Volume 42, Issue 5, November 1967
Index of content:
- PROGRAM OF THE SEVENTY‐FOURTH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session A. Ultrasonic Visualization I: Methods, Instrumentation, and Illustrative Examples.
- Invited Papers
42(1967); http://dx.doi.org/10.1121/1.1910701View Description Hide Description
In ultrasonic two‐dimensional visualization, the spot size of the display unit is the limit of resolution and determines the design of the echoscope. The shortest echo response is obtained from a nonreflectivity backed transducer, but the usual backed or quarter‐wave matched transducer gives adequate axial resolution. The beam‐width of the optimum weakly focused transducer is equivalent to four times the spot size, and some form of signal comparison must be used to make the azimuthal resolution compatible with the axial resolution. The finite beamwidth also degrades the axial resolution of inclined structures and distorts the display by elongating structures along the beamwidth. Off‐axis receiving transducers may be used to receive larger echoes from inclined structures. An improvement by a factor of 3 may be obtained before the employment of these transducers degrades the resolution. The technique is prone to artifacts that are more troublesome in contact than in water delay scanning. These features are illustrated for an echoscope designed for the visualization of the pregnant uterus.
Omnidirectional Scanning and Relief Presentation for Ultrasonic Visualization of Intracranial Anatomy42(1967); http://dx.doi.org/10.1121/1.2143767View Description Hide Description
The application of new scanning (omnidirectional), echogram composition (band assembly), and display (relief presentation) methods to the ultrasonic visualization of intracranial anatomy is described. These methodologic advances are implemented by a general purpose on‐line digital computer that makes possible a flexible approach to the development of a more sophisticated generation of such instrumentation facilities. At this stage of the evolution of instruments for viewing the brain, it is desirable to separate certain problems specifically associated with transskull operation from those concerned with determining what anatomic features can be detected and localized when examining pulses are employed in the absence of enhancement of impedance differences at interfaces and under the condition that the acoustic energy not traverse bone. Results for rhesus monkey brainin vivo under such experimental conditions are illustrated.
42(1967); http://dx.doi.org/10.1121/1.2143768View Description Hide Description
An evaluation of current intensity‐modulated recording systems has shown that they will not produce identical records from the same echo pattern. Differences in the records are due to two factors: the recording transfer function, and the ways in which the zero signal level or “baseline” is established and maintained. To find a correlation between ultrasonic echo patterns and the underlying tissue structure, it is essential to be aware of the changes in records that are due to the recording equipment. Lack of knowledge of a particular equipment can have a disastrous effect upon attempts to duplicate the results of another investigator. Differences in the transfer functions of current equipment arise from the use of different types of cathode‐ray tubes and recording film as well as the use of a video differentiator. An additional effect of not maintaining a constant zero level is to increase the variability of the amplitude of received echoes. Several tests have been devised by which the processing inherent in a particular type of equipment can be assessed and by means of which the changes introduced by different combinations of characteristics can be demonstrated.
42(1967); http://dx.doi.org/10.1121/1.2143769View Description Hide Description
The absolute position determination of reflecting targets in the brain is difficult because of the refraction of the ultrasonic beam and the different velocities in the bones of the skull and brain. Since many brain disorders distort the almost symmetrical brain structures, emphasis should be placed more on the detection of asymmetries rather than on faithful mapping of the brain. The asymmetry can be displayed with considerable precision by symmetrical scanning of the head simultaneously from both sides with two transducers. An ultrasonic immersion scanner that employs this technique will be described, and the results will be discussed.
42(1967); http://dx.doi.org/10.1121/1.2143770View Description Hide Description
In recent years, the ultrasoundimage converters have become available in such a form as to lend themselves to routine day‐to‐day use. The systems are capable of resolving detail in the order of a few hundred microns at sound levels incident of 10−7 W/cm2. The greatest difficulty presently associated with the systems is the need for liquid immersion of the object being examined. It is the purpose of this discussion to delineate the various factors controlling the performance of the system and, through motion‐picture film, show the application of the image system to typical problems in medicine and biology.
42(1967); http://dx.doi.org/10.1121/1.2143771View Description Hide Description
Ultrasound fields, having both spatial and temporal coherence, have been used to produce sonic holograms that can produce three‐dimensional images in a visible light field. The sound field is detected by mechanically or electronically scanning a piezoelectric element and determining both magnitude and phase of the sonic field. The information thus obtained is processed sequentially by electronic, optical, and photographic techniques to produce a hologram transparency. The generation of the images by wavefront reconstruction is accomplished with the coherent light produced by a laser.
- Session B. Psychological and Physiological Acoustics I: Calibration, Thresholds, and Noise
- Contributed Papers
42(1967); http://dx.doi.org/10.1121/1.2143772View Description Hide Description
Routine calibration of large circumaural earphones has long been a problem due to lack of a standard coupler, variability found with placement on a brass plate coupler, and difficulties in probe tube calibration techniques. In order to provide a practical solution to the above problems so that a pair of large circumaural (Pedersen) earphones could be used routinely, four studies were carried out at UCLA. In these studies, a Plexi‐glass adapter ring was developed that, when fitted with a standard artificial ear and attached to the earphones, furnished a method whereby routine acoustic calibration of the earphones could be carried out easily and repeatedly. Comparisons were made between the Pedersen earphones and TDH 39 earphones using: (1) the adapter ring and artificial ear; (2) a probe tube; and (3) psychophysical techniques. These comparisons made it possible to achieve a method for routine calibration of the large circumaural earphones. The above studies also indicated some problem areas in the use of certain psychophysical techniques such as loudness balancing.
42(1967); http://dx.doi.org/10.1121/1.2143773View Description Hide Description
This study describes results based on the calibration of 100 audiometers over a 3‐yr period. The audiometers tested were in current general use from 11 different agencies or individuals, and represented 30 different models from eight manufacturers. The audiometers were calibrated with high‐quality laboratory‐standard equipment under the most careful conditions. Sound‐pressure output levels of the earphones were recorded for each frequency and attenuator setting from maximum output to 20‐dB hearing loss (HL). Some difficulty was encountered with acoustic measurements below 30‐dB HL using ISO standards. Below this level, terminal voltage readings were used. Only two audiometers could be judged in calibration when strict compliance with the standards was observed. The most frequent problem found was incorrect sound‐pressure output of the earphone. Eighty‐nine of the 100 audiometers failed to meet this specification. The second most common problem involved excessive rise time. The third most common problem was frequency outside the tolerance limit. This was followed in order by failure to meet specifications for hearing‐loss interval and hearing‐loss range, instability of SPL output with ac line voltage variations, excessive harmonic distortion, and excessive shock hazard. [Work supported in part by U. S. PHS National Center for Chronic Disease Control.]
42(1967); http://dx.doi.org/10.1121/1.2143774View Description Hide Description
The pressure distributions generated in an external ear replica by a nearby point source have been measured with a probe microphone. Five normal modes have been clearly identified, M1 at 2.9 kHz that is essentially the λ/4 resonance of the canal proper with a large end correction, M2 at 5.5 kHz the fundamental depth resonance of the concha with large radiation damping and weak canal coupling, M3 at 9.3 kHz related to the first transverse resonance of the concha, M4 at 11.2 kHz, and M5 at 12.8 kHz a pair of modes related to the second transverse resonance. M1 and M2 are consistent with limited measurements on real ears and are easily reproduced in a simple geometrical model. Above 6 kHz, transverse wave‐motion in the concha is largely responsible for large variations of response with angle of incidence. Real ears, replica, and model all exhibit relatively low on‐axis response in the 8‐kHz region.
42(1967); http://dx.doi.org/10.1121/1.2143775View Description Hide Description
A 3‐msec burst of a 1‐kHz tone was added to every eighth cycle of a continuous 50‐Hz tone and presented monaurally through a TDH‐49 earphone. The threshold intensity of the high‐frequency burst was determined as a function of two parameters [Deatherage et al., J. Acoust. Soc. Am. 38 (1965)]: (a) intensity of the low‐frequency tone (110, 100, 90, and 80 dB re 0.0002 dyn/cm2, and low‐frequency tone absent); and (b) phase of the low‐frequency tone at which the high‐frequency burst occurred (increments of 45°). At the three highest intensities, changes in phase produced appreciable threshold shifts, repeatable from subject to subject. The results are interpreted in terms of the relationship between polarity of displacement of the basilar membrane and initiation of activity in the auditory nerve (Kiang et al.)
42(1967); http://dx.doi.org/10.1121/1.2143776View Description Hide Description
Threshold determination with the block up‐and‐down, two‐interval forced‐choice (BUDTIF) method has been investigated by obtaining 10 repeated 75% correct thresholds from human subjects. Major parameters were number of trials per block (2, 4, and 8) and number of trials per threshold (16–144). Measures of within‐ and between‐day variability and within‐run variability were closely related to one another and were generally inversely related to block size and number of trials per run. The effect of number of trials on variability with a block size of four trials was minimal however. For example, the mean between‐day standard deviation was 0.80 for 32 trials and 0.73 for 144 trials. Mean thresholds were directly related to block size, as one would expect from the binomial bias. Thresholds also tended to become lower with increased trials per run. Efficiency was generally inversely related to trials per run and directly related to block size, although the trends are somewhat mixed. The variability observed in these data differ from that observed in stimulated listeners. This is interpreted to indicate that the assumption of trial‐by‐trial independence in human observers is much less tenable than commonly asserted.
42(1967); http://dx.doi.org/10.1121/1.2143777View Description Hide Description
The audibility threshold performance of the human ear submerged in water at ear depths of 12, 35, 70, and 105 ft is compared to its performance in air. Threshold SPL's at 125, 250, 1000, 2000, and 8000 Hz from six divers wearing open circuit, air breathing SCUBA equipment were obtained by the Békésy technique. Differences between water and air conduction thresholds ranged from about 30 dB SPLre 0.0002 μ at 250 Hz to 60 dB at 2000 Hz. Water conduction thresholds that are generally independent of test frequency require about 71 dB SPL. No significant effect upon threshold was provided by ear depth. Thresholds were also obtained from three divers at 105 ft breathing compressed air and, in another condition, breathing a mixture of helium and oxygen. Significantly higher thresholds (about 5 dB) at all frequencies were obtained with the helium‐oxygen mixture in the middle‐ear cavity. [Research supported in part by Office of Naval Research and National Institutes of Health.]
42(1967); http://dx.doi.org/10.1121/1.2143778View Description Hide Description
The sound‐shadow effect of the human head in an impulse‐noise field was studied by exposing 27 subjects to gunfire noise so their left ears were normal to the oncoming shock wave (near ear) and their right ears were protected by the shadow of the head (far ear). Noise exposure was continued until the subject's near ear demonstrated 15 dB TTS and the postexposure TTS in near and far ears was compared. Peak pressure level at the entrance of the far‐ear canal was less than one‐half that found at the near ear (153 vs 161 dB re 0.0002 μbar). Mean TTS was significantly smaller in the far ears than in the near ears. The mean “protection” afforded the far ear by the head's shadow ranged from 3 dB at 1 kHz to 12 dB at 6 kHz. The implications of the findings for the protection of weapon crewmen and others is discussed.
42(1967); http://dx.doi.org/10.1121/1.2143779View Description Hide Description
A waveform generator was constructed that provided for the introduction of sounds represented by four different waveforms into a box 21 in. square, 25 in. high, and with an 18‐in. speaker mounted in the top of the box. The four waveforms were an Nwave, a differentiated Nwave, one‐half square wave, and a differentiated one‐half square wave. With their heads sealed in the small box, 16 subjects made discriminations among the six different pairs of stimuli. That the subjects could not discriminate between an Nwave and a differentiated Nwave, or between a square wave and a differentiated square wave, reproduces the results of Zepler and Harel (1965), but with different equipment and psycho‐physical technique. Using earphones, their experiments showed that the loudness of the Nwaves is determined by the two rising parts (pulses), while our experiment shows that when the pulses are identical in amplitude change and direction, discrimination is not possible. That subjects could discriminate among the four pairs of stimuli where compression was compared to rarefaction is probably caused by the nonlinear characteristics of the ear, but could also result from air leakage at the neck seal.
42(1967); http://dx.doi.org/10.1121/1.2143780View Description Hide Description
This investigation was concerned with the subjective effects of high level impulses of short duration, to add to previously reported data [H. R. Silbiger, J. Acoust. Soc. Am. 38, 937(A) (1965)]. The principal parameters under investigation were the click shape, duration, and peak pressure level. The last ranged from 98 to 159 dBt. Subjects gave magnitude estimates of the loudness of the clicks and rated the subjective disturbing effects on an annoyance scale. The developed annoyance scale appears to be linear with positive peak pressure level. The slope of the average loudness function was 0.8. Data on the difference limen for these clicks will also be reported. Because of the level of the stimulus clicks, the subjects' thresholds were continuously monitored, and temporary threshold shift curves were obtained for both single and multiple click presentations. These data again show evidence of both positive and negative TTS, with the amount of negative TTS decreasing as the number and level of stimulus clicks increases.
42(1967); http://dx.doi.org/10.1121/1.2143781View Description Hide Description
A study has been made on the evaluation of natural impulsive noises by subjective and objective procedures. One special example was used to get an indication of whether existing objective calculation methods might give sufficient agreement with subjective tests. The office noise sample studied bursts from a single typewriter operated at repetition rates between 1.5 and 15/sec. A forced‐pair comparison procedure of the constant stimulus type was used for the subjective evaluation. This choice has been prompted by the good results that we obtained with a corresponding method for speech quality measurements. In the subjective tests reported here, we asked for loudness and for annoyance comparisons. Two types of broad‐band noise were utilized as reference signals. In addition to this, narrow‐band noise centered at 1000 Hz was used to calibrate the two broad‐band noises subjectively, and was also compared directly to the test noise. The subjective measurement results of this study are compared with those obtained by several well‐known objective methods for noise rating and loudness evaluations.
42(1967); http://dx.doi.org/10.1121/1.2143782View Description Hide Description
Fifteen subjects were each given separate 15‐min exposures to three bandwidths of fatiguing sound (whole octave band and band centered at 1000 Hz, pure tone of 1000 Hz) presented in three modes (constant level, variable level, and intermittent). The band SPL were 5 dB below the whole octave‐band levels for the various exposure conditions that, according to the CHABA criteria, should have yielded equivalent threshold shifts (TTS). The pure‐tone SPL's equaled the band levels for one set of exposures, and were 3 dB lower in another set. These latter conditions were intended to verify the increased noxiousness of pure‐tone versus narrow‐band noise stimulation, also specified in the CHABA criteria. Comparisons of the TTS produced by the different bandwidths and modes of noise presentation suggested that the CHABA criteria may error on the conservative side, especially in rating the hazards to hearing of band and variable types of noise exposure. Implications of these findings as regards critical‐band‐TTS notions and the action of the acoustic reflex are noted.
- Session C. Noise I
42(1967); http://dx.doi.org/10.1121/1.2143783View Description Hide Description
It is the purpose of this paper to describe an aircraft‐type transonic compressor built especially for noise research studies and to present some preliminary results. This compressor is unique in that it is adjustable over a very wide range of operating conditions. Initial test results indicate that the relative‐tip Mach number is a dominant factor in noise generation. Results of systematic measurement studies for a range of pressure ratios, rotational speeds, and inlet flow angles suggest that variation of in‐flow angle may be an effective technique for markedly reducing inlet noise radiation during high‐tip speed operation.
42(1967); http://dx.doi.org/10.1121/1.2143784View Description Hide Description
The noise radiated by rotor‐stator and stator‐rotor interactions in a duct of negligible length has been analyzed with the aid of the author's general theory. Explicit analytic results for rotating fluctuating source patterns have been found, which reduce to the case of Gutin for the steady propeller case with no axial velocity, and to Garrick and Watkins' results for the propeller problem with axial velocity. Computed results of over‐all power and directionality will be presented for several basic cases, and the practical implication of these theoretical results will be discussed. [This work has been supported by the National Aeronautics and Space Administration under contract.]
42(1967); http://dx.doi.org/10.1121/1.2143785View Description Hide Description
The noise control activity of an acoustics group at a development laboratory dealing mainly in computer peripheral equipment is presented. The cost of product noise control increases rapidly as machines progress in hardware development, becomes expensive when tooling is completed, and usually prohibitive after release to production. The goal, therefore, is to implement noise control early, i.e., on the designer's drawing board before hardware exists. However, to development engineering, noise control is only one of many factors to be considered within limitations of budget and schedule. Therefore, the acoustics group must have an effective program to ensure proper noise control emphasis during various phases of development. The program of the group is presented: before‐hardware participation in machine development; recommendations of machine acoustical objectives based on experience and market requirements; prediction of noise‐control measures required to make machines meet their acoustical objectives from design layouts and power‐level measurements of components and subassemblies; evaluations of complete machines in a semianechoic chamber; interactions with industrial design, human factors, heat transfer, installation planning, product test, and manufacturingquality control groups.