GB336766A - Method of testing wood strips or other materials designed for the production of resonance structures - Google Patents

Abstract

336,766. Kopp, R., and Weickert, E. Sept. 27, 1929. Testing resonant qualities of wood and other material.-Sounding-boards for musical instruments such as pianos, violins, wind instruments, organs, and harmoniums, gramophones, loud speakers, clocks, &c. are built-up ot strips of wood &c. 1 tested acoustically by setting them in a state of vibration by sound waves or electromechanical impulses, as by apparatus 2, 3, diagrammatically shown, and measuring their response by use of a microphone 4 and an amplifying valve 5, in the anode circuit of which is arranged a milliammeter or the like. The strips are tested over the entire frequency range m order to exclude material which fails to give clear tones at all frequencies. Strips, each of which shows a pronounced resonance at its natural period of vibration, are selected. The vibrations may be excited by beats produced by valves operated , at variable frequencies. The variations of anode current may be observed by the use of a milliammeter in circuit or by an electrometer in which mirrors direct the reading upon a steadily moving part, which may be covered by light-sensitive paper. In order to accentuate the response at certain points in the musical scale, for example in the treble of pianos, strips for response at such points are so selected as to show greater resonance than those employed for response at other points, say in the bass.