ajsons

The day after Christmas, I took the C15W out and replaced it with an EVM 15B, the "brother" of the 15L which is in the other channel. The 15L has a brighter sound, the 15B has a traditional bass guitar sound (honestly I can't tell the difference) and the specs are almost the same. The bolt patterns of both EV's are the same as the C15W. Now, the drivers are nearly identical between left and right channels, leaving the horn enclosures as the uncommon denominator. It didn't change the order of things! The C15W has an Fs of 58hz, Qes of .22. I think the EV's (Fs=43hz) are more suited for the Classic which has an Fc of 50hz (per D-man and Egar's estimates. I need to ask D-man's opinion on this. Armando

I didn't build the Speakerlab crossovers. I built a pair of 12db 3 way crossovers (back in the 80's) from Bullock's formulas. Unfortunately, I used el cheapo parts. I changed to ALK's and what a difference! I think the 12db circuit is good, I just used low quality parts. I might have to revisit that sometime. I am presently using the ALK's on the University Classic.

Drew, What kind of mods do you suggest?

Mine has an EVM-15L woofer with a 6 x 13 throat., EVM SM120 for the mid horn. The mid driver is always changing, although my favorite is EV's 1824, which should cross at 3500hz, the correct crossover is still under construction. T35 for the tweet.

It looks like you hibernated for a couple of days before Christmas, didn't see a post from you . I started a new thread under Technical Questions about the Classic. Do you have a chosen name for your horn yet? .

Chris, This thread starts with "Curiosity.....", that's all on my part, and maybe the others, too. I like to learn as much as I can about crossovers, though. Some years ago, I converted Bullock's crossover formulas into a working program. Now I found out, all I need are good schematics and frequency scaling to handle my crossover needs. A little info here and there, helps, even if they're just historical in nature. I don't need a Speakerlab crossover. But I'll keep a copy of the schematic.

I tried the Georgian midhorns on my K-clones. They sounded real good when music is played. When used as a TV speaker, voices sounded split, or cracked. I believe it is caused by the phase difference between the short horn in front and the bigger midhorn itself. It is not noticeable when playing music, at least to my ears.

The Patrician has two of those tubular horn sections firing into the rear of the midhorn as described in the "review".. Armando

CaptnBob, I think youre right! The Georgian also has a single mid driver not two.

The only other thing I have is the change to the instructions.

I have a copy of Q-man's post about the University speaker he built, but I'll wait before I post it, he might chime in. Q-man, I'm sorry I haven't redrawn the plans. Recovering from the hard drive crash was just too much for me, I lost a lot of AutoCAD files. I learned the lesson, though. Back them up!

I knew one of the "senseis" will explain that! In my situation, am I right to say that my squawker's roll off is too far off (3500hz ) from 6000hz that I really need to change my crossover values? The EV 1824 rolls off rapidly like the K-55, only at 3500. The T-35 is good down to that frequency. Some EV products, like the Sentry IV (horn version) cross the mid and the tweeter at 3500.

But if your driver rolls off faster than the crossover, you need the "sensei" for that! Your horn looks pretty cool though!

For you xover gurus a question: the driver I want to try falls off at 4500Hz pretty sharply, what values of components do i need to lower the HF point of my ALKs to cross at that point? Is it economically feasable? Am I nuts? please leave the answer to the last question unamswered. Rick, I'm not an xover guru, but I'm doing the same thing. I'm building my second set of ALK's rossovers, and I'm crossing at 3500 for an EVM 1824 midrange, based on Al K's tips. Here's what Al K said: "Frequency scaling is easy to do. You simply scale the parts by the ratio of the change. For example: if you have a 2.2 uF cap at 6000 Hz and you want to move it to 7500 Hz you multiply 2.2 X (6000 /7500) = 1.76 uF. The inductos work the same way. The problem you will run into is that you can't buy a 1.76 uF cap. You will need to parallel several that add up to what you need. To impedance scale you make scale inductor values proportional to the change in impedance and the caps inversely proportional. I think you will want to keep 8 Ohms though." ---------------------------------------------------------------------------------------------------------------------------------------------- Good luck! Armando

I believe there is a third sheet to this. Drawings normally come with a materials list, and somewhere on these plans, a finish table is mentioned. So I think we're all missing a third sheet. We do have enough information though. My Classic does not have the braces these plans are showing. Three braces were added to the drawing revision in 1969. (The ebay seller (a nice lady, BTW) told me my Classic was built in the late 50's). The drawing shows two triangular braces in the doghouse, dividing the doghouse into three sections. The third brace is behind the doghouse. The braces are a must! There is too much panel vibration (panels are 3/4 plywood) due to the bass energy! The SK's built out of 1/2 plywood do not vibrate like this one. The three added braces I don't think will be enough. And if I build them they will probably be 2 x 4's in the doghouse. I will add braces to the side panels, or double up the plywood material. Rather than me blabber about the rest of its construction, here is a quote from the Audio Asylum from Steve Schell. http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=4519&highlight=This+past+Friday+I+hauled+one+cabinet+with+bass+driver+University+C15W&r=&session= Posted by Steve Schell on October 30, 2000 at 00:15:13: In Reply to: Abaham Cohen's University Classic Basshorn - Anyone here built or heard one? posted by freddyi on October 29, 2000 at 08:37:15: Recently I purchased a pair on ebay from a seller in Idaho. These and several others had been pulled from a dumpster after being placed there as part of an auditorium remodelling. Anyway, these were built in 1974, had unfinished birch cabinets, and contained all the original drivers and crossovers. The seller has sold all that he had; many cabinets were badly smashed, so he parted them out and sold the drivers. They were impressive on first listen, after correcting some driver phasing problems. Very lively, dynamic bass, more extended than I would have expected. Everything present except the extreme, below 30 hz. shuddering pipe organ fundamentals. I then stripped them apart, patched, sanded, and finished the cabinets a medium walnut (in part to hide the remaining flaws). This past Friday I hauled one cabinet with bass driver (University C15W) installed over to Dr. Bruce Edgar, as we both wanted to measure this design. Nearfield frequency response was quite good, remaining within a 5dB window (plus or minus 2.5dB) from 55hz. to 300hz. and sloping off fairly rapidly from those points. Not bad at all for a front loaded horn of this size. I believe Dr. Edgar had previously calculated the design to be an exponential 50hz. flare. Today I hauled the completed Universitys to my brother's house, to upgrade his hi-fi/video system. We began listening after they had been installed on either side of his new big screen TV. His room is quite a bit larger than mine, and built on a concrete slab, whereas mine is not. I was not prepared for the fabulous bass they provide in his room. After working through a few CDs, we put on his laserdisc of the film "Backdraft". The speakers handled all the explosions, elevated trains passing through the living room, and other heart pounding sound effects with effortless ease. This quality of natural, lifelike, realistic low frequency reproduction seems to be available only from front-loaded bass horns in my experience, and these speakers confirm my belief even more. I believe that Mr. Cohen's grand design is a real sleeper and due for a comeback. A few details: the construction of these cabinets was sloppy in some respects. Nothing had been done to properly seal the rear chamber. Particle board dividers on either side of the driver divided the cabinet's central triangular section into three sections, the larger center section containing the woofer. These dividers were improperly cut, allowing unsealed gaps of as large as 1/4" to the side, waste sections. I sealed the rear chamber carefully. The board allowing access to the woofer had not been gasketted, and the boards in contact with it were uneven and did not permit a tight fit. I planed these down as necessary and added a gasket.The board had been installed with an inadequate number of too - short screws. I added more, and longer, deck screws. The Cobreflex midrange horns and drivers look like they should be installed at the airport, but they perform well. I'm going to stick with my RCA theatre drivers and multicellular horns, but these Cobreflexes are not bad. Ditto for the tweeters (forget the model number), which look and sound a lot like EV T35s. The stock crossover contains two iron core inductors for mid and high frequency level. After adjusting driver levels, the system blended together very well. The strongest attribute of these systems is...that bass! Hope this info helps. ---------------------------------------------------------------------------------------------------------------------------------- Armando steve schell on classic.txt

Mungkiman, I redrew the corner version in AutoCAD to check for accuracy. There's a lot of errors on that one. The compound cuts don't line up. I promised Qman I'll send him a corrected copy, but can't find the time right now. Well, right now , I got to go to a party. Will post more pictures tomorrow, hopefully I'll find the spec sheet for the C15W. Armando

Internal schematic of the N3, if you are interested. This is from Cohen's book. I have a better drawing in my sketchbook, with actual part values used. One more picture and I have to go, JC. Will check again when I come back. Christmas party time. Merry Christmas to every body. Armando

A shot of the N-3 crossover, without the pots. First reaction......Where's the beef?

Schematic Diagram N-3 crossover hookup

Start of second sheet. No dimensions on this one.

JC, Are the dimensions readable? Please let me know. That was the first sheet. The second sheet shows the component installed and a schematic diagram. (I'll have a coffee break).

Lower half of the previous one, end view looking at the throat.

This is the block that holds the Cobreflex, and the HF206 tweeter, and an iso view.

It is 40 1/2 long 23 3/4 deep and 31 1/2 high. Here's the lower half of the plan.

Here's a part of the drawing that shows the main dimensions.