Just attach the drivers to timber panels and glue them on to concrete blocks!
C ON C R ET O Speaker System We were tempted – very tempted – to call these the greatest ‘ROCK’ speakers ever. But that pun would fall a bit flat because these speakers are not rock – they’re concrete! More specifically, their ‘enclosures’ are stock standard concrete building blocks – the type you'll find at very low cost in just about every hardware store. Intrigued? Read on...
W
ant to make a cool pair of
sidered by many to be the ideal material from which to make speaker enclosures. speakers, but don’t have the by Allan Linton-Smith Concrete speakers have faded in skills, tools or time to build popularity since then, but are seeing a proper boxes for them? No worries. We have the solution for you! Just bung the drivers into some bit of a resurgence. Besides being practical, they also look timber panels and glue them onto concrete blocks. It might pretty interesting, especially with nicely-finished, routed sound like an odd thing to do, but you’d be surprised how timber front panels. The concrete also helps to improve overall efficiency, well it works. This bookshelf speaker system gives punchy and clean transmitting less than 25% the amount of sound energy that sound, and it’s a lot of fun to build, with excellent bass and a comparable wood or MDF enclosure would. Many people prefer to have smaller speakers, but they oftreble out of one tiny full-range driver, plus a subwoofer or two. For just a few dollars more, you can get a Class-D ampli- ten compromise on sound. These ones emit a solid bass and fier module to drive both, with line inputs and Bluetooth have clarity which you will fall in love with immediately. They also have a really smooth sound, partly because of the wireless audio support. Concrete is actually an excellent material to make loud- lack of resonance and partly because of our choice of drivers. In keeping with the idea of simplicity and cheapness, speaker enclosures from because it’s very stiff and it’s very ‘dead’ – you don’t have to worry about it resonating at all we’ve simply glued the front and rear panels onto the cheap and ‘colouring’ the sound. As a bonus, concrete blocks (also concrete blocks with silicone sealant, and we’ve used a known as concrete bricks, Besser blocks and breeze blocks) coaxial main driver so that no separate tweeter is required. are cheap, readily available and have four square sides That also eliminates the need for a crossover network. Another big advantage of using a single driver is its phase already pre-assembled. This is definitely not a new idea. Building speakers became coherence; that is, its ability to reproduce all frequencies a bit of a fad in the 1950s. At the time, concrete was con- with mostly the same phase.
Features and specifications Frequency response: 90Hz-20kHz, ±6dB Distortion:
<2%, 85Hz-2.7kHz (0.8% @ 1kHz)
Bookshelf efficiency: 91.5dB @ 1W, 1m Subwoofer efficiency: 88dB @ 1W, 1m
The pair of Bookshelf speakers, housed in half-blocks. They’ll give a good account of themselves ‘as is’ but team them up with the full-block Subwoofers and you won’t believe how good they sound for such a tiny investment. Rock on! 30
Power handling:
2x15W (bookshelf) 2x50W (subwoofer)
Impedance:
8Ω (bookshelf) 6Ω (subwoofer)
Inexpensive
From under £100
Practical Electronics | June | 2021
