This paper describes a simple device which simulates a human vocal tract acoustically, and results obtained from systhesized speech sounds produced by the device. It is simple and easy to deal with as compared with an electrical vocal tract simulator. Acoustic models of vocal tracts are made of transparent acryl-resin. They are of box shape. The vocal tract length of a man's model is 17. 5cm, that of woman's model 14cm, about 80% of that of the man's and that of children's models about 11cm and 9cm. The height is 2. 5cm. The cross-sectional areas of these models are made variable by moving 1-cm thick plastic strips which are closely inserted from one side. They have a nasal branch as well. Glottal sounds are sent into one end (glottis) of the models and let out of the other end (mouth). Various vowels and other sustained sounds are produced accrding to the configuration of the models at that time. The driving unit of a horn speaker (NEC-555M, Japan) was used as a sound source. Considering that the acoustic impedance at the human glottis is very high, a bundle of steel wires, each 1. 5mm in diameter and 14mm in length was packed tightly into the throat of the loud speaker. Consequently, the cross-sectional area of the throat is about 1. 3cm^2. By observing sustained seech sounds, we find two features in them. One is phonemic feature, in other words a feature that distinguishes one phoneme from others, and the other is a feature that contributes to naturalness, in other words, a feature that distinguishes not only males, females and children but also individuals from one another. We have successfully made these features clear physically. When the length of a vocal tract is reduced gradually from 17. 5cm, it will be seen that the configuration of phoneme is reduced similarly without spoiling the phonemic feature. As for the cross-sectional areas, relative values are only required. So we can normalize the vocal tract configuration of every phoneme with respect to the vocal tract length and the cross-sectional areas. The use of the normalized configurations will afford us normalized spectra of phonemes. The relation between the vocal tract length and the fundamental frequency of voice, which serves to distinguish speakers from one another in sex and age, can also be nomalized. That is to say, if the ratio of frequency, the wavelength of which is four times as long as a tract to the fundamental frequency of voice, is called a normalized pitch, we can obtain natural synthesized speech sounds when the normalized pitch ranges from 2. 5 to 5. 0. The waveform of glottal sounds referred to herein is saw-tooth form. The decay time T_3(msec) of the saw-tooth-wave form being sufficiently short as compared with one cycle T, the first zero point of glottal spectrum will apper at 1/(T_3)(kc). Glottal sound spectrum has a great influence upon characteristics of each individual's voice. The shorter the decay times, the sharper a voice becomes. Longer decay time (about 0. 6-1. 0 msec) is better for a female voice while shorter one (about 0. 2-0. 5 msec) is better for a child's voice.
Noises of 4 types of aircrafts on domestic routes were measured at 14 points shown in Fig. 1 in Kagoshima-city (a medium-sized city situated in the southernmost prefecture in Japan) for six days from 18 to 23 Oct. 1965, during which the weather was fine, with a wind velocity of less than 5 m/sec, temperature randing from 17 to 23℃, humidity randing from 34 to 48%. The measuring groups were as follows : 8 groups moving from point to point with sound level meters, 1 group with a magnetic recorder, 2 groups at B and C points, with a simple altimeter. The method of a sound level measurment is shown in Fig. 2. Observers start observations at the moment when they catch sight of aircraft. Tab. 2 shows the average sound level of each type of aircraft at 14 points in dB(A) at its taking-off and landing. From this table the mean differences of sound level between types of aircraft and between take-off and landing may be estimated. Fig. 3 shows the average octave band levels at point A, and by applying the A weighting charactor of sound level meter to these spectra, we obtained the full line spectra shown in Fig. 5. The spectra in dotted line shown in Fig. 5 were obtained by correcting absorption by air at a temparature of 20℃ and a humidity of 42%. The above atmospheric conditions correspond to what is shown in Tab. 5. The correction data were taken from ISO-Draft (Draft secretariat proposal for a procedure for describing aircraft noises around an airport). In Fig. 5 relative sound levels are shown in dB(A), based on the sound level at point A (the distance r from the path of aircraft to point A is nearly 200m). It seems that no correction is required for Heron (H). Tab. 4 shows PN-dB estimated from sound levels of Fig. 3 and the difference between PN-dB and sound level dB(A). The value of the above difference is about 13 as already known. Now we tried to work out the contours of equal sound level dB(A) for Heron. Five planes of this type shown in Tab. 5 were selected because the courses of these planes were reported to be very similar. They flew along the courses shown by the curved Gothic line in Fig. 4 and climbed at an inclination of about tan α=0. 11. Now we are able to calculate the distance r from the path to each measuring point. By substituting r and sound levels in dB(A) at points E and F into Formula (I), we can determine the power level PWL(A) of this type of aircraft. Formula (I) corresponds to nondirectional sound propagation in a free field. The mean value of two PWL(A) thus obtained was 142. 5 dB. By Using the formula (I) again we were able to calculate the contours of equal sound level. Fig. 4 shows this result which was drawn along a straight course on the assumption that the planes flew straight on and we referred to Fig. 4 for working out the acutal contours shown in Fig. 6. The contours in Fig. 6 was used to estimate the sound level at each measuring point. They are shown by line (a) in Tab. 6. We compared these estimated levels which actually measured values shown by line (b) (from Tab. 5) and line (d) (from Tab. 2). The defference between estimated and observed values is shown by lines (c) and (e). Errors, of course, arise from many factors : (I) permitted errors of sound level meters, (2) personal errors of observers, (3) change of places where observations are made (most of measurements were conducted on flat housetop of two- or three-storied buildings (4) the fluctuations of atomospheric conditions, (5) change of the pathes on which aircraft flew. The last would be the largest cause of errors. Fig. 7 shows the contours for Convair-240 (CV), worked out by the same procedure. The examination of Tab. 6 and Fig. 7 indicates that errors are within the range of ±4dB (except one point). The values of NNI (proposed in the ISO draft) were calculated by rough method. In Formula (2) dB(A)+13 was used to represent L instead of PN-dB and the total number of flights in one day (from morning till evening) to represent N.