TR a-Acoustic Impedance of Ear Simulators

This contribution consists of a brief PowerPoint summary of the following complete documents: TR b-Acoustic Impedance Measurements B&K 2005.pdf TR c-Acoustic Impedance Measurements B&K 2001.pdf TR d-Equivalent Volumes of Ear Simulators B&K 2001.pdf

Why does the acoustic impedance of an ear simulator matter? “The fundamental purpose of an ear simulator is to test a receiver under conditions that most closely approximate actual use by real persons.” IEEE Please see next slide for illustration...

pSpS ZSZS Receiver ZEZE pEpE Ear Simulator Simplified Equivalent Circuit of Receiver & Ear Simulator High impedance source: Z S >> Z E and q  constant, so p E  Z E qq p S = source pressure p E = pressure at ear q = acoustic “current” Z S = source impedance Z E = ear impedance Low impedance source: Z S << Z E, so p E  constant pepe qq pepe qq

IEEE/STIT: B&K 2001 Volumes of Historical Couplers Except as noted, equivalent volume of most couplers is about 6cc Volume of Type 3.4 is larger mostly due to a larger concha.

The Impedance Probe in Use IEEE/STIT: B&K 2001

Acoustic Impedance of 5 Human Ears at “Normal” force, with Parametric Average Human Parametric Average IEEE/STIT: B&K 2001 Note variation in real ears !! Notice M2 – average about 210dB at about 2.4kHz

Acoustic Impedance of Type 3.3 vs Human Average Human IEEE/STIT: B&K 2001 M2 of Type 3.3 is about 212dB at 2.6kHz

Acoustic Impedance of Type 3.4 vs Human Average Human IEEE/STIT: B&K 2001 M2 of Type 3.4 is about 206dB at 2.6kHz

Research & Graph: B&K 2005 Acoustic Impedance Measurements New Procedures

Acoustic Impedance of 10 Human Listeners Impedance measured with probe in form of cell phone. Subjects held probe in natural position, without further instruction, as they would normally hold a phone. Positions were generally different from HATS. Although the probe was held in positions different from HATS, 1.The “natural position” curves are well-grouped, considering human variation 2.Type 3.3 “35”pinna in HATS position at 10N simulates the group average well Research & Graph: B&K 2005 Note variation in real ears !! Notice M2 of Type 3.3 – about 210dB at about 2.5kHz M2

Conclusions: Human-like leakage is simulated by Type 3.3 or 3.4 Leakage is force and/or position dependent Both types generally require more handset force than humans use for equivalent leakage Acoustic impedance of M1 is similar Acoustic impedance of M2 is different Type 3.3 M2 is similar to humans Type 3.4 M2 is lower, generally resulting in underestimate of receiver response around 2.5kHz (most receivers) Comparison of Type 3.3, with Shore 35 Pinna, and Type 3.4