Sound Absorption and the Noise Reduction Coefficient (NRC)

When sound waves travel through air and encounter another medium, the wall of a room, for instance, a portion of the sound will be absorbed by the wall while the remainder will reflect from the wall surface. Add to the mix the other surfaces reflecting sound waves in various directions within the room, and the result is a jumble of sound reflections which interfere with the clarity of the original, intended sound. The presence of numerous hard, untreated surfaces is often to blame for the heightened noise levels in busy restaurants as the voices of multiple patrons reflect and produce background noise. Acoustical improvement and sound reduction projects often involve the implementation of treatments designed to absorb sound wave reflections as a part of a comprehensive sound control plan.

Taking into consideration the tendency of sound waves to reflect from surfaces, it is apparent why the absorption of sound reflections is an important element of sound control and acoustical improvement. Capturing sound reflections becomes particularly important in environments such as auditoriums, restaurants and places of worship, where the quality of acoustics experienced within an area is fundamental to its purpose.

The reflective tendencies of the particular surfaces present within a room may contribute to the type and extent of sound absorption treatment necessary to achieve the desired result. Carpet, for instance, is more absorptive than tile, so a carpeted floor would produce less significant sound reflection than would a tile floor with other factors constant. How do we know? By performing the standard ASTM C423 test, independent labs quantify the amount of sound a particular surface material absorbs and assigns to it a value referred to as the Noise Reduction Coefficient (NRC). The NRC, calculated based on testing of a material at various frequencies within a concrete enclosure, can be interpreted as a percentage of noise that is captured and converted by a surface while the remaining portion is reflected. A NRC of 0.44, for instance, would be assigned to a surface which on average absorbs 44% of sound while reflecting the remaining 54%.

Like materials used in construction, soundproofing products are also tested for sound absorption at various frequencies and assigned a Noise Reduction Coefficient. The absorptive value exhibited by a particular sound treatment can help determine the circumstances in which the treatment should be applied. A project aimed at controlling low bass tones, for example, would call for more absorptive treatments than one targeting the higher frequencies produced by the human voice. Since each acoustical improvement solution must be tailored based on characteristics of the targeted area and frequencies to be controlled, it is advised to consult with a knowledgeable soundproofing consultant prior to implementing sound reduction treatments in order to ensure that critical variables are addressed.

About the Author: Mark Rustad is President of NetWell Noise Control, based in Minneapolis, MN. Founded in 1991, NetWell is a leading supplier of acoustic products, soundproofing treatments, sound reduction products and online acoustical consulting services. NetWell’s sound management skills are packaged into the industry’s premier website. Discover first hand why so much of NetWell’s business stems from the referrals and repeat orders they receive from satisfied clients around the world.

Sound Control for Sanctuaries

In a sanctuary or other place of worship, hearing the spoken word at the service is an integral part of the congregation’s attendance. However, sanctuaries typically consist of large open spaces surrounded by hard walls and windows, characteristics which significantly diminish the sound quality throughout a room. Long reverberation times caused by sound reflections in the vast open space produce background noise that can hinder the congregation from hearing and understanding the spoken word. The choir and organ music of traditional services and the drums and bass common in contemporary services pose additional sound reduction challenges as reverberations negatively impact acoustical quality throughout the sanctuary. Improving the quality of acoustics in sanctuaries entails reducing the reverberation time of sound waves while controlling reflections and getting rid of background noise. Implementing a combination of simple sound reduction treatments designed for accomplishing these goals can eliminate noise problems and enable the congregation to clearly understand the spoken word as well as the harmonic tones of the music in both traditional and contemporary sanctuary environments.

Wall or ceiling sound panels or acoustic tiles arranged around the perimeter of a sanctuary can absorb noise reflections, in turn shortening the reverberation time of sound waves and reducing background noise. Fabric or suede layered sound control panels designed for such purposes are available with specific features aimed at controlling different types of sound waves. Standard panels control sound reflections from the speech, choir and organ in traditional sanctuaries, while specially designed diffusing absorber panels work to absorb, reflect and diffuse tones such as low bass tones common in contemporary sanctuaries where acoustics are affected by the blend of multiple musical instruments. Installation of the recommended density and quantity of sound control panels can provide the congregation with the delivery of pleasant, harmonious sound throughout the service.

For sanctuaries with large, sound reflective windows throughout, wall mounted sound panels may only be a portion of the solution or may not be feasible at all. In this situation, fabric baffles surrounded by fabric on both sides can be suspended from the ceiling of the sanctuary. Such suspended panels are designed to capture sound reflections in sanctuaries with large windows or considerably high ceilings. Depending on the type of windows in a sanctuary, sound control blinds may also be an effective option for sanctuaries with numerous windows. Large sanctuaries may also benefit from sound partitions, which are sound absorptive curtains that can be used to divide the sanctuary into smaller areas as needed for optimal sound control.

Maintaining control of the noise reflections in a sanctuary brings numerous benefits to a place of worship. The congregation experiences clear delivery of the spoken word as well as quality acoustics of the musical presentation, leaving attendees with a positive impression and resulting in a loyal and content congregation.

About the Author: Mark Rustad is President of NetWell Noise Control, based in Minneapolis, MN. Founded in 1991, NetWell is a leading supplier of acoustic products, sound reduction treatments, and online acoustical consulting services. NetWell’s sound management skills are packaged into the industry’s premier website. Discover first hand why so much of NetWell’s business stems from the referrals and repeat orders they receive from satisfied clients around the world.

Reducing Crowd Noise in a Restaurant

A great restaurant provides an escape where guests can relax and savor their favorite meals while socializing with loved ones. Customers repeatedly patronize restaurants which offer consistently excellent service, quality cuisine and a pleasant atmosphere. The presence of numerous dining establishments makes the restaurant industry extremely competitive, so restaurants must provide a consistently satisfying dining experience in order to develop and retain a loyal customer base. Not only do restaurant patrons demand great tasting food and friendly service, they also seek enjoyable ambience and the ability to intimately converse with other members of their party. A high noise level in a restaurant is enough to drive business elsewhere, making it imperative for restaurant owners to take measures to minimize unwanted sound throughout their dining areas. Fortunately, many easily implemented sound reduction options are available to restaurant owners who want to improve ambience and contribute to the long term success of their businesses.

Excessive noise in restaurants stems from a vicious cycle wherein a jumble of conversations generate reverberations, causing guests to speak louder in order to be heard over the noise. Perpetuating the heightened noise level, restaurants typically require a lot of hard surfaces such as tables, floors and countertops to facilitate cleaning, with the result being an abundance of highly reflective surfaces that intensify sound reverberations throughout the establishment. The goal in restaurant noise control is reducing the background noise level by reducing the reverberation time, thus providing patrons with a pleasant environment where they can hear and be heard.

Reverberations can be held to a minimum through the installation of soundproofing products designed for restaurant walls, ceilings, or both. Soundproofing solutions will not bring dead silence to a room full of talking guests; rather they will absorb excess sound and reduce the overall decibel level such that patrons can enjoy the atmosphere and socialize in normal conversational tones.

Soundproofing panels and tiles designed to be wall mounted for absorption of excess reverberations are widely available and can be custom fitted for use in specific areas. Many are available in a range of colors to coordinate with restaurant furnishings and align with corporate color schemes. However, wall panels are often not an option as they may interfere with the décor that restaurants integrate into their persona. Therefore, ceiling soundproofing tiles or clouds may be used instead of (or in conjunction with) wall panels for increased reverberation control. Some ceiling tiles are designed to be placed in an existing grid based ceiling structure, which are effective but not always desired by restaurants whose design scheme would be affected. Thus ceiling clouds, or decorative suspended sound panels that “float” from the ceiling in even, aesthetically pleasing rows offer a popular solution for restaurants. For areas with large windows, sound absorbing blinds may be installed to capture sound and control reverberations from windows.

Anyone wishing to implement a restaurant sound reduction project is advised to consult a reputable soundproofing company to ensure that all variables are considered and that an effective solution is instated. Volume control is an issue that restaurant owners must address to maximize the comfort and satisfaction of their guests and build a loyal repeat customer base that will contribute to the restaurant’s long term success.

About the Author: Mark Rustad is President of NetWell Noise Control, based in Minneapolis, MN. Founded in 1991, NetWell is a leading supplier of acoustic products, sound reduction treatments, and online acoustical consulting services. NetWell’s sound management skills are packaged into the industry’s premier website. Discover first hand why so much of NetWell’s business stems from the referrals and repeat orders they receive from satisfied clients around the world.