摘要:

A ray‐tracing program which has been developed for the IBM 704 and 7090 computers yields results which show excellent agreement with experimental data. The program permits ray computations for arbitrary source and receiver depths, bottom profiles, and velocity structures. The tabulated results give actual ray trajectories as well as the geometrical spreading associated with each path. Realistic curves of transmission loss as a function of range can be determined by adding individual ray intensities, once reflection loss values have been introduced. Theoretical results were compared with a 100‐cps transmission loss curve obtained using a CW projector and a bottomed hydrophone in a deep ocean area of the North Atlantic. Good agreement was observed at moderate to long ranges. Significant errors at short ranges were attributable in part to the lack of refinement of the methods used. (This work was supported by the Bureau of Ships, U. S. Navy Department.)

ISSN:0001-4966    

DOI:10.1121/1.1936635

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A hydrophone assembly has been installed on the east bank of the Gulf Stream, with terminals in the Lerner Marine Laboratory, Bimini, Bahamas. This assembly is being used to study the feasibility of combining acoustical, biological, and electronic techniques for information on soniferous animals in the natural environment. Sounds from two bottom‐mounted hydrophones, one in 100 ft of water and the other in 1200 ft are recorded on dual‐track magnetic tape on a 24‐hr basis. The tapes are played back at eight times recording speed and monitored for sounds of possible marine animal origin. More than 25 categories of sounds were observed during the initial period from November, 1960 to June, 1961. In general, sound categories at the shallow and deep sites are different. Usually, only a single category is present at a hydrophone at one time. A number of repetitive, diurnal patterns and possible seasonal patterns of soniferous activity are discussed. Some tentative identifications are made. Expansion of the installation is currently in progress; this includes additional hydrophones for the localization of sound producers and for information on migratory behavior of short duration. Demonstrations of the categories are presented from tape recordings. (This work was supported by the Office of Naval Research, the Bureau of Ships, and Bell Telephone Laboratories.)

ISSN:0001-4966    

DOI:10.1121/1.1936637

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The noise spectra in present military aircraft are reviewed, describing the characteristic sources. Objectives for noise control based upon communications, aural damage risk, and comfort are proposed. The probable maximum increases in noise exposure are described, and the prospects for control in future aircraft and space vehicles are discussed. Requirements for personal protection are deduced. Latest methods of evaluation of speech projection and reception systems are based both or physical measurements and intelligibility testing. Highly efficient articulation testing is based upon most difficult consonant sounds and upon simulated flight command sentences. Results permit rating of systems in terms of noise tolerance as a function of speaking effort.

ISSN:0001-4966    

DOI:10.1121/1.1936644

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Highly effective vibration damping materials for metal sheet structures can be obtained by making use of amorphous high polymers in the viscoelastic state. Materials of this kind can be adjusted to provide optimum damping at given frequencies in temperature bands of prescribed position and width. This can be done by mixing high polymers having different glass transition temperatures in suitable distribution or by copolymerizing suitable monomers. Plastification and addition of filling materia[s can play a part in obtaining the desired results. The larger the temperature bandwidth of high internal energy losses the larger is the frequency bandwidth. However, the maximum damping will be diminished when the bandwidth is increased; this follows from the laws which govern the molecular behavior of high polymers. Damping materials have been developed for different combined systems, such as metal sheets with a single damping layer at one side or sandwich systems, according to special technical demands with respect to frequency and temperature dependence. Experimental results obtained with these combined systems will illustrate the damping efficiencies which can be attained in optimum cases.

ISSN:0001-4966    

DOI:10.1121/1.1936646

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Preliminary results and experience with a two‐way analysis/synthesis formant tracking speech system are reported. Parametric information from the analyzer is coded into binary digital form at rates in the range 600 to 1200 bits per sec and transmitted over audio channels by high‐speed voice‐frequency telegraph equipment. (Paper presented by Walter Lawrence.)

ISSN:0001-4966    

DOI:10.1121/1.1936647

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A print‐out system has been developed which automatically records any one of over a trillion different quantized analyses of a spoken syllable. The main purpose is research toward improved methods of recognizing speech by machines. However, other applications for the digitized transmission of speech also are indicated. Results of tests made are analyzed and different approaches to the decoding problem are presented.

ISSN:0001-4966    

DOI:10.1121/1.1936653

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Over the past year numerous communications systems have been evaluated in the NEL High Level Noise Facility. This system, consisting of 16 low‐frequency and 38 high‐frequency horns driven by a 10 000 w amplifier, can reproduce jet aircraft noises to a group of six listeners at levels up to 140 db (over‐all,Cweighting). Two different mobile (flight deck) radio communications systems, a series of developmental sound powered phones, and a Helicopter PA rescue announcing system have been evaluated. In addition, limits of face‐to‐face communications have been established. Satisfactory communications using the best available acoustic components can be carried on in jet noise when both talkers and listeners are in 135‐db levels. Flight deck radio communication sets now in use in the fleet are usable up to levels of 125 db. Developmental models of sound powered phone equipments are usable up to 120 db, although present equipment is good only to 100 db. With no electronic or acoustic aids satisfactory face to face communications between a talker and listener are possible in jet noise up to 97 db at 3 ft, 91 db at 6 ft, and 85 db at 12 ft. Selected data (1) on different noises, (2) when either talker or listener are in quiet, and (3) when ear protection is used also will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.1936659

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Acoustical and seismological research from ships at sea have long made common use of high explosive charges as sound sources. Their principal advantages are intense radiation, broad spectrum, and the highly identifiable features of the waveform, the shock front, and the bubble pulses. In recent years far weaker electrical, and electromechanical impulse sources have been brought to a useful state for many problems of acoustical and seismic research. These sources share the advantages of high explosive except that they are far weaker. However, they have the distinct advantage over explosives that they can readily be repeated at a rapid rate. Very recently two electrical sources called the Sparker and the Thumper have been operated at sea with electrical inputs of 5000 watt sec and higher. With such electrical inputs subbottom reflections have been detected above noise level by a hydrophone towed from the same ship at speeds of two and a half knots in water 3000 fathoms deep. In the acoustical field experimental transmissions have been measured over very weak paths from the same sources. The early bottom reflections have provided new limits about the history of sea mounts and oceanic sediments while the new acoustical research demonstrates how these sources greatly facilitate path identification in sound and seismicP‐wave transmission.

ISSN:0001-4966    

DOI:10.1121/1.1936666

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A new technique for making continuous reflection profiles in the oceans has been developed in which reflection shots are recorded in a manner analogous to that employed in standard echo sounding equipment. This provides automatic correlation and integration of arrivals and makes possible rapid examination and analysis of large volumes of data. During recent months, several thousands of miles of track, mostly in ocean basin areas, have been studied with the Seismic Profiler. The deepest reflector seen in the Profiler records is the upper surface of a layer with seismic velocity 4.5–5.5 km/sec. This reflecting surface is very uneven. In large areas of the ocean basins, it is almost entirely devoid of sedimentary cover, except in pockets, and its roughness is accurately expressed by the sea floor topography. In other areas, principally in the abyssal plains and on the continental rises, the relief in this layer is no different, although it is obscured by up to a few kilometers of flat lying sediments. A prominent reflector within the sedimentary column is seen throughout the latter areas, usually at a depth of about 400–500 m below the sea floor. Its smooth, flat surface which is comparable to the present sea floor in abyssal plains, indicates that turbidity current deposition has long been the dominant process in deep sea sedimentation. The universal roughness of the top of the 4.5–5.5 km/sec layer and the absence of reflections from beneath it are taken as evidence that the layer is part of the original oceanic crust, possibly a less dense differentiate of the crustal material. This opposes the view held by some that the layer consists of older sediments, possibly covered by lava flows.

ISSN:0001-4966    

DOI:10.1121/1.1936667

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This paper will present some recent thoughts and experience directed toward simplification of the methods of developing subjective ratings of partition walls. Any such scheme will depend on the nature of the sound sources: speech, musical instruments, radio and television, machinery equipment, and apparatus, etc. Of these the most discussed is speech. Parkin has proposed and used a frequency weighting curve; Farrell and Watters, an articulation scoring scheme. The present paper presents somewhat simplified and similar ideas which lead to, for example, a parameter called “speech leakage index.” This evolves from a weighted average of the data taken at standard STL and NR frequencies. The same scheme with different weighting factors can be applied to other sound sources such as music and equipment noise. The measurement and evaluation of school room partition isolation given in the previous paper has presented an opportunity to check these assumptions. The results will be presented.

ISSN:0001-4966    

DOI:10.1121/1.1936678

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP