044Ti Deterioration in 250Ti

[kmanusa]

I've had my 250Ti since 2011 and they have given me very little trouble since then thanks in no small part to advice obtained here.

But now things have changed. I also own a pair of Martin Logan CLS 1 and Kinergetics SW-800 subs. Last summer I set them up in place of the 250Ti just to give a listen. The CLS sound quite nice but recently I began to become a bit disenchanted with their limitations (lack of dynamics, impact). And since we are getting ready to do some major home renovation and I expect quite a bit of dust floating around the house (not good for ESLs), I decided to pack up the Martin Logans and move the good old 250Ti back into my system.

Listening to the 250Ti, I was startled to hear a kind of noisy, hissy distortion coming from both 044Ti tweeters. Judging from what I've read, I assume this is the dreaded tweeter damping foam rot syndrome. I thought I had it a couple of years ago but I swapped out my original drivers for a spare set and that seemed to be an improvement but I guess the replacements have it now too. For the record, the distortion is not always there, it's audibility depends on source material, and to a much lesser degree the electronics I use with the speakers. But it looks like I've come to the end of the line with these tweeters as they are. I tried putting the old drivers back in but to no avail-- they all seem to have this distortion. Maybe it was always there but perhaps it took using the other speakers for me to hear it clearly when I switched back to the JBLs.

My question then is what next? It would seem most of us with original 250Ti are in the same boat-- 25-30 year old systems with tweeters that can't easily be replaced and uncertain prospects for repair or refurb. Has anyone found suitable replacement drivers or an outfit that can refurb these?

[gferrell]

Have you tried to replace the foam under the domes? I did it on some 035tia and it was pretty easy. Maybe worth a try.

[SEAWOLF97]

here's how to do it.

http://www.audioheritage.org/vbulletin/showthread.php?29325-044Ti-questions-Help-needed&highlight=044ti+help

[kmanusa]

here's how to do it.

http://www.audioheritage.org/vbulletin/showthread.php?29325-044Ti-questions-Help-needed&highlight=044ti+help

I seem to recall having read that thread before but thanks for bringing it to my attention, it was instructive to read it again. I guess my main concern is taking the tweeter apart, my eyes (and hands) are not what they once were for doing that sort of delicate work. But I guess if there are no other viable options, I might take a swing at it. I do have 4 drivers total so I suppose the worst case would be if I hosed up 2 of them.

Was there ever consensus on whether replacement foam should touch the diaphram?

I did find one online repair place (in Florida) that claims it can refurb 044 series drivers including Ti versions for $125 I think. That might be another option if they are still offering the service.

[SEAWOLF97]

I seem to recall having read that thread before but thanks for bringing it to my attention, it was instructive to read it again. I guess my main concern is taking the tweeter apart, my eyes (and hands) are not what they once were for doing that sort of delicate work. But I guess if there are no other viable options, I might take a swing at it. I do have 4 drivers total so I suppose the worst case would be if I hosed up 2 of them.

Was there ever consensus on whether replacement foam should touch the diaphram?

I did find one online repair place (in Florida) that claims it can refurb 044 series drivers including Ti versions for $125 I think. That might be another option if they are still offering the service.

I'm abt to turn 66 and understand , but it's easier than the thread makes it look like.

using G's help, I made the foam abt a 1/4 in. too tall and let it squish down a bit. Worked well.

[gferrell]

I used egg crate type foam and cut it so just the rounded part just touched the dome.

[kmanusa]

I used egg crate type foam and cut it so just the rounded part just touched the dome.

Interesting, egg crate type foam-- isn't that a kind of styrofoam? After outfitting your tweeters with that material, what difference did you notice, if any, in the sound of the tweeters?

Just out of curiosity-- what kind of symptoms were your tweeters exhibiting before you reworked them? How easy (or hard!) was it to clean out the old rotted foam from the tweeter gaps once you got them apart?

[gferrell]

The foam I used was not styrofoam. It is the type that you may find in a mattress pad or packing material. I did not find any in the VC gap. I just cleaned the old foam off of the magnet. It was more "gooey" than crumbly. It looks like it degrades and shrinks. The reason I did it was preventative. I was not having a problem. Like Seawolf said I made it about 1/4 in. too tall and let it squish down a bit. I think it was made for dampening which may be why you are hearing a difference. Good luck.

[gferrell]

Here is the foam I used. It is just the right size with a rounded top that fits the dome just right. If you need some I can send you some.
64539

[kmanusa]

Here is the foam I used. It is just the right size with a rounded top that fits the dome just right. If you need some I can send you some.
64539

Ah, now I see what you are saying, thanks for the picture. In fact I think I have some of that material, I saved it for packing purposes. Thanks just the same for offering to send me some, I've always been impressed with how helpful LH members are!

I guess I have to set aside some time to do this project. One thing I've noticed about this problem with the tweeters is that it is not always apparent. It seems to be most annoying with music containing chorus singing unaccompanied. With some jazz and rock music, it may not be apparent at all. Also, for some reason I am less bothered by it when I orient the speakers with tweeters pointing directly at me-- it seems that off axis it sounds worse. Strange, these effects must be due to the undamped resonance in the tweeter.

[DavidF]

Unfortunately you do have to take them apart to confirm the foam goo problem. It was not too difficult for me but some caution be taken. Here are some recommendations.

You will want a constant tone source. When replacing the voice coil assembly it really helps to have a tone playing. When the coil is not centered you can tell by the distorted tone. The cheapest way is a CD disc with tones (1,000 Hz or so). Obviously you will need to have a feed from the amp. In the past I took the feed off the upper mid of the 250Ti network. The tweeter feed cuts off too high to get much signal around 1,000 Hz. Taking the feed directly off the amp would risk a short and too much current flow. Don't need a lot of volume that would risk the tweeter for this purpose.

When pulling the protective screen from the tweeter take care not to use too much pressure that will distort the shape. Once the rubber gasket is removed (if it's old it will come out in pieces) there is still a little tension on the screen, some from a any glue residue and the some from the magnet. Just take your time and work all the way around to pull it off. Tweaked paper clip or needle pliers.

The four screws holding the face plate to the magnet assemble should not be over-tightened. When replacing them screw in each a little at time and work them down in opposing order. With tone playing during this operation you can hear when one side of the coil may be rubbing. You will want to hear a pure tone at all times. If you have all screws tight and don't hear a pure tone, you need to back out the screws a bit until you have a pure tone and restart the tightening process.

The photos below show the dimension of the original foam plug used.

6457464573

[kmanusa]

Thanks for the information David, very informative. In looking at the o-ring and metal protective mesh screen, it appears it might be easy to mar the metal finish of the driver or the screen by probing with a sharp metal object to pry off the o-ring or mesh. Would a toothpick work or is that not rigid enough to pry off the o-ring and mesh? I guess it is not clear to me how the o-ring keeps the mesh in place.

Thanks for the tip about using a tone to tighten the screws, it never would have occurred to me to do that. I do have an HP audio oscillator, I could use a little high pass filter network to drive the tweeter with the HP through the filter. In looking at the tweeter networks used in the 240Ti and 18Ti, it appears a series 3uF cap and a shunt resistor of 8-10 ohms should be sufficient. Using that network I think I would use a 2 or 3 kHz tone from the HP.

From the pictures it looks like the foam plug is a cylinder roughly 1 inch in diameter and about a half inch depth from the pictures. I guess this will have to be cut out of a larger piece of foam.

[macaroonie]

The O ring provides friction to hold the mesh in place , that's it. If you get one of those micro screwdrivers that you get in the little sets , the smallest will pop thru the mesh and allow you to lever it up and out. Do this as near to the O ring as you can. If it doesn't give way at the first place you try move around a bit till it gives easily.
I've done dozens like this with no damage.

[DavidF]

Thanks for the information David, very informative. In looking at the o-ring and metal protective mesh screen, it appears it might be easy to mar the metal finish of the driver or the screen by probing with a sharp metal object to pry off the o-ring or mesh. Would a toothpick work or is that not rigid enough to pry off the o-ring and mesh? I guess it is not clear to me how the o-ring keeps the mesh in place.

Thanks for the tip about using a tone to tighten the screws, it never would have occurred to me to do that. I do have an HP audio oscillator, I could use a little high pass filter network to drive the tweeter with the HP through the filter. In looking at the tweeter networks used in the 240Ti and 18Ti, it appears a series 3uF cap and a shunt resistor of 8-10 ohms should be sufficient. Using that network I think I would use a 2 or 3 kHz tone from the HP.

From the pictures it looks like the foam plug is a cylinder roughly 1 inch in diameter and about a half inch depth from the pictures. I guess this will have to be cut out of a larger piece of foam.

My take on the measurements is that the left side of plug, as shown in both pictures, is on the 3" line. The camera angle is shifted to the right to give a clear shot of the total measurement. So you have 7/8ths in dia. and 3/8ths in depth.

I think that a 3uF cap provides a cutoff too high. You could double that value. I would not think that the shunt resistance is useful. If the HP allows for a tone sweep then by all means complete a full sweep from 2K to 20K.

[kmanusa]

David, you are correct, a cap value of 3uF is too low for this application; a 10uF cap should do and I have one in my parts junk box. I have not seen any published spec on the impedance of the driver over its freq range. DCR is fairly low so I would expect the low freq cutoff to be in the 4kHz region using the 10uF cap in the HPF. Have you run a freq sweep of the 044Ti up to 20kHz? I would expect it to be fairly clean at an appropriately low drive level assuming no fouling of the gap.

[DavidF]

David, you are correct, a cap value of 3uF is too low for this application; a 10uF cap should do and I have one in my parts junk box. I have not seen any published spec on the impedance of the driver over its freq range. DCR is fairly low so I would expect the low freq cutoff to be in the 4kHz region using the 10uF cap in the HPF. Have you run a freq sweep of the 044Ti up to 20kHz? I would expect it to be fairly clean at an appropriately low drive level assuming no fouling of the gap.

I have run sweeps, yes, but nothing recorded as an image. DCR is fairly low, 4.0 ohm +- 0.4 ohms.