Our sub woofer has been designed to perform for both home theatre and music applications. It operates as a BANDPASS system and will only reproduce a very narrow range of frequencies, thus not imposing on the main audio channels. It is in the sense a true Sub woofer.
It has a useful lower frequency response below 17Hz, whilst it's upper frequency limit is capped at 50Hz. Bandpass enclosures are essentially 2 chambers (boxes) back to back, with the driver (woofer) mounted between the 2 boxes. The rear chamber operates in sealed or closed box mode, and when combined with driver specifications, governs the lower frequency response. The front chamber is a vented or ported enclosure. This chamber/driver relationship governs the bandwidth or frequency response of the system. Careful design of this type of system is imperative, as the driver has to match not one but two enclosures.
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The driver also has
to have the ability to cope with the demands of low frequencies.
As the frequency response drops, woofer cone excursion dramatically
increases. It is pointless designing a system that is capable
of getting down to sub frequencies, if the woofer does not have
the cone excursion to cope.
The driver used in our system has a linear cone excursion of
45mm., which will cope with very large low frequency demands.
The audio output is directed outside via the vent, which is tuned
to a certain frequency. (Like a single tube of a pipe organ).
The vent/enclosure relationship becomes the natural resonant
frequency of the system, and will only allow frequencies of around
15 Hz either side of resonance to be passed, giving a bandwidth
of approximately 30Hz. Because of the systems narrow bandwidth,
no crossovers are required adding coloration and distortion.
Having the sub woofer's upper frequency response limited to 50Hz., prevents it from interfering with the "sound" coming from the main left/right front loudspeakers. This I believe makes for a great compromise for all types of software material. It is particular noticeable with many commercially made home theatre sub woofers being used in music applications, giving a very hard and boxy sound…It is particularly evident if the operating frequency response is higher than 70Hz., which may sound great on explosions etc., but poor on music discs. These systems audio quality greatly improves, once the sub woofer is turned off.
The twin chambers used in the construction are extensively braced, with the vent being an integral part of the front enclosure and the main internal driver baffle plate, making it very ridged and strong.
