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You won’t believe how good they sound . . . and your friends won’t believe you built them! “Tiny Tim” Horn Loaded Speaker System This low-cost speaker system uses a single 4-inch driver to give surprisingly good bass and treble response. It is quite efficient and only needs a low power amplifier to give excellent sound levels. T his speaker system turns heads, not only because it looks quite different from the speaker systems you may be used to but more importantly because it sounds so impressive. It does not use bulky and expensive eight, ten or twelve-inch drivers and there are no tweeters or crossovers. Instead, the single driver in each box is a four-inch model, which costs 30  Silicon Chip as little as $25.00. Add some pieces cut from a sheet of plywood, which costs perhaps $70, some glue and a few hours of construction time and you’ll have a speaker system which easily competes with much-higherpriced commercial units on the market today. And yes we know that there are By Allan Linton-Smith and Ross Tester quite a number of tower and minitower speakers on the market right now, many with multiple drivers and all sorts of claims. Quite simply, we believe these are better than anything we’ve heard recently at anything like the price! The secret to such a high-performing speaker is in the design of the cabinet. Unlike the simple bass-reflex or other ported designs you’re used to, these siliconchip.com.au are actually rear-loaded horns. They look difficult to build but providing you’re accurate with your woodwork (or you use someone who is!) they are surprisingly simple to put together. The drivers You have a choice of 4-inch drivers for this design. The cabinets are perfectly matched to – and in fact were originally specifically designed for the high-performing Fostex FE103EN models. But we tried a couple of locallyavailable drivers: the Altronics C0626 and Jaycar CS-2310 models, which are significantly cheaper than the Fostex. And while they might not perform quite to the level of the Fostex drivers, most people would be very happy with the cheaper approach. Having said that, several of the SILICON CHIP staff commented that they thought enclosures fitted with the Altronics drivers actually sounded the best! While the Fostex is a single cone driver, the Altronics C0626 is a twincone model and the Jaycar is a coaxial unit with separate miniature tweeter fed by a bipolar electrolytic capacitor. The first two speakers have the advantage of simplicity and there is no problem with phase shift in a crossover network, albeit even the simple crossover capacitor of the Jaycar unit. All three drivers have the advantage of using a single driver with its phase coherency over a wide range of frequencies. This helps in the realistic reproduction of voice, instruments or complex orchestration and in accurate sound staging or positioning of each instrument. Just a note about the Jaycar CS-2310, it’s intended as a car speaker and its nominal impedance is 4 so you will need to make sure your amplifier can handle this low impedance (fortunately these days, most can). The Fostex and Altronics drivers are both 8. So which to choose? If you’re looking for “most bang for your buck” the Altronics would be a good choice because they are the most efficient (95dB/W <at> 1m) vs 89dB for the Fostex and 83dB for the Jaycar unit. Offsetting that lower efficiency is the fact that the Jaycar driver will actually receive twice as much power as the other two (because it has half the impedance) for a given volume setting siliconchip.com.au from the amplifier. This will mean that the difference in efficiency will be less apparent than the raw figures might indicate. The Altronics and Jaycars are similarly priced, at about $30 pair for the Altronics vs $25 for the Jaycars but you’ll pay much more for the Fostex drivers. You can compare the three drivers in the spec table below. The cabinet design The enclosure design for this speaker (which you can download at www.fostexinternational.com/docs/ speaker_components/pdf/FE103En.pdf) can be regarded as a cross between a bass reflex vented enclosure and a horn-loaded enclosure. Horn-loading can be thought of as an efficient means of coupling between the relatively heavy mass of the speaker to the much lighter mass of air. Horns have been used for a very long time. For example, they have been used for centuries in musical instruments and as megaphones – the very first horn speaker. And of course, all the early wireless sets and gramophones used a horn-loaded speaker. In all of these early examples, efficiency was paramount. The tower speaker we are using here uses the 4-inch driver as a direct radiator for the upper frequencies and a horn radiator for the lower frequencies. The internal construction of the tower is actually a folded horn with each section being longer and larger in cross-section, to approximate the exponential taper of an ideal horn. While efficiency is a big advantage of a horn speaker system, they do not necessarily result in the smoothest bass response. However, in our case where we are using tiny drivers, we get a much more extended bass response than could normally be expected with their relatively high free-air cone resonances. Anyone who is reasonably competent in woodworking and has a selection of suitable tools should be capable of putting these cabinets together. In fact, we fully expect these speakers to become the “project of choice” for many students in their Higher Fostex Altronics C0626 CS-2310 Price per pair ($ approx) 150 34 25 Voice coil dia (mm) 20 - - Impedance (ohms) 8 8 4 83 MANUFACTURER'S SPECIFICATIONS SPL (dB/W<at>1m) FE103En Jaycar 89 95 Rated input (W) 5 to 15 8 to 15 15 Magnet ferrite ferrite ferrite Magnet wt (grams) 193 - - Net wt (grams) 580 - - Baffle hole dia (mm) 93 93 93 0.005 - - 7.5  - 122 Cone area (sq m) Re (ohms) Free air Resonance (Hz) 83 120 VC inductance (mH) 0.0398 - -  Qms 2.747 - 4.28 Qes 0.377 - 1.88 Qts 0.33 - 1.31 Mms 2.55g -  - Vas (Litres) 5.95 - 3.31 Xmax mm Frequency response 0.6 - - 83-22kHz 120-20kHz 90-18kHz MEASURED RESPONSE  Frequency response ±5dB 60-15kHz 70-15kHz - Distortion (THD+N) [1kHz 90dB] 0.45% 0.65% - Sound Pressure Level 1kHz 1watt/1m (dB) 92.65 89.97 - The enclosures are designed for the Fostex FE103En drivers but we’ve found the much-cheaper Altronics C0626 or Jaycar CS-2310 do an admirable job as well: in fact, some of our staff members commented they sound better! October 2013  31 # # # #: ALL 150mm WIDE (+SAW CUT) 50 380 x 150 385 x 150 385 x 150 235 380 x 150 235 x 150 190 190 # ONE EXTRA PIECE REQUIRED 840 x 405 4 4 200 200 # 840 x 405 # 7 FIRST CUT 80 810 x 150 # 12 6 810 x 150 13 3 # 13 375 x 150 12 250 180 11 8 20 80 11 375 x 150 6 180 100 19 250 340 x 150 340 x 150 19 7 25 3 10 100 10 25 8 # 17 17 155 C L 9 155 80 2 93mm 93mm DIA DIA 245 80 2 93mm 93mm DIA DIA # C L 9 # 32  Silicon Chip # # 245 15 1 150 # 250 5 150 18 5 250 16 250 # 18 All dimensions shown are finished sizes – allow for saw cut thickness! 21 21 16 250 14 1 15 400 x 150 14 400 x 150 siliconchip.com.au # # 150 # 840 x 405 840 x 405 150 # Fig.1: it’s a tight fit but all except one piece (one of the ‘7s’) can be cut from a sheet of 1220 x 2440 x 15mm ply. This assumes a saw cut thickness of 2.5mm, about normal for a kitchen cupboard maker. Note where the first and second cuts are made. The lemon coloured pieces are for box 1, pink for box 2. # # 20 Plywood is a must! The pieces for both boxes can be cut from one and a half sheets of 15mm plywood (1220 x 2440mm and 1220 x 1220mm). In fact, with care you’ll get all bar one small piece (no.7) from one sheet. See Fig.1: it shows how the pieces are cut – the first cut needs to be made where shown. The missing piece, (235 x 150mm), could even be cut from scrap as it is internal and won’t be seen. Note that this cutting diagram does assume an “imperial” size sheet; some suppliers have taken to making their sheets 2400 x 1200 – this size is not quite large enough as it cannot make allowance for the saw cuts. Your supplier should be able to advise you of the exact size of their sheets. If they are 2400 x 1200, you’ll definitely need a second (half) sheet. We used good quality Aspen Birch veneer because of its fine grain and appearance but you can choose the finish to match your décor. You could use plain plywood, sand it smooth and paint or stain it to your tastes. Note that we DO NOT recommend the more commonly available MDF because it is 16mm thick – the extra 1mm will decrease the width of the “horn” by a cumulative 6mm and will drastically affect performance. You will note from the photos and diagrams that the horns are built up by layers of plywood pieces. It is absolutely vital that these pieces are very accurately cut to size. If you don’t have either the equipment or the skills to cut to close tolerances (to the millimetre!) we suggest you approach a local kitchen cabinet maker – most will do it for a reasonable cost; indeed, many will be # # School Certificate design and technology courses: do the cutting, assembly and finishing in the woodwork room, mount the speakers and wire them in the technology or electronics classes – and best of all they won’t break the bank. And after they earn top marks, they’d have speakers Mum and Dad would be proud to put in the lounge room! 6 385 250 C L 5 15 25 4 80 93 35 2 245 7 190 3 235 1 8 80 2 12 375 150 13 21 250 380 155 340 810 840 21 22 9 10 22 10 180 11 250 200 150 20 240 100 19 18 14 20 17 400 siliconchip.com.au 17 16 14 150 180 Fig.2: looking down on the right side, without the side panels, here’s how all the pieces glue together to form the loaded horn. The photographs later in this article will help explain how it all goes together. able to supply the veneered plywood as well. Just don’t let them talk you into MDF (a lot of kitchen cabinets are made from the stuff these days!). Incidentally, we investigated a major hardware chain offering a cutting service and found them unacceptable for two reasons: first, they guaranteed a 19 18 16 (ALL DIMENSIONS IN MILLIMETRES) (13) 50 tolerance of no better than 5mm – useless as far as this project was concerned and second, they only had “construction grade” 15mm ply. Now that would be OK if you only wanted a painted surface but even then, a fair amount of sanding and finishing would be required. Also, they Fig.3: and here’s the front-on view with the side panels fitted. Piece 13 is actually the rear panel. only had full “metric” sheets (2400 x 1200mm) in stock and, as expected, they tried to talk us into MDF, which did come in half sheets! It may be that in time, some of the kit suppliers will produce a full kit of parts – keep an eye on their advertisements in SILICON CHIP. October 2013  33 +15 Frequency Response, C0626 In Cabinet 14/07/13 17:44:51 Another feature of these speakers is their ability to handle a range of amplifiers. While they’re ideally suited to lowerpower amplifiers (again, that “schoolies” market springs to mind), they can handle more, with sound output to match. All three speaker drivers mentioned above are rated at 15W maximum input so you certainly cannot run them flat out from a high power amplifier. We’ve run them from amplifiers as low as 5W output (eg, “The Champion” from January 2013) and we’ve run them (judiciously!) from the much higher power Ultra LD MK3 (July-September 2011). However, even running from The Champion they certainly filled the large SILICON CHIP warehouse with sound! +10 +5 Relative Power Level (dBr) +0 -5 -10 In line with driver In line with horn -15 -20 -25 -30 -35 -40 20 50 100 200 500 1k Frequency (Hz) 2k 5k 10k 20k Fig.4: frequency response plots of the Altronics drivers in the horn-loaded cabinet. The red trace is the on-axis flat response and blue trace shows the output from the mouth of the horn section. 48 Driver Impedance In Folded Horn Cabinet 22/08/13 12:23:36 44 40 Altronics C0626 Fostex FE103N 36 Impedance ( ) 32 28 24 20 16 12 8 4 0 20 50 100 200 500 1k Frequency (Hz) 2k 5k 10k 20k Fig.5: impedance curves of the Altronics and Fostex drivers, with multiple peaks resulting from the horn loading. This is partly a result of the much higher loading to the rear of the driver’s cone. 100 Driver THD+N In Folded Horn Cabinet 20/07/13 19:00:59 Total Harmonic Distortion Plus Noise (%) 50 Altronics C0626 Fostex FE103N 20 Performance We tried these with all three speaker drivers mentioned above. As you might expect, the Fostex drivers gave the best bass response – but you do pay for it! The others were surprisingly beefy! Fig.4 shows two frequency response plots of the Altronics drivers in the horn-loaded cabinet. The red trace was taken with the microphone on axis and very close to the tweeter cone of the driver and it shows a reasonably flat response to 10kHz and rising to a peak at around 18kHz. The blue trace was taken with a microphone adjacent to the horn section and it measures the augmenting effect of the horn loading. As you can see, the response is quite well maintained to below 60Hz (quite similar to the much more expensive Fostex drivers). Generally speaking, at distances of over 2m, the response will be a combination of the two cuves. Fig.5 shows the impedance curves of the Altronics and Fostex drivers. These are quite different to the equivalent curves you would see with the drivers in a bass reflex enclosure which normally shows two impedance peaks in the low frequency region. The horn loading results in multiple peaks and this is partly a result of the much higher loading to the rear of the driver’s cone. It also results in better bass, as shown by Fig.4. Fig.6 shows the harmonic distortion of the Altronics and Fostex drivers and again the cheaper Altronics driver gives a good account of itself. Note that the distortion is quite low over much of the audible range but rises at the low end, partly as result of the horn loading and also the fact that the fundamental output drops markedly at very low frequencies. Building the speakers 10 5 2 1 0.5 0.2 0.1 The amplifier 20 50 100 200 500 1k Frequency (Hz) 2k 5k 10k 20k Fig.6: harmonic distortion of the Altronics and Fostex drivers. Note that the distortion of both drivers is quite low over much of the audible range but rises at the low end, partly as result of the horn loading. 34  Silicon Chip We have simplified each step so you shouldn’t have any problems. Build one speaker box at a time otherwise mistakes are much more likely; do not rush things and make sure you understand each step before diving in! Again, we must emphasise the need for accuracy in cutting out the panels. Using a hand-held saw of any description will usually result in errors and out-of-square cuts which will inevitably lead to air leaks or malfitting panels. The panels are butt-glued so squareness is next to Godliness! To this end, wipe up any glue excess as you go. And to ensure perfect alignment, the enclosures need to be assembled on a completely flat surface – a work bench is fine if it is flat and stable; otherwise a (say) concrete floor with some single newspaper sheets spread on it. siliconchip.com.au Putting them together Step i: We are assuming you already have all your pieces accurately cut out. Number each piece as shown on the diagram – use “Post-It Notes” or similar to avoid leaving glue – in any case stick them to the “bad” side of the plywood (ie, not the face side). Step ii: Using the diagram (Fig.2) as a guide, on one of the side panels (piece 1) use a pencil on the “bad” side to mark out where all the pieces are going to go. Step iii: Take pieces 2 and 3 and first check their dimensions to make sure you have the right ones – we’re about to glue them together and once stuck, you won’t be able to get them apart. Use 2 or 3 small nails or panel pins to tack them together, then prise them apart without bending the nails and run a 3mm bead of glue* along the join. Push the nails back into the holes and gently tap them with a hammer until you are happy with the fit. Wipe off any excess glue with a damp rag. If for some reason they haven’t ended up where they should, light tapping with the hammer should get them right. You have about 10 minutes to move things around before the glue sets. Clamps or a vice should be used to hold the pieces together to give a really good bond – the glued pieces should be ready to remove after about half an hour. Take the completed pieces and place them on the side panel where they will go – but don’t glue them in place just yet. * We used a caulking gun and “Parfix Maxi Nails Fast” water-based construction adhesive, which will bond wood to just about anything. It’s cheap ($3.95 for a caulking gun tube at our local hardware store), it sets quickly (about 20 minutes) but gives up to 10 minutes or so of “fiddle time” before the glue gets too tacky. This glue (or several other bonding adhesives) are available from most hardware outlets. NOTE: PVA wood glue is not recommended. Lay out all the pieces on a flat surface so you understand how they all go together. Note the identifying “post-it” notes. siliconchip.com.au Now we’ve glued all the pieces together and when dry, have then glued them in position on the left-side panel. October 2013  35 Step iv: Repeat step iii for pieces 4 and 5. Step v: Glue pieces 2 & 3, and 4 & 5, together Step vi: Glue pieces 21, 22 & 10 together, using a square to ensure that the end is perfectly flat. Allow them to set for an hour or so, then glue them to the pieces you made in step v. (They glue to piece 3). Step vii: Now glue pieces 11 & 12 together, allow to set for an hour, then glue those to the pieces in step vi (they glue to piece 10). Step viii: Glue pieces 7, 8 & 9 together and set aside to dry. Step ix: Fit the input (banana) binding posts to piece 13 – drill two 3.5mm holes 50mm down from the top and 25mm apart. Step x: Now glue pieces 16, 17, 18, 19 & 20 together. Step xi: Glue pieces 6 & 13 together, using the side panel to keep them square while they set. Step xii: Glue pieces 13 & 14 together, again using the side panel to keep them square while they set. Step xiii: Now glue all the pieces together from step x, to pieces 13 and 14. Step xiv: Once all of the glue has set, you now should have everything ready to be glued to the side panel. Place all pieces accurately in position on the side panel. Here’s the completed speaker box once the glue has dried. All that remains is a bit of tidying up, finishing the veneer with your desired stain or paint and then fitting the 4-inch speaker. Use small panel pins and clamps to hold your speakers together while the glue is setting. Any blemishes can be smoothed over later. 36  Silicon Chip And here it is with a clear polyurethane finish. This shot of the rear of the speaker (from the top) also shows the input terminals in place. You can see how the rear panel and top are inset 5mm from the rear edge of the side panels. siliconchip.com.au Step xv: Glue all those pieces in place. By now you should have a pretty good idea how much glue is used so you shouldn’t have too much excess. If you do, don’t waste time wiping it away - remember, you only have about 10-20 minutes before the glue sets so you need to work fairly fast. Step xvi: When everything is in place, take the other side panel (piece 15) and without applying any glue, place it on top of the whole assembly with some weights on top. If you have worked fast enough, the glue should still be wet enough so that you can move any pieces that need to be adjusted so they are flush with the side panel. It’s most important that the front of the cabinet is flush to the side because that’s the part that you see. Adjust it first, then the back if you have time (you won’t see the back!). Step xvii: When the glue has dried, solder a 300mm length of figure-8 cable to the input terminals. Remember which is to the red and which is to the black (normally, stripe goes to – or black). Hang the other end of this wire out the front speaker hole. Step xviii: It’s time to complete the enclosure. Add a bead of glue to all the edges and place the side panel in place, adjusting it again so that the front is aligned to the sides. Put the weights back on and wait until it dries. Hopefully, you will have done it all correctly. . . now you get to do it all again with the second enclosure! Finishing off You can now carefully sand off any rough edges or dags of glue then stain, coat or paint your enclosures as you desire. We simply applied a coat of clear polyurethane to the timber as the Aspen Birch veneer really shines with this treatment. But remember that paint hides a multitude of sins if you have made any “oopses” along the way. When the cabinets are completely dry, cut two 150mm x 245mm pieces of cellulose wool (often sold under the brand-name “Innerbond”) and place them loosely behind the speaker area – but do not block the entry to the horn. We found that any packing in the horn reduced the bass by half (6dB) but the little packing behind the speaker had no effect on the bass. However, it did reduce the “hollow” sound at mid frequencies, caused by standing waves and reflections. Fit the speaker drivers to the boxes, making sure you get the phasing (ie + and – connections) the same on both boxes. As a final check, briefly connect a 1.5V battery to the input terminals (+ to red, – to black) and watch the cone. Both speakers should move the same direction when connected the same way. The drivers should have some form of gasket between them and the woodwork to ensure a seal. We wouldn’t use silicone sealant – it works really well but makes the speaker incredibly difficult to remove intact if you have to remove it for any reason. A large “O” ring is ideal; at a pinch you could even use a large elastic band. Just make sure it seals all the way around as you tighten the four screws.‑ If you use the Jaycar drivers, fit the grilles over the front of each speaker. Of course, you can buy grilles to fit the Altronics or Fostex speakers. Grilles are almost mandatory if you have young people with prying fingers around: that speaker height is just about perfect. Training the speakers What’s this? Training speakers? Believe it or not, all speaker drivers “straight out of the box” are a little stiff and benefit from being “run in”. We allowed about two hours of continual music at reasonable volume before we were satisfied that ours were nice and mellow. You will certainly note a significant improvement over time, particularly in the bass response. SC siliconchip.com.au October 2013  37