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There are several different types of loudspeaker enclosures or speaker boxes that can be used - each type has its own characteristics and serves different purposes better.
Selecting the type of speaker enclosure has a major impact upon the performance and determines many of the characteristics of the overall loudspeaker system.
Reason for using speaker enclosure or speaker box
The speaker box or loudspeaker enclosure provides an essential element in the performance of any loudspeaker system.
Sound waves generated by the loudspeaker emanated from the front and the back - the diaphragm moves backwards and forwards. Hence the air is compressed and decompressed according to the movement of the diaphragm. As the diaphragm moves forwards the air is compressed at the front, but decompressed at the back. As a result the sound waves at the front and back are out of phase.
Unless there is a means of separating them, these sound waves would merge and cancel each other out at the rim of the cone. This would occur for all wavelengths longer than the radius of the cone - this is the distance the waves must travel to meet each other.
Frequencies having a wavelength below this point are attenuated at a rate of 6 dB / octave.
To prevent this occurring and ensuring that the lower frequencies are reproduced with the required intensity a loudspeaker enclosure of some form is used. The speaker box or loudspeaker enclosure is used to keep the front and back waves apart in the best way possible and also with a minimum modification to the front wave.
Types of speaker enclosure
There are several different types of loudspeaker enclosure or box. Each type of speaker enclosure or box has different properties.
- Open Baffle / doublet: This type of speaker enclosure is not really a box or enclosure at all. It is simply a board on which the loudspeaker is mounted. The baffle increases the distance by which the sound waves from the front and rear must travel to meet and hence cancel out. In this way, it extends the bass response. To be effective, the baffle must be relatively large. . Read more about the Open Speaker Baffle.
- Infinite baffle: The infinite baffle is the principle by which most loudspeaker systems work. The loudspeaker is contained within a sealed rigid box and in this way the rear travelling wave is contained, and damped within the box. Sound absorbent material is used within the box to assist. Read more about the Infinite Baffle Speaker Cabinet.
- Reflex speaker enclosure: The reflex speaker enclosure has a vent in the enclosure or box by which some sound can escape.
Of the types of speaker enclosure used these days, the infinite baffle is probably the most common, and the reflex speaker baffle concept is also used. The baffle or doublet is rarely used as it requires a large baffle.