as always, my physics book is of no help. dang thing is written in latin as far as i'm concerned. any help would be appreciated.

two loudspeakers are located 3.70 m apart on an outdoor stage. a listener is 16.9 m from one and 18.6 m from the other. during the sound check, a signal generator drives the two speakers in phase with the same amplitude and frequency. the transmitted frequency is swept through the audible range (20 hz to 20 khz).

so, the question is:
a)what are the three lowest frequencies at which the listener will hear a minimum signal because of destructive interference?

and
bwhat are the three lowest frequencies at which the listener will hear a maximum signal?


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i don't have the maths skills to answer this, but i understand the physics bit.... for max signal,you need a complete no. of waves to reach the listener from both speakers, so the waves arrive in phase and add together. for min. volume you need a complete no. of waves from one speaker (and it could be either speaker) and the no. of waves from the other speaker will end in 1/2. i.e. an uneven number of 1/2 waves different from the other speaker, 0.5,1.5, 2.5 etc. to give the most destructive interference.
so, for max signal you need a wavelength that divides into both distances.
for min. signal you need a wavelength that divides exactly into one distance, and has x+1/2 wavelengths in the other. i imagine there is a graphic way to do this but i don't know what it is.. neither do i know how to work out the factors of 16.9 and 18.6m so no help to you there i'm afraid.
but maybe you how to do the maths ! but wait a minute - for max signal the difference between
16.9 and 18.6 (1.7m) will be a complete no. of waves. for min. signal 1.7m will be an uneven no. of 1/2waves. does that make it any easier ? ow my brain hurts... good luck !
i don't see how distance between loudspeakers matters as the important measurements are given, the distance from each speaker to the listener. since you are asked for the lowest freqs, it seems likely that for max signal you need to take 1.7m as the first wavelength, then 1.7/2,1.7/3 etc & hope the figures work out. for min signal 1.7m may be 0.5 x wavelength, 1.5,2.5 etc. you'll have to calculate frequency once you know wavelength, the usual figure assumed for speed of sound is 330 m/s


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