Kuja Posted April 1, 2005 Report Share Posted April 1, 2005 A long question, but I badly need your help!!! I just discovered something strange on one of the dome upper midrange drivers on my new (old) AR speakers. I posted few questions on this forum regarding these speakers (AR98LS) but got no answers. I hope that, since this is a more general question about drivers, I will get some help... I really need it since right now, I don't know what to do with the speakers...I bought these speakers few weeks ago. I went to the seller's home to hear them first and they seemed OK. They sounded a little bit aggressive in their upper mids, but since they are smaller brothers of AR9LS, I figured out that they share the known 2kHz peak problem. I planned to modify the crossover (also to replace old capacitors and put some better wire inside) and upgrade them to the 98LSI version that had this problem fixed.Couple of days ago, I found some spare time to play a little bit more with them when I discovered something odd...At some point, I gently touched the upper mid drivers cones on both speakers. I discovered that the driver on the left speaker was vibrating sigificantly stronger than the driver on the right speaker. I switched to tuner and pressed the mono button, but the difference was still there. Sound seems to come from both drivers... I thought that there might be a problem with the crossover, so I switched the drivers between speakers. The difference remained - so the drivers are behaving differently!I examined them more closely and I found out that weaker vibrating driver, when touched, has stiffer surround. It probably doesn't let it vibrate as strong as the other driver does.Then I made some sort of huge headphones, facing the speakers to each other and putting my head between them. I played some mono recordings and it seemed that the speaker that had stiffer driver was a tiny bit louder! I was surprised, since I expected that speaker that had stronger vibrations would produce stronger sound. Then I examined closely the screws on the outer driver plate. After I saw some microscopic specks of missing paint, I started wondering that maybe the stiffer driver was dismantled once, probably repaired.When I normally listen to them, I hear nothing wrong!But surely one of the drivers must be out of spec. Which one?Does it matter? I mean, they are some twenty years old and woofers and lower mids have been refoamed, probably having a bit different T/S parameters, so they are kind out of original spec too...This bugs me big time, since I had big plans with rejuvenating and upgrading those speakers. Now I'm not sure if they are worth it... The big question is: what could have caused the stiffness difference and can it be brought back to normal?PSThis might be of importance also: It seems that the speaker with stiffer driver was exposed more to the sun.The veneer on it is much more faded on top and on one side compared to the other speaker. The white printed lettering on that ugly plastic front face is also noticeably yellower on it...Could sun rays scortch the surround making it stiffer?On the other hand, the domes that are soft, are equally soft on both drivers! I guess that the strong sun would affect them too!Help!!!Here are some pics:http://www.kujucev.com/ar/AR98LS.jpgThe driver assembly in question:http://www.kujucev.com/ar/AR98LS_drivers.jpg Link to comment Share on other sites More sharing options...
Kuja Posted April 2, 2005 Author Report Share Posted April 2, 2005 Update.I took out the drivers again and connected them directly to the amplifier (low sound level of course). Stiffer driver now sounds a bit quieter that the "normal" driver. It is also more thin sounding. I listened to the BBC radio news broadcast and the male voice of the news presenter was a little bit nasal too. The other driver had fuller and deeper sound and it was quite pleasing to listen on its own. Then I tried to make it closer to stiff driver. I pressed gently but firmly with my four fingers against its surround, to limit its movement and imitate the stiffness of the other driver. No matter how hard I pressed (not too hard of course) the sound was still fuller. It got thinner but not thin as the other driver. The good thing is that the stiff driver is at least working... Link to comment Share on other sites More sharing options...
Guest Bret Posted April 2, 2005 Report Share Posted April 2, 2005 I hope you can get a better answer than I'm going to give you. I just hate to let the silence linger.First - yes, this is extremely bad news. I'm sorry it happened to you.Second - if you can move the midrange with your fingers (which I would stop doing immediately), according to everything I've ever known about AR midranges (none like yours, exactly), there is something wrong with it; it is probably shot. The "stiff" one is probably the more correct of the two, BUT the way you describe it gives me pause so I can't "declare" anything.Third - I do not remember ever hearing that anyone can repair it, but that doesn't necessarily mean it can't be repaired. Hopefully someone can give you some reason to be more optimistic.Fourth - As far as I know - there are none of these available new. There are very, very few of them available on eBay very infrequently. You might be waiting a very long time.Fifth - I would call or email AB Tech and ask Alex and company if they know of anything you can do. I'm sure he gets this question frequently enough that there must be a "standard" answer.Sixth - I hope someone will jump in here with better news and correct everything I've just said. You should take my "opinion" with a grain of salt since it is formed with a dangerously small amount of information.Bret Link to comment Share on other sites More sharing options...
Guest Bret Posted April 2, 2005 Report Share Posted April 2, 2005 IF this has the same upper-driver (check, check, check the numbers) you might consider this or something like it:http://www.audioclassics.com/detail.php3?d...R78LS&nav=brandYou could probably find someone who would love to get the other tweeter/mid combination.Where are you, by the way?Bret Link to comment Share on other sites More sharing options...
Kuja Posted April 2, 2005 Author Report Share Posted April 2, 2005 Bret, Thak you very much for your answer.Yes the AR78LS shares the same driver combo.Unfortunately, from buying/shipping perspective, I live in Belgrade, Yugoslavia... I also see a pair of AR98LSI on audioclassics.com!Can you give me any contact to AB Tech, email preferably.I tried Google, but got possibly hundreds of companies with the same name! I'll visit some local repairing shops. Advice from someone who knows the drivers in question will be very useful, since I think this the only pair of these spekears in Yugoslavia.About the stiffer driver being more correct, I don't know, the other one sounds really nice on its own - it is a pleasure to listen to it... I don't know which driver to fix! Or should I rebuild both, so that they match. This way, they might be both out of spec a little bit, but as I said, the other four drivers are refoamed, so they also are not identical to factory new state.Thanks again! Link to comment Share on other sites More sharing options...
r_laski Posted April 2, 2005 Report Share Posted April 2, 2005 >>Can you give me any contact to AB Tech, email preferably.<<AB Tech:Toll free: 1-800-225-9847 Local: 1-508-478-9800Fax: 1-508-478-9816Email: abtechservices@mindspring.comThis info is in the "Library". >>About the stiffer driver being more correct, I don't know, the other one sounds really nice on its own - it is a pleasure to listen to it... I don't know which driver to fix! Or should I rebuild both, so that they match. This way, they might be both out of spec a little bit, but as I said, the other four drivers are refoamed, so they also are not identical to factory new state.<<As Bret said, I don't think those dual dome drivers are rebuildable. It would help if you could get DCR - resistance and L - voice coil inductance measurements to compare.I don't know if this will help, but there is a pair of AR-9 LS/LSI dual domes on eBay. Unfortunately seller states he will only ship within US. If interested, you should contact the seller and see if he willing to ship to you if you bid / win. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...5764009254&rd=1 Rich Link to comment Share on other sites More sharing options...
soundminded Posted April 4, 2005 Report Share Posted April 4, 2005 Switch the dome driver units between the speakers. Be careful to note the color coded connections and write them down so that you get them correct when you reconnect them. Phasing is very important. If the problem moves from one speaker system to the other then the problem is with the driver. If it does not and stays with the same enclosure, then the problem is in the crossover network. I'd send not one but both units to be tested and repaired as necessary. It is not a good idea IMO to ever touch the cone/dome of this type of driver with your fingers. they are very easily damaged. Good luck. Link to comment Share on other sites More sharing options...
roundhome Posted April 14, 2005 Report Share Posted April 14, 2005 >IF this has the same upper-driver (check, check, check the>numbers) you might consider this or something like it:>>http://www.audioclassics.com/detail.php3?d...R78LS&nav=brand>>You could probably find someone who would love to get the>other tweeter/mid combination.>>Where are you, by the way?>>BretBret I got the 78ls from audio classics today but one of the tweeters is bad I will call them tommorrow and see what they have to say about it some times its hard to tell if they are good with the mids so close and the crossover so high but it reads open on the meter so i guess that says enoughI can use the one, as my center until this is resolved then the other will go into the center back. by the way they came in the original box and packing. The glue dried up on the grill cloth but that is no big deal. these tweeter mid plates are not going to be easy to replace as the age. so we need to take good care of them.Jim Link to comment Share on other sites More sharing options...
Pete B Posted May 24, 2005 Report Share Posted May 24, 2005 I wonder if you might have burnt ferro fluid in the stiffer driver:Here's some information concerning burnt ferro fluid:http://www.roger-russell.com/driverst.htm#d095"The voice coil is in like new condition ... found that the ferrofluid has turned to black sludge ... prevent the voice coil from moving and resulting in no output."Has anyone disected one of these drivers, are there voice coil/dome aligning pins so that it goes back together easily?I've worked on dome drivers but not these.Check your crossover for leaky or failed caps that might have caused this failure.Pete B.>Update.>>I took out the drivers again and connected them directly to>the amplifier (low sound level of course). >Stiffer driver now sounds a bit quieter that the "normal">driver. It is also more thin sounding. I listened to the BBC>radio news broadcast and the male voice of the news presenter>was a little bit nasal too. The other driver had fuller and>deeper sound and it was quite pleasing to listen on its own. >Then I tried to make it closer to stiff driver. I pressed>gently but firmly with my four fingers against its surround,>to limit its movement and imitate the stiffness of the other>driver. >No matter how hard I pressed (not too hard of course) the>sound was still fuller. It got thinner but not thin as the>other driver. >The good thing is that the stiff driver is at least working... Link to comment Share on other sites More sharing options...
Kuja Posted June 1, 2005 Author Report Share Posted June 1, 2005 Well, those AR9LS/98LS/78LS dome combo drivers CAN be rebuilt!I've found a guy that runs a speaker repair shop and also makes speakers under his own brand.I told him that everyone I asked (including AB Tech) said that those drivers couldn't be repaired. His answer was that if human hands did assemble something, it can be repaired whatever the problem is! It is only the matter of cost effectiveness.And he repaired them!One unit had no ferrofluid at all! Due to excessive heat, some sort of blisters formed on the spool. He even managed to make a new spool...I asked him to do his thing to all drivers (renew the ferrofluid, etc...). Then we refoamed again all woofers and lower midranges with softer top quality surrounds. Somebody who did prior refoaming, for some reason threw away masonite rings from 12" woofers."My" guy made new ones. He was/is authorized AR repairman for more than 20 years (I think) so he knows what he's doing.Complete overhaul on all eight drivers was around 300 $.They sound much better now. Right now, I'm in the process of rejuvenating the crossover with polypropylene capacitors, some van den hul, some silver litz wire... I'll upgrade them to the 98LSI schematics too.I also found the source of hand made wool felt, so I'll even add the acoustic blanket that was missing on the originals :-)This guy's website is www.sinevoice.com Link to comment Share on other sites More sharing options...
Pete B Posted June 19, 2005 Report Share Posted June 19, 2005 This is good to hear, yes I agree that some drivers can be repaired. I've done it many times over the years, but it is labor intensive and not usually cost effective. About "spools" we call them voice coils, I've also wound replacements but have found recently that there are supply houses that have a large variety of coils where often the right one can be found.I'd like to know the source for the wool felt that you mention?Regards,Pete B.>Well, those AR9LS/98LS/78LS dome combo drivers CAN be>rebuilt!>>I've found a guy that runs a speaker repair shop and also>makes speakers under his own brand.>I told him that everyone I asked (including AB Tech) said that>those drivers couldn't be repaired. His answer was that if>human hands did assemble something, it can be repaired>whatever the problem is! It is only the matter of cost>effectiveness.>>And he repaired them!>>One unit had no ferrofluid at all! Due to excessive heat, some>sort of blisters formed on the spool. He even managed to make>a new spool...>>I asked him to do his thing to all drivers (renew the>ferrofluid, etc...). Then we refoamed again all woofers and>lower midranges with softer top quality surrounds. Somebody>who did prior refoaming, for some reason threw away masonite>rings from 12" woofers.>"My" guy made new ones. He was/is authorized AR repairman for>more than 20 years (I think) so he knows what he's doing.>>Complete overhaul on all eight drivers was around 300 $.>>They sound much better now. Right now, I'm in the process of>rejuvenating the crossover with polypropylene capacitors, some>van den hul, some silver litz wire... I'll upgrade them to the>98LSI schematics too.>>I also found the source of hand made wool felt, so I'll even>add the acoustic blanket that was missing on the originals>:-)>>This guy's website is www.sinevoice.com> Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.