Everything in the world is resonant at some frequency. This means everything that exists vibrates at a certain rate when struck or excited. Some examples – the Earth has a resonant frequency of 8HZ (Hertz, or cycles per second) and the human eye has a resonant frequency of 19HZ.
Tuning forks are designed to have certain resonant frequencies and that is the tone that is created when they vibrate. When two or more standalone structures have identical or similar resonant frequencies and one is excited, the other will begin to vibrate. For example, if two tuning forks designed for the same tone are place next to each other and one of them is struck, the other will begin to vibrate due to the acoustic energy that is exciting it.
The human voice is capable of reaching a wide range of frequencies and sometimes when people talk loud enough, things in the room begin to resonate because the voice contains the resonant frequency of the object being excited. A good example of this is if someone is in a basement and they yell loud enough, the cylindrical support beams will begin to ring because they frequently have a resonant frequency that is within the human voice range.
In industrial settings, this sometimes becomes an issue when a group of similar machines are placed next to each other and only one of them is operating. When this happens, it is possible for the rest of the group to begin resonating from the acoustic energy and the vibrational energy through the floor. This can be combated by placing isolation pads underneath the structures to isolate them from the vibrations in the floor and if the structure is reinforced in some way (ie. Welding on cross bars) the resonance will change. For more information, contact an acoustical consultant at Memtech Acoustical!
Brendon Doran, Acoustical Consultant