In recent years, consumer electronics and personal electronic music playing devices require the use of accessory speakers for full volume delivery of high quality sound. The increased use of compact speakers has also been fueled by a general trend toward smaller bookshelf or desktop systems, rather than the cabinet work and larger speaker enclosures that had formed the benchmark for audio performance over many decades. A bookshelf speaker is generally used as a conventional speaker. Bookshelf speaker includes a dynamic speaker unit provided in a case, and sound is emitted from the front surface of the speaker unit. Sound is generated by the vibrations of a vibrating plate of the speaker unit. The sound generated is emitted not only from the front surface of the vibrating plate but also from a rear side thereof. However, bookshelf enclosures have resonances in the vicinity of 50 to 90 Hz which, of course, limits the use of speaker systems with such enclosures. Such speaker systems may not be employed for reproduction of any frequencies below about 100 Hz which.
