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Abhijit Kulkarni is the first author, with H. Steven Colburn, of a 2000 study measuring variability in the headphone transfer function. Repeated placements on the KEMAR acoustical manikin changed the measured response, making it difficult to choose one inverse filter that reliably canceled the headphone contribution.^[ref]

The method supplies a clear example of measurement reproducibility. Repeating a measurement after removing and replacing the apparatus tests a different source of variation from repeating it without disturbing anything. The study identified the physical coupling of headphones to the ear region as part of the experimental system, rather than assuming an electronic input alone fixed the acoustic output.^[ref]

Headphones are electroacoustic transducers worn at or near the ears that convert an electrical signal into local acoustic pressure variations. A two-channel pair can deliver different signals to the two ears. The relevant output is the sound pressure reaching the ear, which depends on the transducer, its placement and the surrounding acoustic geometry, not just the electrical input.

For a linear small-signal description, let $V(f)$ be the input electric potential difference and $p(f)$ the complex pressure amplitude at a specified ear location. A headphone transfer function $H(f)=p(f)/V(f)$ describes both amplitude and phase. Two headphones can receive the same $V(f)$ yet produce different $p(f)$; even the same pair can produce different responses after being repositioned.^[ref]

Abhijit Kulkarni and H. Steven Colburn measured responses on a KEMAR acoustic mannequin with repeated placements of the headphone cushions. Placement-dependent variation complicated compensation by a fixed inverse filter. This experiment shows why a measurement needs a defined coupling arrangement: moving the device can change the acoustic system being calibrated.^[ref]

For an illustrative amplitude example, if pressure doubles at a particular frequency while the reference pressure is unchanged, sound pressure level increases by $20{\log }_{10}2\approx 6.02$ decibels. That is a statement about pressure at the measurement point; it is not automatically a doubling of perceived loudness or a uniform change across frequencies. Headphone reproduction is therefore an electrical-to-mechanical-to-acoustic chain that must be assessed at its intended output location.

H. Steven Colburn is a researcher in auditory science and a coauthor with Abhijit Kulkarni of a 2000 study of headphone transfer function measurements. Using the KEMAR acoustical manikin, they repeatedly repositioned headphones and measured how their frequency response changed. This isolated placement variability while retaining the same experimental head and headphone system.^[ref]

A compensation filter based on one placement can become inaccurate after the cushion moves. The experiment therefore distinguishes a nominal device description from the sound actually delivered at the measurement point. That distinction matters when a hearing experiment depends on a precisely specified acoustic stimulus.^[ref]

KEMAR, the Knowles Electronics Manikin for Acoustic Research, is a head-and-torso acoustic simulator used to measure how sound interacts with an approximately human-sized listening geometry. Its external ears, ear-canal system and acoustic loads make it more informative for many hearing-device tests than a microphone placed alone in free space. The manufacturer's description specifies representative adult dimensions and ear-simulation properties. ^[ref]

An original manikin paper by M. D. Burkhard and R. M. Sachs appeared in 1975. Later studies used KEMAR to investigate device coupling as well as the surrounding sound field.^[ref]

For example, Abhijit Kulkarni and H. Steven Colburn repeatedly placed headphone cushions on a KEMAR and measured the resulting headphone transfer function. Repositioning changed the response, complicating compensation by a single fixed inverse filter. The experiment demonstrates that the ear–device interface is part of the acoustic system, rather than an incidental mounting detail.^[ref]

An invented measurement comparison makes the meaning concrete. If the same electrical drive produces pressures of 0.020 and 0.010 pascal at one measurement frequency in two fittings, their sound pressure levels differ by $20{\log }_{10}2\approx 6.02$ decibels. This is a fit-dependent response difference at a specified point, not an automatic judgment of perceived loudness or device quality.

A standardized manikin supports reproducible comparisons but does not reproduce every listener's ear geometry, physiology or perception. Conclusions should specify the simulator configuration and measurement conditions.