Cohousing-L Mailing List: Re: room acoustics

[Sharon Villines (sharon]

This page has good diagrams of direct sound, echoes, and sound reverberations. 
(“Noise" is shorthand for most of us to indicate sounds we don’t want — not a 
technical definition. But for people who deal with the technical production of 
sound, “noise” usually means sound produced in the system or the wires. 
Electronic interference.)

https://www.softdb.com/blog/what-is-reverberation-in-acoustical-analysis/

> Sound waves develop in a compressible medium, such as air, when there are 
> very short variations in pressure. A sound is what the ear perceives from 
> this fluctuation. If the wave created by a sound source crosses the medium 
> and arrives straight at the listener, then we call this a direct sound or a 
> dry sound. By contrast, sound waves generally don’t reach the listener 
> directly. Instead, they are reflected by an obstacle (e.g. wall, floor, 
> object). This phenomenon is what we call an echo. What’s more, if the sound 
> wave is reflected several times before reaching the ear, we call this a 
> reverberation. 

Many musicians also know a lot about acoustics and may be easier to find than 
an educational audiologist. 

> On Mar 5, 2026, at 2:00 PM, Laura Polich via Cohousing-L <cohousing-l [at] 
> cohousing.org> wrote:

> I would suggest that using phone-app decibel meters is not that useful to
> compare two voices or two noises or two rooms. First there are different
> decibel scales for different uses.

What I was talking about was a  person using their phones to obtain an 
objective measure of how loud a person is speaking when they are intending for 
you to hear them. It helps sometimes to tell someone that they may be speaking 
at 60 decibels where they are, a comfortable conversational level, but across 
the room, the sound is 45 or 50 — a whisper. 

We had a teen who had an incredibly loud voice when he was excited on game 
night. It was often over 80 which is about the level of a gas lawn mower 
sitting next to you while you are playing a card game. I was able to put my 
phone where he could see the level. He became more aware and the evening was 
more pleasant.

These apps are not used to measure legally defined sound but in day to day 
life, they are very helpful. 

> There is no single decibel scale.

I don’t know what this means — a decibel (dB) is a relative unit of measurement 
equal to one tenth of a bel (B) or other fixed value. Wikipedia says:

> The bel was named in honor of Alexander Graham Bell, but the bel is seldom 
> used. Instead, the decibel is used for a wide variety of measurements in 
> science and engineering, most prominently for sound power in acoustics, in 
> electronics and control theory. In electronics, the gains of amplifiers, 
> attenuation of signals, and signal-to-noise ratios are often expressed in 
> decibels.

Sound meters are calibrated so that the meter is giving “relative” measurements 
according to a fixed value. There is a legal fixed value used by the police, 
for example, for testing levels at work sites in order to measure violations.

The best example I have found illustrating the logarithmic difference between 
conversations at 60dB vs yelling at 80dB isn’t like the difference between 60 
degrees and 80 degrees. The increase from 1 decibel to 2 decibels is 10x, not 
1x. 

Every 10 dB increase means about 10× more sound intensity and is heard as 
roughly twice as loud by most people. So loud yelling at 80 dB is about 100× 
the intensity of a 60 dB conversation and sounds roughly 4× as loud (two 
doublings), or the equivalent of 320 degrees.

What acoustical engineers need or want to know is much more complicated than 
most of us need to fix or at least help hearing in our common spaces. Just 
understanding that it isn’t the loudness of the sound that is a problem, it is 
the way the sound echoes and reverberates

Sharon
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Sharon Villines
Riderwood Village, Silver Spring MD
Founding Member, 25 years in Takoma Village, Washington DC