Seems there are many sort of silk impregnation : sticky or not, more or less light and hard.
So you can not use impregnation anymore or the result will not be the same everywhere. According to your dome was known about its style of coating (light, sticky) your best bet is a long iteration by using the lighter varnish possible (aqua, petrol, vegetal based, ?) in order of evaporation of the diluent keeps the less heavy deposit.... on both side of the dome ! All the rubber based imo are too much heavy for a dome for a refurbishing option - or it changes too much the former measures.
Your best bet is to know the brand and if possible purchase the dome voice coil spare part to adaptt on your model knowing centering is a difficult thing... on the opposit the refurbishing ask many try and error so is a long process : measurement and hearing test... and to a limit a destructive process when it's dry and you have missed the level of the formergenuine trade off.
my two injections...
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I've had good results with diluted silicone on soft domes. It dampens well and adds little mass, plus is long term stable if applied properly. It also doesn't remain sticky like PVA type coatings so it wont accumulate and retain a bunch of dust particles.
I have a set of newer TW034XO tweeters that I coated with measured amounts of thinned silicone. The stuff I use comes in a tube which I weigh before and after to verify an exact amount, so the coating ends up even between a pair or batch of tweeters. I thin out the silicone with hexane at a ratio of 1 part silicone to 3 parts hexane. The hexane completely evaporates so all you're left with is the silicone. You have to work quickly, especially in warmer temps, so the coating ends up smooth and even. The coating should be applied with a fine brush and not sprayed, mainly because brushing pushes the coating more into the crevices of the fabric from the friction of the brush, while spraying just makes it sit on the top. Using an old modified turntable set to 16 rpm makes it easier to apply and get a nice even coat on the dome and surround. I start the coating by putting the full weighed portion of the mixture on the tip of the dome and work it down the sides, spreading it outwards. The brush needs to remain wet all the time and is first wetted with pure hexane just before starting the coating process.This is what I found to be the only way of getting a consistent coating that looks like it was factory applied.
The main effect i can measure is reduced top end beakup modes that many manufacturers use to create a rising response towards the upper frequencies. This makes the tweeter sound more "euphoric", giving the illusion of space and wider sound stage. The reality of this is increased distortion, which hurts imaging and accuracy. The proper amount of coating reduces the breakup while not overly weighing down the dome and overly reducing top end frequency response. The moving mass on a TW034XO is 500 mg and you dont want to add more than 50 - 75 mg of mass, otherwise it ends up sounding to dark. You'll need a very accurate scale to measure this. I derived this from cutting out an older and newer TW034 dome and weighing them both. The difference bewteen them is roughly 75 mg with the older one being heavier.
I have a set of newer TW034XO tweeters that I coated with measured amounts of thinned silicone. The stuff I use comes in a tube which I weigh before and after to verify an exact amount, so the coating ends up even between a pair or batch of tweeters. I thin out the silicone with hexane at a ratio of 1 part silicone to 3 parts hexane. The hexane completely evaporates so all you're left with is the silicone. You have to work quickly, especially in warmer temps, so the coating ends up smooth and even. The coating should be applied with a fine brush and not sprayed, mainly because brushing pushes the coating more into the crevices of the fabric from the friction of the brush, while spraying just makes it sit on the top. Using an old modified turntable set to 16 rpm makes it easier to apply and get a nice even coat on the dome and surround. I start the coating by putting the full weighed portion of the mixture on the tip of the dome and work it down the sides, spreading it outwards. The brush needs to remain wet all the time and is first wetted with pure hexane just before starting the coating process.This is what I found to be the only way of getting a consistent coating that looks like it was factory applied.
The main effect i can measure is reduced top end beakup modes that many manufacturers use to create a rising response towards the upper frequencies. This makes the tweeter sound more "euphoric", giving the illusion of space and wider sound stage. The reality of this is increased distortion, which hurts imaging and accuracy. The proper amount of coating reduces the breakup while not overly weighing down the dome and overly reducing top end frequency response. The moving mass on a TW034XO is 500 mg and you dont want to add more than 50 - 75 mg of mass, otherwise it ends up sounding to dark. You'll need a very accurate scale to measure this. I derived this from cutting out an older and newer TW034 dome and weighing them both. The difference bewteen them is roughly 75 mg with the older one being heavier.
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Another 'golden oldie' I just remembered is neutral pH water soluble adhesive: https://www.amazon.com/Lineco-901-1008-Neutral-Adhesive-Ounces/dp/B001I6FEHE
Absolutely. The choice of material and geometry of the cone is simply an engineering compromise between performance parameters. No one choice of material or cone geometry is superior to all others. Certainly it is possible to design a turd that does almost everything badly, even with exotic materials
The prejudice that - for instance - metal coned speakers will always sound like banging trash can lids or jingle bells is either expectation bias, or horrid implementation in a multi-way system.
When crossed over properly, any speaker should be completely transparent as it is operating only in it's pistonic region - i.e. the cone breakup is not heard. Even if a driver is used well into it's breakup region, there is no guarantee that it will have a characteristic sound based on the materials that it is manufactured with. Paper cones can sound harsher and more metallic than metal cones.
Some drivers have more benign looking breakup peaks than others but that doesn't mean that they will automatically sound better than the driver when implemented in a multi-way system properly. Usually when a driver appears devoid of any breakup it's a red flag that the cone breakup and voicecoil inductance have equal and opposite effects on the frequency response, and this typically leads to poorer non-linear distortion performance as the inductance is typically higher than normal to cause this effect.
edit:holy thread revival batman
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1 part Permatex 81730 Windshield and Glass Sealant thinned with 3 parts hexane.
Be careful with the hexane. Its a neurotoxin and should be used with adequate ventilation.
I'm interested in this topic because I have several Audax 1" dome tweeters that do not
sound right and measurements confirm diminished output and/or notches in the frequency
response probably due to leakage through the fabric dome.
I remember from the first time seeing this treatment that it remained sticky for many years,
both on domes and as edge/complete cone treatment of paper cone drivers and dust caps.
I'd like to find the exact same material that was originally used but I've not seen anything
posted that remains sticky.
There is cloth edge treatment used to restore vintage AR and KLH woofers that is made to
the original formula but I'm not sure if it is the same as dome treatment or if it remains
sticky. I've read that it is butyl rubber based.
I've also read that this is butyl rubber based but it does not remain sticky:
E6000 - Products | In The Home & On The Job Products
This is available at most of the local supply stores and I hear that their Goop products
are nearly the same formula:
Amazing GOOP Adhesives - Products | In The Home & On The Job Products
I might try this if I ever have the failing Audax tweeters hooked up to my test rig again - plan
to rub it into the dome, then try to remove as much as possible.
sound right and measurements confirm diminished output and/or notches in the frequency
response probably due to leakage through the fabric dome.
I remember from the first time seeing this treatment that it remained sticky for many years,
both on domes and as edge/complete cone treatment of paper cone drivers and dust caps.
I'd like to find the exact same material that was originally used but I've not seen anything
posted that remains sticky.
There is cloth edge treatment used to restore vintage AR and KLH woofers that is made to
the original formula but I'm not sure if it is the same as dome treatment or if it remains
sticky. I've read that it is butyl rubber based.
I've also read that this is butyl rubber based but it does not remain sticky:
E6000 - Products | In The Home & On The Job Products
This is available at most of the local supply stores and I hear that their Goop products
are nearly the same formula:
Amazing GOOP Adhesives - Products | In The Home & On The Job Products
I might try this if I ever have the failing Audax tweeters hooked up to my test rig again - plan
to rub it into the dome, then try to remove as much as possible.
GOOP products are all urethanes.
E6000 are mostly urethanes, with a few cyanoacrylates(if the description sounds like SuperGlue, it's CA)
Gotilla prodocts are, as E6000, mostly urethanes, with a few CAs, and at least one epoxy.
Some domes were coated with urethanes, but as we cannot easily reformulate the products,
I'd suggest playing with a 3-5% solution, then a 10% or 2%, depending on the first results.
Check the data sheets for solvents, pick the least noxious.(regular data sheets will give you solvents,MSDSs will give you components)
Good luck, and of course if you are captured - yada, yada,....etc...etc
E6000 are mostly urethanes, with a few cyanoacrylates(if the description sounds like SuperGlue, it's CA)
Gotilla prodocts are, as E6000, mostly urethanes, with a few CAs, and at least one epoxy.
Some domes were coated with urethanes, but as we cannot easily reformulate the products,
I'd suggest playing with a 3-5% solution, then a 10% or 2%, depending on the first results.
Check the data sheets for solvents, pick the least noxious.(regular data sheets will give you solvents,MSDSs will give you components)
Good luck, and of course if you are captured - yada, yada,....etc...etc
