Audiologists in Industry – Wayne Staab Part 8

Early Industry Audiology Pioneer Involvement

Previous blogs related to my involvement as an Audiology Pioneer in the Hearing Aid Industry focused primarily on how I managed to enter this industry, and many of the initial trials that I, along with my colleagues at the time, had to endure as audiologists when we made this decision.

This blog will focus on some of the events and activities that I continue to recall from my first few years working for Telex Communications, a manufacturer of hearing aids.

My Knowledge About Hearing Aids Was Rapidly Enhanced

This new environment and position were exciting in that I learned so much in the first year that I abandoned my thoughts of considering my employment at Telex as a year of post-doctoral education.  I wanted to stay!

We had done much during the year, and there were so many continuing interesting projects that there was no way I was leaving.  Much of what I was doing was what audiologists should have been doing all along, and it was having a significant effect on the role audiology would play in the future within the communities of academia, clinical work, and the hearing aid industry.  Importantly, I learned about hearing aids – microphones, speakers, circuitry, breadboard testing, measurement, design, manufacturing, inventory, work in process, assembly techniques, soldering, heat sinks, repair issues and solutions.  But, I also learned about business – sales projections, cost of goods sold, budgets, overhead, etc.  In other words, I was now in the “real world,” and all actions had consequences.

I was extremely fortunate to have great colleagues to work with.  I was accepted fully and was never pressured into doing anything that would compromise my principles or professionalism.  This may have been due in part to the fact that Telex Communications was part of a larger diversified, but synergized product group in which we shared some of our engineering, management, and manufacturing facilities, rather than just hearing aids, and I was fortunate to be able to work with them on various projects as well.

I worked with the engineers in researching product needs, the development of new products, and how existing products could be improved.  It was an interesting, and often embarrassing experience to attempt to apply audiology knowledge to an actual product.  Even though I had been immersed and focused on hearing aids for a number of years, and believe that I knew more about them than most audiologists at the time, I know that those at the manufacturing end realized how little useful information I actually could apply to hearing aids.  Engineering rapidly taught me the difference between theory and reality.  Lessons learned were included in my many talks to audiologists.  I learned more about hearing aids in the first year working with a manufacturer than I had learned in my previous eight years working and training as an audiologist.

First Projects

A first project I was involved with was the implementation of the electret microphone into hearing aids.  This was followed closely by directional microphone hearing aids.  Both of these innovations were being introduced by all the leaders in the hearing aid industry.  I developed a new series of publications titled “The Telex Audiological Reports” that focused on hearing aids, wrote the audiometer manual and trade publication articles, and lectured throughout the country – not just to hearing aid dealer meetings, but also invited by state Speech and Hearing Association meetings.  These activities were later followed by the development of the first wireless CROS hearing aid and then the initiation of a new product line of FM auditory trainers to give Phonic Ear serious competition.  It was a busy time and I learned much from Harry Teder and his colleagues in engineering.  KEMAR was new and compression hearing aids were starting to make significant contributions to hearing aid performance.

Wireless CROS – An Entrée to Speaking Invitations

How few, if any people other than Harry Teder* and myself remember the origin of the wireless CROS hearing aid developed at Telex Communications Inc. in the early 1970s.  And, even then, we sometimes have to remind each other about what we have overlooked when recalling the events leading to its development.  For example, attached is an e-mail from Harry to me when I asked him to write up something on the Wireless CROS hearing aid.

Hi Wayne –

Finally, I FOUND the patent that describes the Radiant!  The patent number (3,125,646, applied 2-8-60, granted 3-64) was right at the end of my own 1976 article in HI, “Something New in CROS.”  Note that its date is BEFORE Harford described the CROS concept!  But it does describe a wireless link, even mentions a preferable carrier frequency range between 150 and 250 kHz.  Your memory was sharp and right on, mine not so much.  As the saying goes, “the ancients have stolen our inventions.”

 Harry

To set the stage, in the 1960s, eyeglass hearing aids were the latest thing in hearing aids.  As would be expected, the eyeglass portion was coupled to the ear via a polyethylene tube to an earmold placed in the concha of the ear.  An undesirable feature of eyeglass hearing aids was that the earmold had to be removed every time a person wanted to remove their eyeglasses.

Telex had developed a product in 1960 called the “Radiant” eyeglass hearing aid (patent issued in 1964).  A distinctive feature was that it eliminated the physical connection between the eyeglass temple and the earmold polyethylene tubing connection, and instead transmitted the amplified signal from the hearing aid body to the in-ear piece using amplitude modulation.  The eyeglass portion included 5 transistors and the earmold portion included a single transistor.  The product was relatively short-lived.  The transmitter in the temple broadcast to the in-ear receiver.

As the Classic CROS hearing aid became an accepted fitting option, the Radiant concept was reconsidered as a method to eliminate the wires passing from one ear to the other.  The real question related to the distance that the Radiant transmitter could send to the in-ear portion receiver.  Original discussion cast doubt as to whether it could transmit to the contralateral side and eliminate the wires required of CROS-type hearing aids.

The Wireless CROS According to Harry

This description of the wireless CROS development is paraphrased from Harry Teder’s writings and communications we had relative to this historic event.

The CROS concept was first described in a publication by Harford and Barry in 1965 {{1}}[[1]] Harford, E., & Barry, J. (1965).  A rehabilitative approach to the problem of unilateral hearing impairment: the contralateral routing of signals (CROS). Jour Speech Hear Disord, 30; 121-138 [[1]] and quickly became accepted as an effective solution for the hearing problems of the unilaterally hearing-impaired.  Placing a microphone on the non-functional side of the head was one of those “obvious once you know of it” ideas.  I believe these are the best, yet the most difficult inventions to come up with.  Even the simplest idea has to first occur to someone.

A clear example of this solution concept related to the Radiant patent issued to W. Lewis at Telex in 1964 {{2}}[[2]] Electromagnetically coupled hearing aid, Lewis, F.W., Patent No. 3,125,646, March, 1964[[2]], prior to Harford and Barry describing the CROS.  The patent described a radio frequency wireless link between a microphone in the temple of an eyeglass, and a hearing aid plus receiver in the ear, but on the same side.  It was not a CROS-type instrument.  The hearing aid was called the Radiant.  The benefit claimed in the patent was the elimination of a sound tube and of possible mechanical feedback caused by the microphone and receiver in the same housing.  It was designed for the user to be able to remove eyeglass hearing aids without having to remove the ear coupling from the ear.  Placing a microphone on the deaf side was not described – that concept had not occurred to anyone yet!

Telex Radiant Patent Drawings

The idea of designing a wireless CROS became an active project at Telex in 1974, nine years after the CROS had been described.  The wire connecting the two CROS sides had been a simple and inexpensive, but trouble-prone weak point of the concept.  I do not recall whether the 1964 patent provided the initial impetus for the project, but our patent attorney assured us the Radiant patent would protect the new design, as being “obvious the those skilled in the art”.  Why, of course!

In 1975, Telex Communications introduced the first wireless CROS – the eyeglass model 400.  Its basic wireless concept was untried and unproven.  It had to communicate over a 5-6 inch distance, a lot further than the 1964 design of an inch or two.  In case things did not work out, we minimized tooling investment by using the plastic housing of an obsolete eyeglass aid.  The electrical circuit was a new design approach – something that had not been attempted.  The “unknown-unknowns” were worrisome.  In practice, it proved to be a trouble-free and unique product in a very competitive marketplace.  Not a barn-burner (not that many CROS aids were fitted!), it was, nevertheless, a satisfying success that remained unique for a long time.

Telex 400 wireless CROS hearing aid

This many years later, I’m still impressed with the clever combination of concepts that my two associates built into the little radio transmitter-receiver that signaled across the head, but not much further. Bill Kinghorn and Bob Werner reasoned that inductive coupling similar to the telecoil principle would work, but what radio frequency to use?  It should be a frequency that would not be present in common, everyday environments.  Perhaps we could find a frequency that was rarely used and then only in known, fixed locations.  Inductive radiation weakens very quickly with distance, thus our own signal would be unlikely to cause interference with anything, except maybe another wireless CROS wearer; an unlikely occurrence.

An aviation service called Non-Directional Beacon (NDB) operated at that time over the 190 kHz to 270 kHz band.  As far as I know, it still exists, but currently is rarely, if ever used.  Intended for aircraft navigation, it had low-power transmitters at many airports, continuously transmitting a fixed Morse code letter.  The Minneapolis area had no station at 225 kHz, so we selected that frequency.  As a result, one might think that when near airports the hearing aid would pick up an interfering signal.  Not so.  We certainly worried about it, but finally concluded that our receiving coil antenna was so tiny, 1 inch long, that the coil was picking up virtually no radio energy to speak of.  This is because radio antennas work best when their dimensions are roughly comparable to the wavelength of the operating frequency.  One inch is obviously miniscule compared to the 4700 feet of 225 kHz!

We also wondered about the long wave broadcast band, still popular in Europe at that time.  Not that we expected to sell many aids in Europe, but still…  I was going on a business trip to Europe that Fall and carried an early prototype, carefully listening for the high powered long wave station in Poland that sat exactly on our 225 kHz frequency.  I never heard a peep from any such transmitters from Paris to Gotheburg in Sweden.  Another issue laid to rest.

Radio Station or Hearing Aid?

A strong concern was how the Federal Communications Commission (FCC) would look at our product that, after all, was sort of a radio station.  My memory is hazy on the details, but I seem to recall an informal approach to the FCC lab engineers explaining our product.  Their first reaction was that we would need a broadcast license for every hearing aid!  Appalled, we appealed to their engineering common sense, pointing out how it was not really a transmitter but an induction coil; how our measured field strength at 2 feet distance was so weak it could not be separated from normal urban background noise at night.  I believe the issue just kind of went away, without an official pronouncement being made.

The receiver for the better ear side had to be simple – no integrated circuits for this purpose were available yet.  The fellows went back to some old textbooks to find a simple but novel AM receiver schematic, and it worked just fine.

Why AM versus FM?

We were asked, often, why we had not used FM instead of AM.  FM is more immune to interference than AM, but that is only true for wide band FM.  For hearing aid purposes, we only needed about 5 kHz bandwidth for interference avoidance that would be not much better than AM. Furthermore, an FM receiver is much more complicated, thus more expensive and space consuming.  We had to work with discrete transistors and components and AM did the job.  Overall, we had very few complaints of interfering noise, just an occasional mention of a microwave oven being audible is all I can recall.

For test box measurements, the RF link required some specific precautions, but the test system manufacturers rose to the challenge and it all worked out.  As a sidelight, the Knowles KEMAR mannikin had an aluminum plate that sat exactly where the CROS receiver coil was, totally cutting off the signal.  Minor “brain surgery” by cutting off a corner of the plate took care of the problem.

The success of the model 400 encouraged us to replace it with a newly tooled eyeglass housing, somewhat smaller and more modern, and introduce a BiCROS version as well. This was followed by a BTE version, and eventually with an ITE receiver with a BTE transmitter.  For over 25 years, the Telex wireless CROS system was successful and unique in the market.

Several years after I retired in 1994, the CROS product line was sold to Phonak, Telex management apparently not knowing what to do with it.  The new owners (and other companies) have since introduced more advanced, sophisticated CROS designs, in keeping with hearing aid technology that has advanced greatly in recent years.  Today, hearing aid circuitry has become universally digital; sophisticated wireless designs (both Wi-Fi and Bluetooth) are available, as is FM.  FCC has now set aside a dedicated frequency band for assistive listening devices.  There has been amazing progress in hearing aid design in recent years, but looking back, I’m still pleased with the fun and success we had with the simpler technologies of those days!

*Harry Teder was the Chief Engineer of the hearing aid division of Telex Communications Inc. from 1969 until retiring in 1994, and for many years the Chairman of the HIA Technical Committee.  He graduated from Dartmouth College with an AB degree.