Two years ago in approximately the same time I bought two pairs of lodspeakers. Delta 12 LFA in 30 l bass reflex boxes and EV SH1502. They were OK when brought home, but in a week or two, always the left speaker, started playing softer and with distortion. I could hear the difference in sound. The Delta and DH3 drivers showed the same symptoms - very different impedance from the healthy one (no pronounced resonance peak, just some wiggle higher in frequency and there was like 5-10% distortion even at very low levels. The coils were intact and measured normally at DC.
I wonder what could have happened? The room is always dry and temperatures between 18 - 25 deg C all year. Both failed in their boxes, so the naked drivers were not dropped. Does anyone have any explanation? Could it be e.g. magnetic splinters in the gap (found none visible)? The magnet holds on to iron (in both cases) as strongly as the healthy units. I could not find any mechanical damage while dissecting the Delta and tried brand new replacement membrane in the DH3 - amd it measured exactly the same way as with the old one (which I had to fix with superglue). This has luckily not happened since...
I wonder what could have happened? The room is always dry and temperatures between 18 - 25 deg C all year. Both failed in their boxes, so the naked drivers were not dropped. Does anyone have any explanation? Could it be e.g. magnetic splinters in the gap (found none visible)? The magnet holds on to iron (in both cases) as strongly as the healthy units. I could not find any mechanical damage while dissecting the Delta and tried brand new replacement membrane in the DH3 - amd it measured exactly the same way as with the old one (which I had to fix with superglue). This has luckily not happened since...
So T/S, etc., measure fine, but perform in cab poorly? Got a leak? Frame warped once installed? Or swapped leads to make sure the signal chain is good?
No, T/S is actually unmeasurable - the resonance is moved up in frequency and instead of one peak there is a broad wiggly low peak. The funny thing is that I have not touched them in the period when they failed. They both just started sound a bit strange one day. Not related to the horn or cabinet, it was just the driver itself in both cases.
Could this be a result of a previous hit in transport? I do not think the boxes would survive temperatures, where the magnetism would get lost. It feels like the magnetic resistance somehow increased in the magnetic circuit lowering the field in the gap...if that is even possible. I still have the failed DH3 and might be able to find the basket and magnet of the Delta.
The thing is - I saw speakers damaged by overload in many different ways (by heat, mechanically, etc.), but never this way before.
Could this be a result of a previous hit in transport? I do not think the boxes would survive temperatures, where the magnetism would get lost. It feels like the magnetic resistance somehow increased in the magnetic circuit lowering the field in the gap...if that is even possible. I still have the failed DH3 and might be able to find the basket and magnet of the Delta.
The thing is - I saw speakers damaged by overload in many different ways (by heat, mechanically, etc.), but never this way before.
Some measurements of the Delta are here: https://www.diyaudio.com/community/...oot-cause-can-be-repaired.342745/post-5915906 and DH3 here https://www.diyaudio.com/community/threads/ev-sh-1502er-poor-mans-altec-a7.346254/post-6940057
There was no rubbing and the coil looked like new after dissection. Nothing way loose.
I still use the same amps, no problems.
I still use the same amps, no problems.
Hmm, dropping a ferrite [mud] motor or high heat from being over driven doesn't affect its magnetism like it does with AlNiCo and yes, the extreme temps would destroy the driver/damage the cab, so at this point can only assume it's a faulty mag and/or didn't do a complete demag/drain for a remag, so a new one wouldn't 'take' properly [been there, done that many times with slot-car motors, especially when done in bulk 🙁].
I once had a strange behaving dome tweeter with several wiggles in impedance plot. After some trials i realized it was a slightly twisted front plate that was apparently deformed by uneven screw tension. So i would also suppose there might be some mechanical problem. Are you sure the magnet is actually demagnetized?
Thermal shock? Going from really hot to freezing in an instant can mess up magnets but how would that happen in a house. Large DC motor really close by? Lightning? Act of God?
Have you checked around the glue joint of the voice coil former/cone join? There might be a stress crease around that area where it has gone soft, not enough to cause coil rub, but enough to cause the changes you noticed.
Well, it is really strange. I really could see no damage on the Delta. I threw it away some time ago. I can still experiment with the DH3 and will at some point.
Your symptoms aim at damaged amplifier, not speaker.
Sorry pal, you contradict yourself, so which one is true?
Both can´t be true at the same time:
What´s the chance of:
Again, what´s the chance of same weird symptom happening on two completely different drivers at the same time?
Sorry pal, you contradict yourself, so which one is true?
Both can´t be true at the same time:
vs:
.......
What´s the chance of:
That looks like measurement error or misinterpretation to me.
Again, what´s the chance of same weird symptom happening on two completely different drivers at the same time?
I re-read what I wrote - the memory was bad, there was some minor scratching on the delta - but everything looked nice when dissected - I thought the former or coil went loose, but no, it was all fine, the wires held together fine and also did not move freely on the former. I could not find any reason for scratching - no deformations, nothing. I thought the whole magnet assembly shifted and caused rubbing - it all looked aligned (by eye and basic measurement, not to 1/100 mm). And since the DH3 has a plastic front, that one might be also not centered properly due to some deformation?
One day - but not the same day - it was maybe in a months span where these two failed. They were never running together and the DH3 was connected via a passive crossover.
The impedances I measured are real and were repeated many times (DH3 on the same horn, Delta in free air) - so the symptoms are definitely confirmed.
While thinking about it, mechanical misalignment (small, not really noticeable by eye) could be the cause, since the magnets seem to work normally (attracting iron from outside). As you see, I am really scratching my head about what might have happened. Would a shifted coil on the Delta cause something like this? If it was partially out of the gap and not as it should be? Anyway - I think I will just cross my fingers that this does not happen anymore and will not try to find the root cause of the failure. Maybe someone experienced would be able to tell if he had the damaged drivers at hand - I might still try to find someone to look at the DH3.
One day - but not the same day - it was maybe in a months span where these two failed. They were never running together and the DH3 was connected via a passive crossover.
The impedances I measured are real and were repeated many times (DH3 on the same horn, Delta in free air) - so the symptoms are definitely confirmed.
While thinking about it, mechanical misalignment (small, not really noticeable by eye) could be the cause, since the magnets seem to work normally (attracting iron from outside). As you see, I am really scratching my head about what might have happened. Would a shifted coil on the Delta cause something like this? If it was partially out of the gap and not as it should be? Anyway - I think I will just cross my fingers that this does not happen anymore and will not try to find the root cause of the failure. Maybe someone experienced would be able to tell if he had the damaged drivers at hand - I might still try to find someone to look at the DH3.
are you somehow bending the steel frame of the bass in one of the cabinets due to wrongly cut/fit baffle hole or badly centered bolt holes? these soft steel frames of some size are easily bent which cause all sorts of things.
In theory, the frame could be bent if the box got a hit. There is a chance I bought it already like that and did not notice for a while. There could be no DC at the DH3, it was with a passive crossover.
I think I will just stop thinking about it. It just happened somehow, the life goes on. I will not draw any conclusions about the cause, I wil just write them off.
I think I will just stop thinking about it. It just happened somehow, the life goes on. I will not draw any conclusions about the cause, I wil just write them off.
Dunno.
All of this happened years ago, much worse contradicting data is being offered and symptoms do not match probable cause, so only way to solve this is to have both units on a bench and re- test/measure them.
We´d need also the original amp.
Only "certain" things (sort of) are that magnets were not shifted (voice coils and cones were still moving freely) so they were not pinched, not open,not shorted.
Oh well.
I have dissected EV woofers that had coils which looked completely normal, but had experienced enough heat to cause blistering on the inside of the Kapton former, causing some rubbing and reduced level.
Had I not looked closely on the inside under a certain angle of light, would not have noticed the rub point, which was smooth.
Had one EVX 150 abused in a drum monitor that I suspected the same problem, as the DCR was normal.
Cut the dust cap off, put some emery sandpaper in the gap between the former and pole piece, and sanded the blister off using a 20 Hz sine wave to move the coil.
Blew out the dust, glued the dust cap back on, and the driver worked OK again.
Art
Yup, those stupid polyimide / kapton VC formers are garbage for use in a heavy duty application pro LF driver. This former material has no place in a high excusrion / high power driver. The material itself is weaker from a mechanical standpoint than the VC winding itself, as its hard to spot a thermally compromised former since it deforms quickly from thermal transients well before the VC winding shows any signs of overheating.
Those DH3 EV drivers are ridiculously sensitive to VC misalignment. Those thin kapton VC formers are super fragile and thermally non forgiving. I've replaced countless diaphragms in those throughout the years. Most you couldn't spot as having failed visually. Peavey drivers are like that too, but slightly less fragile. With the horn drivers you always had to play with the centering by rotating the magnet assembly and even screw tightening until it wouldn't buzz with a 500 Hz sinewave. Their woofer replacement baskets were like that too. Good times...
The main problem with Kapton itself as a VC former is its high internal tension and memory to retain the shape it was originally in as sheet stock before being cut and rolled. Every kapton former I've seen has some sharp out-of-round kink where the former butts up to itself radially. That shape memory is always there and in many drivers with tight VC gaps, you have to compensate when centering the VC off to one side 180 degrees out from that kink at the former gap. That doesn't leave much room for expansion, error, etc and 9 times out of 10 will develope a rubbing VC down the road. This is the kind of driver that will be highly sensitive to basket deformation when installed in a cabinet and unevenly tightened.
The solution to a kapton-only former is reinforcement with fiberglass, but that adds weight and reduces efficiency. Fiberglass or kapton reinforced FG is by far the best VC former material as its very stiff and mechanically more forgiving. It will discolor before it deforms from thermal abuse, before the VC windings insulation enamel failure point is reached. Aluminum is much better from a durability point of view, but its heavier and electrically dampens the VC movement. It also can permanently bend if the former bottoms out and hits the rear pole plate. Aluminim VC formers can take way more power for extended periods of time before the VC is permanently damaged. They also don't have as much problem with transient thermal distortion and can deal with extended periods of thermal abuse ie. car audio applications where the driver is in a small sealed enclosure and doesn't get any cooling airflow from outside. If you want to torture test a pro audio cone driver, just install it in a front loaded horn and see how long the VC lasts. Many times in that scenario you will here ZERO distortion when the driver is being overloaded thermally to the point of failure.
Those DH3 EV drivers are ridiculously sensitive to VC misalignment. Those thin kapton VC formers are super fragile and thermally non forgiving. I've replaced countless diaphragms in those throughout the years. Most you couldn't spot as having failed visually. Peavey drivers are like that too, but slightly less fragile. With the horn drivers you always had to play with the centering by rotating the magnet assembly and even screw tightening until it wouldn't buzz with a 500 Hz sinewave. Their woofer replacement baskets were like that too. Good times...
The main problem with Kapton itself as a VC former is its high internal tension and memory to retain the shape it was originally in as sheet stock before being cut and rolled. Every kapton former I've seen has some sharp out-of-round kink where the former butts up to itself radially. That shape memory is always there and in many drivers with tight VC gaps, you have to compensate when centering the VC off to one side 180 degrees out from that kink at the former gap. That doesn't leave much room for expansion, error, etc and 9 times out of 10 will develope a rubbing VC down the road. This is the kind of driver that will be highly sensitive to basket deformation when installed in a cabinet and unevenly tightened.
The solution to a kapton-only former is reinforcement with fiberglass, but that adds weight and reduces efficiency. Fiberglass or kapton reinforced FG is by far the best VC former material as its very stiff and mechanically more forgiving. It will discolor before it deforms from thermal abuse, before the VC windings insulation enamel failure point is reached. Aluminum is much better from a durability point of view, but its heavier and electrically dampens the VC movement. It also can permanently bend if the former bottoms out and hits the rear pole plate. Aluminim VC formers can take way more power for extended periods of time before the VC is permanently damaged. They also don't have as much problem with transient thermal distortion and can deal with extended periods of thermal abuse ie. car audio applications where the driver is in a small sealed enclosure and doesn't get any cooling airflow from outside. If you want to torture test a pro audio cone driver, just install it in a front loaded horn and see how long the VC lasts. Many times in that scenario you will here ZERO distortion when the driver is being overloaded thermally to the point of failure.