Acoustical Design

What does it mean to design the acoustics of a room? At first glance, it may seem similar to decorating a room. While putting down carpet and hanging drapes will affect a room’s acoustics, there is much more involved in acoustics. For starters, the design of a room’s acoustics begins well before the room is built. The acoustics is greatly influenced by the essentials of the room’s architectural design. The room’s volume, geometry, and dimensions all play important roles. Moreover, the structural design of the floor, ceiling, and walls is important. For example, one type of wall design (studs and gypsum board) may absorb bass frequencies while another (masonry) does not. The room’s design will also greatly influence how quiet the room will be even if it is noisy outside.

Beyond design criteria, the quality of the physical construction itself is vital. For example, even if it is well designed, a poorly constructed wall could let sound penetrate into the room. Skilled carpenters and careful interim inspection are just as important as well-conceived blueprints. Following structural construction, acoustics is further affected by the way in which the interior surface areas are treated. Different types of absorbers, reflectors, and diffusers, and their locations in the room will determine the “sound” of the room. Acoustics is also affected by the type of furnishings in the room, and even by the number of people in the room.

Clearly, in many cases, new construction is not possible, so an existing room is used. Room treatment and furnishings are thus the only tools available and depending on the initial room conditions, the ultimate performance of the room may be compromised. For example, an existing room may have inadequate isolation from outside noise, so even if the treatment is successful, the room may be plagued by noise from outside. It is also worth noting that any acoustical design is limited by the space that is available, and the budget. For example, a bass trap might be the best remedy for a particular low-frequency resonance problem, but the room might be too small to permit its installation. Likewise, sound isolation is always desirable in acoustically sensitive spaces, but it is also the most costly aspect of most projects.

It is also important to remember that different types of rooms will demand very different acoustical designs. Some rooms (such as recording studios) are used for sound production while others (such as concert halls and home theaters) are used for sound reproduction. Other rooms (such as classrooms, auditoriums, sports arenas, places of worship, hotels, airports, and restaurants) have their own unique acoustical requirements. Adding to the complexity is the fact that in some spaces the intelligibility of spoken words is the most important requirement, while in others the enjoyment of music is more important. Some rooms must accommodate both. In any case, the acoustical design of a room must be tailored to fit its specific use.

Some acoustics projects focus exclusively on noise control. For example, a room’s acoustic performance may be compromised by an air-conditioning system in the building that introduces low- frequency vibrations, as well as noise at the supply vents. Solutions to the problem could be placed at the air conditioner, along the ducts, and at the vents. For example, to reduce vibrations, the air conditioner could be placed on resilient mounts, and noise could be reduced by placing silencers in the ducts and by using large-opening vents. The vibration problem is an example of structureborne noise, and the duct noise is an example of airborne noise. A complete acoustical design studies potential problems such as these and takes steps to minimize or eliminate them.