DaleShirk

This looks exactly like what my intentions are for the LaScalas I recently aquired, if/when I get them refinished sufficiently that my wife lets them in the house. http://forums.klipsch.com/forums/t/155314.aspx Exactly. Crossovers take time, whether analog, digital, or acoustical. The time offset between raw drivers is not the same as the excess delay that needs to be added to any particular crossover alignment. People like Ed Long were aligning Altec 604's by juggling the passive crossover long before anything digital was viable.

It is an interesting question and since I'm currently on a crusade to learn more about diffraction it would be worthwhile. My preliminary guess is that the vertical might sound good when it's in the middle of a large baffle such as a Cornwall, not because it's vertical, but simply because it's well away from those edges. I did measure vertical on the LaScala, where it's on that narrow strip of wood with the top edge and the squawker edge each only an inch away and there is plenty of ripple. I also want to look into putting a foam covering on the face around the horns to reduce diffraction. Dale

With great respect for the legend and legacy of PWK, after taking these measurements I'd have to say "Bullshit!" [bs][]

Of course. As far as the baffle edge, since the angles are less severe and the shortest wavelength much longer, I might simply bevel the plywood edge a little with a router bit, perhaps a roundover if the screws are far enough away. Considering the wavelengths involved, it would make absolutely no difference. BTW, for reasons beyond my understanding, I love your avatar. Is there an explanation or a larger image?

I did take +/- 15 and 30 vertical front mount and rear mount in the La Scala, and the front mount was slightly smoother. However they both exhibited much more diffraction effect from the nearby top edge of the cabinet and the squawker opening. Mounting the tweeter vertically on a larger motorboard would be smoother. Generally, based on simple observation the horn would show wider dispersion across it's small dimension at lower frequencies and narrower at higher frequencies, while across the wider dimension it would ne more uniform low to high.

OK, I put some front-mount vs rear mount tweeter measurements here: http://forums.klipsch.com/forums/t/155314.aspx

This measurement shows why I believe it's worth the minimal effort required to change the tweeter to front mount. It is the front mount horizontal off axis set. Note how much smoother it is. Also of note is the lower frequency ripple in the 45 and 60 degree sweeps. The ripple spacing of about 1000Hz suggests a path length difference around 1 foot. I suspect this is diffraction from the side edge of the cabinet, which is getting much closer to the direct path at these shallow angles. Conclusion: For my set of La Scalas, which will be actively crossed over and EQ'ed, I'm definitely going with the front mount.

This measurement really shows where the bones are buried in the rear mount scenario. It is the rear mounted tweeter with on-axis overlayed with 15, 30, 45, and 60 degrees off axis horizontally.

This measurement overlays the on-axis response of front mount vs rear mount. Front mount is somewhat smoother. The rear mount does have an edge in output in the 5K-6K region, maximum about 3 dB at 5800 Hz. I believe this is the result of the extra air loading in front of the horn when it's rear mounted. Functionally this lowers the flare rate slightly, making it more efficient at the lower end of its response. This might be important when using a passive crossover since the actual crossover frequency and slope is the combination of electrical components and the acoustic passband of the driver.

These measurements document the differences between a rear mounted tweeter and a front mounted tweeter. The tweeter is a K77 factory rear mounted in a 1978 La Scala, vs. front mounted in the same. To front mount it I trimmed (beveled) the opening with a pocket knife so that the horn flare fit from the front, then attached the horn driver from behind. I did not recess the flange flush. I countersunk the holes in the horn flange slightly and used small flat-head screws typically used for kitchen cabinet hinges. Measurements were made using a TEF20 analyzer driving one channel of a Stewart PA-100 amplifier directly connected to the tweeter with no crossover components. Drive level was 1 Volt RMS sine sweep. Measurements were taken at 1 meter distance using an Earthworks TC30K. Assuming a nominal 8 Ohm impedence, one can get the 1Watt/1 Meter response by adding 9 dB.

This is probably as much a science project as it is to obtain speakers for my listening room. I hope to be measuring and documenting as I go. Someone mentioned that changing from rear mount to front mount on the tweeter won't make much difference. That's probably the first and easiest thing I can measure. I've been studying up on diffraction, and everything about that rear mount looks bad from a diffraction perspective. I've heard these speakers in concert as an audience member and mixed music on them myself a few yarr..mrmmr..mrmr..OK, Decades ago. They had the characeristic clarity y'all here are familiar with, inspite of some obvious problems. I'd like to identify and repair those problems. I'm asking about stuff here to get a better understanding of their history and a better lay of the land before I start. BTW, it's not at all clear if this is the best forum branch for this discussion. If not please direct me.

There is a paper tag on the back, but it is unreadable. Someone, probably the original purchaser, hammer stamped the following on the plywood edge of the back just below the crossover 14S555 on one and 14S556 on the other. Since these seem to correspond with the serial number format, and 1978 is in the ballpark of when I think these were new, I made the fantastic leap of logic from there. They also have the name of the band stamped in "Daybreak" The dead woofer I removed has a square magnet and the numbers 6930009 and 137 7210 and 8 Ohms. I think the polepiece shifted, since the cone is pushed forward and blocked. The VC is open. I'm gonna try attach a pict.

Thanks for the replies so far. The edging is mitered on the corners and not glued, so I think it was added. Also I later found a hardware store sticker on one piece, so I guess that's that. The previous owner thought he had put the edging on, and I thought is was a factory option. I guess that's where he got the idea. They have no rear cover over the mid/hi and have a definitely homemade 1/4" jack installation. Perhaps these were ordered as plain unfinished install speakers. What were the available options in 1978? Any old catalogs online? I'm looking at doing time aligning digitally with DSP, so the only extra WAF problem may be a few extra rack spaces. What I currently plan to use, mainly because I have them, is a McIntosh MC2150 for lows, A Urei 6150 for mids and a Stewart PA-50 for highs, all driven by a Rane RPM26z DSP and a Marantz AV9000 preamp. You probably figured out by now, I'm an pro sound contractor. I'll be dialing these in with a TEF analyzer.[8-|] Dale Shirk

I've managed to obtain a long-wanted pair of 1978 Industrial La Scalas. Now to work them over to make them what I want. They have 1 blown woofer, so I'll probably get two new ones. I also have plans to front-mount the tweeter to reduce diffraction, add some bracing to the bass horn, add some damping to the mid horn, Tri-amp and time-align them with a DSP. I have a few questions I wanted to ask the Klipsch gurus. 1.These speakers have 3/4 inch wide 1/16 inch thick aluminum angles attached to all the exposed edges to prevent damage when they are moved around. They were at one time the main speakers for a local rock band. Are these aluminum angles OEM or were they added later? I'll probably take them off and veneer the cabinets to improve the WAF factor, but I was curious 2.I've seen the bass reflex bottom module mods and I'm considering doing that since I want to raise the Mid/hi to ear level anyway. Since I need a new woofer anyway, I'm looking at possibly selecting a different one that might respond to the reflex box better. I can do the T-S calcs, but I'm curious if anyone else has done something similar. Does anyon know offhand the flare rate of the bass horn? I can measure and calculate it if needed. 3. I've seen numerous mid-horn replacements, but I prefer to stay more stock at the moment. I have this vague recallection of someone adding damping to the mid horn to reduce resonances. Any guidance there? 4. I want to front-mount the tweeter. Any reason why I can't mount the tweeter from the front then attach the driver from behind? 5. Has anyone time-aligned these? I'm curious as to the effect on the sound. I'm wondering if part of "the sound" is highs ahead of mids, which are ahead of the lows. When I do eventually set them up, I'm going to do a preset each way, one as close to original as the physical modifications allow and one as well tuned as possible. I'm really looking forward to this project.