# My new $25 Auditory Neuropathy/Dys-synchrony Sniffer (Madsen ZS76 Tympanometer) This is a two-part story on me scoring a working clinical tympanometer for$25… And why it’s such a valuable tool for both detecting  Auditory Neuropathy Spectrum Disorder, and also for adjusting & troubleshooting hearing aids.¹

One of the big mistakes I made when I closed my hearing aid dispensing lab in 1995 was letting go of my Rexton I-28 tympanometer (impedance bridge), as it was providing valuable auditory neuropathy/dys-synchrony diagnostic information — But I didn’t recognize it at the time… Nor in fact, did almost anyone else in the hearing care profession.  More on this in an upcoming article on auditory neuropathy spectrum disorder.

So, recognizing the need to add a clinical tympanometer back into my arsenal against hearing loss, I had been combing the pages of eBay for another I-28, or maybe something a bit newer (and nicer), to find something that I could properly test stapedial reflex thresholds again. (These are also called middle ear muscle reflexes or acoustic reflexes.) Besides searching for tympanometer  I was also combing through impedance  looking for a mis-labeled bargain, when this gem popped up:

Madsen Impedance Audiometer ZS 76 1B (click to enlarge in a new window)

Headset from Madsen Impedance Audiometer ZS 76 1B (click to enlarge in a new window)

Well, I’m an Electrical Engineer, and I figured that if the seller couldn’t figure out how to use it (there was no manual), there was a either a chance that it indeed worked, or that if it wasn’t working, at least I could use my voltmeter & ‘scope to take a shot at fixing it. Well, guess what folks? It works! So, all that is left to do is get a 1.0 cm³ calibrator cavity (or have my machine shop make one), get some eartips, and I’m off to the races. There is one modification I’ll most likely add: Although I don’t test infants, the 226 Hz probe tone has too long a wavelength to use for tiny ears, so I’ll splice in a 1000 Hz oscillator, to give me that capacity.

Not too shabby for a total of \$39.52, including shipping to my door.

Bootnote:
1) Now, about my statement on  using a tympanometer for adjusting & troubleshooting hearing aids: As it turns out, one trick taught to me many years ago (I think it was by the late Sam Lybarger) is to measure the acoustic reflex thresholds, and use those figures to set the instruments’ SSPL-90 (now called MPO), on the theory that you don’t want to have the hearing aid output constantly triggering the stapedial reflex, as it is tiring to the patient. The fact that this is now being done to set C/M levels on CI’s for infants & others who can’t report back, as described here by my friend Ed Overstreet PhD, appears to validate this tried-and-true concept~

##### Dan Schwartz

Electrical Engineer, via Georgia Tech