Members trevcda Posted September 28, 2012 Members Share Posted September 28, 2012 Well it's learnin' time again! I purchased a couple of diaphragms for the 2425HS horns in my SR4702X. The teardown and cleaning of the gap I've got under control. But I realized that these are not self centering like the drivers I'd done before and need to be aligned. I've got a tone generator and some other test equipment, I don't know the method for actually doing this. Does anybody feeling like imparting some first hand knowledge on the subject or at least posting a link? I bought two of them so I'd have a spare, I was just hoping to not have to use the second one right away! Thanks! Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted September 29, 2012 Members Share Posted September 29, 2012 Well it's learnin' time again! I purchased a couple of diaphragms for the 2425HS horns in my SR4702X. The teardown and cleaning of the gap I've got under control. But I realized that these are not self centering like the drivers I'd done before and need to be aligned. I've got a tone generator and some other test equipment, I don't know the method for actually doing this. Does anybody feeling like imparting some first hand knowledge on the subject or at least posting a link? I bought two of them so I'd have a spare, I was just hoping to not have to use the second one right away! Thanks! I do it by feel with the mounting screws installed and lightly bottomed. I'd be curious if there's a more scientific approach when faced with no centering pins. BTW: Where did you get your replacement 2425 diaphragms? I need some 2445 diaphragms. Link to comment Share on other sites More sharing options...
Members trevcda Posted September 29, 2012 Author Members Share Posted September 29, 2012 I read something about using a 550hz tone at 3 to 4 volts and listening for rubbing. Where? The internet of course! As expensive as these are, I'd like to try and get it right the first time, but I'm also willing to learn to do it correctly. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted September 29, 2012 Members Share Posted September 29, 2012 I read something about using a 550hz tone at 3 to 4 volts and listening for rubbing. Where? The internet of course! As expensive as these are, I'd like to try and get it right the first time, but I'm also willing to learn to do it correctly. I'd think that being a JBL dealer... JBL should be able to offer some hints on how to fix their stuff. Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 29, 2012 Members Share Posted September 29, 2012 Wait a minute, the real 2425 and 2445 diaphragms are self aligning. Something is not right here. Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 29, 2012 Members Share Posted September 29, 2012 I need some 2445 diaphragms. Let's talk next week, I've got this covered. Link to comment Share on other sites More sharing options...
Members trevcda Posted September 29, 2012 Author Members Share Posted September 29, 2012 Wait a minute, the real 2425 and 2445 diaphragms are self aligning. Something is not right here. From the little pamphlet in each box: "THIS PART IS NOT SELF CENTERING! This product should be installed by an authorized factory trained technician! Centering of the voice coil within the magnetic gap etc. etc...." These are directly from JBL parts. Had my local guy not strung me along so badly last time with "back orders" (apparently didn't think I would check) and "delayed shipments" followed by over charging for after market parts, I wouldn't be messing with it. Added: I believe you are correct. I didn't actually unpackage the part, to avoid any accidents, but after reading your post I looked and there are two alignment holes in addition to the three bolt through holes. Are the tolerances loose enough so that no adjustments to the centering are needed? Perhaps the enclosed pamphlet was to scare of the weak of constitution and those smarter than I! Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 29, 2012 Members Share Posted September 29, 2012 The locating pins should be snug enough. Non-self centering diaphragms are rare but do exist. The EV 1829 is an example of one and they suck to replace. Link to comment Share on other sites More sharing options...
Members sibyrnes Posted September 29, 2012 Members Share Posted September 29, 2012 Here's info from some guys who know something about the subject. Maybe you might find this interesting: http://soundforums.net/junior-varsity/5245-hf-diaphragm-question.html Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 29, 2012 Members Share Posted September 29, 2012 Here's info from some guys who know something about the subject. Maybe you might find this interesting:http://soundforums.net/junior-varsity/5245-hf-diaphragm-question.html I just pulled a couple of 2425's out of my stock and there is ZERO ability to align anything. The locating pins are snug enough in the diaphragm housing (actually the aluminum ring on the underside of the bakelite/plastic shell) that there isn't even 0.0001" of motion so it is not at all possible. I don't know what those guys are looking at, but on factory parts it's not an option (or at least any that I have seen in the last 30 years). Link to comment Share on other sites More sharing options...
Members trevcda Posted September 29, 2012 Author Members Share Posted September 29, 2012 Success! It aligns roughly with the three screw that hold it in place. The two other holes I thought were for alignment pins apparently are not used for this assembly. I ran a sine wave into it and moved it around slightly (with out twisting it) to be sure it was as centered as I could get it and reassembled. Works great. Thanks for the link and the help. Best news is that I still have a spare. Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 29, 2012 Members Share Posted September 29, 2012 Do you not have alignment pins on the driver??? There should be 2 pins at 180 degrees. They align with the 2 smaller holes. There were some models that used a machined relief for alignment as well, but again there is no room to allow the diaphragm to move around (of course it can rotate but this is not part of the aligment). Can you post a picture? Link to comment Share on other sites More sharing options...
Members trevcda Posted September 30, 2012 Author Members Share Posted September 30, 2012 No alignment pins. In fact the holes for those pins faced the back of the assembly. Maybe I put it in backwards?!! Just kidding. There was a relief that probably got it sufficiently close and I may have just had it loose enough move it around too much and hear the buzzing from the tone generator. In any case it ended up where it needed to be and it was a good exercise in understanding the method for doing this. Bring on the E.V.s! They're tucked away back in their cases, so no pictures sorry. Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 30, 2012 Members Share Posted September 30, 2012 Wow, in all the years of doing these (on 2400 series) I haven't seen this. Link to comment Share on other sites More sharing options...
Members sibyrnes Posted September 30, 2012 Members Share Posted September 30, 2012 Wow, in all the years of doing these (on 2400 series) I haven't seen this. Believe me, I was surprised too! I have changed a lot of JBL diaphragms and have never thought about allignment. You learn something new in this business everyday! Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 30, 2012 Members Share Posted September 30, 2012 I wonder if on some of the newer stuff (made in Mexico), they are dropping the locating machine work. Dumb as hell if you ask me. In all those millions of drivers there were never any problems. I have been a JBL servbice guy since 1978 and have never seen this. I have seen the notes but assumed that was to discourage idiots from destroying perfectly good parts... Link to comment Share on other sites More sharing options...
Members trevcda Posted September 30, 2012 Author Members Share Posted September 30, 2012 I have seen the notes but assumed that was to discourage idiots from destroying perfectly good parts... Hey! I might resemble that remark! As I said, I think the locating relief may be there, I don't recall. I basically placed it neatly in the gap and put the screws in place and hit it with a sine wave generator. I had the screws loose enough to move it enough to hear when I hit something. There were definitely no alignment pins, however. I'll make an effort to pull it apart and take pictures when I get a chance. Link to comment Share on other sites More sharing options...
Members agedhorse Posted September 30, 2012 Members Share Posted September 30, 2012 The 2 ways of doing this (from the manufacturing end) are using either locating pins (the diaphragm should have the 2 matching holes in addition to the 3 screw holes), or a machined relief about 0.0750" deep that aligns to the aluminum ring on the underside of the housing. both of these should provide no slop, and the machined relief has a very small taper or chamfer that aids in the self centering. There is a third way on housing-less diaphragms, those use 3 pins that hold the outside of the fiberglsss flange centere. These are very tight and actually slightly distort the flange in the centering process. Now true non self centering diaphrahms are a bitch and a half to work with. They do take work, experience and some time to get right. EV and University both has a lot or these models. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted October 1, 2012 Members Share Posted October 1, 2012 The 2 ways of doing this (from the manufacturing end) are using either locating pins (the diaphragm should have the 2 matching holes in addition to the 3 screw holes), or a machined relief about 0.0750" deep that aligns to the aluminum ring on the underside of the housing. both of these should provide no slop, and the machined relief has a very small taper or chamfer that aids in the self centering.There is a third way on housing-less diaphragms, those use 3 pins that hold the outside of the fiberglsss flange centere. These are very tight and actually slightly distort the flange in the centering process.Now true non self centering diaphragms are a bitch and a half to work with. They do take work, experience and some time to get right. EV and University both has a lot or these models.Indeed they are, and I have replaced plenty of ALTEC diaphragms to second that! I just run a sinewave and then move the diaphragm slightly and when I hear the output at its max then I know it is centered.When you are off center the sinewave signal output will decrease. The JBL drivers I have seen all are self centering , and even with non OEM diaphragms. Link to comment Share on other sites More sharing options...
Members agedhorse Posted October 1, 2012 Members Share Posted October 1, 2012 Most of the Altec diaphragms are self center as well. Anybody need some 291-16 diaphragms? Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted October 1, 2012 Members Share Posted October 1, 2012 Most of the Altec diaphragms are self center as well. Anybody need some 291-16 diaphragms?How much Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted October 1, 2012 Members Share Posted October 1, 2012 Most of the Altec diaphragms are self center as well. Anybody need some 291-16 diaphragms?The pins move on the large drivers for adjustment. I do remember playing piano music through large Altecs and certain notes you would hear a buzz. So we pulled the driver and adjusted the diaphragm with a sine wave. They are not like the small Altec or JBLs with that machined step for location. The shim method is kind of a pain. Link to comment Share on other sites More sharing options...
Members agedhorse Posted October 1, 2012 Members Share Posted October 1, 2012 I have a pair of original (not aftermarket) factory 291-16 diaphragms that I kept in stock because I had a customer with a large number of these drivers (I serviced the cinema market before the industry consolidation) and I wanted to be sure I could take care of them without delay. The company got bought by Regal and I was "outsourced". Anyway, how about $90 for the pair? Dealer cost (when they were still available) was over $100 each. Link to comment Share on other sites More sharing options...
Members trevcda Posted October 7, 2012 Author Members Share Posted October 7, 2012 Well crap! Looks like I'll get those pictures sooner than I'd planned. The new driver sounded great for the first couple of hours and then just quit. Not sure what went wrong. Cleaned the gap. Sounded fine on the bench. The other side still works fine and that diaphragm is the one the came with it when I purchased new. I guess I'll have to get a magnifier of some sort and really look into the gap and see if there's something I'm missing. Link to comment Share on other sites More sharing options...
Members agedhorse Posted October 7, 2012 Members Share Posted October 7, 2012 Well crap! Looks like I'll get those pictures sooner than I'd planned. The new driver sounded great for the first couple of hours and then just quit. Not sure what went wrong. Cleaned the gap. Sounded fine on the bench. The other side still works fine and that diaphragm is the one the came with it when I purchased new. I guess I'll have to get a magnifier of some sort and really look into the gap and see if there's something I'm missing. If the new diaphragm has failed, you MUST chack the crossover and wiring to be sure there is no problem. There could be something wrong with the crossover causing your problems and continuing to damage diaphragms. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.