Understanding Noise: Sound Power Vs. Sound Pressure

Sound Power and Sound Pressure have been covered a few other times here on the EXAIR Blog. Once here by Brian who made the visual correlation in regards to a speaker and a musical instrument. And here by Russ who breaks down how you calculate sound power level with the below equation!
Sound Power Equation
too lou Sound Power Level Equation
All machines generate sound when they are in operation. The propagated sound waves cause small changes in the ambient air pressure while traveling. A sound source produces sound power and this generates a sound pressure fluctuation in the air. Sound power is the cause of this, whereas sound pressure is the effect. To put it more simply, what we hear is sound pressure, but this sound pressure is caused by the sound power of the emitting sound source. To make a comparison, imagine for example a simple light bulb. The bulb’s power wattage (in W) represents the sound power, whereas the bulb’s light intensity represents the sound pressure.
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Light Bulb
Sound power does not generally depend on the environment. On the contrary, the sound pressure depends on the distance from the source and also on the acoustic environment where the sound wave is produced. In the case of indoor installations for example, sound pressure depends on the size of the room and on the sound absorption capacity of the surfaces. For instance, say the room walls don’t absorb all the sound but reflect parts of it, then the sound pressure will increase due to the so called reverberation effect. (reverberation time is broadly defined as the time it takes for the sound pressure to reduce by 60 dB after the sound emitting source has been shut off). OSHA puts the following limits on personnel exposure to certain noise levels:
Working in areas that exceed these levels will require hearing protection.
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. Jordan Shouse Application Engineer Send me an email Find us on the Web  Like us on Facebook Twitter: @EXAIR_JS Light Bulb image courtesy of  josh LightWork  Creative Commons License

Sound: What Is It … More Importantly, Weighted Scales of Frequencies

We’ve blogged about sound and what exactly it is before, see the link. Understanding that sound is vibration traveling through the air which it is utilizing as an elastic medium.  Well, rather than me continue to write this out, I found a great video to share that is written in song to better recap how sound is created.

Now that we have that recap and understand better what sound is let’s dig a little deeper to better understand why some sounds may appear louder to a person when they may not appear different on a sound scale that is shown by something like a Digital Sound Level Meter.

Loudness is how a person perceives sound and this is correlated to the sound pressure of the frequency of the sound in question.  The loudness is broken into three different weighing scales that are internationally standardized. Each of these scales, A, C, and Z apply a weight to different frequency levels.

  1. The most commonly observed scale here in the USA is the A scale. A is the OSHA selected scale for industrial environments and discriminates against low frequencies greatly.
  2. Z is the zero weighting scale to keep all frequencies equal, this scale was introduced in 2003 as the international standard.
  3. C scale does not attenuate these lower frequencies as they are carrying the ability to cause vibrations within structures or buildings and carry their own set of risks.

To further the explanation on the A-weighted scale, the range of frequencies correlates to the common human hearing spectrum which is 20 Hz to 20kHz. This is the range of frequencies that are most harmful to a person’s hearing and thus were adopted by OSHA. The OSHA standard, 29 CFR 191.95(a), that corresponds to noise level exposure permissible can be read about here on our blog as well.

When using a handy tool such as the Digital Sound Level Meter to measure sound levels you will select whether to use the dBA or dBC scale.  This is the decibel reading according to the scale selected. Again, for here in the USA you would want to focus your measurements on the dBA scale. It is suggested to use this tool at a 3′ distance or at the known distance an operator’s ears would be from the noise generation point.

Many of EXAIR’s engineered compressed air products have the ability to decrease sound levels in your plant. If you would like to discuss how to best reduce sound levels being produced within your facility, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

1 – Fun Science: Sound – @charlieissocoollike – https://youtu.be/xH8mT2IQz7Y

 

Measuring and Adding Sound Levels

Noise-induced hearing loss, or NIHL, is one of the most common occupational diseases. This doesn’t occur overnight, but the effects are noticed gradually over many years of unprotected exposure to high sound levels. This is 100% preventable! Through proper engineering controls and personal protective equipment (PPE), NIHL can be prevented. It is irreversible, so once the damage is done there’s no going back. OSHA standard 19 CFR 1910.95(a) states that protection against the effects of noise exposure shall be provided when the sound levels and exposure time exceed those shown in the table below.

OSHA Chart

Intensity of the sound pressure level is expressed in decibels (dB). The scale is logarithmic, a 3 dB reduction cuts the sound level in half. A 10 dB reduction decreases it by a factor of 10, and a 20 dB reduction decreases the sound level by a factor of 100. To calculate the dB level, we use the following formula:

Sound SPL

Where:

L – Sound Pressure Level, dB

P – Sound Pressure, Pa

Pref – reference sound pressure, 0.00002 Pa

For example, normal conversation has a Sound Pressure of .01Pa. To calculate the dB level:

dB = 20 log10 (.01Pa/.00002Pa)

 = 54 dB

When designing a new blowoff process, it’s important to consider the sound levels produced before implementation. EXAIR publishes the sound level for all of our products for this very reason. If you’re implementing multiple nozzles, you’ll need to add the sound levels together. To do so, we use the following formula:

Sound Addition

Where:

L1, L2… represent the sound pressure level in dB for each source

A customer was using ¼” open ended copper tubes for a blowoff application removing trim after a stamping operation. They had a total of (4) tubes operating at 80 PSIG. Not only were they VERY inefficient, but the sound level produced at this pressure was 94 dBA. To calculate the sound level of all (4) together we use the above formula:

L = 10 x log10(109.4+ 109.4 + 109.4 + 109.4)

L = 100 dB

At this sound level, permanent hearing loss begins to occur in just two hours of unprotected exposure. We recommended replacing the loud and inefficient copper pipe with our 1” Flat Super Air Nozzle, Model 1126. At 80 PSIG, the 1126 produces a sound level of just 75 dBA.

L = 10 x log10 (107.5 + 107.5 + 107.5 + 107.5)

L = 81 dB

At almost a 20 dB reduction, that’s nearly 100x quieter! Don’t rely on just PPE to keep your operators safe from NIHL. Replacing loud inefficient blowoff methods with EXAIR’s Intelligent Compressed Air Products will take it one step further in ensuring your creating a safe working environment for your employees.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

EXAIR Intelligent Compressed Air Products: Leading the Way in Standards Compliance

EXAIR prides itself in offering products with high-performance and peak efficiency. All EXAIR products are manufactured to meet the strict requirements of a variety of different standards, ensuring that you receive a reliable, high quality product that WILL perform to the specifications we publish.

Safety is a top priority for most companies, EXAIR’s line of Intelligent Compressed Air Products meet or exceed the strict safety standards set forth by both OSHA and the European Union. EXAIR products comply with OSHA 29 CFR 1910.242(b), the standard implemented to ensure safe operation of compressed air blowoff devices, and the EU General Product Safety Directive (2001/95/EC).

sag-osha-compliant
The engineered design of our Super Air Nozzles prevents compressed air from penetrating the skin by eliminating the potential of dead-ending when pressed against the skin.

OSHA Chart

Additionally, they comply with the noise limitation requirements set forth under 29 CFR 1910.95(a) and the EU Machinery Directive (2006/42/EC). From the Optimization product line, EXAIR’s Electronic Flow Control and the Electronic Temperature Control meet the low voltage standards of EU Low Voltage Directive (2006/95/EC). A CE label is placed on all products that comply with applicable directives.

UL

UL, or Underwriters Laboratories, is a third-party safety and consulting organization that certifies products after thorough testing and evaluation. EXAIR’s Cabinet Coolers are UL Listed to US and Canadian safety standards. Static Eliminators are also UL Component Recognized. Within our line of Cabinet Coolers is the Hazardous Location Cabinet Cooler, bearing the Classified UL mark for use in classified areas.

ROHS_Vector

In the assembly of electrical products there can be hazardous materials used during production. The Restriction of Hazardous Substances, also known as RoHS or (2002/95/EC), restricts the use of materials such as: lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (CrVI), polybrominated biphenyls (PBB), polybrominated diphenyl ethers (PBDE), and four different phthalates. The electrical portions of EXAIR’s Static Eliminators, Electronic Flow Control, Electronic Temperature Control, Digital Flowmeter, solenoid valves, and thermostats all comply with the amendment outlined in the European Commission decision L 214/65.

In addition to RoHS, EXAIR is also committed to providing products that are conflict mineral free. In support ofconflictfree_v2 Section 1502 of the Dodd-Frank Wall Street Reform and Consumer protection Act, EXAIR complies with the conflict minerals rule to curb illicit trade of tin, tantalum, tungsten and gold in the DRC region. Using the CMRT 4.20 template, we’re able to document our supply chain to ensure our materials are not being sourced from places that could finance conflict in the DRC and surrounding countries.

reachFinally, per Regulation (EC) No 1907/2006 Title I, Article 3, paragraph 3, the European Union enacted legislation requiring substances and chemicals imported into the EU to be registered to ensure a high level of protection for human health and the environment. Per Title II, Article 7, paragraph 1, articles must be registered when a substance is intended to be released during normal conditions of use that would exceed 1 metric ton per producer per year. Since EXAIR products do not contain substances that are intentionally released, registration is not required.

If you’re looking to maintain compliance in your industry, EXAIR products have you covered. If you have any questions about these standards of compliance feel free to reach out to us. Our team of Application Engineers have years of experience in industry are waiting to take your call.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD