The decibel is a unit of measurement that relates the ratio of a physical value to another value and is expressed on a logarithmic scale. The common symbol for decibel is dB. The decibel is used as a measure for many parameters in science and engineering such as acoustics (sound), electronics (power levels) and control theory.
The decibel originates from methods used to express performance and loss in telegraph and telephone circuits. The term ‘bel’ was coined in honor of Alexander Graham Bell, and the decibel, being 1/10th of a bel was established.
For most of us, the decibel is the familiar term relating to how loud a sound is.
With sound, the sound pressure is typically what is measured and is the local pressure deviation from the base or equilibrium atmospheric pressure, caused by a sound wave. In air, the sound pressure can be measured by a standard microphone, and is measured in pascals (Pa.)
To get to the common decibel reading we are familiar with, a little mathematics comes into play.
where Lp is the Sound Level in dB, prms is the measured sound pressure, and pref is the standard sound reference pressure of 20 micropascals.
The prms is what is measured by a microphone
Below are some representative sounds and the decibel rating – Note that sounds that are above 85 dB can cause hearing issues, and proper protection should be taken.
Some other interesting blogs about sound for you take a look at-
If you would like to talk about sound or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
Energy…all day (and night) long, we humans are surrounded by – and bombarded by – all kinds of energy. Sometimes, the effects are pleasant; even beneficial: the warmth of the sun’s rays (solar energy) on a nice spring day is the sure-fire cure for Seasonal Affective Disorder, and is also the catalyst your body needs to produce vitamin D. Good things, both. And great reasons to get outside a little more often.
Sometimes, the effects aren’t so pleasant, and they can even be harmful. Lengthy, unprotected exposure to that same wonderful sun’s rays will give you a nasty sunburn. Which can lead to skin cancer. Not good things, either. And great reasons to regularly apply sunblock, and/or limit exposure if you can.
Sound is another constant source of energy that we’re exposed to, and one we can’t simply escape by going inside. Especially if “inside” is a factory, machine shop, or a concert arena. This brings me to the first point of today’s blog: sound power.
Strictly speaking, power is energy per unit time, and can be applied to energy generation (like how much HP an engine generates as it runs) or energy consumption (like how much HP a motor uses as it turns its shaft) For discussions of sound, though, sound power level is applied to the generation end. This is what we mean when we talk about how much sound is made by a punch press, a machine tool, or a rock band’s sound system.
Sound pressure, in contrast, is a measure of the sound power’s intensity at the target’s (e.g., your ear’s) distance from the source. The farther away you get from the sound’s generation, the lower the sound pressure will be. But the sound power didn’t change.
Just like the power made by an engine and used by a motor are both defined in the same units – usually horsepower or watts – sound power level (e.g. generation) and sound pressure (e.g. “use” by your ears) use the same unit of measure: the decibel. The big difference, though, is that while power levels of machinery in motion are linear in scale, sound power level and pressure scales are logarithmic. And that’s where the math can get kind of challenging. But if you’re up for it, let’s look at how you calculate sound power level:
Wo is reference power (in Watts,) normally considered to be 10-12 W, which is the lowest sound perceptible to the human ear under ideal conditions, and
W is the published sound power of the device (in Watts.)
That’s going to give you the sound power level, in decibels, being generated by the sound source. To calculate the sound pressure level:
Lw is the sound power level…see above, and
A is the surface area at a given distance. If the sound is emitted equally in all directions, we can use the formula for hemispheric area, 2πr2 where r=distance from source to calculate the area.
These formulas ignore any effects from the acoustic qualities of the space in which the sound is occurring. Many factors will affect this, such as how much sound energy the walls and ceiling will absorb or reflect. This is determined by the material(s) of construction, the height of the ceiling, etc.
These formulas may help you get a “big picture” idea of the sound levels you might expect in applications where the input data is available. Aside from that, they certainly put into perspective the importance of hearing protection when an analysis reveals higher levels. OSHA puts the following limits on personnel exposure to certain noise levels:
EXAIR’s line of Intelligent Compressed Air Products are engineered, designed, and manufactured with efficiency, safety, and noise reduction in mind. If you’d like to talk about how we can help protect you and your folks’ hearing, call us.
EXAIR offers the model 9104 Digital Sound Level Meter. It is an easy to use instrument for measuring and monitoring the sound level pressures in and around equipment and other manufacturing processes.
Sound meters convert the movement of a thin membrane due to the pressure waves of sound into an electric signal that is processed and turned into a readable output, typically in dBA. The dBA scale is the weighted scale that most closely matches the human ear in terms of the sounds and frequencies that can be detected.
To protect workers in the workplace from suffering hearing loss OSHA has set limits to the time of exposure based on the sound level. The information in the OSHA Standard 29 CFR – 1910.95(a) is summarized below.
The Digital Sound Meter can be used to monitor and measure sound levels of manufacturing processed such as blowoffs for cooling or drying. Many blowoffs, especially open or drilled pipes are very inefficient and can be identified as a source of excessive noise, outside the OSHA exposure ranges. Once the noise violators are identified, a review can be done and the implementation of engineered solutions such as Super air Nozzles or Super Air Knives can be investigated. Keeping harmful noise levels in check benefits everyone involved.
The EXAIR Digital Sound Level Meter is an accurate and responsive instrument that measures the decibel level of the sound and displays the result on the large optionally back-lit LCD display. There is an “F/S” option to provide measurement in either ‘slow’ or ‘fast’ modes for stable or quickly varying noises. The ‘Max Hold’ function will capture and hold the maximum sound level, and update if a louder sound occurs.
Certification of accuracy and calibration traceable to NIST (National Institute of Standards and Technology) is included.
There is an informative Video Blog, presented by @EXAIR_LE that can be found here.
If you have questions about the Digital Sound Level Meter, or would like to talk about any of the quiet EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
EXAIR offers meters to measure the level of physical parameters such as sound and static. Each meter has sensitive electrical circuitry and a periodic calibration is recommended to ensure the meter readings are tried and true.
The model 9104 Digital Sound Level Meter is an easy to use instrument that measures and monitors the sound level pressure in a wide variety of industrial environments. The source of loud noises can be quickly identified so that corrective measures can be taken to keep sound levels at or below OSHA maximum allowable exposure limits.
The sound meter comes from the factory with an NIST (National Institute of Standards and Technology) certificate of accuracy and calibration. As a good practice, EXAIR recommends a yearly calibration of the instrument, and we offer a service that calibrates the unit to the same NIST standards and provide a written report of the calibration.
The model 7905 Static Meter allows easy one-hand static measurements. It is useful in both locating sources of high static charge and checking the reduction of static after treatment with an EXAIR Static Elimination product. The unit is sensitive and responsive, and indicates the the surface polarity of objects up to +/- 20 kV when measured from 1″ away.
It is also recommended that the Static Meter be calibrated on a yearly basis. EXAIR offers (3) levels of calibration service. The first two provide calibration in accordance with MIL Standards using accepted procedures and standards traceable to NIST. The third calibration service conforms to the same Mil Standard, as well as ISO/IEC standards.
Annual calibration service of your EXAIR Digital Sound and Static Meter, along with proper care and storage, will keep your meter performing tried and true for many years, providing accurate and useful measurements.
To initiate a calibration service, give us a call and an Application Engineer will issue an Returned Good number, and provide instructions on how to ship the meter to EXAIR.
If you have questions regarding calibration services for your meters or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
Last week, the EXAIR Blog featured an article about the OSHA Standard 1910.242(b) – Reduction of Air Pressure below 30 psi for Cleaning Purposes. This week, we will review another OSHA standard that affects many of you in manufacturing and other industries.
OSHA 29 CFR 1910.95 – Standard on Occupational Noise Exposure discusses the effects of noise and sets limits for exposure. Occupational noise can cause hearing loss, and also interfere with concentration and communication, disrupting the job performance. Below is a summary from the standard of the Permissible Noise Exposure (OSHA Table G-16)
From the chart, the time an employee can be exposed to loud noise is greatly reduced as the sound level goes up. The use of hearing protection is helpful but relies on the operator to use consistently and correctly. Ear plugs or ear muffs can be uncomfortable and hot, leading to possible reduced usage. OSHA can come on site, and if violations to the sound level exposure limits are found, they can impose fines and mandate corrective action be taken place.
The recommended course of action when an operator is subjected to sound exceeding those in the chart above is to enable feasible administrative or engineering controls. Engineering controls is the arena in which EXAIR can be a great resource.
The first step in understanding and addressing any sound level issues is to measure the sound. The easy to use Digital Sound Meter, model 9104 shown below, allows for accurate testing of noise levels throughout the facility. Noisy areas can be quickly identified, leading to review, design and implementation of the engineering controls.
Some of the worst offenders for noise violations is compressed air usage. A prime example would be inefficient blowoffs, used for cooling, drying, or cleaning. Open pipe, copper tube or drilled pipe are a few of the common culprits. Not only do they consume excessive amounts of compressed air, they can produce noise levels above 100 dBA.
EXAIR manufactures a wide variety of engineered products that utilize compressed air and deliver it in a controlled manner. This allows for the most efficient use of compressed air and keeps the sound levels much lower than the inefficient methods. A Super Air Knife can replace a drilled pipe, reducing sound by as much as 20 dBA, while using 50-70% less compressed air. An engineered Super Air Nozzle can replace an open pipe or copper tube and reduce sound levels down to 74 dBA, and even down to 58 dBA for the smallest available nozzles.
EXAIR has been providing Intelligent Compressed Air Products since 1983.
If you have questions regarding noise limits and how to solve any issue with an EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
As an Application Engineer, one of the interesting aspects of working with customers on applications is the varied types of solutions an EXAIR product can provide. The Air Amplifier family – Super Air Amplifier, Adjustable Air Amplifier, and the special High Temperature Air Amplifier can be used in a wide variety of process and applications. Below highlights several of those from past experiences.
A defense contractor was performing maintenance service on a Navy ship, and the ventilation system had to be shut down. To keep the personnel cool and safe, an auxiliary ventilation was to be supplied. Rather than use a cumbersome blower assembly, which has to mounted on the top deck, and ducted down to the lower decks, they chose to utilize (2) 4″ Super Air Amplifiers. They are very portable and can be set up in minutes. This solution provided the necessary air flow, providing a safe environment for the maintenance crew.
A light bulb manufacturer needed a better solution for a cooling operation. During manufacturing of a mercury lamp, the bulb must be cooled from 700°C to 600°C in just 15 seconds. The current method, an open brass pipe, was working but the noise level was too high (95 dBA.) The goal was to maintain the 15 second cooling time, but reduce sound levels to 85 dBA. By utilizing (2) of 3/4″ Adjustable Air Amplifiers, the customer was able to maintain the cooling rate, and reduce the noise level down to 80 dBA, a 15 dBA reduction.
A garbage collector presented a problem that needed a solution. The garbage was incinerated and when the furnaces were first started up, there tended to be issues with getting the flue to draft properly. Using the High Temperature Air Amplifier, the high velocity air flow and draw provided the needed draft until the stack warmed up and the natural draft would be established. Since the unit is capable of handling temperatures up to 700°F, it was able to withstand the heat of the process after the compressed air was turned off.
These and other Applications for the Air Amplifiers and all other EXAIR products can be found on the EXAIR website on the Products page, under the Related Info section toward the bottom of each page.
If you have questions regarding Air Amplifiers or any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
The Super Air Knife is the latest generation of EXAIR engineered air knife that dramatically reduces compressed air usage and noise when compared to other blowoffs.
From the chart above, the Super Air Knife when supplied with 100 PSIG of compressed air has a sound level of just 72 dBA (A-weighted decibel scale) when measured from 3′ away. 72 dBA is a moderate sound level, and some common comparisons are ‘normal speaking voice’ at 70 dBA and ‘living room music’ at 76 dBA.
For many processes, such as a bottling line drying operation, a pair of the air knives delivers the best performance. When asked, “what is the sound level for (2) of the knives,” a little Acoustic Engineering is in order. Because the decibel scale is logarithmic, the result is not as simple as adding 72 + 72 = 144. 144 dBA is in the range of a jet aircraft take off! Thankfully, both the actual sound level and the numerical value are determined another way. I’ll spare you a lot of the math but the equation is as below.
… where SL1, SL2, SL3 are the sound levels in dBA of the each sound makers, for as many that are being combined.
In the case of (2) Super Air Knives operated 100 PSIG, the combined sound works out to be a quiet 75.0 dBA — a powerful, efficient and quiet product ideal for many applications and process within the manufacturing environment.
As a helpful rule of thumb- combining any (2) items will yield an increase of 3 dBA, combining (3) results in a rise of 4.8 dBA, and combining (4) results in a 6 dBA rise over just (1) of the items.
The Super Air Knives have been successfully used in a wide range of applications, including part drying, sheet and conveyor cleaning, web cooling, scrap removal, pre-paint dust blowoff, and many, many more.
To discuss your application and how an EXAIR Intelligent Compressed Air Product can make your process better and quieter, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.