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March 1969 Radio-Electronics
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
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 Building speaker enclosures was a popular
project for stereo enthusiasts in the 1969 time period when this article appeared
in Radio-Electronics magazine. Lots of well-designed speakers were
commercially available, but they tended to be expensive. High-end speaker
enclosures typically had high-end speakers within, which contributed to the
increased cost. I built a pair of wooden enclosures while in the USAF at
Robins AFB, Georgia (click on thumbnail image). It had a very nice woodshop. The
speaker cabinets had a very simple internal design; the removable front frame was the hardest part to
build. Mine were made from pine. For my
level of music appreciation, I found that a quality set of car speakers (Radio
Shack p59, 40-1341) provided great sound for all but the deepest bass frequencies.
An added advantage was that the crossover circuit was built in, so all I needed
was to build a
crossover to split the really low frequencies to 10" bass speakers that were
purchased at
Radio Shack (p58, 40-1331). The Radio Shack crossover circuits were too high
(1 kHz) so I found an article showing how to build one that split at around
500 Hz; admittedly, it didn't work very well. The grille cloth also came from
Radio Shack (p61, 40-1936).
You Can Build These 16 Speaker Enclosures
Fig. 1 - A doubly expandable, tuned-duct University system. Start
with 12" model M12 wide-range speaker (1). Add 15" C15HC woofer to extend bass response
(2), and a HF206 tweeter (3). Note boxing of 12" speaker and duct.
Fig. 2 - Another University system, similar to Fig. 1, starts
with an 8" M8D wide-range speaker (1), using a duct. If a 12" M12 woofer is added
(2), duct length is changed. The addition of MS tweeter (3) extends response of
system.
Fig. 3 - A 2 speaker-2 way Altec-Lansing bass reflex system.
Use a 15" 416A woofer, 811 treble horn with a 806A driver.
Fig. 4 - This infinite baffle Altec-Lansing system uses two 416A
woofers. Use 511B treble horn with 802D driver.
by Abraham B. Cohen†
Despite the quantities of low-cost, assembled loud-speaker systems on the hi-fi
market, do-it-yourself projects are still very popular. If you're planning such
a project, your choice of a loudspeaker enclosure should take several factors into
account: performance, cost, size, appearance and expandability.
The speaker system should be installed in the room where your family does most
of its "living," and the space available in this room will influence your selection.
The table below and the following figures describe 16 enclosures whose construction
information was supplied by six leading loudspeaker manufacturers. The enclosures
selected vary in size and may be installed in room dividers, hung from walls, inserted
in alcoves and placed on counters or desks. Larger enclosures, which are regaining
some of their early popularity, may be built as floor furniture pieces.
To simplify construction, the manufacturer's original external design is not
included. The builder can select the enclosure's exterior appearance to match room
furniture. Several of the systems shown are expansible or include adapter boards.
This permits either an 8-, 12- or 15-inch speaker, for example, to be installed
without major changes in the enclosure.
Expansible systems minimize obsolescence, enabling you to increase the audio
"fullness." of the system as your budget permits.
Optimum performance will be obtained only if the proper lumber is carefully assembled.
Here are a few construction tips.
Plywood of 3/4-inch thickness should be heavily glued at all mating surfaces.
When joints are clamped or screwed together, surplus glue should seep out along
its entire length. Small glue blocks are often used to reinforce interior edges
of the panels. Apply glue to surfaces between the blocks and panel, and secure the
blocks to both panels with screws.
Bass-reflex and infinite-baffle enclosures must be especially rigid to avoid
distortion and loss of bass response. Use at least four good-sized screws along
each edge of the rear panel. At least 1 inch of sound-insulation material should
be applied to all interior surfaces in any enclosure. Large panels may require diagonal
cross-braces to minimize vibrations, and a cross-strut can be used between large
surfaces.
Make sure the speaker mounting panel is very flat, especially where the speaker
is mounted. If possible, make the front panel thicker than the others.
If wood screws are used to mount the speaker, drill small guide holes and drive
the screw in carefully. A better method of speaker mounting is with machine bolts
and T-nuts, which are pressed into a hole in the baffle board.
Avoid grille cloth material that is acoustically opaque, as this will ruin high-frequency
response. The cloth should be loosely woven - at least 50% of its area should be
open space. Tighten and secure the cloth to the back side of the panel. R-E
† From Hi-Fi Loudspeakers and Enclosures, by Abraham B. Cohen, Hayden
Book Co., Inc., Copyright © 1956, 1968.
* Add cost of enclosure and for multiple-speaker systems, crossover networks.
Manufacturers can provide crossovers and details.
Posted April 17, 2023
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