When selecting hearing protecting it is important to understand how humans hear sounds. Part 1 of this series discussed a the mechanics of hearing and how damage can occur. In Part 2 we will look at what we hear and the best way to protect it.
We are able to hear due to the sound waves interacting with the ear. The loudness of sound is described in decibels or dBA. Sound waves are the vibration of molecules caused by a change in pressure.
Sound waves are actual waves. The pressure of the sound causes molecules of air to move just like waves in an ocean. The vibration is described as the number of wave crests that pass a given point during a given time. This is called the frequency of the sound. Frequency is measured in hertz (Hz)
What we hear, the pitch, tone, note, etc. depends on the frequency of the wave. Every note or sound has specific frequency. A natural low A as played on a piano is 440 Hz. Bagpipes tune the note low A to about the frequency of 478 Hz. F# above middle C is at 396Hz
The range of sounds, all the frequencies, that humans are able to hear is called the frequency response. The average is in the range of 20 Hz to 20,000 Hz. The sound has to be at a certain decibel (dBA) to be heard. The best way to show this is in a graph called a equal-loudness contour.
The equal-loudness contour is a measure of the sound pressure over a frequency spectrum that a listener will perceive as a constant loudness. The shape of the human ear allows certain sounds to be heard at a lower decibel. This is because of the way sound waves bounce around the inside of the ear canal.
The important thing to take from this graph is that it is easier to hear certain frequencies of sound.
The one sure way to protect your ears is to block all the sound waves from reaching the ear drum. Totally blocking the ear canal will prevent any damage. Unfortunately, this makes it pretty hard to play, or listen to, the bagpipes. What we want to do is prevent damage but at the same time allow us to hear what we are doing. This is where ear plugs come in.
The most basic type of earplug is the standard foam safety earplug. These are designed for overall protection of the ear. They are very good at reducing the overall dBA but they do it in a way that does not match the equal-loudness contour of human ears. This is why everything sounds strange when you wear them. Sounds, or frequencies, that we hear better at lower decibels are blocked the same as all the other frequencies. This just sounds unnatural.
The best ear plug will be the one that most closely matches the equal-loudness contour of the human ear. This is called "flat attenuation." These types of ear plugs are also known as musician’s ear plugs and will outperform standard foam safety earplugs for the piper. Stay tuned for Part 3 where we will review different available ear protection.