Helmholtz Resonator Calculator (To Suppress Resonances)
|Calculated at 20 ℃|
Any subwoofer that is in a cabinet with a tub will have a resonance. In fact, all bass-reflex speakers use the principle of the Helmhotz resonator.
What Is Helmholtz Resonance?
Helmholtz Resonance essentially states that any cavity of air with an opening will resonate at a natural frequency when the air is excited. This phenomenon was discovered by German physicist Hermann von Helmholtz (1821-1894).
The phenomenon has been used for hundreds of years to make instruments and audio devices. While the Helmholtz resonator is commonly applied to musical instruments, it is also found in automobile mufflers and subwoofers.
What Is A Helmholtz Resonator?
A Helmholtz resonator consists of a cabinet and a tube. You can check the simple illustration below for an idea:
Helmholtz Resonator and Ported Subwoofers
The concept of the Helmholtz Resonator has been used in subwoofers for many years. Many subwoofers are designed as ported subwoofer boxes that take advantage of Helmholtz Resonance. Check out the design of a 6th order subwoofer box to learn more.
Using A Helmholtz Resonator To Suppress Resonance
Helmholtz Resonators may also be used to suppress resonance by providing a resonance trap otherwise called a Helmholtz trap.
This can be used in addition to or instead of bass traps. In this case, the Helmholtz resonator is used to reduce undesirable low-frequency sounds (standing waves, etc.). This is done by building a resonator tuned to the problem frequency, therefore eliminating it.
To suppress room resonance, the Helmholtz absorber has to be built like shown below:
Note also that to suppress cabinet resonance, the absorber has to be put into the cabinet.