BEC Posted November 25, 2004 Share Posted November 25, 2004 This is something I have wanted to do for quite some time. The older square magnet K-33E woofers and the new ones sold now are somewhat different. The new ones have a round (and it seems a smaller) magnet. The square magnet drivers weigh at least a couple of pounds more than the new round magnet ones. I have wanted to compare a new one to the older ones. Since now my driver test box is ready to perform its duty and a forum member sent me a pair of the older square magnet woofers to test, I thought I would post results of this comparison test. Test methodology: This test is a comparison test only. All values are simply relative to the "standard" woofer, the new K-33E which I tested first. It was new, just out of the box. The two older K-33E woofers are from a set of 1974 Khorns and are, as far as I know, originals from the factory. Each woofer was in turn installed in my driver test box and a group of sine wave signals at listed frequencies were sent to the woofer. SPL was measured at a specific distance from the woofer. Since the new K-33E is considered in this case to be the "standard" it will be considered to have an output of "0" and the values for the other two woofers will be shown in db plus or minus relative to the output of the new K-33E. To read this chart consider the first line. For an input of 40 hz, all three woofers had the same output. For the second line, at 50 hz, the two old woofers were 1 db lower in output than the new woofer. Results: New Woof Woof labeled AA Woof labeled B 40 hz 0 0 0 50 hz 0 -1 -1 60 hz 0 0 0 70 hz 0 0 +0.5 100 hz 0 0 -1 200 hz 0 0 0 300 hz 0 0 0 400 hz 0 +1 0 This is closer than I would have expected. Neither of the 30 year old woofers differ in output by more than 1 db from the new woofer or from each other. Bob Crites Quote Link to comment Share on other sites More sharing options...
3dzapper Posted November 25, 2004 Share Posted November 25, 2004 Good info Bob. Thanks for sharing. Rick Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 25, 2004 Share Posted November 25, 2004 Bob, There's a little trick that might help make an even better comparison. It's called close-mikeing. Actually run a curve using white noise or swept CW with the mike about 1/4 inch (quarter inch) from the dust cap on the woofer. It's easily good up to where the crossover would be (400 Hz or so). The sound so close to the woofer overwhelms the room effects and give you a good idea what the woofer is doing. This sin't my idea by the way, it's out of a book! Al K. BTW.. You also have to stick the mike in the port opening. The port output ads to the low end in a proportion to it's area relitive to the woofer area. Quote Link to comment Share on other sites More sharing options...
BEC Posted November 25, 2004 Author Share Posted November 25, 2004 Al, I know what you are talking about. When I first tried this at about 1 meter, I got total garbage. At 50 hz, a nearby cabinet door was louder than the woofer. I kept moving closer and reducing the level until I got rid of the room resonances and read about 100 db SPL. I did it at a few inches from the cone. Likely at even closer would be better. I would like to do these tests at higher power but I guess I would have to take the driver test box outside to have any good results with power. Bob Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 25, 2004 Share Posted November 25, 2004 Bob, Yep.. Your on the right track. The book said the mike should be LESS THAN 1/4 inch from the dust cap! Try it, It works great! Al K. Quote Link to comment Share on other sites More sharing options...
Good2BHome Posted November 25, 2004 Share Posted November 25, 2004 ---------------- On 11/25/2004 8:06:43 PM Al Klappenberger wrote: BTW.. You also have to stick the mike in the port opening. The port output ads to the low end in a proportion to it's area relitive to the woofer area. ---------------- Al, I'm interested in accurately calculating this for a Cornwall: 1)Do you include the dust cap as part of the woofer? 2)Where do you measure the diameter of the woofer. 3)Do you only measure the port openings(in my case 3) on the front or something else? Thanks, Mike Quote Link to comment Share on other sites More sharing options...
Marvel Posted November 25, 2004 Share Posted November 25, 2004 Mike, Are any of those goldens yours? They are beautiful dogs, eh? Marvel Quote Link to comment Share on other sites More sharing options...
Good2BHome Posted November 25, 2004 Share Posted November 25, 2004 dupe Quote Link to comment Share on other sites More sharing options...
Good2BHome Posted November 25, 2004 Share Posted November 25, 2004 Well I think I've learned how duplicates & triplicates are created!! Quote Link to comment Share on other sites More sharing options...
Good2BHome Posted November 25, 2004 Share Posted November 25, 2004 ---------------- On 11/25/2004 9:54:27 PM Marvel wrote: Mike, Are any of those goldens yours? They are beautiful dogs, eh? Marvel ---------------- Sadly no. Just a tribute to one great Golden named "Wheels" Mike Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 25, 2004 Share Posted November 25, 2004 Mike, The correction for the port is: x = square root (port area / woofer cone area) db = 20 X log_n (x) Reduce the input to the woofer by "db" when you measure the output from the port. Simply add the frequency response curves from the port to the close-miked response from the woofer cone. The port area is simply: pi X radious X radious for a round port simple formula for the area of a circle). For a rectangular one like the Cornwall has, use the total area of the port. The cone area is the actual moving area of the woofer driver including the dust cap. Al K. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted November 26, 2004 Share Posted November 26, 2004 Bob, not to sound critical here, because you are obviously the engineer, but I have a question on the 'test box' used. If this is the Cornwall-volume box that is 2'x2'x2', isn't there a potential problem with standing waves in the cabinet? I realize that for the purposes of this test you are just comparing the output of older square mag drivers to that of newer types, but if you are ever to give actual frequency response curves from this test box, wouldn't it be better to have a box with closer to 'golden ratio' measurements, or closer to actual Cornwall measurements? My thinking is that the sides of the cabinet act much like the walls in a listening room, reinforcing and cancelling certain frequencies (apologies to Artto for my simplicity here). Klipsch would no sooner design a cabinet with 2' equal measurements than Artto would design a listening room 16'x16'x8'. Kindly correct if I'm off base here. We DO appreciate your efforts and reports. Hope the reconing efforts are coming along well for you. Michael Quote Link to comment Share on other sites More sharing options...
boom3 Posted November 26, 2004 Share Posted November 26, 2004 Bob, Thanks for doing this test. I'm sure you appreciate that what is remarkable here is not the difference but that there is so little variation. Even between new woofers, fresh off the line, these would be considered normal production tolerences. Says a lot for stability of pulp cones and fabric accordian edges. Makes me wonder what kind of woofer-to-woofer tolerence Klipsch uses and what kind of system-to-system matching was/is done between consecutively numbered systems. I'd be surprised if the slight difference in magnet mass would have any impact on amplitude response. Normally, a larger magnet equals greater efficiency (up to a point) and control where the voice coil is reaching its limits of excursion. Since the Heritage line didn't use trick field geometries or shorting rings on woofers, it's hard to believe that a round vs. square magnet was anything more than the result of one vendor's tooling versus the other. Quote Link to comment Share on other sites More sharing options...
BEC Posted November 26, 2004 Author Share Posted November 26, 2004 ---------------- On 11/26/2004 8:43:06 AM boom3 wrote: Bob, Thanks for doing this test. I'm sure you appreciate that what is remarkable here is not the difference but that there is so little variation. Even between new woofers, fresh off the line, these would be considered normal production tolerences. Says a lot for stability of pulp cones and fabric accordian edges. ________________________________ Yes, the surprise here is how close the 30 year old woofers and new woofer are in performance even with obvious manufacturing differences. Bob Quote Link to comment Share on other sites More sharing options...
BEC Posted November 26, 2004 Author Share Posted November 26, 2004 ---------------- On 11/26/2004 8:23:19 AM colterphoto1 wrote: Bob, not to sound critical here, because you are obviously the engineer, but I have a question on the 'test box' used. If this is the Cornwall-volume box that is 2'x2'x2', isn't there a potential problem with standing waves in the cabinet? I realize that for the purposes of this test you are just comparing the output of older square mag drivers to that of newer types, but if you are ever to give actual frequency response curves from this test box, wouldn't it be better to have a box with closer to 'golden ratio' measurements, or closer to actual Cornwall measurements? My thinking is that the sides of the cabinet act much like the walls in a listening room, reinforcing and cancelling certain frequencies (apologies to Artto for my simplicity here). Klipsch would no sooner design a cabinet with 2' equal measurements than Artto would design a listening room 16'x16'x8'. Kindly correct if I'm off base here. We DO appreciate your efforts and reports. Hope the reconing efforts are coming along well for you. Michael ---------------- Michael, I did maintain (close to) the internal volume of the Cornwall in my test box. I also maintained the same port area. I am not a "speaker engineer". Without the proper acoustic environment for the test, specifying actual frequency response will be a problem. My thought is, though, that a comparative response test using a real Cornwall compared to my new test box may give real data. That test would be sort of like the woofer test described above. In the present case, all test conditions remained the same while the woofers got changed out. In the proposed Cornwall vs "Cornscala" test, all test conditions would remain the same while the two boxes get changed out. I think this method would yield valid "comparative" results without necessarily giving absolute frequency response or sensitivity results. Bob Crites Quote Link to comment Share on other sites More sharing options...
Q-Man Posted November 26, 2004 Share Posted November 26, 2004 I believe there is an old Dope From Hope artical that stated that you would hear a slight improvement in the sound if you replace the old K-33P square magnet driver with the K-33E round magnet driver. I replaced all my square magnet drivers years ago, but I never tried to A/B them to see if I could hear a difference. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted November 26, 2004 Share Posted November 26, 2004 AAAHHHH, I understand. Knew there was a methodology to your madness. Should you ever get your carpenter shop set up with actual Cornwall-box NC data, I know there would be many Klipsch HT and 3-channel users who would love to obtain an inexpensive Cornwall box with cutouts for vertical horn layout (or even with blank motor board) in order to have a 'horizontal' Corn center channel cabinet. This should work well for K-horn, Corn, or LS users. A 'decorator' unfinished birch Vertical Cornwall box only could easily be painted, lacquered, given a finish or choice, or veneered to match the users existing Klipsch Mains. Thanks, Michael Quote Link to comment Share on other sites More sharing options...
BEC Posted November 26, 2004 Author Share Posted November 26, 2004 ---------------- On 11/26/2004 12:06:05 PM colterphoto1 wrote: AAAHHHH, I understand. Knew there was a methodology to your madness. Should you ever get your carpenter shop set up with actual Cornwall-box NC data, I know there would be many Klipsch HT and 3-channel users who would love to obtain an inexpensive Cornwall box with cutouts for vertical horn layout (or even with blank motor board) in order to have a 'horizontal' Corn center channel cabinet. This should work well for K-horn, Corn, or LS users. A 'decorator' unfinished birch Vertical Cornwall box only could easily be painted, lacquered, given a finish or choice, or veneered to match the users existing Klipsch Mains. Thanks, Michael ---------------- Michael, The problem (as I see it) is how to come up with a suitable midrange horn in current production that will fit inside the Cornwall cabinet. The K-600 used in the originals is difficult to find used and is not produced new. The K-401 horn (which I prefer to use anyway) is much too long to fit into a Cornwall cabinet. What this requires is a horn with an overall length of about 13 inches inclulding the driver. Bob Quote Link to comment Share on other sites More sharing options...
Jim E Posted November 26, 2004 Share Posted November 26, 2004 Bob, Just curious. Could you go into a little more detail in how you did the measurements. What instruments, mics and/or pre-amps do you use? If a sound pressure meter was used was any weighting applied? What signal source source was used? Thamks, Jim Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted November 26, 2004 Share Posted November 26, 2004 I see Bob, so then we cannot manufacture our own exact replicas of Cornwall Vertical. In your estimation, would there be any other horn complement that would retain similar characteristics (ie dispersion, xover, natural hf rolloff) as the K600? I take it that replacing the squawker/tweeter with a modern Tratrix horn would be so far off base that it would seriously compromise the 'three matching fronts for the sake of TIMBRE' debate? Then we'd also be in the situation of custom manufacturing a xover as well. Option 1: Increase the cabinet depth to accomodate K401 and create the LaCorn cabinet Option 2: Probably less desireable, look of outside vendors for a source for the mid horn, still utilizing Klipsch mid-driver, tweeter and xover. Michael- sorry to 'sidebar' your engineering report, I'll post this under my HT Cornwall thread as well. Quote Link to comment Share on other sites More sharing options...
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