摘要:

Acoustical effects of violin varnish—those of mass, stiffness, and internal friction—are examined qualitatively and quantitatively. Dynamic measurements of Young's modulus, real and imaginary, are made for films of typical oil varnishes on a substrate of cross‐grain spruce through aging periods of 1 yr or more and expressed in the practically useful terms of modulus over density. After112 yr, the hard varnish had a real modulus per unit density of 2.5 × 1010cm2/sec2andQabout 23; after 1 yr, the values for the soft varnish were 1.6 × 1010and 8. A high‐grade floor varnish had intermediate values. The imaginary component of the soft one was substantially independent of frequency from 400 to 5600 cps. Exact calculations of added loss and tuning shift, made for a “pseudofiddle” comprising rectangular top and back of orthotropic materials simulating spruce and maple, are believed roughly representative of the violin. Added loss is more apt to be damaging than is detuning of plates. The loss comprises two components: (1) a reduction in sound caused by the reactive parameters of varnish, i.e. mass and stiffness, and effective irrespective of resonance; and (2) one caused by internal friction and greatest at a resonance. With an intermediate varnish, a coat of 0.0127 gm/cm2(thickness about 0.005 in.) causes “flat” loss of about 1 dB and resonance loss about 3 dB; this is excessive. Varnish loss in the top plate is about three times that in the back; unless the spruce is overly resonant, its varnish should be thin. Top is more subject to detuning than back. Loss due to varnish is best controlled by weighing, with final adjustment of wood thickness after varnishing.

ISSN:0001-4966    

DOI:10.1121/1.1911243

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An analytical approach for predicting the rotational sound due to blade loadings in propeller ducts, based on definable propulsion quantities is presented. It is assumed that the sound field in the propeller plane may be represented by expanding the rotating net blade pressure distribution in a suitable series that satisfies both the wave equation and the boundary conditions associated with the duct and hub. The equations allow for the calculation of the spectral and spatial sound‐pressure distribution along the axis and radius. The validity of the analytical approach is investigated by exploring the sound field of a full‐scale model duct under measured operational conditions. Calculated and measured sound pressures along the duct wall in front and in the propeller plane are in good agreement. Behind the propeller plane, the deviations increase. This effect may result from an increased turbulence behind this plane as demonstrated by a spectral analysis. The analytical approach did not consider a finite tip clearance. Effects of a variable tip clearance on the sound field were explored experimentally. An increase of tip clearance from 0.38 to 1.5 in. resulted in a reduction of the over‐all sound pressure level by 5 dB.

ISSN:0001-4966    

DOI:10.1121/1.1911244

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

This paper describes a preliminary experimental investigation of pressure fluctuations in a separated flow behind a thin fence. Methods of determining the position of recombination point, which is closely related to the position of maximum sound‐pressure level, are discussed. Noise sources within the flow are identified. Significant and parasitic variables are noted and a dimensional analysis is presented. A similarity relation is also presented, relating sound levels to frequencies and free‐stream velocities. Graphs of the variation of power spectral density with frequency, and sound level with distance behind the fence are given for distances up to 50 fence heights behind the fence. It has been found that the frequency spectra alter considerably with distance behind the fence and that the maximum sound level behind a fence is about eight times that in a turbulent boundary layer, with the same free‐stream dynamic head.

ISSN:0001-4966    

DOI:10.1121/1.1911245

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The ultrasonic cleavage of cyclohexanol in aqueous suspension produces acetylene. The rate of the reaction is independent of the concentration of cyclohexanol and is unaffected by the addition of the solid radical scavengers, acrylamide and allylthiourea, but is reduced in the presence of oxygen and nitric oxide. These results are consistent with the idea that the ultrasonic reaction takes place within the cavitation bubbles. Oxygen and acetylene in aqueous solution react to form carbon dioxide when treated with ultrasonic waves.

ISSN:0001-4966    

DOI:10.1121/1.1911246

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The propagation of the higher modes of longitudinal wave propagation in a dispersive elastic rod was investigated, both analytically and experimentally. The Pochhammer‐Chree equation was solved for the mode shapes and group velocities as a function of wavenumber for the axisymmetric modes of longitudinal wave propagation. By integration of the axial displacement across a cross section, an indication of the planeness of the waves was obtained. In the experimental investigation, elastic waves generated in a colored‐glass pressure bar by absorption of luminous energy from aQ‐switched laser were measured using a thin piezoelectric crystal sandwiched in the pressure bar. The gross experimental results showed good agreement with the response as predicted by Love's modified wave equation. Higher modes of wave propagation not predicted by the one‐dimensional theory were evident in the experimental record. These effects were related to the results obtained from the Pochhammer‐Chree equation.

ISSN:0001-4966    

DOI:10.1121/1.1911247

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A study has been made of the acoustic transients generated in water by transducers made of materials that undergo electric field‐forced antiferroelectric‐ferroelectric transitions. The amplitude and time profile of the pressure pulses have been examined in detail. It has been seen that finite amplitude signals may easily be generated using such transducers. This behavior indicates that they may be of use as nonresonant generators of high‐amplitude acoustic waves.

ISSN:0001-4966    

DOI:10.1121/1.1911248

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The solution of the diffraction of sound waves by an axially moving fluid cylinder is obtained. Results indicate that there is no Doppler frequency shift for the scattered wave and when the angle of incidence is normal to the cylinder axis, the scattered wave is independent of the movement of the medium. Numerical computations for the magnitudes as well as the radiation patterns of the scattered wave as a function of the velocity of the moving medium were also carried out for various incident angles. It is found that the magnitudes and the radiation patterns of the scattered wave are quite sensitive to the variation in the angle of incidence even for slow relative movement of the fluid media.

ISSN:0001-4966    

DOI:10.1121/1.1911249

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The normal modes and natural frequencies of a structure are determined from a knowledge of the normal modes and natural frequencies of its components parts. Only linear elastic structures resting on an immovable base are considered. The total structure is mentally broken down into a primary structure (part including base points) and one or more substructures. The displacement of the total structure is expressed as a series expansion of the scaled normal modes of the primary structure. The scaling factors involved are determined from the equilibrium equations of the primary structure with the secondary structures removed and replaced by their internal forces of connection.

ISSN:0001-4966    

DOI:10.1121/1.1911250

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Optical holographic interferometry is used to study the vibrational characteristics of a sonar transducer. Experimental methods are described, and photographs of 13 resultant hologram images are included. Each is an interferometric fringe pattern from which the peak‐to‐peak amplitude of every point on the vibrating surface can be computed. The result of an exact theoretical analysis is stated; the solution for a simplified model is derived; and numerical results are compared.

ISSN:0001-4966    

DOI:10.1121/1.1911251

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The effect of rotatory vibration of a rigid circular die on an elastic half‐space has been studied. Two cases are considered: (a) half‐space with a circular cylindrical hole in the middle, and (b) half‐space made of two materials. The dual‐integral equation technique of Noble is utilized to solve the mixed‐boundary‐value problems.

ISSN:0001-4966    

DOI:10.1121/1.1911252

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP