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Help me pick a replacement tweeter! (KEF 107)

J

judgeschreber

Well-Known Member
I picked up a pair of beautiful KEF 107s at an estate sale this weekend, but one of the tweeters is blown.

Apparently the KEF-authorized replacements are overpriced and bad-sounding. (This according to most message boards I've checked out).

There's a few posts here and elsewhere that recommend the vifa MG27, but those are unobtainable now.

So, here are my options (I've attached spec sheets below):

1) Morel MDT29 (Wilmslow Audio in England recommends these, but the specs don't make sense)
2) Fostex FT28D (these have also been used by some people, but again the specs don't make sense to me)
3) Vifa DX25 (these look the best on paper, but the cutout diameter is 1/8" too large)
4) Vifa XT25 (these also look good, and they will fit, but the impedance curve is much different - does that matter?)

Here are some specs for the KEF T33 SP1210 that the new tweeter will be replacing:

Crossover Frequency: 2500 Hz
Nominal imp: 4 ohms
Frequency Range 3-20 kHz
Sensitivity: 93 dB
MMS: .3g
RMS: 1.0
CMS: .51x10E-4
FS: 1280 Hz
QM: 2.41
QE: 1.52
QT: .93


The impedance curve peeks at 1280 at around 8 ohms, and dips to just under 4 ohms between 2500 and 5000.

I have a full spec sheet for the KEF driver, but I don't think I'm supposed to post it here. I will gladly email it to anyone who desires it.

Thanks!
 

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That looks like another good contender - and the price is right too!

I took apart the old tweeter that doesn't work, and the ferro fluid is hardened. So, while the working one sounds pretty good right now, I suspect it isn't in spec. It will be nice to have it to compare against, though, so that I can know if I'm heading in the right direction with the replacement.
 
judgeschreber said:
That looks like another good contender - and the price is right too!

I took apart the old tweeter that doesn't work, and the ferro fluid is hardened. So, while the working one sounds pretty good right now, I suspect it isn't in spec. It will be nice to have it to compare against, though, so that I can know if I'm heading in the right direction with the replacement.
Click to expand...

I'd compare with the working tweeter as is, then if the match is reasonable see if you can remove the ferro fluid. You might even see if Madisound will simply add new ferro fluid or sell you a small amount. Is the bad tweeter just frozen due to the ferro fluid or is it also open circuit?
 
Pete B said:
I'd compare with the working tweeter as is, then if the match is reasonable see if you can remove the ferro fluid. You might even see if Madisound will simply add new ferro fluid or sell you a small amount. Is the bad tweeter just frozen due to the ferro fluid or is it also open circuit?
Click to expand...

The bad tweeter is an open circuit, so there's no possibility of rehabbing it.

I was planning to compare it to the working tweeter as is, but that's a good idea to try to remove the old ferro fluid and maybe even replace the fluid. I've read on other forums that this never quite gets them back to their original condition, but it might be pretty close.
 
judgeschreber said:
1) Morel MDT29 (Wilmslow Audio in England recommends these, but the specs don't make sense)
Click to expand...

Sensitivity looks pretty low. I would think you'd have to rework a tweeter pad if there is one. Does the speaker have a tweeter adjustment?

What doesn't make sense to you?

2) Fostex FT28D (these have also been used by some people, but again the specs don't make sense to me)
Click to expand...

Lower sensitivity and higher impedance.

3) Vifa DX25 (these look the best on paper, but the cutout diameter is 1/8" too large)
Click to expand...

They do look good. Up to you whether or not to modify the cabinets.

4) Vifa XT25 (these also look good, and they will fit, but the impedance curve is much different - does that matter?)
Click to expand...

The impedance curve probably won't matter all that much in this case. The fact that the resonance peak is higher will be buried by the crossover. It's well below the cutoff. In the crossover region it seems to be about the same as the original. Sensitivity is a little lower but not drastically. Might be audible, might not depending on the room, the crossover, etc. Again, a tweeter adjustment would make a big difference here.

Ray
 
RayW said:
Sensitivity looks pretty low. I would think you'd have to rework a tweeter pad if there is one. Does the speaker have a tweeter adjustment?

What doesn't make sense to you?



Lower sensitivity and higher impedance.



They do look good. Up to you whether or not to modify the cabinets.



The impedance curve probably won't matter all that much in this case. The fact that the resonance peak is higher will be buried by the crossover. It's well below the cutoff. In the crossover region it seems to be about the same as the original. Sensitivity is a little lower but not drastically. Might be audible, might not depending on the room, the crossover, etc. Again, a tweeter adjustment would make a big difference here.

Ray
Click to expand...

It's not the specs that don't make sense, its the fact that people seem to call both the Morel and Fostex a drop-in replacement, when they are both quite different in terms of sensitivity and impedance.

There is no tweeter adjustment, unfortunately. The external "Kube" processor has adjustments for bass response, including a "contour" adjustment, that pads down (or increases) the woofer level. So although I'll be able to lower the bass level a bit, the midrange-tweeter balance is fixed.

It's good to know that the impedance curves won't matter too much. I was also thinking that the spike would be buried by the crossover, but I was worried that the existing crossover might have been designed with the tweeter's particular fs in mind, and that a new tweeter with a much lower resonance would change the crossover's function.

Thanks for the nice response!

The AC25 that Pete B posted looks the closest that I can find to the original, but if the resonance curves don't make that much of a difference, I may be leaning towards the smoother-looking XT25 or DX25 (although the cost difference is significant).

Maybe I'll buy a pair of each, and return all but the best pair. . .
 
Haven't taken the time to try to compare specs, sizing, etc., but perhaps take a look at Hiquphon tweeters to see if any of those would work (not a big selection to review).

They're not too common, but I really like the sound of them in some DIY speakers I have.
 
whoaru99 said:
Haven't taken the time to try to compare specs, sizing, etc., but perhaps take a look at Hiquphon tweeters to see if any of those would work (not a big selection to review).

They're not too common, but I really like the sound of them in some DIY speakers I have.
Click to expand...

Thanks for the suggestion - I checked those out, but unfortunately, like the Morels and Fostex, they aren't sensitive enough, and the impedance is too high.
 
Just curious, which tweeter did KEF recommend? I have a KEF SP1239, 4Ω, sitting here.

Yes, I know you need two. If GordonW doesn't jump in on this thread soon, PM him. The older KEF Reference Series crossovers were amazingly complex, and part matching between each pair of speakers was about as anal as you could possibly imagine. He's heard my pair of KEF 104/2 before, and recently, so he'll have a good ear for what tweeter will work.

By the way, if you happen to run across an auction listing for the head units of a KEF 105 of any of the various iterations, don't bother. The 105 used the T55 tweeter.

Also, if the bolt pattern on the VIFA DX25 matches the T33, you can switch the faceplates.
 
I'm also looking for a replacement as one of the T33 drivers in my 104/2's is not working (it is working, but you have to be right next to it to hear anything). I've seen people recommend the Vifa MG27s, but since they're not making them anymore, they're hard to find. The DX25's are what Madisound says people are using and according to the specs I've seen, they're a couple mm narrower than the MG27's. The problem may be that they're also a couple mm deeper, so may not fit under the wood block that holds the speaker in place. Has anyone installed the DX25's?
 
BrassTeacher said:
Just curious, which tweeter did KEF recommend? I have a KEF SP1239, 4Ω, sitting here.

Yes, I know you need two. If GordonW doesn't jump in on this thread soon, PM him. The older KEF Reference Series crossovers were amazingly complex, and part matching between each pair of speakers was about as anal as you could possibly imagine. He's heard my pair of KEF 104/2 before, and recently, so he'll have a good ear for what tweeter will work.

By the way, if you happen to run across an auction listing for the head units of a KEF 105 of any of the various iterations, don't bother. The 105 used the T55 tweeter.

Also, if the bolt pattern on the VIFA DX25 matches the T33, you can switch the faceplates.
Click to expand...

The DX25 has three screws holding the faceplate on while the T33 has four. From what I've seen, the faceplate comes off anyway. Can anyone confirm this?
 
I have been doing a little digging around looking for new replacement tweeters for KEF SP1210's, in case my current replacements (KEF SP1349+) fail and they are no longer available. The Tang Band 25-1166SJ looks like a possibility, although the sensitivity (90dB) is a little low.
 
An old thread I know, so perhaps too late fo you guys but for others:

I recomend the Scan Speak 9300/9500/9700 tweeters.

Firstly, they have the EXACT same mounting holes so can be used with the original Kef, square mounting plates (one thing to you do need to do is widen the centre hole by 1 mm by running sandpaper evenly around the inner rim).

Secondly, from memory anyway when I was checking it all out, they have the same impedance plots as the T33, peaks and troughs match up. Same crossover frequency.

The only caveat is that the nominal impedance and sensitivity were different BUT (again from memory) these work together to cancel each other out in output level terms i.e. were more sensitive but also harder to drive.

The frequency plots were also very similar but of course the 9700 going on to 35KHz.. no need for super tweeters here!

I say all from memory as I did lots of research for upgrades for my Kef 107s but after buying some secondhand 97000s, I never finished the project - still waiting for my attention.

search out the Scan Speak specs and T33 specs and take a look - I've a strong suspicion that the similarities were intentional. They are expensive but have a great reputation.
 
judgeschreber said:
There's a few posts here and elsewhere that recommend the vifa MG27, but those are unobtainable now.
Click to expand...

The MG27 are still available at Solen in Montreal for under $30 each.
I am about to purchase a set to store away, for my Kef 107. Just in case.

http://www.solen.ca/pub/cms_nf_catalogue_fiche.php?id=617&nobut=1

http://www.solen.ca/pub/cms_nf_catalogue_fiche.php?id=647&nobut=1

mg27sg.jpg
 
reviving a very old thread....
I just picked up a pair of 107's and need to replace a tweeter...any new info or recomendations for drop in replacements?
Ed
 
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BTW, if you have issues with distortion, or cutting out of any drivers on KEF 107s, before you jump to any conclusions, pull the lower woofer out (from the bottom), and check the connections on the inside of the binding posts. KEF used eyelets on the internal wiring, and the nuts that secure them to the binding posts tend to loosen over time. A distorted, or even completely inoperative tweeter, may just be a loose connection... I learned this only after recapping the crossovers, and still having an issue with my RT tweeter. On closer inspection, ALL of the nuts on the binding posts (eight, in the case of my 107/2s) were loose! Not even close to finger tight!! Tightening the posts to the cabinet, and all the nuts to the posts, brought back crystal clarity to the tweeters.
 
frommerstop said:
BTW, if you have issues with distortion, or cutting out of any drivers on KEF 107s, before you jump to any conclusions, pull the lower woofer out (from the bottom), and check the connections on the inside of the binding posts. KEF used eyelets on the internal wiring, and the nuts that secure them to the binding posts tend to loosen over time. A distorted, or even completely inoperative tweeter, may just be a loose connection... I learned this only after recapping the crossovers, and still having an issue with my RT tweeter. On closer inspection, ALL of the nuts on the binding posts (eight, in the case of my 107/2s) were loose! Not even close to finger tight!! Tightening the posts to the cabinet, and all the nuts to the posts, brought back crystal clarity to the tweeters.
Click to expand...

Sorry to dig up an old thread, but Frommer, you just saved me a lot of hassle, I think! On one of my 107's, I had already tightened up the speaker terminals...that speaker would cut out every now and then...it would cut out COMPLETELY.

Now, I was hearing distortion in the tweeter...very static-y, spitty, distortion. Everything else sounded okay to me though (the mids and bass). I thought it had to be the tweeter. I took the tweeter out, was going to ohm it out but my meter needs a battery. Was going to swap it over to the other speaker to see if the problem followed the tweeter...but it was getting late. So I research and find this and this morning take my speaker apart...sure enough, loose speaker terminal!!! (In the other speaker, the one I didn't already tighten it down on previously). Haven't put it back together yet so can't confirm this was the only problem, but I highly suspect it is going to fix the issue. Great news (I think/hope)!

EDIT - Also forgot how much of a B**** it is to hook those orange and purple woofer wires back up. I understand why they don't use longer wires, but sometimes I wish they would! It's going to be my lunchtime project, hopefully an hour will be long enough, lol! If anyone who's done it has any tips...I'm thinking I'm going to put a piece of tape on the orange wire, so I can tell which wire is which, by FEEL rather than sight...since once you have the woofer in the hole, you can't see what you're doing at all, and the wires aren't long enough to attach with the woofer not yet in place.

Another EDIT - would it be terrible to extend these wires to the woofers? Or I could completely replace the wire, going all the way back to the crossover, but that requires more disassembly. I'm having no luck at all getting this woofer connected. That hour lunch break wasn't long enough. Getting pretty frustrated by it! I have extended wires like this in some other speakers. I have some 12 gauge wire around, which is bigger than the wire currently going to the woofers. Any problem with using larger wire to splice? And to do the splice, I'm guessing soldering is the only "proper" way here, right? No wire-nuts or anything allowed? I may worry about the wire nuts vibrating too much, plus it would look like crap (even though you'd never see unless you took it apart...)!
 
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