v7.0, 20040922, me
Saturday, October 30, 11:00 am 12:30 pm
Session L INSTRUMENTATION AND MEASUREMENT
Chair: Eric Benjamin, Dolby Laboratories, San Francisco, CA, USA
L-1 Determining the Peak Sound Level Capability of Loudspeakers and Sound SystemsBill Waslo, Liberty Instruments, Inc., Liberty Township, Ohio, USA
One of the more relevant characteristics of a sound system is the maximum level at which it will function in its intended environment before the output becomes objectionably distorted. Because of design, construction, or thermal limitations, this characteristic can vary with both the frequency content and the duration of the applied stimulus at each measurement. Further complicating distortion measurement is the variation in frequency response due to reflections in the environment. This paper describes an automated technique using shaped tone-bursts under software control to generate the stimuli, acquire the responses, process and correct the data for room response, and present a graphical representation of the peak sound level capability versus test frequency. Also described is a novel technique for separating noise and distortion energy from stimulus energy in an in-room measurement.
Convention Paper 6267
L-2 Plane Wave TubesUses and LimitationsMarshall Buck, Psychotechnology, Inc., Los Angeles, CA, USA
The use of a plane wave tube (PWT) is standard practice for the testing of audio compression drivers, as the damped tube provides an acoustic impedance load for the driver that is similar to an infinitely long horn of the same throat diameter. When properly terminated, it is anechoic. Uses of plane wave tubes for compression driver testing include: (1) Frequency response measurements, (2) distortion measurements; (3) coherence measurements; (4) power testing; (5) power compression testing; (6) listening tests; and (7) driver impedance measurements. The use of a PWT does not replace testing a driver on a horn in an anechoic environment; it is an adjunct to it. A construction method is described that provides an effectively terminated PWT. A calibration method is described that can be used to assure that the anechoic response of a PWT is within a stated error level. Various microphone locations are evaluated for performance of frequency response and distortion. Error analysis is provided based on modal calculations and experimental data.
Convention Paper 6268
L-3 Measurement of Audio Equipment with Log-Swept Sine ChirpsThomas Kite, Audio Precision, Beaverton, OR, USA
The log-swept sine chirp provides a way to measure the transfer function and harmonic distortion of an audio device simultaneously. A deconvolution operation separates the linear and nonlinear responses in time. Results on real audio equipment are compared to classical methods and found to agree. An extension for simultaneously measuring crosstalk is suggested.
Convention Paper 6269