Mexicomike Posted March 3, 2009 Report Share Posted March 3, 2009 Yesterday I was playing some low freq tones through my LSTs at not-loud levels, using my SPL meter to figure out standing wave areas in the room. At the 30HZ tone, the woofer in the left channel also produced a bit of rattle. I had never heard it with music but it was quite apparent with the tone. The volume of the tone itself is not diminished compared to the other woofer. I assume that the rattle is caused by the voice coil rubbing. The woofer surrounds were replaced before I bought them so I'm wondering if perhaps they were not centered properly. I have to admit that since I can't hear it at all with music I'm wondering whether to even bother messing with it. Will it get worse/cause more serious problems?Any thoughts/suggestions...Leave it alone, fix it? Link to comment Share on other sites More sharing options...
Carlspeak Posted March 3, 2009 Report Share Posted March 3, 2009 I'd suggest try rotating the speaker in the cabinet to see if it goes away before doing anything else. Otherwise, it should be attended to. If there's any rubbing, the delicate VC wires will eventually fray and break in the area of the rub.When you remove the woofer to rotate it, try stroking it gently by hand and listen for any rubbing. You may also have a partially damaged back edge of the VC former. Link to comment Share on other sites More sharing options...
Mexicomike Posted March 3, 2009 Author Report Share Posted March 3, 2009 I just tried lightly pushing on the surround at various places, impelling the woofer slightly in different directions with the 30HZ tone playing. When pressing at the 12 oclock position, thus moving the cone slighty toward the 6 oclock position, the rattle ceases. This would make me think that changing the woofer position would not help since gravity is already doing everything it can to move the cone downward. So I would think that rotating the speaker 180 degrees would actually make it worse. Do you think that's true or are there some other dynamics at work?Heck, I suppose I should just try it anyway, it's just 8 screws and some duct seal and I've got two more blocks of that! Link to comment Share on other sites More sharing options...
genek Posted March 3, 2009 Report Share Posted March 3, 2009 Heck, I suppose I should just try it anyway, it's just 8 screws and some duct seal and I've got two more blocks of that! Or you could just flip the whole cabinet over. I don't know which would be harder. How much does an LST weigh? Link to comment Share on other sites More sharing options...
Mexicomike Posted March 3, 2009 Author Report Share Posted March 3, 2009 Or you could just flip the whole cabinet over. I don't know which would be harder. How much does an LST weigh?DOH! Yeah, a lot easier than fooling with the woofer for a test..They are pretty heavy but not impossible... Link to comment Share on other sites More sharing options...
Carlspeak Posted March 4, 2009 Report Share Posted March 4, 2009 Or you could just flip the whole cabinet over. I don't know which would be harder. How much does an LST weigh?Over 90 lbs. each.I'd still try rotating the woofer even though the push test suggested otherwise. Link to comment Share on other sites More sharing options...
Mexicomike Posted March 4, 2009 Author Report Share Posted March 4, 2009 Yeah - too heavy. I rotated the woofer but the rattle was worse. The woofer is now out and, with it facing upwards, I can a tiny "scronch" sound as I gently move the cone in and let it return The noise is on the 6 0clock side as the speaker was originally mounted. So I GUESS the cone was not properly centered when the speaker surround was replaced. So now I'm wondering if I can work a putty knife under the surround where it is attached to the basket and reposition it....I've never done any speaker surround replacement but I guess the worse thing that can happen if I try to reposition the existing surround is that it won't work and I'll have to learn how to replace a surround!Also, more bad news for that same LST...one of the tweeters (same speaker) is not working. Since there are 4 of them, I didn't notice at all when it quit working. I'm sure I checked them all when I got the speakers - I remember listening to each tweeter through a cardboard tube - but obviously at some point it quit OR, I didn't check as thoroughly as I thought. But with the 1.5 v battery to speaker wires test, no sound out of that tweeter. Bummer... Link to comment Share on other sites More sharing options...
Mexicomike Posted March 4, 2009 Author Report Share Posted March 4, 2009 Little more info re the tweeter. I removed it and rechecked with the battery. There IS some sound but at a much reduced volume than the other tweeters. I measured the resistance - 6.5 Ohms as opposed to 3 on one of the good tweeters. What causes resistance to go up in that situation? I can understand a burnt out (broken wire) coil with infinite resistance or a shorted coil with extremely low resistance but how can a coil go from the correct rating, 3 Ohms, up to 6.5? Now I'm wondering if this tweeter was an incorrect replacement previously. It looks exactly like the others....There is a smeared white ink stamped number on the back that APPEARS to be 561 8435 but some of the numbers are difficult to read. None of those numbers correspond to AR part numbers for the tweeters used in the 3a or LST as listed in the AR3A restoration guide. But it LOOKS identical to the tweeter shown as A19 in the guide. Link to comment Share on other sites More sharing options...
Carlspeak Posted March 4, 2009 Report Share Posted March 4, 2009 Bummer on the tweeter. You may have an 8 ohm version there. It does look just like the 4 ohm unit.If your very careful, you may be able to lift the surround off all around the outer shim. Don't use a sharp tool. Use a dull, but thin one. Work around the edge until you find a spot where it lifts easily and start there. Once you get it started, you can work the tool sideways whilst rocking it to get the surround to lift up. New surrounds are pretty tuff. Once you get it completed lifted, I suggest you remove the DC and shim the VC before you try re-gluing it. Especially if this is your first time messing with surrounds.Good luck. Link to comment Share on other sites More sharing options...
Mexicomike Posted March 4, 2009 Author Report Share Posted March 4, 2009 Got the surround unglued and the dustcover off, both with no damage. Here's a pic. The surrounded is folded down between the cone and the edge of the basket so I could scrape the glue off the mounting surface. Surround and mount surface is now clean so I'm ready to shim the voice coil and reglue. I'll do a search on shimming... Link to comment Share on other sites More sharing options...
Mexicomike Posted March 4, 2009 Author Report Share Posted March 4, 2009 OK, shims are in...nothing to that! BUT...what kind of glue should I use for the surround to basket. Searches yield everything from superglue to silicone including "special speaker surround glue." Can't believe any adhesive company makes a glue that is ONLY for speaker surround gluing. I was planning to use contact cement which seems to be what was used when the surrounds were installed previously. Link to comment Share on other sites More sharing options...
Carlspeak Posted March 4, 2009 Report Share Posted March 4, 2009 You can use Aileen's tacky glue found at craft stores. If you can find something about .010 inches (10 mils) thick, cut it slightly smaller than the circumference of the voice coil and set it down in the gap good and tight to the bottom. A business card sometimes works. Lift the cone and apply the glue to the frame shim and lower the cone STRAIGHT down until the outer flange of the surround meets the glue. Gather up a whole lot of clothespins and put them all around to clamp the surround to the frame shim.Then, gently pull the VC shim up and out and stroke the cone up and down and listen carefully for any rubbing. There shouldn't be any. IF successful, make a loop of masking tape and attach it to the top of the dust cap and apply some Aileen's to the lip of the DC and glue it in place.The Aileen's doesn't set quickly, so you have time to remove the clothespins, lift the surround, re-shim and start over again before it dries.Good luck! Link to comment Share on other sites More sharing options...
Mexicomike Posted March 4, 2009 Author Report Share Posted March 4, 2009 Thanks Carl! Turns out my wife had a tube of the Aileens! Sometimes the karma is perfect. Anyway, the surround is now glued back in place and the voice coil moves in/out perfectly smoothly without the slightest rubbing at all. I couldn't use business cards - they were too thick so I used some wallpaper - worked great. I've read that folks do this without shimming but based on my first experience with this, I agree with your advice to shim since it seems like an essentially bulletproof method. I'll glue the dustcap back on later this eve and tomorrow the woofer should be back in place and rattle-less! Guess the only thing to do about the tweeter, which as you suggested, must be an incorrect 8 Ohm replacement, is try to find a proper 4 Ohm replacement on Ebay. As I said earlier, it does work, contrary to what I first thought, playing at a much lower volume than the other 7 in the two LSTs. And since the Ohm reading is essentially double what the others are, it MUST be an 8 Ohm tweeter. But where did AR use an 8 ohm version of the 3a tweeter circa 1972?Oh...thought I'd add: Carl, your advice for the tool to "unstick" the surround was excellent, dull but thin. I used a .006 feeler gauge! Link to comment Share on other sites More sharing options...
genek Posted March 4, 2009 Report Share Posted March 4, 2009 Guess the only thing to do about the tweeter, which as you suggested, must be an incorrect 8 Ohm replacement, is try to find a proper 4 Ohm replacement on Ebay. As I said earlier, it does work, contrary to what I first thought, playing at a much lower volume than the other 7 in the two LSTs. And since the Ohm reading is essentially double what the others are, it MUST be an 8 Ohm tweeter. But where did AR use an 8 ohm version of the 3a tweeter circa 1972?The 8 ohm version of the 3/4" dome tweeter was used in the 2ax, 5 and LST2. Link to comment Share on other sites More sharing options...
Mexicomike Posted March 4, 2009 Author Report Share Posted March 4, 2009 The 8 ohm version of the 3/4" dome tweeter was used in the 2ax, 5 and LST2.And I hate 'em for it. AR should have used ONLY 4 Ohm drivers, as God intended! Link to comment Share on other sites More sharing options...
genek Posted March 5, 2009 Report Share Posted March 5, 2009 And I hate 'em for it. AR should have used ONLY 4 Ohm drivers, as God intended!I dunno. There does seem to be a way lower incidence of people blowing the 8 ohm units... Link to comment Share on other sites More sharing options...
Mexicomike Posted March 5, 2009 Author Report Share Posted March 5, 2009 Here's a pic of the woofer back together and some pics of the tweeter. Again, how could anyone tell whether its 4 or 8 ohm without measuring? It's identical to the 4 Ohm. RE part numbers...there are no part numbers on any of the tweeters that correspond with the part numbers listed in the AR3 resto guide. All the other tweeters measure around 3 Ohms but none of them have part numbers like those in the guide. Where would these part numbers be located? Link to comment Share on other sites More sharing options...
RoyC Posted March 5, 2009 Report Share Posted March 5, 2009 Here's a pic of the woofer back together and some pics of the tweeter. Again, how could anyone tell whether its 4 or 8 ohm without measuring? It's identical to the 4 Ohm. RE part numbers...there are no part numbers on any of the tweeters that correspond with the part numbers listed in the AR3 resto guide. All the other tweeters measure around 3 Ohms but none of them have part numbers like those in the guide. Where would these part numbers be located?Hi Mike,I have never seen the part numbers stamped on the front-wired tweeters...only manufacturing codes/dates. The 4 and 8 ohm tweeters (part #'s 200013-1 and 200013-2 respectively) were indeed identical. The only way to tell the difference is by measuring them. (The 8 ohm version was discontinued in the late 70's, and the 4 ohm version was used in conjunction with a 4 ohm series resistor to replace it.) The same issue exists with the 4 ohm AR-3a/LST and the 8 ohm AR-5/LST2 midrange drivers. I have seen a number of 8 ohm mids passed off as "AR-3a/LST" midrange replacements on Ebay.Roy Link to comment Share on other sites More sharing options...
genek Posted March 5, 2009 Report Share Posted March 5, 2009 Here's a pic of the woofer back together and some pics of the tweeter. Again, how could anyone tell whether its 4 or 8 ohm without measuring? It's identical to the 4 Ohm. RE part numbers...there are no part numbers on any of the tweeters that correspond with the part numbers listed in the AR3 resto guide. All the other tweeters measure around 3 Ohms but none of them have part numbers like those in the guide. Where would these part numbers be located?In the pre-Teledyne period or the early Teledyne period when old stock was still being exhausted, most likely on the boxes the drivers came packed in from the OEM vendor and on labled stock bins on the factory floor. These weren't considered "user serviceable" parts at the time. Link to comment Share on other sites More sharing options...
Mexicomike Posted March 5, 2009 Author Report Share Posted March 5, 2009 In the pre-Teledyne period or the early Teledyne period when old stock was still being exhausted, most likely on the boxes the drivers came packed in from the OEM vendor and on labled stock bins on the factory floor. These weren't considered "user serviceable" parts at the time.The tweeter needs to be replaced with the correct 4 Ohm version but it really doesn't make any obvious difference between the speakers as currently placed. I guess that's the good thing about having 3 other tweets in each speaker. LST is back together (with the 8 ohm tweeter) and the woofer is completely noise free now, no rattle at all with that 30HZ tone. Thanks again Carl for the advice - ended up being a pretty quick repair. Now it's just an ebay search which will hopefully turn up a tweeter at some point. I'd hate to do anything else...I don't want 8/9ths of an AR LST! Link to comment Share on other sites More sharing options...
Guest oldfart Posted March 6, 2009 Report Share Posted March 6, 2009 hola genlemen, ,that 4 or 8 or whatever ohm, is NOT the DC resistance.....it has to be impedance, and that is the AC resistance, mostally existing out of a combination, of inductance capacitance and eventua&lly an amount pure resistive.....sound is ac, not dc,so ijn combination with the x-over , well it might be correct, the dc method is only suitable to check if the voice coil is burnt out....hint, go check differences in the cross over, it is possible that the x-over will be somewhat different, and thus the xover corrects the situation, just an idea that came up greetzz luc Link to comment Share on other sites More sharing options...
genek Posted March 6, 2009 Report Share Posted March 6, 2009 that 4 or 8 or whatever ohm, is NOT the DC resistance.....The DCR of the 4 ohm rated tweeter usually measures between 2.5 and 3 ohms; the 8 ohm rated between 5 and 6 ohms. Link to comment Share on other sites More sharing options...
Mexicomike Posted March 6, 2009 Author Report Share Posted March 6, 2009 Re the crossover, all the tweeters are wired to the same two crossover output leads so there is no crossover differences between the 4 tweeters.I don't know diddly about electronic circuits so if I called it resistance when I should have called it capacitance or something else, I apologize. The ohm reading on the MM showed 3 of them for the "loud" tweeters and 6.5 of them for the "weak" tweeter. Link to comment Share on other sites More sharing options...
genek Posted March 6, 2009 Report Share Posted March 6, 2009 Re the crossover, all the tweeters are wired to the same two crossover output leads so there is no crossover differences between the 4 tweeters.I don't know diddly about electronic circuits so if I called it resistance when I should have called it capacitance or something else, I apologize. The ohm reading on the MM showed 3 of them for the "loud" tweeters and 6.5 of them for the "weak" tweeter. "Resistance," "DC resistance" or "DCR" are correct for the MM measurements you made. Link to comment Share on other sites More sharing options...
Guest pbda Posted March 9, 2009 Report Share Posted March 9, 2009 Yesterday I was playing some low freq tones through my LSTs at not-loud levels, using my SPL meter to figure out standing wave areas in the room. At the 30HZ tone, the woofer in the left channel also produced a bit of rattle. I had never heard it with music but it was quite apparent with the tone. The volume of the tone itself is not diminished compared to the other woofer. I assume that the rattle is caused by the voice coil rubbing. The woofer surrounds were replaced before I bought them so I'm wondering if perhaps they were not centered properly. I have to admit that since I can't hear it at all with music I'm wondering whether to even bother messing with it. Will it get worse/cause more serious problems?Any thoughts/suggestions...Leave it alone, fix it?I've got a similar problem with one of my woofers as well (it had been reconed at some point). It's only obvious when playing organ music, or heavy acoustic bass. I've spoken to Carl about it; he feels that it's fixable, but will require yet another reconing. I may leave well enough alone. Link to comment Share on other sites More sharing options...
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