While the iTravelers are loud enough for personal use, in a large room and noisy environment they aren't really loud enough. There is also a lack of the 2 lowest bass octaves. A subwoofer can improve both of these deficiencies. A sub/sat system can work well if the satellites have response to at least 100 Hz, because any signal above that can be localized. The output of the subwoofer has to be low distortion, low noise, and not have significant energy above 100 Hz. It preferably extends the bass response to approximately 45 Hz, because that is the lowest note on a string bass and is about what is available on many recordings.

The audio output must be free of peaks so that each note can be heard. A subwoofer of 200 cubic inches with a 3 inch driver was designed to meet the above requirements. It is a ported system which uses the same philosophy as the iTraveler in that the system is tuned lower than normal and the response is corrected by signal processing circuits. The port is noise free because of a unique, curved design which reduces the tendency to create turbulence and noise at high signal levels. This allows to have a much smaller cabinet volume and port diameter.

The 3” driver has extreme excursion capability along with low distortion. This combination gives sufficient level at low distortion to match the iTraveler properly.

For this application, the audio signal is passed through the electronics of the subwoofer and then to the iTravelers. This allows a DSP based crossover to separate the signal to the iTraveler and filter out signals below 100 Hz. The signal to the subwoofer is adjusted to flatten the response and also has a signal limiter for signals which would overload the amplifier.

The power amplifier in the subwoofer is a 20 watt switching amplifier, so that there is little power wasted. It also incorporates a built in universal power supply which also will run the iTravelers and keep them fully charged when they are attached.

The resulting system provides response to 46 Hz without compromising the image and soundstage of the iTravelers. The power supply of the subwoofer and the removal of signals below 100 Hz allows the iTravelers to play about twice as loud.

A wired remote volume and input is included so that if the subwoofer is placed out of the way a volume control and input are still accessible.