Hi ! there is an interesting video tour of PMC factory on youtube
I was surprised to see that the treatment of the dome of their mighty 3" midrange is done by hand 😵 with some kind of secret compound
Anyway i have some questions
Have you ever treated a driver ? how ? what have been the results ?
if i had mass to the diaphragm of a driver my guess is that the fs should go down and the Qts up Am i wrong ?
i have two domes at hand that i could play with they are now out of spec
To be honest i do not know the original specs but i cant think of a 2" dome with fs around 1kHz I would expect at least half that
The domes are the only parts that can have aged badly and I cant find dome replacements for now
i dont think that ferrite magnets have lost their strength
I was surprised to see that the treatment of the dome of their mighty 3" midrange is done by hand 😵 with some kind of secret compound
Anyway i have some questions
Have you ever treated a driver ? how ? what have been the results ?
if i had mass to the diaphragm of a driver my guess is that the fs should go down and the Qts up Am i wrong ?
i have two domes at hand that i could play with they are now out of spec
To be honest i do not know the original specs but i cant think of a 2" dome with fs around 1kHz I would expect at least half that
The domes are the only parts that can have aged badly and I cant find dome replacements for now
i dont think that ferrite magnets have lost their strength
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Hi thank you for your kind and valuable advice I see no trace of fluid on the coil
Does anybody sell it maybe ? i would love to try it
i wonder what kind of effect can have ferrofluid presence or absence on TS parameters Substantial or marginal ?
Does anybody sell it maybe ? i would love to try it
i wonder what kind of effect can have ferrofluid presence or absence on TS parameters Substantial or marginal ?
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Maybe it is fully dried out and only "gunk" in the coil gap. Alternatively your speaker never had ferro fluid and that there is something else causing issues.
A friend of mine used this source for fluid with good success.
https://speakerrepairshop.nl/en/questions/ferrofluid/c-34
A friend of mine used this source for fluid with good success.
https://speakerrepairshop.nl/en/questions/ferrofluid/c-34
Thank you very much again For sure they are old parts maybe abused during time
I have bought another vintage speaker with the same mids that i have to measure Their domes look more black
I start to think that the domes could have been replaced
what i really love of compression drivers is the possibility to replace broken coils and diaphragm very easy
the motor and the horn are pretty much neverending
I am thinking seriously to pass to those kind of drivers Horns are still a mystery to me But they remind me of the old times
I have bought another vintage speaker with the same mids that i have to measure Their domes look more black
I start to think that the domes could have been replaced
what i really love of compression drivers is the possibility to replace broken coils and diaphragm very easy
the motor and the horn are pretty much neverending
I am thinking seriously to pass to those kind of drivers Horns are still a mystery to me But they remind me of the old times
I replaced the ferrofluid in a pair of tweeters a few months ago. It thickens to a tarry substance. With the tweeters I repaired, the oil had migrated out of the fluid apparently by capillary action and was distributed between the magnet and the plate holding the dome. Note that ferrofluid has oil as its base (nowadays synthetic oil). It was a relatively easy job. I used a Ferrotec product.
I also treated the cloth domes with dome treatment purchased from the Dutch shop linked to above. As an aside, I'm fairly sure this stuff is mainly artists acrylic pouring medium or a similar acrylic artists product, judging by its characteristics. Again, this was relatively easy. However, the dome on these tweeters was located by raised bumps on the magnet structure fitting to matching holes on the dome retaining plate, so no special alignment techniques were necessary to align the voice coil.
Hi thank you very much for the precious advice Have you measured the tweeters before and after the treatment ?
the viscous oil could work also as a damper for the moving diaphragm ? the doping of the dome instead should lower the fs by adding mass to the dome
from the video i understand that they have spent a lot of time to get the right compounds
i have to measure the exact size of the coil and look around for any compatible parts
the viscous oil could work also as a damper for the moving diaphragm ? the doping of the dome instead should lower the fs by adding mass to the dome
from the video i understand that they have spent a lot of time to get the right compounds
i have to measure the exact size of the coil and look around for any compatible parts
No, I didn't measure the tweeters. They are the infamous Tonegen tweeters on which the yellowed coating of the dome flakes off on all examples it seems. The dome becomes very porous - it ends up looking like miniature fly screen - so they lose much of their output. They're not like many domes which have that soft and sticky coating; these have what looks like shellac on them. However, it's not shellac because it doesn't dissolve in alcohol.
Therefore, any 'before' measurement would be worthless I guess.
Fortunately, the remaining coating can be totally removed with white spirit (and then alcohol to remove the white spirit), so hopefully the replacement coating would cause the dome to have a similar mass to the original as you're not adding it on top of the old.
According to speaker manufacturers, the ferrofluid does actually damp the movement of the voice coil, as well as allegedly cooling it.
Therefore, any 'before' measurement would be worthless I guess.
Fortunately, the remaining coating can be totally removed with white spirit (and then alcohol to remove the white spirit), so hopefully the replacement coating would cause the dome to have a similar mass to the original as you're not adding it on top of the old.
According to speaker manufacturers, the ferrofluid does actually damp the movement of the voice coil, as well as allegedly cooling it.
Hi thank you very much again Very interesting
Again from the PMC video any action on the moving parts of the drivers is followed by a measurement check
There is an interesting video about Borresen speakers The scientist from Borresen shows two coils mounted on formers made out of Al and Ti
The one mounted on the Al former descends slowly in the gap while the one mounted on the Ti former drops fast
Fwiu they consider this latter behaviour superior
For sure a high viscous fluid in the gap will make the former slower But also less prone to ringing ?
Again from the PMC video any action on the moving parts of the drivers is followed by a measurement check
interesting This is exactly what some manufacturers want to avoid for instance by using a titanium former
There is an interesting video about Borresen speakers The scientist from Borresen shows two coils mounted on formers made out of Al and Ti
The one mounted on the Al former descends slowly in the gap while the one mounted on the Ti former drops fast
Fwiu they consider this latter behaviour superior
For sure a high viscous fluid in the gap will make the former slower But also less prone to ringing ?
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This is from the maker of the ferrofluid I used.
https://ferrofluid.ferrotec.com/pro...:text=Damping,the viscosity of the ferrofluid.
https://ferrofluid.ferrotec.com/pro...:text=Damping,the viscosity of the ferrofluid.
Hi again I see My personal problems start when one says that voice coil damping is a good thing to have and another says that is it bad and they prefer instead to dampen the diaphragm with resins They do not like to use viscous fluids in the gap
the increased thermal conductivity i guess it is good for anyone
But i have come to a conclusion Measurements tell almost all I believe in lab testing
i was watching a video comparing two inductors one small and one huge 20 times the cost of the small
Only a complete set of measurements could convince me to buy the more expensive A listening opinion is not enough It is almost offensive
the increased thermal conductivity i guess it is good for anyone
But i have come to a conclusion Measurements tell almost all I believe in lab testing
i was watching a video comparing two inductors one small and one huge 20 times the cost of the small
Only a complete set of measurements could convince me to buy the more expensive A listening opinion is not enough It is almost offensive
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You may want to compare Seas 27TDC datasheet with the 27TDFC datasheet.
https://seas.no/index.php?option=com_content&view=category&id=45&Itemid=239
As for influence on sound quality I guess it is al about finding the compromise needed in your specific design. Do you need the added heat-disipation fluid offers how loud do you play, what's your crossover frequency and what viscosity oil and do you need the more benign impedance curve gained by using fluid.
https://seas.no/index.php?option=com_content&view=category&id=45&Itemid=239
As for influence on sound quality I guess it is al about finding the compromise needed in your specific design. Do you need the added heat-disipation fluid offers how loud do you play, what's your crossover frequency and what viscosity oil and do you need the more benign impedance curve gained by using fluid.
thank you very much the two datasheets look quite similar
fs looks the same with and witout FF
Unfortunately they do not report Qts
thank you for the link I am reading it now
a better heat transfer from the coil to the metal aound is a very good thing Probably it can be done with some venting systems
The dampening could also be done by treating the domes with proper substances
fs looks the same with and witout FF
Unfortunately they do not report Qts
thank you for the link I am reading it now
a better heat transfer from the coil to the metal aound is a very good thing Probably it can be done with some venting systems
The dampening could also be done by treating the domes with proper substances
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I only replaced the ferrofluid because it was originally used. However, I think many (most?) high quality tweeters nowadays do not use it.
I have no data to back this up, but intuitively I doubt the claims about cooling. The amount of ferrofluid in the gap is tiny - for example, in those I repaired I used 0.1ml - and despite containing iron, it is largely oil. I think this tiny amount of fluid of this type wouldn't conduct a lot of heat. Of course I may be wrong.
I have speculated to myself that the fluid was designed mainly for damping resonance but 'ferrofluid cooled' sounds good in marketing and gives the impression of 'high performance'.
That said, I have not attempted to find data on this. Maybe a manufacturer has measured the temperature effects, but I wasn't interested enough to search. I'll just replace it if necessary on tweeters that use it.
I have no data to back this up, but intuitively I doubt the claims about cooling. The amount of ferrofluid in the gap is tiny - for example, in those I repaired I used 0.1ml - and despite containing iron, it is largely oil. I think this tiny amount of fluid of this type wouldn't conduct a lot of heat. Of course I may be wrong.
I have speculated to myself that the fluid was designed mainly for damping resonance but 'ferrofluid cooled' sounds good in marketing and gives the impression of 'high performance'.
That said, I have not attempted to find data on this. Maybe a manufacturer has measured the temperature effects, but I wasn't interested enough to search. I'll just replace it if necessary on tweeters that use it.
Thiele Small parameters only matter in regards to the low frequency behaviour of direct coupled (non horn loaded) cone drivers. They tell nothing about mids or how a tweeter behaves.
Our intuitions differ here. I am inclined to believe a fluid is better at conducting heat away from the coil and onto the magnets better than an airgap.
Take a look at the datasheets for the two SEAS tweeters motioned as examples in post #12 above.
According to Seas datasheet long and short term power handling is higher with fluid. lowest crossover point with 3rd order filters is also lower at 1500 vs 2000Hz.
It could well be (is likely) that crossed over at 2500-3000 Hz the TDC will sound better than the TDFC, however if you need to cross over at or below 2000 my money is on the TDFC. Everything is a compromise.
PS - I should add that I have not heard and compared sound for these tweeters. using datasheet as reference only
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oil can have a decent thermal conductivity I guess better than air
They are used in some voltage transformers
looking at the datasheets of a same tweeter with and without FF the fs is the same Unfortunately Qts is not provided
My guess is that dome doping instead can have a substantial impact on TS parameters even only adding mass to the dome
they should lower fs i guess and raise the Qts
Doping substances can have high density The doping as the video shows very well is a critical point in the production process
The charming Lady must be an institution at PMC A very gifted person
you mean that fs is not important for a tweeter ? or a dome midrange ?
personally i despise manual treatments completely They are not repeatable and accurate I would much prefer to develope special materials to produce the domes
For instance if i remember well Lynn Olson was promoting the idea of using the polymeric material out of which the old floppy disks were made
It must be very cheap and with great mechanical properties Stiff and well damped at the same time
I do not know why no one has followed his extremely smart advice
Domes are not for painters For those there are canvas
Fs might be the only T/S parameter relevant for a tweeter as it tells you a minimum crossover frequency and filter steepness to not destroy the tweeter. But all the other T/S parameters are meant to be used to figure out the lf behaviour of a direct radiating driver in a box.
See here: https://en.wikipedia.org/wiki/Thiele/Small_parameters "Thiele/Small parameters (commonly abbreviated T/S parameters, or TSP) are a set of electromechanical parameters that define the specified low frequency performance of a loudspeaker driver."
See here: https://en.wikipedia.org/wiki/Thiele/Small_parameters "Thiele/Small parameters (commonly abbreviated T/S parameters, or TSP) are a set of electromechanical parameters that define the specified low frequency performance of a loudspeaker driver."
Hi ! thank you so much for your kind and extremely valuable advice
Now i understand why the tweeters datasheets were only mentioning the fs There was no different between with or without FF Exactly 550Hz the same
i wonder why many pro drivers have replacements and hifi drivers not It would be nice to keep a great magnet and be able to replace only the moving assembly Like audio surgery
I will try to get compatible domes I can measure the diameter and the weight of the originals I have still another pair to check
I have fallen in love with the Dayton dats v3 device
Now i understand why the tweeters datasheets were only mentioning the fs There was no different between with or without FF Exactly 550Hz the same
i wonder why many pro drivers have replacements and hifi drivers not It would be nice to keep a great magnet and be able to replace only the moving assembly Like audio surgery
I will try to get compatible domes I can measure the diameter and the weight of the originals I have still another pair to check
I have fallen in love with the Dayton dats v3 device