Not long ago I was doing an internet search on some specific acoustical problems, looking for soundproofing products or solutions (my neighbor runs noisy power tools), and I came across some YouTube videos on soundproofing. I mistakenly assumed the video lecturers had some expertise on the subject of soundproofing. Having worked in an acoustical consulting firm, I can assure you that most of these video lecturers were hardly experts.
In one video, the guy was showing examples of acoustical materials and was inaccurate in his naming of the types of products. This got me thinking that some review of basic acoustical principles and products may still be needed for people newer to the subject.
The Basics
Let’s start with some fundamental textbook terminology. There are four primary areas of traditional architectural acoustics:
- Room acoustics or interior space acoustics (classical concert hall)
- Building envelope sound isolation and inter-space noise control
- Mechanical equipment noise control
- Electro-acoustics — now known as audio or sound systems
Of course, there are many other types of more modern acoustics outside of architectural applications, such as defense (threat warning systems). Sonar is used as a means of acoustic location and of measurement of the echo characteristics of “targets” in the water. Acoustic location in air was used before radar was developed. Environmental noise has several subtypes, including concert spillover and transportation noise. Over the past few decades, electronic architectural acoustics (to modify the sound of concert halls on demand) has advanced considerably.
Even more recent electro-acoustical applications include smart speakers (that take voice commands) and many other types of product development, including personal active noise cancellation and automotive applications. We do not work in the areas of sound isolation, mechanical noise control nor defense applications, and the fourth primary area of acoustics is audio or sound/public address systems, which our readers routinely practice. So in this article, we will focus on the topic of room acoustics.
A Quick History of Architectural Acoustics
Architectural acoustics — more specifically building interior or room acoustics — is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering. The first application of modern scientific methods in architectural acoustics was carried out in the late 1890s by Wallace Sabine in Harvard University’s Fogg Art Museum lecture room. He then applied his newfound knowledge to the design of Symphony Hall, Boston. Sabine found that the reverberation time is proportional to room dimensions and inversely proportional to the amount of absorption present.
Architectural acoustics typically concerns achieving good speech intelligibility in an auditorium, church or temple, enhancing the quality of music in a concert hall/theater or recording studio, or suppressing noise to make airports, railway stations, offices and homes more productive and pleasant places to work and live in. Architectural acoustic design was usually done by acoustic consultants, but some P.A./sound system designers have also become skilled in how room acoustics interact with musical instruments on stage and P.A. loudspeakers in an auditorium, church or theater. This room and array/system interaction is critical to sound quality in large venues, so that will be a focus of this basic article on venue acoustics.
Architectural Acoustics Treatment Materials
John Eargle, former VP of JBL Pro, explained “There is little that we can do after the wall has been built to improve isolation (reduce transmission) between adjacent rooms, since those characteristics are inherent in the design and construction of the wall. However, what we can do is increase absorption at the surface and reduce reflections coming back into the originating room. This can take the form of externally applied damping materials, such as fiberglass battens or multiple folds of heavy drapery.”
The reflection of sound from a wall normally involves some degree of scattering. In Fig. 1-A, we see what happens when sound of a fairly short wavelength strikes an absorptive surface at an oblique angle. Most of the sound is absorbed, but some reflects at an angle equal to the angle of incidence. In Fig. 1-B we see what happens when the wall surface has very little absorption; most of the reflected sound is concentrated at the complementary angle.
We also know that sound striking irregular surfaces tends to scatter to a large degree. When the surface has been mathematically designed to maximize this effect, as in Fig. 1-C, the sound is essentially reradiated in all directions in the plane of reflection. The specific diffusing surface illustrated here is the “quadratic residue diffuser” (Schroeder, 1984; Dr. D’Antonio, 1984).
For more graphics and expansive explanation on this topic, originally written by the late, great John Eargle, see the March 2020 “Tech Feature“ and April 2020 “Tech Feature“ in FRONT of HOUSE. Next month, we’ll dig a bit deeper into room and array interaction and look at how reverberation time should be optimized and the longest echoes controlled (to improve perceived sound quality).
Acoustic and Sound Design for Modern Churches and Music Venues
Careful coordination of the design and orientation of loudspeaker arrays with asymmetrical vertical polar patterns — with sufficient direct sound coverage of the seating area (see Fig. 2) and selective treatment of the walls the arrays are aimed toward (at the optimum elevation to control the longest echoes) — allow the design goals described below to be achieved with minimum acoustic treatment (lower-cost solution), thereby improving acoustics for music performance, worship speech and congregational singing.
Over the past three decades of working as an acoustical sound consultant and loudspeaker designer, mostly in the contemporary worship market, I frequently have taken calls from church leadership, asking about acoustics and loudspeakers. They often ask if they need to do something about modifying the acoustics in their worship space. Like a doctor working to find the cause of a patent’s symptoms, I feel compelled to also respond with a series of questions, since I can’t see or hear their worship space first-hand over the phone. These include:
Were they told new line-arrays could eliminate the need for good acoustic design?
Do they turn the sound up too loud to overcome noise from an adjacent space?
Do they have to turn the sound up to overcome noise from the HVAC system?
Have they recently changed their worship style and introduced drums?
Was acoustics a key design component of their worship space?
Are they getting complaints about lack of sound clarity?
Have any new personnel just become involved in worship, such as a new
worship leader, drummer or sound tech?
Are they hearing excessive echoes or reverberation?
Have they upgraded their sound system recently?
What kind of loudspeaker arrays are they using?
Do they have curved walls or dome ceiling?
Have they done any acoustic treatment?
For good acoustics to be achieved, churches and music venues need:
A qualified acoustic and sound systems consultant, as part of the
architectural design team, at the beginning of the design process.
Reasonable freedom from excessively long echoes, to provide high-levels of speech intelligibility and impactful/tight music (by having enough acoustic absorption, especially opposite the loudspeaker arrays). As shown in Fig. 2.
Reasonable freedom from excessive reverberation time and level (known as a positive direct-to-reverberant ratio).
Reverberation time vs. frequency appropriate to the program material;
overtreating a worship space like a cinema is not the answer.
Sufficient acoustic diffusion to support worship singing (or acoustic music).
Artificial/electronic reverberation when needed to enhance music (only).
Reasonable isolation from adjacent spaces and outside noise.
Reasonably quiet HVAC, electrical and plumbing systems.
Proper shape or treatment of wall and ceiling surfaces (avoid dome ceiling and concave walls). See Fig. 2.
Control of the electronic sound level on the stage.
Control of footfall noise – especially in aisles.
David K. Kennedy operates David Kennedy Associates, consulting on the design of architectural acoustics and live-sound systems, along with contract applications engineering and market research for loudspeaker manufacturers. He has designed hundreds of auditorium sound systems. Visit his website at immersive-pa.com.
