A rigorous equation is set up for the velocity of sound in gases. This is used to calculate the velocity of sound in dry air at standard conditions from data taken in independent measurements. The result of this calculation is 331.45±0.05 meters sec.−1 An extensive survey of previous reported measurements has been made. After proper corrections are taken into account, the weighted mean is 331.464±0.05 meters sec.−1 The results of very precise interferometer measurements by the authors give 331.44±0.05 meters sec.−1.

No abstract

Resonant curves of loaded felt pads in compressional vibration give values for the damping and dynamic stiffness which show that felt in vibration is quite different from an equivalent perfect spring with viscous damping. The un-symmetrical resonance curves and the fact that, within experimental error, the stiffness is inversely proportional to the square root of the thickness indicate a decrease in stiffness with increasing amplitude. The increase in stiffness with pressure is so large that the ratio of dynamic elastic modulus to pressure (stiffness over mass) does not vary greatly between pressures of three to one hundred pounds per square inch. In this range the natural frequency of a mass on a felt pad is determined by the thickness of the pad rather than by its area and static load. An analysis of the performance of felt in reducing vibration transmission shows that its effectiveness is limited in most cases to frequencies above forty cycles per second. Practical installations have been studied and tables drawn up to give the acoustical engineer “handbook” information for the solution of problems in vibration reduction.

The probable shape of a limiting spectrum for noise in a working environment where there is long daily exposure is determined by reasoning from previously determined data of the hearing mechanism. It is assumed that hearing loss is due to a progressive fatigue phenomenon, the fatigue being a direct function of the energy stimulus in the inner ear. From the characteristics of this stimulus as a function of frequency, it is shown that the most sensitive region for loss is around 3000 cps, the low frequencies being as much as 20 db less sensitive than this region. The 4000 cps "notch" in audiograms of industrial workers is thereby explained. The limiting spectra are essentially equal-loudness contours for broad-band noise when the noise spectrum is plotted in octave bands.Two limiting loudness curves and their corresponding spectra are tentatively suggested as damage risk criteria. If the noise exceeds 100 sones in any octave band, it appears very probable that long time daily exposure will result in hearing damage and in a frequency region slightly above the frequencies of maximum stimulus. If the sound does not exceed 50 sones in any octave band, it appears to be unlikely that damage will occur even with long exposure. These criteria are confirmed by the few literature references which have enough data to be used. The need for more research to test these conclusions is emphasized.

In order to provide engineering information for the use of felt in vibration isolation, the dynamic stiffness and damping of three widely different grades of felt were measured by means of resonance curves. The dynamic stiffness, which was much greater than the static stiffness, decreased with amplitude so that the resonance curves were unsymmetrical. Except for pressures below 6 p.s.i., the stiffness modulus of felt increased with static pressure at a rate which made their ratio nearly constant. The natural frequency of a mass supported by a felt pad is, therefore, nearly independent of the static pressure load on the felt. Curves are given showing natural frequencies for 1 inch thicknesses of soft, medium, and hard felt for a range of static pressure between 1.5 and 100 p.s.i. It is shown that, except at low pressures, there is little difference in the natural frequency of hard or soft felt, and that there is a low limit of about 20 c.p.s. for 1-inch felt.