“It sounds so echo-y in here.” This thought is expressed, usually in a negative context, by people who are unhappy with a room’s acoustics. “Echo-y” is a term people use when the sound seems to keep hanging on for longer than it should. Let’s explore the details of what that means.
Acoustical consultants will explain that sound travels and propagates in waves, and can travel through any medium that is able to compress or flex, even slightly. Air, water, earth, cement, pretty much any substance can transmit sound…some more effectively than others. Like the tag line from the original “Alien” movie, “in space, no one can hear you scream,” because in empty space, there is no substance that will compress or flex.
Hard surfaces tend to allow sound waves to bounce all around, sometimes off of many surfaces, before reaching the listener. Each bounced instance of the original sound wave is a copy – an echo – of the direct, or “dry” sound. Because the speed of sound is relatively slow (about 1130 feet per second), each individual echo has a slightly different arrival time at the listener’s ear, depending on how many surfaces it has bounced off. The human ear will blur them all together as the thing laypeople call “echo.” They say “echo-y,” but they mean “reverberant.” And reverberation is simply millions of echoes, arriving at the ear at millions of different times.
Acoustical engineering consultants will tell you that the more hard surfaces you have, the less clear and distinct a sound will be, in a given space. And soft surfaces, like carpet, will result in more clarity, as they tend to absorb sound. Clarity and detail are traded for spaciousness and majesty when the surfaces in a room are all hard and solid.
The clearest and most detailed sound happens when sound waves travel straight from the source to the listener’s ear, without bouncing off any surfaces. A “soft” room delivers mostly direct, dry sound. When a sound wave bounces around in a “hard” room, its many echoes have to make a longer trip before reaching the listener’s ear. This results in later arrival times for the many echoed versions of the original sound, creating reverberation, which in turn results in less clarity and less detail.
When acoustic consultants in Toronto are designing a room, they combine hard, reflective surfaces and soft, sound-absorbing surfaces to strike the right balance of clarity and spaciousness. The right amount of acoustically tuned reverberation determines how much detail the listener gets from a spoken voice, for example. It also determines how spacious and majestic the violin player sounds. Acoustical consultants can make different areas of a space behave in different ways, and custom-design that room’s acoustical character. And it all starts with reverberation.
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