This article will explain how to read a hearing aid specification sheet in general, easy to understand terms. The information was original written for a mother who posted to a newsgroup requesting help. This information has been requested numerous times by other hearing aid users since then, and so we decided to post it as a brochure. Although some of the information is specific to this child's hearing aid, most of the information can be applied to other hearing aids.
Q: I am trying to understand the specification sheet for my 3yrs old daughter's hearing aids, can you tell me what each item means?
A: The model is a "Super-Front PP-C-4"
The PP means push pull. This is a means of amplifiying sounds to higher intensities with less distortion.
The C =compression. This is a limiter for how loud the hearing aid can make sounds. The audiologist can adjust the maximum amount of sound that the hearing aid can produce.
The 4 is how many adjustment controls are on the hearing aid.
SSPL 90: 140dB SPL
This is the most amount of sound that the hearing aid will make. It means that if we put a 90 dB (decibel, or unit of loudness) sound into the hearing aid, 140 dB will come out of the aid. 90dB is a very loud sound and will test the limits of the aid. SPL=Sound Pressure Level. SPL is just a unit of reference for the decibel.
HF Average SSPL 90: 132dB SPL
This is the average level of just the high frequencies with the same 90 dB of input as listed above.
HF Average Full-on Gain/Input 50dB SPL: 70 dB
This is the High Frequency average of the amount of gain (increase in volume) with a 50 dB input sound and the volume control set to maximum. In other words, if I set the volume to maximum and put in 50 dB of sound, then 70 dB of increased sound will be added in the high frequencies.
Reference Test Gain: 55dB
This is the average of the amount of gain (increase in volume) when a 50 dB input sound and the volume control set to approximate the users level. In other words, if I set the volume to the level that your daughter will probably wear it and put in 50 dB of sound, then 55 dB of increased sound will be added (avg).
Frequency Response Range with setting
These tell you over what pitches the hearing aid will amplify sound. LC is low cut and HC is high cut. The nembers 0 through 8 are different settings from no reduction of gain to maximum reduction of gain. The audiologist will set the LC and HC adjusters so that the aid matches the shape or configuration of your daughters hearing loss.
THD at 500Hz: < 6.5%
THD at 800Hz: < 2.5%
THD at 1600Hz: < 1.5%
These are tests of Total Harmonic Distortion. It tells you how well the aid is able to reproduce sound clearly. The higher the level of THD the more distorted the sound will be.
Battery Current Drain: 3.3 mA
This is telling you how fast the battery will go dead. We know how much storage a battery has and so if we find out how fast the hearing aid will drain that storage, we know how long a battery should last.
Induction Coil Sensitivity: 126 dB SPL
This tells you how well the induction coil (telephone or t-coil) works. The induction coil allows a person to use a telephone or other assistive devices via electro-magnetic fields instead of the regular microphone. This prevents whistling (feedback) and also it will prevent sounds from the surronding room from interfering with the sound from the telephone. Since your daughter is 3 years old, the telephone is not the only thing that she can use the induction coil for however. Many schools, churches and other social places have a special setup that allows a hearing aid wearer to choose the t-coil setting while wearing a small induction loop, thereby eliminating the room noise and focusing on hearing a person wearing a microphone instead.
This article was submitted by:
Glen R. Meier, M.S., CCC-A, FAAA