I might add that the cost is about what you'd pay for the components - the design is essentially free which is how kits should be priced - IPL do this but others certainly don't - I think they make enough by selling the drivers etc without fleecing us for a box design. So really it's not so much a 'kit' as a set of basic parts and some plans to build the speakers. For your 275 e you get four Fostex/ACR 103 drivers (yes four.) sufficient damping felt, a pair of ports and two binding posts. They're also ideal for use with full range drivers, something which brings it's own advantages - no crossover, good phase relationships, a point source, less doppler effect (see Loth-x Polaris review) and in some cases a lower cost.Īnd here we have one of the cheapest. So why bother? Well they are very efficient and so produce speakers suited for use with low powered valve amps but they're a lot smaller and easier to build than horns. You're starting to get the picture aren't you? Yup TQWT's are much like transmission lines and horns - there's some basic theory and a hell of a lot of fiddling and tuning and rebuilding to get their compromises working together. The taper helps, as does putting the driver half way down the line, as does judicious use of damping materials and of course the port at the end of the pipe has an effect. For more theory go to the Single Driver Website which is a mine of interesting information.īut as always things aren't quite that simple as with the re-enforcement comes a suck-out at a higher frequency, then another re-enforcement - then suck-out, resulting in a comb filter effect of a lumpy bass response. In a TQWP the tapered pipe is folded in half, but the theory is the same, it just makes a more conventional looking cabinet than a 6 foot high tapered pipe. By tapering the pipe the re-enforcement is 'spread' over a wider range of frequencies and it also has some 'horn' characteristic. The 'quarter wave' refers to the length of the pipe, which is a quarter of the wavelength of the frequency you are trying to re-enforce - sort of like an organ pipe or blowing over the end of a bottle. The idea was that putting a drive unit half way down a pipe you'd get a bass resonance that would boost bass output. Back in the '30's that pioneer of hi-fi Mr P.Voigt designed the Voigt Pipe. They also allow access to unusual designs not usually seen in the commercial world, the IPL's transmission Lines, the PMT "tubes" and now a TQWP from BD-designs.Ī Tapered Quarter Wave Pipe (or sometimes Tube - hence TQWT). The savings that can be made are considerable and rely on pretty minimal woodworking skills. In the past couple of years I've tried to have a look at some of the more unusual kit loudspeakers that are available to the home constructor.
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