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Are you broke, impecunious, skint, destitute or just plain poor? If so, then these could be the speakers for you. Called the Stoney Broke Loudspeakers, they are cheap to put together & require no carpentry skills but still sound surprisingly good. The Stoney Broke Loudspeaker System By LEO SIMPSON T HERE AREN’T TOO many bar- gains around in loudspeakers these days so when Jack O’Donnell of Altronics in Perth proposed these “Stoney Broke Loudspeakers” for people on a budget, we were dubi­ous. Very dubious in fact. OK, so you’ve got two reasonable quality drivers and a simple crossover network but the idea of sticking them inside two plastic zippy boxes stuck together did not inspire us. Still, Jack was not about to be put off and he sent us a pair of these Stoney Brokes. We were so under-whelmed to see the package arrive that we left it behind the door for six weeks until Jack phoned several times and nagged us to take them home and have a listen. Eventually, very grudgingly, we did. I mean, there 36  Silicon Chip was no real incentive was there? But when we started to listen to them we had to admit that they didn’t sound too bad. In fact, as we later said to Jack O’Donnell on the phone, they sounded far better than he had any right to expect! Now we’re not going to turn around and say that these are the answer to an audiophile’s prayers but if you have a need for a compact pair of speakers for the bedroom or as “multi­ media” speakers for your computer, they are worth considering. They certainly sound better than most so-called “multimedia” speakers for computers. Actually, as we have already indicated, the speakers them­ s elves are quite good quality units. The tweeter is a dome unit with a 12mm diaphragm while the woofer is a nominal 100mm (4-inch) unit with a foam roll surround and an effective cone diameter of 80mm. It has quite a large ferrite magnet and a double layer voice coil 25mm in diameter. Its free-air cone resonance is 30Hz and in the right design of cabinet, it is probably capable of a quite respectable performance. Linking the two speakers is a 2-way crossover network centred on 3.5kHz with attenuation slopes of 6dB/octave for the woofer and tweeter. The inductor is ferrite cored while the capacitor feed to the tweeter is a non-polarised electrolytic capacitor. The cabinet is where the real wizardry has been wrought. What looks to be two standard black Jiffy plastic cases (Altron­ics Cat H-0202) have been cunningly attached front to front and PARTS LIST (for a pair of Stoney Broke enclosures) 2 plastic enclosures, with holes machined (see text) 2 100mm roll surround woofers (Altronics Cat. C-0629) 2 12mm dome tweeters (Altronics Cat. C-3010) 2 two-way 3.5kHz crossover networks (Altronics Cat C-4005) 2 12Ω 1 watt resistors 2 sheets of Innerbond wadding, 200 x 150mm 8 adhesive rubber feet 2 port tubes, 60mm x 27mm O.D. 8 3mm diameter 25mm long studs Miscellaneous Hookup wire, silicone sealant or PVC adhesive, solder Where to buy them Note: the complete kit is available from Altronics (Cat. C3200) for $89.95 a pair. whammo – a speaker enclosure is the result. You’d be amazed that such a thing could happen but the photographs don’t lie. No carpentry required If you’re not confident about your carpentry skills then this project will be doubly attractive. The kit comes with the plastic boxes already machined. Both speaker cutouts are there and the screw holes are countersunk where required. Assembly is just that – you put it together. You will need a screwdriver and a soldering iron though. The two cabinet halves are reasonably easy to distinguish. The front half or baffle is the one with the two big round holes for the speakers. The other half is the back. It has a slot for the speaker terminal panel and a 26mm round hole for the port tube. You attach the woofer to the rear of the baffle using the countersunk screws and nuts supplied. We suggest you use shake­proof washers under the nuts because once the speaker is put together it is permanently together. Make sure that the terminals for the woofer are facing towards the centre The kit for the Stoney Broke loudspeaker system comes with all parts, including machined plastic boxes. The tweeter is a dome unit with a 12mm diaphragm while the woofer is a nominal 100mm (4-inch) unit with a foam roll surround & an effective cone diameter of 80mm. of the baffle as this will make it easier to solder on the connecting wires. The woofer should sit centrally on the machin­ed aperture and will be a snug fit. The tweeter is mounted from the front of the baffle, again using countersunk screws, nuts and shakeproof washers. The three holes in the tweeter’s mounting flange will need to be opened up slightly to enable the supplied 4mm screws to be used. Now where do you put the cross­over network? That had us tricked since there are no holes drilled to mount it. Someone who is extremely canny at Altronics has worked out how to mount it without drilling holes. It is mounted by sliding it diagonally across one corner of the baffle section June 1994  37 This photo shows how the parts are mounted in the two halves of the case, prior to the wiring being installed. Note how the crossover network is installed by sliding it diagonally across one corner of the baffle section so that it is held in place by the PC board slots. Be sure to connect the positive terminal on each speaker to its appropriate terminal on the crossover network & note that the 12Ω resistor is installed in series with the negative terminal of the tweeter. The C & I inputs on the crossover network are connected to the input terminals. and it is held in place by the PC board slots. The photo tells the story. The board may need to be filed on one edge to allow it to slide into the cabinet half without distorting. Once in position and the wiring complete, it could be held in place with a couple of blobs of silicone sealant. 38  Silicon Chip We’ve included two photos with this article which show progress in assembly. The first of these show the hardware in place in both halves of the cabinet but with no wiring. The second photo shows the wiring from the crossover to the speakers. This is quite straightforward since the six terminals on the crossover board are clearly labelled; ie, W+ and W- for the woofer, T+ and T- for the tweeter, and C and I for common and input. The positive terminals of both speakers are indicated with red paint on the relevant solder lug. Note that the tweeter has three solder lugs. One of these is a dummy and is not connected to either side of the speaker voice coil but it is not for use in Irish loudspeaker systems. Instead, it provides a convenient tie-point for the 12Ω attenuator resistor which is wired in series with the tweeter. The port tube is a 60mm length of 27mm O.D. PVC tubing. It is a close fit in the machined hole in the rear half of the enclosure. Altronics suggest that it be held in place using silicone caulking compound. Our approach would be to use PVC adhesive as used by plumbers (ie, MEK-based) – it gives a much stronger result. Beware though: PVC adhesive must not be used indoors as it can damage your eyes and your respiratory system. Now for the final steps in putting the enclosure together. You need to insert a small sheet of Innerbond BAF (bonded acetate fibre) into the back half of the enclosure – you will need to cut a slit in the sheet to allow the port tube to poke through it. Altronics suggest the following method of assembly. First, fit four 3mm studs into the threaded pillars of one enclosure half – you need to hammer them in and be careful to make sure they go in straight otherwise you might split the pillars. This done, run a bead of silicone sealant around the mating edge of one half of the enclosure, then carefully push the two box halves together until the sealant pushes out from the mating surfaces. The two halves are then clamped together until the sealant sets. The excess sealant is then cleaned off using mineral turps or scraped off using a utility knife. Our suggested method Quite frankly, we don’t like the suggested method for assembling the enclosure because too much brute force is re­ quired. Our suggestion would be to glue the two enclosure halves together using PVC adhesive. The enclosure halves should be carefully lined up and then clamped in place. Use a minimum of adhesive because you cannot clean off the excess. SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Either way, once the box is assembled, you are unlikely to get it apart again without destroying both halves. So which ever method you choose, make sure that all screws are tight and all connections are correct before the final assembly step. We sug­gest you also test the system on a music signal (low volume please, otherwise you will damage the woofer) to make sure that all connections are working. Where do you get em? Stoney Broke Loudspeakers are available from Altronics in Perth or any of their dealers. The cost is $89.95 for a pair (includes all components). We should make one final comment about their use as multi­media speakers in conjunction with a computer. Most so-called multimedia speakers have shielded magnets and so they can be positioned right next to your computer’s video monitor without fear of degrading the purity. The magnets on the Stoney Broke speakers are not shielded and so they should not be placed any­ where closer than 30cm from your video monitor. If you do place them on top of or next to your moni­tor you will grossly distort the picture and also degrade the purity so that the colours will be mottled and poorly defined. If that happens, the monitor will require degaussing which means a trip to your service agent and SC payment of a service fee. Disc size:   ❏ 3.5-inch disc   ❏ 5.25-inch disc ❏ ❏ ❏ ❏ ❏ ❏ ❏ Floppy Index (incl. file viewer): $A7 + p&p Notes & Errata (incl. file viewer): $A7 + p&p Bytefree.bas /obj / exe (Computer Bits, May 1994): $A7 + p&p Alphanumeric LCD Demo Board Software (May 1993): $A7 + p&p Stepper Motor Controller Software (January 1994): $A7 + p&p Printer Status Indicator Software (January 1994): $A7 + p&p Switchers Made Simple – Design Software (March 1994): $A12 + p&p Note: Aust, NZ & PNG please add $A3 (elsewhere $A5) for p&p with your order Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date______/______ Name _____________________________________________________ PLEASE PRINT Street _____________________________________________________ Suburb/town __________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 979 6503; or ring (02) 979 5644 and quote your credit card number (Bankcard, Visacard or Mastercard). ✂ This rear panel view shows the port tube & the spring-loaded input terminals on the Stoney Brokes. Use PVC adhesive to hold the tube in place & to provide an airtight seal. Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. Whether it is a feature article, a project, a circuit notebook item, or a major product review, it doesn’t matter; they are all there for you to browse through. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use a word processor or our special file viewer to search for keywords. Now with handy file viewer: the Silicon Chip Floppy Index now comes with a file viewer which makes searching for that article or project so much easier. You can look at the index line by line or page by page for quick browsing, or you can make use of the search function. Simply enter in a keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Note: requires CGA, EGA or VGA graphics card, IBM-compatible PC, MSDOS 3.3 and above. June 1994  39