The adiabatic piezoelectric constants du and d u of alpha-quartz have been measured between room temperature and 571.5°C. At the latter temperature, dn is about one-half of its room temperature value, whereas du has increased by a factor of almost three. At 573°C (the inversion temperature) the crystal structure changes to that of beta-quartz, and dn vanishes. The constant d u for beta-quartz has been measured between 584°C and 626°C. d u appears to be substantially constant over this short range of temperature, and differs from du for alpha-quartz at about 570°C by only a few percent. The piezoelectric constants were deduced from measurements (with a Q-meter technique) of the equivalent circuits of long thin bars driven electrically at frequencies near resonance.
This is a detailed report on the technical activities of ISO's Technical Committee on Acoustics No. 43, Working Group on Threshold of Hearing, which led to the ISO Recommendation R389, "Standard Reference Zero for the Calibration of Pure-Tone Audiometers," November 1964. The activities described are the determinations of the transfer factors from loudness balancing experiments between the five earphonecoupler combinations in R389, the incorporation of the transfer data into the computation of the reference equivalent threshold sound-pressure levels (RETSPL) in R389, and the details of the weighting of the original threshold determinations. A statistical analysis estimates the average standard deviation of the RETSPL in R389 to be 2 dB due in large part to the variance in the transfer factors. The present USASI standards are definitely outside the ISO uncertainty limits at all frequencies. The standard deviation of the differences between adjacent columns in R389 (or the equivalence of the RETSPL for the different earphonecoupler combinations) was estimated to be 2.5 dB. To improve accuracy in audiometry, it is suggested that the variance due to the transfer factors be eliminated by agreement on one standard earphone type. ForewordThe working Group No. 1 on Threshold of Hearing, of ISO/TC43 on Acoustics, constituted itself as a body of technical experts in 1955 to arrive at a best value for an international threshold reference level for the measurement of hearing. The six members, all associated with laboratories carrying on researches into audiometry and the measurement of hearing threshold, were from Europe and the United States of America. They agreed early in their deliberations (1) to examine carefully all available published data from various laboratories on threshold levels expressed in physical terms, (2) to make additional threshold measurements to resolve any outstanding differences between laboratories, and (3) to carry on any measurements needed to place all the data on a common basis, such measurements to be made in the members' respective laboratories. Completion of these monumental tasks culminated in ISO Recommendation R389.The details of their efforts are recorded in Mrs. Weissler's paper. Each of the several members, some now retired, had an opportunity to comment on the paper in draft form. Chairman Ltischer aptly remarked: "Es geht daraus die grosse Grfindlichkeit der ISO-Untersuchung hervor, so dass an der Richtigkeit des vorgeschlagenen Standards nicht zu zweifeln ist." R•c•Am• K. Coo•:, Member
In an effort to provide guidelines for law enforcement personnel to protect their hearing, the peak pressure level and signal duration (A and B duration) of eight popular firearms were measured and compared with the requirements of OSHA (1970), CHABA DRC (1968), and EPA levels (1974). Small condenser microphones and a storage oscilloscope were used to record the blast wave signatures from a 9-mm automatic, 0.357-cal. Magnum revolver, 0.41-cal. Magnum revolver, 0.22-cal. revolver, 0.45-cal. automatic, 0.44-cal. Magnum revolver, 12-gauge shotgun, and 0.22-cal. rifle. Measurements were made at the ear of the person shooting and at the approximate position of a neighbor at a firing range. Some measurements were also made at a practice firing range. A portable tape recorder was found useful for recording gun signals and measuring B durations. The peak pressure levels of the signatures of all the firearms tested exceed the OSHA maximum of 140 dB. It was found that in an anechoic environment the noise from five of the handguns exceeded the CHABA DRC (1968), while the noise from all of the firearms tested, except the 0.22-cal. rifle, exceeded the EPA levels (1974). At a sound-insulated firing range, the noise from all the firearms tested, except the 0.22-cal. rifle, exceeded the CHABA DRC (1968), while all the firearms tested exceeded the EPA levels (1974).
Published material on the calibration of circumaural earphones is briefly reviewed. The present lack of knowledge about these earphones and about the earphone-to-ear coupling is indicated, and the resultant limitations on the routine use of circumaural earphones in clinical and industrial puretone audiometry are presented. IN TI-IIS LETTER, TI-IE TERIV[ circumaural earphone REFERS TO TIIAT class of earphones which are sealed to the head by a resilient cushion surrounding the pinna and do not allow close contact between the driver unit and the surface of the pinna.In recent years, the use of such circumaural earphones has increased. Some of the most obvious reasons for this are that they are comfortable to the wearer and that they can be designed to have low sound transmission through the cap. Other qualities of these earphones, such as those which arise because of their low acoustic-source impedance at low frequencies (Shaw, 1966), are less obvious but of no less importance. It has come to the attention of the authors, all of whom are members of the United States of America Standards Institute Writing Group S3-1-W-37 on the coupler calibration of earphones, that circumaural earphones are presently being used in some situations where their use cannot reasonably be justified. Therefore, although there is relatively little relevant published material, we would like to review briefly some of the existing literature on circumaural earphones and their calibration and from this infer some of the present limitations on their use. Shaw and Thiessen (1962) investigated the physical acoustics of some types of circumaural earphones through acoustic impedance models of the earphone systems. They also measured with a probe-tube microphone the pressure produced by two circumaural earphones, both when applied to a real ear and when applied to the artificial ear or coupler. Their "flat-plate coupler" has a large coupling surface which accommodates the cushion of the circumaural earphone, and the measurement microphone is mounted flush with this surface. Tillman and Gish (1964) measured the sound pressure developed by two circumaural earphones on a flat-plate coupler when the earphones were excited by the voltages corresponding to the median threshold of hearing for a group of six experienced listeners. Charan, Cox, and Niemoeller (1965) investigated three couplers for testing circumaural earphones and demonstrated from the responses of two types of earphones on these couplers that, particularly above 2000 Hz, large variations in responses are caused by variations in earphones of a particular type, in cushions of a particular type, in applied force on the earphone, and in placement of the earphone on the coupler. Shaw (1966) used a probe-tube microphone to measure earcanal sound-pressure levels (SPL's) of 10 subjects each with three different circumaural earphones and two different againstthe-ear earphones. He also measured relative responses between a Sharpe HA-10 circumaural earphone on the flat-plate coupler and a Telephonics T...
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