Marco: Take the top off of your La Scala's, pull the horns & crossovers and then open up the woofer chamber. In the long run, you're going to leave this open and seal the rear of the horn chamber that used to be open. You may have to do some fabrication in terms of a partial plate where the original woofer hatch was, but this drastically increases the bass chamber volume. That tiny bass chamber is what raises the resonant frequency of the driver, limiting bass extension.
Once all that is done, fill what is now the shared bass / horn chamber with fiberglass. This will also increase apparent box volume AND damp the vibration of the horn bodies even further. Altering the amount and type of fiberglass used will change the Q of the system, but 2 lbs per cubic foot is typically a good place to start with any sealed and stuffed design. Don't forget to take into account the internal volume lost from the horn bodies and crossover boards when trying to factor the actual weight to use.
You might find that you like slightly less than 2 lbs per cubic foot, which is easy to deal with. I think that i ended up with about 1.7 lbs per cubic foot or so when all was said and done. At 2 lbs, the chamber is absolutely crammed full to the point of over-flowing. At 1.7 lbs, it is still VERY full, but not billowing out quite as badly.
The end result is that you lower the resonance of the system by appr 12 - 15 Hz, which is quite a bit. The Q is lowered from appr .85 down to appr .57 or so, which is a phenomenal gain. This reduces the peak at resonance for more control AND at the same time, improves transient response. The peak at impedance is also reduced, increasing power transfer from the amp to the woofer where it needs it the most. In many other attempts to increase bass extension via increasing the Q, "speed", "control" and "definition" are sacrificed, but not with this approach. Low Q with a good design is a "win, win, win" situation.
Due to the lower peak at resonance via the reduced Q, the bass is also now more extended. That is, you can either get greater apparent bass with less control ( like a vented design or the stock Klipsch high Q design ) or more control and greater extension ( like a "good" low Q sealed design ). We are opting for the latter, which is what i've always promoted in previous posts. This ends up giving us appr +4 to +5 dB's at 30 Hz compared to the stock La Scala.
While reducing the resonant frequency by 12 - 15 Hz definitely improves bass extension, that added +4.5 dB's REALLY improves bass solidity and "thunder". We've now got REAL deep bass without near as much "false" upper bass and the "snap" of the bass has been improved.
To sum things up, you end up with a completely different speaker that is far superior in every respect. Greater bass extension, improved transient response and more bass "weight" without introducing gobs more distortion or losing impact or definition. The really cool thing about this is that everything is 100% reversible with no signs of external cosmetic modifications if done properly.
Outside of doing this and the basic horn damping / crossover mods / wiring changes / removal of the screens within the horn throats, one has to get into doing MAJOR bass horn modifications to go to the next level of performance.
It is my opinion that it is easier to build new cabinets from scratch than it is to try and modify the existing bass horn for improved performance. While doing that, one could factor in front mounted horns for reduced diffraction as compared to the factory rear mounted design. They could also build a larger ( taller ) low frequency section, improving the extension due to having a larger horn mouth without eating up more cubic floor space. Radiusing the bends inside the bass horns is a huge benefit, minimizing standing waves ( muddy lower midrange / upper bass ) even further.
Some of the muddiness in the lower mid / upper bass can be reduced in the stock design by bracing the outer cabinet walls to the "V" of the bass chamber, but this may introduce introduce non-reversible cosmetic changes to the cabinet. If done tastefully though, you can't tell that the braces aren't stock and the sonic benefits far outweigh the small cosmetic drawbacks. One can temporarily do something like this by carefully wedging a form fitting piece of wood between the "V" and the outer walls without permanently attaching it. The use of felt between the contacting areas will minimize the potential for any scratches to take place. To be honest here, and that's what this thread is about, most of the vintage Klipsch cabinets are poorly built and designed from a performance standpoint. From a mass production standpoint, they are engineering marvels. Sean
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PS.... Some of the facts & figures quoted are strictly ballpark. Due to the tolerances on the mass produced drivers that Klipsch used, each woofer will respond just a hair differently than others. Following the basic guidelines as listed above though will DEFINITELY improve the performance of the system on the whole, regardless of the absolute accuracy of any individual spec's quoted.
PPS...Much of what i learned about Klipsch's came from personal experimentation. Another great source that really helped me, on La Scala's in particular, is Dennis Kleitsch. You can find some of his posts at AA in the "high efficiency" Asylum and at the Klipsch forums under the name of djk ( all small letters if doing a search by author ). Dennis is truly a wizard when working with these and other horn loaded speakers.
