DIY Audio
Audax Mini-Monitors
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Firstly, it goes without saying that these tiny boxes won't shake the walls. But I'm a firm believer in no-bass rather than poor-bass, and I'm pleased with the compromises here - the bass that exists is clean and tuneful, and with the help of positioning, is quite well extended. I would estimate the -3dB point to be around 100Hz, but thanks to the sealed enclosure falling away at 12dB's per octave, there is audible output at lower frequencies. At medium and higher levels, when the human ear is more sensitive to frequency extremes, it's surprising how well-balanced they sound. For low-level use, I'm investigating active equalisation schemes, such as a Linkwitz transform.
As I've already mentioned, John's crossover does an excellent job, and it's really this that makes this system sound so good. Seriously, if you have these two drive units, don't bother trying anything else unless you're trying to improve your own skills and knowledge. You used to be able to read much more about the design of this at Zaph's site, but he has since archived the project because the drivers are no longer easily available..
After a first listen, I felt that these were a little bright at the top end. The TM025F1 doesn't have a terribly smooth frequency response, and the crossover works hard to tame the brightness. The 8R2 and 1µF series combination are responsible for equalising the HF, but I found that increasing the capacitor to 2.2µF made the response fall away more naturally, bringing the treble response more in line with the other speakers I had to hand at the time. But for the time being, I decided to stick with John's design and get used to it before trying modifications. And during the first few days, the treble seemed to improve a bit - perhaps the tweeter also needs time to run in?
Another minor criticism is that the tweeters resonant peak sometimes seemed audible at high levels. Certain piano notes and vocals seemed to sound a bit "hard". I isolated the effect to the tweeter when initially experimenting with the crossover, and from reading John's write-up, it seems he feels that the tweeter could perhaps benefit with a slightly more complicated crossover, but reading between the lines, I think he feels a better tweeter would be a more sensible approach. I tend to agree with this.
Speaking as an amateur, I wonder if the attenuation might be rejigged slightly to reduce the source impedance seen by the tweeter? Instead of the series 24 ohm resistor, an L-pad would improve the electrical damping to the tweeter. With a high-Q neodynium tweeter, this might be an academic because the tiny airspace behind the dome probably means that the mechanical Q dominates. These parameters aren't specified by Audax, but I suppose I could measure them. Against that, an L-pad will reduce the impedance seen by the high-pass filter, meaning that larger value reactive components would be required - and I guess this is why John chose the layout he did...
Perhaps the small size is a factor here, but the soundstage and imaging are really very impressive. The crossover is key to this, of course, as the correct phase tracking through the crossover region is essential to construct a convincing stereo image. Classic reference jazz recordings such as "Kind of Blue" and "Time Out" sound really very special. Female vocals such as Diana Krall are handled very well. Compared to the LS3/5a's, vocals can sometimes sound slightly "thin" - I don't mean lacking in bass; rather a more forward presentation. But while LS3/5a's are renowned for their vocal quality, they are also slightly coloured compared to other monitors such as my ATC's. For now, I'll reserve judgement until these are out of storage!
The acid-test of imaging is Roger Waters "Amused to Death", which uses Q-Sound to place effects behind the listener and well beyond the stereo pair. I hadn't really heard these effects properly until I bought the ATC's, but was pleased to hear that these speakers are nearly as impressive. Again, the crossover design is responsible for this, as Q-Sound uses precise phase shifts that need to be faithfully reproduced by the loudspeakers.
Quality contemporary recordings, such as Solomon Burke's "Don't Give Up On Me" and Norah Jones' "New York City" and "Feels Like Home" work best with these speakers which excel in delivering the texture and detail of the recordings. Electonica can a bit less successful as a lot of these recordings rely on the bass for atmosphere - for example the distorted treble of Röyksopp's "So Easy", found on Melody A.M., is distracting without the normal sub-bass details to balance the presentation. Lemon Jelly suffers the same fate. And steer clear of stuff like Blur and Radiohead - these speakers are just too revealing for anything with mainstream production values.
The overall performance of this system has been a bit of a surprise, and they clearly would be wasted as PC speakers. I'm thinking about using them in a bedroom or perhaps a dining room - somewhere where high SPL's wouldn't be required. Unfortunately, these have got me thinking about more projects. Perhaps a subwoofer? Or, a miniature power amplifier, built into a matching case? This latter idea is already quite well-developed - a GainClone, which can use a motorised Alps volume potentiometer that I bought many years ago. Perhaps even incorporate an FM tuner? Just need a display, a PIC and a real-time clock IC to make a pretty decent bedside radio!
Finally, it's one thing to make speakers that sound good, but as any speaker builder will tell you, ending up with equally good aesthetics is pretty unusual! I can't stop looking at the enclosures, and still don't quite believe that I made them all by myself! All those days of sanding have really paid off in the quality of the finish - they look and feel amazing. The Danish oil leaves a slight sheen to the finish - not quite mirror-like, but still glossy enough to show reflections.
Update - 15 January, 2006
After spending their life at work in the office, I finally got the chance to bring them home to try in my reference system. However, so far I have only compared them briefly because this system isn't eally set up yet - the room needs a lot of work to get things right.
Tonally, they sound remarkably similar to the ATC's above 100Hz. The forward treble mentioned above is present, but not too oppressive. That said, because these aren't top class tweeters, I probably will make the crossover mod mentioned above, which should stop them drawing too much attention to themselves.
The mid-range hardness does make itself known at medium to high levels, and these speakers can sound congested as a result. But this isn't really fair when you consider the size of the poor driver - while I have yet to try it, I bet the woofer will make a far better job of midrange when relieved of bass duties. Certainly they sound much cleaner at lower levels when the cone excursion is more reasonable.
More positively, these speakers still surprise me, and putting them against a pair of ATC's is hardly fair! For the time being, they've been installed in the office, driven by the Micro-Amp, and thanks to the more favourible acoustics they're doing a great job! I even found some office accessories in matching birch ply...
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