The acoustic quality of a room for music cannot easily be determined. As timbre is important in music it is possible that the perceived change in timbral quality of a sound in two spaces may give the basis for a measure of acoustic quality. The smallest perceivable change in the timbre of steady-state stimuli was measured in different listening environments through two experiments featuring a spectral centroid and rise time, respectively. Five component harmonic stimuli at 440 Hz were employed. The centroid of the standard stimuli was fixed at 2.95, in which the median amplitude of each component of the standard was set at 0.5, while those of comparison stimuli were varied from 2.93 to 2.41 in steps of 0.02 with a negative spectral tilt. The smallest perceivable change in the rise time was also measured using complex tones containing ten harmonics of 200 Hz (F0) with linear spectral slopes of −6 dB/oct. Rise times of comparison stimuli were varied from 5 to 25 ms in 2-ms steps, while the fall time was fixed at 5 ms across the stimuli. Results are presented and comments are made on how the acoustics of the listening environment influences the perception of timbre.
Many measurements of sound attenuation rates in forests have been made but there is little in common in the measuring procedures used or the results obtained. Consequently there is a considerable divergence of opinion on the effectiveness of vegetation as a noise control measure. The paper looks at the factors controlling the transmission of sound through vegetation, the attenuation rates achieved in pine plantations, and the reasons for the important perceived reduction in noise that hedges and plantations give. (Author/TRRL)
A theoretical determination of the location and size of blockages in the one-dimensional duct has been carried out. It is found that the blockage cross-section area function can be calculated from the measured eigenfrequencies obtained using two boundary conditions, i.e., closed–closed (or open–open) and closed–open ends. When the blockages are small, the area function of the blocked duct can be expressed as a one-dimensional spatial Fourier transform, whose spatial frequencies are related to the eigenfrequency shifts caused by the blockages in the duct. The method developed can be applied to the detection of the multiple blockages. The experimental results show that the accuracy of the calculated blockage area function is dependent on the number of the eigenfrequencies used. The agreements between the calculated blockage area and the actual blockage are excellent when the half-wavelength of the eigenfrequency used is greater than the length of the blockage.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
'%3e%3cg id='b'%3e%3cpath id='a' stroke='%23000' stroke-width='2' d='M-6-25H6m-12 3H6m-12 3H6'/%3e%3cuse xlink:href='%23a' y='44'/%3e%3c/g%3e%3cpath stroke='%23fff' d='M0 17v10'/%3e%3ccircle r='12' fill='%23cd2e3a'/%3e%3cpath fill='%230047a0' d='M0-12A6 6 0 0 0 0 0a6 6 0 0 1 0 12 12 12 0 0 1 0-24z'/%3e%3c/g%3e%3cg transform='rotate(-123.69)'%3e%3cuse xlink:href='%23b'/%3e%3cpath stroke='%23fff' d='M0-23.5v3M0 17v3.5m0 3v3'/%3e%3c/g%3e%3c/svg%3e)
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
