ACOUSTIC WALL PANELS
Acoustic wall panels are used primarily for controlling sound in a space in order to comprehend what is being communicated, whether speech, audio reproduction, or live performance. This could be a factory where safety paging needs to be heard, a call center where cross talk between phone operators is an issue, or a recording studio where a predictable outcome is necessary so that playback is consistent across other audio systems. One of the biggest misconceptions of acoustic absorption materials is that they will block sound. Absorption materials are only used to tone down a space by treating the hard reflective surfaces thereby reducing reverberation; they will not stop sound energy from passing though them, this requires sound blocking products.
When an initial or direct sound is created, reflections occur as the sound bounces off nearby walls arriving a few moments after the direct sound, making speech intelligibility difficult. The amount of time it takes for these secondary reflections to dissipate is called the reverberation decay time. The further two parallel surfaces are apart, the longer the decay time. If you clap your hands in an empty room, you will hear the sound ricocheting off the walls, ceiling, and floor. This is called flutter echo and is caused by hard parallel surfaces in the room allowing the echo to sustain itself. Reducing reverberation time is a matter of increasing the amount of absorption material in the room through the use of acoustic absorption panels. The more panels you add, the more sound energy will be absorbed.
Acoustic wall panels work by absorbing the sound energy being reflected off of the hard parallel surfaces of the room through thermodynamic transfer. When sound energy strikes a fiberglass absorber it causes the minute fibers to vibrate converting the sound energy into heat energy. Open cell absorbers such as melamine or urethane foam absorb sound similarly through friction among its cell structures. Acoustic wood panels absorb sound by allowing it to pass through perforations within the panel causing the sound energy to be diffused and attenuated by an absorptive backing.
Acoustic panels are rated in NRC, (Noise Reduction Coefficient). For example, a 1” thick fiberglass acoustic panel has an NRC of .80 which means that it will absorb approximately 80% of the sound energy hitting it. Since NRC is an arithmetic average across the center octave bands, performance is dependent on frequency. Higher frequencies such as in the speech range of 300 to 3500 Hertz are short and easy to absorb, whereas lower frequencies are much longer and harder to absorb. The lower the frequency, the thicker the absorber needs to be. Another important specification is fire rating, particularly in commercial spaces where a lot of people congregate and work. In the United States the ASTM-84 test is the standard to verify smoke development and flame spread. In the case of a fabric wrapped fiberglass panel, the panel must be tested as a complete unit as the fabric and adhesive may alter the results of the core fiberglass tested alone.
Solving reverberation problems utilizing acoustic wall panels doesn’t necessarily have to be a complicated process. The basic steps are:
- Identify the problem frequency range
- Select the correct panels to solve the problem
- Estimate the coverage needed and available budget
- Install panels in the most strategic areas for maximum performance
Determining the amount of absorption needed in a space primarily depends on its intended use. While large venues such as gymnasiums should be kept somewhat “live” and may only need to have 25% coverage, applications such as home theaters may require 40% and recording studios 80% or more. Acoustic ceiling absorbers can be used in conjunction with acoustic wall panels where available wall space is limited such as rooms with large doors and windows, existing artwork, or visual aid materials that cannot be relocated. There are no absolute rules when it comes to how much coverage will do the job. Where maximum speech intelligibility is desired, acoustical engineers generally specify a reverberant time of less than 1 second. In larger rooms such as a classical music concert hall, long trailing reverberation is usually preferred to create a live ambiance exciting the room and audience.
With the advancement and affordability of high end audio video equipment, home theaters have become one of the most widely used applications for acoustic wall panels. A properly tuned room with average AV equipment will outperform a poorly tuned room with top of the line equipment, so always budget for acoustic treatment. The good thing about adding absorption panels to a room is that it’s hard to be too far off. If you start with 10% to 20% coverage and it isn’t enough, you can simply add more panels.