Production of sound, effects of noise and sound pressure in devices
Your old electric appliance was louder than an aircraft taking off and is now being disposed of! Excited sign for the parcel service’s package with your new purchase in it, a purchase where you paid attention not only to price and design, but also to the decibel specifications. And really, it purrs like a peaceful kitten. You feel relieved instantly, cooling down yourself and the house equally. A constant, heavy sound pressure leads to stress and can cause irreparable hearing damage as well as awful diseases. But is sound actually produced and how can operating noise be reduced? We’ll explain in our guide!
Contents:
- Noise in everyday life
- Health effects
- Scientifical: How is sound pressure produced and what does sound level mean physically? (Who was Blaise Pascal?)
- Sound volume of axial and centrifugal fans
- Tips for quiet fans and fan-powered appliances
Noise in everyday life
Due to increasing noise pollution in cities, constantly ringing phones and the invention of portable music players our sense of hearing is stimulated simply too much nowadays and is more vulnerable than it was in preindustrial times. Irregular generation of noise on busy roads and train and tram platforms count amongst the most uncomfortable sources of noise for humans. Even quaint villages with grazing cows and sheep have trucks passing through in the wee hours of the morning. The national result: More than half of the citizens feel bothered by traffic noise. Until modern, silently running electric cars have become standard equipment in the average household, at least the own home should provide some peace. Neighbour’s children learning instruments and football fanatic husbands might let themselves be regulated down to a more acceptable level with a bit of encourage or a few goodies, however household appliances on the other hand can pose a strain in the long run, especially if they are constantly switched on, for instance refrigerators.
Due to evolution, the ear does not differentiate between ominous signals and conventional everyday sounds – all are sensed the same way, consciously trying not to listen is impossible. A constantly unpleasant background sound is incredibly annoying!
Even when we are asleep our sensitive ears detect the smallest sound. New mothers sometimes experience a certain type of sleep, where during deep sleep noise from cars driving past, barking dogs or the snooring sweetheart are filtered out and ignored, however the smallest sound made by their newborn immediately wakes them up!
Health effects
It is irrevelant to our body whether or not we are conciously aware of the fact that household appliances do not pose a danger: The stress hormone cortisol is released to motivate us in fight or flight situations. In order to supply extremities with enough blood, the heart beats faster and tension in the muscles increases. If the noise occurs only briefly (vacuum cleaner), our health is not affected seriously. If the disturbance continues for days, without a possibility for the body to calm down through activity, reactions to the stress measurably become much more noticeable.
Studies have shown that constant exposure to the relatively low noise level of 40 db(A) can lead to increased risks of cardiovascular disease, especially during night when the body should be in its regenerative phase. Mental illness also become more of a problem for otherwise healthy people, only one (!) day of sleep deprivation can already trigger symptoms comparable to schizophrenia or a psychosis, according to an international research team of the University in Bonn. The symptoms include illusions like hallucinations, impaired perception of time as well as thought and concentration disorders. These results have also surprised experienced researchers. Noise may be evaluated individually by each person, however the average limit of 60 db(A) causes humans to feel disturbed. According to the workplace requirements directive including the directives about noise and vibration, the range of 85 db(A) and higher obligate workers to wear ear protection, as this level is rated as causing acute harm to the hearing.
Noise level by comparison
no health hazards:
10 dB(A) mosquito buzzing, PC running
20 dB(A) clock ticking, leaves rustling
30 dB(A) whispering, breathing sounds
35 dB(A) Indoor fan
beginning at 40 dB(A) concentrating becomes problematic
40 dB(A) street noise with double-insulation
50 dB(A) Refrigerator in 1 m distance, gentle rain
55 - 80 dB(A) increased risk for illness
60 dB(A) conversations, frogs croaking
70 dB(A) normal traffic
80 dB(A) motor bike engine
beginning at 85 dB(A) health is threatened with exposure over 40h/week
90 dB(A) tram, thunderstorm, lawn mower
100 dB(A) pneumatic drill in 1 m distance
110 dB(A) club, rock concert
120 dB(A) very dangerous, painful sensation, hearing loss begins to occur after short exposure
Negative consequences of noise
- insomnia and poor quality of sleep
- stress damaging the heart and other nervous damages
- bad temper or desire for isolation
- general sense of well-being at home is affected
- decrease of mental concentration and learning aptitude, danger of accidents
- neglect of sufficient ventilation and airing due to street noise
- decrease in value of residential areas
- slow loss of hearing leading to deafness (when subjected over long periods)
- costs for medical procedures, medication and therapies
Scientifical: How is sound pressure produced and what does sound level mean physically?
(Who was Blaise Pascal?)
Blaise Pascal (1623-1662), born in France and raised during the confusing years of the the Thirty Years‘ War, he lost his mother at a young age. His lifetime was somewhat overshadowed by feeble health, however despite this and his noble heritage and his family’s wealth he still decided to spend his life as a religious hermit. His research about measuring air pressure and the discovery of geometric principles made him an acclaimed mathematician and physicist and continues until this day to influence our understanding of science and technology. The internationally used unit of pressure and of stress was named Pascal (abbr. Pa) in his honour.
Pressure = force applied per area
The atmosphere of the earth has a huge mass and a calculated net weight of about 10,000 kg per 1 m2 surface. You might know this effect from hiking in the mountains, the higher you get, the more air pressure and air density decrease. Diving underwater, thus coming closer to Earth’s centre, pressure increases.
Sound is defined as a tone or sequence of tones that become audible to humans and animals through their hearing. Depending on air pressure and temperature the sound is propagated as wave (therefore sound wave) and can be calculated. The auricle catches the vibrations, leading them through the ear canal where they become more concentrated. In case of important information, the perceived sound is transmitted to the brain which filters the information from discussions, singing and music, categorising them as useful, or not useful in case of noise, sounds from construction work or traffic. The different pitches of the “waves“ per second – the frequency (as unit Hertz) – is only audible to humans in the range from 16 Hz to 20 kHz. Many animals have a much more advanced spectrum of hearing or even communicate through high-frequency sound.
If the sound pressure level is increased by a mere 10 dB, humans perceive it twice as loud. Our subjective senses let us experience a device operating in the range of 52 dB as much more quiet than a product with 58 dB. The bigger the distance to the source of the sound, the more the audible sound pressure level decreases as well.
Sound is not only spread as a carried medium through the air, but also in water and through solid bodies. If domestic appliances that are mounted to the ground or ceiling, or standing on other solid surfaces, their vibration is transferred to the material, causing resonance sounds like the body of a guitar – just less pleasant.
Sound volume of axial and centrifugal fans
The strongest possible air pressure is important for a flawless operation of ventilation devices and systems. Particularly the ventilation of through long ducts or in large, spacious factory buildings the applied fan requires a lot of power so that so that the air flow does not lose momentum halfway. This motor power in combination with the fast movements of the blades inevitably produce operating noise. The sound level of domestic fans ranges from 30 to 70 db(A) depending on the model (pedestal, floor, ceiling or industrial fans). For that reason big fans in ventilation systems are installed in isolated, unused rooms. Improvements concerning the noise development are made, amongst other things, by using high-quality designs of the devices. Brand manufacturers prevent rattling, bucking and buzzing with sophisticated designs of their models. Furthermore the basic design axial or centrifugal is the decisive factor when it comes to determine how far the noise development will go.
Popular for use at home, axial fans create a negative pressure through the high rotation speed of their blades. The air inside the room is the sucked into the fan where it is transported in a straight (axial) path by the rotation of the blades. This causes the air to speed up with a slight increase in pressure, which is absolutely sufficient for standard ventilation in summer and heat recovery in winter. To overcome air friction or form drag however, this pressure is rather insufficient. The sound volume of axial fans is connected to the rotation speed and is often more loud compared to centrifugal devices.
The blades in centrifugal fans are shaped like a paddle wheel that captures the incoming air, centrigualises it and ejects it in a 90 degree angle, usually directly into an attached air duct. This processed air is now condensed more and has a higher physical density. Under pressure it can also cover longer distances and cushioning obstacles like filter boxes inside the duct. Compared to axial fans, centrifugal models handle the same volume of air movement in low speed settings and are therefore more quiet.
More about benefits and drawbacks of the application of axial and centrifugal fans here!
As noise development cannot be determined solely by the construction of the fans, but varies depending on manufacturer and model, please take note of the reliable data about noise level in each item description. You will find those listed under technical details. Often we are also able to add important information about each product for you in the item description, or, if required, request them from the supplier.
Tips for quiet fans and fan-operated devices
The blades of the fans with larger diameters can reach an enourmous speed! If the blades are low-quality and incorrectly attached, their ends seesaw and create irregular flapping noise on top of the sound of the air flow. Slightly bent (profiled) blades on the other side wobble much less. The more surface is available, e.g. by installing the Melton on an angled ceiling, the more air is moved in one revolution. Fans like these require less energy to break through the natural resistance of the air. When it comes to blade sets that optionally offer three to five piece, you need to decide between air volume and noise level, the weight of the device actually also influences the noise development and motor performance.
All these factors are calculated accurately by brand manufacturers, adjusted carefully and review in thorough product tests. Low-priced fans from discount supermarket chains often cannot keep up with that. The motor inside all devices for example creates vibrations, which often become very audible in case of cheaper designs. Our manufacturer CasaFan however attaches great importance to extraordinary quality of the motors with self-lubricating ball bearings made of stainless steel, and even grants up to 25 years warranty!
All tips at a glance
- If you prefer device made by top-class manufacturers, please do pay attention to the details about noise level during low and high speed in the technical data, if possible compare test reports and customer reviews, as noise levels are perceived differently by each individual.
- Look out for profiled blades with an ideal blade pitch.
- High-quality motors with frictionless ball bearings are much more quiet.
- Motor vibrations in ceiling fans can be cushioned, prevent surfaces that resonate
- Small portable fans are often more quiet than free-standing pedestal models
- Replace worn-out devices with outdated technology or motor damages
The same goes for other types of household appliances, because fan heaters, devices for air improvement, cooling units and dryers, and even insect killers operate with an integrated fan unit.
Despite a high-quality product you still experience unpleasant resonance sounds in your ceiling fan? That probably means the fan is not attached to the ceiling as well as it should be. In this case the vibrations of the motor unit are directly passed onto the ceiling (like a resonance body) or a different solid material, however they can be cushioned easily. These tricks will help you ensure low-noise operation!
Image sources:
Product images © creoven.de
Trumpeter © chalabala, www.fotolia.com
Snoring © Andrey Popov, www.fotolia.com
Traffic © diego cervo, www.fotolia.com
Sound waves © psdesign1, www.fotolia.com
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