As far as I know, I am the only person that has ever posted to any of the 'normal' audio forums that is using the U15's. I searched long and hard for feedback/experience with them as audio speakers rather than PA cabinets before purchasing, and came up empty. $2k isn't exactly expensive for high-end speakers, but it was a real leap of faith to plunk down that much on what was essentially a blind flyer. Considering the original Unity kits offered by Lambda ran something like $1500 without woofers or cabinets, the purchase price of the U15's is very reasonable in comparison.
This is an edited/excerpted version of a reply I sent to another person that was asking about the Yorkvilles. I'm very hesitant to put too much stock in my own subjective impressions, since I stopped listening to convential hi-fi gear long ago and so my basis for comparision is questionable. I do have ACI Sapphire XL's which I quite like, but they are set up in a very unoptimized video system and so don't really offer an opportunity for a fair comparison.
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First, I'm driving them with very pedestrian gear by conventional standards. My amp is an Alesis RA-150, and it's fed from an Emu 1820M soundcard. I've tried a couple other budget amps (Nad, Tripath, Panasonic Equibit) and the Alesis is a clear winner. I suspect the fact that it's fully balanced helps greatly given that the source is a soundcard - helps to mitigate common-mode PSU noise and EMI from the PC.
Given all that, my summary is that the U15's are everything I hoped for when I bought them. Given that they are aimed at the pro crowd, I was expecting to have to do some work on them to get them suitable for home use, but really it hasn't been that bad. Straight out of the box they were a bit disappointing, but removing the grilles solved most of that problem - they absolutely must be removed for 'hi-fi' results (even if doing so drops the already questionable aesthetics down another notch or two).
They do benefit from some judicious EQ - there is a resonance around 190 or so (I think) that needs to be notched out, and I think some upper freq shaping was beneficial. I don't really remember the 'stock' settings as I added a Summa-style foam 'phase plug' to the horn which of course needed it's own correction. I originally filled virtually the entire horn with the foam, but eventually backed off to using (I think) 6" starting an inch or two from the throat. This required a managable amount of eq to handle.
After all this, I simply find that the speakers play music. I don't conciously find them lacking in any way, and they are the easiest to 'listen through' that I've ever personally owned. I find the dynamics exemplary, although I don't have much experience with conventional horns so I can't compare too well. Still, even on folk-ish material at moderate volumes it seems like there is more of a sense of ease and freedom from strain than I would have expected. Detail is good without seeming artifically etched as I've experienced with many audiophile systems. Tonal balance is obviously set largely by the eq used, but I have managed to get what I think is a very neutral presentation without undue effort. My only complaint is that ewven for a music-only system they don't get quite low enough to be completely satisfying without a sub. In my room they start to head south a bit below 60Hz. I'm still trying to integrate a sub - the efficiency mismatch causes some problems on that front..
I should mention something about room/placement as this is most of the reason I chose the U15's. My room is very small - 7.5' wide by 16' long. I have the U15's placed directly in the corners - a placement that I believe is only possible due to the narrow 60-degree dispersion (well, plus the fact that they have no baffle-step correction build in). With fiberglass panels placed between the speakers and on the side walls handling first reflection points, the overall setup is somewhat overdamped and reduces lateral reflections probably more than would be ideal. Imaging is very good in this arrangement - no localization to the speakers occurs, but overall soundstage size is limited and that elusive sense of space isn't up there with good systems I've heard in larger rooms. I'm hoping to play around with some diffusor and/or hybrid panels on the side walls to try to mitigate this.
I still have vague ideas about doing more tweaks/upgrades to the speakers - rip out the components and place them in new cabinets, or pull the crossovers and either upgrade the components or go all-out with a full DSP phase-coherent xover etc. However, the truth is that they are sounding so good right now that it all strikes me as a lot of work for relatively minimal return. (Oh, I should point out that I'm using them in single-amped mode. The U15 is directly bi-ampable, but in this mode the woofer is unfiltered - you have to include a woofer xover in your signal chain. I will experiment with this at some point, but don't have the volume control problem solved yet)
So, I guess my conclusion is that if you can live with the look and have a way of including transparent EQ of some sort in your system, the U15's may be worth looking into. In many respects their value proposition is off the scale for normal high-end audio, but they certainly aren't for everyone.
