Room Acoustic Testing and Analysis
Room Acoustic Testing and Analysis helps us to understand the quality and qualities of sound within a room. “Room Acoustics” pertains to the propagation and quality of sound within a room. Special purpose rooms in homes (such as media rooms), offices (including meeting and conference rooms), classrooms, auditoriums and theaters require special consideration. Sonic-Shield helps clients achieve optimal room acoustics by performing a range of acoustical tests designed to insure that the room is “purpose optimized” for speech and/or music. That is, the acoustics in certain rooms, like classrooms or lecture halls should be optimized to convey speech; rooms such as concert halls, should be designed to convey music; rooms such as libraries or health care treatment rooms should be designed for silence. The acoustics in multi-purpose rooms, such as gymnasiums, pose special challenges, since the rooms must be adaptable for speech, music and sporting events.
The key to creating the correct acoustic ambiance is to create an acoustical design before the room is built. However, this is not always possible, and treatments must be implemented after the room is built. Room acoustic testing and analysis can properly diagnose and solve room acoustic problems.
To ensure good room acoustics, it is first necessary to block unwanted or extraneous noise from entering the room. This includes sound transmission through the walls, floors, windows and doors, as well as sound flanking paths through the ceiling, seams, and electrical outlets. Other sources of extraneous noise include air conditioning vents and fans. Using a sound level meter (SLM), we measure the overall or average sound levels within the room. We then scan the sound level meter in close proximity to features on the outside walls to identify potential acoustic leaks. For more challenging problems, we use an acoustic camera, which enables us to rapidly “see” the sound leaks in real time. Once the unwanted or extraneous noise sources are identified and addressed, it is possible to perform tests to improve the room acoustics.
The key to obtaining good room acoustics is to optimize acoustical reverberation time within the room. The reverberation time relates to the time that a sound wave will extinguish to an unintelligible level (usually 60 dB less than the incident sound level) within a room, and is often referred to as RT60. If a room has too little reverberation, it will sound “dead” and sound will not carry or propagate. If a room has too much reverberation, the reflected sound will continue to interfere with the incident sound. Speech will be unintelligible and music will sound “muddy”. The optimum reverberation time for speech is about 1.0 to 1.5 seconds, and for music, it is about 1.5 to 2.0 seconds. Reverberation time over two seconds is undesirable for either speech or music, and should be addressed with sound attenuation materials.
Sonic-Shield performs reverberation tests by creating a loud acoustic impulse, using a hand clap, balloon pop, or loudspeaker, and then we measure the acoustic decay at several locations within the room. An example RT60 measurement, using the mobile application, iAudioTools (JJ Bunn) is shown in Figure 1. This is a test of a general purpose facility where sound from the PA system was unintelligible due to excessive reverberation. Although the RT60 is good in many of the high frequencies, it is unacceptably high in the 63-250 Hz bands. For this room, we would recommend the optimum depth and placement of acoustic absorption materials for these frequency bands to eliminate acoustic reflections. Without room acoustic testing and analysis, we could not make this recommendation.
Another aspect of room acoustics concerns the apparent amplification of bass frequencies, particularly for theaters and auditoriums. This is due to the loudspeaker system exciting natural acoustic modes within the room. At higher frequencies, the acoustic modes are highly packed and dense, and thus these modes are not sustainable. At lower frequencies, however, the acoustic modes are distinct and acoustic standing waves can be created. If acoustic standing waves are perceived, we use a sound level meter to identify variations in acoustic amplitude, throughout the room which will indicate acoustic nodes and anti-node locations. We then recommend the use of bass traps, tuned to the proper frequencies and placed at optimum locations to remove these standing waves. Once again, room acoustic testing and analysis is the enabling factor to help a room reach its optimal acoustic performance.
Sonic-Shield has an engineering staff with advanced technical capabilities and instrumentation that can assist individuals and building owners in room acoustic testing and analysis. Our room acoustic testing and analysis services can properly diagnose acoustic problems, leading to the ideal configuration and placement of sound attenuation materials.