Sealed or Closed Subwoofer Box Design Calculator

Car Audio - Home Theater Sound System

AJ Sealed Designer calculates the required sealed/closed enclosure parameters for woofers and subwoofers.

Subwoofer Box Comparison Calculator:
Compare bandpass, sealed and vented frequency output graphs for a subwoofer in one program.


driver resonance frequency
system response maximum dip or peak
frequency where the 3 decibel power drop occurs
net enclosure volume(internal)
system response maximum dip or peak


Vas air volume equal equal to compliance of driver suspension
Qts total driver Q at fs
fs driver resonance frequency
Qtc total system Q at fc
Vb net enclosure volume(internal)
f3 frequency where the 3 decibel power drop occurs
fb box resonance frequency
dbpeak system response maximum dip or peak

Input Parameters:

  • Theile Small parameters are required for input. These values can be found in the speaker's manual or on the manufacture's web site.
  • For Qtc, choose a value between 0.1 and 2.0. A value between 0.5 and 1.2 gives the best results. Try varying this parameter to see how the size of the box and the frequency response can be changed.
  Theile/Small Parameters  
Vas  liters
Qts  unitless
fs  Hz
  User Defined Parameter  
Qtc  unitless

Calculated Values:

  • f3 is the most meaningful parameter. The lower the f3 parameter the deeper the bass will sound. An f3 below 50 Hz is suitable for a sealed enclosure. An value below of 40 hz gives the best results.
  • Vb is the net size (volume) of the enclosure to be built. Generally, the lower the bass the larger the box.
  • In the frequency response plot, the output SPL, sound pressure level, is based at 1 watt/meter.

Vb  =  58.369750479846  liters
f3  =  49.626591140227  Hz
fb  =  49.122807017544  Hz
dbpeak  =  0.0018091834542131  db

frequency graph


  • Dickason, Vance. 1991. The Loudspeaker Design Cookbook. Audio Amateur Press. 4th ed.
  • Steele, Brian. 2002. The Subwoofer DIY Page v1.1.

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