Brighter 025Ti diaphragms

[manfred]

Hello all!
I've managed to find the repair kit 102124J for my JBL Ti2K tweeters, sadly blown during playback of a badly distorted recording.

My concern is: they sound significantly brighter than the original ones, and especially adding some sibilance to female voices. I have noticed too that the old diaphragms had a green marking on the edge, these new have two, blue and red. Does anyone have any idea if there are differences between such kind of parts, and if yes, does the replacement involve some modification in the crossovers?

My best regards.

[spkrman57]

Give them approx 100 hrs of playing time and see if they tame down some after that.

Your old ones might have been diminishing on the top end towards the end of their lifespan and you might be looking for the new ones to sound the same.

Let us know how it sounds after some playing time!

Ron

[manfred]

Thank you, Ron.
I left them to burn in for almost an year now, how much more could one have to wait
As I mentioned before I got suspicious after this while as you can all imagine, and became even more intrigued when re-checked the resemblance with the old ones and I found that peculiar marking (green vs. red-blue).

Some late developments:
Last evening I found this thread http://www.audioheritage.org/vbullet...ighlight=025ti
(god bless the author for enlighten me) where it says :
The 025Ti’s are from the Audax factory in France and has a sensitivity of about 94db and stretches out to over 20kHz. Should work fine since they sound good in the TIK.

I did some further research on the internet, and here is what I got:

Yes Audax manufactures those tweeters, yes it was a French repair shop that supplied the parts, at a more than fair price, it's only that Audax makes them in 8 Ohm and 4 Ohm impedance. Obviously mine are the wrong value (lower I suppose).
http://www.reparationhaut-parleur.co...s/tw025a16.htm
http://www.reparationhaut-parleur.co...s/tw025a14.htm

Since I have no more the intention of messing up with the crossover, I've decided to order the proper replacement, and furthermore, ask for an extra pair of silk diaphragms to give them a run just for fun.

http://www.reparationhaut-parleur.co...ournitures.htm

I will keep you posted with the results, just please wish me luck to bring my speakers back to their original sound.

Cheers,

manfred

[Earl K]

Hi Manfred,

I've managed to find the repair kit 102124J for my JBL Ti2K tweeters,,,, snip

Forgive me if I am restating the obvious, but ;
- Did you buy actual JBL repair kits that were labelled 102124J ?
- Did you install these diaphragms yourself ?

My concern is: they sound significantly brighter than the original ones, and especially adding some sibilance to female voices.

- Your tweeters sound like they are underdamped .
- I see at least a couple of explanations here ;

(1) You installed the official JBL kit ( with JBL markings on the box ) but neglected to install any damping materials that were shipped with the repair kit ( if included & if necessary ) .

- Examples of damping;
(i) ferrofluid in the gap ( providing mechanical damping in a viscous form ). I've seen a Japanese reference ( translated into "Manglish" ) that the original TW025ti used ferrofluid in the gap. or maybe
(ii) a small foam pad that is placed under the diaphragm ( & centered on the pole-piece ) , providing some acoustical & maybe mechanical damping to the diaphragm . A few JBL tweeters ( such as the 044ti & 035ti ) use these foam pads for diaphragm damping .

(2) Perhaps the repair kits installed a year ago were the wrong ones .

ie;
-You installed someones "best guess" using a stock Audax tweeter model to approximate a match ( from Audaxs' line of tweeters having 25 mm voice-coils )
- This approach would be a crap shoot and unlikely to match JBLs' original specification .
- Audax makes a few lines of tweeters having different magnet weights ( 240 grams seems to be the heaviest ) . Diaphragm weights need to be matched to the magnet strength.
- JBL has typically ( in the past ) used more weighty magnetic assemblies than other companies.
- Retrofitting a lighter weight diaphragm ( than OEM ) into a stronger motor would result in different response than was originally designed .

I have noticed too that the old diaphragms had a green marking on the edge, these new have two, blue and red. Does anyone have any idea if there are differences between such kind of parts, and if yes, does the replacement involve some modification in the crossovers?

- JBL uses colored ink on some diaphragms to denote impedance / as well as + & - polarity .
- Modification of the crossovers shouldn't be necessary if you bought kits labelled as JBL original equipment / and they were installed correctly .



ps ; here's a pic of one of my 035ti tweets disassembled, clearly showing the foam damping pad that I'm referencing .

[manfred]

Hi Earl.

Yes I bought the original 102124J repair kit from Reditech, located in Paris, Fr, as indicated from customer support at Harman Int'l. The product code was labeled on the shipping box as well on the invoice.

No ferrofluid came out at the moment of dissasembling the old ones, and as JBL advertises about this tweeters, they use the metal dome do dissipate the heat, hence they are obviously air cooled.

The inner damping material remains in place as it is glued in at the bottom in the central venting.

There are two issues that led me to my conclusion:

1. The markings on the diaphragms are definitely different. You cannot reverse the polarity since the connectors are specific by width, so the connectors wouldn't fit. That leaves the impedance matching to be doubted.

2. I do not expect JBL to lead me to Audax directly. The back of the tweeters says "Made in France". Code name of the product "025Ti" matches the Audax product list, specifications are identical, and the domes look exactly the same. The price paid was the same as in Audax price list, €18 each, plus tax.
I figured out that Reditech supplies repair kits for both Audax TW025 and JBL 025Ti tweeters, and since are the same after all, they probably occasinaly do not pay attention to the fact that Audax come in 4 and 8 Ohms, while JBL is 8 Ohms only. I wasn't aware of this fact so didn't care much for the color coding until now.

Tell me, is it right to presume the higher output level of the tweeters is due to a lower impedance, in this case 4 Ohms instead of eight?

Thank you all for your replies.

[johnaec]

Tell me, is it right to presume the higher output level of the tweeters is due to a lower impedance, in this case 4 Ohms instead of eight?

That's what I would assume. Can you take a resistance measurement? Then maybe someone can compare that with an original one.

John

[manfred]

That's what I would assume. Can you take a resistance measurement? Then maybe someone can compare that with an original one.

John

You got me there, I don't have a digital multimeter in the household, waiting till monday to borrow one.

Some photos:

1. Magnet with the damping material in place, new dome with blue and red marks.


2. Old dome, green marking



3. Rear of the magnet, "made in France"

[Earl K]

Hi Manfred,

Thanks for all your answers & clarifications ( & pictures ) .

It's good that you realize that you can try out a few diaphragms in that 025ti magnetic assembly until you find something that you like / though some choices may require network modifications .

Tell me, is it right to presume the higher output level of the tweeters is due to a lower impedance, in this case 4 Ohms instead of eight?

- Yes, a lower impedance will draw more current & therefore be louder .
- The DCR of the original 025Ti is listed as 3.8 ohms ( according to the JBL spec. sheet ) / meaning the tweeter likely has an AC impedance curve that would be in the mid 4 to 6 ohm area .

- According to the included schematic, I see that JBL states the load impedance of the Ti2K is 6 ohms .
- "R1" ( 1.8 ohms ) in the network schematic when added to a "4 ohm" tweeter would be in the 6 ohm neighbourhood / adding that inline resistance to an 8 ohm tweeter takes the AC resistance of the network up to 10 ohms ( for the HF portion ) .

- Maybe JBL calls the original tweeter an eight ohm model / I don't know since it's not mentioned anywhere within the tech sheet.

- I guess time will tell if 8 ohm replacements will work better for you .

No ferrofluid came out at the moment of dissasembling the old ones, and as JBL advertises about this tweeters, they use the metal dome do dissipate the heat, hence they are obviously air cooled.

- Well, ferrofluid generally won't leave the gap area of a transducer due to magnetic pull on the ferric-fluid unless it is cooked out by overheating the voicecoil .
- To check if a gap has ferrofluid in it , one needs to swab/clean the gap to see if a dirty brown liquid is soaked up by the swab .
- Sometimes a visual inspection of the voicecoil can indicate the presence of ferrofluid .

[manfred]

Hi all,

Things are moving fast.

I just got the email from an Audax parts dealer and he says:

Bonsoir,

Il s'agit des mêmes équipages mobiles, donc vous aurez une qualité
acoustique équivalente.- which means: "they are the same units, so you will have same sound quality".

Now Earl got me thinking again: 3.8 DCR is specific to TW025 on 4 Ohms impedance, as 5.8 DCR for TW025 on 8 Ohm. (talking about Audax now).

This reverses the impedance issue as I thought it.

Earl, i've inspected both the gap and the coil for traces of ferrofluid, and looked it up on the internet, still no mention about it, so hopefully it was never present therefore never missed.

Now, hilarious as it seems, I will just ask Sylvain to find those with a green mark.

[Earl K]

Hi manfred,

- Here is a link to the Audax Archives .

- The page includes mostly .jpgs ( & a few pdfs ) for past & present products ( just some, but not all ) .

- Take a look through the TWO25xxx listings to see if you can find anything of value for your search.

Now, hilarious as it seems, I will just ask Sylvain to find those with a green mark.

- Hopefully it can be as simple as that .

Now Earl got me thinking again: 3.8 DCR is specific to TW025 on 4 Ohms impedance, as 5.8 DCR for TW025 on 8 Ohm. (talking about Audax now).

This reverses the impedance issue as I thought it.

- Well, you really must take a DCR reading of the present repair so that you will know what impedance diaphragm you presently have .

Yes I bought the original 102124J repair kit from Reditech, located in Paris, Fr, as indicated from customer support at Harman Int'l. The product code was labeled on the shipping box as well on the invoice.

- Did Harman actually tell you this 102124J repair kit was the one to use ( or was it Reditech that came up with the number ) ?

Bonsoir,

Il s'agit des mêmes équipages mobiles, donc vous aurez une qualité
acoustique équivalente.

- Hmmm, "Acoustic Equivalent" is pretty ambiguous nowadays .
- It means different things to different people .
- That of course, is just the opinion of a sceptic .

- As mentioned earlier, it's nice that you have more than just a couple of choices for replacement diaphragms .

[manfred]

Hello again,

- The 102124J was indicated by Harman parts support, they sent me to Reditech repair shop.

- Thank you all for baring with me these two days, I got information flowing from all directions, one thing I am not certain of, if I was able to measure the DC resistance before I wouldn't waste your time.

Earl, the term "qualité acoustique equivalente" may sound tricky, but it doesn't mean quite "acoustic equivalent", but more like "same acoustic quality". As a matter of fact, I am aware that some speaker manufacturers do not supply spare parts, instead they require that the whole defective speaker or the pair be sent back to them when repair needed, so when a driver has to be replaced they are reviewing the whole unit and even make adjustments to the crossovers (Revel speakers a f a i k - and the Performa series' tweeters look amazingly similar to 025Ti, or I'm just beginning to see things)



The next common sense thing for me to do is get an exact reading of the DC resistance of the current voice coils. Hope this will occur tomorrow.

Thanks again.

manfred

[Earl K]

Hi manfred,

- The 102124J was indicated by Harman parts support, they sent me to Reditech repair shop.

Ahh, okay, then it's a genuine Harman parts number .

- Thank you all for baring with me these two days, I got information flowing from all directions, one thing I am not certain of, if I was able to measure the DC resistance before I wouldn't waste your time.

- You're Welcome & Thank You for allowing me to keep pestering you for clarificatiions ( it's all good for the sake of the archives ) .

- I do hope this is all able to be easily straightened out .



ps , I'm out of town most of this week so I won't be online here till @ Friday .

[Guido]

Manfred,

maybe I missed it but what is the measured DCR of your fresh diaphragms?
If you measure 3.8 Ohms your fine
If you measure 5.8 Ohms then order the 3.8 kits.

At these low prices it isn't a problem to order twice.

[manfred]

Manfred,

maybe I missed it but what is the measured DCR of your fresh diaphragms?
If you measure 3.8 Ohms your fine
If you measure 5.8 Ohms then order the 3.8 kits.

At these low prices it isn't a problem to order twice.

Thanks for your reply, Guido

I managed to finish work earlier today so I found an electronic workshop and ask them to measure the DCR. It only deepened my confusion when they read 3.6 Ohm. I know for a fact from the schematic Earl supplied that it is the right DCR but how come these sound louder anyway?

Of course I do not mind ordering other kits and even a few more but I feel kind of lost now. I must have offended the jbl gods and I'm ready to confess: the coils went off during tarkan - shikidim at a party. Shouldn't have done that, OK? I repent. OK? I repent. Now what?

I almost saw this coming when I hung onto that tiny detail: the green paint trace on the back of the magnet and the edge of the diaphragm that blew. So anything not green - not good. This is what I got reduced to.

o m g

[Guido]

I know for a fact from the schematic Earl supplied that it is the right DCR but how come these sound louder anyway?

I suspect the tweeters were somehow broken before.

I must have offended the jbl gods

There's no JBL god

Ithe coils went off during tarkan - shikidim at a party.

Contact me if I should build you a pair of 4345. There will no longer be any problems with party sound. PROMISE!