Divide by two for each successive harmonic. Even order harmonics are the second, fourth and so on. Odd harmonics are the first, third and so on.
Let's say a metal has a resonant frequency of 6mhz. That means the first harmonic is 3mhz, the second is 1.5mhz and so on. Extrapolate that down to the khz range and you may find that there is a resonant harmonic at 20khz and 10khz. The best frequency to detect that metal will fall exactly between those two at 15khz. At 20khz and 10khz, the item would be "invisible" or nearly so.
Please note that I did not calculate the audio range harmonics. I just plucked two numbers of 20 and 10 out of thin air for the purpose of explaining what I meant.
To answer your question, 20 is not a harmonic of 60. The first harmonic of 60 is 30, the second is 15 and the third would be 7.5.
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« Last Edit: February 18, 2010, 02:44:19 pm by GoldDigger1950 »
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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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