Patent GB-1069129-A (GB)
Title: Flight noise monitoring equipment
IPC: H04R1/08
Filed: 1965-06-24
Abstract: 1,069,129. Measuring sound levels; microphones; sound magnifiers. ROHDE & SCHWARZ. June 24, 1965 [July 2, 1964; Oct. 17, 1964], No. 26723/65. Headings H4D, H4J and H4X. Flight noise monitoring equipment comprises a plurality of sound level measuring devices A, Fig. 1 (also Fig. 2, not shown), situated in the vicinity of an airport the outputs of the devices being transmitted in analogue form by wire 12 (or by modulations of a H.F. transmission path) to a central station, e.g. in the airport building 2. Such device A includes a microphone 1 feeding a known noise level meter 5 which evaluates the frequency spectrum of the input and supplies a D.C. voltage to a converter 10 which operates to generate an output signal of frequency proportional to the measured noise amplitude levels. The output signals are transmitted over a normal telegraph wire 12 to the central station (Fig. 2, not shown) at which proportional D.C. voltages are derived via converters 20 and supplied to classification devices 21 which divide the (noise level representative) D.C. voltages into five distinct levels. (This classification may be performed at the devices A and devices 21 omitted.) The classified voltages are then effective to operate coloured signal lamps 24 appropriate to the particular device A and the particular noise level; to operate a timing counter 25 and an acoustic signalling device 26 when a predetermined noise level is exceeded; and to operate a digital printer 23 on which all noise levels are recorded. The operation of device 26, and of the lamp 24 appropriate to the highest noise level (i.e. level 5) are printed in red and the device and lamp together with counter 25 require to be re-set by hand. The printer 23 operates in response to pulses from generator 27 (producing, e.g. one pulse per-second) and in addition to printing the various noise level sensed by the devices A also prints the time in hours, minutes and seconds. Additionally, other data such as flight numbers and expected noise levels fed into a store 28 are printed by 23 at the instant of take-off. Generator 27 also produces pulses (e.g. one pulse per hour) which cause counters 29, running in parallel with counters 25, to print out the overall duration of excess noise levels during the intervals between such pulses. For testing the equipment a control generator 31 operated either automatically by generator 27 or by hand, controls a standard generator 33 supplying brief test signals to respective reproducers 30 acoustically coupled to the microphones 1 in the assemblies 2 of devices A. Each assembly 2 comprises a sound-conducting tube (101, Figs. 4 and 5, not shown) cupped by a protective bead consisting of two elements (103, 105) spaced by supports (104) to form an annular opening communicating with tube (101) and operating as a folded exponential horn, with a cut-off frequency, determined by the outside diameter of the head in accordance with the desired frequency range. The microphone capsule (120) is supported in an opening in the tube wall and the reproducer for testing the equipment (30, Fig. 1) comprising an earpiece type device (124) is mounted opposite the capsule. The latter is enclosed in a protective cap (121) and a protective grid may be positioned at the opening in the tube wall. The tube is terminated to be free from reflection by a wedge (122) of sound absorbent material contained in a cut-away tube (123) inserted in tube (101). Elements such as amplifiers, impedance transformers etc. are mounted at (126) and the whole assembly is protected by a housing (125). The annular opening in the head (102) is closed by a fine wire mesh (127) which may be electrically heated to prevent icing.