Goldfish and in-ear monitors

The last thing that one would expect a goldfish to ask is something about the water. Fish are surrounded by water, are born in water, live their lives in water and, in short, know nothing about water.

Fish take water for granted because that is all they know. You will never find a course on water in any fish school curriculum.  It is so ubiquitous that why question it?


The same goes for in-ear monitors. There are some things in our field that seem to be simply the way they are, because they were always like that, and why even question it.  In-ear monitors or any earphones that one may purchase for their smart phone or MP3 players come with some eartips made of plastic Christmas tree-line conical rings, and also some foam tips that have a piece of tubing down the main bore.  And the tubing is always glued to the foam.  Ever wonder why the tubing needs to be glued to the foam insert?

This is clearly a “fish-in-water” story.

It all starts with Dr. Robert Oliveira, the president of Hearing Components, Inc.  In the 1980s Dr. Oliveira was with the 3M company, and then spun off his own company that manufactured items for the hearing aid industry, such as Comply wax guards and several patents about gluing a piece of tubing into a foam earplug that can serve as an ear coupler for an earphone or in-ear monitor.  The history of this can be found in an earlier blog series by me from several years ago , but it’s worthwhile returning to inventions that have changed the field, even though it’s not even explicitly thought about anymore.  Without this innovation of Robert Oliveira we simply would not have certain important things in our field that are as ubiquitous as water is to a fish.


Have you ever wondered why insert earphones for puretone audiometry are coupled with glued plastic tubes? What about insert earphones for ABR testing?

Here is the story.

Once upon a time (in the early-1980s) Dr. Robert Oliveira, who was then at 3M company in Minnesota was looking for a spin-off innovation that he could develop. Bob comes from the biochemistry side of science and was rather new to hearing and hearing protection.  The 3M company (in conjunction with the Cabot company) of course at the time was playing with the now-famous yellow colored EAR earplugs that are made from compressible polymeric foam that springs back to its original state when the compression force is removed.  That in itself was an amazing innovation that we take for granted today.  But the interesting thing is that when one drilled a hold down the main bore length-wise, in an attempt to couple or join an earphone, the earphone fell out of the ear.  Did I also mention that Dr. Oliveira developed the first FDA approved cochlear implant?

Dr. Oliveira tried drilling smaller and smaller holes, in hopes that he could obtain a friction fit that would provide enough “grab” onto the insert earphone shank. This did work somewhat but every time the foam plug was rolled up and squished to be placed in the ear canal, the earphone because lose.


It turns out that when the compressible foam is squished and rolled up, the internal diameter of the hole increases. To this day, I find this very counter-intuitive even though the mechanics and physics has been explained to me many times.  If you are skeptical, simply do the experiment.  Drill a longitudinal hole about 2.5 mm in diameter down the main sound bore and then place a piece of #13 hearing aid tubing through the earplug.  This size of hearing aid tubing has an outer diameter of about 3 mm (and an internal diameter of just under 2 mm) so the 3 mm diameter tube should fit very snugly into a 2.5 mm diameter drilled hole.

Now this is where my intuition goes to pot. Roll up the foam and compress it just as you would when you want to place it in your ear- the #13 hearing aid tubing is now loose in the hole and will fall out.  Compressing the outside of the foam will make the inside hole larger!  Well, so much for my intuition.

It was this discovery that allowed Dr. Oliveira to be able to patent the idea that “we should glue the tube to the inside of the foam plug” and indeed he did this with a series of patents in 1986.

Since patents have a 20 year lifespan, they were valid until 2006 and I assisted Dr. Oliveira as an expert witness in a trial in the late 2000s when another company tried to use the same idea from 2001-2005. (Incidentally Dr. Oliveira and Hearing Components, Inc. won the case).

Glue is a wonderful substance and without it, we would not be able to have insert earphones for pure tone or ABR testing, or for use with listening to music with insert foam earpieces.


About Marshall Chasin

Marshall Chasin, AuD, is a clinical and research audiologist who has a special interest in the prevention of hearing loss for musicians, as well as the treatment of those who have hearing loss. I have other special interests such as clarinet and karate, but those may come out in the blog over time.