Silicone In-ear Monitors

[zerozorro]

Hello everyone,

Me and few other members of head-fi forums are thinking of making some custom silicone in-ear monitors. Being silicone noobs, we hope you guys with your experience might land a hand. We have molds, but got stuck in silicone choice and pressure equipment.

Basically, we have just 2 questions:

1. What silicone would you suggest safety-wise, considering the contact with skin?
2. Is a pressure / vacuum pot a must? Are bubbles more of a visual issue or they have a critical impact on the construction?

Any of your suggestions, advice and links are most welcome.

[mangozac]

Welcome to RA Zerozorro!

This sounds very interesting and if I had my casting skills several years back when I was playing in a band I would probably have done something similar!

I believe most silicones are pretty inert once cured, but indeed many are also rated as being "food safe". The Pinkysil that I use is stated as being "skin safe", but that is with regards to actually moulding body parts.

How do you plan on making the earpiece? You're not going to pour the silicone into your ear and wait for it to cure, right?

For this kind of application a silicone with a suitably low viscosity won't require any fancy pressure or vacuum techniques.

Some quick Googling found this: http://www.howtogeek.com/57481/how-to-m ... -monitors/
Is that the idea here?

[zerozorro]

Thanks for the welcome, Mangozac,

The approach you've linked is just a consumer headphones stuck into Radians, our aim is a bit more ambitious: a self-assembled dirvers combo that resides in a better grade silicone, like ACS T1:


Or ACS T3 (mini shell):


It's done via ear impression -> mold etc. And while most others do it with acrylic, some of us wanted to try silicone, like or already mentioned .

As we went on and on and on arguing on what silicone (medical grade? any?) to use and can it be done without vacuum, it became clear that it is better to ask people who actually might have a clue :)

So if you have an opinion on a particular silicone and possibility to make it without vacuum, please share. Even if it's theoretical, I guess it'll still be better than ours.

[geomod]

OK, here goes. Please note that this is from a position of moderate ignorance on the subject of what is effectivly medical moulding.

I have a co-worker that has had custom ear-plugs made, much the same as what you describe, but solid.

This was done by putting a small plug in her ear (to protect the ear-drum) then the plastic was injected into her ear, where it set (by what sounds like a chemical reaction).

I have recently begun experimenting with a material called 'polymorph' or instant mould. It is a thermoplastic that becomes soft at 62 degrees celcius, but remains plastic while it cools. The important part is that once the plastic is cooled, it can be machined, drilled etc.

My approach (remember I am just floating ideas here) would be to use a sufficiently cool lump of polymorph to firmly plug the ear canal (being careful not to push it too far in) and adjacent ear structures.

Once the plastic is hard, it should be (carefully) removed, then can be drilled etc to allow for the speaker components. Once the part is finished, then you could either use the finished part (as my co-worker effectivly does) or make a silicone mould so you could replicate the plug as needed.

In this case, you would not need to vacuum the silicone (although I would, but I have the equiptment already ), just use pressure to ensure a good mould.

Then you can cast the plug as often as you need. In whatever material you want.

Please remember, I am not an expert, and you should be VERY careful doing anything with your ears.

I'll be interested in hearing what others think of my idea.

[Joey]

Could this be a task for sugru?
http://sugru.com/

It certainly won't break the bank, and if it doesn't work -well then you have a new cool way of hacking things.

[mangozac]

While Geomod's suggested technique could work quite well, I'd be inclined to give the Sugru a go first (thanks for the link, Joey!).

Anything moulded to your ear is only going to be suitable for you, so there's no need to have a mould that can continually reproduce them. I'd build up the driver and temporarily glue it to a bit of rod coated with release agent (probably vaseline). Then mash some Sugru around it, stick it in your ear, mould to shape and remove to let it cure. Once cured break the glue connection and pull out the rod. Easy!

[zerozorro]

Thank you for the link, Joey!

However there are 2 problems with Sugru:
1) It seems to be harder than the silicone used in the shells I've linked above. For those a 40 Shore silicone (mini shells) and 60 Shore (big shells) is used.
2) It has no health certificate yet, they are only working on it.

I'm still very impressed with Sugru, thinking to use it for a low-profile diy jack, headphone wire Y-split and maybe strain reliefs. And if it be certified as hypoallergenic, for harder shells.

But we still are trying to find a softer silicone. Molding, ear impressions, etc aren't problems. The problem is to find a 40-60 Shore hypoallergenic silicone that could be molded without vacuum or pressure.

[zerozorro]

Ok, here's the 1st candidate: - skin safe 40 Shore silicone.

The viscosity and cured hardness seem to be suitable to my noob eyes (but not sure about the strength and tear resistance numbers). Also I wonder why is it marketed as "moulding" (and not general purpose - is it important?) and if it could be done without the pressure equipment.

Any comments / alternatives?

Edit 1: Btw from the Sugru : "Avoid contact with skin. Some ingredients have been identified with irritant properties. Repeated or prolonged contact may cause skin irritation. May cause an allergic reaction."

Edit 2: Any opinions on (Shore 30A) or (25A)? Both skin-safe, it seems, however both msds are kinda sketchy on prolonged skin contacts.

Edit 3. I also wonder how serious all these "skin-safety" and "irritation" claims are. Some sites like ResMed just say "True allergic reactions to silicone are extremely rare. In fact, skin irritation, sores (pressure sores) and blisters are more commonly caused by other associated factors rather than the silicone material itself. " So should just any non-toxic silicone compound be just considered "somewhat skin safe" with rarely possible allergies and irritations caused by closed pores etc? I.e. there's no difference between non-toxic silicone A and B, despite A labeled as "skin-safe"?

Pretty hard to be a noob, ladies and gentlemen...

[zerozorro]

Answering some of my questions:

There is a great on silicone, covering all aspects, including medical. Here's what it says on medical aspects:

"The current health-care market supports a small group of manufacturers of silicone raw materials, companies such as General Electric, Wacker, Bayer, Dow Corning, Rhodia, Shin Etsu, Nusil Technology.

The primary differences among these suppliers involve their level of testing and commitment to serving particular applications. Historically, concerns over potential liability have driven most large silicone manufacturers to aggressively exclude themselves from providing silicone intended to be used in the human body for more than 29 days. The author knows of only one supplier willing to continue serving the long-term implantable silicone market: Nusil Technology."

Here is the , but I cannot find any retailer.

[mangozac]

You have a good point - silicone is in general pretty inert and it's rare for someone to have a reaction. That said though, I would certainly shop around for a 2-part silicone putty certified specifically for skin contact use.

I doubt there's anything special about "moulding" silicone other than the general strength and hardness characteristics that make it more suitable for moulding applications.

I can't see you needing vacuum or pressure for any of these applications.