“How do Musicians Earplugs actually work?”
This is one of the most common questions I answer during Hearing Conservation Consultations, so it is as good a place as any to start a blog series on Musicians Earplugs. Further installments in this series will cover the available filter levels, importance of build material, purpose an acoustic seal in the ear canal, and tips for acclimating to the use of earplugs during rehearsal, performance, and audio production work.
What are Musicians Earplugs?
Custom musicians earplugs are the standard professional option for reducing sound levels while maintaining the fidelity of the signal. They are custom built molds made from impressions of the individual's ears. The design allows them to mimic the natural resonance of the open ear canal, which differs from the acoustics of foam earplugs or other generic 'music earplug' options.
How do they work?
The answer is wonderfully simple, but it also speaks to the high level of quality control that is required on the part of the lab to ensure a relatively flat broad-band attenuation (sound level reduction). This is accomplished by combining a sound attenuating filter with a resonance channel that emulates the acoustic parameters of an open ear canal. The following technical information is presented by Etymotic Research, the company that developed the design and manufactures the ER-series filters:
Musicians Earplugs™ buttons have a diaphragm which functions as an acoustic compliance, while the volume of air in the sound bore of the custom earmold acts as an acoustic mass. The combination of the two produces a resonance at approximately 2700 Hz (as in the normal ear), which results in smooth, flat attenuation.
ER-9 Provides flat 9-dB sound reduction through the mid range and 15 dB in the highs
ER-15 Provides uniform 15-dB sound reduction across frequencies
ER-25 Provides 25-dB relatively flat sound reduction across frequencies
What do they sound like?
In the simplest terms, listening through Musicians Earplugs sounds like the original signal, but quieter; it could be said that they are the closest thing to a volume control for real-world sounds available. Dr. Brian Fligor created a clear demonstration of the sound of Musicians Earplugs by using data from in-ear sound level measurements. You can listen to these sound examples on the Boston Audiology Consultants webpage.
Though Musicians Earplugs are often marketed as "flat" or "uniform", it is important to point out that nothing is every truly flat. If you've ever worked with any sound device, electronic or acoustic, this is an accepted and understood fact. It would be more fair to describe Musicians Earplugs as "balanced" and "accurate", as they maintain the relative balance of tonal components and harmonics across a very broad spectrum. Everyone has a different perception and response, so check out the tutorials section for individual reactions.