Poor's man silk soft dome liquid impregnation

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diyiggy

diyiggy

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Joined 2019
#1
Hi,

what to do for "recoating" a dome you can't source anymore

I'm looking for a cheap solution for impregnating a non coated silk style soft dome. Cheap if I dare... poor's man coating for tweeter for 12k-20k breaks up:scratch2:

I think about Polyisobutylène liquid for a dome bath which maybe stay sticky without drying or aqua solvant acrylic coating a la Audax they used to on domes and cones, but have no idea if it's a good choice, if one can find it at low price for few units, and if it is light & liquid enough for a tweeter dome bath?😕
Or maybe already made hifi products if good enough , I looked at Vinylflex or Stabilon, but not sure on how it works for dome tweeter?

I alo read from an old thread some use butylon solvant and mouses trap glue but I'm not confortable with the idea! Maybe butyl adhesive tape disolved with a solvant that dry and keep the stick damping property ?

Thank you if any idea comes in mind.
 
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#2
5 years later, but still....
I own 2 pairs of Heybrook HB2 speakers , with Polydax ( Audax ) silk dome original tweeters. All the tweeters have impregnation/coating that have aged, and more than 50% of the dome surfaces lack coating. Sound has degenerated accordingly.

I am desperately searching for a liquid, as close as possible to the originally used or better, for redoping / reimpregnating the domes myself.
This because I tried the "drop-in" Audax tweeter replacements sold by Falcon Acoustics, that sound not even close to the originals.


You mention aqua solvant acrylic coating, as what Audax supposedly used, and Polyisobutylène as another alternative you had in mind.
Have you done any experiments and found a well working solution ?
Where to buy such stuff in that case ?

Best regards,
Magnus , Gothenburg, Sweden
 
#3
Found this thread;

R

Thread 'Soft Dome Tweeter Coatings'

Hi all,

Ive become fascinated in the technology that is involved in coating tweeters to help reduce their resonance and/or even their frequency response.

My question is:

I would like to experiment with tweeter doping (i know i know, not too liked around here), in doing so, what are the most recommended doping/soft dome coatings recommended out their? (not too crazy about water soluable materials, i want it to last- ie no mod podge). Eventually i would like to construct my own soft-dome tweeters but i cant seem to find out this type of information anywhere.

In particular, i prefer the...
 
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#5
Domes are tricky, i have little experience. I have tried thinned acyrilic gloss on some. It wasn’t the only thing i did thou so i can’t really say much about its efficacy.

You want to add some stiffness, but not too much, and you want to do some damping but not too much.

I wouldn’t hesitate on a metal dome tweeter.

dave
 
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#9
While the PEARL PR2 design document is utterly fascinating, and describes unbelievably serious and scientific approach to speaker design, I did not find any paragraph aimin at doping of soft dome tweeter elements, or anything closely parallelling that. Did I miss something all others see?
 
#15
Coincidentally I have a pair of Polydax(Audax) tweeters with coated cambric domes that have lost enough coating to affect output and now sound 'dull and weak' with a notable lack of transient response.

From my investigations at various sites I have this information...hope it is useful to you. (Excerpts quoted intact from sources)

The sealant is nothing more than butylene rubber dissolved in toluene, with coloration of the normal amber butylene provided by carbon black, and you trivially can make your own.

I have elsewhere on AK provided summaries of the detailed research and outstanding work by RoyC and others (much of it over at ClassicSpeakerPages.net). They tested, and notably debunked, a variety of formulations and ruined a number of drivers in the course of experimentation with other sealants. You can also find the KLH memo on making this concoction with a search.

The relevant bits are:

Retrovert said:
audiokarma.org/forums/index.php?threads/klh-model-17-new-idea-for-redoping-cloth-woofer-surrounds.608604/
The original sealant, according to my research and reading at any rate, was supposedly a fairly simple mix: butyl (aka isobutylene) rubber dissolved in a low-molecular weight solvent carrier such as a mix of toluene and xylene. Not rocket science today, and it certainly wasn't in the 1950s and 60s. The carrier evaporates leaving the rubber behind. The latter mix had carbon black added to make the surround opaque.

Butyl is very sticky as everyone has experienced: chewing gum is a food-grade butyl rubber. If you know how sticky that remains over time, you can appreciate that butyl rubber is likely the right material for surrounds which are to remain flexible and tacky over time.

Silicone will harden as will many of the gasket cements.


RoyC said:
audiokarma.org/forums/index.php?threads/klh-model-17-new-idea-for-redoping-cloth-woofer-surrounds.608604/
Retrovert is correct...The Vintage AR formula is mostly butylene and toluene, and remains tacky. It required research into the original formula, as well as a great deal of testing and measurements. The toluene also helps soften the original sealant. The goal was to re-seal with minimal added material to the surround.


Regarding the solvent carrier:

Retrovert said:
Mineral spirits is usually just a name for naphtha, which is a non-standard blend of hydrocarbons that varies by the batch, as it's left over from petroleum cracking. The component molecules all have between 5 and 12 carbon atoms.

Toluene and xylene are similar: toluene has 7 carbons and Xylene has 8. Using known solvents allows you to control the evaporation rate with greater accuracy.

Your caulking may have other ingredients that are labelled as "inert" but which affect the properties nonetheless. Given that food-grade butyl rubber is dirt cheap (the food grade just means greater purity and elimination of unreacted raw materials), why use anything else?

As I always say, use these solvents in a well-ventilated area as low-molecular weight solvents are known to be carcinogenic, hepatotoxic, and neurotoxic. Don't breathe the stuff any more than you must, leave the windows open, and if you can do it outside, so much the better.
Click to expand...
Butyl Rubber is a black, premium grade, flexible 50 Duro Corrosion resistant butyl rubber sheet which has high-temperature resistance and chemical resistance to acids and alkalis. It also has low fluid and gas permeability and is UV stable and is resistant to ozone effects and extreme weather conditions.
Additionally, Butyl Rubber Sheet has low resilience making it suitable for vibration damping and shock absorption sealing applications.
Click to expand...
I have yet to try this though I'm attempting to source the materials. Problem of course is that suppliers are not willing to supply small amounts so min 20 litre Toluene and several metres of rubber !
I'm yet to approach other end users to see if I can purchase some of their scrap offcuts and a little Toluene...100ml should do several tweeters..lol.
 
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#16
Let me start by saying, thank you, thank you thank you, Drone7! The data you have gathered and kindly supplied me, more than convinced me that isobutylene ( butyl rubber ) indeed was the original tacky stuff used by manufacturers. I have read doezens of threads and searched internet, but have not managed to come up with so convincing proof that you have. It has been a mixed basket with "try shellack!" "I used silicone !" "Water solution of akrylic glue" etc etc and of course every now and then "I think it was isobutylene...". Now my efforts start to find any sources where I can buy/aquire isobutylene and toluene, in reasonable amounts and money for tweeter restoration, not running a large scale business...! If I find something of interest, I will let you know.

Again, Thank you !

Best regards,
Magnus, Gothenburg, Sweden
 
#17
The info I quoted refers mostly to doping/redoping fabric surrounds though as you have said there are several mentions elsewhere of isobutylene ( butyl rubber ) for tweeter doping and some surmising that Audax/Polydax used the same.
I have seen a comment that raw butyl is needed as Toluene does not dissolve vucanised rubber though I have no confirmation of this.
Having searched some more for materials I see that Wikipedia show butyl with a picture of chemical handling gloves...and realised I have several pairs!
Once I find some affordable Toluene I will shred a pair of gloves and see how well they will dissolve.

I am guessing that a stock solution needs to be made, then perhaps diluted with more toluene and very light coating applied to the fabric domes.
Perhaps after drying and testing another coating if needed ?

Glad the info is of use.
Cheers, Bob.

https://en.wikipedia.org/wiki/Butyl_rubber
 
#18
Hi Bob. I guess as well that experimenting with toluene dissolved raw isobutylene, in different viscosities will be required before daring to put it on the actual Polydax silk domes. So, coming from the very thin solution side is likely the sensible way. Regarding the possible difficulty in getting smaller quantities of isobutylene at reasonable prices, I think I saw diyiggy speculate if the adhesive from ordinary duct tape could be extracted and diluted, since adhesives for tape seem to be a common use of isobutylene commercially. As well as for chewing gum...! Possibly a well chewed bar of Wrigley's "Spear Mint" dissolved in toluene would do the trick, haha !

Best regards,
Magnus
 
#19
mod podge gloss lustre lustre. -> https://www.vaessen-creative.com/en/blog/what-is-mod-podge-ideas-tips I'm doing cone and edge coating with it, nice product!

2025-05-13_130000.jpg
 
#20
I tried the Visaton LTS50 on the Dynaudio D28AF and it worked fine. First was the replacement of the ferrofluid, then the coating. The original coating has dried and accumulated dust. One thin coat solved the problem. First cleaning with adhesive tape, then with distilled water, then drying, and finally LTS50 one coat. It's normally intended for coating paper speaker membranes, and I've used it for that several times.
 

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