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isacoustic
isacoustic adj. 
/ˌaɪzəˈkustɪk/ (a) applied to a curve passing through those points (in a theatre, concert-room, etc.) at which a speaker or performer may be heard equally well; (b) Seismology applied to a line (imaginary or on a map) connecting places where an equal percentage of observers heard the sound of an earthquake.
Brit. /ˌʌɪsəˈkuːstɪk/
, /ˌʌɪsəˈkuːstɪk/U.S. /ˌaɪsəˈkustɪk/
, /ˌaɪsəˈkustɪk//ˌaɪzəˈkustɪk/ΘΚΠ
the world > the earth > earth sciences > geography > map-making > map > [adjective] > line on map > geological features or phenomena
isacoustic1842
isoseismal1883
isopachous1913
isograde1924
isogradic1924
1842 J. Gwilt Encycl. Archit. iii. iii. 804 The points which indicate the places of the spectators will lie in..a..curve, which may be termed the iseidomal or the isacoustic curve, that is, one of equal seeing or hearing.
1900 C. Davison in London, Edinb. & Dublin Philos. Mag. 49 43 An isacoustic line may be defined as a line which passes through all places in which the percentage of persons who hear the sound is the same.
1938 L. D. Leet Pract. Seismol. viii. 282 Curves passing through the places at which equal percentages of the observers heard the earthquake sound were drawn in 1899, and Davison, followed by Knott and de Montessus, called them isacoustic lines.
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