Understanding Noise
Sound & Sound frequency
A sound is a vibration of air, a variation in air pressure, that makes the membrane of the ear vibrate thus becoming "audible". Different types of sounds can be defined by measuring the frequency of sound waves per second in the unit Hertz (Hz):
The human ear can only perceive and "hear" those sound waves if their frequency lies between 20 Hz (20 vibrations per second) and 2000 Hz (20,000 vibrations per second).
Sound loudness
The loudness of sounds can be defined by measuring their intensity in the unit Decibel (dB):
It is worth noting that Decibel are expressed on a logarithmic scale, which makes explaining changes in loudness a little complicated. For instance, a reduction of 7dB means that the sound intensity has been divided by 4. An augmentation by a factor of 1000 corresponds to a 30 dB change in level.
What is noise?
A noise is as an unpleasant, disturbing sound. The perception of a sound can vary from one person to another, but louder sounds are generally considered noise, especially when they have higher frequencies.
How can noise levels be measured?
The unit used in acoustics to define and measure sound intensity is Decibel (dB). Decibel uses a logarithmic scale which works very differently from a linear scale. Human perception of loudness is not linear, so a logarithmic scale is well suited to express our experience of sound. In fact, when the human ear receives a sound stimulus it tries to amplify very weak sounds and to attenuate very strong sounds.
So calculating the Decibel is based on the comparison between the input signal and the output signal. A linear scale as used on a ruler, where a distance of 30 inches is three times as long as a distance of 10 inches, couldn't adequately express a decrease or increase in sound intensity.
When using a logarithmic scale to measure noise levels, adding 3 dB means multiplying the loudness by two. If we divide the intensity of a sound by 2, the sound level only drops by 3 dB.
EXAMPLE : Using 2 vacuum cleaners simultaneously in one room doesn't double the decibel level, but only increases it by 3 dB. To put it simple: 70 dB plus 70 dB doesn't equal 140 dB, but only 73 dB. Following this rule, 4 vacuum cleaners will create a sound level of 76 dB.
If we measure noise on a scale from 0 to 130 Decibels: 0 dB represents the threshold of audibility, 130 dB represents the threshold of pain. Most of the sounds of everyday life are between 30 and 90 dB.
Decibel levels for everyday noises:
What is the increase in sound intensity between two different Decibel levels ?
Sound intensity is the energy needed to produce a given level of sound and not to be confused with sound volume which is the level at which we perceive the resulting sound.The mathematical relationship between Decibel (dB) and sound intensity works as follows: each 10 dB increase results in a 10-fold increase in sound intensity which we perceive as a 2-fold increase in sound volume. Thus, from 0 dB to 10 dB there is a 10-fold increase in sound intensity, just as there is from 10 dB to 20 dB or from 34 dB to 44 dB.
Decibel levels for everyday noises VS. increase in sound intensity and perceived volume:
Sound
Decibel level
Increase in sound intensity
Increase in perceived volume
0 dB
Breathing
10 dB
10 times the sound intensity
2 times as loud
Rustling leaves
20 dB
100 times the sound intensity
4 times as loud
Whisper
30 dB
1,000 times the sound intensity
8 times as loud
Quiet conversation
40 dB
10,000 times the sound intensity
16 times as loud
Light trafic at close range
50 dB
100,000 times the sound intensity
32 times as loud
Normal conversation
60 dB
1,000,000 times the sound intensity
64 times as loud
Vacuum cleaner
70 dB
10,000,000 times the sound intensity
128 times as loud
Loud traffic noise at close range
80 dB
100,000,000 times the sound intensity
256 times as loud
Headphones at full volume
90 dB
1,000,000,000 times the sound intensity
512 times as loud
Club
100 dB
10,000,000,000 times the sound intensity
1024 times as loud
Car speakers at full volume
110 dB
100,000,000,000 times the sound intensity
2048 times as loud
Air plane take-off, jackhammer
120 dB
1,000,000,000,000 times the sound intensity
4096 times as loud
Rock concert
130 dB
10,000,000,000,000 times the sound intensity
8192 times as loud
Actual sound levels VS. noise perception
The intensity of a sound can be measured by using a microphone to convert the sound into power and then interpreting the power obtained in terms of Decibels (dB). However, this physical sound level does not really correspond to the perception of the sound that we are having.
Measuring human noise perception
The human ear does not perceive all the sound frequenciesin the same way: we are deaf to low-frequency sounds (below 20 Hz) and high-frequency sounds (above 20,000 Hz), and are most sensitive to sounds around 2000 Hz.This is why there are different versions of the "dB" scale which are decibel readings that have been adjusted to take into account the varying sensitivity of the human ear to different frequencies of sound:
dBA (A-weighted sound levels) - measurement of common sound intensities, using a filter to account for the loudness as perceived by a human ear (everyday noises).
dBC (C-weighted sound levels) - measurement of higher sound intensities, specifying the effect of peak and high impact sounds on the human ear (extreme loudness such as a live concert).
It is not possible to reproduce the behavior of the "average" human ear with a single filter (and even less that of the ears of each particular individual), but in most situations our hearing can be measued with the the dBA scale. This scale is a good starting point from which to measure sound perception, but gives us only an idea of the perceived noise levels.
Factors impacting noise perception
In reality, the overall noise is composed by many different sound levels all across the frequency spectrum, which is why measuring the perception of sound is very complex and depends on a large number of factors:
Individual sensitivity (depending on age, culture, time of day...)
Spatial configuration (inside/outside, construction of the building, furniture in the room...)
Distance to the noise source (sensor position)
Sound frequency (low, medium, high)
Sound repeatability (continuous, intermittent, impulsive)
Temporal exposure (long-term, short-term)
These are the most common reasons that explain a difference between the actual sound and the perceived noise. The Decibel measurements can only give a limited representation of the perceived "reality", especially as the sensitivity to noise varies greatly from one individual to another. Some populations can be more vulnerable to noise exposure than others, such as students during an exam or people affected by hearing loss.
Types of noise
There are many different categories of noise, from natural to man-made. In big cities we are confronted with man-made sounds, often quite aggressive.
We try to find soundproof solutions to create a quieter environment and get rid of diffrent types of noise:
continuous noise (like machinery that runs without interruption, car traffic): is noise which remains constant and stable over a given time period
intermittent noise (trains, aircrafts, sirens): is noise which does not remain constant and stable over a given time period
impulsive / impact noise (gun shot): is a very short burst of loud noise which lasts for less than one second.
The noise we find the most disturbing and that we are the most exposed to (unless you live in the countryside) is traffic noise. Unfortunately, this is also the hardest type of noise to reduce, let alone cut out.
The best bet to dampen traffic noise is to combine different solutions: noise-reducing curtains, rugs, window frame insulation foam, etc.
The difference between sound proofing and sound absorption
To understand the difference between sound absorbtion and sound proofing let's remember how the noise travels: when a sound wave is emitted, it is modified by parameters such as distance or obstacles. When a sound wave meets an obstacle like the wall of a room, a certain amount of energy is reflected back into the room. These successive reflections are called reverberation.
Sound proofing
Sound proofing (or sound insulation) attempts to stop noise by blocking the acoustic wave from traveling to adjacent spaces.
Insulation can only be achieved with mass and/or multiple layers ot material in the walls or windows. It means, that the construction of the building is essential in this matter, and that additional sound proofing is not easy once the structure is already built.
Sound absorption
Sound absorption aims to reduce noise by limiting the reverberation of the sound wave within a space.
Absorption can be obtained with light materials (such as specific fabrics) that are applied to walls or windows, meaning it is easier to achieve once the structure is already built.
How can "soundproof" curtains help?
The impact of any sound insulation curtain depends on the kind of noise you are experiencing and the construction of your building.
As mentionned before, there are different types of noises with either high, medium or low frequencies. Different applications and treatments are needed to confront this spectrum of noises and there is no one-for-all solution.
Each sound environment is different and the intricacies of one's home have to be taken into account, because the noise does not come in simply from your windows but also seeps in through the walls and various openings.
Moondream sound insulation curtains aim to adress both - sound proofing and sound absorbtion - as best as possible with a solution that is equally functional and aesthetic. Our patented curtains have three strategically assembled layers of fabric to reduce the transmission of the sound wave and absorb the reverberation of the sound as well:
The result of both actions is a quieter acoustic environment that will contribute significantly to your wellbeing. To improve the curtain's results you can add other absorbent materials to your floors such as carpet or a rug.
You have to be aware that if you wish to cut out certain low frequency sounds such as traffic noise completely, a curtain might not be enough (soundproof windows and thick walls would be necessary). Moondream curtains can however dampen the noise which can already be an important improvement and is a much more cost effective solution, especially if you are just renting.
Outdoor sound blankets are a great cost-efficient and highly effective way of reducing loud noises. These flexible quilted panels are extremely versatile, which is why they are so popular among construction companies.
If you are in the market for some outdoor sound-proofing these are a great option. However, outdoor sound blankets are not a one size fits all solution. There are a few different types of sound absorbing and blocking blankets; some will render better results than others. To help you out, we have put together a summary of what exactly outdoor sound blankets are, what features you should look for and where to buy them.
Outdoor sound blankets are large weather-resistant vinyl encapsulated panels that are engineered to absorb and block noise. These exterior sound panels are typically used to deafen the sound of large equipment, HVAC systems and construction projects. They are also great to help comply with local noise ordinances.
Outdoor sound blankets are popular because they are extremely durable, highly effective and cost-efficient. These panels can withstand intense wind, freezing temperatures, high heat and prolonged UV exposure. Additionally, the unique design of these flexible panels allows installation on nearly any support structure, such as fences or frames. Outdoor sound blankets are a permanent or temporary solution.
There are a few aspects of outdoor sound blankets to evaluate while deciding what type of barrier will be best for you. These include the NRC rating (Noise Reduction Coefficient), the STC rating (Sound Transmission Class) and the temperature range/weather resistance.
There is a bit of science involved when shopping for sound blankets. The first term we will cover is the NRC. This rating measures the absorption of sound; the higher the rating, the better the product is at absorbing sound. The thickness and density are the two determining factors in calculating the NRC rating.
The NRC rating ranges from 0.0-1.0. For example, if an outdoor sound blanket has an NRC rating of .65 this means 65% of the sound in the space absorbed and the other 35% reflected back into space. While reviewing sound blankets, keep in mind the higher the NRC rating and the thicker the product the better.
In addition to reviewing the NRC of outdoor sound blankets, you should pay attention to the STC (Sound Transmission Class) rating. The STC rating also measures how much the product is able to reduce noise; but instead of measuring the amount of absorption, it measures the transmission loss (or how much sound will still come through the barrier).
STC ratings are found based on sound frequency measurements in Hertz (or Hz). To give a frame of reference, most humans are born with the ability to hear frequencies as low as 20 Hz and as high as 20,000 Hz. However, for standard sound testing purposes, the soundproofing industry measures barrier performance based on a range of 125 Hz to 4,000 Hz.
Generally speaking, the higher the STC rating the better. However, it is important to not solely rely on the STC rating as it can be misleading in certain soundproofing scenarios. For example, if you are wanting to deafen the sound of construction noise or heavy bass music, you should rely more heavily on the NRC rating. This is because noise sources such as traffic noise, heavy equipment, and bass drums are all below 125 Hz and will not be applicable to the STC rating since the scale starts at 125 Hz. For higher pitched frequencies, STC ratings are extremely reliable.
The final most important aspect of an outdoor sound blanket you should take into consideration while purchasing is the weather durability. Considering these barriers will brace the natural elements at any given time of year, you will want to ensure they are capable of withstanding high heat in the summer, freezing temperatures in the winter and everything in between.
Keep in mind these blankets are extremely cost-effective because of their reusability. If you have to keep replacing them due to their lack of weather resistance, you lose the cost-benefit; so, invest in a higher quality blanket upfront.
The installation of outdoor sound blankets isn’t as difficult as it may seem. The most difficult aspect of installation is setting up or preparing the structure the outdoor sound blankets attach to.
If a fence is not conveniently located around the space you wish to soundproof, consider building a temporary structure that can hold the blankets. Building temporary fencing framework is a great option that will allow you to strategically place the barriers to get the maximum amount of soundproofing, as opposed to haphazardly securing them to closest stable structures.
Once you have identified or built the structure that the outdoor sound blankets attach to, securing the barriers themselves is as simple as zip-tying the grommets or installing hooks to hang them.
Here at eNoise Control, we provide a wide selection of high-quality outdoor sound blankets to suit a variety of soundproofing needs. eNoise Control’s removable velcro-sealed sound blankets help address sound directly at the source. Our reusable, high temperature, sound control blankets are an ideal fit for compressor noise and fan housing noise applications.
If you are looking for more information or are ready to purchase the best outdoor sound blankets, give us a call at 888.417.1903 or send us an email to info@enoisecontrol.com.
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