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Resonant Frequencies

By March 5, 2012March 12th, 2012No Comments

Wikipedia defines resonance as ” the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system’s resonant frequencies or resonance frequencies. At these frequencies, even small, periodic driving forces can produce large amplitude oscillation, because the system stores vibrational energy.” It goes further when it talks about resonance in specific. It states,” Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes (such as kinetic energy and potential energy in the case of a pendulum). However, there are some losses from cycle to cycle, called damping. When damping is small, the resonant frequency is approximately equal to the natural frequency of the system, which is a frequency of unforced vibrations. Some systems have multiple, distinct resonant systems.”

Our listening, home theater, and mixing room are all systems that have a resonant frequency. Our room due mainly to its dimensions and parallel surfaces is definitely a system that has resonances. Can our room store sound energy and easily transfer that energy between certain storage modes. A room can “load” with excess low frequency energy and then store for brief time intervals and then transfer that energy into the next room passing through the existing room physical structures. There is some type of an energy transfer cycle that the room exhibits and the frequency of resonance is room dimension dependent. Our room can also have multiple resonance systems within itself.

How do we damp our system or room to minimize these resonances. We want to cause energy losses within our room’s energy transfer cycle. We must use the physical structure of the room. Can we make it larger , so we can spread out the multiple resonance systems within our room and provided more time and distance between the peaks and valleys in our room’s energy transfer cycle. This is usually not an option. We now must go into the room and work within the physical shell of the room. We must use damping from the inside out.

Our damping methodology must focus on the energy created from within the room. Can we reduce sound pressure at major room boundary reflections by “venting” or providing pressure release valves such as physical holes at surface pressure points? If we do that, we must prevent that energy from causing other acoustical issues in adjoining rooms and then we must also keep unwanted external energy from getting through our “vents” Can we absorb excess sound pressure energy close to the vibrational producing source such as our speakers to reduce the bandwidth that our system or room operates at? Can we reduce the mechanical resonant frequencies within the room’s wall structure? I think the answer is yes to all of these if we view the room as a pressurized box with a resonant system.


Author MikeSorensen

I am a structural engineer as well as a master furniture maker. I design cabinets for low frequency, activated carbon absorbers. Connect with me on Google+

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