Sound advice: choosing hearing protection

Above: Earmuffs range from $10 upwards. Earplugs are inexpensive, one-use or multi-use, and corded or uncorded. There are also variations with headband, neckband or helmet attachments.

Words and photos: David Luckensmeyer 

I no longer need a reminder to wear hearing protection thanks to constant tinnitus (ringing in my ears) and diminished hearing. More ringing and less hearing are transactions I’d like to reverse. I’ve been reasonably careful over the years but obviously not careful enough.

 This story explores options commonly available for personal protection equipment (PPE) like earplugs and earmuffs. It is not about the reduction of sound levels in the workshop.

What is ‘sound’?

Sound travels through the shop atmosphere (and objects) as a vibration wave, or sound wave. I’ve wondered then, why do scientists refer to ‘pressure’? Well, a sound wave changes atmospheric pressure, oscillating between areas of low and high pressure. This is described as a sound pressure wave (fig.1).

The strength of the wave can be measured as ‘sound pressure level’ (SPL). The unit of measure is the ‘decibel’ (dB), which is one tenth of a ‘bel’ (after Alexander Graham Bell). The decibel is a logarithmic unit, so an  increase of 10dB is a ten-fold increase in SPL. For example, going from 10dB to 20dB is not twice as loud, but ten times as loud.

A very quiet workshop might have a background SPL of 40dB(A), typical conversation might be 60dB(A), and machinery generally produces much higher levels, requiring hearing protection.

According to Safe Work Australia, the threshold beyond which hearing damage is likely to occur is 85dB(A) or higher for eight or more hours. The time parameter is important. Our ears can be exposed to higher sound levels for shorter periods of time without protection or damage.

How loud is my workshop?

Table 1 shows published and measured data for common machinery. Check user manuals or online for specific sound emissions for your machines. For the ‘measured readings’, I downloaded and used the SPLnFFT App and took measurements at 1m (the ‘1m rule’).

Earplugs

Above: Simply put, SLC80 ratings represent the ‘acceptable range’ between workplace SPLs and SPLs inside the hearing protector. Class ratings denote attenuation or reduction of sound levels.

Before writing this story, I had the mistaken impression that earplugs do not attenuate loud noises well enough. In fact, they perform quite well, and typically fit under Class 3 or 4, although there are some versions that meet Class 5 requirements.

But the class rating is not the whole of it. What about comfort? And fitment? I don’t like the feeling of compressed foam putting pressure in my ear canal. While the pre-moulded plastic and silicon earplugs feel better, I can’t deal with the constant ringing from tinnitus. But they might be right for your situation; just double-check the class rating you require.

Always make sure the packaging refers to Australian Standards 1270. Hearing protection in Australia should be tested to a trusted standard. The results are given according to SLC80 ratings (sound level conversion, valid for 80% of wearers) and/or Classes 1–5.  By comparing the figures in Table 2 with the sound levels of machines, we can see the minimum class of hearing protection required to avoid hearing damage.

Earmuffs

Earmuffs are widely used. They are often more comfortable than earplugs, offer a wider range of attenuation, can be whipped on and off quickly, and may offer communication and play-back options.

With earmuffs, there’s more to it than just selecting the right level of hearing protection. Some are downright uncomfortable: the foam is too hard, the earcup doesn’t fit the ear properly, or the headband is too loose or too stiff. The reality is that some work better with glasses, beards, skinny cheeks and not-so- skinny. Fitment is important!

An inexpensive pair of muffs may meet the Class 5 attenuation rating but not fit your head/face very well. More expensive pairs generally offer higher comfort levels and last longer.

Look for earmuffs of the right class for your needs as it is possible to over- attenuate sound levels. WorkSafe QLD suggests attenuating below 70dB(A) can increase feelings of isolation and hinder communication. A good working target when selecting hearing protection is between 75–80dB(A).

Above: ANC tech has improved significantly over the years and offers a genuine alternative for certain sound emitting processes in the shop. But remember these earplugs and muffs are not tested to Australian Standards 1270. This is one of those ‘use at your own risk’ scenarios.

Active noise control (ANC)

So far we’ve considered passive noise control, where sound pressure waves are stopped from reaching our ear canals. Such passive methods can be combined with active noise control (ANC) technology (fig.2). ANC-equipped hearing protection can emit a sound wave, more or less in real time, that is the inverse or opposite of noise emissions.

Combined low and high pressure areas cancel each other, hence the alternative moniker: active noise cancelling. Small microphones are located on the outside of ANC earplugs or muffs, and small speakers are located on the inside, at the ear canal. It is quite remarkable.

ANC works best with lower frequencies as it is easier for the tech to match sound pressure waves with larger wavelengths. Likewise, ANC works better with continuous sound waves (say from a thicknesser or sander), and does not work well with intermittent sounds (e.g. hammering a nail).

Does ANC have a place in the shop? You’ll have to make up your own mind. ANC earplugs and muffs can attenuate at Class 5 levels, or about 30dB(A), but not across all frequencies and only for continuous sounds. I use ANC sets for machinery that emits lower levels of sound, but not for the louder, higher frequency sounds from a tablesaw or router, for example.

Final word

Among other things, I haven’t mentioned hearing protection that incorporates in-ear playback. There is a danger of attenuating damaging sound levels, and then listening to in-ear playback at a level above the recognised 85dB(A) threshold.

Let’s say my tablesaw emits an SPL of 100dB(A). I use Class 5 earmuffs which attenuate the sound by 30dB(A). The sound level that reaches my ears is 70dB(A). But while I’m working, I listen to my fav music at 30dB(A), which is not that loud. The real-world sound level that reaches my ears is right back up at 100dB(A). In this scenario, the in-ear music cancels out the 30dB(A) of attenuation and the resulting SPL is of a very damaging level.

Above: An older set of WorkTunes muffs (maroon) which broadcasts AM/FM radio. The newer set on the left streams playback through Bluetooth and offers ANC to protect from hearing damage.

Let me reiterate that such math glosses over the complexity of this subject. Hearing protection does not provide flat attenuation across all noises. And a workshop environment often has sounds coming from multiple sources. Plus throwing in the variables of ANC and fitment concerns just adds to the complexity.

Disclaimers aside, I hope this story helps you make ‘good ear choices’. I know I’ll be reaching for my hearing protection more often when I’m in the workshop.

David Luckensmeyer @luckensmeyer is a designer maker and regular contributor to Australian Wood Review. Learn more at www.luckensmeyer.com.au