Double Hearing Protection
Questions and answers about wearing double hearing protection.
three basic types of hearing protection device:
Ear plugs, "ear muff" hearing protectors, and ZEMs. Each of the three types has its advantages and disadvantages, and each is appropriate for various situations and according to your individual preferences. But to get the maximum possible level of hearing protection, there are times when you might want to double up and wear two types of hearing protection at once.
What Does Double Hearing Protection Consist Of?
Double hearing protection means wearing both
at the same time. With
neither ear plugs nor ear muffs can be worn at the same time, so it's not possible for ZEMs to be part of a dual hearing protection system.
How Much Extra Hearing Protection Do You Get?
The degree of extra protection can vary widely, but typically the combined noise reduction rating (NRR) will be about 4 to 8 decibels (dB) higher than the higher of the two individual NRRs. For example, if the ear plugs have an NRR of 25, and the ear muffs have an NRR of 21, the combined NRR might be between 29 and 33 dB. As a rule of thumb, an improvement of 5 dB is often assumed, for a combined NRR of 30 in this example.
This 4 to 8 dB of additional protection translates into a 60% to 85% reduction in sound intensity, a marked reduction in the risk of hearing damage.
Factors that affect the degree of improvement in hearing protection include:
- The frequency range of the noise being protected against
- The protection level of the ear plugs for the noise frequency range
- The protection level of the ear muffs for the noise frequency range
- Whether the ear plugs are inserted correctly
- The depth of insertion of the ear plugs
- Whether glasses are worn (which reduce the effectiveness of ear muffs)
The total protection afforded can't be calculated from the protection levels of the individual devices, because they do not function independently (due to mechanical coupling effects). Also, beyond a certain point, it is not possible to achieve any further attenuation of sound, because even when the airborne pathways have been thoroughly blocked, sound will still be able to arrive at the eardrum by traveling through the skull, via bone conduction.
Which One Is More Important, Plugs or Muffs?
Typically the ear plugs will have a higher NRR than the ear muffs, so they are the more critical component of a double protection system. To get the best hearing protection from a dual system:
- First choose an ear plug with a high NRR (normally a foam ear plug).
- Pick an ear muff that is comfortable for you to wear; it can be lightweight and inexpensive. Research has shown* that once an adequate ear plug has been selected, the amount of further protection that the ear muff can contribute is about the same regardless of the specific muffs selected.
- Be sure to insert the ear plugs properly, following the instructions.
If the noise being protected against is all in the high frequency range (above 2000 hertz), most combinations of ear plugs and ear muffs will give an equivalent level of protection.
When Is It a Good Idea to Use Double Hearing Protection?
Double hearing protection is recommended for
noise levels at or above 105 dBA,
about the noise level of a table saw. The dual protective effect will be most noticeable against noises in the lower and middle frequencies (below 2000 Hz). Firearms also generate high noise levels, and many shooters prefer the added assurance of dual protection, especially on indoor firing ranges.
Is There Any Benefit to Wearing Ear Plugs under Electronic Hearing Protectors?
Yes. Just as in ordinary ear muffs, the protection provided by
electronic hearing protectors
is due to the sound-blocking material in the ear cups, not the electronics. (The electronics are there to transmit and/or amplify low-level sounds so that you can still hear them.) So just as with regular passive ear muffs, ear plugs can offer an extra level of protection (although the sounds that are electronically transmitted will lose some of their clarity).
Similarly, if you already wear digital (electronic) ear plugs, you can wear passive ear muffs at the same time to further reduce your noise exposure. Again, some of the clarity of the electronically transmitted sounds will be lost, but the quality of the overall listening experience will still be much improved over the combination of regular ear plugs and passive ear muffs.
These electronic hearing protection devices are often used by shooters, who are exposed to the dangerously high noise levels of gunfire, for which double hearing protection is especially appropriate.
Can Double Hearing Protection Be Used to Block Out Sound That Is Not Hazardous but Is Still Annoying?
Sure. Maybe you're at home trying to work or study and you're not interested in hearing the neighbors' noise. If ear plugs aren't reducing the noise quite enough, you can try wearing ear muffs as well. The additional 4 to 8 dB of reduction will make the noise sound about 25% to 45% quieter. Keep in mind that while wearing dual protection, you may not be able to hear someone speaking to you at normal levels.
Elliott H Berger, "Attenuation of Earplugs Worn in Combination with Earmuffs," American Industrial Hygiene Association Journal 45(5) (1984): B36.
You can get double hearing protection for as low as $10 (US dollars) (plus shipping).
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