Volume 52, Issue 5A, November 1972
Index of content:
52(1972); http://dx.doi.org/10.1121/1.1913244View Description Hide Description
The purpose of this study is (1) to examine whether the differences of sound‐field qualities among seats in a music hall are accountable by a kind of multivariate procedure, (2) to examine whether subjective characteristics of several music halls are comparable with this technique, and (3) to propose a new method to estimate sound‐fieldcharacteristics of music halls from physical terms, in place of words used in conventional techniques. Experimental procedures: (1) First, program sources are recorded in an anechoic room, and those sources are reproduced through a omnidirectional loudspeaker system on the stage of a music hall, Yamaha Music Camp. Those reproduced sounds are recorded stereophonically at each seat. (2) Then the hearing tests for those reproduced sources are carried out with dynamic receivers in a sound‐proof room. (3) At the same time acoustic characteristics of the room such as percent‐articulation, directional diffusivity, definition, reverberation time, transmission characteristics,SPL variation, etc., at the respective seat are measured. Subjective characteristics were first analyzed by multidimensional scaling(MDS), which yielded three orthogonal factors. Then, principal axis method (PAM) was applied to the correlation matrix of these factors and the physical measurements. The results were that three factors were extracted by PAM; the first represents SPL level, the second reverberation time or definition, while the third is not interpreted. An interpretation of these subjective characteristics in terms of physical measurements is proposed.
52(1972); http://dx.doi.org/10.1121/1.1913245View Description Hide Description
A direct correlation between the flow and noise of a jet—between the “cause” and the “effect”—has been measured. Two kinds of correlations were explored, namely (1) the broad‐band turbulence signal (hot‐film) with the broad‐band acoustic signal(microphone), and (2) the narrow‐band filtered turbulence signal with the narrow‐band filtered acoustic signal; the latter approach was ultimately adopted. The correlations were analyzed in terms of an extension of Proudman's form of Lighthill's integral for aerodynamic noise; this yielded the relative intensity and spectrum of the noise originating from unit volume of a jet (35 locations) and received at a farfield point (r = 96D, φ = 40°); this in turn led to the relative emission of successive “slices” of a jet versus axial distance X over the measurement range (1D ⩽ × ⩽ 7D). Qualitative agreement was found with Ribner's X° law, and the spectral peaks for each slice were located in frequency essentially as predicted by Powell. The maximum normalized broad‐band correlation of 1%–2% implies roughly that a turbulence “eddy” centered at the hot‐film contributes only 1%–2% of the rms sound pressure at the microphone. The total effective number of uncorrelated noise‐producing eddies is thus of order (1/0.02)2, or some 2500 on an equal strength basis.
52(1972); http://dx.doi.org/10.1121/1.1913246View Description Hide Description
Transportation noise, and motor‐vehicle noise in particular, account for the steady or slowly varying ambient noise level, particularly in urban areas. Being so numerous, motor vehicles can be treated statistically, and this establishes consistent noise emission characteristics.Vehicles are categorized as: passenger cars [including light delivery trucks up to 6000 lb gross vehicle weight (GVW)], light, medium, and heavy trucks with GVW ranges of 6000–15 000, 15 000–30 000, and over 30 000 lb, respectively, tractor trailers, buses, cement‐mixer trucks, and motorcycles. Speed ranges are 20–29, 30–39, 40–49, 50–59, and 60–69 mph. The sound level of the average vehicle of a given category increases consistently with speed and weight. The average vehicle is defined as the hypothetical vehicle having a sound level (A, B, or C weighting) and band‐pressure levels equal to the weighted‐mean decibels in the statistical distributions. The rate of increase with speed is such that in going from 30–39 mph to 60–69 mph, the sound level (A weighting) increases 8.5 dB for passenger cars, 9 dB for trucks and buses, 7 dB for tractor trailers, and 12 dB for motorcycles. For an estimated doubling of weight (motorcycles not included), sound levels increase 3.5 dB. For motorcycles, maximum noise occurs for full throttle setting, independent of road speed, gear, or engine loading. The octave‐band spectrum of the average vehicle has a shape which is characteristic of each category and shows progressive change in level and shape with increasing speed. The octave‐band spectra of four motorcycles, as examples, indicate dependence of level and shape on such parameters as type and size of engine, muffler configuration, and throttle setting. The sound level for acceleration is equivalent to about 40–49 mph cruising speed for tractor trailers and heavy trucks, and 30–39 mph for cement‐mixers, but the octave band spectra for the two modes of operation exhibit consistent differences. Sound levels recorded continuously for 24‐h periods at five locations, and analyzed for percentile distributions in each 1‐h interval, have a diurnal cycle that follows a consistent pattern in response to motor‐vehicle traffic.