摘要:

A high‐intensity sound test chamber capable of producing 145 db and having a working area of6×3×112ft is described. The chamber uses the principle of reverberant sound to test electronic packages used in aircraft and missiles. Double wall construction and use of Aquaplas for panel damping provides the necessary sound insulation. Complete instrumentation and the loudspeaker generator will be described.

ISSN:0001-4966    

DOI:10.1121/1.1907711

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The effect of the frequency of occurrence of words upon their intelligibility in noise was examined under two conditions: (1) in unknown message sets where the specific words under test were initially unknown to the listener; and (2) in known message sets where the specific words under test were known to the listener. Substantial effects of word frequency are observed with unknown message sets, but not with known message sets. In known message sets, the prime factor determining intelligibility is the phonemic interconfusability among the words. In unknown message sets, it is suggested that the important determinant of the intelligibility of a word is its frequency of occurrence relative to the frequencies of the words with which it might be confused.

ISSN:0001-4966    

DOI:10.1121/1.1907712

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Intelligibility is defined as a property of speech communication involving meaning. Since only meaningful units have normal linguistic distributional properties, only meaningful units have the phonetic properties of actual speech. An auditory intelligibility dialect ratio is defined for a listener relative to a specified message. An analysis is presented of the Harvard PB lists, and a set of 10 lists of 50 monosyllables each is presented having an almost exact first‐order phonemic balancing.

ISSN:0001-4966    

DOI:10.1121/1.1907713

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

An improved buffer rod‐specimen unit is described for measuring longitudinal wave velocities in solids at temperatures up to 350°C. The method is particularly useful in determining elastic moduli of single crystals since very small path lengths in any prescribed direction can be employed. The use of molten metals to provide coupling at still higher temperatures is discussed.Two methods involving mode conversion at an impedance discontinuity are described for measuring shear wave velocities. Application to crystals of cubic symmetry is detailed, with a note on possible extension to less symmetrical crystals of any orientation.Data for fused silica and single crystal germanium are listed for temperatures up to 300°C in illustration of the methods described.

ISSN:0001-4966    

DOI:10.1121/1.1907714

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

An experimental program was conducted with a212 × 10 in.model ramjet combustor directed towards understanding the mechanisms which maintain high‐frequency combustion pressure oscillations (commonly referred to as “screech”) in the air‐breathing jet engine. Results show that pressure oscillations characteristic of transverse acoustic modes occur as fuel‐air mixtures approach stoichiometric values. The particular mode excited is related to orientation of the flame fronts in the duct, which in turn are functions of the particular flame holder geometry. It is shown that heat release associated with the flame fronts occurs in high‐impedance zones for the modes excited. High‐speed motion pictures of the combustion zone during screech show that the flame fronts are serrated, the number of serrations being proportional to screech frequency. The serrations are interpreted to be related to vortex shedding from the flame holder lips. High‐amplitude oscillations corresponding to the fundamental longitudinal mode occurred when conditions of intense screech were achieved. This mode transference is attributed to increased heat addition in the forward portion of the duct, a position favorable for driving longitudinal modes. Preliminary results show that high‐turbulence levels produce screech at lower values of fuel‐air mixture.

ISSN:0001-4966    

DOI:10.1121/1.1907715

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Absorption and velocity of sound in the range 0.5 to 10 Mc have been measured for solutions of hemoglobin under various conditions of temperature, concentration, and chemical environment. The hemoglobins of several species of mammals and different chemical forms of hemoglobin have been studied.In the absorption per wavelength only minor variations with frequency have been observed. Dispersion in the velocity of sound of these solutions has been measured. It has been possible to relate quantitatively the magnitude of the absorption and dispersion through relaxation theory by assuming broad distribution of relaxation times.

ISSN:0001-4966    

DOI:10.1121/1.1907716

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Beta‐quartz, the high‐temperature form of quartz, which exists from 573°C to 850°C, is examined for use as a piezoelectric device. The formulas for the piezoelectric constants and elastic constants are given for rotated reference frames. By suitably rotating the crystal plate, it is possible to piezoelectrically excite lengthwise extensional, face shear and thickness shear modes of vibration. Thickness extensional modes cannot be excited. It is thus possible to make both high‐ and low‐frequency piezoelectric resonators and transducers out of β‐quartz for very high temperature applications.

ISSN:0001-4966    

DOI:10.1121/1.1907717

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The piezoelectric relations and equations of equilibrium for an elastic spherical shell permanently polarized in the radial direction are derived. The solution for the radial displacement corresponding to uniform pressures on the inner and outer surfaces of the shell and a given voltage difference between the surfaces is obtained.

ISSN:0001-4966    

DOI:10.1121/1.1907718

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The problem of the propogation of harmonic signals in a slightly rough duct is investigated. The analysis made tractable by the assumption that the heights of the roughness peaks are small compared to the average separation of the duct walls. Both acoustic and electromagnetic waves are treated. In the case of a duct with harmonic roughness, it is found that waves are not scattered upstream if the frequency of the transmitted signal exceeds certain critical values related to the natural modes of the wave guide and the wavelengths of the wall roughness. It is also found that the scattered signals are amplified whenever the frequency of the transmitted signal is equal to any of a series of critical frequencies determined by the natural modes of the guide and the spectrum of the wall roughness. Statistically rough walls are also treated, and specific results worked out for roughness functions having Dirac delta function correlation exponential correlation.

ISSN:0001-4966    

DOI:10.1121/1.1907719

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

If the criterion is adopted that a schematic diagram of a system must give a complete representation of all the physical or engineering principles involved including a specification of the characteristics of each part and how the various parts are joined to form the system, it follows that perfect couplers must be included the list of items available to anyone creating schematic diagrams. It is shown by examples that perfect couplers produce their action by the imposition of constraints and that the set of constraints for a given coupler imposes the condition of no power loss or gain. Conversely, if a conceptual device is known to be a perfect coupler and some constraints are known, then the remaining ones can be deduced. It is shown that perfect couplers may be of two types and that examples of each type are common. It is further pointed out that perfect couplers present no problem if an investigator is always aware of their possible existence. The discussion closes by showing that couplers can be dealt with mathematically in a systematic manner.

ISSN:0001-4966    

DOI:10.1121/1.1907720

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP