How To Make Cheap SpeakersNov 06 '02 Write an essay on this topic.
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The Bottom Line Cheap DIY Speakers Talk Throuh.
Preface This “DIY” (Do It Yourself) article covers an idea on how to make cheap affordable speakers that are currently not available, in the UK at least. The aim here is to make simple boxes which you wouldn’t normally find on the store shelves. The speaker we are in need of is a compact box, un-amplified, so that it can be used on a mini or micro system. If you want to replace some pretty crude speakers you already have, and make new ones which look better and will probably sound better too. Before I start, this article is based on a couple of “self-built” boxes which I currently use, well one of them I use, in place of a micro systems speakers, in fact I even re-used the drivers. However that is one option you can consider, the other is to buy your own drivers. Target The aim here is to make something substantial, nothing spectacular, but something you are happy listening to as a wake up alarm (like I do), while still able enough to fulfil needs in terms of radio or tape playback. If you want something which is musical and as good as professional Hi Fi speakers, stop and look else where. The design of these boxes won’t be anything special, no more than what you are prepared to do. The driver, the wires the actual material is up to you, this is a guide to use, you could follow it along and make your own alterations later. Speaker Driver Characteristics Drivers (transducer, or the thing that makes noise) are used to produce sound. ‘Transducer’ is their technical term, but basically they use the theory of electromagnetic, to propel a cone from a fixed large magnet to produce vibrations which cause sound. Technically transducers are cheap, and easy to make. A typical transducer uses paper cone, but other use other stiff materials like metal, or composite materials. This cone produces sound by the vibrations caused by a fixed “voice coil”, the voice coil has a wire wrapped around it thousands of times, when current passes through, it produces a magnetic field that is either attracted or detracted from the fixed magnet. Now a transducer has two sides, literally, the front part is where the sound is meant to come from, but it also comes from the back, unless the manufacturer makes it a “sealed driver”, those are typically mid-range drivers, or tweeters. Tweeters won’t, and neither will mid-ranges, be used in this article. The air behind the cone also is vibrated producing a sound, which is out-of-phase. If these two sounds were in contact through air, they would almost cancel each other out. That is why we need a box to contain the reward projection, and stop it from effecting the sound from the front. There is an advantage to using a box, such as, you could add a port, which will enhance the bass, since the box (usually made from heavy mass materials like wood) creates reflections improving sound energy, or you could use the box to give the driver a tighter sound, as the air pressure is like a cushion to it. Box types There a number of different types of box. Sealed Box A sealed box has no escape for the air inside the cabinet, this creates a tighter sound, but restricts the efficiency of the driver. Ported Box A ported box uses a port (tube) to evacuate the air when the driver is moving, which means that any sound in the box also gets chucked out. The driver is more efficient but the port must be tuned not to cancel the sound out. Bandpass Box A bandpass is almost like a box in a box. You usually have a single cabinet, which on the front of that is another cabinet, effectively sealing in the front sound, but then a port is added which usually means a tight sound with a lot more bass from the front, this is usually used with subwoofers. Bandpass is a good way of increasing bass in a small space, but that’s not the need for this article. What Driver? For this article, cheap speakers are what we need. In my view, car speakers are relatively cheap (£10/$14 and up) and readily available. They are almost perfect, since their sensitivity is always in the high 90dB/W/M. Though they are usually made for the high current/low voltage of car batteries. They tend to be at most 4ohm, which means you have to be sure not to overpower the amp and the speakers if you use them on an amp not made for them. In my view car speakers are the cheapest way to go. However if you feel like it, you could order a specialized driver that are called “all-range” drivers, which means that the drivers are made for all frequencies. They cost more but usually are nicer to listen to. In fact many of these all-ranges are used in the highest of the high level Hi Fi speakers. You would typically see a “horn” speaker with a tiny 10cm driver, but the box is the size of a fridge. Now car speakers vary in size, efficiency, power, shape and design. For you to pick one, make sure you consider what your current amplifier is capable. The usual car speaker is one which is a high resistance to be more efficient since cars use a lot of amps. Now 4-6ohm is the typical range you would find them. Now efficiency isn’t quite as important, as for shape and design, these are important. Oval speakers are terrible to cut holes for in wood, especially if they are small ones. Pick one that has a grill, and one that is a full range one. They usually specify the range they are capable of, this should be in the regions of 100Hz or lower, to 20,000Hz. Now the best thing about car speakers is that they are very compact, many are made to fit inside car doors and so, have to be within 6cm deep or less. This means that your box can be smaller, however I would restrict that thought to a level that will ensure that backward reflections do not interfere. If you are choosing a proper speaker, then you will have more trouble, in most cases car speakers have templates, special screws and all sorts to help you, normal speakers usually do not. They also tend to be more sensitive to where you put them, most will come accompanied with a sheet of specifications, such as the SPL (Sound pressure levels) and anything that goes with making speakers. And remember, they usually don’t come with screws, or even wires. Solutions to Problems Car speakers or “all-range” speakers have one thing in common. They each don’t require a crossover or network/filter, unless the car speaker uses two drivers in itself. Normally this means that you would just need the wire to hook them up, and indeed, unless you are an experienced electrician you can leave them like this. However, if you have a SPL meter, computer, and the right software, you can do something. You can usually find that a speaker has a number of peaks or valleys in its output over the range of sound frequencies it produces. These can be dampened or softened by the use of the right electrical components. You may find that by adding a capacitor across the wires actually helps, although you would need to know the whys and hows to do this. This is optional but you have the possibility to improve the driver just by adding your own crossover. All it takes is a bit of research and the specifications sheet for the driver. The Box, Cabinet, and Body The box that will house the driver doesn’t have to be anything more than a sheet of MDF. You can get fairly cheap sheets at any hardware store. Now the one thing you have to consider is the thickness. Drivers have to be firmly held in place, a box holds them by using its own mass to stop it moving, therefore the box has to hold the driver. However make a box from cardboard, load it with any large speaker and it will collapse or at least not sound great. It has to be strong enough to hold it in place and not wobble or be loose. Typically these will work together: Thickness / Driver Diameter ± 2cm 0.5cm / 8cm 1.0cm / 12cm 1.5cm / 15cm 2.0cm / 18cm 3.0cm / 20cm and upwards For this article, I would imagine that the typical size of driver is around 12cm. For a 12cm driver, it will only need a 1.0cm thick MDF sheet. While bracing the box is a good way of keeping it straight and solid. The design of the box is up to you, but the shape is even more of a matter. I have currently built a triangular and long rectangular box. The latter one had a bent port. Now the advantage I had with the triangle design is that it could be put up against a wall or even corner, however it needs a driver, which is not deep. My first speaker project was a 1.5cm thick MDF rectangle box, which housed a 10cm Pioneer car speaker, however it was clearly over weighted, but it sounded fantastic. Now the second, triangle, box was made using 0.5cm thick MDF sheeting, which now houses the said driver, and they still sound fine, although the boxes have begun to break. To make a good box, you have to spend enough time preparing, when I did the first box, I first bought some 1m long sheets (by 0.5m), and drew the lines I wanted cutting. The cut offs, were then first dry fitted to check that they would indeed fit and then glued. I don’t recommend screwing other than to hold the drivers in, since screws can fall out with excessive vibrations. And nails are even worse. If you do want to use screws, make sure you buy some epoxy glue to stop them vibrating. Before you start cutting, decide where the driver will sit, whether there is enough room for it, or if the other walls will stop you from putting it in. Also, be careful to judge the size, if it is too small it may not perform as well as possible. You also have to consider if you are adding a port. If you are, then try to avoid lining the back of the speaker up with the port, since the sound will reflect of any walls (if it’s a rear port). If it is a front facing port, be aware that the port has to be slightly longer. If you are going to apply bracing, and I recommend you do, try to get complete cross sectional areas, which will slot into the sides of the box, these add mass and stiffness. Corner triangles work well too, especially for getting right angles. Mitred corners work best, although are very difficult to glue. Now if you are building a typical box, then a standard butt joint will suffice, unless the external walls are real wood. I recommend you buy PVA glue since it’s super strong and very cheap. Make sure you have enough clamps, I used two G clamps which are the hand pump type, these save time and work well. When applying the glue, let it show, too much is better than too little. When it comes time to cut holes, try to find a circular drill, which could be used to drill a port. When you are ready to cut the driver holes, first check the diameter of the outside, and the inside, there should be a “lip”, which is used to hold the driver down, or at least some catches. Most car speakers use their plastic grill to hold the speaker down, so don’t cut the hole to big. If anything cut the hole about half a centimetre short, so you can check it won’t fall through. When you are about to place the last panel, like the top or bottom of the box, think about whether adding foam or some old carpet would help. Adding foam helps fill out the volume and soften the sound, and improves bass. You could do lots of things at this stage that would otherwise be impossible afterward. And make sure that you have put the wire through safely. When it comes time to finish the box, check that all glue is dry before removing clamps. At least 12 hours should be enough. If you are decorating the boxes, then do it now, you could add a spray job to it, or apply some fancy veneer panels to it. At this stage you should be able to put the driver in, just follow the instructions. When it is in, add the grill or what ever to finish it off. Other Resources I recommend you talk to the professionals, the ones who have done speakers before to get an idea of what can be made. DIY speakers are surprisingly common. Check out Part’s Express Tech Chat: http://www.pesupport.com/cgi-bin/config.pl To view some very professional DIY speakers check out: http://www.speakerbuilding.net/ Have A Go.  |
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