DIY Project #2 -
The Accessible 1.0 - Design by Bill Eckle - February, 1997
Introduction by Ralph Calabria
Table of Contents (Click on item to go to specific area of text.)
About the Design and Designer
Cabinet
Diagram
The Drivers
Crossover
Schematic
Cabinet
Construction
The
Finishing Touch
Miscellaneous Construction Tips
Parts
List and Pricing
How do
they sound?
About the Design and
Designer
by Ralph Calabria
The Accessible 1.0 is a small 2-way speaker that was designed and
built by Bill Eckle. Bill has been building and designing
speakers for many years. Among his accomplishments are the Aria
5, designed by Joe D'Apollito, and a small mini-monitor/computer
speaker that he designed based on the Radio Shack Linaeum tweeter
(from the PRO-LX5) and the Tonegen 458 (the same midrange driver
found in the NHT Super Zero). The Accessible 1.0 is based on the
Access T1 fabric dome tweeter and the Audax HT100FO 4 1/2"
fiberglass mid/woofer in an acoustic suspension enclosure. The
crossover is a simple 1st order type (6 dB/octave). The woofer
crossover point is at 420 Hz, and the tweeter crossover point is
at 5.1 Khz. This speaker was designed for use with computers;
however, there is no reason why these speakers couldn't be used
as mini-monitors, surround speakers, or satellites coupled with a
powered subwoofer. The sensitivity of the speaker is 88 dB/w/m,
and the nominal impedance is 8 ohms. Frequency response had not
been measured at time of publication.
I think this project is a perfect one for someone who may be
interested in the hobby of speaker building, and as a first
project. Construction and crossover network are simple and
straightforward, and the total construction cost for a pair of
speakers of this quality is very reasonable.
Cabinet Diagram
Here are the cabinet plans for the Accessible 1.0.
The Drivers
The HT100FO is a 4.5" woven fiberglass woofer, and is part
of Audax's Classic Series. This material is relatively stiff,
however, not as stiff as carbon fiber or Kevlar. Fiberglass is a
good compromise when comparing price vs. performance. Here are
the Thiele/Small parameters and various specs on the driver.
Voice coil diameter: 25mm
Impedance: 8 ohms
Magnet weight: 240 gm
Fs: 60 Hz
Re: 5.8 ohms
SPL (1W/1m) 88 dB
Vas (liters) 5.03
Qms: 1.87
Qes: 0.52
Qts: 0.41
Xmax: ± 3 mm
Pe: 30 watts
The Access model T1 is a 1" semi-rigid fabric dome tweeter.
Here are the tweeter's parameters.
Impedance: 8 ohms
Fs: 1,550 Hz
SPL (1W/1m) 90 dB
Pe: 50 watts
Re 6.4 ohms
Frequency Response 2.0-20 KHz
Crossover Schematic
Following is the crossover schematic for the Accessible 1.0.
The 3.0 mH inductor provides a
nominal 6 db/octave low pass at approximately 420 Hz. The 3.9 µF
capacitor provides a nominal 6 db/octave high pass at
approximately 5.1 Khz. (The 6 dB/octave slope allows for signal
above 420 Hz in the woofer and below 5.1 kHz in the tweeter to
fill in the information between those two frequencies.) The
resistors 5 Ohms and 4.7 Ohms (both 10 watt) attenuate the
tweeter to match the sensitivity of the mid/woofer. The inductor
coil is attached to the bottom of the interior of the cabinet
with a brass machine screw, installed from the outside, into the
threads provided in the coil. The two resistors and capacitor are
attached to a piece of 1/4" plywood with silicone glue, then
this assembly is glued to the bottom of the interior of the
cabinet using wood glue. Interconnect wires from the crossover
were 16 gauge, with the appropriate wire terminals crimped and
soldered.
Cabinet Construction
The enclosure is fairly easy to assemble but requires a router to
get those neat edges. It's these edges that give this speaker a
very unique look. All pieces were assembled using yellow
carpenter's glue and clamps.
Frame the box out using 1/2" MDF (medium density fiberboard)
with glue and clamps. The sides are 9 1/2" x 4" and the
top/bottom are 6 1/4" x 4". Note that the top and
bottom are assembled extending over the sides (see Figure 1 of
the cabinet diagram). Next add the front and back, again using
1/2" MDF. The front and back dimensions are 10 1/2" x 6
1/4". Note that the front and back fit flush with the
sides/top/bottom (see Figure 2 of the cabinet diagram). This will
give you a box with an internal volume of approximately 3.1
liters.
Now add to the front a piece of 1/2" MDF measuring 9
1/2" x 5 1/4", leaving 1/2" clearance on all
sides. Cover the entire box with 1/4" finish plywood of your
choice (see Figure 3 of the cabinet diagram).
Rout all the edges of the 1/4" plywood even with each other.
Now rout a "V" groove 3/8" x 3/8" on all
front-to-back edges and on all four back edges (you will note
that you already have a 3/4" x 3/4" "V"
groove around the front baffle). Obtain solid 3/4" x
3/4" quarter round molding to match your finish plywood and
install with mitered ends around the front baffle. Obtain
3/8" x 3/8" quarter round molding to match your plywood
and install in the four front-to-back "V" grooves, and
install in the four back "V" grooves, mitering the
ends. If you match your finish plywood and moldings carefully,
you will have an apparently seamless "wrap around",
side to front, to side, to back, to side again (getting dizzy
yet?).
The 3/4" x 3/4" quarter round molding makes a nice
rounded corner to minimize "edge diffraction" as well.
The 3/8" x 3/8" molding eliminates the need to miter
and match the sides to the top and bottom, nice for the DIYer
with limited tools and expertise.
The driver cutouts were made at this point. See miscellaneous
construction tips for details.
The Finishing Touch
The assembled cabinet is sanded with 120 grit sandpaper. Sanding
sealer is then applied, using Enrich 015. It dries in 4-5 hours
and does not ball up like most other sealers. The cabinet is then
sanded with 320 grit paper. A coat of polyurethane is applied,
sanded using 400 grit paper, and finally another coat of
polyurethane. This results in a glass-like finish that is very
durable.
Miscellaneous Construction Tips
The cutouts and flush mount ridge for the drivers are made using
a router. The cutout for the woofer is 3.6" with the flush
mount ridge being 4 3/4" diameter. The depth of the flush
mount should be made by measuring each driver and adjusting the
router accordingly. The center of the woofer cutout from the
quarter round on the bottom is 2 3/4". The cutout for the
tweeter is 3.2 inches diameter with the flush mount ridge being 4
1/16" inches. Again, the depth of the flush mount should be
made by measuring each driver and adjusting the router
accordingly. The center of the tweeter cutout from the bottom is
7 1/4".
Note: Double check all cutout measurements using your drivers to
avoid mistakes.
A 1/4" stereo phono plug is used with a 1/4" phone jack
to 1/8" stereo phone plug adapter, because the 1/4"
stereo phone lug is much easier to solder the speaker wires to
the larger terminals. [Click here to see photo of enclosure with speaker
cutouts.]
The banana jacks specified have set screws to hold the speaker
wires, so be sure to tin the bare wire to prevent fraying, after
you strip about 3/8" insulation form the wire. Of course you
may use terminal cups, etc., but I prefer to use quality
connectors and have them compatible with my other equipment. The
terminal plates that hold the banana jacks are made from scrap
1/8" steel plate. The jacks require 1/2" holes for
mounting. Aluminum or other material may be used. [Click here to see
photo of rear of enclosure with speaker terminals.]
You may make the speaker wires any reasonable length. Keep in
mind that these speakers are NOT shielded; however, they will not
affect the dynamic convergence or purity of your monitor if you
keep them a minimum of 6 inches from the monitor. This is
preferred anyway, to take advantage of the great imaging and
stereo effect these speakers offer. [Click here to see
photo of finished speaker.]
Parts List and Pricing
Below is the parts list which includes the itemized and overall
cost of the project.
Available from Speakers Etc. (and others)
2730 W. Thomas Rd.
Phoenix, AZ 85017
(602) 272-6696 Voice
(602) 272-8633 Fax
Two Audax model HT100FO mid/woofers 4 1/2" @ $31.75ea =
$63.50
Two Access model T1 soft dome tweeters @ $14.50ea = $29.00
Two 3.0 mH inductors @ $5.60ea = $11.20
Two 3.9 µF capacitors @ $2.50ea = $ 5.00
Two 4.7 Ohm, 10W resistors @ $0 .40ea = $0.80
Two 5.0 Ohm, 10W resistors @ $0 .40ea = $0.80
---------
Subtotal
$110.30
Available from Allied Electronics
(800) 433-5700
Two Allied part #645-0030 Banana jacks (black) @ $3.25ea = $6.50
Two Allied part #645-0032 Banana jacks (red) @ $3.25ea = $6.50
Two Allied part #885-0460 Banana plugs (black) @ $1.17ea = $2.34
Two Allied part #885-0462 Banana plugs (red) @ $1.17ea = $2.34
--------
Subtotal
$17.68
Available from Radio Shack
One Part #64-2342 (8) cushion feet @ $1.49
One Part #274-875 Headphone adapter (gold) @ $2.99
One Part #274-265 1/4" phone plug @ $2.49
--------
Subtotal
$6.97
Grand total
$134.95
Plus wood, glue and finish materials for the cabinet (your
mileage may vary), necessary 16 gauge hook up wire and speaker
cables, wire terminals, solder, etc.
How do they sound?
Although there were no measurements made on this speaker, the
overall tonality and imaging of this small gem was excellent.
Compared to the Linaeum/458 speaker mentioned earlier being rated
as a 10 (on a scale of 1 to 10), the Accessible 1.0 would be
rated an 8.0. There's just no contest when comparing these
speakers with the el cheapo powered speakers available for
computers. It would be hard to beat the overall sound in this
price range.
So, load up your copy of Marathon 2: Durandal (or Infinity), set
your preferences to Total Carnage, and be amazed at how real
those Spnkr-XP SSM missiles sound when they whiz past your
head....if you're lucky!! These speakers will put you IN the
fighting!
© Copyright 1995, 1996, 1997
Secrets of Home Theater & High Fidelity
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