Rather than hijacking the S7 vs Model 19 thread where this was originally posted, I thought that I would start a new thread in response to garyl posting following:

I have NEVER, not even once, heard anyone say they needed to do any sort of upgrading to make them sound better.
As a current Model 19 owner I think I am in a position to offer an opinion on this. Like any speaker, the Model 19 is not without its faults and there has actually been a fair bit of discussion on this board and on Todd White's Altec board on useful upgrades.

The most common complaint regards the resonant 811B horn and its effects on coloring the midrange response. There are many reported solutions that all have their adherents. The first line of attack is usually attempting to damp the horn. I've heard of techniques from applying putty to the outer bell, coating the horn with the same goop used in auto rustproofing to a mix of paint and sand. Another line of attack has been to cut the three webs at the mouth of the horn along the weld line. Supposedly Altec did this themselves in the last production runs of the similar 511 horn and used a rubber fitting to connect the top and bottom halves of the webs.

The second issue regards the network. While it was innovative in its use of EQ, it is still somewhat primitive compared to what can be accomplished today. Iconic Manufacturing recognizes this limitation and has announced that they will be developing a "Model 19 Super Crossover" that more comprehensively tunes the response.

Personally, I have not been keen to make any physical modifications so that I have turned to outboard EQ to address these issues and a third one - restricted LF response. While deeper than the preceding Valencia, the Model 19 still has a noticeable bass roll-off starting at around 50hz. I use a parametric equalizer to bump up the response around 3db at 40 hz over a narrow one octave band and this seems to be effective at gaining extension. I have the upper midrange cut back around -4db centered at 3khz with a 2.5 octave band to address the resonance and network limitations. I also have the UHF boosted at around 12kz to address a lack of UHF response in my room.