Prior to the invention of electrically powered amplifiers, persons with hearing loss relied on mechanical devices to to direct and amplify sound. This image to the left shows a page from a 1904 Sears Catalog depicting a variety of devices available at that time.
You don't have to shop for antiques on Ebay to find a passive sound amplifier. In the early 21st century, Earglasses, which are similar in concept to the auricles pictured in the Sears Catalog, became available. I purchased a pair from one of those catalogs that are mailed to every residence within a particular zip code. The Earglasses are shown here in the original ad.
An honors student in Speech-Language-Hearing Sciences who was enrolled in my Hearing Science course signed up for an honors contract to measure the effectiveness of the Earglasses.
She worked with a graduate student in Audiology to make measurements using a hearing aid test box. The hearing aid test box generated a wideband sound that was produced by a speaker. This is how the effectiveness was tested.
1. A small microphone placed near the eardrum of a subject to measure sound level in one ear.
2. The loudspeaker generating a wideband sound was rotated 360 deg (azimuth) around the subject's head while the sound pressure level was measured. These measurements were made with and without the Earglasses.
3. The difference in level (in dB) between what was measured with and without the Earglasses represents how sound was changed by the Earglasses.
4. The plots below show the results for two azimuths. The 0 deg plot (upper figure) was obtained with the speaker about 1 meter from the subject's head and directly in front of him. A useful device would amplify the sound yet there is very little difference in dB between the two conditions (with and without Earglasses). The lower plot shows results from 180 deg, directly behind the person. Sound was reduced a few dB in the high frequencies and not at all in the low frequencies (this is expected because the wavelength at low frequencies is longer and can wrap around the device). Although this is a favorable oucome, the difference in dB is small.
We concluded the a wearer of Earglasses would probably not experience meaningful changes in their ability to communicate.
As the inventor of Earglasses™ I must disagree with your "damn with faint praise" summary of the benefits of my hearing assistance device. The results that your student measured match closely with the more sophisticated measures derived by the testing labs I employed. The BENEFIT of that "modest" gain can be heard in a demonstration I posted at http://www.earglasses.com/demo.htm
Incidentally, I've received unsolicited letters of thanks and effusive praise from hundreds of users among the hundred thousand customers we served while we still marketed the former product.
I suspect that my passive device produced greater satisfaction rates among those with mild to moderate hearing losses than the typical electronic aid. After all, six out of seven purchasers of even digital hearing aids still wind up setting them aside after a few months of frustrated efforts to get satisfactory results.
Posted by: Mike Riley | 11/10/2010 at 11:54 PM
This is interesting I've never encountered an "earglass" before!
Posted by: hearing solutions | 04/19/2012 at 01:12 PM