The Importance of Acoustics in an Auditorium
- Speech, vocal performances and music should all sound clear rather than distorted or echoey.
- Sounds should be loud enough for the audience to hear, including those sitting at the very back of the auditorium.
- The right sounds should be isolated, meaning performances and speeches ring clearly over other sounds from the room.
Factors That Affect Auditorium Acoustics
1. Size of the Auditorium
In any room, size has an important influence on acoustics. Size includes the length, width and height of the room. Larger and smaller auditoriums come with their own acoustical advantages.
For instance, a small room generally won’t allow music to ring out at richly as it will in a large room. When it comes to volume, you’ll have an easier time getting the whole audience to hear clearly in a small room, while a larger auditorium can pose some volume challenges. This is why you need the other aspects of a large room to contribute to good acoustics and why you need a quality sound system.
Another concern related to auditorium size is reverberation, which we’ll discuss more below. Larger rooms can cause longer reverberation times, which can become excessive. Smaller rooms can cause shorter reverberation times that may seem too short, making the room feel acoustically “dead.”
2. Shape of the Room
Like size, the shape of your auditorium will play an important role in determining the acoustics. This is why it’s feasible to have a computer program that can reconstruct a room’s geometry based solely on the input of one sound emission. Auditoriums come in many different shapes, though you won’t see some shapes as often because they’ve proven to be poor for acoustics.
Generally, you want to avoid square rooms or narrow, rectangular rooms since the parallel walls can cause sound waves to bounce back and forth continuously — creating undesirable reverberations that muddy the overall sound clarity. This is why many auditoriums have more of a fan shape. Some auditoriums also feature curved walls, which help diffuse sound. In addition to the general shape of a room, other architectural features like the ceiling pitch and structures in the room will affect the way sound waves behave in the space.
Some architects specialize in building spaces with the right shape to achieve the appropriate acoustics for performances or lectures. If your auditorium is already built, you may not be able to alter the shape, but you can find other ways to improve your acoustics.
3. Materials in the Room
A common problem in auditoriums is reverberation, which occurs when sound waves bounce off surfaces and congregate. If you’ve ever attended a lecture where the speaker’s voice echoed and made it difficult to understand what they were saying, you’ve experienced the issue of excessive reverberation. Some level of reverberation is a good thing, especially when it comes to musical performances, since otherwise the room will feel acoustically dead.
In a general-purpose auditorium where you want speech to sound clear and music to sound rich and full, the ideal reverberation time — the time it takes a sound to die away — is around 1.5 seconds to 2.5 seconds.
For most auditoriums, the reverberation time will be too long unless there are sound-absorbing materials throughout the room. This includes acoustic panels, upholstered chairs, curtains and other soft, porous surfaces. If your auditorium is full of surfaces that are hard and nonporous, like windows or wood floors, these materials will reflect sound waves and contribute to higher levels of reverberation.
4. Balconies and Orchestra Pits
If your auditorium includes an orchestra pit and any balconies, these features can affect the acoustics in the room. Balconies can be a helpful way to include more seating in a room without lengthening the room to the point where attendees in the back have trouble hearing. The shape and size of a balcony and the materials it includes all affect the way sound waves behave in the room.
Orchestra pits also affect the structure and acoustics of an auditorium. Installing soundproof curtains around an orchestra pit can help a conductor control the sound levels that emerge from the pit.
The inside of an orchestra pit also has acoustics to consider. You want musicians in the pit to be able to hear themselves and hear others clearly. In surveys regarding opera halls, most of the issues people cited with orchestra pits had to do with acoustics, so it is important to design orchestra pits strategically for the acoustics to be ideal.
5. Auditorium Use
Many auditoriums, especially those in schools and universities, are used for a variety of purposes. This presents a challenge acoustically since the ideal acoustics for speech are not the same as the ideal acoustics for music. This is because speech should have a shorter reverberation time than music. You can continue to make distinctions beyond speech and music. For example, the ideal acoustics for a cappella choral music are not the same as the ideal acoustics for rock music.
You may be dissatisfied with the acoustics of your auditorium because you’re using it primarily for speeches when that same auditorium would be excellent for a musical. This is part of what makes acoustic design a complicated subject, and it’s why acoustics experts approach every space as a unique project with its own challenges and solutions.
If your auditorium is primarily used for a certain type of event or performance, you should factor this into your acoustic design. If you want to create a space that offers good acoustics for a range of uses, an acoustic engineer can help you achieve that.
6. Doors and Buffer Zones
It’s also important to consider the spaces outside an auditorium and how they can affect acoustics within the auditorium. If there are other activities, conversations or footsteps outside that are audible inside the auditorium, this will interfere with the sounds you want the students or audience to hear.
Doors can be a point where outside noises are let in. Solid-core doors with higher sound transmission control (STC) ratings will do a much better job of blocking outside noises than hollow-core doors with lower STC ratings.
Some auditoriums use buffer zones to help prevent noise from getting into the auditorium. These are areas that lie between your auditorium and other rooms used for other purposes, such as classrooms, restrooms or dressing rooms. These areas, which can take the form of hallways or foyers, provide a blanket of space around your auditorium that should be relatively free of noise and activity during a performance.
7. Background Noises
Even if you have soundproof doors and buffer zones to keep out noise from the outside, that doesn’t mean the auditorium will sound completely silent when empty. All rooms have ongoing noises from HVAC equipment and even plumbing pipes running in the background. In most situations, we hear these as white noise, and it’s not much of a bother. These sorts of background noises may not pose a problem in an auditorium if they are very quiet. However, if the air conditioning comes on and is noisy, it will interfere with the quality of a performance on your stage and may make it harder to understand a speaker.
Fortunately, there are solutions you can employ to eliminate these problems. Duct liners and mufflers can help absorb sound from your HVAC system so it doesn’t bleed into your auditorium. You can also choose HVAC systems that are quieter than others. With the right design, you won’t have to sacrifice comfort, and you also won’t have to sacrifice sound quality in your auditorium.
How to Improve Auditorium Acoustics
1. Custom Acoustics Analysis
Blocking sound may involve creating buffer zones, installing more soundproof doors or even providing better insulation for the room. The idea is to eliminate noises from outside so the audience in the auditorium only hears the lecture or performance they came for.