How to Calculate Bass-Reflex Enclosure

By Ron Roberts

A two-way bass-reflex speaker enclosure.
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The size of a bass-reflex enclosure is mainly determined by the size of the loudspeaker/driver being put in the cabinet. The Thiele-Small parameters help with all the design issues of a bass-reflex enclosure, and are provided with any good-quality component speaker. If they're not provided, the Thiele-Small database provides all relevant data for more than 5,000 different loudspeakers.

Consult the data sheet for your speaker for the Thiele/Small (T/S) parameters. Copy the following data:

Electrical resistance of voice coil (Re )

Resonant frequency of loudspeaker (Fs)

Electrical Q of loudspeaker (Qes)

Mechanical Q of loudspeaker (Qms)

Total Q of loudspeaker (Qts)

Equivalent air volume (Vas)

Download free software for building speaker boxes. WinISD is a well-regarded Windows-based choice that also has a downloadable Mac version (see References).

Enter your copied data (from Step 1) into the speaker-building software to produce the box and cutout sizes for your bass-reflex enclosure.

Medium-Density Fiberboard (MDF) and birch plywood are the leading woods for speaker enclosures.
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Print the data and take all measurements with you to aid in cutting when you purchase the wood for the speaker enclosure.