High Efficiency Speaker Asylum

Posted by AstroSonic (A) on February 06, 2003 at 14:47:42

In Reply to: Re: Aperiodic enclosure for RS 40-1284 posted by diyJohn on February 06, 2003 at 05:03:53:

John,
You will get more bass without the vent damping, but it will have poor definition (loud, but without impact, pitch and definition). A somewhat simplified explanation is as follows: The driver is incapable of controlling the helmholtz resonance formed by the cabinet-enclosed air (acts as a spring) and the vent (acts as an air mass). Without the vent damping you get a double peak in the bass: one in the upper bass and one in the mid-bass. The driver and vent contribute to each peak (because this is realy a coupled resonant system with the driver/amplifier providing all the energy). The driver is the dominant contributor for the upper peak while the vent is dominant for the lower peak. Without vent damping, the driver provides nearly all the damping of both the cabinet resonance and its own (formed by the cone mass and suspension/spider compliance). The driver is too underdamped (Qt is too high) to control the cabinet resonance. Therefore damping is added to the vent to damp that resonant system. It also damps the upper peak by turning some of the drivers acoustic energy into heat. The interaction of the driver and cabinet are more complex than is portrayed above, and we are fortunate to have computer programs that do a pretty good job of modeling this.

If you build one of these you can try it with a full range of conditions, from open vent, through increasing amounts of damping, to packed with damping material so tightly that it is sealed. You will find this project very instructive! Enjoy.
AstroSonic