Design sealed and ported enclosures using Thiele-Small parameters. Select a driver from our database or enter specs manually.
Search our database of subwoofers with T/S parameters
Calculate both sealed and ported options to see which enclosure type is recommended for this driver based on its EBP (Efficiency Bandwidth Product).
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A sealed (acoustic suspension) enclosure is airtight and produces tight, accurate bass with a smooth rolloff. A ported (bass reflex) enclosure has a tuned port that extends low-frequency output, producing louder bass at the tuning frequency but with a steeper rolloff below it. Sealed boxes are typically smaller and easier to build, while ported boxes are larger but more efficient.
Thiele-Small (T/S) parameters are electromechanical measurements that describe a speaker driver's behavior. The three critical ones are Fs (free-air resonance frequency), Qts (total Q factor combining electrical and mechanical damping), and Vas (equivalent compliance volume). These values determine the optimal enclosure size and type for your specific subwoofer.
Calculate the EBP (Efficiency Bandwidth Product) by dividing Fs by Qes. An EBP below 50 suggests sealed, above 100 suggests ported, and between 50-100 means either will work well. Drivers with low Qts (under 0.4) and low Fs typically perform best in ported enclosures, while higher Qts drivers often sound better sealed.
Qtc is the total system Q factor of the driver in its sealed enclosure. A Qtc of 0.707 (Butterworth alignment) gives the flattest possible response. Lower values (0.5-0.6) sound tighter with better transient response but less bass extension. Higher values (0.8-1.1) add a bass bump that sounds punchier but less accurate. For car audio, 0.707 is the standard recommendation.
Port length depends on the box volume, tuning frequency, and port cross-sectional area. This calculator handles the math using the standard port resonance formula. As a rule of thumb: larger ports need longer lengths, lower tuning frequencies need longer ports, and larger boxes need longer ports. Always ensure minimum port diameter of 3" for 10" subs, 4" for 12" subs, and 6" for 15" subs to avoid port noise.
Round (aero) ports are easier to build and have less turbulence at high output levels. Slot ports can be integrated into the box walls, saving internal volume and allowing for larger port area. For most builds, round ports with flared ends are the best balance of performance and simplicity. Slot ports are preferred when space is tight or when you need very large port area for SPL competition builds.