What is meant by ‘good acoustics’? What makes some spaces carry sound so well, that a person doesn’t need to speak or sing very loudly to be heard way back?
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Rooms with good acoustics attenuate (reduce) any noise that isn’t from the desired source (usually a stage) including excessive echoes that the source sounds may generate.
This is accomplished through wall geometry, acoustic padding, and speaker placement.
Good acoustics is defined by what the room is being used for. But for performance venues then good acoustics means the sound is carried accurately and evenly to the audience.
Different materials will reflect or absorb different frequencies so a good combination is needed to balance out the sound to the desired quality.
Think about a pool full of water. When you splash, the waves move away from you, hit the walls, and bounce off.
Sound does the same thing, invisibly.
Waves (sound or water) will bounce differently, depending on the shape of the walls and the material they’re made of.
Good acoustics just means that the waves bounce in a way that helps hear, without causing overlap or choppy waves.
Coming from some background in Barbershop Quartet Singing, this term was thrown around a lot.
Generally I take it as meaning ‘tight reverb’. Voices are being bounced back and suddenly 4 voices sound more like a chorus. But you don’t want too much of this ‘echo’, you want a diminishing echo.
This is usually going to occur in a room with a high vaulted ceiling with some soft surfaces to dampen.
There is further magic that happens as sound waves bounce around and combine into overtones.
A little trick in guitar or vocal mix-down is to delay a signal slightly on L channel compared to R. This fattens the sound.
The delays created as you hear sound directly versus bouncing off a wall and coming back is a similar concept.
Overall, acoustics create a fatter sound out of thin air.
Imagine a flat wall in front of you. When you clap your hands the sound emits from your hands, reflects directly off the wall and you hear an immediate sharp echo after.
Now imagine a wall with lots of deep cracks, crevices and curves. When you clap your hands the sound comes out and bounces off the wall but this time the uneven wall causes the sound to reflect in a more random way. Some parts of the wall reflect the sound directly back like the flat wall but other parts bounce the sound around and it doesn’t make it back to your ears until a little bit later.
Good acoustics typically tries to minimise the direct echo and stretch it out over time, making it sound more pleasant.
Human perception of sound is a big factor in the acoustic performance of a space. You have to understand the way our brains integrate incoming sound information into a complex 3-dimensional sonic picture.
The most important thing to realize is that the straight line from the sound source (emitter) to the listener is the direct sound. The sound emitter actually radiates sound in all directions in deep bass and as you go higher up toward treble shifts toward a tight beam. This off axis sound bounces off every surface, but each time it reflects it loses some energy to absorption by the surface and the air itself.
The key here is that bounced sound that arrives very close in time to the direct sound is perceived by our hearing as being a part of the original sound. These are called early reflections by acoustic engineers and tend to reinforce the sound.
Late reflections that arrive just long enough after the original direct sound to be perceived as different from it are destructive. That is, they reduce our ability to make sense of the original sound.
Very late reflections fall into the category of reverberation. They arrive late enough that they don’t interfere with the direct sound and can be pleasant, giving the listener a sense of the spaciousness of the environment.
The secret to acoustic engineering is to both absorb and diffuse the destructive reflections that can make the sound confusing to the ear. Absorption reduces the energy of early reflections while diffusion scatters them, pushing them more into the category of reverberation.
There is a lot more to acoustic engineering than just this. Parallel walls tend to cause troublesome flutter echoes as sounds ping-pong back and forth between them. Absorption can reduce echoes and making the walls non-parallel or curved can eliminate them.
Acoustics are a combination of how a room absorbs, reflects, diffuses, resonates, and otherwise interacts with various sound sources, like musical instruments, voices, speakers, or other sources. Those traits alter how you perceive the total sound. In the case of sound recording, they alter the total sound picked up by the microphones used in that recording.
“Good acoustics” are when a room alters the sound in ways that are regarded as pleasing to the listener.
Good acoustics are subjective in nature, and can change depending on the desires of the performer and the listener. For example: a renowned classical concert hall sounds great when listening to a solo piano, orchestral music of various subgenres or even opera, but may sound boomy and muddy with a large sound system and a rock band. Another example from recording: drums recorded in a bedroom may sound boxy and cramped, but sound epic in a nice live room, or clean and groovy in a highly deadened room. Performers, recording engineers, concert venue designers and even audience members seek out different traits depending on their end goals.
That being said, there are commonalities between different acoustic spaces that make them objectively good or bad, from the standpoint of an acoustician.
Some traits that oftentimes create rooms with bad acoustics: Symmetrical rooms with mostly hard surfaces are highly resonant (or like to ring) at certain frequencies. Rooms that reflect many frequencies in ways that create what are known as “standing waves” or “modes” that will emphasize or cancel out certain frequencies, often result in bag listening experiences at different locations.
Traits that are typically regarded as good: Rooms that reflect sounds in many different ways (diffuse), rooms that reduce standing waves (absorbs low frequencies), rooms that allow listeners to clearly hear sound sources (absorbs mid and high frequencies).
Hope this helps and that the knowledge enhances your listening experience!
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