Most of the "horn colouration" that you folks hear is due to the horn body itself "ringing". Believe me, they ring like MAD. If you completely damp the throat of the horn ( the ENTIRE "body" or "casting"), the sound will DRASTICALLY change. Minimize the diffraction taking place at the mouth of the horn by chamfering the cabinet to an equal flare ratio or flush mount the horns and the imaging and soundstage will also improve quite noticeably.
As to the bass horn itself, stiffen the cabinet with small internal braces ( large diameter dowel rods unevenly spaced ) and "round" the internal corners. Just like a mid or tweeter horn body, the bass horn should have smooth flares with a gradual radiused flare for best results. Squared corners produce "flat spots" in air turbulence and create internal nodes within the horn that do not help us at all. This mimizes the "boxy" or "hollow" characteristics in vocals that you hear. Most of this is due to the drastic reduction of the box "talking" and the reduction of standing waves and reflections WITHIN the horn body itself.
If you REALLY want to get serious, play with the size of the opening that the woofer feeds into. It is MUCH smaller than the driver itself, creating what is known as a "compression" effect. While this does increase the velocity of sound waves and play with SPL levels generated, it too can contribute to the "boxy" vocal effect. I don't recommend this for the mass majority of "diy'ers" or "tweakers" though.
Improving the wiring in ALL Klipsch speakers can make a HUGE difference in sound quality. My experience is that solid wire works best here, but everyone has their preferences.
As i mentioned in another thread recently, check the polarity of the drivers. Some earlier Klipsch designs fed the "squawker" ( mid horn ) out of phase when compared to the polarity of the woofer and tweeter. Try it both ways and see what sounds best to you. I and several others have always preferred the "in phase" approach as it sounds much more natural. Sean
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