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DIY Project #2 - The Accessible 1.0 - Design by Bill Eckle - February, 1997

Introduction by Ralph Calabria

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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 F 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 F 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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