Editor’s Pick
We as an industry deliver sound at very high levels which can contribute to hearing loss. As workers in the industry, high sound levels combined with repeated exposure put us at high risk of hearing loss later in life.
Hearing damage is caused by a combination of sound energy level and time. Safe Work Australia has determined that a workplace noise of 85 dB (A weighted), averaged over 8 hours (Leq,8h) is the upper limit. That is, over 8 hours, an average of 85 dBA is the exposure level where damage can occur. At that limit, 15-20% of people will suffer damage later in life.
Exposure is related to sound to the energy of the sound, and not so much sound pressure level (SPL). Energy and pressure level are related, but not the same thing.
Stay with me, the next bit is important.
Energy is the measure of power, which is the work that a sound wave can do (IE, generate heat) and is referenced to 10-12 Watt (0.000,000,000,001 Watt) . Sound energy doubles with every 3dB increase whereas Sound Pressure Level doubles every 6dB (SPL is analogous to voltage).
Most people are used to working with SPL which doubles with every 6 dB increase and that is how confusion often occurs. For completeness, a doubling of loudness (which is different again to energy and SPL) is generally accepted as 10 dB but this is subjective.
As sound energy increases, the safe exposure time reduces proportionally. Therefore, if the sound energy increases from 85 dBA to 88 dBA, experts have determined that the safe exposure time is halved to 4 hours.
Safe Work Australia have produced a Code of Practice called Managing Noise and Preventing Hearing Loss at Work.
The table below extracted from the Code, sets out the equivalent exposure times.
|
Noise Level dB(A) |
Exposure Time |
|
85 |
8 |
|
88 |
4 |
|
91 |
2 |
|
94 |
1 |
|
97 |
30 |
|
100 |
15 |
|
103 |
7.5 |
|
106 |
3.8 |
|
109 |
1.9 |
|
112 |
57 |
Now that is scary! 100 dBA at the mix position is common and according to the safety experts, 15 minutes is the maximum amount of exposure time before injury could occur. At 106 dBA, damage could occur after just under 4 minutes!
To be clear, if your ears are ringing after an event, a hearing injury has occurred, but damage can occur before it gets that bad.
As professionals, we are at high risk. That is why it is recommended that we go for a hearing test with an audiologist once a year. It is the only way to determine if we have done damage to our hearing so it is really worthwhile.
Obviously if we are to maintain our hearing, we need to take steps to manage our exposure. That of course will be balanced against the artistic needs of the show.
Here are some suggestions if you are responsible for the sound at loud shows:
- Mix with room to move. Add some dynamics to the show by starting at a lower level, giving you some headroom to come up at the end of the show.
- Not all songs need to be at the same level. In particular, ballads can be softer.
- That haystack in the bottom end could be reduced. Reducing the bass might even improve the intelligibility of your mix!
- Have a sound level meter at the mix position that calculates the average sound level (Leq).
- Be conscious that a difference of 3 db has a dramatic effect on safe exposure time.
- You hearing never sleeps. That means noise from the sound check, the noisy flight, the traffic, the support acts etc all contribute to the overall exposure, plus the gig.
- Consider earplugs to give your ears a rest, especially when you aren’t mixing.
- Club level and festival engineers are probably at greater risk due to the longer exposure time. Take a break.
- If you are running foldback, invest in some quality In Ear Monitors (IEM’s) that block the external sound.
As well as improving the quality of the foldback for the performers, In Ear Monitors (IEM) also permit a lower level getting into the ears which allow a longer are exposure. That is of course, provided they are turned down and block out the external sound.
However, most performers and engineers don’t turn them down. A study was conducted by the Vanderbilt University School of Medicine in the US where they got together a group of 15 musicians and studied their foldback levels both with floor monitors and IEM’s
3 gigs were done with floor monitors, and a further 3 with IEM’s. Remarkably, all 15 musicians set their monitoring to exactly the same levels over the 6 gigs (0.8 dB difference). Consequently, there was no safety benefit with IEM’s.
They were then asked to set a level that they would accept. In the floor monitors, they only came down 2 dB before they started to complain. In the IEM’s however, they came down between 6 and 10 dB. As noted previously, a reduction of 6 dB can permit exposure time to be 4 times as long.
It appears that by blocking the external sound and delivering a tight focussed mix, musicians could play at a lower level.
It must be noted though that a serious problem exists with the improper use of IEM’s. That is, just using one, and relying on floor monitors for the other ear.
When IEM’s are used in both ears, an effect known as binaural summation produces a perceived 6 dB increase in volume without raising their actual output level. This is free money as it give the impression of being 6 dB louder without the associated risk of hearing damage.
But when a single IEM is used, the opposite happens. The sound from the IEM and the floor monitor will be uncorrelated so both will be turned up to compensate. Suddenly levels have increased in both ears by about 9 dB, and reduced safe exposure time by 1/8th!
Another masking effect happens too. Think of when you are using you phone in a loud environment. By blocking your other ear, you can hear the phone more clearly. The same effect happens when using a single IEM. That further motivates the musician to turn it up even more.
Dr Michael Santucci, is an audiologist and head of Sensaphonics In-Ear Monitoring Solutions in the US. Michael’s clinic sees about 2,000 musicians and engineers a year. According to him, you are much safer with no IEM’s and using floor monitors, rather than using a single IEM combined with floor monitors.
If you are running IEM’s:
- You have a role in discouraging performers in using single IEM’s. All or nothing.
- Start off only with the essentials in the mix that is needed by the musician
- Good signal to noise ratio is the key.
- You probably don’t need the kick drum in IEM’s
- Keep your mix focussed.
- Always know your level, keep a track of it.
- Insert a hard limiter as a safety.
Go for a hearing test with an audiologist once a year! It is the only way you can determine if your hearing is being injured.
If you are in this industry as a career, looking after your hearing is critical.
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How hearing works Video – By far the best explanation that I have seen.
https://www.youtube.com/watch?v=GPZ5gadKQh0
Safe work Australia – Managing Noise and Preventing Hearing Loss at Work
Sound Advice (British website) contains practical guidelines on the control of noise at work in music and entertainment.
I am a contributing writer to CX Magazine and they own this article. CX Network is the voice of technicians in entertainment and audio visual across Australasia.
To read this article online (and ALL of their articles dating back to 1990 for free!), head over to the CX Network.
http://www.cxnetwork.com.au/cx-magazine/cx-december-2016/
Lot’s of great stuff!
