AES San Francisco's July, 2004 meeting was held at Plantronics Inc., in Santa Cruz, California.
Fifty people attended.
The speakers were Steve Burson, Osman Isvan, and Allen Woo. Their titles are: VP of Development and Technology, Sr. Acoustics Engineer, and Principle Acoustics Engineer, respectively.
Plantronics designs and manufactures lightweight communications headsets. Millions are in use. Uses include telephones, aviation, gaming and entertainment.
Headsets seem like simple devices. On investigation they are surprisingly complex.
Steve Burson gave an overview of Plantronics' philosophy, and described its capabilities. Plantronics has comprehensive acoustic test and measurement facilities at its company headquarters.
The company has several hundred employees in Santa Cruz, California, and about three thousand
world wide.Osman Isvan talked about methods for characterizing headsets. The main criteria are: audio quality, sensitivity
, frequency response, linearity, quiescent noise, and ambient noise cancellation.Plantronics uses advanced methods for headset testing. A Head and Torso Simulator (HATS) imitates the human body acoustically, from the waist up. A pinna coupler simulates the size, shape and consistency of the human ear. The pinna is the part of the ear that projects outside the body.
Ear size and shape varies from person to person, creating problems for designers. Fit affects the audio experience considerably. Plantronics has more than four hundred unique ear moldings, to find the best compromise.
The human ear is a complex structure. Test results vary greatly, depending on which reference point they represent. The ear Drum Reference Point (DRP, next to the ear drum), the Ear Reference Point (ERP, a point located in the pinna), and various points in the free field, are commonly used reference points.
The combination of the ear canal and pinna has about 17 dB acoustic gain, at 2.8 kHz, when no headset is present.
Allen Woo spoke about headset hearing safety.
Bad design presents the risk of hearing damage. Users are tempted to listen at higher levels, through headsets or headphones, than would be acceptable from free-air sources. It is important to design headsets or headphones, that protect the user's hearing.
There are several regulations for hearing protection. They include the OSHA (Occupational Safety and Health Administration) standards in the USA, and the European Directive in the EU. All current safety regulations refer to the free field. The regulations have to be interpreted to test reference points, on or inside the ear, before being applied to headsets or headphones. Allen Woo serves on several committees, which are developing safety standards for headsets and headphones.
by Paul Howard