Acousticians speak physics. They don’t speak convenience. :). But here’s a post outlining the basics of what you’ll hear them talk about.
Yes, I know you know what loudness is. You may even know that we measure this in decibels. But what you should know is that the human ear perceives loudness logarithmically, not linearly. What does that mean to you? It means that we humans therefore use a logarithmic scale to measure loudness. And that means, that a 10 dB increase in noise levels means a doubling of the noise you hear. Similarly, to bring down noise to half of what you’re hearing, you need a 10 dB loss.
This is roughly the ‘pitch’ of the sound you hear. Buses, bass guitars, bass drums, and all rumbles in general are ‘low’ pitches. Most vocals figure in the ‘mid’ frequency range. Shrill voices, instruments, female opera singers figure in the ‘high’ pitch range. Generally, if you have a piano before you, low pitch is to the left, and high pitch is to the right.
Why do you need to know this? When you get a room acoustically treated, you must know that high frequencies scatter more easily and predictably around a room. Low frequency sounds tend to bend around life-size objects such as chairs, sofas, etc, producing irregular shadow regions. Absorption helps kill most high frequencies, but it can’t keep the low frequencies from bouncing around the room. Trying to ‘absorb’ low frequencies would eat up most of the space you have – around 3 feet on all sides.
Of course, this is about how sound bounces off walls. High frequencies bounce off walls and surfaces like light does. Low frequencies have a mind of their own. They bend around objects, ignore most wall treatment, and pretend that your single partitions don’t exist. These are what your neighbours will most often complain about. Quite simply, sound acts like a particle at high frequencies, and like a wave at low frequencies.
This really needs a separate post, but we’ll stick to the definition for now. So absorption is the fine art of reducing sound energy in a room. Absorber materials are essentially porous in nature – sound goes where air goes, and then while passing through a maze of pores, being in frictional contact with maximum surface area, sound energy gets dissipated into miniscule amounts of heat.
This is the process of scattering sound around a room. Egg crates work here, only for high frequencies, though. Nowadays, there are products available which absorb as well as diffuse. Again, space constraints in most site conditions make it difficult to build diffusers for low frequencies. These constraints are sometimes marginally overcome by making the opposite wall surfaces non-parallel.
This is a measure of how long it takes for sound to die out in a room. Well, not exactly die out – reduce by a certain amount.
Isolation This may seem too elementary to define, but the number of times people confuse this with reverberation treatment makes this worth mentioning. Isolating is to prevent sound from leaving a certain space. Materials that ‘absorb’ sound seldom ‘block’ it.
There are plenty of other terms – depth, clarity, speech intelligibility, etc. There are also terms describing what sound sounds like – warm, cold, bright, mellow, intimate, etc. These will be dealt with in another post. For now, the above terms should lessen some of the the geek (!) and latin in your conversations with your consultant.