I have a vifa d25ag xx metal dome tweeter which sounds very airy when starts playing, but in 2-3 minutes the treble becomes muddy. More vocals starts coming up through it. If I slightly pushed the tweeter it becomes more airy and less vocals starts coming up through it. Is the tweeter suspension became bad that it cannot pull back the vibrating tweeter ? But funny thing is , if i turn off the speaker for some time and then again turn on, it’s alive again for 2 minutes. I contacted the manufacturer and he mentioned the inductor parallel to the tweeter could be bad.
I am not convinced that a inductor can ever go bad. After all it’s a much thicker coil and how would it degrade ?
I am not convinced that a inductor can ever go bad. After all it’s a much thicker coil and how would it degrade ?
That all sounds very peculiar.
I don't think it should be sagging, but a lot of other things could go wrong.
Dry joints in the crossover. Maybe a bit of cracked solder. Why not reflow it with a soldering iron. Loose or corroded speaker cable? Strip back to fresh copper.
Worn out electrolytic capacitor to tweeter? Maybe replace.
Dried up ferrofluid in the tweeter voicecoil gap. Inspection time:
Scanspeak Voice Coil (600058) for D27TG35 or D27TG45 Mission
Maybe a bad amplifier switch or pot. Spray with switch cleaner. Good luck. Sounds frustrating.
I don't think it should be sagging, but a lot of other things could go wrong.
Dry joints in the crossover. Maybe a bit of cracked solder. Why not reflow it with a soldering iron. Loose or corroded speaker cable? Strip back to fresh copper.
Worn out electrolytic capacitor to tweeter? Maybe replace.
Dried up ferrofluid in the tweeter voicecoil gap. Inspection time:
Scanspeak Voice Coil (600058) for D27TG35 or D27TG45 Mission
Maybe a bad amplifier switch or pot. Spray with switch cleaner. Good luck. Sounds frustrating.
What do you mean by slightly pushing the tweeter ? Mechanically by touching it or electrically by raising the volume a bit ?
What happens if you cross the speaker cables (i.e. left speaker to right amp output and vice versa ?).
Regards
Charles
What happens if you cross the speaker cables (i.e. left speaker to right amp output and vice versa ?).
Regards
Charles
I have had drivers that suffered from some bad quality control. Woofers, mids, tweeters all. I first suspect it may be the glue at the surround. I have seen this many times. An imperfect glue joint all the way around can show up much later and be perfectly fine for several months or even years. Of course, woofers move much more than tweeters and you can see the separation on a woofer or mid surround. It may be impossible to see on a tweeter though. Just a guess...
Charles, I meant mechanically pushing the tiny surrounds of the tweeter. The amp is fine as I have 2 other pairs of speakers at home which works without problems with the amp. To wherever channel I connect this particular box the effect is same. After 3-4 minutes, the tweeter starts playing more lower frequencies slowly which makes the airy highs. The box has a dedicated mid range. So now we have this midrange and mids (if I listen closely, I can hear the singer clearly from the tweeter, as opposed to just tiny fraction of the upper mids like the other working tweeter. There is a capacitor (new one - mundorf 4,7 uF and an inductor or some unknown value (but presumably 0.10mH from winding thickness and winding wire gauge) in parallel with this tweeter.
This particular crossover is a band pass for the mid range and high pass for the tweeter. There is another crossover for the two woofers in the second compartment of this box.
Attachments
This is a box which had been running fine for 25 years and I checked the ferrofluid. They are to the brim, and not yet solidified. Like I said, the issue happens only after few minutes into playing . On cold start everything sounds fantastic, after few minutes it sounds like the high pass xover point slowly directed to a lower freq. resultant is we have mids from mids and tweeter now giving a huge unnatural size of midrange which compeletely masks the treble. Of listened closely the treble is still there but the louder midrange is covering it up too much.
Strange. Can it be an oscillating amp heating up the tweeter that therefore ends up with much higher impedance and in turn the X-over doesn't do what it has to do?
Sounds to me like it's probably an electrical or mechanical issue with the tweeter, more likely mechanical because pushing lightly on the surround fixes it temporarily as you said.
My first guess is that oldspkrguy is right because that would be directly affected by the act of touching the surround. Might just be that the glue got worn out after 25 years.
My other thought is that it may be heat related because it takes time for it to start (time for heat to build up) and fixes itself temporarily after turning off (time to cool down). If something is causing the tweeter's impedance to change from what it is at rest that would change the crossover point (if I remember correctly, increasing impedance with the same crossover will reduce the XO frequency), which could be what's happening. There are any number of ways that this could happen - increasing stiffness of the surround increasing the impedance mechanically, excessive voice coil heating causing a higher electrical resistance component to the impedance curve, surround coming loose from bad glue joint adding a resonance to the tweeter near the XO point, etc.
If you happen to have a tool like DATS that can measure the impedance curve of the tweeter, it would be useful to do so for both the good and bad one to compare and see if we can identify an issue there. Might have to figure out a way to do that immediately after running them for a few minutes to see the difference though if there's not anything obvious in a test with them not warmed up already.
My first guess is that oldspkrguy is right because that would be directly affected by the act of touching the surround. Might just be that the glue got worn out after 25 years.
My other thought is that it may be heat related because it takes time for it to start (time for heat to build up) and fixes itself temporarily after turning off (time to cool down). If something is causing the tweeter's impedance to change from what it is at rest that would change the crossover point (if I remember correctly, increasing impedance with the same crossover will reduce the XO frequency), which could be what's happening. There are any number of ways that this could happen - increasing stiffness of the surround increasing the impedance mechanically, excessive voice coil heating causing a higher electrical resistance component to the impedance curve, surround coming loose from bad glue joint adding a resonance to the tweeter near the XO point, etc.
If you happen to have a tool like DATS that can measure the impedance curve of the tweeter, it would be useful to do so for both the good and bad one to compare and see if we can identify an issue there. Might have to figure out a way to do that immediately after running them for a few minutes to see the difference though if there's not anything obvious in a test with them not warmed up already.
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Like system7 says, it could be a dry joint somewhere on the crossover (the inductor part of the tweeter cct)
Because if the inductor cct goes o/c then you have more lower frequencies going to the tweeter, and then when you touch the surround of the tweeter, you end up pushing the voice coil out of alignment (ie. touching the pole piece)
Which then probably stops the dome from reproducing the lower frequencies and then you just hear the higher frequencies
Have you checked for any dry joints?
cheers,
Because if the inductor cct goes o/c then you have more lower frequencies going to the tweeter, and then when you touch the surround of the tweeter, you end up pushing the voice coil out of alignment (ie. touching the pole piece)
Which then probably stops the dome from reproducing the lower frequencies and then you just hear the higher frequencies
Have you checked for any dry joints?
cheers,
Nothing in the speaker should be warming up within a couple of minutes to affect the performance like this. If it was then after a few more minutes something would catastrophically fail from overheating.
You need a monumental amount of voice coil hearing to shift the xover point down significantly enough to matter such as in a case like this. The tweeter surround would get hot and to be honest you'd smell it too.
Something wearing out, like a glue join, with the tweeter doesn't make sense either. It would affect the performance permanently and isn't something that would shift after a couple of minutes listening, only to shift back.
Mild heating of the voice coil, causing thermal expansion, could cause the tweeter coil to start rubbing against the gap and generating what sounds like more midrange coming through. Pushing the surround on one side could realign it and stop the rubbing. What happens if you push on other areas of the surround? If it was rubbing pushing on one side would rock the coil to one side, realigning it, but pushing on the other side would do the opposite and make it worse.
I've no idea why the coil would be heating up to start with though, nor why a rubbing coil would be fine for a few minutes then start rubbing, unless it was hearing up a decent amount.
Can you try a different amplifier?
Also you could try the tweeter without a crossover, playing on it's own, connected directly to the amplifier. At low volumes this is absolutely fine and would let you hear if the tweeter alone is at fault.
You need a monumental amount of voice coil hearing to shift the xover point down significantly enough to matter such as in a case like this. The tweeter surround would get hot and to be honest you'd smell it too.
Something wearing out, like a glue join, with the tweeter doesn't make sense either. It would affect the performance permanently and isn't something that would shift after a couple of minutes listening, only to shift back.
Mild heating of the voice coil, causing thermal expansion, could cause the tweeter coil to start rubbing against the gap and generating what sounds like more midrange coming through. Pushing the surround on one side could realign it and stop the rubbing. What happens if you push on other areas of the surround? If it was rubbing pushing on one side would rock the coil to one side, realigning it, but pushing on the other side would do the opposite and make it worse.
I've no idea why the coil would be heating up to start with though, nor why a rubbing coil would be fine for a few minutes then start rubbing, unless it was hearing up a decent amount.
Can you try a different amplifier?
Also you could try the tweeter without a crossover, playing on it's own, connected directly to the amplifier. At low volumes this is absolutely fine and would let you hear if the tweeter alone is at fault.
Perhaps thermal expansion causing voice coil rubbing? That'd take a lot less heat than increasing the resistance enough to affect impedance noticeably 😀
I put this down to the old Engineer's standby here. Gremlins! 😀
I had an old Rotel-931 amp. One channel was distinctly weak at the top end.
Thorough investigation took me uncomfortably into Amplifier design.
Having read the manual, I decided the problem might be Class A/B bias wandering off into uncertainty with increasing heat and time:
How hard can it be to twiddle the bias pots after a few minutes of settling down.Those blue things.?
Got the old Voltmeter out and discovered the output bias pot had wandered with age on one channel.
TBH, amplifiers are not my strength. Some smoke and a bright blue flash got let out with my probings, causing me alarm and distress. But it kept that old Rotel Amp going for a few more years. But at a certain stage, we must buy new stuff.
I had an old Rotel-931 amp. One channel was distinctly weak at the top end.
Thorough investigation took me uncomfortably into Amplifier design.
Having read the manual, I decided the problem might be Class A/B bias wandering off into uncertainty with increasing heat and time:
How hard can it be to twiddle the bias pots after a few minutes of settling down.Those blue things.?
Got the old Voltmeter out and discovered the output bias pot had wandered with age on one channel.
TBH, amplifiers are not my strength. Some smoke and a bright blue flash got let out with my probings, causing me alarm and distress. But it kept that old Rotel Amp going for a few more years. But at a certain stage, we must buy new stuff.
Wow! Thanks everyone for the overwhelming response on this. I never played the amp beyond 9 o clock! So it’s very very unlikely that the tweeter got a heat damage. But by pushing the tweeter very very slightly I think I am increasing or decreasing the circuit impedance itself there by fixing the crossovers issue If I am not wrong. I think I would just try swapping the tweeters left and right to see if the tweeter shows the same behavior on the other crossover. Then, it must be the tweeter. If that’s the case I am doomed!
I had previously tried a vifa Aluminium dome which is currently avaialable in market on this speakers bookshelf version and though they look the same , except face plate sonically the Orginal one for Alr is a customized coil if I am not wrong which sounds faster than the new ones vifa sells. I will get back to you guys.
I had previously tried a vifa Aluminium dome which is currently avaialable in market on this speakers bookshelf version and though they look the same , except face plate sonically the Orginal one for Alr is a customized coil if I am not wrong which sounds faster than the new ones vifa sells. I will get back to you guys.
Tis one is possible.
Thermal time constant for a voice coil is consistent with 2 minutes to start failing.
A voicecpil can scratch "inside" against the pole piece or "outside" against the top plate.
It may have developed bubbles during an earlier overload (Junior playing DJ in a house party), said bubbles grew until they touched gap walls stopping there (of course) and scratching big time.
Cooling afterwards contracts them slightly so next time, starting cold, they don´t scratch ... briefly.
If you ever recone those tweeters, take a good hard look at voice coils, with ajeweler´s loupe and under good light.
When repairing a speaker I often perform an autopsy to find cause of damage.
Air bubbles embedded inside epoxy adhesive tend to bubble under high temperature, those bubbles expand "outwards"; some tweeters us Nomex voice coils (it´s lighter than Kapton and Aluminum) , notably old Celestion or Goodmans tweeters, and Nomez which *always* has air trapped inside produces large bubbles when overheated, in this case "inwards" (in the VC former material)
With respect, everybody. My money is always on a loose connection in Electrical Matters.
It's extremely unlikely that a tweeter voicecoil sags. They weigh NOTHING!
Anyway, ferrofluid is supposed to centre the voicecoil.
Stops rubbing.
My money is still on the Amp or a loose connection somewhere. But I don't know. 🙂
Time will tell.
It's extremely unlikely that a tweeter voicecoil sags. They weigh NOTHING!
Anyway, ferrofluid is supposed to centre the voicecoil.
Stops rubbing.
My money is still on the Amp or a loose connection somewhere. But I don't know. 🙂
Time will tell.
I like the simple idea of just swapping the tweeters; I didn't read all the details. If one tweeter is acting up but not the other; this should be a simple thing to try first. Many things in the wiring, crossover, connectors, could be cause for some nastiness. The idea that they were over driven at some point may have partly fried a few voice coil turns that may or may not short out intermittently. I have certainly seen this on woofers and mids; pushing or touching the driver moves the "bad" section of the VC into a different region and the distortion gets less. A deformed former will act in a similar way. Curious to see what the end result is...
A capacitor could be breaking down but physically touching the thing making changes makes me thing there is a mechanical issue with the VC or former or surround or suspension...
A capacitor could be breaking down but physically touching the thing making changes makes me thing there is a mechanical issue with the VC or former or surround or suspension...
Turn your speaker upside down and try it. If this is due to mechanical sag this will either fix it or possibly worsen it. First things first before resoldering or the other suggestions.
The way people talked, back when plasma tweeters were the thing, they may as well have been made from lead.
Are replacement VCs for these tweeters still available at a reasonable cost?
If so is it worth the experiment of a changeover?
But that tweeter in the photo looks nothing like my own D-25AGs
If so is it worth the experiment of a changeover?
But that tweeter in the photo looks nothing like my own D-25AGs
I have a regular d25 AG, but this one has a slightly flatter VC customized by vifa if it m not wrong for ALR. So it’s just not the faceplate. The regular one comes with the triangle like face plate. But the dome itself is more “dome” shaped. I think I am out of luck for the voice coil because of this. Same story about the woofers. I slapped a regular p17 wj 00 for the place of p17 wj 35 they have in this box as it was lying around. Even with similar spec on paper the Orginal one was much better than the new p17 I bought. It had less midbass boom by nature. Also timing was much faster.
This whole speaker is a deceptive one when we look in the used market. It seems it’s made of generic drivers so fixing them is easy, but when looked closely the similarlity ends in aesthetics. Not worth picking up if something is not working. I have one box working so I have something to compare. Also another full working pair with my brother so I know how this should sound like. The only reason I am still hanging on to this thing is I have a maxxx budget of 1500€ for new speakers and I compared kef r3 against this and though I liked it, the ALRs were still better in terms of massive soundstage, separation and low bass clarity. I cannot peacefully live with the r3 knowing this is there my basement ! I am currently scavenging parts but given the age I think I may not have a luck with the tweeters. Everyone would be having the same problem.
This whole speaker is a deceptive one when we look in the used market. It seems it’s made of generic drivers so fixing them is easy, but when looked closely the similarlity ends in aesthetics. Not worth picking up if something is not working. I have one box working so I have something to compare. Also another full working pair with my brother so I know how this should sound like. The only reason I am still hanging on to this thing is I have a maxxx budget of 1500€ for new speakers and I compared kef r3 against this and though I liked it, the ALRs were still better in terms of massive soundstage, separation and low bass clarity. I cannot peacefully live with the r3 knowing this is there my basement ! I am currently scavenging parts but given the age I think I may not have a luck with the tweeters. Everyone would be having the same problem.