Sound Transmission Measurements Research Articles

Long-Range Sound-Transmission Measurements in the North Atlantic Ocean

Although the qualitative aspects of long-range transmission in the deep sea have long been known, little has been reported about its quantitative features, other than travel time, since the pioneering work of Ewing and Worzel nearly 20 years ago. In the present work, standard Navy Sofar bombs, dropped by an aircraft at intervals of about 100 miles between Bermuda and the British Isles, were recorded at Bermuda on hydrophones at various depths. For a Sofar-axis hydrophone and for shots dropped between Bermuda and the Azores, an energy-transmission loss of the form 10 log r0r+ar was found, where r0 is a transition range between spherical and cylindrical spreading and a is an attenuation coefficient. r0 was found to be about 2000 yd, in rough agreement with the hypothesis that the energy carried by a ray bundle becomes diffused throughout the channel width it occupies. The attenuation coefficient was found to be of the form A+Bf, and to be much higher than that caused by absorption alone. The mid-Atlantic ridge produced a loss of 5 and 15 dB for shots at 1500 and 3500 ft. In the absence of this loss, a maximum range of 7000 miles for a 4-lb Sofar bomb would be predicted.

Magneto-acoustic oscillations in thallium

Longitudinal sound wave transmission measurements were made nt frequencies up to 270 Mc/s in a single crystal of thallium. The resulting dimensions of the Fermi surface are compared with the predictions of the free electron model. The agreement is very good if a sirgle zone scheme is used, demonstrating the importance of spin-orbit effects on the band structure of metals having high atomic number. (H.D.R.)

Laboratory Measurements of Sound Transmission through Suspended Ceiling Systems

A laboratory facility is described as evolved for the measurement of sound transmission through suspended acoustical ceilings under field conditions of erection over part high partitions. The results of exploratory measurements are reviewed for a wide range of the dimensional and acoustical parameters of the ceiling-plenum system. Consideration is extended to the ceiling-partition system and to the importance of an accurate simulation of field conditions of erection for the testing of all elements, individually and interacting, in the ceiling-plenum-partition system. The compatibility of this approach with conventional test methods is suggested.

A New Method for Laboratory Measurements of Sound Transmission Using Small Sized Test Materials-

A New Method for Laboratory Measurements of Sound Transmission Using Small Sized Test Materials-

The New Reverberation Chambers for the Measurements of Airborne and Impact Sound Transmission

The New Reverberation Chambers for the Measurements of Airborne and Impact Sound Transmission

American and European Standard Methods for Measurement of Sound Transmission in Buildings

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Recent Methods for the Measurement of Sound Transmission in the Ocean

The transmission of sound in the ocean has recently been investigated by two methods. In one, a transducer mounted on a submarine served as a sound source of controllable depth, range, and frequency. A string of six hydrophones suspended from a surface vessel enabled the sound field to be measured at six different depths. Measurements at eight and sixteen kilocycles were obtained on a cruise in Caribbean waters and have been plotted as transmission anomaly cross sections showing contours of equal sound level after the removal of spherical divergence. In the other method, the submarine was replaced by a surface vessel from which a sound projector could be lowered to specified depths. This method, employed on a cruise in Middle Atlantic waters, permits longer ranges to be reached, but yields a density of data insufficient for contouring. A second method of lucidly representing the sound field is given.

Sound Absorption and Transmission Measurements

Report is given of the research performed in the last ten years in the field of architectural acoustics, with special reference to measurements of sound absorption coefficients of materials and sound transmission losses of partitions. The absorption of sound by systems of resonators is particularly handled.

Transmission of Sound Through Homogeneous Walls

Current methods of measuring the transmission of sound through structures include the random incidence or reverberant sound field method, and the normal incidence or tube method. The latter method has the serious defect that only normally incident sound waves are used to drive the specimen, whereas, in actual use it is probable that waves having oblique angles of incidence will be experienced. Furthermore, considerable deviation from the mass law, in the direction of increasing transmission, occurs as a result of flexural waves induced in the specimen by non-normally incident waves. Random incidence sound-transmission measurements made on homogeneous walls of aluminum, plywood, and plaster-board, are in satisfactory agreement with a theoretical treatment, which postulates that the wall impedance has a resistive component in addition to its mass reactance, and a stiffness reactance resulting from the occurrence of flexural waves.

The Dependence of Sound Transmission Measurements on Microphone Position

In the customary method of determining the transmission loss of a wall or floor partition it is necessary to measure the difference in sound levels existing in two rooms which have the partition as a separating wall. Also, the ratio S/A2, where S is the transmitting area of the partition and A2 the total sound absorption of the receiving room, must be known. It was found that despite adequate precautions the sound energy density in both test rooms was not entirely uniform. In particular, on the quiet side a sharp drop in level occurred within a region of 2 or 3 feet from the panel face. The sound energy density existing at the panel face on the quiet side may be considered to consist of a direct component arising from energy radiated directly off the panel and a reverberant component arising from reverberant energy existing throughout the entire room. On this basis a formula was computed which allows one to determine transmission losses by restricting measurements on the quiet side to positions at the panel face. The formula was found to be in very good agreement with experimental results over a wide range of variation of A2. All of the above data were obtained with a pressure microphone. A number of similar measurements, using a pressure gradient (ribbon) microphone of special design, were also taken. The results so obtained were independent of the amount of absorption in the room and the area of the panel, although to secure the actual transmission loss a constant correction is required.

Architectural Acoustic Testing with Electro-Thermal Noise as a Test Source

The warble-frequency test tones from a vacuum-tube oscillator have been generally used in reverberation and sound transmission measurements. The method of employing selected frequency bands of electrical thermal noise as test sources in conjunction with the high speed level recorder is presented. Typical data taken under actual “job conditions” encountered by the consulting acoustical engineer are included. The advantages of the new technique are discussed from the standpoint of simplicity of instrumentation and reliability of results.

Recent sound-transmission measurements at the National Bureau of Standards

Recent sound-transmission measurements at the National Bureau of Standards

XXX.On the measurement of the sound transmission of a partition

XXX.On the measurement of the sound transmission of a partition