My experiences with anything but the "vintage" Klipsch models is less than enthusiastic and even the "vintage" models need a LOT of help in my opinion.
The main things that the "vintage" models have going for them is that they are very simple designs that utilize sealed cabinets, which are almost "fool proof" in terms of working with. The newer models utilize lower grade parts in the crossovers and you have to deal with the various bass alignments used in a vented design.
As a side note, the older models weren't so much "bright" as they were "ringy" due to the metal horns resonating like mad. The newer models ARE "bright" and the plastic horn bodies tend to have a very specific albeit "forward" upper midrange sound to them. On top of that, the passive radiators are tuned to produce a large peak in the bass, which reduces transient response and definition. In effect, you end up with a speaker that is bloated on the bottom, thick in the warmth region, forward in the mids and piercing in the treble. In effect, you ended up with a Klipsch speaker that sounded more like a Cerwin-Vega. Both are LOUDspeakers that can rock & roll, but lack any type of finesse and refinement. When driven hard, these newer speakers just sound flat out "abrasive" to me. How do you fix this? It's called a LOT of work.
Probably the easiest things to do that are completely reversible would be to buy a bag or two of polyester fiberfil at your local Wal-Mart ( $2 per bag ) and play with the amount of stuffing in each cabinet. By varying the density of stuffing within the cabinet, you can fine tune the bass response to your liking. Just make sure that any stuffing that you add to the box does NOT interfere with the movement of any of the drivers.
The next thing to do would be to cover the baffle area surrounding the horns with felt. You can pick up enough felt and some "temporary double sided hem tape" at your local fabric shop for about $10. Not only will this help to tame the peaky response of the upper mids and treble region, imaging should improve. You might end up losing a bit of the "snap" or "jump factor" on horns and / or cymbals, so experiment with how much felt you use.
Personally, i would probably felt the entire baffle on these myself, but others may find this to sound TOO subdued. I know that at least one guy posted over on AA that Heresy's as modified as i suggested ended up sounding "dark" to him. Then again, he was used to years and years worth of "ringing" in his system and going to a more natural, less resonant presentation may have sounded "flat & dull" to him. That's why i said start with the simple and easily reversible stuff for now and see how you like the initial results.
As to the ALK crossovers, i've never used them but i have seen them. They make use of Solen cap's, which are not bad so long as you keep the leads as short as possible and damp them where they enter the body of the cap. Something along the lines of "blu-tak" or "fun-tak" can work wonders here. If you don't do this, the caps will ring and sound bright. The cap bodies themselves are so lightweight that the solid core metal leads become microphonic, causing the cap body to resonate. By damping the leads where they enter the body of the cap, you damp & decouple any ringing that the lead picks up before it can excite the body of the cap. If you doubt this, hold a Solen ( or other similar cap ) at he far end of one lead with your fingertips and "flick" the other lead with your finger. You won't believe how much and how long the cap vibrates once you "flick" the leg. Nor will you believe how loud the leg rings. In this respect, the original Klipsch's used paper in oil caps, which are somewhat self-damping to begin with. In this respect, the stock caps aren't bad in the older models and may sound more natural than newer caps that are poorly implimented.
The ALK's also make use of Solen Litz wound coils which are of a stranded design. Personally, i think that stranded wire is typically a step backwards in performance from a well chosen solid wire or a foil conductor. This is strictly a matter of personal preference though and some would debate the viability and cost effectiveness of other approaches.
As a side note, Audio Xpress had a recent article about the ElectroVoice T35 tweeters as used in the vintage Klipsch models. In this article, they show graphs and response curves of this tweeter, demonstrating how limited in bandwidth it really was and that it had a noticeable peak at appr 11 - 12 KHz falling off rapidly above that.
The author of the article ended up replacing his T35's as found in his K-Horns with some JBL's and the differences were like night and day according to what was published. I would not doubt that Marco's Fane swap provided much the same type of results. Personally, I'm using some $6 tweeters that are easily superior to the EV's in every way, shape and form. Only problem is, these $6 tweeters are now discontinued :( Sean
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PS... You guys aren't helping me any. I'm trying to stay off of the forums and get some other things done!!!