An audiometer is a machine used for evaluating hearing loss. The invention of this machine is generally credited to Dr. Harvey Fletcher of Brigham Young University. Audiometers are standard equipment at ENT clinics and in audiology centers. They usually consist of an embedded hardware unit connected to a pair of headphones and a feedback button, sometimes controlled by a standard PC. Audiometer requirements are specified in IEC 60645, ISO 8253, and ANSI S3.6 standards.
An alternative to hardware audiometers are software audiometers, which are available in many different configurations.
Screening PC-based audiometer These use a standard computer and can be run by anybody in their home to test their hearing, although their accuracy is not as high due to lack of a standard for calibration. Some of these audiometers are even available on a handheld Windows driven device.
Clinical PC-based audiometer These are generally more expensive than hardware audiometers, but are much more accurate and efficient. They are most commonly used in hospitals, upper-class audiology centers and research communities. Due to the fact that these audiometers can be calibrated to 1/10 of a dB, calibration is more accurate than hardware audiometers. Some audiometers even provide you with a software developer's kit that provides researchers with the capability to create their own diagnostic tests.
-  National Physics Laboratory Guidelines on Audiometric Calibration
- MedlinePlus Encyclopedia 003341
- Department of Communication Disorders at BYU - Audiology department at BYU