# What is the effect of a pair of different sounds or frequencies upon an object?

I am new to learning about the physics of sound, resonance, resonant frequency, and standing waves. Most of the sources I am reading describe the effect of a single frequency on an object when that frequency matches the resonate frequency of the object.

For example, in the video in the link below, the man sets the tone generator to 337hz. This is the resonate frequency of the wine glass. At a certain volume the sound breaks the glass. https://www.youtube.com/watch?v=BE827gwnnk4

What I am having a hard time finding is information on the effect of multiple frequencies on a single object.

For example: 440hz is a concert pitch A and 528.01hz is the C which is a minor third above the A. What happens to an object whose resonate frequency is 440hz and both 440hz and 528.01hz frequencies are played simultaneously in a similar scenario to what was done in the video?

• A stimulus that is off resonance has little effect, the object would resonate with the 440 Hz component. It is like singing a tone into a piano, only strings that are in resonance will sound. (Nice video!) – Pieter Dec 21 '16 at 2:13
• But singing into a piano is only a single frequency. The human voice can only produce one frequency at a time. The waveform of the combined tones would change from a pure sine wave. It would look something like this. (I think.) desmos.com/calculator/pga88rt3hq – Christopher Gaston Dec 21 '16 at 3:11
• Another example I saw was of cymatics where resonating a Chladni plate with sand salt on it to create standing waves at different frequencies. youtube.com/watch?v=wvJAgrUBF4w Again, it is only a single tone. How would it react differently if it had two tones which were a minor third apart? – Christopher Gaston Dec 21 '16 at 3:19
• Singing actually produces many frequencies, all integer multiples of the fundamental frequency. This is what differentiates the vowels - though they have the same fundamental frequency, the contributions at higher harmonics are different. In any case, Pieter is right. – probably_someone Dec 21 '16 at 4:36
• The resonance frequencies of Chladni plates do not come in harmonic sequences, so two tones a minor third apart would not both be in resonance. But you pose an interesting question: what happens on a Chladni plate when excited by a superposition of two (or more) of its resonance frequencies. I may ask my students to do the experiment. – Pieter Dec 21 '16 at 15:21