Current ANSI Research Articles

Anechoic wedge design and development/anechoic chamber qualification testing

The initial research conducted at Harvard University’s Electro Acoustic Laboratory for the development of the anechoic chamber will be reviewed in this presentation. These findings, which were originally presented in the Office of Scientific Research and Development National Defense Research Committee Report No. 4190 (OSRD, No. 4190), will be discussed. The research conducted by Leo L. Beranek and his colleagues during WWII established the basic design and construction for anechoic wedges and chambers for years to come. Contemporary design and materials used in anechoic wedge construction have evolved to encompass a variety of room acoustic treatments, to include fiberglass, foam, and metallic wedges. Design and construction of current commercially available chambers and wedges will be reviewed. The second half of the presentation will focus on the development of anechoic and hemianechoic chamber qualification procedures to current ISO and ANSI standards. The use of various sound sources will be discussed as well as the correlation between these standards and other test methods in determining chamber performance.

Proposed maximum permissible exposure limits for ultrashort laser pulses.

Recent studies have provided considerable ED50 data for both visible and near infrared wavelengths from single laser pulses below one nanosecond of exposure. The current ANSI Z136.1 standard does not offer an approved maximum permissible exposure limit for subnanosecond single laser pulses and the current suggested maximum permissible exposure limit may be overly conservative. Lacking an approved standard industrial, medical, educational, and military uses of these types of laser systems may be limited or prohibited. A new set of laser maximum permissible exposure limits for subnanosecond visible and near infrared single laser pulses is recommended, along with the steps taken to develop the proposed standard.

Reverberation room qualification using the m-sequence as multitone signals

There is a revised interest in replacing the time-consuming and burdensome methods in the current ANSI and ISO standards for qualifying reverberation rooms for sound power measurements of discrete frequency sources. With the advent of digital signal processing, a combination of a deterministic multitone test signal and an FFT routine could be used to perform a fairly quick qualification test. A more elegant method using the m-sequence as the deterministic multitone signal has been tested in the IRC/NRC laboratory. This method has the advantage that it is relatively immune to external background noise so that the near field response of the test loudspeaker could be determined outdoors without using an anechoic room. In addition, all the required frequency components in the different one-third octave bands can be obtained in one single measurement. A detailed description of the procedure and results obtained will be presented.

Analog and digital signal processing in a high-performance miniature sound-level meter

The design of a relatively low-cost Type 2 pocket-size sound-level meter with an embedded 8-bit microcontroller is described. The key design goal was to provide 110 dB of dynamic range without the need for user-controlled range switching. The miniature instrument meets all the current ANSI S1.4-1983 (R 1990) and IEC 651 (1979) sound-level meter standards. Relevant features in the future IEC 1672 sound level meter standard, such as level linearity, tone-burst response, over-range and under-range indication, measurement accuracy, and resolution are reviewed. Due to judicious separation of the functions performed by analog and digital hardware and software, the wide dynamic range is implemented with only 8 bits of A–D conversion. Extensive type testing confirmed that the instrument can satisfy the requirements of the standards over the required temperature range. [Work supported by Etymotic Research, Elk Grove Village, IL.]

Comparison of WG11 study variability to that of other interlaboratory studies

The variability of the data measured in the WG11 interlaboratory study was compared with that measured in three other interlaboratory studies conducted in this country, in Europe, and in the Scandinavian nations. All studies utilized a real‐ear attenuation at the threshold measurement paradigm and basically followed the procedures described in the current ANSI and ISO hearing protector measurement standards, with one major exception. The WG11 study utilized naive subjects and hearing protector fitting procedures that were relatively free from experimenter influences instead of the trained subjects and the ‘‘best fit’’ procedures required by current measurement standards. A subject fit (only hearing protector manufacturer’s printed instructions handed to the naive subjects) and an informed user fit (manufacturer’s instructions plus experimenter general comments to the naive subjects only relative to the instructions) were utilized for the WG11 study measurements. Comparisons indicate that the variability of the data collected under the less rigorous subject and fitting procedures of the WG11 study is at least equivalent to that measured in the other interlaboratory studies.

A history of C++

This paper outlines the history of the C++ programming language. The emphasis is on the ideas, constraints, and people that shaped the language, rather than the minuitiae of language features. Key design decisions relating to language features are discussed, but the focus is on the overall design goals and practical constraints. The evolution of C++ is traced from C with Classes to the current ANSI and ISO standards work and the explosion of use, interest, commercial activity, compilers, tools, environments, and libraries.

Frequency-Importance and Transfer Functions for Recorded CID W-22 Word Lists

Frequency-importance and transfer functions for the Technisonic Studios' recordings of the CID W-22 word test are reported. These functions may be used to calculate Articulation Index (AI) values or to predict scores on the W-22 test. The functions were derived from the word recognition scores of 8 normal-hearing listeners who were tested under 308 conditions of filtering and masking. The importance function for the W-22 test has a broader frequency range and a different shape than the importance function used in the current ANSI standard on the Articulation Index (ANSI, 1969). The transfer function is similar in slope to the ANSI transfer function for 256 PB-words, but is shifted to the right of that function by 0.05 AI.

Intraocular lens resolution in air and water

The resolution of 96 polymethylmethacrylate intraocular lenses with convexo-plano optics, ranging in power from 13 to 27 diopters, was measured in air and water. The resolution of each lens was expressed in linear units of resolving power, which is the maximum number of line-pairs that can be resolved per millimeter, as described in the current ANSI Standard Z80.7-1984. There was no clearly defined relationship between linear resolving power measured in air and that measured in water. Measurements on high power lenses (> 20 diopters) indicate that it is possible for an intraocular lens to meet the current 100 line-pair per millimeter standard for resolution and still be a limiting factor in a patient's best attainable visual acuity. An alternative method for evaluating lens resolution is to determine the resolution efficiency (the relative percentage performance of a lens compared to a diffraction-limited lens of the same dioptric power). Using these units, a consistent and predictable relationship from air to water was demonstrated. Our findings confirm that if a minimum standard of 30% resolution efficiency in air is established, in contrast to linear resolving power, the lens will perform near its diffraction limit when implanted in the eye. For intraocular lenses of materials other than polymethymethacrylate, a minimum resolution efficiency in air other than 30% may be required.

Specific Absorption Rates of Energy in Man Models Exposed to Cellular UHF Mobile-Antenna Fields

Thermography, nonperturbing temperature probes, and E-field sensitive diodes were used to quantify the SAR patterns in human models exposed to UHF mobile-antenna fields. The exposure conditions include man, woman, and child models in the standing position close to roof- and trunk-mounted antenna; man sitting in the back seat near a trunk-mounted antenna; child kneeling in the back seat and looking through the rear window. Incident power densities near the antennas were also measured. Based on the current ANSI radio-frequency protection guide, the exemption of 7-W input power will violate the ANSI primary exposure criterion, but satisfies the 8-W/kg exclusion clauses. A maximum power of 3.5 W would satisfy all of the ANSI guides.

Aerodynamic impact sound from colliding spheres for calibration of microphone systems

Tentative damage-risk criteria for hearing and material design standards require measuring the peak values of impulsive sounds. However, use of current or proposed ANSI and IEC standards provides only the magnitude calibration in response to sinusoids, and does not ensure accuracy in measuring the peak values of impulsive sounds. We have used digital transient capture and FFT techniques with a 3.2-mm-diam microphone system calibrated in magnitude and phase to measure peak sound pressure levels and spectra of impact sounds produced by a prototype source. This source uses an essentially identical pair of colliding steel spheres of either 25.4- or 44.5-mm diameter to produce peak sound pressure levels within the range 100-120 dB re 0.00002 Pa with precisions (ranges of peak amplitudes of nominally identical impacts) of 0.5 dB or better, and with spectra exhibiting fairly broad maxima within the range 3-10 kHz. For some conditions, at least, the waveform of sound pressure is approximately diphasic, and of duration <0.5 ms. The results demonstrate the feasibility of a simple, robust sound source suitable for use in moderately noisy, nonanechoic environments to check the free-field response of microphone systems, and subsequent instrumentation, to impulsive sounds.

Motor Operated Disconnecting Swith Ice Tests at a Climatic Laboratory

As a result of full scale indoor operational ice tests performed in the Spring of 1973, it became apparent that high voltage air disconnecting switches built and tested under current ANSI standards will not perform satisfactorily when coated with 3/4 (1.9 cm) inch of ice and operated with a motor mechanism. It was also demonstrated that one motor operation both opening and closing under iced conditions is a piactical requirement and is within the design capabilities of most switch manufacturers.