Don’t Believe Everything That You Hear: Debunking Myths About Acoustics

Acoustics is subjective. Whenever I explain the concept of acoustics, I tend to share this: Sound is me cutting my lawn. Noise is my neighbour cutting his lawn. Music is my neighbour cutting my lawn. It’s not always about how loud something is, but how it affects us, sometimes consciously and often unconsciously.

5 Common Myths About Acoustics

While acoustical design can be artistic, it’s by no means art or even magic. Acoustics is firmly rooted in science. It is defined as the science that deals with the production, control, transmission, reception, and effects of sound. It is often a misunderstood field which can lead to investing in solutions that won’t create your desired acoustical environment.

In my 20 years as an acoustical engineer, I have heard just about everything. Here are some of the most common misconceptions:

1) Myth: Acoustic design is strictly about room finishes

Truth: Acoustics is much more than interior design and room finishes. A lot of acoustic design is hidden from view and if it’s done properly, most people don’t realize how much design has gone into a building. In my opinion, the best acoustical design delivers a seamless experience. It works architecturally, mechanically, and acoustically. It’s when acoustics is an integral part of the design and construction process, that the best buildings are built no matter if it is a concert hall or a hospital.

2) Myth: All rooms should be pin-drop quiet.

Truth: It depends on the room’s purpose. Some noise is actually desirable if you are trying to provide privacy such as in an open office environment so the sound of the HVAC system might be incorporated into the acoustical design of the space. But in a high-end concert hall, no noise is desirable. At times, full building or room isolation is implemented to mitigate noise from subways, streetcars, elevators, etc.

3) Myth: Acoustic design does not need to be considered early in the project.

Truth: The best noise control is no noise control. Why create an issue to solve if you can avoid the issue in the first place? Creating buffer spaces between noise making areas and noise sensitive spaces is much easier to do in the schematic design phase of a project. When an acoustician is brought into a project later in the process, the layout is effectively set. In the case of Pyatt Hall, a recital hall in Vancouver, BC, the design included an elevator shaft right next to the recital hall. Because this issue was identified at the outset, we were able to isolate the floor of the concert hall from the elevator shaft. Without early design intervention, it is much harder to solve noise issues and no one wants elevator noise to accompany a recital hall.

4) Myth: Acoustic properties are described in a single number.

Truth: There are countless acronyms for the various properties being measured. Often, acoustics is distilled into single number descriptors. This is done for simplicity sake but does not give the whole story. Sound is made up of different frequencies that a single number descriptor does not capture. It’s the parameters by frequency that an acoustical engineer needs to provide a complete design. The following are just a few of the numbers you might hear when discussing acoustics:

  • Sound Transmission Class (STC): The numerical value that represents the overall amount of sound a wall will reduce noise from 125 Hz to 4000 Hz.
  • Noise Reduction Coefficient (NRC): The average rating of how much sound an acoustic product can absorb from 250 Hz to 2000 Hz.
  • Reverberation Time (RT): The time it will take for energy to decay in a room.
  • Distinctness (D50): A ratio of the acoustic early energy, defined by the amount of energy measured within the first 50 milliseconds of the direct sound.
  • Clarity (C80): How clear individual sounds are heard.

5) Myth: Glass Fibre/Mineral Fibre Stops Sound

Truth: Mass stops sound. With acoustics, more mass typically means better noise control. This includes impact noise from footfalls, or from airborne sound. It’s critical to understand that absorbing sound and isolating or blocking sound are not the same thing. Sound absorption is about affecting the interior room acoustics. Sound isolation is about stopping or blocking sound from transmitting to an adjacent space. When you see glass fibre panels on the walls of a recording studio, it’s not the glass fibre that is blocking the sound. It’s mass inside the wall that is blocking the sound from travelling through. The glass fibre breaks up the resonance and controlling the sound within the room.

Acoustic Design is Not ‘One Size Fits All’

Acoustics is not simple and one design does not fit all. An amplified rock band will sound terrible in a concert hall and a choir will sound terrible a movie theatre. Why? Usage is the key. Every project will have its own unique acoustical challenges based on the space and its purpose.

Some projects with minor acoustical issues might be resolved with some acoustical treatments but the vast majority require work that isn’t visible to the eye and is best incorporated in the initial design process to avoid the mess, stress and cost of tearing down and starting over.

Addressing acoustical details earlier in the design process saves costs in the long-term. My hope is that by debunking some common myths about acoustics, we can bring a greater understanding and appreciation of what it takes to have good acoustics. When it comes to acoustics, there really is more than meets the eye—so don’t believe everything you hear!