A Speaker Box Calculator is designed to help audio enthusiasts and professionals determine the optimal enclosure dimensions for loudspeakers.
Speaker Box Size Chart
| Driver Size (inches) | Recommended Box Volume (cubic feet) | Typical Port Diameter (inches) | Typical Port Length (inches) |
|---|---|---|---|
| 6.5 | 0.3 – 0.5 | 2 | 4 – 6 |
| 8 | 0.5 – 0.8 | 3 | 6 – 8 |
| 10 | 0.8 – 1.2 | 3 – 4 | 8 – 10 |
| 12 | 1.2 – 2.0 | 4 | 10 – 12 |
| 15 | 2.0 – 3.5 | 4 – 6 | 12 – 16 |
| 18 | 3.5 – 6.0 | 6 – 8 | 16 – 20 |
Speaker Box Calculator Formula
The speaker box size calculator formula used is the Thiele-Small parameters, which include factors such as Vas (equivalent volume of air), Qts (total Q factor), and Fs (resonant frequency).
Vb = Vas / ((Qtc / Qts)^2 - 1)Where:
- Vb is the box volume
- Vas is the equivalent volume of air
- Qtc is the desired system Q (typically around 0.707 for optimal transient response)
- Qts is the total Q factor of the driver
Let’s say we have a driver with Vas = 20 liters, Qts = 0.4, and we want a Qtc of 0.707. Plugging these values into the formula:
Vb = 20 / ((0.707 / 0.4)^2 - 1) ≈ 13.6 litersThis calculation suggests an optimal sealed box volume of approximately 13.6 liters for this particular driver.
How do you calculate speaker box size?
Calculating speaker box size involves several steps and considerations:
- Obtain the Thiele-Small parameters from the manufacturer’s specifications.
- Decide between sealed, ported, or other enclosure types based on your goals.
- Determine the desired frequency response and efficiency.
- Input the parameters into a speaker box calculator or specialized software.
- Consider internal bracing, port volume, and driver displacement.
Let’s calculate the box size for a 10-inch subwoofer with the following parameters:
- Vas = 40 liters
- Qts = 0.35
- Fs = 30 Hz
For a ported enclosure targeting a Qtc of 0.707 and an F3 (lower -3dB point) of 35 Hz:- Use a calculator to determine the box volume: approximately 45 liters.
- Calculate port dimensions: 3-inch diameter, 8 inches long.
- Add 10% for bracing: 45 * 1.1 = 49.5 liters.
- Convert to cubic feet: 49.5 / 28.317 ≈ 1.75 cubic feet.
The final recommended box size would be approximately 1.75 cubic feet with a 3-inch diameter port, 8 inches long.
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