slows. Most users find that within a session or two, they easily and automatically follow the changing frequencies and patterns into the desired state.

    With any mind machine, if you selected a session with a target frequency in the low alpha or theta range, you should feel a change in awareness within a few minutes. Many people report a floating feeling. Your attention may start to wander as your thoughts become less linear and logical. You may find yourself in a lucid dream complete with sights, sounds and feelings. Some people, auditory types, often hear words in the pulsed sounds. This indicates theta activity and heightened creativity. Because your sense of time changes during the session, it may seem as if you have slept. If you felt tired before starting, you may fall asleep during the session or when it ends. Usually, you will feel a definite difference between your state before the session and how you feel during the session. This state should linger for a while after the session ends.

    Brain Wave Frequencies

    EEGs show that at any given time, the human brain produces distinct waveforms in four frequency groupings, called beta waves, alpha waves (8 to 13 Hz), theta waves (4 to 7 Hz), and delta waves (1 to 3 Hz). Beta waves (14 to 30 Hz) are the dominant set of frequencies, the ones with the highest amplitudes and occur when the body is most active and alert with the highest frequencies in that range often described as "fight/flight" mode. Delta waves (1 to 3 Hz) are strongest in the deepest part of the sleep cycle (3rd and 4th stages) when the body's metabolism is at its lowest, breathing is slow and even, temperature is low, pulse rate is low and blood pressure is low.

  • Summary
  • Beta Waves (14 to 30 Hz) are associated with alertness - the highest range (30 Hz) with the human "fight/flight" mode.
  • Alpha Waves (8 to 13 Hz) have long been associated with meditation and relaxation.
  • Theta Waves (4 to 7 Hz) are considered by some to be associated with a dreamy, creative states.
  • Delta Waves (1 to 3 Hz) are generally strongest in the deepest part of the sleep cycle.

    Further sources of Information

    More and more populations are reporting the persistence of ultralow pitch sounds which render them disorintated, weak and fatigued. Having often unexplained sources, we find the bibliography flooded with cases of persistent 'atmospheric...and underground sounds :
    INFRASOUND by John D. Cody.)

    TMI Research Index
    Mind Machine FAQ
    Munro Institute - Binaural beat sound: Exploration, training, and applications


    A picture is worth a thousand words - see the throbbing sound !
    (For a more detailed picture click here - 56KB file)

    The Apollo DC fans were switched off for a period of some 15 minutes to enable this test to conducted. The debilitating "throbbing" noise stopped after the last fan was switched off and only started again when the fans were restarted. There was a light air movement was from the direction of Apollo.

    After a period of exposure to low frequency noise people become sensitised to the noise and this can result result in allergic-type reactions to low frequency noise sources.

    After a period of some six months of exposure to the Apollo noise our son Gernot was found to be "incredibly" sensitive to LF noise. The audiologist said "he has the most incredibly sensitive low frequency hearing - by far the most sensitive hearing that I ever measured in a patient".

    Silent Noise: Broner and Leventhall's "Low Frequency Noise Rating Curves (LFNR) for indoor use" show that complaints can be expected when tonal noise, with for example a frequency of 33Hz, just reaches the the threshold of hearing. The noise radiated by each of the large cooling fans at Apollo is centred on 33Hz. Domestic dwellings have multiple resonances at these low frequency and, at best, are totally transparent to very low frequency sound.

    The debilitating Apollo "throbbing", that at times can be felt rather than heard, is the result of the "beat affect" between the noise signals, and the noise signal harmonics, being radiate by the multiple banks of identical fans. There is the possibility of lower frequency components being present as well due to fan blade shape variations.

    Even at low levels, irregularly repeating tonal sounds can be particularly annoying.

    A neighbour, situated about a kilometer due east of Apollo, related his experience of this "silent noise" as follows: "I was working outdoors and become aware of a strange thumping sensation in my chest and a pulsating pressure in my ears. I thought I had a medical problem until a colleague said that he was experiencing the same sensations. On checking we found that the phenomena was not related to our heart beat rates."

    Within a few kilometres radius of the ESKOM station Apollo the LFNR "complaints limit" is being exceed by nearly 20dB. This means that people living in the area are being subjected to sound power levels approaching a hundred times more than the tolerable level.

    Totally Silent Noise: It is important to note that at even lower frequencies complaints can also be expected for levels as low as 20dB below the threshold of hearing - for example complaints can also be expected when noise, with a frequency of 16Hz, reaches a level of 20dB below the threshold of hearing.

    Psychoacoustic sounds

    Pulsed sound, or percussive sounds like drumming, will produce a frequency following response in people. This frequency following response (entrainment) forms the foundation for the functioning of "mind machines. Commercial mind machines use pulsed and/or binaural signal sounds.

    Binaural sounds create a resonance effect that synchronises the two hemispheres of the brain. Feeding one tone to the right ear and a slightly different tone to the left ear produces a beat frequency in the brain. Because the process requires the cooperation of both brain hemispheres, a unique mental condition occurs. With the beat frequency adjusted to the alpha or theta range, most people feel an entraining effect.

    Note: See the pulsed random beat, or random drumming affect, of the Apollo noise signal in the above image.

    About theWaterfall Image - A picture is worth a thousand words

    Place and Time
    Farm Salbu : indoors in bedroom area : observations and measurements recorded over a period of years between the hours of 22h00 and 06h00

    Traffic noise
    The low frequency component of traffic noise can be heard for limited periods of time during peak traffic hours - the traffic noise often becomes "modulated" by the Apollo " throbbing noise".

    Apollo DC Fan Noise
    The Apollo DC fans causes an atmospheric disturbance that results in an incessant and debilitating "pulsating" vibration that increases in intensity and becomes a "throbbing noise" a few hours after sunset.

    The "throbbing noise" is most obvious on cold nights with little or no air movement.

    The "throbbing noise" level is aggravated by a light air movement from the direction of Apollo.

    B&K Meter settings
    31.5 Hz Filter

    Meter peak readings
    55/65 dB It should be noted that the level of noise is 12/22 dB above the "Low Frequency Noise Rating" (LFNR) "complaints" threshold.

    Spectrum Analyser settings: BOOST ON
    See Noise Peaks at 30Hz/33Hz (the white + marks the 33Hz peak - see arrow as well)

    Captured Audio - Scope display period
    1-4 seconds (Scope display period) The "throbbing" component of the beat between the Apollo DC fans is clearly shown. The pulse repetition rate of plus/minus one pulse per second is clearly evident - compare the pulse with the Delta Sleep pulse repetition rate of plus/minus 1 pulse per second. They are nearly identical.

    For more detailed images see "Measurement taken at Salbu" - Spectral Images


    Aiken, L.R., (1988). Psychological Testing and Assessment. Allyn and Bacon, INC.: Newton MA.

    Broner N and Leventhall H.G., (1983). Low Frequency Noise Annoyance Assessment by Low Frequency Noise Rating (LFNR) curves. Broner N: Vipac & Partners Pty Ltd., 30-32 Clarement Street, South Yarra, Victoria, Australia 3141. Leventhall H.G. : Atkins Research and Development, Woodcote Grove, Ashley Road, Epsom KT18 5BW, U.K.

    Leventhall H.G. : History of Active Noise Control - Active Control Strategies

    Carroll, G.D. (1986). Brain Hemisphere Synchronization and Musical Learning. University of North Carolina at Greensboro. (Available through The Monroe Institute, Rt. 1, Box 175, Faber, VA 22938)

    Cozby, P.C. (1989). Methods in Behavioral Research. Mayfield Publishing Company: Mountain View CA.

    Domjan, M., & Burkhard, B., (1982). The Principles of Learning and Behavior. Brooks/Cole Publishing Company: Monterey, CA.

    Edrington, D. (1983, January). Hypermnesia experiment. Breakthrough. (Available from The Monroe Institute, Rt. 1, Box 175, Faber, VA 22938)

    Edrington, D. (1985). A Palliative for Wandering Attention. Tacoma, WA. (Available from The Monroe Institute, Rt. 1, Box 175, Faber, VA 22938)

    Edrington, D. (1985). Binaurally Phased Sound in the Classroom. Tacoma WA. (Available from The Monroe Institute, Rt. 1, Box 175, Faber, VA 22938)

    Edrington, D., & Allen, C. (1985). 1984-1985 EEG Experiments with Binaurally Phased Audio Stimuli. Tacoma, WA. (Available from The Monroe Institute, Rt. 1, Box 175, Faber, VA 22938)

    Hutchison, M. (1994). Mega Brain Power. New York: Hyperion.

    Kramer, P.D., (1993). Listening to Prozac: A Psychiatrist Explores Antidepressant Drugs and the Remaking of the Self. New York: Viking.

    Leventhall H.G. : History of Active Noise Control - Active Control Strategies

    Malherbe, F le R., (1997). THE NOISE IMPACT ON THE PROPERTY OF MR DAVID LARSEN. Report No. 3150/782102, September 1997. SABS Laboratory for Vibration and Acoustics.

    Ochs, L., (1993). Electroencephalographic Disentrainment Feedback (EDF). Concord, CA. (Electronically published manuscript available from author: Len Ochs, Ph.D., 3490 Silver Spur Court, Concord CA. 94518, or by email at 72040.3433@compuserve.com.)

    Ostrander, S., & Schroeder, L. Supermemory: The Revolution. New York: Carroll & Graf Publishers, Inc.

    Owens, J.D. (1984). Some reports from teachers using Hemi-Sync. Unpublished manuscript, Tacoma Community College, Tacoma WA.

    Pawelek, Y., & Larson, J. (1985). Hemispheric Synchronization and Second Language Acquisition. US Army Educational Services Division, Fort Lewis, WA.

    Peele, S. (1989). Diseasing of America Addiction Treatment Out of Control. Boston: Houghton Mifflin Company.

    Peniston, E. G., & Kulkosky, P.J. (1989, March/April). Alpha-Theta Brain wave Training and B-Endorphine Levels in Alcoholics. Alcoholism: Clinical and Experimental Research,13, (2), 271-279.

    Peniston, E. G., & Kulkosky, P.J. (1990). Alcoholic Personality and Alpha-Theta Brain wave Training. Medical Psychotherapy, 3, 35-37.

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    Waldkoetter, R. (1982a). The use of audio guided stress reduction to enhance performance. Unpublished manuscript, The Monroe Institute, Professional Division, Rt. 1, Box 175, Faber, VA 22938)

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    1. NO 10213 Low frequency noise assessment metrics - what do we know?

    Broner N

    USA, Ashrae Transactions, 1994, Part 2, pp 380-388, 9 figs, 1 tab.

    Notes that sound quality in office and other occupied spaces has been of continuing interest since the 1950s. Existing assessment methods do not account adequately for the low-frequency background sound (less than 250 Hz) in particular low-frequency rumble produced by operating HVAC systems. Discusses the results of research in which more than 75 HVAC noise samples were collected, normalised and categorised in terms of sound quality. Proposes a modified set of room sound quality curves.

    noise pollution, office building, ventilation system

    1. NO 10217 Sick building syndrome: the acoustic environment.

    Burt T

    Indoor Air '96, proceedings 7th International Conference on Indoor Air Quality and Climate, held July 21-26, 1996, Nagoya, Japan, Volume 1, pp 1025-1030, 13 figs, 10 refs.

    Reports on a case where low frequency noise centred around 7 Hz was found to occur in several office rooms. States symptoms resulting from exposure to infrasound are typical of sick building syndrome. Many of the occupants exhibited such symptoms. Shows that the low frequency component of ventilation noise is often being amplified in tightly sealed rooms. Maintains that repeated or long-term exposure to such amplified infrasound may be triggering an allergic-type response in individuals.

    sick building syndrome, noise pollution

    1. NO 10218 Thermal and acoustical performance of "buffer rooms".

    Mahdavi A

    USA, Ashrae Transactions, 1993 (1), pp 1092-1105, 12 figs, refs.

    The term "buffer room" refers in this context to spaces built between thermally, visually and acoustically "controlled" indoor rooms and the "noncontrollable" outdoor environment. Examples of buffer rooms are sunrooms, atria, (enclosed) staircases, and air locks. In a long-term research effort carried out in Austria, buffer rooms were studied with regard to their hygrothermal and acoustical performance within a human-ecological framework. Special attention was paid to the problems of temperature fluctuations and risk of overheating, ventilation rates, and humidity control as well as sound transmission. The research agenda included studies under controlled conditions in SHA, a facility dedicated to building physics research in Vienna, Austria, as well as field investigations. Gives a summarised overview of the content and results of some of these studies, focusing on the issues of thermal performance as well as the acoustical insulation effect of sunrooms and its relationship to natural ventilation.

    thermal performance, noise pollution, sunspace, atrium, natural ventilation

    1. NO 10226 Wall of sound.

    Macneil J

    UK, Building, 22 January, 1993, pp 46-47.

    Describes the use of active noise control, which relies on creating more sound to counter the effects of the offending sound. It has been used in the construction industry to dull sound from generators and fans coming through ducts, and plans are being devised to use it to stop noise entering through curtain walls. One of its main advantages is that it is effective with low frequency sounds which are hardest to control with passive techniques.

    1. The role of low frequency noise and infrasound in sound quality


    H.G. Leventhall, Digisonix Inc., London, United Kingdom

    Volume 2, Page 933


    (No abstract available for this paper)

    Acrobat PDF file of scanned paper: in950933.pdf

    Reports on the Impact of 'Modulated' Low Fequency Sounds

    More and more populations are reporting the persistence of ultralow pitch sounds which render them disorientated, weak and fatigued. Having often unexplained sources, we find the bibliography flooded with cases of persistent "atmospheric...and underground sounds". Meantime, thousands of sufferers are having the quality of their lives severely affected and feel extremely bitter that so little is being done to help them.

    At a Conference on The Hum held at The Royal Society of Medicine, London, on the 25th of November 1989 the majority of people suffering from the problem stated that the noise appears to have two differing components. There is a a straightforward "hum" plus another lower frequency modulation component.

    Sufferers report that the noise appears to reach them through walls, floors, and ceilings when inside, and externally when outside. It causes them considerable stress and loss of sleep which greatly lowers the quality of life.

    Acclimatisation is difficult as the human brain cannot pinpoint the directionality of low frequency acoustic signals. As with all strange new noises, the brain seems to seek to label the source and presumably designate it as safe or dangerous - safe noises can be put aside, but unidentified noises could be dangerous. This is a very primitive response to possible danger. In the wild, little animals are alerted to the approach of big animals, as big animals tend to make lower frequency sounds.

    THE PHENOMENON OF LOW FREQUENCY HUMS from a book by Leslie and Clive Sheppard
    INFRASOUND by John D. Cody.)

    TMI Research Index
    Mind Machine FAQ
    Munro Institute - Binaural beat sound: Exploration, training, and applications

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