Most are quite effective at reducing highway noise, construction noise and many other forms of noise pollution, but depending on their properties, they could be causing more problems than they’re fixing.

This article will discuss the properties that should be considered when shopping for one of these sound barriers, specifically reflective vs. absorptive properties.

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Firstly, we would like to say that the best sound barrier has both absorptive and reflective properties.

A sound barrier's performance is measured in two ways. One is Sound Transmission Class (STC), and the other is Noise Reduction Coefficient (NRC). STC measures the amount of sound that passes through the wall or barrier while NRC measures the amount of sound the barrier actually absorbs vs. the amount of sound that is reflected.

A STC rating of 30 or more means that 0.1 percent of the sound reaching the barrier passes through. If the barrier is not absorptive though, 99.9 percent of the sound is reflected. We'll explain in a moment why that isn't always a good thing.

Many state departments of transportation require STC ratings in the range of 24 to 32.

An NRC rating is between 0 and 1. If a barrier has an NRC rating of .85 it means that 85 percent of the sound reaching the barrier is absorbed and 15 percent is reflected.

A good sound barrier is a sound-absorbing wall with a STC rating of 30 or more and a minimum NRC rating of .85.

In the illustration below you can see that the noise source, represented by a yellow dot, directly affects the house that is level with it and does not affect the house on the hill because the ground absorbs the sound.

In the next illustration we see the addition of a sound barrier that is only reflective. It does a great job at reducing noise at the lower house. What happens though, is the house on the hill is suddenly affected when it wasn't before.

The third illustration shows an absorptive sound barrier in place of the reflective barrier. It both keeps sound from troubling the lower house and absorbs the sound that was being reflected at the house on the hill.

Absorptive qualities are also important when it comes to parallel sound barriers

In the illustration below we see two reflective sound barriers with no absorptive qualities. Not only does the reflection between the two barriers increase noise levels inside, but most of the noise eventually escapes and continues to bother whatever exists outside the barriers.

The next illustration shows that barriers with absorptive qualities will reduce reflection, helping with noise levels between as well as outside the barriers.

Angles of Diffraction

Diffraction is a characteristic of all wave phenomena including light, water and sound. It is described as the bending of waves around objects.

Similar to the way light casts shadows, diffraction causes sound waves to cast "noise shadows" when they strike an object. Due to their much longer wavelengths, however, "noise shadows" are not very well defined and amount to noise reductions rather than an absence of noise.

Greater angles of diffraction will result in more noise reduction. The position of the source relative to the top of the barrier determines the extent of the shadow zone and the diffraction angle to the receiver.

As you can see in the two illustrations below, having two reflective walls in place reduces the effectiveness of the first wall because the diffraction angles are altered. This reduces the "noise shadow."

Walls with absorptive properties, particularly when there are two, are more effective.

Classrooms are the most important place in a school to have proper sound quality and speech intelligibility, but there are a number of other places in which schools need acoustical treatment.

From cafeterias and gymnasiums to band rooms and auditoriums, we’ve treated every space in a school. We even stamp out classroom noise by treating school parking lots and courtyards where large chillers or generators are often far too loud.

Read on to see some of our work and to learn about various approaches to improving school acoustics.

Cafeterias

The hard parallel surfaces in a school's lunchroom are perfect for bouncing voices and general noise throughout the space. this bouncing is called reverberation, and it can seriously reduce speech intelligibility, which is a big problem for both teachers and students.

Here we see acoustic baffles hanging from the ceiling. Hung from the ceiling at two points, these highly absorptive products are normally used in larger rooms.

Music Rooms

Proper band and chorus room design should take into consideration not only what the room will sound like, but also how the music in that room will affect the adjoining rooms.

Acoustical products used to treat how the room will sound are applied to the walls, corners and ceiling. They include acoustic wall panels, sound diffusers, acoustic ceiling tiles and bass traps.

Acoustical products used to ensure the music doesn't disturb adjoining classrooms can be installed inside the walls, floor or ceiling or on their surfaces. These products include sound blockers (as opposed to absorbers and diffusers) such as floor underlayment and high-mass vinyl.

Gyms

Gyms are often treated with a combination of acoustic wall panels and hanging acoustic baffles or banners. Here we see Acoustic banners in a large university's basketball/volleyball facility

Hanging acoustic banners are the same as acoustic baffles, but while baffles are hung from two points, banners are hung from four.

The Integrity Christian School in Newberg, WV, had a multipurpose room very similar to those found in most churches or schools. However, due to the acoustics in the room, it wasn't suitable for many purposes.

Before acoustical treatment the room was used only for recreational purposes such as basketball because of the excessive reverberation or echo within the room.

Click here to read about the room's treatment and results

Auditoriums

With plays, band concerts, classes and much more happening in auditoriums, they are places in which speech intelligibility is vital.

To the left you see a combination of custom-sized/custom-cut acoustic wall panels and hanging acoustic banners.

Below you see and auditorium equipped with sound diffusers along the side walls and acoustic wall panels along the back wall.

A combination of absorption and diffusion was used in this case because too much absorption would have left the performance hall sounding 'dead.' The diffusers work to break up or disperse the sound that isn't absorbed, making the room sound more 'alive.'

Outside

The three large chillers at Meadowbrook High School were causing serious sound problems. The units weren't exactly in the best places, which were the school's courtyards.

Acoustical Solutions, Inc. was called in and chose to use an absorptive sound wall around each chiller to combat the noise.

Today, the school's courtyard is both quieter and prettier. Click here to read more about the treatment and results at the school.

First though, have a look at the baffles in our new collection.

Acoustic Lanterns are innovative ceiling baffles designed for hotel lobbies, restaurants and other architecturally demanding environments where acoustic control must integrate with its surroundings.

Available in four shapes (hexegon, square, triangle or circle) and made from sound absorbing materials (high-density 6lb glass wool), these Acoustic Lanterns come in black, grey or beige.

Sonex Rondo™ Baffles offer design versatility and excellent sound absorption across all frequencies—preventing noise build-up that interferes with speech intelligibility. Sonex Rondo™ Baffles are made from acoustic foam.

Available in lengths up to 24" with 6" or custom diameters, these baffles are offered in natural white or light grey.

Whisperwave™ curved accent products allow you to unleash your creativity while reducing noise and reverberation. Made from Class 1 fire-rated acoustic foam, Whisperwave™ Baffles are offered in standard and custom sizes and curve patterns.

Whisperwave™ products are available in natural white and light grey.

Whisperwave™ Ceiling clouds are suspended on ceiling-mounted cables using corkscrew hangers. They differ from Whisperwave Baffles in that the clouds are hung from four points while the baffles are hung from two points.

To learn about how and why these products work, read on>>>

Acoustic baffles are free hanging sound absorption products that are often used to acoustically treat large rooms such as gymnasiums and lobbies.

By hanging from the ceiling, baffles reside in space where sound tends to get "stuck" because there isn't anything up that high to absorb or diffuse the sound waves.

Sound reflects off of hard surfaces (walls, ceilings, floors) in rooms and continues to echo or reverberate often for long periods of time.

The lingering sound decreases speech intelligibility and generally makes communication difficult. As communication becomes more difficult, voices tend to rise, which only perpetuates the problem.

Acoustic wall panels are a great choice when trying to combat the problems described above (echo and reverberation). They absorb direct sound and, if placed correctly, sound that has bounced off other surfaces (walls, ceiling, floor).

This absorption greatly reduces reverberation and echo within rooms, which increases speech intelligibility and communication in general.

Generally, acoustic baffles are used when wall space is limited or when the room is very large. Just like wall panels, they absorb both direct and reverberant sound.

The difference, however, is that all sides of a baffle are exposed and able to absorb sound. the increased surface area is one of the main reasons baffles are used in large spaces.

"School Pride" tells the stories of communities coming together to renovate their aging and broken public school, which is why Acoustical Solutions is extremely excited to have contributed.

The episode in which we participated chronicles the renovation of Detroit's Communications and Media Arts High School.

According to the Detroit Public Schools Web site, the high school, which boasts a 97 percent graduation rate, "was originally slated to close this summer due to lack of funds to repair the building. It was saved after being selected to receive significant repairs as part of "School Pride."

Read on to learn about the products and their applications within the school ...

Within the school, we mainly helped with a media room. In that room we provided:

A ClearSonic Vocal Booth (IsoPac G)- These voice over and vocal booths are lightweight and portable. The acrylic wraps around the front of the booth, while the Sorber panels wrap around the rear. Since Sorber panels don't actually connect to the ClearSonic Panels, you can simply use one side of an S5-2 (two sections hinged together) as a "door" for easy entry.

IsoPac G is a small vocal booth that will hold a single vocalist. This IsoPac works well in situations where space is at a minimum. Constructed in a similar style to our MegaPac, the IsoPac G uses a combination of clear panels and SORBER to achieve maximum sound reduction. This booth is often used for voice-over work, vocal recording, and practice.

Whisperwave™ Baffles - Whisperwave™ curved accent products allow you to unleash your creativity while reducing noise and reverberation. Whisperwave Baffles create movement and are easily hung using a wall-to-wall system.

Made from Class 1 fire-rated willtec® foam, Whisperwave™ products are offered in standard and custom sizes and curve patterns. Whisperwave™ products are lightweight and easy to install. The line also includes ceiling clouds, panels and awnings.

This rule comes into play most often when it comes to doors. Whether a regular door or a soundproof door, small openings almost always exist at the bottom, top and sides.

It is because of the 1% Rule that these openings around doors effectively cancel out any acoustic functionality.

For example, a 1/8" opening around all four sides of an acoustic door(STC rating of 56) can significantly reduce the door's STC rating (to as low as 21), which means the door is close to useless acoustically.

The picture below illustrates different size openings when it comes to airflow versus sound transmission. As you can see, a smaller opening reduces the amount of airflow, but does not reduce the amount of sound transmission.

So, how do we seal the door and defeat the 1% Rule? Read on>>>

Door Seal Kits - Include automatic door bottoms (see below) and high-grade neoprene door jams for the vertical sides and top of the door.

Automatic Door Bottoms - Our automatic door bottom sweeps utilize a concealed flat spring mechanism, which activates when the door is closed, lowering a neoprene seal insert against the floor or saddle.

Door Jamb Seals - This acoustical seal features our unique compress-o-matic design with a sound absorbing meoprene rubber gasket that compresses to form a tight seal as the door is closed.

Door Thresholds and Saddles - These acoustical door thresholds, commonly called saddles, feature a neoprene bulb fitted with a protruding rubber finger to help correct any misalignment in the door as it is closed.

Cam Lift Door Hinges - The can lifting action greatly improves the sealing characteristics along the door perimeter, lifting and lowering the door with the swing.

Meeting Stiles for Double Doors - Acoustical door astragals are designed to effectively seal off the air gaps that create sound leaks where the doors meet.

Click below to see a before and after video of an acoustic door seal kit

This kit provides the customer with all she needs, including everything from the acoustical wall panels down to a drill bit, in one convenient and complete package.

Included in this noise control kit are (2) broadband panels, (8) control columns, (12) scatter blocks, (24) surface impalers, (8) corner impalers, (100) wall anchors/screws and (1) drill bit.

The finished room will look like this:

Bellow are illustrations of how these sound control products work ...

Before After

We'll start in the back of the room where the 12 scatter blocks are installed.

These scatter blocks complete two tasks. First, they diffuse (break up) the sound, reflecting it in separate directions. This reduces the amount of indirect reflections in the room and allows for the direct sound to be heard more clearly.

Before After

In working with the two broadband panels and two of the control columns at the front of the room, the scatter blocks also absorb a large amount of the room's front-to-back reverberation.

Before After

With the remaining six control columns, we treat the walls directly beside the editor/ producer/ engineer. These columns diffuse or absorb most of the side-to-side reverberation in the space.

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In creating a home theatre, two issues need to be addressed, soundproofing and sound absorption. ...

Soundproofing - blocking sound from entering or leaving a space

Before/during construction - If acoustical issues are addressed during this phase, treatment will be most effective and more choices will be available. Options include:

• AudioSeal™ Sound Barrier - Can be installed in walls, ceilings or floors and blocks sound using sheer mass.
• Resilient Isolation Clips (pictured at right)- An economical choice, these clips stop sound transfer by creating space between walls, ceilings or floors and what is opposite them (studs, concrete, wood, steel, etc.).
• Green Glue - Used between two rigid building materials such as drywall, Green Glue absorbs vibration within the wall. This reduces sound on the other side of the wall.

After construction - If your walls and ceilings are already fully constructed don't fret, it's not too late. While not ideal, soundproofing treatment can be applied to the outside of a wall.

• Absorber/Barrier Combination Blanket - These blankets can be hung on walls and are made of one barrier layer sandwiched between two absorptive layers.
• Door Seal Kits - These kits seal gaps in doorways. This is important because a 1 percent opening will allow up to 50 percent of sound to pass through that opening.

Sound Absorption - stopping sound from reverberating or echoing within a space

Countless combinations of options exist in this area, but we have a few suggestions:

• Commonwealth Collection (pictured at right) - Definitely one of the most aesthetically pleasing choices, this line of wall panels and bass traps is designed for home theaters.
• AlphaSorb™ Acoustical Panels - Used in many applications, these versatile panels work in home theaters by absorbing sound waves and converting them into heat energy. This eliminates sound from bouncing from wall to wall (echoing).
• BassTraps - These absorptive traps are important to have in the corners of a home theatre because bass and other low frequency sounds build up in corners.

The CEDIA EXPO, which will be held this year in Atlanta at the Georgia World Congress Center, is the #1 trade show in the residential electronic systems industry.

Acoustical Solutions will be at booth #4619, where anyone is free to come chat, learn, buy or browse. As experts in the soundproofing and noise control industry, we take pride in providing effective solutions for all home entertainment situations.

From bass traps and sound diffusers to acoustic wall panels and acoustic foam, we have countless products and product combinations that can make any room sound like a movie theater.

Or if 'movie theater' isn't the sound you're going for, we can reduce echo, fix reverberation times, make bass hit harder, soundproof and just about anything else you might want done acoustically to compliment a residential electronics system.