The single most important aspect regarding sound in a church, synagogue, mosque, or chapel is intelligibility. In other words, making sure that all of those that are there to hear the message are able to understand what is being said.
One of the biggest misconceptions of all is: purchasing a new sound system will solve the problem. This in fact is rarely the case and only after many thousands of dollars are spent do folks come to the realization that unless the acoustics in the room are managed, a louder PA system will only cause the problem to get worse.
For the most part, large assembly rooms are built with hard surfaces. Windows adorn the walls while gypsum board or concrete surfaces abound. These hard surfaces allow sound to reflect off of them creating a dense reverberant field and decay times that can exceed 5 seconds. 500 years ago, this flattered certain types of music such as Gregorian chant and the pipe organ, but did little to enhance the spoken voice. Back then, only the educated understood Latin while the common person was simply awed by the spectacle so verbal communication was not important.
When you increase the sound level in a highly reverberant space, the room quickly becomes overexcited and exceeds the room’s ability to naturally dissipate the energy. Echo on top of echo elongates the reverb and the sound becomes an annoying nightmare.
Today, the House of Worship has changed. It is a place where ideas and guidance is communicated. And with the advent of music performance, the acoustics in the room have taken on an even more important role. It is therefore critical that the reverberant field be reduced so that communicating to the patrons can be effectively achieved. This is known as improving the intelligibility of the room. Ideally, one must reduce the reverb decay time to below 1 second. In other words, if you clap your hands once loudly, the sound should dissipate very quickly.
Image 1 shows a typical assembly hall where the initial direct sound (green) competes with powerful first order reflections and the reverberant field. The listener must at once try to understand what is being said while trying to ignore or ‘turn off’ the other competing sounds in the room.
Image 2 looks closer at the phenomena. The direct sound from the loudspeaker arrives at a given amplitude (sound pressure level) while the first order reflection arrives slightly afterwards as it must travel a further distance. When the hard reflective surface is nearby, the reflection is louder.
Image 3 shows the resulting effect of the acoustic panel as it absorbs the energy, greatly reducing the amplitude of the offending reflections. Less noise interferes with the message and intelligibility is vastly improved.
This graph shows the frequency range of a typical male voice. And as evident, most of the energy contained in the human voice ranges between 300Hz and 2000Hz. Because we communicate in this range, it makes sense that the treatment we plan to apply should, for obvious reasons, be effective in this range. In other words, because we are most concerned about controlling the sound in the vocal range, the choice of acoustic panel used to absorb the energy sound should be one that performs well throughout the voice range.
The second superimposes the frequency and amplitude of voice range relative to the absorptive performance of a Broadway 2-inch thick acoustic panel. The amount of absorption relative to the voice will be dependent on the number of panels used in the room. But as evident, the Broadway panel is ideally suited to absorb voice energy.
There is certainly truth to the statement that longer reverberant decay times will enhance music. But this really only applies to classical instruments that employ the room as part of their sound. For instance ‘chamber music’ sounds best in a reverberant space. But given the fact that so many of today’s music performances are ‘contemporary’—controlling drums, bass and electric guitars needs to be addressed differently. In these instances, increasing the absorption by adding a greater number of acoustic panels (more surface coverage) and using thicker ones will help absorb low frequencies.
This graph shows the difference between a 2-inch thick and a 3-inch thick Broadway panel. Notice that the 3-inch panel continues to absorb energy down to 125Hz. It is important to note that the density of the panel plays a critical role in how the panel will perform. One can further increase the low frequency absorption by introducing an air cavity behind the panel. Special primacoustic off-set impalers are used for this very purpose. Thicker panels tend to be applied to the receive end of the room or in the longer axis while panels design to work in the voice range tend to be distributed along the walls.
If longer reverberation times are needed for a choral performance, this can easily be re-introduced into the room by using artificial means such as a digital reverb. This eliminates the need for ‘movable panels’ which reduces the cost of the installation.
High and mid frequencies tend to beam like a flashlight. As such, any large flat wall surface will reflect energy like a mirror. By drawing vectors from the loudspeakers to these hard surfaces to the seating positions, you can predict where the most obvious problems will be. Strategically distributing acoustic panels on the available wall surfaces will help attenuate room reflections. For instance; in a long narrow room, most acousticians tend to focus treatment on the side walls and the rear ‘receive-end’ of the room so that powerful first order reflections are eliminated and front to back flutter echo is reduced. In wider rooms than fan out, a greater percentage of the acoustic treatment tends to be applied on the balconies where sound is in direct line of fire from the speaker system.
Some ceilings are particularly problematic: Rooms that have vaulted ceilings tend to focus the energy towards the middle of the room as sound echoes off the angles. Domes and ‘tunnels' are even more problematic. In these types of spaces, treating the ceiling can be very beneficial.
As a general rule of thumb, 15% to 30% wall coverage will provide adequate absorption for a large assembly hall. The greater the surface coverage you treat with acoustic panels, the shorter the decay time will be. And as can surmise, the more treatment you put up, the shorter the reverb decay. A shorter decay of less than 1 second will help tremendously at improving intelligibility.
When treating large surface areas, using multiple Broadway panels together in a ‘modular fashion' can create a very attractive and uniform appearance while providing significant cost advantage over ordering custom made oversized panels. Primacoustic Broadband panels can be shipped on a regular pallet or via UPS therefore eliminating the high cost of shipping using a flat bed truck. And during installation, you do not need a crew of five people or a crane to raise and hold the panel. One or two people can easily do the installation.
To get you started, we have created a series of tables that look at floor space and wall height and will estimate the panel requirements for either light or normal treatment.