When choosing which product is perfect for your acoustic reduction needs, there are a number of factors that must be considered prior to making the purchase.  As any individual expects, you want to make sure that the acoustic product fulfills what it promises.  But in order to do that, there are questions that need to be considered, such as:

1)    What is your source of noise?

2)    Is the “volume” of the sound source loud?

3)    Is it high or low pitched?

4)    How far will the sound reducing product be from the source of sound?

5)    Can you describe the overall environment of the sound source?

6)    What are the main issues that the source of noise causes?

7)    What are the current ceiling wall and floor surfaces made of?

Sometimes, you find that less sound reduction is enough to fulfill your needs or worker safety standards.  Other times, you may find that just cutting down the echoing solves the noise issue.  Noise absorbing baffles, sound-reducing curtain dividers, acoustic reduction enclosures all fulfill specific sound abatement purposes that would create a viable solution to your noise problem.

When Do I Use Sound-Reducing Curtain Dividers?

Sound-reducing curtains and curtain enclosures are generally used to encapsulate the sound at its source at a close proximity, to meet federal regulations on noise pollution, to keep noise out of a designated area, and/or to maintain a sound level that is comfortable for workers that are in the noisy area for the majority of their day.  The level of sound reduction can range from a slight decibel reduction to a more drastic decibel reduction.

With a core made up of absorptive material and a flexible, acoustic membrane, sound-reducing curtain dividers have been known to reduce the decibel level to 20-21dB below the original sound source (which was a low frequency and high decibel source – the most difficult noise to attenuate).  Using alternate construction methods as well as a combination of different sound products, the range could possibly go up to a 30-40dB reduction.  These panels can be customized to fit whatever your needs are.

Assuming that your acoustic reduction curtain divider system is sufficiently sealed on all edges, the benefit of using sound curtains may mean the difference between the use of inexpensive preventative gear for each worker and the in-depth implementation of an OSHA-approved sound monitoring program to adhere to federal guidelines.

Perceptions of Change in Decibel Levels

Perceptions of Change in Decibel Levels
Imperceptible 1dB
Barely Perceptible 3dB
Clearly Noticeable 5dB
Twice as Loud / Soft 10dB
Four Times as Loud / Soft 20dB

This chart indicates change in decibel levels and how they are perceived to the average human ear.  One thing to keep in mind while looking at this chart is that the percentage of decibel loss is not proportional to the actual decibels lost.  Although a 5dB reduction may seem like a smaller number, the human ear perceives this as a dramatic change.  For example, if a 100 dB sound source is reduced to 80dB, the 20dB loss that occurs is not a 20% loss (in respect to the perception of a human ear).  This results in a loss of approximate 75%.

STC Explained

The term, sound transmission class (STC), is used to describe sound reduction capabilities of a material.  It is a numerical scale that is used to rate the material – basically, the higher the STC value, the greater sound reduction capability.  This value is based off of a set of noise frequency levels that range from 125 Hz to 4000 Hz.  It is a general standard of exhibiting the noise reducing qualities of material.

When Do I Use Noise-Absorptive Baffles and Banners?

There are times when operations managers and staff are unaware that instead of a complete decibel reduction sound curtain system, it may just be an echoing issue that needs to be resolved.  The large, open area could have a number of reflective surfaces (glass, tile, cement, metal) which causes sound to “bounce” off these surfaces, creating a longer reverberation time for each sound wave.  If a noise absorption baffle system is not in place, this can create a barrage of sound waves, which indicates that the general work environment has allowed the noise to travel far distances, thus creating an uncomfortable situation of past and present noises all being “re-circulated” into one general work area.

Noise-absorption baffles and banners act as a sound wave “dissolver.”  When a sound wave reaches a noise baffle, it absorbs a relative percentage of the wave (depending on the material used and its NRC rating), and bounces back only a fraction of the sound coming in.

NRC Explained

This is where the term – noise reduction coefficient (NRC) – comes into play.  NRC is a standard, numerical scale based off of a set of general sound frequencies (250, 500, 1000, and 2000 Hz) used to dictate what the quality of absorption is for that material.  The NRC value will let you know what percentage is absorbed.  The value of zero (0) indicates a perfect sound reflection, and a value of one (1) indicates a perfect absorption rate.  A lower NRC value tends to work best in larger areas, and a higher NRC value tends to work best in a small room, or in an area that has a great deal of noise.

So, if a material at 1000 Hz has an NRC of .90, This means that 90% of the noise will be absorbed and 10% will be reflected back into the area (see illustration).

But keep in mind that as you move into different sound frequencies, the NRC may change.  Using the same example – if 1000 Hz has an NRC of .90, it will not perform at .90 at 125, 250, 500, and 4000 Hz.  This same material could perform at a higher level at 4000 Hz and a lower level at 125 Hz.

A rule of thumb to explain NRC is, lower frequency noise is a sound wave that is much harder to reduce than higher frequency noise – a lower frequency sound wave tends to be much longer than a higher frequency wave.

Moving Forward: Facts to Consider

Moving forward, some facts to consider are the following (and a chart for sound description relative to every day noise):

–          NRC and STC are based off a set number of sound frequencies ranging from 250 Hz to 4000 Hz.  Higher frequency noises above 4000 Hz and lower frequency noises below 250 Hz are not taken into account.

–          Low frequency noises that are most common in industrial applications are primarily measured at frequencies of 500 Hz and below.  High frequency noises can be described as anything above 4000 Hz.

–          Reflective surfaces, distance from the sound source, and effective edge sealing all are significant factors in creating a more successful sound reduction capability.

–          An STC rating does not consider “fractures” in the noise barrier, such as not using a sufficient amount of edge sealing.

Because of the very custom nature of sound products, it is always important to discuss your details with a specialist.  Contact AmCraft today to speak with one of our technical specialists for your project!  You can call 847-439-4565, email sales@amcraftonline.com, or click the button below:

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