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.
Sometimes you need more power. I received a phone call from a bottling facility that was currently using a blower style type of air knives. They increased their production rate from 220 bottles/min to 300 bottles/minute, and they started to see issues in the labeling process. Their operation consisted of a wash cycle, rinse cycle, drying cycle, then labeling. They determined that the bottles were not getting dry enough during the drying cycle before the labels were applied. They had a VFD (Variable Frequency Drive) for the blower system, and they reached the maximum rate. Still the bottles were not getting dry enough to allow the label to stick to the surface properly. This meant that they would have to increase the size of their blower system. With the capital cost of a blower system, they decided to call EXAIR to see if we could help them with the drying application.
Compressed air is the best way for establishing a strong blowing force. Instead of air pressures in the range of inches of water, the compressed air system can generate over 40 times the amount of pressure than a typical blower system. EXAIR products uses this power of the compressed air to give you a wide range of blowing forces for drying, cooling, or moving products. For the above application, I recommended two model 110212 Super Air Knife kits. The kit includes the Super Air Knife, a filter, a regulator, and a shim set. They mounted one knife on each side of the bottles to blow off and remove the liquid after the rinse cycle. Even at the increased bottle speeds, the EXAIR Super Air Knives had no issues in keeping the bottles dry. With the regulator and the shim, it was easy for them to dial in the correct amount of force without using excess compressed air. The labels remained glued and the bottling process ran smoothly. Because the company was impressed by the Super Air Knives, they wanted to comment on the comparisons between the blower knife and the Super Air Knife.
Blower System – The reason for contacting EXAIR. Blower-type air knives are an expensive set up. They require a blower, ducting, and a knife. To have any flexibility, a control panel with a VFD will be needed.
Super Air Knife – It is a fraction of the cost. With their system, we were roughly 1/10 the cost; even with the kit. No capital expense report would be needed for the two air knives.
Blower System – They stated that it took them a week to install the entire system before they were able to operate. They had to run electrical wires, controls, ducting, and they even had to change the conveying system slightly to accommodate the blower size.
Super Air Knife – They mounted the filter and the regulator on the conveyor, and ran tubing to the Super Air Knives. Even with a fabricator making a bracket to fit into their system, they had the system up and running is less than two hours.
Blower System – The foot print of the blower is large and it takes up floor space. The 3” ducting had to be ran to an oversized air knife. With the congestion of the bottle system, it made it difficult to optimize the position and the blowing angle to adequately dry the bottles.
Super Air Knife – With the compact design, the Super Air Knife packs a large force in a small package. It has a footprint of 1 ¾” X 1 ½” X 12” long. The air knife only required a ¼” NPT compressed air line to supply the compressed air. It opened up the floor space as well as the bottling area.
Blower System – The blower filter had to be changed regularly, and system had to be checked. Being that the blower motor is a mechanical device, the bearings will wear and the motor will fail over time. These items should be checked quarterly as a PM which increase the cost to run the system.
Super Air Knife – No moving parts to wear out. The only maintenance would be to change the filter once a year.
Blower System – They did have a VFD to control the blowing force. But it was still very limited. With a 36% increase in the bottle speed, they went beyond the maximum capacity of the blower.
Super Air Knife – With a regulator and the shim set, the blowing force can be controlled easily from a breeze to a blast. With their application, the customer only required 40 psig with a standard 0.002” shim to clean and dry the bottles. They had the option to adjust the regulator or change the shim to get the appropriate amount of blowing force. So, with any changes in the bottling operations, the Super Air Knife could easily be adjusted. Also, with the blowing force being optimal from a distance of 3” to 12” from the target, they had more flexibility in angle and distance to hit the moving target.
Blower System – With the blower and turbulent air flow, the units are very loud. It had a sound level near 93 dBA, and with the operators working around the system, they needed PPE to protect them from the high potential of noise induced hearing loss.
Super Air Knife – These units are very quiet. At 40 PSIG, the sound level is only at 61 dBA. (Even operating at a pressure of 100 PSIG, the sound level is only 72 dBA). This was very nice for the operators to work around as it wasn’t a constant noise nuisance.
In using the compressed air, the Super Air Knives are engineered to be very efficient. The design creates a 40:1 amplification ratio which means that for every 1 part of compressed air, 40 parts of the ambient air is entrained. But, even with the use of compressed air, the customer still wanted to share the ease of installing, the effectiveness of blowing, and the improvements to their process. With the 6 points noted above, the customer wished that they would have contacted EXAIR at the beginning.
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.
When you work with us here at EXAIR, we strive to have all the ancillary items that you might need to make your installation a success, without having to find components at the last minute or perhaps using the wrong sized components. Each specific product line such as Super Air Knives or Line Vac air operated conveyors have specific accessories such as mounting brackets or plumbing kits which EXAIR has made to simplify the installation of those particular products. We also carry generalized accessories which work across all of the product lines so you do not have to use multiple vendors or purchase orders.
Silencing Mufflers – Per OSHA Standard 1910.95(a), a worker must not be exposed to sounds levels above 90 dBA for any eight hour shift of a 40 hour work week. EXAIR offers several types of mufflers including – Reclassifying, Sintered Bronze, Straight-Through and Heavy Duty. For reducing the noise associated with an EXAIR E-Vac Generator, Vortex Tube, Cabinet Cooler System, or the exhaust air from cylinders, valves and other air powered equipment, we’ve got a muffler that will help to keep the noise level at an acceptable level.
Solenoid and Manual Valves – The easiest way to reduce compressed air usage and save on operating expense is to turn off the compressed air to a device when it isn’t needed. EXAIR carries a wide assortment of solenoid valves, with offerings in the NEMA 4/4X classification, and supply voltages of 24VDC, 120VAC, and 240VAC. We also have manual ball valves from 1/4 NPT to 1-1/4 NPT and a foot operated valve, with 1/4 NPT connections.
Swivel Fittings, Stay Set Hoses and Magnetic Bases – To provide a great degree of flexibility for positioning an EXAIR Super Air Nozzle, Air Jets or Air Amplifiers, EXAIR offers several items. The Swivel Fittings have 25 degree of movement from the center axis, providing a total of 50 degree of adjustability. The position is locked in place and holds until adjustment is needed. For applications where frequent re-positioning of the air device is required, the Stay Set Hoses are ideal. Simply mount the hose close to the application, bend it to the shape preferred, and because the hose has “memory”, it will not creep or bend. Lastly, the Magnetic Bases are another option for flexible, movable installations. The base has a on/off valve, and a powerful magnet to hold in any vertical or horizontal mounting arrangement.
Hoses – EXAIR can provide hoses for your application. For the Line Vac air operated conveyor applications, we offer conveyance hose – a durable, clear reinforced PVC hose, in diameters of 3/8″ to 3″ ID, and lengths up to 50′. On the compressed air side, we can provide 12′ Coiled Hoses with 1/8, 1/4, and 3/8 NPT connections, and also 3/8″ and 1/2″ ID hose in lengths to 50′.
Filter Separators, Oil Removal Filters and Pressure Regulators – Perhaps the most important accessories for use on a compressed air device are filters and regulators. Filtering the compressed air of dirt, debris, moisture and oil will help to prevent build up inside the EXAIR products, leading to longer service life, and less time spent cleaning, while providing optimum performance. Regulating the air pressure allows for tuning of the performance, using the proper amount of compressed air to obtain satisfactory results.
If you have questions regarding accessories for use with 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.