My Single Driver Speaker Project by Marco …It all started over a year ago, when I came across James Melhuish's site on Single Driver Speakers while peacefully surfing the web. I was well aware of the fact that a poorly designed cross-over can seriously impair the performance of even the top drivers, but I had never considered the rather radical idea of building a speaker system that tries to reproduce the whole audio spectrum (OK, most of it) using a single driver. I had indeed heard of Lowthers before, but I must admit that I was rather sceptical of their performance (that was before I actually listened to them), and somehow shared many people's belief thet they must be unacceptably lacking in bass and treble, and therefore not "real hi-fi". The wealth of information contained in James' site and his forum made me more and more curious about this "single driver" idea, to the point that I decided I would give it a try. Shying away from the amount of woodworking necessary for backloaded horns, and from their seemingly rather unpredictable behaviour, I decided to settle for a simple bass-reflex enclosure. This called for a suitable driver, and after a long tug of war between the Fostex FX-200 (see DIY 16) and the JBL LE8T-H (see DIY 22), I chose the much cheaper Fostex FE 164 (!), mainly because I did not yet trust the single driver approach completely, and was afraid of investing too much money on this project. The cabinets were recycled from a pair of old speakers from the sixties (15 mm solid teak wood), to which I added a substantial amount of internal bracing, both to stiffen their structure and to reduce the internal volume to the desired 25 L. Here are the driver technical details: Driver: 1 ACR (Fostex) FE 164 Box type: Bass-reflex, Vb = 25 L, Fb = 63.6 Hz Ports: 2 Monacor MBR-75 (Æ 75 mm, length 114 mm) Wood: 15 mm MDF + 2 mm cork (front), 19 mm MDF (back), 15 mm solid teak (sides, top & bottom), extensive 25 x 25 mm solid spruce horizontal and corner bracing Stuffing: Monacor MDM-40, 40 mm moulded polyurethane foam on back, sides, top & bottom ( » 50% fill) Cable: Van den Hul M.C. Royal Jade (45 cm) Notes: 24K gold plated input terminals, all soldering using silver-tin alloy Pictures of construction The Drivers: All the stuff except the wood (drivers, reflex ports, stuffing material, cable, input terminals, etc.): Building the cabinets: Almost finished: And here's one of the finished babies! Simulated SPL response Bass Reflex Box free air SPL (1w/1m), simulated using LSPCad Lite 1.00: Additional details: -3dB point: 56 Hz When they were finished, the speakers replaced my trustworthy B&W DM602 in my audio chain, consisting of an old Pioneer turntable with a Shure M94E pickup, a Rotel RCD 951 CD-player and a 40W Rotel integrated amp. …So, what do they sound like? Listening impressions Before going into details, let me say that I like these speakers much more than I expected, and that they have now permanently replaced the B&W's in my audio chain. Nevertheless, I will try to be objective and state their faults clearly at the beginning, before waxing on their virtues. 1) I have heard (much) better low bass from a number of commercial speakers (including my B&W 602s). Anyway, this is not to say that they are completely lacking in this area. Although you can certainly forget about that "punch in your stomach" feeling, it is more the quality than the quantity of the bass that leaves me wanting. In fact, the bass is somewhat "slow" and not particularly tuneful, and this is probably due to the chosen bass-reflex alignment, which tries to squeeze more bass from the drivers than the "optimal" QB3/SBB4 alignments. Mind that I am talking about real bass here, let's say sub-80 Hz. The mid-bass (80-250 Hz), on the contrary, is in my opinion very good and detailed. 2) The maximum linear displacement of the driver cone (Xmax) is only ±1mm, which means that the speakers will not stand for loud music containing much energy below the box tuning frequency. Modern dance music is particularly critical in this respect. 3) These speakers are VERY directional, and can only be listened to from within a narrow "sweet spot". Done with the faults, let's start with the virtues: These speakers are GREAT at imaging. Compared to most multi-way speakers I have listened to, including some costing over ten times as much, they project a "holographic" soundstage, with all the instruments perfectly locatable. For me it was as if a blurred image to which I was accustomed was suddenly made sharper than it had ever been. Moreover, the micro-dynamics in the music are very faithfully portayed, contributing to the overall feeling of "presence". The illusion of intimacy with human voices is sometimes scary! The sound is very well balanced throughout the entire audio spectrum, from the box F3 all the way up to 20kHz. In particular, the highs have taken some time to break in (over a month of regular listening), but are now crystal clear, and have nothing to begrudge the best dome tweeters of (provided you listen on axis, of course, which means the speakers have to be toed in quite a bit). There is also no sign of the nasty "shout" in the mid-treble for which many full range drivers are notorious. I could go on and on, but to cut a long story short, I will just say that the realism with small- and medium-scale acoustic material (classical or jazz) is outstanding, and that it is always coupled with a remarkable freedom from listening fatigue. I am starting to believe that after getting used to single driver speakers, common multi-way speakers may at first sound more extended or powerful, but they will invariably end up being less natural. Marco Top