Hei!

Der prates meget her inne om modifikasjon av Vifa XT25. En diskant som jeg liker meget godt i utgangspunktet, men tenkte jeg skulle modifisere i et prosjekt sammen med noen Peerless HDS 164. Det står mye her på dette forum, men har ikke funnet noen god guide med bilder og slikt. Jeg fant en som bor i nærheten av meg gjennom et annet forum og fikk noen tips om hvordan fra han...., så da gikk jeg i gang med modifiseringen og har tatt litt bilder for å kunne bidra litt og vise hvordan det gjøres.

Jeg skriver resten på engelsk i tilfelle det er noen andre der ute som kan ha nytte av dette.

Here's the guide on how to mod the excellent Vifa XT25 tweeter and hopefully make it even better.

Tweeter before mod;


First unscrew the front plate.
You'll end up with something like this:


Use a small but somewhat stiff brush to apply water around the phaseplug:


The glue will expand and become white like this:


Now carefully try and insert a small and flat screwdriver in under the phasepluc and try to twist and ... turn.... and make the phaseplug come off. When it's not attached to the membrane anymore, just pull it out using... some pure force. ... And then lift the whole part with the voicecoil and the membrane off the magnet part. It will then look like this;


Remove the glue. If you let the glue have some time to dry a bit before you try to remove it, it will go easier (a minute or so). After you have removed the glue; you'll have these parts;


Membrane with the glue removed;


The magnet gap and where the phaseplug was glued to:


Then ... The modding starts. The thing you have to do is to remove some excessive glue around the outer edge of the membrane (on the inside). You also have to close the gap in the voicecoil with some glue (seen in the upper right corner).
The inside WITH glue looks like this (the reflective part is the glue that you have to remove):


Another picture before modification:


Use a small brush here as well (the same brush if you're smart) and apply water. Then use some small tools to rip the glue of. ... The glue will become white here as well;


The tweeter with the glue removed;


Another one:


assemble the tweeter (use some glue to attach the phaseplug to the membrane):


... and you're done!

The sound should now be improved... More "open" and with somewhat more sensitivity.

So how does it sound? ... Well... I have just mounted them and had only a couple of minutes with them now, and I'm amazed by the sound they produce. I'm not able to tell you "how much better", but at least there was a difference in sensitivity as I had to modify the tweeters crossover. It was also at night, so ... maybe the cleaner powergrid has to take some of the blame, but I could have spent hours ... maybe weeks listening to them. ... then something called me to bed. This tweak should also improve distortion at higher levels, but I'll try that later today. Anyway; No cons so far... only pros :)

Hope it works though! :)

Thanx to people in the hifi-community for "exploring" this speaker and providing some info on how to do this. Especially thanks to the guys at the hifi4all.dk forum and Steen Duelund which has played his part in the "exploration" of this excellent tweeter.

I hope some of you might find this guide helpful... and feel free to contact me!

Fornem gennemgang med gode billeder osv.

Det kunne være rigtig spændende at se en før/efter måling af frekvens, step og harmonisk forvrængning.

Nice workflow you have managed, and very nice pictures. Good explanations.

The overall goal you want, I guess, is to have "redundant glue" removed, and when that is done, the weight of the moving system is reduced, and thereby the sensitivity is increased. Redundant glue can be explanained with productions methods, where you have to have some redundant glue in order to have sufficient glue. Not all production workers have the 100% right feeling of what is just enough glue, so the production engineers hav to make specification full proof, and thereby taking the last percentage out of the performance, allthough giving the whole production series a high value. It's a trade off.

But "redundant glue" could also imply, that the glue have two jobs: assembling parts, and reducing resonances, which is commend in scandinavian development and production of driver units, specially the more expensive ones. As the glue used is waterbased leeds me to think that the glue also the damping effect, because older fsshion waterbased glus has that effect, and is that case your modification has removed the damping, causing resonances which could be seen in distortion and resonance measurements. I think the development engineers and production engineers at Vifa spent a lot of time and experiments to optimize this. Carefully listening would also detect the now reduced damping of resonances to less resolution, fewer details and more coloration.

Also, when you close the gab in the voicecoil former, you can risk that the voice coil assembly have less ability to "breathe", which can imply higher compression at higher levels.

You said you have not yet had the time to longer listening sessions, so I'm anxious to hear you comments later.

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Kappen; Takk! :) Jeg skal gjøre noen målinger når jeg får kalibrert utstyret og slikt... så får vi kanskje se noe..., men foreløpig må jeg bare stole på ørene mine. :)

Hifiigen; Yes, you will alter the resonance frequency, but far beond the xo point of the tweeter (400hz-ish?) ... I've seen some measurements on this, but I don't "have them here". ... But I think Steen Duelund and some others wrote about this some time ago on this forum.

I'll listen more later this evening... and looking forward to it... :D

DethZaint skrev: Hifiigen; Yes, you will alter the resonance frequency, but far beond the xo point of the tweeter (400hz-ish?) ... I've seen some measurements on this, but I don't "have them here". ... But I think Steen Duelund and some others wrote about this some time ago on this forum. I'll listen more later this evening... and looking forward to it... :D

I did'nt mean the resonance frequency, but resonances in the membrane/cone and connection with voice coil and mounting plate, through the entire frequency band, mostly in the upper range.

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hifiigen skrev: DethZaint skrev: Hifiigen; Yes, you will alter the resonance frequency, but far beond the xo point of the tweeter (400hz-ish?) ... I've seen some measurements on this, but I don't "have them here". ... But I think Steen Duelund and some others wrote about this some time ago on this forum. I'll listen more later this evening... and looking forward to it... :D I did'nt mean the resonance frequency, but resonances in the membrane/cone and connection with voice coil and mounting plate, through the entire frequency band, mostly in the upper range.

Aha.... Well; Steen Duelund considered this excessive amount of glue as a pure production fault, and claimed that it should be removed. This can affect the sound other than the increased sensitivity .... (resonances and such), but I don't think this mod would have been considered as a "must" unless it in fact improved the driver. Anyway; I should try to measure it and provide some graphs on how it perform

I do not want to go so much into details regarding Steen Duelunds design principles, as do not know them so much. I recall from some contacts with him in the past, that he wanted efficient damping of resonances by quite a lot of soft glue/coating, and did not care so much about efficiency, but I think that efficiency is one of the factors to go for if you are loking for dynamic reproduction. However, the two systems I heard of Duelunds was very dynamic and significant and extremely clean, compared to speakers I until that time have heard.

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Der må også være tweaks til bagkammeret som er dæmpet med 1-2 runde vat-rondel-dimser fra Netto.  Dem som damer bruger front-placed under kur

Mik112 skrev: Der må også være tweaks til bagkammeret som er dæmpet med 1-2 runde vat-rondel-dimser fra Netto.  Dem som damer bruger front-placed under kur

Visse vatrondeller, som kan købes i detailhandlen, er faktisk karakteriseret ved 100% ren uld, i enesartet størrelse, og i ensartet vægt. Dermed et temmelig velvalgt dæmpemateriale til bagkammer på en diskant. Forudsat mængden og størrelsen passer kan det næppe gøres bedre.

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hifiigen skrev: Mik112 skrev: Der må også være tweaks til bagkammeret som er dæmpet med 1-2 runde vat-rondel-dimser fra Netto.  Dem som damer bruger front-placed under kur Visse vatrondeller, som kan købes i detailhandlen, er faktisk karakteriseret ved 100% ren uld, i enesartet størrelse, og i ensartet vægt. Dermed et temmelig velvalgt dæmpemateriale til bagkammer på en diskant. Forudsat mængden og størrelsen passer kan det næppe gøres bedre.

Det var bare en tanke. Når man kan modde lim og bruge tid til det - i en i forvejen fin konstruktion tænkte jeg bare at Netto-pladerne også kunne moddes