AES San Francisco 2008
Paper Session P5
Audio Equipment and Measurements
Friday, October 3, 9:00 am — 11:30 am
: John Vanderkooy
, University of Waterloo - Waterloo, Ontario, CanadaP5-1 Can One Perform Quasi-Anechoic Loudspeaker Measurements in Normal Rooms?
—John Vanderkooy, Stanley Lipshitz
, University of Waterloo - Waterloo, Ontario, Canada
This paper is an analysis of two methods that attempt to achieve high resolution frequency responses at low frequencies from measurements made in normal rooms. Such data is contaminated by reflections before the low-frequency impulse response of the system has fully decayed. By modifying the responses to decay more rapidly, then windowing a reflection-free portion, and finally recovering the full response by deconvolution, these quasi-anechoic methods purport to thwart the usual reciprocal uncertainty relationship between measurement duration and frequency resolution. One method works by equalizing the response down to dc, the other by increasing the effective highpass corner frequency of the system. Each method is studied with simulations, and both appear to work to varying degrees, but we question whether they are measurements or effectively simply model extensions. In practice noise significantly degrades both procedures.
Convention Paper 7525 (Purchase now)P5-2 Automatic Verification of Large Sound Reinforcement Systems Using Models of Loudspeaker Performance Data
—Klas Dalbjörn, Johan Berg
, Lab.gruppen AB - Kungsbacka, Sweden
A method is described to automatically verify individual loudspeaker integrity and confirm the proper configuration of amplifier-loudspeaker connections in sound reinforcement systems. Using impedance-sensing technology in conjunction with software-based loudspeaker performance modeling, the procedure verifies that the load presented at each amplifier output corresponds to impedance characteristics as described in the DSP system’s currently loaded model. Accurate verification requires use of load impedance models created by iterative testing of numerous loudspeakers.
Convention Paper 7526 (Purchase now)P5-3 Bend Radius
—Stephen Lampen, Carl Dole, Shulamite Wan
, Belden - San Francisco, CA, USA
Designers, installers, and system integrators, have many rules and guidelines to follow. Most of these are intended to maximize cable and equipment performance. Many of these are “rules-of-thumb,” simple guidelines, easy to remember, and often just as easily broken. One of these is the “rule-of-thumb” regarding the bending of cable, especially coaxial cable. Many may have heard the term “No tighter than ten times the diameter.” While this can be helpful, in a general way, there is a deeper and more complex question. What happens when you do bend cable? What if you have no choice? Often a specific choice of rack or configuration of equipment requires that cables be bent tighter than that recommendation. And what happens if you “unbend” a cable that has been damaged? Does it stay damaged or can it be restored? This paper outlines a series of laboratory tests to determine exactly what happens when cable is bent and what the reaction is. Further, we will analyze the effect of bending on cable performance, specifically looking at impedance variations and return loss (signal reflection). For high-definition video signals (HD-SDI) return loss is the key to maximum cable length, bit errors, and open eye patterns. So analyzing the effecting of bending will allow us to determine signal quality based on the bending of an individual cable. But does this apply to digital audio cables? Does the relatively low frequencies of AES digital signals make a difference? Can these cables be bent with less effect on performance? These tests were repeated on both coaxial cable of different sizes and twisted pairs. Flexible coax cables were tested, as well as the standard solid-core installation versions. Paired cables consisted of AES digital audio shielded cables, both install and flexible versions, were also tested.
Convention Paper 7527 (Purchase now)P5-4 Detecting Changes in Audio Signals by Digital Differencing
, Liberty Instruments Inc. - Liberty Township, OH, USA
A software application has been developed to provide an accessible method, based on signal subtraction, to determine whether or not an audio signal may have been perceptibly changed by passing through components, cables, or similar processes or treatments. The goals of the program, the capabilities required of it, its effectiveness, and the algorithms it uses are described. The program is made freely available to any interested users for use in such tests.
Convention Paper 7528 (Purchase now)P5-5 Research on a Measuring Method of Headphones and Earphones Using HATS
—Kiyofumi Inanaga, Takeshi Hara
, Sony Corporation - Tokyo, Japan; Gunnar Rasmussen
, G.R.A.S. Sound & Vibration A/S - Copenhagen, Denmark; Yasuhiro Riko
, Riko Associates - Tokyo, Japan
Currently various types of couplers are used for measurement of headphones and earphones. The coupler was selected according to the device under test by the measurer. Accordingly it was difficult to compare the characteristics of headphones and earphones. A measuring method was proposed using HATS and a simulated program signal. However, the method had some problems in the shape of ear hole, and the measured results were not reproducible. We tried to improve the reproducibility of the measurement using several pinna models. As a result, we achieved a measuring platform using HATS, which gives good reproducibility of measured results for various types of headphones and earphones and then makes it possible to compare the measured results fairly.
Convention Paper 7529 (Purchase now)