DIY Audio & Video

Tutorials, FAQs, Calculators and Examples
for Speaker Boxes, Crossovers, Filters,
Wiring, Home Automation, Security & more

Speaker Box Designer / Calculator Help

Use the Speaker Box Designer.

The Vas, Fs, and Qts parameters should be provided by the speaker manufacturer. Fb can be provided or you can let the calculator determine the value on its own. The cone diameter is only used to determine an appropriate port diameter.

To achieve the smoothest roll-off with the box, use a System Q (Qtc) of 1/sqrt(2) = .707    A higher Q can be used for a better bass response at certain frequencies, but this may damage the driver by causing it to bottom out (driver moves beyond the Xmax). Use caution when playing at loud volumes. The effect of different Q's is shown in the graph below.

Note: Some vendors will recommend a higher Q in their proposed enclosure volumes. For car audio, trying to get a perfectly smooth response from a subwoofer in the trunk is a waste of effort, especially when the user only wants more bass.

Box Q

The most important question is what type of enclosure to use. For the novice builder, conventional thinking says a sealed enclosure will typically produce a more accurate sound. A ported enclosure will produce louder deeper bass at the expense of sound quality. The ported enclosure also requires a more volume. A 4th order Butterworth Ported enclosure is even larger than a standard ported enclosure, but it should provide a smoother roll-off.

These statements are only generalizations, and a ported enclosure can be as good as (if not better) than a sealed enclosure. Sealed enclosures are very forgiving and are much easier to construct if you are a novice builder. You could make the box 10% too large or too small without a very noticeable change in sound quality. The port on a ported enclosure must be a specific length, and 1/4" too short or long can have a dramatic effect on sound quality. If done properly, the port on a ported enclosure can allow the speaker to have a lower flatter f3 roll-off.

Note: Some speakers are just better suited to ported or sealed enclosures. Speakers designed for small enclosures might not work well in a ported enclosure because the port would need to be longer than the box itself. The Sealed vs. Ported Calculator will tell you if a specific enclosure will work better for your driver.

These are the formulas for calculating the size of a sealed box. Refer to the audio terms list for information on the different variables. In some cases, variables are used on the left and right of the = sign, as in f3 and fc. It is confusing, but these are two different variables. The driver f3 and fc variables are being used to calculate the box f3 and fc.

Sealed Enclosure

Sealed Speaker Box Enclosure Formulas

Ported Butterworth B4 Enclosure

Ported Speaker Box Butterworth B4 Enclosure Formulas