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CAR SOUND ON THE CHEAP Pt.1: By JULIAN EDGAR You can put together a good in-car sound system for just $200-300. Here’s how to go about it. I F YOU’RE LUCKY enough to sit in a late model Audi or Lexus or BMW, take the opportunity to crank up the sound system and have a good listen. Especially in the Lexus, you’ll be blown away by the brilliant sound system – a system with crystal clear highs, realistic mid-range and bass which is strong but never overemphasised. If you’ve got time, look at the compo- nents that make up the sound system. To your surprise, you’ll probably find a fairly normal looking “head” unit, a few amplifiers tucked away under seats or in the boot, and a subwoofer in the rear deck that looks paltry compared to what you probably expected. By now, you will probably be wondering how come this system sounds so good compared with those owned by the “doof-doof” guys, who always seem to think that multiple 30cm woofers and about a kilowatt of amplifier power are needed to get even semi-decent sound. There will be other questions as well – such as, where are the huge cables, the gold-plated connectors and the sheer physical intrusiveness of the sound system that you thought were necessary for good in-car sound? Of course, the answer is that if you This ex-Mercedes Benz AM/FM CD head unit (made by Eurovox) cost only $100 secondhand. It lacks line-level (RCA) outputs but boasts a clear and logical layout, “key-off” play (ie, it can be kept playing for a while after the ignition key is removed) and bass and treble controls. It’s typical of the sort of quality secondhand car gear that’s now available. 12  Silicon Chip siliconchip.com.au don’t want to make your ear drums bleed. Most of that stuff simply isn’t needed! There’s no getting away from the fact that premium car sound systems are good – it’s just that most of us don’t have the $180,000-odd needed to buy the car that fits around that type of system. In fact, chances are, the sound system budget that you’ve got to work with will be limited to just two or three hundred dollars. But even with that sort of budget, you can do a lot better than you’d first think. So, in this article, we’ll look at the techniques and tactics you can use to acquire and install a sound system in your car that’s more than just competent. It won’t be an ear-bleeder but if you like accurate imaging, very good frequency response and excellent clarity, it’ll be just fine. In fact, it’ll be about as good as the systems featured in cars costing around $75,000. Head unit The current buzz in car sound can be spelled out by three characters: MP3. Most new CD players on the market will read MP3-encoded CDs and even many CD stackers will work with this compressed music format. Other MP3 car systems use computer hard-drive based designs and there are some head units that accept MP3-encoded memory cards. As for us – well, we can forget about all of them. Why? Well, with the current fashion being MP3, “old format” CD players are being discarded in large numbers. This has driven down their price in the used market to the extent that you can now buy a used good-quality single CD AM/FM head unit for under $100. Yep, less than one hundred dollars. For that, you get original equipment quality with a competent power rating per channel (eg, 4 x 35W), bass and treble controls and even RCA linelevel outputs (so you can connect an amplifier if you want). Of course, you could also buy the very same thing new for about $300. In case you’re wondering, this isn’t one of those stories where the author doesn’t have first-hand experience. In the last six months, I have bought and installed three good quality secondhand single CD AM/FM car radios: an ex-Mercedes Benz unit (manufactured siliconchip.com.au These ex-Mitsubishi 5-inch wide-range speakers have excellent efficiency. High efficiency is vital if you are to generate adequate sound pressure levels (SPLs) without spending a lot of money on amplifier power. by Eurovox) which cost $100 secondhand, a near new Hyundai CD radio ($75) and a Philips unit ($100). None was older than two years. But let’s be clear about the disadvantages: these head units won’t read MP3-encoded CDs, they’re single CD rather than multi-CD capable (and they usually can’t control a CD changer), and they’re all fairly conservative in appearance. The first two downsides are the sort where you shrug and look at the low cost, while the latter is actually a potential benefit – most car dashboards are visually staid and in a few years time, this type of head unit won’t look garishly silly, as will some current head units on the cutting edge of fashion. Where to go, what to look for So where do you get a new front-end at this sort of cost? On-line auction site eBay is a good source, as are secondhand stores like the Cash Converters chain. The classified ads in major newspapers and in newspapers such as the “Trading Post” (which also has an excellent website) are also worth a good browse. And what do you look for? As with many secondhand goods, the desirability of an item depends on its brand name, features and history. Let’s look at each of these in turn: BRAND NAME: today, many electronics goods are made very cheaply, branded with a newly-minted name and then sold off to make a quick dollar. You don’t want one of these head units! Instead, look for known, wellestablished brands – though remember that some old brands have been bought by new vendors who have no interest in good design and production. It’s therefore best to go for names that are associated with current premium consumer electronics – rather than older brands from hifi circles. FEATURES: in the price bracket we’re talking about, you should be able to get a full digital unit with bass and treble controls, random and repeat CD functions, and line level (RCA) outputs. It should also have an inbuilt 4-channel amplifier with reasonable power outputs. HISTORY: why is the vender selling the unit? The best answer is that they have just bought the car and they’ve decided to immediately upgrade the head unit. When buying a secondhand head unit, it’s critical to be absolutely certain that you have access to the security code. Nearly all modern original November 2005  13 Here’s another $100 bargain. This Philips RC604 AM/FM CD is a fully-featured, original equipment unit that was bought on-line through the eBay auction site. When buying a head unit, make absolutely certain that the vender has the correct security code available for it. Without the code, it’s just junk. equipment head units are security coded – if the vender doesn’t have the code, you won’t be able to make the device work. That’s a very important aspect to keep in mind – it’s easy to be blinded by an apparent bargain without realising that without the code, it’s actually no bargain at all! Of course, you don’t need to buy ex-original equipment players – there’s also a multitude of secondhand aftermarket head units to pick from. However, because they’re more likely to have flashing lights and be every colour but black, these command higher prices. Full-range speakers As anyone who has played with hifi speakers will ruefully attest, speakers are something of a black art. That’s even more the case in a car where the enclosures(?) often comprise sonically awful spaces like the insides of doors and kick-panels. 14  Silicon Chip When looking for secondhand speakers, there are a few basic factors to keep in mind, as follows . . . EFFICIENCY: often completely overlooked, the efficiency of the speakers is vital in car applications. Why? – well, when amplifier power costs lots of money, you can save literally hundreds of dollars by picking up speakers which have high efficiency. In this context, the word “efficiency” has a very specific meaning: we want as much sound output as possible from the speaker for a given input of electrical power. Efficiency is measured as the Sound Pressure Level (SPL) that’s developed on axis with an input power of one watt (1W). The higher the number the better, because if you drop by 3dB, you’ll need to double the amplifier power to get the same SPL! POWER HANDLING: this is measured in watts and in cheap speakers is a largely meaningless specification! The naïve might think that a speaker rated at 50W can handle an input power of 50W without distortion. But nothing could be further from the truth. It’s very likely that with a 50W input, the speaker will sound awful! In fact, long experience has taught me that with full-range speakers, I can basically ignore what ever power figure is written on the back. Instead of worrying about watts, just make sure that you get efficient speakers and then never drive them into audible distortion. SIZE: this is important for two reasons. The first is that larger speakers are typically more efficient and secondly, the speakers will need to fit in the designated spots – unless you do lots of metal cutting, of course. Three-inch (7.5cm), four-inch (10cm), five-inch (12.5cm), six-inch (15cm) and 4 x 6-inch oval speakers are the most common full-range sizes used in cars. This means that you should have a good look at the factory spaces provided in the car for speakers, including (critically!) the available mounting depth. If the speakers are to go in the doors, don’t forget to lower the glass before you make your measurements! DESIGN: as with all speakers that need to develop a bass response, look for a long-throw suspension (eg, a deep rubber surround) and a large magnet. As a very broad rule of thumb, better designed speakers are heavier – their frames are made from thicker materials and the magnets are larger. That’s not to say that a heavy speaker is inevitably a good one but more often than not, a light speaker is a bad one. If you don’t intend to use separate tweeters, dual-cone drivers will have a slightly better top-end response than single-cone speakers. Watch what you buy Buying cheap speakers new usually ends in tears. These speakers often have miserable power handling capacity and worse still, terrible efficiency. So to get decent SPLs (sound pressure levels) out of them, you drive them into distortion and that’s a really good way of damaging them. Great! Instead, it is better to do one of two things: (1) either source secondhand speakers from other cars; or (2) source secondhand speakers from other appliances. On the car scene, really good bargains can often be picked up – say $10 for a pair of dual-cone 6-inch exsiliconchip.com.au Matched midrange/woofers and tweeter combinations can easily be gained cheaply from non-automotive sources. Discarded large-screen stereo TVs often have a pair like this inside – just make sure that they are 4-ohm units. original equipment car speakers. Yes, that’s right – $10. However, if you don’t mind getting your hands dirty, there’s an even cheaper source. Big sound TVs of the last 15 years run speaker systems that are ideal for car applications. And like CD players, TVs are being discarded in a fashion frenzy – this time, due to consumer demand for direct S-video and component video inputs and for widescreen picture formats. At roadside kerb collections and municipal tips, you can get a stereo TV for nothing – well, for one or two dollars, anyway. The speakers inside normally comprise four or five-inch, roll-cone woofers (or combined midrange/woofers) and matched tweeters, complete with crossover capacitors. Sure, the power rating written on the woofers might be only 5W or something similar but ignore this. A genuine manufacturer’s 5W can easily be equivalent to the fantasy 50W markings on many cheap car sound speakers. Follow these basic steps In any case, when buying speakers, you should follow these basic steps: (1) Cull the selection down to the sizes that suit your application; (2) Manually move the cones of the larger speakers up and down (ie, by spreading your fingers and applying pressure across the face of the cone), to siliconchip.com.au This dome tweeter gives excellent treble and has a crossover capacitor already attached. It costs only $5 from Jaycar Electronics and was part of a job-lot of original equipment tweeters bought by the company. November 2005  15 How To Identify The Wires make sure that nothing is binding; (3) Inspect each unit for water damage, perished rubber suspensions and cone damage, etc; (4) Check to see if they carry a wellknown good-quality brand. Once you’ve done all that, you can select individual speakers on the basis of magnet weight, power rating and cone throw, etc. Buy 4-ohm speakers If you buy a secondhand head unit that comes without wiring instructions, you could be in for a rude shock – there might be 15 or more unlabelled wires emerging from its rear panel! Connect them up wrongly and the head unit might never work again! The first step to solving this is to check the unit itself. Often, there will be a wiring diagram attached to the top of the unit. If not, do a web search for the brand and model number. If that doesn’t bring up a clearly labelled wiring diagram, go back to the unit and take a close look at the wiring harness. Assuming a 4-channel unit, the first step is to identify the leads that go to the four speakers – ie, eight wires in all. These eight speaker wires are likely to be grouped into pairs – eg, two yellow, two green, two orange and two white. One of each pair is always marked with a trace, which indicates the positive lead. Next, you need to identify the power (+12V) and earth wires – and it is critical that you get this right! The earth wire is usually black, green or brown. The +12V power lead is usually red and often has an inline fuse or external noise suppression filter. There will also be an ignition-switched lead (often yellow) and a lightson input (often orange). In addition, there may be a telephone mute input (sometimes pink) and an electric aerial wire (also often yellow). However, before exploring the other lead functions, make sure the device powers up correctly – but only after you’re reasonably sure that you’ve identified the power leads. If you have a variable-voltage power supply with current limiting, start off with both its voltage and current settings wound right down. You can then gradually bring both up, while keeping an eye out for any problems – most head units at idle draw only about 0.75A. Once the supply connections have been sorted, you can carefully work out the functions of the others. Don’t forget that you’ll need the security code handy when the unit powers up on the bench. With this done, connect a single speaker to each pair of “like” colour speaker wires and then twiddle the fader and balance controls. This will soon allow you to sort out which speaker wire pair is which. Be sure to label the wires as soon as you know their function! 16  Silicon Chip It’s important that you select speakers that have an impedance of four ohms (4W) rather than 8W. That’s because car sound systems are generally designed to drive 4-ohm speakers and so they will not deliver as much power to an 8-ohm speaker. In practice, this may not be important because the 8-ohm speaker may well be more efficient that the 4-ohm speaker. And if you have the space, you can always install two 8-ohm speakers in parallel to get more power. If you have a number of speakers to choose from, make sure that you do some comparative bench testing. Tested bare on the bench, the speakers will sound terrible in that they will lack any bass response – but there shouldn’t be any “pops” or “buzzes”. Furthermore, you should be able to get a feel for the relative power handling and efficiency. Using your domestic hifi amplifier for this testing is usually fine, despite the lower speaker impedance. However, always turn down the wick if you hear distortion – a rule that applies in any sound system. How much so far? Depending on how resourceful you are, a pair of wide-range speakers – or, better still, two sets of matched woofers/midranges and tweeters – should cost you no more than about $25. Most cars have four full-range speakers (ie, front left, front right, rear left and rear right) but consider the option of using only the front speakers. If there’s frequently only one or two occupants in the car, those people will get improved imaging and you’ll also save some money. So depending on which way you go (and we’ll take the more expensive 4-speaker set option), so far you’ve spent about $150. Next month we’ll look at amplifiers and subwoofers and describe how to set up the system. SC siliconchip.com.au