By John J. Lupo
Division Manager, North Florida, Dynamark Systems

This is part 5 of a multipart series of articles that will provide a solid understanding of the principles of sound and acoustics as it relates to design and construction of both public and private spaces. Part 1 covered the basics of Sound, Part 2 covered Decibels, Part 3 covered STC Ratings and Part 4 covered Soundproofing.

A basic understanding of the types of methods and materials available to control the quality of sound in an interior space is an integral ingredient in the proper planning and design of any room or public space. If you’re concerned about improving the experience of residents, occupants or guests utilizing you facility then learning about sound quality control is vital to the success of your project.

“What did she say?” “I missed that.” “Why can’t I understand the dialog?”

When you’re trying to deliver a message to an audience that is not the result you hope for. I can’t tell you how many times I’ve attended an event in a public venue and have not been able to understand one word that was said. Excessive reverberation or room echo is generally the cause for bad sound quality. The good thing is that it can be corrected.

Most rooms are constructed with highly reflective materials such as drywall, concrete, wood, glass, metal, etc… This creates the need for quality sound control products.

There are four basic types of treatments used to improve the audio quality of any listening room:

1. Absorptive: by absorbing excess middle and high frequency reflections we can remove excess echo.
2. Reflective: if a room is overly dull adding reflective surfaces will brighten the room.
3. Diffusive: by diffusing frequencies we eliminate direct reflections to offer a more balanced sound.
4. Bass Traps: absorb/remove unwanted low frequency bass resonance improving overall quality.

Quick Point #1, About Excessive Reverberation

As sound energy travels from the speakers or source it will collide withal the surfaces within a room or area. The sound waves will be reflected off of the untreated reflective surfaces of the room. Control of these sound waves is necessary otherwise we run the risk of the room sounding like the inside of a cave. Not good if you’re trying to deliver a clear message or pleasing music to an audience.

Quick Point #2, The Padded Cell

Overtreating a space may be just as bad as not treating it at all. Rooms where the wall surfaces are completely covered with sound absorbing panels will result in a loss of brightness. The room becomes dull sounding and lifeless. Both are bad ideas.

When we achieve the proper balance the vocal & musical performances are more enjoyable. This is due to the quality of sound within a room. This result is due to the design and planning that went into the room or space. The only way to achieve optimum sound quality is by adhering to the principles of room acoustics and sound control. Acoustic panels perform the important function of “tightening” up the sound in a room, making dialog, music & sound effects more intelligible and therefore more enjoyable.

When we speak about interior room acoustics we refer to the treatment of rooms or listening room surfaces to address the quality of sound received at the listening position. This is typically where form and function collide. Some Interior Designer professionals may resist the placement of sound treatments due to a lack of understanding of room acoustics. It is important to remember that the interior design of the room must work in harmony with the necessary placement of sound control treatments. A good design accomplishes both superior appearance and superior sound quality.

Thankfully this mindset is beginning to change as more and more Interior Design professionals become educated of the many benefits of proper sound control treatments. More and more they are consulting with professionals regarding the proper integration of acoustic treatments into their designs. Sound Control and Acoustic treatments can be integrated into the design without dominating. It is a careful and necessary balance to achieve success. It is also important to consider that the proper placement of treatments is essential to success. It is not enough just to throw some acoustic panels up anywhere.

The most common measurement used in rating the effectiveness of sound control products is the Noise Reduction Coefficient (NRC) rating. As with STC ratings the NRC ratings focus on the frequencies between 125Hz and 4000Hz. The difference from the STC ratings is that the NRC refers to the materials ability to absorb sound as opposed to containing the sound.

Noise Reduction Coefficient (NRC) (definition republished from http://www.nrcratings.com)

“The NRC is a single-number index determined in a lab test and used for rating how absorptive a particular material is. This industry standard ranges from zero (perfectly reflective) to 1.00 (perfectly absorptive).

The NRC is simply the average of the mid-frequency sound absorption coefficients (250, 500, 1000 and 2000 Hertz) rounded to the nearest 5 percent. The absorption coefficient is a measure of the efficiency of a surface or material in absorbing sound. If 75 percent of the sound energy is absorbed, the absorption coefficient is said to be 0.75. One square foot of the material gives.75 absorption units. A rating of 1.0 means that no sound passing through the material is returned to the room and is an excellent means of room sound control. As with the STC Rating, the materials performance will diminish as the frequencies descend. So we need to look at the full testing to be sure we are addressing the frequencies we desire to control.

There are many products on the market that claim some type of sound absorption capabilities. Many open cell foam products are available. It is my opinion through personal and professional use along with laboratory and personal testing that the Glass Fiber Boards offer the best production for the money and installation effort.

I will go into more detail regarding the available sound control products in a future writing.

Hopefully this article gives you a better understanding of the importance methods of treating your room for sound quality available. If you have any questions or comments please contact me at John@Electronics-World.net

John J. Lupo
Manager, Comercial Audio Video
Electronics World
Gainesville, FL

This article was reprinted with permission from John J. Lupo and originally appeared here.