BEC Posted November 26, 2004 Author Share Posted November 26, 2004 ---------------- On 11/26/2004 1:34:57 PM Jim E wrote: 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 ---------------- Jim, Since this was just a comparison test, I did it a rather quick and dirty way. I do have a pretty well equipped audio lab with a Wavtek specturm analyzer, HP programmable sweep/signal generator, calibrated mike with mixer and phantom power for the mike, a scope and so on. For this test, though, since I am only interested in how the old woofers compare to the new one, I just input sine waves generated by a computer into an amp and had the woofers connected to the amp. I looked at the output on a Radio Shack SPL meter. Bob Quote Link to comment Share on other sites More sharing options...
John Warren Posted November 26, 2004 Share Posted November 26, 2004 If you want to determine if a difference exists you must measure driver Qes, Vas and Fs. Your measurements will tell you nothing. Quote Link to comment Share on other sites More sharing options...
John Warren Posted November 26, 2004 Share Posted November 26, 2004 ---------------- On 11/26/2004 5:11:18 PM John Warren wrote: If you want to determine if a difference exists you must measure driver Qes, Vas and Fs. >>Why? Electro-acoustic efficiency is proportional to (Vas x Fs3) / Qes. Calculate the ratio for the sq magnet, then calculate the ratio for the round magnet, comapre the two (by taking the ratio of both) and you have acoustic efficiency factor difference. ---------------- 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 5:11:18 PM John Warren wrote: Your measurements will tell you nothing. ---------------- John, I disagree. It will tell me something between nothing and everything but certainly not "nothing". Bob Quote Link to comment Share on other sites More sharing options...
John Warren Posted November 26, 2004 Share Posted November 26, 2004 ---------------- On 11/26/2004 5:59:24 PM BEC wrote: John, I disagree. It will tell me something between nothing and everything but certainly not "nothing". Bob ---------------- Suit yourself. You most likely have the proper instruments to accurately measure the paramters I cited above. AND you have the test box wish you can use to determine Vas. Measuring driver Qs is a straightfwd task and can be done with reasonable accuracy. If done properly with a calibrated setup you will be able to determine the difference in electro acosutic efficiency to within a couple of percent. And you will get detailed engineering information of the two drivers that will lead to further understanding between the two (Qes is related to Bl-product for example). If you wish to putz around with a toy SPL meter then by all means do so. If you want to do it the proper way email me to discuss, I will expalin to you how to do it. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted November 27, 2004 Share Posted November 27, 2004 "It will tell me something between nothing and everything but certainly not "nothing"." Bob, a true Zen saying. Back to HS Science class, what was your hypothesis... just to see how much if any difference in LF efficiency at various frequencies exists between modern new magnet K woofers and older style magnet 30-year old K woofers. I believe your test and results showed that there was exactly, almost, no difference between the three drivers tested. Sounds successful and useful to me! Thanks for your efforts! Michael Quote Link to comment Share on other sites More sharing options...
Dylanl Posted December 5, 2004 Share Posted December 5, 2004 Bob, thanks for running the tests on my drivers. Did you ever try the test that John Warren is describing? I have seen the tests john is talking about in my speaker building books. It does not look hard just slightly different tools and parameters Quote Link to comment Share on other sites More sharing options...
BEC Posted December 5, 2004 Author Share Posted December 5, 2004 I have the first part of the T/S testing done on your old K-33Es and a couple of new K-33Es. I am working (as I have time) on the in cabinet tests. Bob Crites Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted December 5, 2004 Share Posted December 5, 2004 Bob, generally speaking, it is advantageous to time-align all the drivers so they at least point out the same side of the motorboard. This also avoild phase anomalies. LOL I know you had other things in mind with this test, the photo just tickled me. Sorry. Michael Quote Link to comment Share on other sites More sharing options...
BEC Posted December 5, 2004 Author Share Posted December 5, 2004 ---------------- On 12/5/2004 5:49:56 PM colterphoto1 wrote: Bob, generally speaking, it is advantageous to time-align all the drivers so they at least point out the same side of the motorboard. This also avoild phase anomalies. LOL I know you had other things in mind with this test, the photo just tickled me. Sorry. Michael ---------------- Just checking to see if anyone is awake. Michael seems to be. Internal volume calcuations are easier with the woofer mounted backwards. Bob Quote Link to comment Share on other sites More sharing options...
Deang Posted December 5, 2004 Share Posted December 5, 2004 Reverse Engineering Quote Link to comment Share on other sites More sharing options...
IB Slammin Posted December 6, 2004 Share Posted December 6, 2004 ---------------- On 12/5/2004 6:42:44 PM DeanG wrote: Reverse Engineering ---------------- Known as Bas Ackward in Arkansas.... Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted December 6, 2004 Share Posted December 6, 2004 Ok, Bob, I'll bite again. Agreed that with the woofer cone area outside the box you don't have to subtract the volume of the cone, but wouldn't you likewise have to now ADD the cone volume back in for your cabinet internal volume calculation. The volume of the box is now bigger by the size of the cone, yes? Michael Quote Link to comment Share on other sites More sharing options...
BEC Posted December 6, 2004 Author Share Posted December 6, 2004 ---------------- On 12/6/2004 9:46:26 PM colterphoto1 wrote: Ok, Bob, I'll bite again. Agreed that with the woofer cone area outside the box you don't have to subtract the volume of the cone, but wouldn't you likewise have to now ADD the cone volume back in for your cabinet internal volume calculation. The volume of the box is now bigger by the size of the cone, yes? Michael ---------------- That is correct. It is bigger by the volume of the cone plus the thickness of the woofer gasket (less the recess into the motor board) plus the thickness of the motor board. More specifically we could say larger by 3.83 liters for the one with the square magnet (thinner gasket) and 4.43 liters for the new ones with round magnets (thicker gaskets). Bob Crites Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted December 7, 2004 Share Posted December 7, 2004 Fascinating, you even take the gasket thickness into account. But that alone can't be the reason for .6 litre difference. Can we surmise then that the current round magnet woofer is also a considerably deeper and possibly stiffer design, accounting for the volume difference? I understand that the exterior mount makes changing the woofer simplier with less openings in your test box, but how then are measurements made? Michael Quote Link to comment Share on other sites More sharing options...
D-MAN Posted December 7, 2004 Share Posted December 7, 2004 I'm confused (again or of course) - the displacement of the driver inside the back chamber is less than 236 cu. inches (about 1 gallon of displacement). What is the point of testing the driver with no porting? A sealed back chamber of that size (2 cu ft) is TOO SMALL to get down to the proper fc for the driver and the porting reduces resistance on the cone which improves excursion. Also, the pressure difference between the sealed back chamber and the atmosphere will increase modulation distortion due to unequal excursion. I am at a loss as to what you are attempting to determine? DM Quote Link to comment Share on other sites More sharing options...
John Warren Posted December 7, 2004 Share Posted December 7, 2004 ---------------- On 12/7/2004 1:43:58 PM D-MAN wrote: I am at a loss as to what you are attempting to determine? DM---------------- He is attempting to determine Vas. (btw Bob, that port seal looks a bit "leaky" as shown. It is imperitive that the box be tight and that no leakage occurrs in the box and thru the driver, i.e. the dust cap, gasket, surround). Quote Link to comment Share on other sites More sharing options...
D-MAN Posted December 7, 2004 Share Posted December 7, 2004 ---------------- On 12/7/2004 6:16:53 PM John Warren wrote: He is attempting to determine Vas. ---------------- Somebody please SPLAIN this to me! How does this work? DM Quote Link to comment Share on other sites More sharing options...
BEC Posted December 7, 2004 Author Share Posted December 7, 2004 ---------------- On 12/7/2004 6:16:53 PM John Warren wrote: (btw Bob, that port seal looks a bit "leaky" as shown. It is imperitive that the box be tight and that no leakage occurrs in the box and thru the driver, i.e. the dust cap). ---------------- John, I think the box is pretty tight, but am at a bit of a loss on how to prove that. Just had a thought while typing this. I think I will pump some LF power into the woofer and see if I can feel any leaks. Bob Quote Link to comment Share on other sites More sharing options...
BEC Posted December 7, 2004 Author Share Posted December 7, 2004 Michael, Yes, that difference is all gasket. The new K-33Es have a very thick gasket. Bob Quote Link to comment Share on other sites More sharing options...
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