Specifications

189
Example - Vent Volume
The vent volume calculation goes as follows:
The spec sheet outlines the need for two vents,
each with an internal diameter of 2.5 inches
each with a length of 8.25 inches. To calculate
the volume of each vent, we need to determine
how much space those vents will occupy in the
enclosure:
Area of a circle formula: R2 = 3.1416 x R x R
Where R is the radius of the outside of the vent.
Most round vents are made of ABS plastic drain-
age pipe with a wall thickness of 0.125 - 0.25
inches. For a 2.5" pipe, the outside diameter
would be approximately 2.75 inches.
Part of the vent extends through the face of the
enclosure, so we can subtract the thickness of
the front panel of the enclosure from the volume
calculation.
3.1416 x 1.375 x 1.375 x (8.25 - 0.75) = 44.546
cubic inches.
We have two vents, so we double that volume:
44.546 x 2 = 89.09 cubic inches
Then convert back to cubic feet:
88.03 ÷ 1728 = 0.05 cubic feet.
Example - Total Volume
We need to add the air volume required to the
displacement of any objects inside the enclo-
sure.
Here are the items we need to consider:
Net Air volume: 2.0 cubic feet
Driver displacement: 0.12 cubic feet each
Vent Displacement: 0.05 cubic feet total
Total air volume = 2.0 + 0.12 + 0.12 + 0.05 =
2.29 cubic feet.
For this example, the dimensions are within 1%
of the target volume, and we can use the 35 x 14
x 11 dimensions.
Step 4a: Alternate Volume Calculations
If we needed a smaller volume, let's say 1.5 cubic
feet gross air space, then the enclosure dimen-
sion calculation would go as follows:
Convert cubic feet to cubic inches:
1.5 x 1728 = 2592 cubic inches.
Divide by internal height:
2592 ÷ 12.5 = 207.36
Divide by internal width:
207.36 ÷ 33.5 = 6.189
6.189 is the internal depth of the enclosure. Add
the thickness of the front and rear panels and you
have the outside depth of the enclosure:
6.189 + 0.75 + 0.75 = 7.689
You may need to massage the width or height
dimensions of the enclosure to provide adequate
mounting depth and port clearance for your
design. You can alter any dimension necessary
to achieve the desired result.
Car Audio Reference Guide