Introduction to

Acoustics

Acoustics By Definition

Acoustics is total effect of sound, especially as produced in an enclosed space. It is the scientific study of the generation, transmission and reception of sound.

simple definition: the total effect of sound in a room

In terms of church audio – acoustics determine the intelligibility of the spoken and sung word in the worship environment. Inappropriate acoustics mask the sermon text and render the music lifeless. Appropriate acoustic qualities in a sanctuary enliven the music and improve retention of the sermon.

 

What They Do: Architectural Acousticians
An architectural acoustician is responsible for making sure that sound waves travel effectively from their source to the listener's ear. Every time you can hear a speaker clearly in an auditorium or music in a theater or even a teacher in a classroom, you can thank an acoustician for making that clear sound possible.

Architectural acousticians help design performance spaces in all kinds of facilities for a wide spectrum of applications – from live music to worship to education. They consult with architects to plan the shape, size, dimensions, seating, and surfaces of a space so that sound is reflected and absorbed properly. They create quiet, comfortable interior spaces by minimizing noise from outside and from heating and air conditioning systems. And they can help to modify existing spaces with solutions for improving acoustical accuracy.

One of several sites with a national directory of acoustical engineers is www.acoustics.org.

Sound Waves

"Knowing the enemy is the first step toward sound success. The less the room is excited, the less the room will have to be controlled."

Sound waves propagate, or spread out, in a spherical (globe-like) pattern. As they move further from the source, they dissipate (drop in level) at a relatively constant rate (6dB per doubling of distance) until they encounter a reflective surface, such as a wall, floor, or ceiling. Depending on the boundary’s properties, the sound waves will, contingent on frequency and angle, bounce back into the room linearly, diffuse across the plane, or pass through the surface material. If the sound wave is a low frequency, there is a strong possibility the wavefront will excite the boundary and create unwanted vibrations in the room. If two boundaries are acoustically parallel to one another, they will reinforce certain frequencies, with a resulting flutter echo issue or standing wave.

Source: "Good Sound in Bad Rooms: How Acoustics Work and What You Can Do About It". www.worshiptech.com

Finding a Balance

So many advances have been made in the area of church sound, that the bar for acoustical standards has been raised, along with the expectations of your church’s worshippers. People will not stay if they cannot hear.

Appropriate acoustics are those transmission and reception qualities in a room that enhance the musical performance and improve the ability of the listener to understand speech. There are no "good" or "bad" acoustics, only "appropriate" or "inappropriate" acoustics for the intended use.

In a worship environment, the sermon requires short reverb time and the absence of discreet delays in order to deliver intelligible speech. However, music benefits from longer reverb time and constructive delay. Worship acoustics, then, must find a balance between the "dry" qualities desirable for speech and the "wet" attributes that benefit music since both are important to the service.

Making Choices

One way to develop an appropriate balance is to weigh the content of music versus speech in a given environment. If more than one facility is available for differing worship services, selecting the "best" room will be beneficial.

For contemporary services, the use of bands and praise teams integrates well with the spoken word’s need for shorter reverb times. Drums and pop vocals work well in "tight" rooms, where the room signature is short and unobtrusive. This means that the contemporary service should be held in a "drier" room for the benefit of both the sermon and the music. On the other hand, a traditional service, with its dependence on choir and organ, should be held in a "wetter" environment with the knowledge that the advantage the room holds for music is detrimental to the understanding of the sermon.

Isolation and Absorption

Interaural transmission is the undesired flow of sound from one occupied space to another. Isolation prevents sound from escaping its intended destination. By using dense door materials, tight seals, and double pane windows, transmission can be kept in check. Additionally, minimizing wall and ceiling penetrations will improve isolation. If possible, a loud sourced room, such as the youth facility, should be separated from adjacent meeting rooms by hallways and unused closets and storage areas.

Absorption and diffusion are acoustic control measures used within a room. They do not prevent Interaural transmission –but they are the means to improving clarity within the room.

Absorption uses a combination of dead air and mass to prevent the reflection of acoustic energy back into the occupied space. From mineral fiber to acoustic foam, different types of absorbers stop detrimental reflections that mask intelligibility.

If absorption is akin to covering an acoustic mirror with a blanket, diffusion is breaking that mirror into small segments to prevent a fully reflected image.

Diffusion creates multiple small reflections from one or two large ones. The result is more pleasing to the ear, with an increased sense of "space" and "depth" as compared to a harsh two-dimensional slapback reflection. In a gym, where the slap and flutter from large parallel surfaces creates unpleasant sound, diffusion, in the form of panels and clouds, can rearrange the reflected energy into a usable soundscape.

With a careful study of the desired room signature, cost-effective changes can be made to improve the overall sound in any room, whether the need is for isolation, absorption or diffusion.