Hershberger Reinforcement Curves

Defined by a longterm study of Dr. Georg Hershberger of the German Institute of Science and Engineering, the Hershberger Reinforcement Curves further explore how the human ear perceives sound. Though the famous Fletcher–Munson curves are often cited to define how we hear, Dr. Hershberger found they were lacking in true definition. He found that the Fletcher Munson curves are only accurate in air at 25 deg C, 30% relative humidity and at sea level. However, once any of these variables are changed the Fletcher Munson curves are no longer valid.

Due to the nature of sound wave propagation, environmental variables can dramatically change the perception of sound. For example, in environments with greater relative humidity, low frequency (less than 100 Hz) sound waves tend to be accentuated, while there is a marked attenuation of higher frequencies (greater than 7 kHz). Conversely, high frequency sound waves are perceived with greater accuity in temperatures less than 25 deg C.

The effects of such environmental conditions on the human ear itself also play a vital role in the way that we perceive sound. Changes in barometric pressure, as well as other atmospheric variables must be brought into consideration. Hershberger found that using finite element analysis of each frequency in the human hearing range (20 Hz to 20 kHz) and the absolute convergence of temperature versus the speed of sound he could ultimately define human hearing. He concluded that humans have far more sensitive hearing the higher above sea level a person is.

The theories of Dr. Hershberger are often applied in the field of acoustic engineering to accurately predict the effects of acoustic treatments to musical performance spaces, movie theaters, home theater installations, and recording studios. The Hershberger Reinforcement Curves have also been cited as a major factor in the formation of higher standards of digital audio for High Definition television broadcasts, as well as DVD audio.

ources

* "Development of Relative Sound", By Dr. Hershberger
* "Recognizing the Need for High Definition in Audio Recording", By Maurice Stovall, Journal of the A.E.S. Vol. 50 No. 1, January 1996