Calculating Volume of a Wedge Box
This example is a wedge shaped enclosure that is commonly used behind the seat of pick-up trucks. For this application, we will be using a pair of 10" woofers in a sealed enclosure. Having taken measurements in the vehicle, the following dimensions resulted:
Exterior dimensions Accounting for 3/4-inch thick material, the interior dimensions are then calculated. The thickness of the material (wood) is subtracted twice from each dimension, representing the two sides for each dimension. In the case of width, the material thickness is subtracted three times; representing the two sides and the partition that divides the chambers.
Interior dimensions
Volume can now be calculated. This enclosure will require the use of two different volume formulas. After each volume is calculated, they will be added together to obtain the total gross volume.
Let’s look at the side view of the wedge enclosure
We can divide the enclosure into two separate volumes that look like this
Now we calculate volume for each object
Rectangular
Box Volume |
= |
Length x Width x Height |
V = |
2.5 x 54.75 x 15.5 | |
V
= |
2121.563 cubic inches | |
Triangular
Box Volume |
= |
Length x Width x Height x 0.5 |
V = |
4 x 54.75 x 15.5 .5 | |
V = |
1697.25 cubic inches | |
Adding the two volumes together gives us total volume for the wedge shaped enclosure.
Total Enclosure
Volume |
= |
Rectangular Box Volume + Triangular Box Volume |
V = |
2121.563 + 1697.25 | |
V = |
3818.813 cubic inches | |
The volume of this wedge shaped enclosure measures 3818.813 cubic inches. We now compensate for speaker basket displacement by subtracting the volume of the speaker baskets from the Gross Enclosure Volume.
The basket displacement for these cast basket 10 inch woofers measures 131 cubic inches
When calculating, we multiply the speaker displacement by the number of speakers being used.
Usable
Airspace |
= | Enclosure Volume - Speaker Basket Displacement(s) |
= |
3818.813 - (2 x 131) | |
= |
3556-813 cubic inches | |
Finally, we convert this figure to cubic feet. Since we are using two speakers in this enclosure, it is necessary to divide the Total Usable Airspace by two.
Volume
in cubic feet |
= | 3556.813 / 1728 |
V = |
2.058 cubic feet | |
Volume
per speaker |
= | 2.058 / 2 |
V
= |
1.029 cubic feet per speaker | |
Important Note:
This example just happened to work on the first attempt, and happened to achieve an enclosure that matched the recommended volume for that speaker. In most cases you will need to vary the physical dimensions (length, width, or height) accordingly until the desired enclosure volume is achieved. This means one might have to calculate the enclosure volume a few times before obtaining the appropriate enclosure for your specific application.
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