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isoundBar with built-in woofer Many of us spend an enormous amount of time watching TV, movies and playing video games. Even if you only use your TV occasionally, life’s too short to put up with the lousy sound quality of typical TV speakers. Commercial soundbars cost a bomb and often aren’t that much better. Why not build this awesome soundbar and enjoy your favourite programs in high fidelity? By Allan Linton-Smith A soundbar is a set of speakers in a wide, slim package that’s ideal for putting just under or in front of your TV. There are two big problems with these: the ones that are any good are usually unjustifiably expensive (sometimes more than the TV they’re paired with!), and the requirement to be slim usually limits the amount of bass they can produce. Cheap soundbars abound and are best avoided; many of these have cheap external subwoofers (if they have one at all), which can be very boomy and annoying. In some households, these end up being switched off entirely due to ‘subwoofer fatigue’. On the other end of the scale, decent hifi soundbars from well-respected audio manufacturers are now around the $1000-2000 mark, which can be hard to justify when 65-inch (165cm) 4K TVs start at around $700! Hence this design – a DIY soundbar with excellent frequency response, decent bass and low distortion that won’t break the bank. The soundbar is punchy and will suit many listeners, but if you want to go all-out, we’ve designed a matching sub that rounds out the sound with plenty of bass. It’s a fairly cost-effective design, so even with the sub included, the whole thing will cost a fair bit less than that cheapo 65-inch TV. The total cost of all the drivers used in the isoundBar is around $260, so even when you add in the amplifier module, timber etc, you will probably be able to build it for under $400. You can buy a soundbar for that, but we doubt it will sound anywhere near as good. Design I spent considerable time designing this self-contained system with an internal woofer in a small box that is just 1240mm wide, 70mm tall and 200mm deep. There were significant (and unexpected) challenges, not the least of which is that the slim design restricts us to forward-facing drivers no larger than 55mm in diameter. Also, the internal volume has to be shared by the separate left and right channels and the internal woofer. The solution was to create three isobaric chambers (see side panel overleaf) using four 5cm (2in) drivers for the left & right channels (two each) and two 9cm (3.5in) drivers for the woofer, mounted horizontally. The use of isobaric chambers is critical because this halves the required internal volumes for a good low-­ frequency response. The double isobaric design enables good upper bass from the small L & R inner enclosures, leaving just enough space for an internal woofer, also in an isobaric configuration. The final design added 2.5cm (1in) Vifa tweeters to the 5cm and 9cm Vifa drivers, giving outstanding performance! The isoundBar has spectacular highs from its small tweeters and includes Bluetooth connectivity. A critical aspect of the drivers chosen is that we have checked that they are all available in reasonable quantities, and hopefully should remain available for some time after this article is published. The whole design is tri-amped, with separate amplifiers for the left and The isoundBar uses four TC6FD00-04 drivers (left), two TG9FD10-04 (centre) and two BC25SC55-04 tweeters (right). Not shown to scale 48  Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.1: the frequency response of the isoundBar is quite smooth up to 20kHz (blue curve). It has a very acceptable bass response, which is significantly enhanced with the woofer (red curve) and even further by the optional subwoofer (green). While it might look like the subwoofer creates a bass peak, in practice it sounds good, with strong bass that isn’t boomy or annoying. right channels and the internal woofer. In fact, there is a total of five separate amplifiers: two for the left and right main drivers, two for the left and right tweeters and one for the woofer, each with a maximum output 50W RMS and each with its own volume control for balancing. To do this, I used a Yuanjing class-D 4.1 amplifier module, which I previously reviewed in the May 2019 issue (siliconchip.au/Article/11614). The module has three Texas Instruments TPA3116D2 high-efficiency class-D audio amplifier ICs with two 50W channels per IC. If you refer to that article, you will see that it dedicates one whole TPA3116D2 for the subwoofer channel to theoretically deliver 100W RMS. However, testing showed the actual maximum output to be closer to 60W. Nevertheless, we selected that module for its low cost and ease of use. It provides plenty of power to handle the vast dynamic range from modern signal sources such as streamed movies, CDs, DVDs, Blu-rays etc, with sufficient headroom before clipping. The sound quality is also pretty respectable for a low-cost class-D amplifier module. Many movie soundtracks feature realistic whispers and then instantly impose super-loud sounds from bombs, jets and vehicles, so you need a substantial dynamic range. Any clipping in the amplifiers could siliconchip.com.au Fig.2: total harmonic distortion for the isoundBar is generally less than 2% above 120Hz and well under 1% across much of the critical midrange. This is excellent when you consider that the amplifier’s distortion is much higher than most Silicon Chip amplifiers. It’s less than 10% down to 40Hz, which is exceptional for tiny 9cm (3.5-inch) drivers! quickly damage these little speakers, especially the small tweeters. So you need more power in reserve than you might think. These ICs also have short-circuit/ overload protection, over-voltage and under-voltage protection and are around 90% efficient. So they only need a tiny heatsink each and run from a 12-24V high-current plugpack, meaning no mains wiring is required. The tiny amount of heat generated means that special cabinet ventilation is unnecessary. This module also has a built-in Bluetooth receiver which activates a relay when pairing occurs. A signal can also be fed in via the onboard 3.5mm socket. The signal priority is set up to select whichever input is active first. If you require a bigger sound, we’ll also describe an external subwoofer output to interface with the subwoofer. As we said earlier, the sound has plenty of punch without it, but the subwoofer adds a whole new dimension and is required if you want an authentic hifi experience, or are just a bass fiend! the 60-80Hz region, and adding the external subwoofer extends it further, to about 35Hz. That might not ‘sound’ like the external woofer would make a big difference, but trust us, it does! The overall sound quality goes from good to great when you add the subwoofer. Still, the internal woofer is pretty good for watching ordinary TV programs. When you want to listen to music or watch a movie cinema-style, the extra bass is really worthwhile. Fig.2 shows the measured distortion Performance The frequency response of the system without the internal woofer and that of the woofer on its own are shown in Fig.1. Without the woofer, it has a pretty flat response from around 120Hz to 20kHz. Adding the woofer extends the bass response down to Australia's electronics magazine The optional sub adds plenty of bass and only measures 45 × 30 × 15cm. August 2022  49 What is an isobaric speaker? Two identical drivers are used with the isobaric box speaker design, but only one radiates sound. The other is coupled to the first one by a small sealed enclosure where the pressure remains constant as the speakers move in the same direction, by the same amount, at the same time – see Fig.3. Harry Olson invented this configuration in the 1950s. It uses speaker drivers (usually bass units) mounted in a sealed enclosure and driven in parallel or series to ensure they move in ‘lock step’. This configuration lowers the effective Vas by half. In other words, it effectively doubles the speaker enclosure volume and extends the bass frequency response beyond what would be possible for otherwise identical speakers in the same sized box. Although the power handling capability doubles, the efficiency and sound pressure level do not increase. The main disadvantage is the doubling of driver cost without a corresponding increase in sound output. Fig.3: the isobaric arrangement has two drivers connected in series, driven with the same signal. at one watt. Importantly, it’s quite low (below 1%) in most of the region between 150Hz and 3.5kHz, where the majority of the most critical sounds like the human voice and many instruments lie. That results in a clear sound with excellent dialog intelligibility. Layout and calculations Similar to what’s shown in Fig.3, the woofers are set up in an isobaric box in opposite positions. However, the cones are wired to move in the same direction. The sound output from underneath the drivers travels to the woofer port at the front, which is designed so that only a 32mm hole is required. There is no extended port tube, simplifying construction. This isoundBar uses Vifa/Peerless drivers throughout (Vifa and Peerless merged in 2000). The main left and right speakers are 5.5cm TC6FD00-04 drivers, with two 9cm TG9FD10-04 drivers as the woofers. All are available in Australia via Wagner Electronics (www.wagneronline.com.au). The majority of the sound from the soundbar comes from the four TC6FD00-04 drivers, two on each side. They are wired in series because the amplifier cannot handle the 2W load they would present if wired in parallel. These little speakers have a very smooth frequency response in the midrange, but lose a bit at the top end frequency due to their isobaric positioning, which damps them somewhat. Hence, the inclusion of one Vifa BC25SC55-04 25mm tweeter on either side. These tweeters are rated at 6W and are driven by a separate amplifier with its own volume control. They are mounted on the ends of the soundbar and are fed via 6.8μF capacitors. These add some nice treble which tends to bounce off the walls adjacent to your All drivers must be sealed with a selfadhesive foam weather stripping. TV room to create a spaced-out effect. Their cut-off frequency (-3dB point) is close to 4kHz due to the capacitor value. The volume control for these tweeters offers very easy adjustment of the amount of treble, which is especially useful for those with some HF hearing loss. Their independent amplifier also means that there is no interference with either the mid-range or the bass speakers, significantly reducing the overall distortion. Because of their natural roll-off at high frequencies, the main 5.5cm drivers do not need any choke, as would be the case in a typical speaker arrangement. This reduces the overall cost of the system. The woofers are wired in series for a total impedance of 8W and fed from the subwoofer channel of the class-D amplifier. The LEAP program predicts a -3dB point at 39Hz, although We mounted the drivers using 3mm nuts and bolts, although wood screws would work too. All gaps must be sealed with weather stripping or filled with silicone sealant. The woofer mounted to the mezzanine points downward while the one mounted to the top panel folds over and nestles neatly beside it. Make sure the wiring to the subwoofers does not interfere with the cones. 50  Silicon Chip Australia's electronics magazine siliconchip.com.au our Audio Precision measurements indicate a somewhat higher roll-off at around 55Hz. Still, this is quite impressive, considering the small space allocated and the low sensitivity of these drivers at 84dB/W <at> 1m. The woofers are rated at 10W, but with the two in series, we can drive them at up to 20W. The class-D amplifier subwoofer channel can deliver more than 50W; so the speakers will audibly distort well before the amplifier clips, so the voice coils should not overheat even if they are over-driven (within reason). The design includes a switchable output for driving an external passive subwoofer, and it can drive just about any speaker with an impedance of 4W or higher. The optional subwoofer presented later works very well when connected to this output. Soundbar construction The isoundBar is a fair bit more challenging to build than, say, our Concreto Loudpeaker System (June 2020; siliconchip.au/Article/14463), although, to be fair, it doesn’t get much simpler than the Concretos. Bear in mind that we have to jam everything into a relatively small box, and the result has to offer quality performance from small speakers. The more expensive hifi commercial soundbars also use pretty complex designs, which is part of the reason they are so costly. But if you DIY, you can eliminate a lot of that cost. As long as you work steadily, you will find that the construction is easier than it might look from the diagrams. In fact, the average DIYer should be able to build it using minimal power tools. The pieces of timber you need to cut and drill are shown in Figs.4 & 5, while the way they go together is shown in Fig.6. Start by cutting the pine boards into the required lengths, then cut the holes for the speakers and the ports with hole saws or a jigsaw. Next, assemble the outer frame by screwing and gluing the four outer pieces together, followed by the internal pieces. Drill small pilot holes for the screws, so they don’t split the timber. Fig.4: here are the larger panels you need to cut for the top, bottom, back and front of the isoundBar. The top and bottom are cut from 4mm ply, while the front and back are 19 × 64mm DAR pine. siliconchip.com.au Australia's electronics magazine August 2022  51 Fig.5: there are also 11 smaller panels to cut. The mezzo baffle is cut from 3mm MDF, while the other pieces are from 19 × 64mm or 12 × 40mm DAR pine. 52  Silicon Chip Australia's electronics magazine siliconchip.com.au Those who are more advanced at woodworking may prefer to use better joining techniques such as dovetailing, but whatever method you choose, make sure you keep the frame square. You can do this by clamping, or you can just nail a piece of scrap timber diagonally to keep it square until the glue dries. Next, build the woofer box and mount the timber strips flush with the bottom using screws and glue. Glue the mezzanine baffle to the side strips and then mount one of the 9cm speakers as shown. All drivers must be sealed with self-adhesive foam weather stripping, as previously shown. The next step is to mount the remaining drivers using timber screws into pilot holes, or nuts and bolts through 3mm holes drilled right through. Make sure you use the weather stripping because the whole arrangement needs to be airtight. Mount the tweeters in the holes on each side of the frame, then mount the second 9cm speaker to the hole in the top panel. Fill any gaps that air might be able to pass through using silicone sealant. For the amplifier panel, cut a piece of blank copper laminate or unclad FR4 and drill holes for the potentiometers, the power socket, the 3.5mm jack socket, the external subwoofer terminals and the selector switch. Paint it black, then screw and glue this panel to the rectangular cut-out at the back of the soundbar. Our prototype used 3mm nuts and bolts, although you could use self-tapping wood screws. Mount the class-D amplifier to the panel and then mount all the other ancillary sockets. Solder/attach the speaker wires as per the wiring diagram, Fig.7, and mount the amplifier in the soundbar. Once everything is in place, it is time to test it. You can either connect the 3.5mm input to an audio source (eg, via a 3.5mm stereo jack plug to 2 x RCA lead) or just pair your smartphone, tablet or another device via Bluetooth. The amplifier will simply select the source you choose. Run the unit at a low volume initially to avoid overloading the speakers before they are fully enclosed with the top and bottom panels. Ensure all the speakers are operating; dial in the tweeters slowly until you achieve enough volume to verify that they are working. Similarly, dial in the woofers last to ensure there are siliconchip.com.au Fig.6: a plan view of the isoundBar along with a detailed view of a crosssection of the woofer chamber. Australia's electronics magazine August 2022  53 no unwanted vibrations from their mounts. Once you are happy that all is good, cut the acoustic wadding into rectangular pieces that fit into each section and place them loosely inside. There is not enough room in the small woofer chamber, but fill the rest. You can then mount the bottom panel with screws or glue. We attached the top and bottom panels to our prototype using screws with thin weather stripping to seal it, so that we could easily open it up again to make changes during the development phase. Once the bottom panel is in place, you can seal the joins with a silicone caulking compound. Also seal the holes that wires pass through to ensure everything is airtight. Mounting the top panel can be a little tricky because the top woofer needs extra wire length (slack), and this needs to be carefully nestled inside the soundbar so that nothing touches the cones. It is a good idea to locate the top panel in position and hold it in place with weights, then test it out with an audio signal to ensure nothing interferes with the cones before permanently attaching it. Now screw and glue the top panel in place. Test everything again to ensure the soundbar gives a clean sound; then, you are ready to finish it off with grille cloth. We painted it black before covering it with speaker grille cloth for a ‘stealthy’ appearance, so you won’t notice it sitting under the TV. To do this, simply cut the grille cloth to the right size, wrap the soundbar, then glue it with a hot melt glue gun. You are now ready to enjoy some beautiful sound from your TV! Subwoofer construction As stated earlier, the isoundBar has punchy bass by itself but lacks the deep bass that makes sound super realistic for both movies and music listening. As this subwoofer doesn’t cost the earth to build, we highly recommend it as an add-on. Subwoofer design This little sub is really easy to build as a sealed enclosure and can be screwed or glued from 18mm melamine. Its slim design means it can easily be hidden from view. The class-D amplifier in the isoundBar can put out more than 50W RMS, so it will drive this mini-sub to generate pretty generous amounts of bass. The class-D amplifier (bottom right) is mounted to the back panel after the woofers are in place. Allow some slack in the wiring for easy removal or replacement of the drivers. Our prototype used felt weather stripping to seal the top and bottom panels, which were screwed on for easy access, but you can glue them instead. Fig.7: here’s how to wire up the various drivers to the amplifier module. Don’t forget the capacitors in series with the tweeters, or they could easily be damaged. 54  Silicon Chip Australia's electronics magazine siliconchip.com.au The selection of a driver for this subwoofer was inspired by the JBL Club WS1000, a 25cm (10in) speaker which has a really low resonance (26.62Hz) combined with a low VAS of 40.37L. This means you can achieve great bass in a little sealed box of around 15L; that’s tiny for a subwoofer that can reproduce such low bass! This driver cost us $148 (including shipping) at the time of building and comes with a full data sheet and brochure, plus a JBL sticker! The 18mm HMR melamine we used to build the cabinet was from an offcut we already had, the acoustic innerbond filling was also left over from other speaker projects, and the wire was also from the junk box, so it was a budget project. To make it look nice, we covered it with a 2mm-thick black felt carpet that’s explicitly sold for use with subwoofers, costing $19.99 for a 1m x 1m square. So the total cost to build the sub was just $168 in our case. Even if you have to buy all the materials new, you’re probably only looking at around $200. While the driver is powerful, it is also very shallow at 80mm deep, allowing for a very slim box design. An earlier JBL W10GTi MkII 25cm woofer we tried was 232mm deep, so JBL have made their designs significantly more compact over time! We tried using the W10GTi MkII as part of our Senator loudspeakers (May & June 2018; siliconchip. au/Series/300) but found it to be too expensive and heavy and not suitable for a slim enclosure. The new WS1000 design is much lighter and thinner, with an easier wiring system, yet it performs almost as well! This JBL driver was designed mainly for use in cars, so it has a “selectable smart impedance” (SSI) switch allowing it to present either a 2W or 4W impedance. For the isoundBar, the class-D amplifier is not suitable for driving a 2W load, so the 4W option is the one to use. JBL recommends a 14.15L sealed enclosure. They also have recommendations for larger ported enclosures, but the smaller sealed box is much easier to make and can be put together quickly. Subwoofer performance Parts List – isoundBar 2 Vifa/Peerless TG9FD10-04 9cm/3.5-inch drivers [Wagner Electronics] 4 Vifa/Peerless TC6FD00-04 5.5cm/2-inch drivers [Wagner Electronics] 2 Vifa/Peerless BC25SC55-04 2.5cm/1-inch tweeters [Wagner Electronics] 1 100 × 45cm piece of acoustic wadding [eg, www.ebay.com.au/itm/185046067357] 1 TPA3116D2-based class-D 4.1 amplifier module [eg, www.aliexpress.com/item/32911419084.html] 1 5m length of figure-8 medium-duty speaker cable 2 6.5-6.8μF 250V metallised polypropylene crossover capacitors [Jaycar RY6956] 1 24V 5A power ‘brick’ with DC barrel plug 1 panel-mount barrel socket to suit the power supply 1 panel-mount speaker connector [Jaycar PS1082] 4 knobs (to suit amplifier module; most likely fluted types) 1 bottle of wood glue 1 tube of neutral-cure silicone sealant Timber & hardware 3 1.24m length of 64 × 19mm DAR pine 1 1.24m length of 40 × 12mm DAR pine 1 2400 × 1200mm sheet of 19-20mm plywood 1 1240 × 900mm sheet of 4mm plywood 1 600 × 900mm sheet of 3mm MDF 1 5m roll of 9mm-thick, 9.5mm-wide grey closed-cell foam weather-seal tape [eg, Bunnings 0077668] 50 8G × 15mm button-head wood screws (for mounting drivers) OR 50 M3 × 25mm panhead machine screws with flat washers and hex nuts 50 7G × 30mm or 8G x 30mm countersunk head wood screws (for joining pieces) 20 small Nylon cable ties (P-clamps; optional) 4 M3 tapped Nylon standoffs & 6mm M3 machine screws (for mounting amp module) 1 300 × 100mm sheet of clad or unclad FR4 1 1m x 1.5m piece of dark speaker grille cloth [Jaycar CF2752] Parts for optional (but recommended) subwoofer 1 JBL Club WS1000 24cm/10-inch subwoofer driver [eBay] 1 100 × 45cm piece of acoustic wadding [eg, www.ebay.com.au/itm/185046067357] 1 1200 × 596mm (or larger) sheet of 18mm-thick plywood, MDF or similar 1 pair of panel-mount speaker terminals (optional) 1 1m+ length of heavy-duty twin loudspeaker wire (to suit installation) 8 8G x 15mm button-head wood screws (for mounting the driver) OR 8 M3 × 25mm panhead machine screws with flat washers and hex nuts 20 7G x 30mm or 8G x 30mm countersunk head wood screws (for joining pieces) 1 tube of neutral-cure silicone sealant external − Sub Sub O/P 12-24V DC CTR+ + internal Master Volume Tweeters Volume Front Volume Sub Volume 3.5mm input The control panel for the isoundBar. You might find it useful to make your own label so others can easily see what each connection does. The frequency response for our subwoofer is very smooth down to a very siliconchip.com.au Australia's electronics magazine August 2022  55 Fig.8: the subwoofer frequency response has a modest peak at around 65Hz and produces usable sound down to about 30Hz. It combines nicely with the isoundBar’s sound output and gives it more oomph! Fig.9: the subwoofer distortion plot. It might seem quite high, but subwoofers are notorious for having high distortion levels; around 2% in the middle of its range is actually quite decent. Fig.10: despite being nominally a 4W driver, the subwoofer impedance doesn’t dip below 5W, and its resonant peak is 25W at around 46.5Hz. 56  Silicon Chip Australia's electronics magazine respectable 30Hz, with a peak around 60Hz, as shown in Fig.8. The upper cut-off frequency can be as high as 300Hz, but the setting on our class-D amplifier is fixed at 150Hz (-6dB). That turns out to work quite well with this sub. As shown in Fig.9, distortion from the subwoofer is below 5% from around 35Hz to 120Hz. The higher distortion below 35Hz is due to the output level decreasing, while above 200Hz, it is due to the high moving mass of the driver. While 5% might sound high, it is a pretty clean response for a subwoofer, with low harmonics that are troublesome with many subwoofers. The final impedance of the JBL driver mounted in the little box shows an impressive resonance peak at 46.62Hz – see Fig.10. The speaker was set to 4W, but the actual measurements are higher, with a minimum of 5.3W at 83.1Hz, because of the added resistance of the speaker wire and the connectors. Construction Since this is a sealed enclosure, it is much easier to build than a ported design which would have been three times the volume as recommended by JBL. We used 18mm HMR melaminecoated particleboard, but any material at least 18mm thick is suitable, including plywood, timber or MDF. Remember that the finished enclosure must be airtight, so make sure you cut the pieces for a tight fit and seal all joints well with silicone sealant. Start by cutting the pieces as shown in Fig.11, then glue and screw the box together as shown in Fig.12. We fitted the front panel using foam weather stripping and screws so that we could open it up later if necessary. Given the simplicity of the sub, you could easily glue and screw it instead, like the rest of the box. Covering the sub Depending on the type of material you used to make the box, you can varnish it, paint it or cover it. We chose the last option and used a 1m x 1m piece of 2mm-thick black subwoofer felt fabric, attached using hot melt glue. You can use contact adhesive if you prefer. If you loosely wrap the bare speaker box, sausage-roll style, with a 1m-long siliconchip.com.au Fig.11: the subwoofer is a simple box made from six pieces, with only two holes that need to be made. 240mm hole saws are not that common, but you can trace the circle with a nail, pencil and string and then carefully cut it out with a jigsaw. siliconchip.com.au Australia's electronics magazine August 2022  57 The finished isoundBar (not to be confused with the bar it’s sitting on) is quite a large unit at over 1m long, so make sure you’ve got enough room to actually fit it! piece, it should overlap about 4cm at the back and extending at least 16cm past the top and bottom of the box Before starting, read the following instructions and ensure you understand them. The whole process has to be done fast, before the hot-melt glue sets. Ensure you use a decently-­sized hot melt glue gun and let it warm up fully before starting to give you as much time as possible. Check that it overlaps sufficiently, then use a hot melt gun to first glue down just one edge, at the back (top to bottom). Allow it to set, which will take a few seconds, then unwrap it to expose the bare box. Glue around the circumference of the speaker hole and quickly put a few stripes down the front and sides, then roll the carpet back around the wet glue. Tension it slightly and press the material around the front and sides and over the speaker, then tension it so that it overlaps at the back. Apply glue to the back and fold the carpet over, then press it down until dry. If all has gone well, you should be ready to affix the top and bottom. Cut the material at the top in line with the corners, then cut the side and back flaps to allow about 3cm overlap, but don’t cut the front flap yet. Glue down the sides and back flaps, then fold over the front flap, cut it to size and glue it down. Repeat this at the bottom, and the entire box should be covered, including the speaker hole. Using a sharp blade, cut out the speaker hole. Drill or cut a hole at the back for the speaker wire or terminals. Mounting the driver Start by checking that the driver is set for 4W operation. We soldered heavy gauge speaker wire to the JBL driver terminals, fed that through a 4mm hole at the back of the box and stuffed a 40 × 30cm piece of “innerbond” acoustic wadding The amplifier module is mounted to the back panel opening using blank PCB material, including the 3.5mm panel-mount line input jack. A selector switch for an optional external subwoofer and 12-24V barrel power socket is included. The banana sockets are for the external subwoofer. Keep all wiring secured using ties and silicone sealant to prevent unwanted vibrations. 58  Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.12: the subwoofer box assembly is not difficult but make sure it’s properly sealed, and note that you’ll need more than the handful of screws shown here. loosely into the box. We then lowered the driver into place, sealing around the edges with an adhesive gasket, and attached it using wood screws. You could use speaker terminals, but making the wire captive is easier – there are terminals at the amplifier anyway. The only disadvantage of this approach is figuring out how much wire you need in advance. Either way, ensure the wire exit hole/terminals are sealed airtight. We filled the hole with silicone sealant. Remember to leave a bit of slack in the wiring inside the box in case you need to remove the driver later for inspection, repair or replacement. With the acoustic wadding sitting loosely in place, screw the driver firmly in place, and you are now ready to test it and run it in. Having already built and tested the isoundBar, you just need to switch it over to external subwoofer mode, connect the subwoofer wires to the appropriate terminals on the back and adjust the subwoofer level to match the rest of the system. Then you’re ready to rock and rumble! SC siliconchip.com.au We made our subwoofer out of some melamine-coated MDF kitchen cabinet cutouts. It doesn’t need to be pretty, just square, since the carpet covering hides the material it’s made of. Note the acoustic wadding and slack wiring. Australia's electronics magazine August 2022  59