bluuebunny/crossref_metadata_2025 huggingface dataset:
The importance of external and middle ear contributions to bone conduction in man
Authors: Gatehouse S.
Published: October 2005

Differences between air conduction (a–c) and bone conduction (b–c) thresholds are commonly used to determine the presence and magnitude of a middle ear abnormality in the human audiotory system, making the tacit assumption that b–c directly stimulates the cochlea. Animal experiments have long established that b–c transmission is a complex phenomenon [J. Tonndorf, in Foundations of Modern Auditory Theory, Vol. 2 (Academic, New York, 1972)] with significant contributions from middle and external ear components. An artificial reversible middle ear abnormality may be induced in man by maintaining an air pressure in the external meatus. The shifts in a–c and b–c thresholds provide a means to evaluate the relative importance of the external and middle ear components. At the lower frequencies of 250 and 500 Hz, these components predominate; at 500 Hz there is an a–c shift of 15.9 dB accompanied by a b–c shift of 15.8 dB. These results have important implications for the interpretation of air and bone conduction thresholds.
Ear-canal resonances and the assessment of hearing thresholds at high frequencies
Authors: Stevens K. N. , Blumenthal S. H. , Green D. M. , Krasner M.
Published: October 2005

Standing waves in the ear canal cause substantial difficulties in the assessment of high-frequency (8000–20 000 Hz) hearing thresholds because of uncertainties in the specification of the acoustic stimulus. A calibration procedure is proposed for estimating the sound prcssure p1 at the inner end of the ear canal by measuring the poles of the impulse response at the entrance to the ear canal when an acoustic source is coupled directly to the canal through a short tube. This calculation is based on the fact that the transfer function from the source to p1 is an all-pole function. As a step towards implementation of this procedure, frequencies and bandwidths of ear-canal resonances for a number of ears have been measured. The data show that these resonances have bandwidths as small as 300 Hz, and deviations from equal spacing that are usually no greater than 10%. The pressure p1 has been calculated from the appropriate all-pole transfer function, and shows systematic and predictable differences with measured peak sound pressures in the outer 1 to 1.5 cm of the ear canal, as expected on the basis of measurements with models. [Supported by a contract from NINCDS.]
Acoustic and auditory nerve measurements of distortion products
Authors: Fahey P. F. , Allen J. B.
Published: October 2005

We have made measurements of distortion products responses in the ear canal and in the auditory nerve of the cat. The frequencies and levels of the primaries, f1 and f2, were varied in such a way that the frequency and level of the distortion product, as measured by the response of a neuron at its threshold, were held constant. In particular, we found, as has been previously reported by others, that the amplitude of the primaries needed to give an isoresponse was relatively independent of frequency for the f2-f1 signal and strongly frequency dependent for the 2f1-2f2 signal. The level and frequency dependence of the distortion product 2f1-f2 as measured in the ear canal (which were not seen when the driver was terminated with an acoustic cavity) seem to agree with the level and frequency dependence of the distortion products that were detected by single neurons in the auditory nerve.
Performance testing of a large reactive silencer
Authors: Rand Robert W. , Strong Walter F.
Published: October 2005

The conversion of a 650-MW power station unit from oil to coal included conversion from forced to balanced draft boiler operation and the addition of two induced draft fans rated at over one million CFM each. The fans required 25 dB tonal noise reduction to meet nondegradation noise criteria. Two tuned reactive/absorptive discharge duct silencers were purchased. Detailed performance tests were required in the purchase specification and were conducted on a prototype silencer to assure the manufacturer's guarantee would be met. Several performance indices were measured: insertion loss, noise reduction, attenuation, and pressure drop. Narrow-band frequency analysis was utilized. Community noise measurements were made following silencer installation. They indicated the silenced fans were inaudible.
Noise reduction by a barrier in a small boat
Authors: Nábĕlek Igor V. , Donahue Amy M. , Thompson M. Virginia
Published: October 2005

Noise problems in recreational settings have drawn much less attention than the noise in industry. One source of recreational noise is small boats with outboard motors in which the users are sitting in close proximity to the motor. The levels with A-weighting (LA) and without weighting (LLIN) reached 94 and 102 dB, respectively, in a 4.5-m (14 ft) boat measured at a distance of 180 cm from an 85 HP motor and 90 cm above the floor of the boat with boat speed at 40 km/h. The noise reduction by four barriers (71 and 56 cm tall, and 1.9 and 0.3 thick) in two different positions was determined. In the lower position, B, the barrier was 45 cm from the motor. In the higher position, M, the barrier was raised 10 cm and moved closer to the motor (to the 15-cm distance). As expected, taller, higher, and thicker boards resulted in greater noise reduction. However, thinner boards showed slightly greater noise reduction at frequencies 2 kHz and above, especially in the M position. Dependent on condition, LA reduction was between 5 and 12 dB, and the LLIN reduction was between 0 and 4 dB. In octave frequency bands between 1 and 4 kHz, barriers in various conditions produced 11–18-dB noise reduction.
Design of a test station for accurate aerodynamic and acoustic testing of small box fans
Authors: Gray Leslie M.
Published: October 2005

In order to correctly assess the impact of the noise of a box fan in a system, the test apparatus must model correctly the environment mechanisms which affect fan noise. This apparatus must not introduce any unintentional bias in the measurement of fan noise, either in level or frequency structure. This paper reviews the physical mechanisms which cause fan noise, and reviews how these mechanisms are affected by both the fan design, and by the fan environment. Careful consideration of these mechanisms results in a set of acoustic and aerodynamic requirements for measurement of fans. These requirements result in the design of a test station for comparative testing of fans. This design is reviewed, and the benefits compared to other approaches. The paper discusses the limitations of the results that can be expected from these laboratory tests, and proposes a standardized test procedure.
Comparison of measured and predicted mode scattering associated with spinning mode transmission through a peripherally segmented liner
Authors: Parrott T. L. , Watson W. R.
Published: October 2005

An experiment to assess mode scattering in lined circular ducts with peripheral segmentation was conducted. This work is a first attempt to experimentally quantify scattering effects for peripherally segmented liners in a laboratory environment. Mode insertion losses were measured for a six segment, two segment, and uniformly lined duct in the Langley Spinning Mode Synthesizer. Selected spinning modes generated in the synthesizer hardwall source section were allowed to propagate through the lined section into a hardwall duct section with anechoic termination. Estimated mode insertion losses were obtained from a comparison of transmitted mode amplitudes for the various test liners with those for a hardwall duct configuration. Significant mode scattering was predicted and measured for the two segment liner for incident spinning mode orders of 1 and 3. For spinning mode order 1, scattering into spinning mode order 2 was observed. For incident spinning mode order 3, scattering into spinning mode order 4 was observed. For the six-segmented liner, measureable mode scattering was difficult to measure. This was thought to be due in part to inadequate incident mode isolation and to the choice of impedance for the segments.
Application of the two surface method to determine sound power in-situ in the tobacco industry
Authors: Baki Kenneth R.
Published: October 2005

This paper reports the results of tests conducted on tobacco processing and cigarette making machinery using the two surface method for the determination of sound power in-situ. This test method, currently in draft form in the ASTM E33.08D committee, was originally intended for sound power measurement of heavy power plant equipment. Described in this paper is the suitability of this method to measurement of light, high-speed machinery. Also described are the benefits of this method, namely the ability to obtain sound power levels of equipment under typical operating conditions in the environment in which it normally operates. This technique also compensates for the presence of extraneous noise sources as well as the directivity of the machine being studied.
Design of a robotic acoustic intensity measurement system
Authors: Morse Ivan , Flanagan P. M. , Atherton W. J. , Coy John , Stephens David
Published: October 2005

A robotic acoustic intensity measurement system (RAIMS) was designed and constructed to automate the analysis of sound fields using acoustic intensity techniques. Key system features include a five degree of freedom manipulator arm, a six element acoustic intensity transducer, a digital control unit for the manipulator, dedicated spectrum analysis and desk top calculator. The manipulator arm was designed for a 45-in. maximum vertical and horizontal reach. The acoustic intensity probe is attached to the robot's wrist. Scanning velocity profiles for the intensity transducer are programmable with a maximum velocity of 5 in./s and absolute position information. In addition, the manipulator/acoustic intensity transducer unit weights less than 100 lb. The acoustic intensity probe designed for this system helps minimize errors in calculating acoustic intensity by using three pairs of microphones. Preliminary results using this system and future applications will be discussed.
Interference effects of neighboring source on acoustic intensity measurements in the nearfield
Authors: Krishnappa G.
Published: October 2005

The sound powers estimated from acoustic intensity measurements are subject to local variations depending on the acoustical environment. Interference from the neighboring sources affects intensity measurements. Changes in the sound power levels determined from intensity measurements in the nearfield of a source due to the interference from a neighboring source were examined using two identical (320 mm square) loud speakers. Acoustic intensities were measured in planes parallel to the face of the speakers using the two-microphone technique. The sound power levels measured in front of speaker 1 at close distances was not significantly affected when speaker 2 was generating up to 5 dB higher sound power levels than speaker 1. The above experiments were carried out in an anechoic chamber. When the speakers were mounted 1.1 m from a reflecting floor, the changes in the sound power levels due to the reflections were not significant. Theoretical results of acoustic intensities in the nearfield due to the interference of two point monopoles were presented.
An overview of high-resolution sonar developments
Authors: McKinney Chester M.
Published: October 2005

This overview paper is intended to serve as an introduction to the order papers in this session. It will discuss some definitions of high-resolution sonar in terms of sonar acoustical parameters and in terms of target imaging. Several genetic types of sonars (forward scanning, side scanning, etc.) will be described and a brief history of the development of each during the past 40 years will be presented. Various techniques to achieve high cross-range resolution for target imaging will be emphasized. These include large real apertures, synthetic aperture arrays, nonlinear parametric arrays, monopulse techniques, and interferometer arrangements. Techniques for target classification (target size and shape, shadow size and shape, target strength, and resonances) will be described briefly. The status of research on target echo structure and the ocean environment in support of the development of high resolution sonar will be summarized briefly. Some of the applications (both naval and civilian) for such sonars will be enumerated.
High-resolution sonars
Authors: Lallement B. , Clavelloux N. , Grall Georges , Joseph Jacques
Published: October 2005

Submarine search and detail sea-floor studies are problems of a different nature and they do not lead to the same sonar design criteria. High-resolution sonars are the key to an efficient detection and classification of small ground objects, and shadow target imaging reveals to be a very powerful tool. The characteristics of various Thomas-CSF high-resolution sonars are given as examples of implementation of these design principles. Their effectiveness is illustrated by a complete set of pictures obtained at sea by both hull-mounted and towed, side-scan sonar. Finally, different images obtained with a high-resolution sonar simulator are presented to conclude on future trends in this field.
High-resolution sonar system techniques
Authors: Andrews James
Published: October 2005

Advances in sonar hardware and signal processing are having a significant impact on our ability to measure and image the sea floor. These capabilities are in turn rapidly improving our understanding of sea floor morphology and structure and the processes which create and modify them. Side-scan sonars have increased ranges from a few hundred meters to 10 to 30 km. Four systems are of interest in current applications; these are Gloria, Sea Marc, SWATHMAP (SQS-26), and Sea Beam. The information derived from these systems goes beyond simple bathymetric mapping to permit discrimination of sediment types and sea floor roughness. Examples of long-range sonargrams will be discussed in a geologic context to demonstrate these capabilities.
Hybrid focusing for side-look sonar
Authors: Gilmour George A.
Published: October 2005

Two focusing principles are presently used in high performance (0.1° beamwidth) side-look sonars (SLS), the mechanical arc, and electronic all-range focusing. Hybrid techniques to combine the two principles are described in this paper. Focusing is partially accomplished using the mechanical are principle, then completed electronically. This can be thought of as a vernier to allow a mechanical arc SLS to be flown at an altitude other than the radius of curvature. Alternatively, it can be considered to be a way to expand the depth of field of a mechanical arc, or to restrict the depth of field of electronic focusing. The techniques described best fit a very high resolution SLS, e.g., 0.05° beamwidth, the requires only about three parallel beams per side.
Synthetic aperture sonar—Theory and system design
Authors: Loggins C. D.
Published: October 2005

The synthetic-aperture technique is described and differences between the radar and the sonar implementations of this technique are discussed. Synthetic-aperture beamforming is discussed and compared to beamforming in a conventional (real aperture) sonar. Sonar performance for the synthetic aperture sonar is compared to that of a conventional sonar with respect to area-coverage rate, maximum range, and azimuth resolution. The vernier technique for increasing area-coverage rate and incoherent averaging for reducing image speckle are also discussed.
Data processing for high-resolution active sonar
Authors: Pridham R. G. , Zentner C. R.
Published: October 2005

Active sonars which have high resolution in range and angular sector generate large volumes of data which must be interpreted by the sonar operator. Often the magnitude of the data volume greatly exceeds the capabilities of both modern display technology and the human element. This paper discusses the use of computer-assisted data evaluation and display techniques which address this data mapping/reduction problem. The importance of simulation and real data analysis in studying this problem is explained. Results of a typical simulation are given to show the impact of various performance and computer loading parameters.
Log-periodic acoustic lens-acoustic filter plate study II
Authors: Sternberg Robert L. , Anderson Warren A. , Ilson Howard F. , Dickson Owen P.
Published: October 2005

Graphical experimental data in the form of passive receiving patterns is presented for several high resolution acoustic lens-acoustic filter plate combinations showing the comparative properties of various types of flat and curved filter plates. Experimental data relating the achieved frequency independent constant beamwidth of the lens-filter plate combination to the governing slope parameters of the filter plate are summarized for empirical design purposes. The basic experiments were conducted over the frequency range from 25 to 500 kHz but can be scaled to any band of the corresponding scaled width. [Work supported by ONR and NUSC.]
The bottom topography survey subsystem (BOTOSS)
Authors: Boehme Hollis , Sullivan Roy L. , Scott V. Dan
Published: October 2005

The AN/SQN-17 Bottom Topography Survey Subsystem (BOTOSS) is a high-resolution sonar used to obtain precise bathymetric data from which bottom topography charts are made. BOTOSS employs a downward looking, multibeam, pulsed sonar and digital signal processing equipment to acquire, process, and store bathymetric data. BOTOSS is one of four subsystems that comprise the Bathymetric Survey System (BASS) and is functionally interfaced with the other subsystems. The projector and hydrophone arrays are mounted beneath the ship's hull in a T-shaped configuration. The projector array consists of 76 projectors in a support frame located in a streamlined projector dome mounted along the ship's keel. The hydrophone array consists of 128 hydrophones located in a foil assembly athwart the ship's keel forward of the projector dome. Transmit and receive beamforming are computer controlled and independently stabilized against platform pitch and roll through use of ship motion components supplied by the Navigation Subsystem. Other significant components of BOTOSS include control/monitor/interface equipment, a Sperry SP 900 High Speed Signal Processor, Hewlet-Packard HP 2100 computer and peripheral equipment, transmitter equipment, and receiver electronics. The subsystem has been installed and tested on USNS WYMAN (T-AGS 34) and is currently employed in making bathymetric surveys.
High-resolution portable scanning sonar with integral digital display
Authors: Low John M.
Published: October 2005

A 500-kHz 360° mechanically scanned portable sonar with PPI display is described. The underwater unit [21 (d) × 35 (h) cm] has a rotating assembly which accomodates two transducers, a transmitting array with a − 3-dB beam of 1.4° by 27° and a receiving array of 2.7° by 27°. The surface control and display unit [44(w)times;32(h)×4(d) cm] incorporates a standard television format 9-in. display and all controls. Although the sonar is of conventional Ping and Listen analog design, the microprocessor controlled 256×256 digital display with eight grey levels has considerable advantages over long persistance equivalents typically used in sonata of this type. For example, there can be no blooming or picture fade, display manipulations and expansions can be readily achieved and the output can be recorded on a standard video recorder. Critical to the system design is its ease of operation and interpretation by unskilled operators, leading to a number of new sonar users. Therefore among the applications are civil engineering inspection, underwater archaeological monitoring, seabed debris surveys, wellhead relocation, navigation of free swimming and bottom contact vehicles; seabed scour inspection, etc.
Low grazing angle bottom reverberation measurements at 25, 35, and 45 kHz
Authors: Kenton C. , Moritz E. , Pipkin E. , Richardson S. , Martin S.
Published: October 2005

The results of measurements, utilizing a mobile platform, of bottom backscattering at grazing angles of 1° to 30° are reported. The experiments were carried out in the vicinity of Stage I off Panama City and are comprised of measurements at 25, 35, and 45 kH for cw and FM transmitted signals of different pulse lengths. Statistical features of this reverberation data will be discussed as well as comparisons to other bottom reverberation measurements and models. [Work supported by Naval Sea Systems Command.]
Dynamic behavior considerations of floor systems
Authors: Linehan Patrick W.
Published: October 2005

The suitability of a floor system is affected by its dynamic behavior characteristics. The physical properties of the floor system including the stiffness, damping, and natural frequency characteristics are factors which influence the vibration behavior as a result of human (e.g., walking) activity. Further, external forms of excitation (e.g., machinery) adjacent to the floor system can also produce undesirable effects in terms of human response considerations. Wiss, Janney, Elstner and Associates, Inc. have been involved in many programs, including research projects sponsored by the American Iron and Steel Institute, to evaluate the vibration effects of floor systems. Analytical techniques have been developed to calculate the dynamic characteristics, as well as evaluate their behavior from the viewpoint of human response considerations. This presentation will give typical case histories, discuss the breadth of the problem in this area, as well as recommend techniques that can be used to quantify the dynamic characteristics of floor systems including human response considerations.
An overview of vibration problems in fossil power plants
Authors: Kao George C.
Published: October 2005

Vibration problems pertaining to fossil power plant operations are generally recognized in three major areas: flow-induced vibrations, rotary-machine induced vibrations, and operating equipment induced vibrations. Such vibrations have caused failures of structures and equipment and psychological problems to equipment operators. When severe vibrations occurred to operating plants, engineering repairs were implemented often with field vibration data. Several case studies will be used to illustrate sources of vibration and related remedial solutions. Recommendations to minimize such vibration problems are presented.
Structural response to low-frequency acoustic excitation
Authors: Hottman Steven D.
Published: October 2005

Many noise sources at Army installations are of a low-frequency (25 to 125 Hz) impulsive nature (e.g., artillery and explosives training, or helicopters). Mitigation of the impacts due to these sources, both on- and off-post, require an understanding of the response of a structure to low-frequency excitation. Little information is available in the literature for response below about 63 Hz. In order to study the response below this band, a structure of typical residential construction has been erected inside the CERL Bi-Axial Shock Test Machine (BSTM) building, and extensively instrumented for vibrational and acoustic response. The BSTM has been utilized to produce impulsive acoustic excitation (114 to 130 dB, 25- to 40-ms duration) of the structure. A set of specially designed speakers has been utilized to produce nearly pure tone excitation (90–100 dB, 20 to 125 Hz). Production of the excitation signals and preliminary structural response results are presented.
Effectiveness of a two-layer damping treatment partially covering a beam
Authors: Cole John E.
Published: October 2005

A damping treatment for an elastic beam consisting of a layer of viscoelastic material beneath an elastic bar is considered. The treatment extends axially over a portion of the beam. Under the assumption of simple end supports and a point force excitation, the vibrational response of the damped structure is analyzed by expanding the beam displacement in a series of normal modes. The normal modes for the bar are taken to be those of a free-free beam and are therefore coupled to each of the simply supported beam modes. A numerical procedure is used to calculate the modal response of the beam from the system of coupled equations. The damping effectiveness of the partial treatment is determined by evaluating the modal loss factor as a function of the extent of coverage. Several equivalent methods are examined to evaluate conveniently the modal loss factor. An efficient numerical scheme is to evaluate the loss factor using the real and imaginary parts of the damped resonance frequency. The results obtained are interpreted with the aid of asymptotic limits for the loss factor of the damped dynamic vibration absorber, and conclusions regarding sensitivity of damping effectiveness to extent of coverage are drawn.
Pitch extraction by adaptive window time averaging (AWTA)
Authors: Miller Joan E.
Published: October 2005

A running time average applied to a periodic signal will produce a constant, nonvarying output if the averaging interval is equal to the period length or a multiple thereof. Hence, pitch detection may be accomplished by finding the averaging interval which minimizes the variation in the output and taking the reciprocal of this time interval as the fundamental frequency. This notion has been implemented for the extraction of pitch from speech signals. Some important features of the techniques are (1) time integration, an inherent aspect of this method, contributes to the robustness of its performance, (2) the variance of the averaged signal may be normalized, which facilitates a voiced-unvoiced decision, and (3) crucial parameters of the analysis can be easily adapted to the current pitch estimate for better results in sections of changing period length. Details of the procedure will be described, and results obtained for a variety of speech samples will be shown.
Performance evaluation of a real-time LPC coding technique
Authors: Vemula N. Rao , McLaughlin Phil T.
Published: October 2005

There are a number of LPC-based speech synthesis integrated circuits available on the market today. For many practical applications of these chips, it is advantageous to utilize a real-time code generation system. Traditional LPC analysis techniques, such as covariance, autocorrelation, and PARCOR, process blocks of speech samples yielding one set of LPC parameters for each block. Autocorrelation and covariance techniques require matrix inversion and are too complex for hardware implementation. PARCOR-type lattice techniques require a large amount of data storage at each stage of the lattice. In this study we have evaluated a fast and efficient LPC analysis technique suitable for hardware implementation for real-time operation. Unlike the traditional LPC analysis techniques, the real-time technique processes individual samples of speech. The LPC parameters are first initialized and then updated as each sample is processed. Computer simulation has shown that the real-time technique yields reasonable spectra. Computer generated synthetic sounds from the real-time technique have almost the same quality as those generated from the block-data techniques. Sounds synthesized using the real-time technique on our SP0256 chip are indistinguishable from those synthesized using traditional techniques.
Synthesis of continuous speech by concatenation of isolated words
Authors: Randolph Mark A. , Zue Victor W.
Published: October 2005

This paper reports a feasibility study of synthesizing continuous speech by concatentation of modified isolated word templates. Continuous speech obtained simply by word template concatenation has several inherent problems. It cannot account for the prosodic features normally found in continuous speech, nor can it account for coarticulation; the natural transitions that occur at word boundaries. In an effort to alleviate the first problems, the synthesizer is provided with information describing the duration, the fundamental frequency (f0) contour, and the energy contour of each sentence. The synthesizer draws from a dictionary of word templates each stored as a sequence of LPC parameters. Before concatenation, the time scales of the synthesis templates are nonlinearly warped using the alignment path obtained from a level building connected speech recognition algorithm. In addition, the f0 and energy contours of the word templates are modified. To account for coarticulation, the various parameters are smoothed at word boundaries. The goal of this synthesis system is an output information rate of 200 bits per second of speech. A demonstration tape will be played.
Implementation of a prosody scheme in a constructive synthesis environment
Authors: Goudie Kathleen M. , Lin Kun-Shan , Frantz Gene A.
Published: October 2005

In a constructive synthesis environment, lack of natural prosody detracts both from the naturalness and from the intelligibility of synthetic speech. It is time consuming and frustrating for the linguistically untrained user of a constructive-synthesis system to assign pitch patterns and unit durations by mere guesswork. A semi-automatic prosody assignment scheme has been designed here which takes the majority of the prosody-assignment burden off the user and which is capable of assigning fairly natural-sounding pitch patterns to a constructive synthesis string of allophones. The user is required only to mark the primary and secondary stress locations in the text or in the allophone string, plus an indication of whether the constructed phrase should rise or fall in pitch at the end. These stress marks serve as anchor points for the system to compute both an intonation contour and a timing-adjustment contour for the whole phrase. Thus, with a minimum of effort and linguistic knowledge, the user may achieve a relatively natural-sounding constructive speech phrase.
Phase and group delay in the auditory nerve relative to the cochlear microphonic
Authors: Allen J. B.
Published: October 2005

We have extended our earlier measurements of cochlear phase response by measuring the round window potential phase, which is then used as a reference phase. This normalization greatly simplifies the phase and group delay because it appears to remove middle ear artifacts. After being normalized, the group delay shows a monotonically increasing delay with increasing frequency. This data seems to be inconsistent with a large class of “second filters.”
Effects of stimulating frequency on discharge patterns of single eighth nerve fibers in the bullfrog
Authors: Megela Andrea L.
Published: October 2005

Temporal discharge patterns to tone bursts at best excitatory frequency (BEF) have been examined in single eighth nerve fibers of many vertebrates. There are few descriptions, however, of how discharge patterns may vary in response to tone bursts at other frequencies within a fiber's excitatory tuning curve. Discharge patterns of single eighth nerve fibers in the bullfrog were studied in response to tone bursts at BEF, and at those frequencies representing upper and lower flanks of the tuning curve at 10 and 20 dB above threshold. High-frequency-sensitive fibers innervating the basilar papilla showed no changes in their discharge patterns, analyzed as PST histograms, with stimulating frequency. For these fibers, the shape of the PST histogram at BEF provides a good prediction of the histogram shape at frequencies at the tuning curve flanks. On the other hand, the discharge patterns of low-frequency-sensitive fibers innervating the amphibian papilla varied with stimulating frequency, from a more sustained mode of firing at BEF to a more phasic mode of firing above BEF. Thus, the discharge patterns of amphibian papilla fibers show more variability with stimulating frequency than do those of basilar papilla fibers. [Supported by NIH grant NS09244 to R. R. Capranica.]
Responses of cerebellar units to acoustic stimuli in the CF-FM bats, Pteronotus parnellii parnellii and Pteronotus parnellii rubiginosus
Authors: Jen Philip H.-S. , Sun Xinde , Kamada Tsutomu
Published: October 2005

Single units which faithfully fired action potentials to pure tones (35 ms in duration and 0.5 ms rise and decay times) could be recorded from the cerebellar vermis and hemispheres of the CF-FM bats, Pteronotus parnellii parnellii and Pteronotus parnellii rubiginosus. Most units were recorded at a depth less than 1000 μm from the brain surface and they fired less than five impulses to acoustic stimuli. Only a few units fired tonically to acoustic stimuli. Off responses could be recorded from those units with best frequencies tuned at around 61 kHz which is the predominant CF component of the bat's echolocative signals and Doppler-shifted echoes. Response latencies of these units were between 1.5 and 27 ms and minimum thresholds were between 2 and 83.5 dB SPL. While most of the threshold curves of these units were either broad or irregular, those curves with best frequencies tuned at around 61 kHz were extremely sharp. The highest Q10-dB value obtained from the sharply tuned threshold curves was 153. These data indicate that auditory specialization for processing of species-specific echolocative signals also exists in the cerebellum of the CF-FM bat. [Work supported by NSF BNS 80-07348 and USPH 1-K04-NS-00433-03 to P. Jen.]
Coding of fundamental frequency at low rates
Authors: O'Shaughnessy D.
Published: October 2005

Speech coding at low rates usually requires the coding of excitation information such as fundamental frequency (F0). Typically, F0 is calculated every 10–25 ms and represented using 5–6 bits. Thus 200–600 bits/s are dedicated to excitation. Since F0 does not change radically between consecutive voiced frames, a differential coding scheme can partially reduce the F0 rate without perceptual degradation in the synthetic speech. However, even lower rates can be achieved by approximating the F0 patterns as linear rises and falls. Each such change is coded as a pair of F0 values and a duration. Specifically, each peak or valley in a smoothed F0 contour is coded, as well as the elapsed time since the previous point. Typical English utterances (not including pauses) appear to average seven peaks and valleys per second. If the durations are coded using 4 bits/sample, F0 contours would occupy less than 70 bits/s with little degradation in speech quality. Such a reduction in F0 storage rate could be useful in very low rate vocoders.
A speech data base facility using a computer-controlled cassette tape deck
Authors: Shipley K. L. , Rosenberg A. E. , Bock D. E.
Published: October 2005

A speech data base collection facility is described which uses a cassette tape deck interfaced to a laboratory computer for storing and accessing speech samples. The computer, under program control, has access to the transport functions as well as the position counter of the cassette deck. In addition, there is a capability of reading and writing digital headers. Digital headers are particularly useful in enabling descriptive information to be written directly with the speech samples as well as enabling precise location of individual samples in a data base. The facility offers an attractive means for compactly storing large data bases of speech samples with relatively easy access to individual samples. An experiment is described in which speech sample utterances were digitized and processed on-line simultaneously with recording directly onto cassette tapes with descriptive digital headers. The recorded speech samples were digitized and processed in the same way and compared with the directly digitized and processed samples. No significant degredation was obtained attributable to the analog cassette recording.
Displacement measurements of vibrating transducers
Authors: Hughes W. Jack
Published: October 2005

An in-air measurement procedure has been developed to measure the displacement of a vibrating surface. Specifically the amplitude of vibration has been measured for the radiating surfaces of several transducers (primarily tonpilz type) of different designs. The objective being to determine to what degree the radiating head of a transducer acts as a rigid piston at resonance. In some cases it was known prior to measurement that the radiating head was vibrating with a modal structure, i.e., the corners vibrated out of phase with the center. A fiber optic measurement system was used in order to perform noncontact vibration displacement measurements. The usable frequency range is dc to 100 kHz. Displacement amplitudes on the order of one micron have been measured accurately. The apparatus, which was built at the Applied Research Laboratory at The Pennyslvania State University, allows displacement mapping of the entire surface of a transducer's radiating head. [Work supported by NAVSEA.]
Sound intensity probe calibration
Authors: Rasmussen Gunnar
Published: October 2005

Calibration methods and data for sound intensity probes using two microphone technique will be discussed. Choice of configuration and data to be expected for a given configuration is important for the frequency range and the accuracy. Calibration accuracy overall, in the high-frequency range and in the low-frequency range, will be discussed along with recommendation regarding the choice of microphone type. Especially the problems associated with the ANSI standardized method of using grazing incidence for pressure measurements will limit the performance of a two microphone soundintensity probe due to diffraction and scattering phenomena. A configuration is proposed which will minimize problems with diffraction, scatter, rotational symmetry, and phase shift and maintain a well defined spacing Δr between the two microphones, and at the same time allow multiple choice of different spacings Δr.
Microphone placement factors for one-half inch diameter microphones
Authors: Seller John P.
Published: October 2005

A series of tests were conducted to compare the measurement of an undisturbed acoustical field with a 1/2-in.-diam microphone to the measurement of the aocustical sound with a 1/2-in.-diam, shoulder mounted, man-worn microphone. One-third octave band spectrum measurements were made and the positional-center head microphone placement factor was determined for three shoulder positions, and five microphone orientations. The acoustical tests were performed in a reverberation room and in an anechoic chamber on five test subjects. The free field measurements were conducted for azimuthal angles from 0°–360° in increments of 45°. Averaged microphone placement factors are presented for a 1/2-in.-diam microphone, in one-third octave bands, from 200 to 8000 Hz, for all test locations, microphone orientations, and acoustical environments. Where possible comparisons are made between the results of this study and, earlier work which determined the microphone placement factors for a 1-in.-diam microphone. A computation of the best microphone location orientation was made for four defined types of noise spectra. This was done in order to predict the optimum position for the location of a noise dosimeter microphone under free and diffuse field conditions.
Measurement of phase of the surface reflection coefficient using two harmonically related signals
Authors: Tighe Frank
Published: October 2005

A method for measuring the phase of the surface reflection coefficient using two harmonically related signals was developed and experimentally verfied on samples of high and low loss elastomer and foam materials. This method utilized the property that two harmonically related signals maintain a constant relative phase when propagating over identical paths in a nondispersive medium. When both signals were reflected simultaneously and then detected, the phase angle of the complex surface reflection coefficient was determined by comparing the two reflected signals. The theoretical study resulted in equations which show the reflection coefficient to be a function of frequency and of material properties (sound velocity, density, and absorption) of a medium and a reflecting or boundary surface. Underwater acoustic experiments were conducted using reflected collinear, harmonic acoustic signals to analyze sample material with measured parameters comparing closely with predicted values. [Work from author's Ph.D. dissertation, Catholic University 1982 by same title.]
The boss model for reflection and scattering by rough surfaces
Authors: Twersky Victor
Published: October 2005

This review emphasizes the effects of including pair correlations and dense packing on coherent reflection and incoherent scattering of sound by distributions of protuberances (bosses) on rigid or free base planes. The earlier energy conserving forms for the specularly reflected wave, the surface impedance, and the differential scattering cross section per unit area, are obtained in terms of a transform of the scattering amplitude of an isolated boss. Low-frequency approximations are developed to delineate the roles of the packing density and multipole coupling effects, and explicit results are given for semi-elliptic cylinders and hemi-ellipsoids. It is shown that for lossless bosses, the reflection coefficient has a minimum, and the incoherent scattering a maximum, at the packing density corresponding to maximum fluctuations in the number of bosses per unit area. It is also shown that multipole coupling effects may be misinterpreted in data inversion programs as changes in boss shape; if such effects are not accounted for, then, e.g., hemispheres may be mistaken for hemi-ellipsoids broadened along the base plane and shortened along the normal. Illustrations include problems of the gaseous boss adhering to a rigid bottom.
Scattering from two and three gratings of densely packed compliant tubes
Authors: Radlinski Ronald P. , Janus Robert S.
Published: October 2005

In previous studies [R. P. Radlinski and M. M. Simon, J. Acoust. Soc. Am. 72, 607–614 (1982)] of scattering from two gratings of compliant tubes, excitation of higher order antisymmetric modes was shown to degrade insertion loss performance. In this presentation, scattering from gratings which are densely packed with tubes is considered for both two and three layer configurations. For these cases, additional types of structural modes must be incorporated into the analysis. The low-frequency scattering from the multiple gratings can be understood in terms of equivalent circuits. The restricted benefits from the use of three gratings are discussed in terms of the parameters which control the frequencies of transmission maxima. Calculations will be compared with experimental data. [Work supported by NAVSEA.]
The acoustic radiation force on a heated (or cooled) rigid sphere. Theory
Authors: Lee C. P. , Wang T. G.
Published: October 2005

A finite amplitude sound wave can exert a radiation force on an object due to the nonlinearity of the wave field [L. V. King, Proc. R. Soc. (London) Ser. A 147, 212–240 (1934)]. In this work we study the radiation force on a rigid small sphere (i.e., in the long wavelength limit), which temperature is different from that of the environment, in the absence of gravity. This investigation is relevant to material processing in space using acoustic levitation. We first calculate the temperature-induced perturbation of the incident wave plus the wave scattered from the sphere surface using Bonn approximation. Then we evaluate the radiation force on the sphere using the time-averaged integral momentum equation. Both isotropic and nonisotropic temperature profiles are considered. In this calculation the acoustic effect and heat transfer process are essentially decoupled because of the long wavelength limit. The heat transfer information required for determining the force is contained in the parameters which are integrals over the temperature distribution. [Work supported by NASA.]
Computer-controlled measurement of dynamic compressibility of polymers
Authors: Nolle A. W. , Lin T. S.
Published: October 2005

Some years ago a method for measuring the complex compressibility of polymers was reported from the National Bureau of Standards [J. E. McKinney, S. Edelman, and R. S. Marvin, J. Appl. Phys. 27, 425–430 (1956)], and used in several comprehensive studies. The sample is in a rigid chamber small compared to desired wavelengths, along with two piezoelectric transducers and a liquid under controlled static pressure. To find compressibility, one needs the complex transmission factor for this system, that with a standard sample, and that for liquid only. We have adapted the experiment to computer control. The transmission factor is read repeatedly from a precision two-channel lockin detector during a single 100-min temperature scan while recurrent 100-s frequency scans occur. A smaller chamber permits measurements above 10 kHz. The reduction procedure smooths the data and determines the compressibility for specified standard frequencies and temperatures. Results are shown for a poly-urethane for −2° to 30°C and 0.4 to 11 kHz. [Supported by ONR. Assistance of ARL, Penn State is also acknowledged.]
Can the opposite ear provide profile information?
Authors: Green David M. , Kidd Gerald
Published: October 2005

Consider a spectrum produced by 21 components, all equal in amplitude and spaced in equal logarithmic steps in frequency. (The frequency ratio between successive components being 1.12, or about 6 tones/oct.) The signal is an increment in the middle component, near 950 Hz. A two-alternative, forced-choice method is used to measure the signal threshold. The overall level of the spectrum varies randomly within trials by ±20 dB. We have described the detection process as profile analysis since it amounts to detecting a “bump” in an otherwise flat spectrum of uncertain overall level. For practiced observers the threshold for the signal, added in phase to the 950-Hz component, is about 14 dB below the level of that component (a Weber fraction of about 0.2). In this experiment we determine the threshold for the increment in the 950-Hz component when the other 20 components are eliminated from the test ear and are presented to the opposite ear. The signal threshold increases by about 12 dB (a Weber fraction of approximately 1.0). Apparently, the information in the opposite ear cannot be effectively integrated with the signal component to create a profile. [Work supported by NIH.]
Characterizing the impact of materials on transducer reliability
Authors: Smith R. Lowell
Published: October 2005

Achieving high reliability for an acoustic device depends ultimately on its design, materials of construction, fabrication processes, testing, correct installation, and the environment and conditions of use. This paper focuses on evaluating the impact of materials on transducer reliability. It is sometimes appropriate to characterize materials reliability using the familiar exponential reliability, or constant hazard rate model. Commonly in the marine environment, however, degradation processes operate which imply instead wearout reliability descriptions. Attention is focused on distinguishing, characterizing, and representing the reliability impact of these two situations. Failure definition, failure mode, and service limit concepts are introduced and their implications explored. The interpretation of chemical kinetics and other physical rate processes as the microscopic bases for macroscopic reliability descriptions is investigated. Under favorable circumstances this leads to the availability of time compression techniques referred to as accelerated testing, as a reliability evaluation tool. Suggestions are made concerning how reliability methods may be used to reduce the scope of the overall product or device improvement problem. Examples illustrating the use and implications of materials reliability methodology are presented.