How to Create Great Auditorium Acoustics

When thinking about auditorium acoustics, acoustic treatment is a key component of a properly functioning space.

An auditorium is a large, enclosed public event space or hall used for entertainment, community gatherings, presentations, and performing arts. A stage is typically situated at one end of the space, with the audience seated throughout the remainder, at floor-level and often in balconies arranged in tiers at the back (and sometimes sides) of the space.

Auditorium Acoustics and Architectural Design

Auditoriums are constructed to house large numbers of people, so proper acoustics are critical to their function. Regardless of where a person is seated, they expect to clearly hear the performance or speaker. However, poorly designed or acoustically untreated spaces result in unpleasantly long reverb or echoes that interfere with speech intelligibility and musical clarity.

Before the advent of amplified equipment, auditorium design was based on the concept of pushing sound from the stage out into the audience. Walls and other reflective surfaces were strategically placed to allow sound to be heard clearly, even in the most distant seat from the stage or stage balconies.

Some modern auditoriums incorporate loudspeakers throughout the facility. Movie theaters are the best example as they can use dozens of loudspeakers embedded in the walls and ceiling. Most auxiliary speakers are used for sound effects and “surround sound” while stage-mounted speakers are used primarily for dialog and music. This presents different acoustical challenges compared to an older auditorium.

Reverberation and Echo in Auditoriums

In any enclosed space including auditoriums, there are at least six hard, reflective surfaces. The floor is generally left untreated, as carpet, seats, and people absorb a tremendous amount of sound energy. However, walls and the ceiling are often flat, reflective drywall surfaces. When these surfaces are parallel to each other, they can, if you’ll pardon the expression, “amplify” sound problems in the space.

Sound striking hard surfaces simply rebounds into the auditorium, causing longer reverberation times and flutter echo. This is distracting to both the listener and performer/presenter. Improving speech intelligibility and musical clarity is therefore imperative because without acoustical treatment, audiences will have a poor listening experience.

Speech intelligibility is a necessary part of a functional auditorium. To hear properly, the reverberation time (RT60) should be approximately 1.0 to 1.5 seconds. The goal for ideal acoustics in an auditorium is to have the reverberation time equal throughout the venue./p>

Because a large open space is often far too reverberant, in most cases incorporating acoustical concepts and treatment into auditorium design is a must. Acoustically treating an auditorium after it has been constructed can be a tricky thing to do, so the earlier that treatment is considered, the better.

Achieving Great Acoustics in Auditoriums

Achieving great auditorium acoustics is difficult because — in layman’s terms — it requires a happy medium between the room sounding “alive” and sounding “dead.” Fortunately, at Acoustical Solutions, we are experts at perfecting auditorium acoustics.

We understand that with live performances (bands, orchestras, plays, speeches, etc.), words and notes need to ring clearly throughout the space. This increases sound quality and allows for the entire audience to better enjoy the performance. The problem is that there is a fine line between a pleasant ring and an echoic mess. If sound rings too much it quickly — and quite dramatically — reduces sound quality and the audience’s ability to hear clearly. Some frequencies may be effectively amplified by an untreated room!

The converse is true as well — too much absorption can result in an unnaturally anechoic, or “dead” room. While an RT60 time of less than one second may be desirable for critical listening environments like mixing or mastering studios, it is far too short for an auditorium.

Acoustic Treatment for Auditoriums

So, what is the best way to achieve great acoustics in an auditorium? The answer is to use a combination of absorption and diffusion, strategically placed for optimal effect.

Absorption reduces the amount of reverberation in the room so there is less echo and reflected noise. Absorptive material is often added at important reflection points on the walls and ceiling for optimal treatment of the space.

Diffusion disperses the sound waves that aren’t absorbed, which reduces slap-back echo (reverberation between two parallel walls) and allows for the leftover sound to reverberate without being disruptive. Unfortunately, diffusers don’t absorb any of the noise, so the sound remains in the room.

Please read our articles on Sound Absorption and Sound Diffusion for a deeper understanding of these topics. You might also want to read our post about reverb.

Acoustic Treatment Approaches for Auditoriums

To reduce the echo between walls, the most common approach is to add sound absorbing acoustical panels. Most sound panels consist of a fluffy, porous material that traps sound. Any area with large amounts of flat, hard surfaces creating a reflective space should receive treatment, especially when surfaces are parallel to each other.

Apply acoustic material to stage areas, side walls, back walls, ceilings, and balcony faces. This prevents sound from reflecting into the room by absorbing its energy.

For spaces that only require music clarity, they may use a combination of absorptive panels in conjunction with sound diffusers. Sound Diffusers disperse and scatter the sound to reduce standing waves while maintaining sound clarity.

If the stage is higher or larger than the rest of the room, more material may be necessary to create a uniform reverberation time. Spreading acoustical materials throughout the space reduces echo and prevents reflections that interfere with the sound reinforcement, performances, and presentations.

Adding acoustic panels to the back wall absorbs sound after it has passed the audience once. This reduces the amount of secondary waves (waves that have bounced off of an object) the audience hears. If there is no absorptive material on the back wall, music and sound will simply reflect into the room. This distracts from the audience experience.

If the auditorium does not have carpet and padded chairs, there will most likely be issues with floor-to-ceiling reflections. Address these concerns by suspending ceiling clouds. These are more effective than wall panels since the back side of the cloud will absorb sound as well. As an alternative to ceiling clouds, acoustical foam may be glued directly to the ceiling surface. Finally, sound baffles may be used to handle wall-to-wall echo near the ceiling.

Acoustic Treatment Aesthetics in Auditoriums

But what about appearance? Can acoustic treatment blend with the décor of the auditorium? Of course it can! Acoustic wall panels, often the preferred choice for acoustical treatment, are available in a wide variety of core materials and finishes.

The most popular are fabric-wrapped acoustic panels. With so many color and fabric pattern choices available, you are sure to find something to complement the existing décor. Plus, with a range of sizes, they offer the most versatility when designing the auditorium’s acoustic treatment. There are even options for panels with printed artwork.

If a seamless look is desired, a fabric stretch panel system may be professionally installed. A fabric track system provides the flexibility to use different materials behind the fabric, to either increase or decrease absorption.

Conclusion

While sometimes tricky, creating great auditorium acoustics isn’t impossible. Just remember that too much absorption will eliminate the ring which is necessary for performance halls. Next, control the leftover sound with diffusers and your auditorium will be sounding great in no time!

Case Studies

Woodberry Forest School

A perfect example of acoustic treatment in an auditorium is at Virginia’s Woodberry Forest School. We treated the back wall of the school’s auditorium with absorptive wall panels. To further correct the sound in this auditorium, we applied diffusion to the side walls.

Williamsburg Players

Acoustical Solutions treated the side and back walls with acoustic panels to even the reverb in the room. Now all seats can hear the Williamsburg Players‘ performance!

Richard Bland College

We mitigated excess reverb in a room at Richard Bland College with sound control issues caused by painted concrete block walls.

Patricia Theatre

Acoustical Solutions used sound absorbing panels to complement the acoustics of the Patricia Theatre in British Columbia as it was upgraded to a new digital projection system.