Ported Bass-Reflex Enclosure

The bass-reflex enclosure makes use of a tuned port which projects some of the sound energy from the back of the loudspeaker, energy which is lost in a sealed enclosure. But care must be taken to avoid the back-to-front cancelation of low frequencies which characterizes unenclosed loudspeakers. This is avoided by tuning the cavity resonant frequency of the enclosure to the free-cone resonant frequency of the loudspeaker. This has the effect of projecting bass frequencies from the port in phase with the sound from the front of the cone, at least at the resonant frequency. The overall effect is the increasing of bass efficiency and the extension of the bass response to lower frequencies.
Effect on loudspeaker resonance
Index

Loudspeaker concepts
 
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Effect of Bass Reflex Enclosure

After Rossing, Science of Sound, 2nd. Ed.

Index

Loudspeaker concepts
 
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Enclosure Effects on Resonance

Putting a loudspeaker in a closed box will eliminate the back-to-front cancelation effect, but will shift the ouput curve upward in frequency compared to the infinite baffle. A bass reflex enclosure can extend the bass response significantly below the loudspeaker resonance.

Index

Loudspeaker concepts

References
Rossing
Science of Sound
Ch. 20

Cohen
 
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