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Buying Second-Hand SPEAKERS Bargains can be had, but you need to know what to look for! ~ Feature by Julian Edgar ~ I t’s great fun building your own speakers, and excellent results can be gained from doing so. However, it is not a cheap process if you want good results. By the time you pay for new drivers, crossovers, wiring and connectors, then build the cabinets, the cost can really add up. So what do you do if you’re on a tight budget? The answer is to buy second-­ hand speakers. But how do you select speakers that are good, especially when you often cannot listen before buying? Size It’s a fundamental fact of life that small loudspeakers will usually sound worse than large speakers. Yes, small enclosures can sound good – but it’s technically much more difficult to achieve good outcomes, especially in the production of bass. Chances are then, the smaller the speaker, the worse it will sound. Another reason for selecting larger speakers is efficiency – larger speakers are generally much more efficient than small speakers. What this means in practical terms is that a given sound volume will be achievable with less amplifier power. While the cost per watt of amplifier power has come down a lot in recent years, lower-power amplifiers still cost less than high-power amplifiers! When browsing second-hand speakers, you’ll find many home theatre systems that use five small speakers. Often, each about as big as a closed fist. Irrespective of their brand, don’t buy these! The same applies to the tall, thin and shallow speakers often used as the front and rear speakers in home theatre systems. Again, avoid them. About the smallest enclosure you can be confident will sound OK is what used to be called a large bookshelf speaker, say 20 litres in volume, using a 5-inch (12cm) or 6-inch (15cm) diameter woofer. To roughly calculate the enclosure volume, multiply the height by width by depth in centimetres, divide by 1000 and subtract 20%. For example, if a cabinet is 40cm tall, 25cm wide and 30cm deep, the product of those is 30,000 (40 × 25 × 30). Dividing by 1000 gives you 30, then subtracting 25% (to account for the material thickness etc) gives you an estimated volume of 22.5 litres. However, for main speakers, larger enclosures of around 40-60L will likely sound better. Speakers are widely available secondhand – but how do you tell if they’re any good, especially when often you cannot listen first? Tiny speakers invariably sound terrible, no matter the brand. With speakers, bigger usually equals better. 68 Silicon Chip Australia's electronics magazine siliconchip.com.au Note that the shape of the enclosure doesn’t matter nearly as much as the internal volume. If you need narrowbut-tall tower speakers to achieve your desired aesthetics, that’s fine – as is an older, more squat enclosure. Rule #1: bigger = better. Weight The next step in selection is to feel how heavy the speaker is for its size. Almost invariably, heavy speakers will sound better than lightweight designs. There are several reasons for this. Woofers with larger magnets are much heavier than those with small magnets; crossovers that use inductors and not just capacitors are heavier; and cabinets with thicker walls and internal bracings are heavier than those without. So just by picking up the speakers, you will get a quick but usually quite reliable indicator of sound quality. Rule #2: heavier = better Passive radiators There is an enclosure design that, in effect, combines both sealed and ported approaches. This design uses a passive radiator, which is like a second woofer, but it does not have a magnet or coil. The passive radiator moves back and forth like the air in a port but without ever fully unloading the woofer. Some passive radiators are obvious (eg, they have a flat panel), while others look just like a second woofer. Passive radiator designs have the theoretical ability to develop excellent bass from small enclosures, but unfortunately no second-­hand passive radiator speakers I’ve ever bought have sounded very good! Excluding rarer designs like folded horns and similar, enclosure design falls into two basic categories: sealed and ported. A sealed design, as the name suggests, has no openings in the box – the air behind the drivers is trapped within the enclosure. The old name for this design approach – acoustic suspension – gives an indication of how the enclosure works. The springiness of the air within the enclosure provides the restoring force for the woofer’s suspension. When gently moved by your fingers, true acoustic suspension woofers tend to have a viscous, slow return movement. On the other hand, many cheaper sealed speakers use a conventional woofer that springs quickly back into position. In general, unless it is a true acoustic suspension design, a sealed enclosure is likely to deliver worse bass than a ported enclosure. The exception to this is if the sealed enclosure is large compared to the size of the woofer – and the woofer is large as well! A ported design has openings – ports – in the enclosure. These are usually on the front of the enclosure, but some speakers have them on the back. Always check both the front and the back panels for ports. Generally, a ported enclosure can achieve deeper bass from a given size of enclosure. Importantly for buyers of second-­ hand speakers, the port also allows you to see inside the enclosure without pulling out a driver. When assessing a ported speaker, use a torch and peer into the enclosure through the port. Normally, you’ll be able to see either the inside of the back or front panels. In both cases, if you can see bare chipboard, mark down the speaker. Instead, what you want to see is some type of acoustic absorbing material (foam or a fluffy material) covering the panel. This material stops internal sound reflections that tend to colour the midrange. Another thing to look at when examining the port is its design and finish. A well-designed port has flares at both ends. This reduces port noise as the air moves back and forth in the port. The rear of a lightweight speaker with a plastic enclosure – horrible! A pair of these speakers was priced quite high – many second-hand sellers have no idea of the value (or lack thereof) of the speakers they’re selling. Ports should be flared at both ends (not with square edges, as shown here) and have no internal steps. Ports also allow you to inspect the interior of the enclosure without removing a driver. The woofer cone should be able to be gently pushed inwards without any binding or scratchy sounds. Enclosure design siliconchip.com.au Australia's electronics magazine October 2025  69 Also, the inside of the port should be smooth – many ports on cheaper speakers have an external piece that connects to an internal cardboard tube, with a distinct step at the join. Finally, be wary of speakers that have either very large, very small or very short ports – yes, all of these can be correctly used, but more often than not, they’re giveaways of a poor design. Rule #3: Prefer ported enclosures Drivers The next step is to examine the drivers carefully. Let’s start with the woofer. The woofer should have a longtravel suspension. Using the spread fingers of one hand, carefully push the cone inwards. The cone should move with no binding (a voice coil that catches often gives a scratchy feel and sound) and the edge suspension should not distort or collapse. Furthermore, the cone should not change in shape, ie, obviously flex. The larger the woofer, the less distance it needs to be able to move. So if you’re looking at an older speaker with a 12-inch (30cm) woofer, don’t be concerned if it can be moved only 5mm – there will still be plenty of bass. On the other hand, a 6-inch (15cm) woofer needs to have a lot of travel to be effective. The more woofers the enclosure has, the less travel each one needs. Sharply tapping the ends of your Speaker specifications Many speakers have specifications written on the back of the enclosure. For brand name designs, you can do a quick Google search and find the same information. However, more often than not, this information is of little help – to put not a fine point on it, it’s often garbage. Really, only one specification is likely to be semi-accurate – and that’s nominal impedance. If the plaque says “4 ohms”, the AC impedance is likely to be near 4W. Stated frequency response? It’s often the complete stuff of fantasy – or the response was measured at ±12dB, making it equally useless! Power handling? Is it RMS or peak power? Or power on normal music material? Or power at great distortion just before the voice coil melts? Who knows? Without the speaker efficiency being stated, the power figure gives you no idea of how loud the speaker can play anyway. Instead, when using it, you would simply turn it down when it starts to distort (or it’s too loud for comfort). Where they are available, look at the specifications, but don’t expect to gain a lot from them. Personally, when buying second-hand speakers, I mainly just check the impedance, to ensure the designated amp can safely run them. fingers on the woofer cone will excite its resonant frequency – the resulting sound should be as deep as possible. This is an excellent test that evaluates both the woofer and its enclosure. If the speaker is fitted with a large midrange speaker, again, very gently move its cone with your fingers. It will be able to be moved only a short distance, but again, there should be no binding. The tweeter should preferably be a dome design – and don’t try to move it! Some cone tweeters can sound fine, but on any speaker of the last 20 years, a cone tweeter usually indicates it is a cheaper, lower-quality design. If you can, apply a 1.5V cell across the speaker terminals. The woofer should leap forwards or backwards (forwards, if you’ve observed the correct polarity). If you put your ear to the tweeter and midrange, you should also be able to hear sounds as the cell is connected and disconnected – especially if you draw the wire across the battery terminal to produce a scratchy noise. This test shows that all the drivers are working. Many second-hand speakers, especially at thrift shops and similar, have been damaged while on display. For example, the centre caps on woofers and dome tweeters can be pushed in. Woofer centre caps can usually be pulled out by using a fine needle or by careful use of a vacuum cleaner nozzle, but dome tweeters damaged in this way are usually ruined. Don’t buy speakers with non-­ removable grilles. The risk is simply too great; for example, the woofer’s foam suspension may have completely perished. Rule #4: carefully check the drivers Clues to quality The centre dust cap in the left photo is damaged, although it could probably be pulled back into shape with the careful use of a vacuum cleaner nozzle. However, note how badly the outer suspension is distorting when the cone is pushed inwards. This is one to leave behind! Speakers like the one on the right with dome tweeters are preferable to those with cone designs. 70 Silicon Chip Australia's electronics magazine In addition to weight, there are other clues to quality. The first is the brand name. This is a tricky area. Some wellknown consumer electronics brands have speakers that range in quality from awful to very good, while some specialist speaker brands have reputations that are vastly overblown. Definitely don’t buy on brand alone – always ensure that the above four rules are met by the speakers you’re considering. siliconchip.com.au Another clue to quality is the terminal block – if there is one! Cheap and nasty speakers typically don’t have a terminal block; instead, the cable just comes through a hole in the rear panel. Small spring clip terminals indicate the manufacturer has been cost-­cutting – not very reassuring about what’s inside the enclosure! Better speakers use gold-plated binding posts and often can be bi-wired – that is, there are separate connections for the upper and lower frequencies, invariably bridged with plates. Any speaker with adjustable tweeter and/or midrange level controls is likely to be of better quality. Editor’s note: usually only relatively modern hifi speakers offer bi-wiring – plenty of excellent older speakers have a simple pair of binding posts. Bi-wiring is mostly just a fad anyway. On some enclosures, you can see how the box was made. If that’s the case, look for the thickness of the board and whether the tweeter has been recessed to give better phasing with the woofer – in fact, anything that shows that care was taken in the design and construction. Be very wary of any speaker that looks home designed and built. It may be a brilliant design – but more often, it’s been built by someone using rules of thumb... or no acoustic design at all (if they used quality drivers, such speakers can make good donors for a new design). Do not buy speakers where some or all the drivers have obviously been replaced. Many people buy replacement drivers based only on size, not the acoustic match for the enclosure and/or crossovers. Speakers that use only one fullrange driver are typically quite inferior. Many are at the cheap and nasty end of the range, and those from higher-­quality brands usually require dedicated amplifier equalisation to sound even half reasonable. Rule #5: look for quality clues Conclusion I am a bit of a nut when it comes to speakers – I have bought literally dozens of pairs over the last 50 years. What I have found is that if the speaker is large, heavy and ported, the drivers are in good condition, and the enclosure design and construction look fine, the chances are very much that you have SC a quality pair of speakers. siliconchip.com.au Silicon Chip PDFs on USB The USB also comes with its own case ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). 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