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This section describes the acoustical considerations associated with highway noise barrier design, beginning with a brief technical discussion on the fundamentals of highway traffic noise. Highway traffic noise originates primarily from three discrete sources: truck exhaust stacks, vehicle engines, and tires interacting with the pavement. Finally, another characteristic of sound is its frequency, or tonality, measured in Hertz (Hz), or cycles per second. For highway traffic noise, the LAeq1h are most often used to describe continuous sounds, such as relatively dense highway traffic.
Divergence is referred to as the spreading of sound waves from a sound source in a free field environment.
Thus, with this equation, it can be shown that sound levels measured from a point source decrease at a rate of 6 dB(A) per doubling of distance. With this equation, it can be shown that sound levels measured from a line source decrease at a rate of 3 dB(A) per doubling of distance.
Ground effect refers to the change in sound level, either positive or negative, due to intervening ground between source and receiver. Atmospheric refraction: Atmospheric refraction is the bending of sound waves due to wind and temperature gradients.
Shielding by a building is similar to the shielding effects of a short (lengthwise) barrier. Diffraction, or the bending of sound waves around an obstacle, can occur both at the top of the barrier and around the ends. An important aspect of diffraction is the path length difference (δ) between the diffracted path from source over the top of the barrier to the receiver, and the direct path from source to receiver as if the barrier were not present (see Figure 10). The path length difference is used to compute the Fresnel Number (N0), which is a dimensionless value used in predicting the attenuation provided by a noise barrier positioned between a source and a receiver.
The amount of incident sound that a barrier absorbs is typically expressed in terms of its Noise Reduction Coefficient (NRC).
Measurements to determine the αsab of a barrier facade should be made in accordance with the ASTM Recommended Practice C384 (Impedance Tube Method) or C423 (Reverberation Room Method). The amount of incident sound that a barrier transmits can be described by its sound Transmission Loss (TL). In most cases, the maximum noise reduction that can be achieved by a barrier is 20 dB(A) for thin walls and 23 dB(A) for berms. It should be noted that there are other ratings used to express a material's sound transmission characteristics.
This section describes the various acoustical considerations involved in actual noise barrier design. Typically, a 5-dB(A) IL can be expected for receivers whose line-of-sight to the roadway is just blocked by the barrier. Properly-designed noise barriers should attain an IL approaching 10 dB(A), which is equivalent to a perceived halving in loudness for the first row of homes directly behind the barrier.
Noise barriers should be tall enough and long enough so that only a small portion of sound diffracts around the edges. Sometimes due to the community and roadway geometry, there is not enough available area to ensure a proper-length barrier.
Highway noise barriers are typically characterized as a wall, a berm, or a combination of the two (see Figure 16). It is a common phenomenon for residents to perceive a difference in sound after a barrier is installed on the opposite side of a roadway. Parallel barriers are two barriers which face each other on opposite sides of a roadway (see Figure 18). That is, a single barrier with an insertion loss of 10 dB(A) may only realize an effective reduction of 4 to 8 dB(A) if another barrier is placed parallel to it on the opposite side of the highway. For parallel barriers, ensure that the distance between the two barriers is at least 10 times their average height.
There has been limited research into varying the shape of the top of a barrier (see Figure 23 and 24) for the purpose of shortening barrier heights and possibly attaining the attenuation characteristic of a taller barrier. Studies have shown that a T-profile top barrier (see Figure 25) provides insertion losses comparable to a conventional top barrier when the difference in their heights is equal to the width of the T-profile top. A berm requires more surface area, but provides 1 to 3 dB(A) additional attenuation versus a wall. Ensure the ratio between overlap distance and gap width (between barriers) is at least 4:1.
The cost of constructing these special shapes typically outweigh the cost of simply increasing the barrier's height to accomplish the same acoustic benefit. Audition Frequency refers to the number of compressions per second and is measured in hertz.
Theories of Pitch Perception Frequency theory - the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency.
Theories of Pitch Perception The current pitch theory combines modified versions of both the place theory and frequency theory: –Low frequency sounds best explained by the frequency theory.
Theories of Pitch Perception Volley principle states that the auditory nerve can have volleys of impulses (up to 4000 per second) even though no individual axon approaches that frequency by itself.
Hearing Loss About 99% of hearing impaired people have at least some response to loud noises. Hearing Loss Conductive or middle ear deafness: –Bones of middle ear fail to transmit sound waves properly to cochlea –Caused by disease, infections, or tumerous bone growth near the middle ear. The Mechanical Senses Mechanical senses respond to pressure, bending, or other distortions of a receptor. The Mechanical Senses The vestibular sense refers to the system that detects the position and the movement of the head. The Mechanical Senses Which part of the brain helps process information about our vestibular sense? The Mechanical Senses Touch receptors can be: –simple bare neurons –elaborated neuron ending –bare ending surrounded by non- neural cells that modify its function Fig.
The Chemical Senses: Taste Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and four types of receptors. The Chemical Senses: Taste Various areas of the brain are responsible for processing different taste information. With Bonfire Night around the corner and New Year celebrations not far behind, we can expect a season of fun, festivities and of course fireworks. Up close, the noise of a firework can easily exceed 140 decibels, which has the potential to do permanent hearing damage.
Ear plugs might not be suitable for babies and younger children, in which case child-sized ear muffs should be used. If you’re planning your own firework display, be sure to follow the correct safety procedures.
When it comes to the health and safety of your family, prevention is always better than cure, but if any of you experience any warning signs of hearing damage, it is vital to consult your GP immediately. Nearly 40% of hearing loss is preventable with the correct hearing protection and precautions.
Medical Disclaimer Statements on Get Holistic Health about health issues aren't meant to identify, treat, cure, or protect against illness. But many of the well-intentioned posts to a thread on which user magicmuk asked Redditors to name seemingly harmless things are actually surprisingly unhealthy contain more than a little bit of truth. Here are just a few of their suggestions for seemingly-harmless habits that could be doing more harm than good -- plus a little science to help convince you to change your ways. As much as we desk-jockeys would like this not to be true, the Redditor who mentioned sitting in office chairs five days a week is correct.


Not only is it time that could be spent being physically active, but too much time spent in front of the screen, as one user suggested, can also mess with your sleep. Headphones or earbuds are the culprit for another user, who wrote, "Most people have them turned up too loud.
We know you're trying to drown out your noisy coworkers, but pumping up the volume can mean trouble.
User coffeebeancatfish elaborates, saying sleep deprivation is linked to changes in cognition, depression rates and immune function, and that only scratches the surface.
Even without the typical risk factors, like being overweight or having a family history, short sleep can up your risk for stroke, according to 2012 research. These sources each produce sound energy that, in turn, translates into tiny fluctuations in atmospheric pressure as the sources move and vibrate.
That is, because decibels are expressed on a logarithmic scale, they cannot be combined by simple addition.
As stated earlier, sound sources produce sound energy that, in turn, translates into tiny fluctuations in atmospheric pressure as the sources move and vibrate.
Frequency is defined as the number of cycles of repetition per second, or the number of wavelengths that have passed by a stationary point in one second. As stated previously, sound levels measured for highway traffic noise use an A-weighting filter to more accurately simulate the response of the human ear. The LASmx and LAE may be used to describe single events, such as an individual vehicle pass-by. In the case of highway traffic noise, two types of divergence are common, spherical and cylindrical. Ground effect is a relatively complex acoustic phenomenon, which is a function of ground characteristics, source-to-receiver geometry, and the spectral characteristics of the source. Near-ground wind effects are, typically, the most substantial contributor to sound refraction.
During daytime weather conditions, when the air is warmer closer to the ground (temperature decreases with height), sound waves tend to refract upward away from the ground (temperature lapse). Further, measurements should not be performed in conditions where strong winds with small vector components exist in the direction of propagation. The amount of attenuation provided by these structures is determined by their size and density, and the frequencies of the sound levels.
Building rows can act as longer barriers keeping in mind that the gaps between buildings will leak sound through to the receiver. If the path length difference increases, the Fresnel number and, thus, barrier attenuation increases.
The Impedance Tube Method can be used to measure the sound absorption of normal incident sound on a small sample of a material.
Most barrier manufacturers prefer to use the Reverberation Room Method because of its lack of constraints on sample size. Such material would be adequate for a noise reduction of at least 10 dB(A) due to diffraction. Therefore, a material that has a TL of at least 25 dB(A) or greater is desired and would always be adequate for a noise barrier.
Some materials, such as wood, however, are prone to develop openings or gaps due to shrinkage, warping, splitting, or weathering.
Design goals may not be limited simply to noise reduction at receivers, but may also include other considerations of safety and maintenance as well. A general rule-of-thumb is that each additional 1 m of barrier height above line-of-sight blockage will provide about 1.5 dB(A) of additional attenuation (see Figure 13). For those residents not directly behind the barrier, a noise reduction of 3 to 5 dB(A) can typically be provided, which is just slightly perceptible to the human ear. If a barrier is not long enough, degradations in barrier performance of up to 5 dB(A) less than the barrier's design noise reduction may be seen for those receivers near the barrier ends. In those cases, highway barrier designers may decide to construct the barrier with the ends curved inward towards the community (see Figure 15).
A reflective barrier on one side of the roadway can result in some sound energy being reflected back across the roadway to receivers on the opposite side (see Figure 17). Although theory indicates greater increases for a single reflection, practical highway measurements commonly show not greater than a 1 to 2 dB(A) increase in sound levels due to the sound reflected off the opposing barrier. Sound reflected between reflective parallel barriers may cause degradations in each barrier's performance due to multiple reflections that diffract over the individual barriers. A general rule-of-thumb is that the ratio between overlap distance and gap width should be at least 4:1 to ensure negligible degradation of barrier performance (see Figures 21).
This type of barrier can also be visually pleasing to motorists because it provides variation in form (see Figure 22). The technical rationale is that additional attenuation can be attained by increasing the number of diffractions occurring at the top of the barrier.
When the two barriers are the same height, the T-profile top barrier has been shown to provide an additional 2.5 dB(A) insertion loss over the conventional top barrier. Sound reflected between parallel barriers may cause degradations in each barrier's performance from 2 to as much as 6 dB(A), but in most practical situations, the degradation is smaller.
Place theory - each area along the basilar membrane is tuned to a specific frequency of sound wave. Primary auditory cortex located in the superior temporal cortex Each hemisphere receives most of its information from the opposite ear. These colourful pyrotechnics can be amazing to watch, but they should be treated with caution and respect.
When watching a fireworks display with your family, be sure to sit at a comfortable distance – at least 500 feet away – to limit your exposure to loud noises.
You can find affordable foam or silicone ear plugs at your local pharmacy; fit them snugly in your ears, and you’ll find they allow you to hear conversation and music in your nearby surroundings, while dangerously loud noises are effectively filtered out.
Only adults should handle the fireworks, and the noise and size should be suitable for the available space.
Signs to watch out for are pain in the ears, ringing or buzzing in the ears, or the inability to understand speech following exposure to loud noise. Follow these simple tips and make this festive season a happy, healthy and safe time for your loved ones! She’ll also be taking precautions to protect her hearing, and is even considering an auditory enhancement course to help her hear better than before. In fact, the effects of being sedentary are quite dramatic: Sitting more than three hours a day could take two whole years off your life. In kids, the amount of time spent with electronic gadgets and gizmos seems to affect well-being and mental health. Adults who regularly slept fewer than six hours a night had four times the risk of stroke symptoms, HuffPost reported. For example, if a single vehicle pass-by produces an SPL of 60 dB at a distance of 15 m (50 ft) from a roadway, two identical vehicle pass-bys would not produce an SPL of 120 dB. As the sources move and vibrate, surrounding atoms, or molecules, are temporarily displaced from their normal configurations thus forming a disturbance that moves away from the sound source in waves that pulsate out at equal intervals. For greater angles, the ground becomes a good reflector and can be considered acoustically hard.
Upwind conditions tend to refract sound waves away from the ground resulting in a decrease in sound levels at a receiver. Readers may refer to Reference 18 for more information on performing highway-related noise measurements.
However, for vegetation to provide a substantial, or even noticeable, noise reduction, the vegetation area must be at least 5 m (15 ft) in height, 30 m (100 ft) wide and dense enough to completely obstruct the line-of-sight between the source and the receiver.


Generally, assuming an at-grade building row with a building-to-gap ratio of 40 percent to 60 percent, the noise reduction due to this row is approximately 3 dB(A). However, for this Method, the sample size chosen and method and angle of mounting may have substantial effects on the determined absorption coefficients. The following table gives approximate TL values for some common materials, tested for typical A-weighted highway traffic frequency spectra.
STC is a single-number rating derived by fitting a reference rating curve to the TL values measured for the one-third octave frequency bands between 125 Hz and 4000 Hz.
IL is defined as the sound level at a given receiver before the construction of a barrier minus the sound level at the same receiver after the construction of the barrier. A rule-of-thumb is that a barrier should be long enough such that the distance between a receiver and a barrier end is at least four times the perpendicular distance from the receiver to the barrier along a line drawn between the receiver and the roadway (see Figure 14). The considerations that are examined in deciding whether to build a wall or a berm, include available area, materials, costs, aesthetics, and community concerns.
While this increase may not be readily perceptible, residents on the opposite side of the roadway may perceive a change in the quality of the sound; the signature of the reflected sound may differ from that of the source due to a change in frequency content upon reflection. The decision to add a sound absorptive surface should be determined by weighing benefit versus cost. Y- and arrow-profile tops also performed better than conventional tops, however, to a lesser degree than the T- profile tops. Protect your hearing, and that of your loved ones, by taking some simple precautions this festive season. Choose a spot where you can marvel at the lights and colours without the worry of loud explosions. Put these ear plugs in place before the festivities begin, and keep them in until the show has ended.
Once again, make sure these are in place before the fireworks start, and do not remove them until they have stopped.
Keep friends and family at a safe distance, and insist of appropriate hearing protection, such as ear muffs or ear plugs. Material shown by Get Holistic Health is for educational purposes only and isn't meant to substitute for the recommendation of a doctor and other medical professional. We typically listen at about 110 decibels, but 80 or below is probably safer, Real Simple reported. The sweet flavor tells the brain to expect calories, but when none come, it might send out some hunger signals to compensate.
One container of Nissin's beef-flavored Cup Noodles contains 1,110 milligrams of sodium, only about half as much as is recommended per day, plus 13 grams of fat (7 of which are saturated), about 20 percent of your daily limit. Commercially-prepared juices are often high in added sugars, as this user mentions, plus, "the isolated sugar from fruit looks very much like sugar from any other source -- it is merely a mixture of fructose and glucose, to which your body responds identically," Healthy Living's Meredith Melnick reported. For simplicity, the outward propagating waves can be approximated by the trigonometric sine function (see Figure 6). A-weighting emphasizes sounds between 1,000 Hz and 6,300 Hz, and de-emphasizes sounds above and below that range to simulate the response of the human ear. Other noise descriptors include the maximum sound level (MXFA or MXSA, denoted by the symbol, LAFmx or LASmx), the equivalent sound level for a one-hour period (1HEQ, denoted by the symbol, LAeq1h), the sound exposure level (SEL, denoted by the symbol, LAE), the day-night average sound level (DNL, denoted by the symbol, Ldn), the community noise equivalent level (CNEL, denoted by the symbol, Lden), and the ten-percentile exceeded sound level (denoted by the symbol, L10). The Ldn and the Lden may be used to describe long-term noise environments (typically 24 hours or more).
Hard ground refers to any highly reflective surface in which the phase of the sound energy is essentially preserved upon reflection; examples include water, asphalt, and concrete. Keep in mind that these relationships are quite empirical but tend to break down for distances greater than about 30.5 to 61 m (100 to 200 ft).
Conversely, downwind conditions tend to refract sound waves towards the ground resulting in an increase in sound levels at a receiver.
Conversely, when the air close to the ground cools during nighttime weather conditions (temperature increases with height), sound waves tend to refract downward towards the ground (temperature inversion). Further, for each additional building row, another 1.5 dB(A) noise reduction may be considered typical.
Figure 11 shows the relationship between barrier attenuation and Fresnel Number for a frequency of 550 Hz. The reference rating curve is fitted to the TL values such that the sum of deficiencies (TL values less than the reference rating curve), does not exceed 32 dB, and no single deficiency is greater than 8 dB. The construction of a noise barrier usually results in a partial loss of soft-ground attenuation. Another way of looking at this rule is that the angle subtended from the receiver to a barrier end should be at least 80 degrees, as measured from the perpendicular line from the receiver to the roadway. Acoustically, for a given site geometry and comparable barrier height and length, a berm barrier will typically provide an extra 1 to 3 dB(A) of attenuation.
That is, what noise abatement benefits can be achieved for how many residents versus the costs of the application and maintenance of the absorptive treatments? Always read the instructions before lighting a firework, and ensure that you follow the correct precautions. Whether it's surprising sources of high fructose corn syrup or foods you'd never expect to contain gluten, what's most harmful is forgetting to read the labels.
Because of this wide range, sound pressure is measured on a logarithmic scale known as the decibel (dB) scale. To combine decibels, they must first be converted to energy, then added or subtracted as appropriate, and reconverted back to decibels. For practical highway applications, measurements have shown a 1 to 2 dBA increase for the first and second row residences adjacent to the highway. For a more detailed discussion of ground effects, the reader is directed to References 20 and 21. Finally, some barrier systems are designed with small openings at the base of the barrier to carry water, which would otherwise pond on one side of the barrier, through the barrier. This is due to the barrier forcing the sound to take a higher path relative to the ground plane. On this scale, a value of 0 dB is equal to a sound pressure level (SPL) of 20 µPa and corresponds to the threshold of hearing for most humans. Table 2 presents the curve in tabular form for one-third octave band frequencies from 20 to 20,000 Hz. For situations where the buildings in a building row occupy greater than 80 percent of the row area, it may be assumed that the leakage of sound due to gaps is minimal.
The disadvantage to using the STC rating scheme is that it is designed to rate noise reductions in frequencies of normal speech and office areas, and not for the lower frequencies of highway traffic noise. Therefore, barrier IL is the net effect of barrier diffraction, combined with this partial loss of soft-ground attenuation. First, the flat top of a berm diffracts the sound waves twice, resulting in a longer path-length difference, a larger Fresnel number, and, thus, more attenuation. In this case, noise attenuation may be determined by treating the building row as a noise barrier, which is discussed in Section 3.4.
For frequencies of traffic noise, the STC is typically 5 to 10 dB(A) greater than the TL and, thus, should only be used as rough guide.
Second, the surface of a berm is, essentially, grass-covered acoustically soft earth with side slopes closer to the sound path, which provides additional attenuation. However, because a berm is wider than a wall (thus, requiring more land than a wall when constructed) and because the 1 to 3 dB(A) additional attenuation is, at best, only barely perceptible to the human ear, a berm's acoustical advantage does not necessarily guarantee its choice versus a wall.



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