SpeakerTalk

[Thierry]

Hi,

Haven't been around for a while, but I'm happy to see there's (little) activity in here.

I have a question for KEF experts : I have always thought the B200 SP1256 fitted in the KEF104/2 had a foam "donut" (which of course becomes a concern after so many years). It happens that have been given a mint pair of 104/2s (yes, I'm very lucky) and to my surprise I see that the B200s have a rubber donut instead of the usual foam model

Now my question : could this be a retrofit or a repair performed by an authorized KEF workshop, since it seems it has been done professionnally, or did KEF themselves changed switched to rubber during the 104/2 production life ?

Of course, the T33s need an oil change, treble is reproduced as if there was a thick blanket in from the speakers, but I shall receive fresh ferrofluid in a few days from this company https://media2.supermagnete.fr/docs/MFR-DP1-TDS.pdf

Thanks fro your insights.

T.

[speakerguru]

[Thierry]

SpeakerGuru, thank you very much for clarification.

I have started to check every bit of the 104/2s just to find that the tweeters are in fact dead. They weren't fried due to abuse, but most likely from corrosion. The miniscule leads connecting one of the terminals to the voice coil are broken. Maybe they can be repaired, but I doubt about it.

I took pictures of the disaster, look at the last two shots https://photos.app.goo.gl/1im8Q6bWkRK7CmBA9

I have started searching alternative solutions, surprisingly enough there are some :

- Audax TW025A2 - 4 ohms https://www.falconacoustics.co.uk/audax-tw025a2-kef-t33-tweeter.html

- Chinese copies of the T33 https://www.midwestspeakerrepair.com/shop/home-audio/tweeters/dome/mw-audio-mt-1191-1-inch-dome-tweeter-for-kef-104-2-speaker/

Or even cheaper : only replace the diaphragm, which I'm 100% sure is the one used in the "T33 erstatz" sold by Midwest Repair : https://www.ebay.com/itm/1pair-Silk-Diaphragm-for-the-KEF-104-2-Speaker-SP1191-4Ohm-Tweter/272558474964?

I know that none of these alternatives are really satisfying since KEF did match the crossover components to each driver used in the Reference Series, but I am saying to myself that a imperfect 104/2 is preferable to a mute 104/2.

As usual, suggestions and advises are much appreciated.

Thierry

[ebf]

I went for the midwest speaker T33 China replica, while I was trolling the used marked for a spare one, as one of mine worked, and the other was blown/burnt (and I could not find/see where).

At first they sounded real harsh, and was unbearable to listen to in my opinion.
But after break-in, they now sound very OK, and I have not spent any time thinking about changing them for my restored T33s pair that I now have... I guess they are replicas, but made very close to match the KEF T33 specs...?!?!

One day I will do the swith, and I will hear how they (104/2) are supposed to sound, but for now, Its all OK.

[Thierry]

Thanks for your feedback.
The T33s finally went to a repair shop to try salvaging them. After they will be reinstalled I'll make measurements to check frequency response.
Along with this, I ordered a pair of Audax TW025A2 (https://www.dibirama.altervista.org/home-page/tweeter/253-audax-tw025a2-tweeter-1-4-ohm-110-wmax.html)
It seems to be the closest match to the T33 on the efficiency / impedance / mechanical dimensions criteria. Will see which of both is a better choice.

[Thierry]

The refurbished T33s are on their way back from the repair shop. Meanwhile, the AUDAX TW025A2 tweeters arrived and I installed them in the 104/2s. Various programs listening revealed nothing wrong, highs are sweet and detailed and they do match well the rest of the audio range. Maybe there's a lack of openness or clarity in the high mids, not sure though.
To confirm that, I made some frequency response graphs using two different measurement microphones and a digital preamplifier connected to my laptop. Measurements done on tweeter axis @ 1,2m from midrange baffle. These are the raw traces. Speakers A & B perfectly matched, however I am a intrigued by the big dip around 3KHz (see smoothed frequency response). Could this be down to the new tweeters ?

Speaker A https://photos.app.goo.gl/1WbcPEAVJSW3Z4Da9
Speaker B https://photos.app.goo.gl/kpZpFhbUTQnFWd3J7
A & B https://photos.app.goo.gl/cJMtctCMQ1N6W2EB8

Smoothed frequency response from 100Hz to 20KHz.
https://photos.app.goo.gl/yChHZqDQ8QHpUMv47
Note how perfectly the speakers are matched ! (except when the Audax tweeters start playing)






T.

[Thierry]

Although this forum seems to be dead, I post my last contribution here.

The T33s have been overhauled by Peiter Akustik (Germany) and I reinstalled them in the 104/2s. Here are three frequency response graphs :

KEF T33 vs AUDAX TW025A2, showing a phase issue @ 3KHz with the T33 (blue trace) : https://photos.app.goo.gl/Q4PqTkoDJNrULvmF8
Explanation : the repair shop inverted the + and - connecting lugs, thus me connecting the tweeter wrong (180° electrical phase). Once phase has been inverted, things improve a lot (green trace) : https://photos.app.goo.gl/oZirtaAzHPRzGGi97

Third graph is answering my questionning about "how a repaired pair of T33s compare to each other ?" . I know that KEF did match them carefully, so I was expecting a disaster when they came back from the shop. As a matter of fact, there's a 3dB sensitivity loss on one of them, but the frequency response is very similar : https://photos.app.goo.gl/xNwrNyJy2ArHGPPb7

Last but not the least : even though the Audax TW025A2 show better linearity compared to the SP1191, I prefer the latter when listening, it brings better consistency, higher transparency and better imaging to 104/2.

That's all for now, of course comments and suggestions will be most appreciated (altough I doubt about it, I am really sorry to see this space dying from lack of contributions).

T.

[Mind_Drive]

Hi Thierry,

Although I do not own 104/2, I have enjoyed reading your contributions.

Forums are an older part of the internet. They seem unfashionable now. For some weird reason, people seem to prefer posting on Facebook groups. I cannot understand this as Facebook is a dreadful way to give information, impossible to collate, search and store in the long term.

Here we have a KEF library! We are very lucky to have it indeed. Imagine if it was lost- priceless information gone forever. I would certainly be willing to pay a small sum of money towards maintaining it.

[Thierry]

Hi Mind_Drive,
You are right. I am probably too old
KEF library is indeed invaluable.
Thierry

[Mind_Drive]

Thierry, I am not old yet, just in the middle

But I know forums are the best, like a real library.

Rohan

[allanson]

It is great to hear that you feel that this forum contains a wealth of useful information in an easily accessible manner.

Although I don't often contribute to the forum, the contents are maintained and backed up fairly regularly and so they should be safe for quite some time yet.
_________________
Forum Manager

[speakerguru]

[RR105-3]

The 104/2 and the 105/3 B200 woofers will all suffer from foam rot after 30+ years. so none of these still working speakers are no longer original .


I bought my 105/3 in 1990, after 13 years the woofer were broken by foamrot, importer TransTec in the Netherlands could not deliver an original replacement, but did deliver on spec's non-kef replacements made by " Castle " I think, now after 17 years These woofers are still healthy ....
_________________
history: 1978 RR104ab /1984 RR104-2 /1990 RR105-3
-------------------------------------------
in my posession at this moment -
RR105-3 / RR104ab / C95 / C75 / C60 / C10 / Chorale / Cresta 1970 / Corelli /

[audiolabtower]

As far as the tweeter sensitivity is concerned, I would try a resistor in the higher one to match the lower one and see if that is an improvement. A lot of the time slight definciencies in frequency response are less troublesome if the channels are well matched? Above 10kHz it probably does not matter.

[Thierry]