Posts Tagged sound absorbers

Demystifying Acoustic Data: Part 2 – Test Material Mounting

For anyone new to the world of acoustics, there is a multitude of terms, coefficients and numbers that are thrown around.  This flood of information can seem intimidating, especially to beginners. In this series, acoustician Cameron Girard of Acoustics First® hopes to help you distinguish between what’s useful and what’s not.

Part 2: How Mounting in Testing Affects Sound Absorption Data

As I discussed in my previous article, the best way to compare the performance of sound absorbing panels is by referencing the Sound Absorption Coefficient (SAC) and Noise Reduction Coefficient (NRC). However, these coefficients are often used as marketing tools. Be on the lookout for companies that list absorption coefficients and NRCs without mention of a particular testing standard or mounting method. It’s vital to check for this information, as direct comparisons to competitors and other materials can only be made if their testing procedures are the same.

The sound absorption of a material that covers a flat surface not only depends on the physical qualities of the material but also on how the material is mounted during installation. The mountings specified in laboratory tests are intended to simulate conditions that exist in normal use, such as direct wall mounting and installation into a ceiling grid.

Many materials for treatment of walls or ceiling are tested using what is called Type ”A” mounting. Type ”A” mounting means the test specimen was placed directly on the test surface of the reverberation chamber. Lay-in ceiling tiles, on the other hand, are often tested using ”E400” mounting. The ”E” designates a sealed air space behind the specimen (simulating  the air gap between a dropped tile ceiling and the structural ceiling) and the number after the ”E” is the depth of the airspace in millimeters. The airspace behind the acoustic material affects the sound absorption by acting as a bass trap. The deeper the cavity behind the panels is, the lower the fundamental of the “trapped” frequencies will be.

To see what this look like in terms of actual numbers, let’s take a look at how different mounting methods effect the sound absorption coefficients of Acoustics First’s HiPer® Panel (a low-profile, composite absorber/diffuser panel).

Since the HiPer® Panel can be used effectively in multiple applications; we had it tested in accordance to the two most-common mounting procedures, Type E-400 and Type A. The results of the laboratory tests are as follows:

Product Info

Sound Absorption Coefficients

Product Name Thickness Mounting 125Hz 250Hz 500Hz 1kHz 2kHz 4kHz

NRC

1″ HiPer® Panel 1″ E-400 0.43 0.28 0.51 0.76 0.99 1.10 0.65
1″ HiPer® Panel 1″ A 0.09 0.28 0.78 0.75 0.94 0.85 0.70

 

As you can see from the chart, the sound absorption coefficient at 125 Hz varies greatly between E-400 mounting (SAC of .43) and Type-A mounting (SAC of .09). If mounting the HiPer® Panel in a ceiling grid, with a sizable airspace, you can expect significant low-frequency absorption, but mounting it on a wall (Type-A) will result in much less absorption at 125Hz.

Other mounting methods are available, but are not used as frequently. Here are some of the basic mounting designations (See ASTM E795 for more information.)

Type A mounting – Test specimen laid directly against the test surface (wall panel on drywall).

Type B mounting – Test specimen cemented directly against the test surface. Type B mounting is intended to simulate acoustical ceiling tiles or other sound-absorptive products adhered to a hard surface with an adhesive.

Type C Mounting—Test specimen comprising sound-absorptive material behind a perforated, expanded, open facing or other porous material.

Type D Mounting—Test specimen mounted on wood furring strips.

Type E Mounting—Test specimen mounted with an air space behind it (dropped tile ceiling).

As we’ve discussed, acoustical data can vary greatly depending on the mounting method used during testing. Acoustics First tries to include as much information about testing procedures as possible, because we feel an informed client makes the best client.

Contact Acoustics First for your all your sound control needs!

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Demystifying Acoustic Data: Part 1 – Absorption vs Isolation

For anyone new to the world of acoustics, there is a multitude of terms, coefficients and numbers that are thrown around.  This flood of information can seem intimidating, especially to beginners. In this series, acoustician Cameron Girard of Acoustics First® hopes to help you distinguish between what’s useful and what’s not.

NRCvsSTC

Part 1: Acoustic Terminology – Sound Absorption vs Sound Isolation

In order to make informed decisions about acoustical treatment, it is vital to know the difference between materials that are meant to absorb sound within a room and materials that are meant to block sound from leaving or entering it. In an overly reverberant auditorium, absorptive treatment is needed to reduce echoes and improve speech intelligibility. If the problem is sound passing in between spaces, like offices or apartments, then isolation treatment is required. These are two separate acoustic issues which require separate solutions.

In both scenarios, it is important to know which data is relevant and helpful. Also, given sheer volume of information available on the internet, it is perhaps unavoidable that some info will be incomplete or simply incorrect.  It should not be assumed that something which sounds technical is, in fact, backed up by proper testing.

Terms for Sound Absorption

We recently encountered an acoustical ceiling tile which was said to “absorb 50% of sound”. On the surface this sounds like an extremely efficient product.  However, let’s delve in closer and decipher what is actually usable information, and what is just marketing.

When sound waves meet a room surface such as a wall, ceiling or floor, some of the sound energy is reflected back into the room and the rest is considered to be “absorbed”.  The absorbed sound energy has not vanished, it’s actually been converted into kinetic (vibration of a solid material) and thermal energy (heat due to friction within a porous material) or has simply passed right through the material (transmission). The more surface area a certain material has the better absorber it will likely be. “Soft” materials, like heavy blankets, fabric and fiberglass, have loads of nooks and crannies, which sound tries to “fill”. These porous materials are great for reducing reverberation within a room, but will only marginally reduce the sound that leaves it (but more on that later).

Sonora® wall and ceiling panels are used for absorbing sound within a space.

Sonora® wall and ceiling panels are used for absorbing sound within a space.

When comparing sound absorbing products, there is a particular set of terms you should look for: The Sound Absorption Coefficient (SAC) and Noise Reduction Coefficient (NRC). These are used to specify the fraction of incident sound that a material absorbs per 1’x1’ area. An NRC of 1.0 indicates perfect absorption (an open 1’x1’ window) and a value of 0.0 represents perfect reflection (polished concrete has an NRC of .02).

To measure sound absorption, a large sample of the material is placed in a reverberation room with all other surfaces being hard and reflective. The time it takes a test sound signal to decay by 60dB (rough point of inaudibility) after the source of sound is stopped is measured first with the sample in the room and again with the room empty. The difference in decay time defines the efficiency of the absorbing material and thus the absorption coefficients.  Large spaces with low-NRC materials (tile, drywall, etc.) have longer reverberation times, while small rooms furnished with high-NRC materials sound much more “dead”.

Clearly, a single 2’x2’ ceiling tile is not going to reduce the reverberation in a real-world space by 50%. So is the above claim false? Not exactly… The ceiling panels do have an NRC rating of .50, so the tile does absorb 50% of incident sound. However, one might assume a much more drastic improvement based on the “50%” claim. In reality you’d need a large square footage of these ceiling tiles to cut the amount of total reflected sound in half. Always be sure to check the NRC number!

Terms for Sound Isolation

Our customers often call with issues related to neighbor noise or office-to-office privacy and are looking for “sound proofing” treatment. Unfortunately, many do not realize that simply installing acoustic foam or fiberglass panels will not appreciably reduce the level noise entering and leaving their space. These absorptive materials are great at reducing unwanted reflections within a room because they are porous and air/sound energy can flow through them. That being said, they are generally poor sound barriers for this exact reason.  They will help to reduce noise buildup in a room and improve the ‘acoustics’, but will do very little to “block” sound coming in or out.

BlockAid® is a heavy impermeable barrier for stopping the transmission of sound.

BlockAid® is a heavy, impermeable barrier for stopping the transmission of sound.

Sound is like water; it will “flow” into an adjacent space if everything isn’t sealed up. Materials that are air tight and heavy, like our BlockAid® sound barrier, provide the most relief of air-born sound transmission. Continuous coverage of floors/ceilings or walls is necessary to ensure that sound doesn’t ‘flank’ around these barriers. Multiple layers of varying materials, the use of resilient clips or channels, and additional walls will provide even more control.  For a demonstration of how different materials affect sound isolation, check out our video http://acousticsfirst.com/educational-videos-the-barrier-and-the-bell.htm

Like NRC for sound absorption, there is also a laboratory tested figure that can be used to compare the sound “blocking” properties of acoustic barriers and wall constructions: Transmission Loss (TL) and Sound Transmission Class (STC). These describe how much air-born sound is attenuated through a given material.

In the lab, the material to be tested is mounted over an opening between two completely separated rooms, one with a speaker (source) and the other with a microphone (receiver). Save for the open “window”, these rooms are completely isolated with thick and massive walls, so virtually all the sound energy transmitted between rooms will be through the test specimen. The difference between sound levels in the source room and the receiving room is the transmission loss (TL). The TL is measured at multiple frequencies, which is fitted to a Sound Transmission Class (STC) “curve” at speech frequencies (125Hz-4kHz). The STC of the material is the TL value of the fitted curve at 500 Hz. For example, a material with an STC of 27 typically “blocks” 27dB of sound. Keep in mind though, the STC’s of materials do not add up linearly; in other words, adding a material with an STC of 27 to an existing wall with an STC 45 will not result in an STC of 72.

As always, Acoustics First is here answer questions and help you find the best solutions.

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Custom Panels and the Aesthetics of Acoustics

There is a saying in our industry: When it comes to designing a space, acoustic consultants are blind and architects are deaf. In reality, it is in both parties best interest to consider the other side when designing a space, so visual form meets acoustic functionality.

Let’s be real, standard acoustic treatment is far from sexy. Typical 2’x4’ panels, while fully functional, don’t present the architects with much in terms of visual interest. This is where Acoustics First can supplement the design goals of the architect/interior designer with our technical expertise to find a custom solution that sounds and looks great.

Hexagonal ToneTiles™ at Kramer Middle School.

Hexagonal ToneTiles™ at Kramer Middle School.

Recently, Acoustics First® was asked to provide the custom panels for the cafeteria at Kramer Middle School in Washington DC. It was settled that hexagonal ToneTiles™ would be suspended as clouds in a geometric pattern around the ceiling. The resulting “honeycomb” effect is not only visually appealing, but the treatments effectively cut down the overall reverberation; increasing speech intelligibility and making the space more comfortable for a variety of activities.

Acoustics First® enjoys the inherent challenge in making these custom panels a success. We have plenty of experience in fulfilling the design goals of architects and interior designers. Interested in seeing more of these custom projects?

Visit http://acousticsfirst.com/installations-education-school-museum.htm to see some more examples.
Feel free to give Acoustics First® a call to discuss your custom treatment needs!

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DIY: Back Wall Diffuser Array/Bass Trap

Getting more out of your back wall diffuser array with a simple hanging DIY array/bass trap.

One of the big “back wall” questions people have is “If I have a large diffuser array, how can I get the bass trapping I need?”  A great answer to this question is to turn the entire array into a hanging bass absorber.  If you are already planning on getting diffusion for your back wall, here is a great way to use that wall space for more than just diffusion.

Stuff you need:

bass trap foam diffuser -decon- front

Assembly instructionsbass trap foam diffuser - side

  • Screw the two IsoHangers to the plywood, using a fender washer on each screw. These should be about an inch in from each end -drill small pilot holes first. (These will be used to hang the panel, this side will be designated as the back from here on out.)
  • Use Construction adhesive to attach the Cutting Wedge® Foam to the back of the panel in a checkerboard pattern (each panel 90° rotated from adjacent)
  • Use Construction adhesive again to attach the 8 Diffusers to the front of the Plywood (Follow the installation instructions for adhesive placement)
  • Attach the Rings or Wire to the free end of the IsoHangers.

What you have created is a hanging panel that will diffuse mid-high frequencies and trap the lows.  The hanging mass absorbs low frequency energy by moving slightly when pushed by the energy of the Low frequency Waves.  The rear facing fiberglass also absorbs low frequencies by dampening the panel, but it also absorbs any of the waves that happen to get trapped behind the panel.

bass trap foam diffuser - rear

Hanging the Diffuser/Trap Assembly

  • Measure and attach the Closet Brackets to the Wall – Use appropriate anchors!  If you have standard or double wall construction without Resilient Channels, use the studs – The IsoHangers will keep vibrations from transmitting through the wall.
  • Hang the panel on the Closet Brackets using the rings/wire with the Diffusers facing you and that’s it!

bass trap foam diffuser - frontThis simple DIY project is provided as a way for our customers to learn better ways to use our products and get more value out of the products they buy.  For those customers who are planning on purchasing diffusers to make an array, or maybe already have an array and are looking to try a new configuration – this project may be what you’re looking for.

A little History…

If you embark on this little construction project, you will be constructing studio elements that have remained basically unchanged since at least the early 1970’s.  Hanging plywood wrapped in studio foam or fiberglass has been used “behind the curtains” of many of the top studios for effective bass control for over 40 years – just no one has ever seen it, as it has been hidden in walls; masked as a false wall of fabric stretched across wooden louvers!

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Acoustics First Corporation supplies acoustical panels and soundproofing materials to control sound and eliminate noise in commercial, residential, government, and institutional applications worldwide.  Products include the patented Art Diffusor®, sound absorbers, noise barriers, acoustical fabrics and accessories. Acoustics First® products are sold for O.E.M applications, direct, and through dealers.  For more information on acoustical materials and their application, please visit www.AcousticsFirst.com or call Toll Free 1-888-765-2900 (US & Canada).

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DIY: StratiQuilt™ Room Treatment

There are some situations where people are looking for a more temporary (yet still durable and effective) room treatment.  Maybe you have a garage, or a practice space, or a place where you are looking for a usable solution that isn’t a permanent installation.  Here is a great (not to mention tax deductible) treatment that can address many of the isolation and absorption issues of a space, while remaining durable (Washable), and easy to remove and reuse.

qfm-wallpanel

Stuff you need:

  • Enough StratiQuilt™ Double-Faced Barrier Blanket to cover all of the wall and ceiling surfaces of the room you need to treat.
  • 2”x4” lumber for the edges (Used to attach the barrier to the walls and maintaining an air gap.)
  • Short Lag bolts and Washers
  • Misc. hardware to attach 2”x4” lumber to walls.

Here’s what you do.

Attach the 2”x4” lumber to the walls with enough spacing to line up the grommets on two overlapped edges of the StratiQuilt™ blankets – if you have purchased the roll, the finished edges are 4 feet wide.  Leave enough room to overlap the edges and bolt the quilts to the 2”x4” lumber as shown in the diagram above.  Continue around the room, overlapping the edges of the StratiQuilt™ blankets to seal off the room.  The blankets can be left loose over doors to allow for entry and egress while maintaining a good acoustic seal.

stratiquilt room treatment

If desired, continue the process across the ceiling to “lock in” the room acoustics.  This treatment may be considered by some to be a little on the “dead” side (High Absorption); however, The benefits of the treatment far outweigh this issue, which can be compensated for by adding a few acoustically reflective surfaces to the room (Drum Kit, Amplifiers, Racks, Diffusers, etc.)

Why use this system?

Other than it being very simple to install, take down and move with minor modifications to the structure, it performs a few vital acoustic tasks – all with one product.  The StratiQuilt™ design is two layers of quilted acoustic fiberglass with a layer of BlockAid® barrier in the middle.  The BlockAid® help the soundproofing of the room by it’s STC of 29, which will add significant isolation to the room.  Mounting on the 2”x4” lumber is not just done for ease – adding the air gap behind the barrier increases both its STC and NRC allowing it to work as a limp mass barrier/absorber.  The material absorbs on both sides (being double-faced), forcing in-room reflections to be attenuated immensely through the many layers of material it must pass through.

And on a final note, this economical start-up solution has the benefit of not being a “Building Material” for tax purposes, allowing for its immediate deduction as an expense.

Record your garage band without sounding like you’re in a garage, Try StratiQuilt™.

This simple DIY project is provided as a way for our customers to learn better ways to use our products and get more value out of the products they buy.  If you are looking for more ways to use the products you have, look to Acoustics First for Ideas.  http://www.acousticsfirst.com

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Acoustics First Corporation supplies acoustical panels and soundproofing materials to control sound and eliminate noise in commercial, residential, government, and institutional applications worldwide.  Products include the patented Art Diffusor®, sound absorbers, noise barriers, acoustical fabrics and accessories. Acoustics First® products are sold for O.E.M applications, direct, and through dealers.  For more information on acoustical materials and their application, please visit www.AcousticsFirst.com or call Toll Free 1-888-765-2900 (US & Canada).

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