I've been happily listening to my ProAc Studio 125s for two or three years now, but two things prompted me to consider an upgrade: (1) release of 130 and 140 and positive reviews (well awards, but I haven't seen a proper review yet!), and (2) arrival of unexpected salary bonus. All speakers have to be in non-ideal location, six inches from wall and not toed in, for reasons of aesthetics and domestic harmony (no marital advice please...). All auditioning below done in the comfort of my own home. [B]Studio 125[/B]: Around £1000. I ran these with the optional bungs for most music as the bass was boomy like you'd expect so close to the wall, though heavier stuff like Led Zep or Muse was better with them removed. I never had a problem with lack of bass power but I thought I was missing something in bass extension and clarity. Top end and mid-range are/were an absolute joy. [B]Studio 130[/B]: Around £1100. Positioned as the replacement of the Studio 125. Not much difference to note in the top and mid range; instruments a little more distinct perhaps but that's it. Much more bass clarity; unlike the 125s you can really tell what the instrument is when it plumbs the depth e.g on the 125s, double bass could sometimes end up as an anonymous thump at the lower reaches, but not on the 130s. Unlike the 125s, the 130s are floor ported which makes them much less sensitive to positioning - great for me. I couldn't help think that I was losing something in the overall integrity of the sound, though; the individual instruments were more distinct but the overall musicality lacked something (I'm not an expert on the terminology here). I may just have been listening too analytically of course, given that I was testing certain aspects; I never did a long sustained and relaxed audition. Overall, I would imagine the Studio 130 to be a better speaker than the Studio 125 for a wide range of musical tastes, though lovers of heavy rock might still find something missing. [B]Studio 140[/B]: New model, around £1400. Given the extra bass in the 130s, I was concerned that the 140s might be overpowering. Basically they are a 2.5 way speaker, with twice the (same) woofer of the 130. Listening at the same test volume was difficult as they clearly put out more oomph, so I dropped the volume back. Bass and mid-range were a revelation, a significant step up from the 130s and one I was not expecting. Clear and strong, these are excellent speakers. I'd be surpised if anyone said they lacked weight at the bottom end, and the mid and top are in line with ProAc's reputation. These appeared to be more musical overall (whatever that means), though I still wonder whether in gaining detail and separation I am losing something musically - extended and relaxed audition to follow. [B]Response D15[/B]: Around £1800. My dealer suggested that you get a lot extra for that £400. First impressions were very favourable, with great soundstage and musicality; the closest to the sound I have enjoyed in the 125s but with much more edge and crispness. At first I thought these were the ones for me, but when I listened closer to the bass it simply faded away where the 140s kept diving deep. A different listening experience and one which got my foot tapping; excellent speakers, perfect for some folk, no doubt, but not those who like their bass deep and crisp and even. [B]Overall conclusions[/B]: I am going for the Studio 140s. The 130s are a noticable improvement over the 125s, but the 140s are several steps further ahead of the 130s. To me the D15s are good (much better than the 130s), but not as good as the 140s, and if they were the same price, I'd take the 140s. The fact that the D15s are £400 dearer makes that an even easier decision. Hope this helps someone else out there! Nigel