MadSci Network: Engineering
Query:

Re: what are the design implications of the hole in the back a speaker?

Date: Thu Apr 27 20:28:57 2000
Posted By: Dwayne Rosenburgh, Senior Electronic Engineer
Area of science: Engineering
ID: 956291458.Eg
Message:

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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