5
Sealed Band-pass Enclosure
Sealed band-pass enclosures enclose both sides of the woofer(s). An
airtight enclosure is built around the front and back of the woofer and
one chamber is ported to a specific frequency.
Pros
•
High power handling
within the operating
frequencies
•
Very high output
within the range of
the operating
frequencies
Cons
•
Low power handling
beyond the tuning
frequency
•
Poor to moderate
transient response
•
Poor low frequency
extension
CALCULATING NET INTERNAL ENCLOSURE VOLUMES
When constructing any type of enclosure, you must be aware that the
outside dimensions DO NOT represent the true (Net) volume inside.
Such things as woofers, ports, thickness of enclosure material, dividing
walls, and any internal bracing will reduce the total amount of the actual
air space available. The following worksheet has been designed to
provide you with the necessary steps to accurately calculate the absolute
(Net) internal volume of any given enclosure.
Calculating Cylindrical Port Volume
1. Measure the outside diameter of the port and divide by 2 for the
radius.
2. Square the radius and multiply by 3.14 (pi) to arrive at outside port
area.
3. Multiply the area by the length of
the port
inside
the enclosure for the
port volume.
SELECTING AN ENCLOSURE
6
BUILDING THE ENCLOSURE
•
Determine the dimensions of your enclosure.
•
Be certain the box you have designed will fit into the location you
have chosen. Sometimes making a cardboard box with the same
outside dimensions is helpful.
•
Use 3/4 inch thick Medium Density Fiberboard (MDF) or High
Density Particleboard. It is preferable to cut the wood with a table
saw to ensure straight, even joints. If a table saw is not available,
a circular saw is acceptable.
•
Use a "T' square to verify precise right angle gluing.
•
Use a high quality wood glue and air nails or wood screws to
assemble the enclosure. Elmer's
woodworker's glue and
Weldwood
work well. To guarantee an airtight box, seal each
inside joint with silicone sealant.
•
For Sealed Enclosures, stuff the chamber with 50-75% filling
(approximately 1.5 pounds per cubic foot) of fiberglass insulation
or Dacron
.
•
For Vented Enclosures, staple 1-inch thick fiberglass insulation or
Dacron
to all walls of the enclosure except the baffle to which
the woofer is mounted.
•
Use the eight (8) wood screws or T-nuts and bolts to seal the
woofer in the enclosure. Progressively tighten each of the bolts or
screws to prevent warping the woofer frame.
