I have it on good authority that before Shakespeare became a writer, he enrolled in one of the fist Audiology programs in England- Audiology on Avon. And one of his university papers was entitled, “To vent or not to vent”. Of course, everyone knows that Shakespeare flunked out and became the Bard we know and love. He used his audiology training to write one of the best known soliloquies: “To vent, or not to vent. That is the question. Whether ‘tis nobler in the minds of other…” and I think that we all know the rest. When he was revising Hamlet, he did change the word “vent” to the word “be”, but it still remains an important, though non-existential question.
When it comes to hearing aids, generally the largest vent that can be used, the better will be the fitting. And with modern feedback management techniques, we can frequently get away with a non-occluding fitting, especially for behind the ear hearing aids.
However, when it comes to hearing protection such as the ER-15 musician earplugs, venting will reduce the effective attenuation in the lower frequency region. But sometimes a small 1.4 mm vent can be the difference between acceptance (and at least wearing the hearing protection, albeit with non-optimal efficiency) and not wearing the hearing protector at all.
This is especially the case for brass players, some reeded woodwinds, and depending on the music, some vocalists.
Brass players (and clarinet/saxophone players where the top tooth is in contact with the hard mouthpiece) can feel some “back pressure”. Interestingly enough, this is not always the case, but as soon as the brass players comment on this issue, venting will quickly resolve it. I have a 2 mm diameter drill in my office ready to go. With soft material, such as silicon, using a 2 mm diameter bore, will result in a 1.4-1.5 mm diameter vent- the silicon snaps back a bit. For our American friends, 1.4 mm is roughly 1/16”. And for our non-American friends, this is still roughly 1/16″.
This vent diameter came out of the work of Mead Killion who found that a 1.4 mm vent is all that is needed to completely resolve the occlusion effect, as long as the bore length is sufficiently long. For shorter ear canal bore lengths, a larger diameter vent is required. I believe, but am not absolutely sure, that Shakespeare learned the same thing in audiology school.
This “venting” trick has been a mainstay of my clinical practice for more than 25 years at the Musicians’ Clinics of Canada, and works quite well. Clinical work is always about finding a balance; too wide a bandwidth may seem harsh, at least initially, but results in better intelligibility. But forcing a new hearing aid user to listen to a wide bandwidth may result in rejection of amplification. The same thing follows for hearing protection- more may be better, at least up to a point, but sometimes, less is better so that the wearer can use it with increased comfort, albeit, slightly less than optimal performance.
In the case of music, most of the sound energy is above 500 Hz in any event, so compromising the attenuation at 250 Hz and below, may be a non-issue.
From time-to-time, a musician or other user of hearing protection, may find that the vented hearing protection may be worse than an occluding one. In fact, this happened to me just last week.
A musician (who had a perfectly drilled 1.4 mm vent) felt that there was a hollow resonance when he wore the hearing protection…. Stay tuned to part 2 of this blog series to find out why!