MadSci Network: Engineering |
The hole to which you are referring is called a "tuned port." Speakers that use a tuned port fall into a category called "bass reflex" speakers. Bass reflex speakers use the port to increase their efficiency in reproducing low frequency (i.e., bass) sounds. It is always to dangerous to make broad statements, but in general, bass reflex speakers are not considered "good quality" speakers. Bass reflex speakers are popular because they economically produce low frequencies -- a main component of today's music. The port will almost always face either the front or back (it is possible for the port to face any direction). There are several design considerations that determine the placement of the tuned port. One design consideration is -- since it is hard to pinpoint the source of low frequencies, the port is sometimes placed at the rear of the speaker enclosure. This configuration allows the placement of more (or larger) mid-range and tweeter radiators at the front of the enclosure. The result can be more sound being generated from the speaker (compared to the same size speaker enclosure with a front facing port), or an overall size reduction if the size and number of mid-range and tweeter radiators are not increased. Another consideration is -- the design and size of the speaker enclosure often determines the horizontal and vertical placement of the port. It may not be possible to place the port in the front facing position because the desired horizontal and vertical position may be occupied by one of the other higher frequency radiators (e.g., a tweeter). There is little flexibility in placing the high frequency radiators, they should face the front. I hope that this helps.
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