Often it is desirable to add very low frequency bass to the sound output of an existing loudspeaker system. Home Theater setups provide a low frequency effects (LFE) signal for such sounds as dinosaur footsteps and explosions. Here, quantity of bass is often more important than quality, in order to shake the house and instill primordial fear. For music reproduction high accuracy and resolution of bass is most desirable. Unfortunately, this is often degraded by low frequency room resonances. To reduce their effect I have chosen open baffle woofers for the PHOENIX system.

Room modes cannot exist when 1/2 of a sound wavelength exceeds the longest room dimension. If this is 7.5 m (24.6 ft), then a wavelength will be 15 m and the lowest mode frequency is 343 m/s / 15 m = 23 Hz. Below this frequency bass response may increase due to room gain, if the woofer is a monopole. For a dipole woofer the response may stay flat or drop off, depending on the rigidity of room surfaces and lack of any openings. Thus, there will be situations where the addition of a monopole woofer below 40 Hz or so, in a range where there are few room resonances, can add to the realism of sound reproduction.

The THOR monopole, sealed box woofer is meant to augment a dipole woofer or any other loudspeaker where accurate, non-booming sub-bass is desired. This woofer requires its own power amplifier and relies on electronic equalization for its low frequency response. It is simple to construct. The description of the design process can serve as an example of how to account for different drivers and cabinet sizes, when you consider your own woofer design.

This is meant to be a DIY project for the music loving hobbyist. Should you consider using part or the whole of my design for commercial purposes, then contact me for permission and contractual agreement before using any of the information provided.