Blaupunkt Blau PCwg100 User Manual page 10

F S
INAL UBWOOFER
Before final design, wood cutting, and assembly of the enclosure some basic box construction issues need to be
understood. These items are acoustically related, some are construction tips, and some are simply to ensure a long lasting
product for the listener.
Infinite baffles are simply a piece of wood holding up the woofer to the back deck of a car. If you chose this installation
(which is generally a poor performer) you must take great care in sealing/caulking all holes that vent into the back seat for
proper bass response.
Wedge shaped boxes are simply a triangular box added to a rectangular box.
Mathematically add up the volumes of these two boxes and you have the total of a wedge shaped box.
When making the calculations, be sure to adjust interior box volumes for port volumes and woofer displacement volumes.
All calculations should be made in advanced of cutting wood out. If the final box is off by +/- 5% of optimum values don't
worry about it; you will rarely be able to hear the difference! This is very important since prefabricated boxes often work
well even if off a little bit. Also, if you do forget to compensate for woofer and port tube volume displacement, it is rarely
acoustically noticed by most people.
Very low frequencies simply do not care about the shape of the box. Such wavelengths allow for nearly any reasonable
shape or length but really odd shapes should be avoided so they can be easily cut and glued.
Particle board, MDF, or high grade birch plywood are good materials to build boxes with thicknesses of 5/8"-1" (14-
25mm). Solid wood panels should actually be avoided of splitting and warping over time in the car environment.
All seams in the box should be glued, screwed, then caulked to prevent panel separation and air leaks over time.
Cross bracing of panels is important for large boxes to prevent the panels them selves from radiating sound.
Acoustical damping material (e.g., fiberglass batting material 2-4" thick) should cover about 50% of the interior walls. This
helps reduce high frequency resonances and increase the box volume as seen by the woofer by about 10-15%.
Spraying the interior walls of the box with a damping material such as tar based automotive undercoating is one of the
best things to help dampen wall resonances.
The final box should allow for servicing the woofer at a later time should it be damaged for any reason.
5-way binding posts mounted on the box for electrical connections are highly recommended. It is then easy to remove
the box from the vehicle for service or theft protection.
Where possible, use the largest diameter port tubes to prevent wind noise. PVC plumbing pipe is inexpensive and is
common in 3, 4, and 5" diameters. PVC "elbow" connectors allow you to make turns inside the box with the average
diameter being along the centerline of the tube.
Try to always use active (electronic) crossovers. Today, most power amps have them built in. The mounting distance from
the side of the woofer and the port should be less than 12" or so if possible. Regarding simple vented boxes, you
CANNOT achieve lower frequency response by simply lowering the port tuning frequency from its recommended value.
This severely over-damps the box and results in a very "muddy" sound for the box.
Before gluing and screwing everything together, lightly "tack nail" the sides together and make sure the box fits in the
vehicle. Also, look carefully to see if the woofer magnet has enough depth of clearance from the back wall. There are many
other things to think about when design and building subwoofer boxes but they are too numerous to mention here. But, for
those interested, please refer to some of the related reading for more information on speakers and audio in general.
A R
DDITIONAL
The following is a list of materials and sources of recommended reading for the person interested in loudspeakers,
acoustics, and audio in general. Subjective comments are noted for each.
DESIGNING, BUILDING, AND TESTING YOUR OWN SPEAKER SYSTEM, David Weems, Copyright 1984, TAB Books
#1964, Blue Ridge Summit, PA 17294. (This is an excellent introductory book on designing speakers for the home but is
quite applicable to the car since many concepts are carried over.)
LOUDSPEAKER DESIGN COOKBOOK, Vance Dickason, copyright 1991-1996, distributed by Old Colony Sound Lab,
Peterborough, NH, 03458. (A significant technical step up from Weems addressing complex woofer box and crossover
designs. Clearly a reference book useful for all.)
BLAUBOX WOOFER BOX DESIGN COMPUTER PROGRAM, Thomas Breithaupt, Blaupunkt div. Robert Bosch
Corporation, 2800 S. 25th Avenue, Broadview, IL 60153. (This is a simple to use IBM PC computer program used to
predict the frequency response of a subwoofer in 10 different enclosures including sealed, vented, and bandpass
configurations. Basic passive crossover designs are covered as well. It is provided free of charge as a download from
the Blaupunkt Internet site at: http://www.blaupunkt.com.)
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NCLOSURE
I
EFERENCE NFORMATION
C
ONSTRUCTION
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