August 1, 2007
In the defense against hazardous noise exposure, earmuffs have the advantage of including electronics. Electronic earmuffs not only provide significant reduction of hazardous noise, but also offer an impressive array of options for specialized applications.
But user beware! Not every piece of electronics that covers the ear protects hearing. Electronic features are available in many headsets that offer little or no protection from hazardous noise, and are not intended for use in hazardous noise levels. At some frequencies, these headsets may even amplify background noise due to resonance in the earcup. To provide hearing protection, an earmuff must be designed to be a hearing protector from the start, and clearly labeled as such.
Let’s look at four common types of electronic earmuffs that can enhance your hearing conservation efforts in particular applications:
1) Radio earmuffs
On the surface, the idea of using radio earmuffs in hazardous noise levels seems counter-intuitive: Doesn’t the radio just add more noise to the noise?
Ideally, a radio headset would allow the enjoyment of music at controlled safe levels, but also reduce the background disturbance in a noisy environment.
Today’s new hearing protectors do just that: Radio earmuffs contain circuitry that limits their output. When the radio is turned on, the sound output is electronically limited to a safe level (around 82 dBA), even when the radio is set to full volume. This means the radio earmuff can be safely used in ambient noise exposures up to 100 dB. The combined level of the attenuated ambient noise and the radio output is still safely in the low-80 dB range. In a high-noise job that is also repetitive or tedious, a radio earmuff can improve worker satisfaction, without sacrificing hearing protection.
Radio earmuffs are not for every job, and certainly not for workers near moving heavy equipment, or jobs that require concentrated focus. But for tedious or monotonous jobs, one study found that 79 percent of workers felt their productivity increased by listening to music on the job.
2) Amplification earmuffs
Impact noise poses one of industry’s most difficult challenges in hearing protection: high noise levels at unpredictable and intermittent intervals. How can you offer hearing protectors that allow workers to hear speech and warning signals, yet still protect from occasional high-impact noise?
The short duration of impact noise lulls workers into a false sense of protection. Not recognizing the hazardous impact of intense sound energy in short noise blasts, workers often ignore the hazard.
Hearing protection manufacturers have responded with level-dependent earmuffs. Microphones mounted on the surface of the earcups feed the signal to an amplifying circuit with a built-in limiter â€” maximum output cannot exceed 82 dB, still a safe level for occupational noise exposures. Worn at a construction site, for example, the worker would clearly hear warning signals and co-workers’ voices, but also be protected from the intermittent noise of power tools or unexpected impact sounds.
But the electronics in an amplification earmuff do not cancel incoming noise â€” they simply cap the amplification of the incoming noise. Nor does the limiting circuitry improve the passive attenuation of the earmuff. The greatest benefit of amplification earmuffs is the ability to still hear warning signals and co-worker voices clearly through the background noise. This is particularly true for workers with existing hearing loss or who wear a hearing aid.
3) Communication earmuffs
Communication earmuffs are similar to amplification earmuffs: They offer good attenuation of ambient noise, and the incoming communication signal is amplified to a comfortable level, usually with a limiting circuit to prevent too much gain. The difference, however, is that while amplification earmuffs obtain their input signal from built-in microphones on the earcup, communication earmuffs obtain their signal from an external radio source.
These earmuffs have moved from traditional hardwire connections (plugged into a communication radio) to wireless systems utilizing FM or Bluetooth technology. Earmuffs can be configured for listen-only or two-way communication, usually with an attached boom mic. Applications that require communication earmuffs are typically found in forestry, mining, aviation, construction, first responders and military. But it is critical to test the configuration before purchase to ensure the earmuff is compatible with the user’s needs and hardware.
4) Active noise reduction earmuffs
Active noise reduction (ANR) earmuffs have microphones mounted inside the earcup to monitor incoming noise. That signal immediately passes through a circuit that reverses the phase of the noise, effectively creating an “anti-noise” signal. This reverse-phase signal is then sent to a speaker within the earcup. When the unmodified noise combines with its own reverse-phase mirror image, there is a cancellation effect that results in an overall reduction in the noise level.
ANR circuitry is impressive to a listener: Incoming noise levels can be reduced with the push of a button. But ANR circuitry has its limitations. ANR works well when the incoming noise is low-frequency, but is relatively ineffective against the shorter-wavelength high frequencies (most ANR circuits have little effect over 500 Hz). There is also a slight time delay for the circuit to activate, meaning ANR is ideally suited for continuous noise, not intermittent noise or speech.
ANR circuitry also interferes with an earmuff’s ability to attenuate noise in two significant ways. First, the addition of any electronics makes an earcup less efficient in blocking noise. The passive attenuation rating of an ANR headset will always be lower than its comparable non-ANR counterpart. And second, ANR circuitry generates a small amount of internal noise, heard by the user as a high-frequency hiss. Because of these limitations, ANR has been marketed more for annoyance noise than for hazardous occupational noise.
The advantages of electronic earmuffs must be weighed against their higher cost and bulkier size. But electronic earmuffs offer specialized benefits for workplace as well as non-occupational applications. Features in earmuffs change with the fast pace of the electronics industry, and the innovations in design and utility continue to make electronic earmuffs a valuable tool in a hearing conservation program.
SIDEBAR: Common applications for electronic earmuffsAM / FM Radio
- Repetitive or routine work
- Machining, assembly, metalwork
- Light manufacture, electronics
- Textile, printing
- Impact / impulse noise
- Intermittent noise or mobile workers
- Hearing impaired workers
- Drop forge, metal stamping, riveting
- Critical two-way radio communication
- Forestry, mining, construction
- Aviation, first responders, military
- Continuous, low-frequency noise
- Motors, turbines
- Commuter noise (aircraft, trains, etc.)