Ferrofluids - What's in Your Speakers?

[The Grand Wazoo]

I have a habit of being enthralled every year by the Royal Institution Christmas Lectures, which are an attempt to get kids excited about science - something we'll be relying on more & more as we have been Con-Demmed by our government to university-lite.

This year the theme is 'Size Matters' and the lecturer is Dr Mark Miodownik, who is a materials scientist, a specialist in jet engineering and is currently researching the possibilities of self-healing materials.

The size matters thing comes to play because when you change the scale of objects they are influenced in different ways than normal by the various forces at work. Anyway, as an opening flourish on the lecture that was broadcast tonight, one of the things he did was to play some tricks with ferrofluids. He demonstrated how by applying a magnetic field to them, you can make a liquid flow uphill.

There are some amazing videos on You Tube which illustrate this beautifully.
I firmly believe that where there is science, there is beauty.

So, here's the beauty:

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.........and here's the science:

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The clips are not camera trickery or time lapse photography, it's merely the application and manipulation of magnetic forces on a liquid that is loaded with metal particles.


In a ferrofluid, the carrier (or liquid) is usually a synthetic oil - the fact that its oil is fairly apparent in the videos above. The particles are normally Magnetite (Fe3 O4 - sorry, I can't do sub-script 3's & 4's!).

So, why do they put ferrofluids into loudspeakers then?

1. It conducts heat away from the voice-coil. These are made of extremely thin, fragile wires which can burn out if over stimulated. It helps to make a speaker more efficient.
2. It's relative density ('stiffness') keeps the voice coil concentrically aligned with the magnet
3. That density assists with damping the moving parts of the motor (as well as those that aren't supposed to move).

So when were ferrofluids introduced to the loudspeaker world?
And is the result all good?








The Royal Institution Christmas Lectures website - http://www.rigb.org/contentControl?action=displayContent&id=00000004333

BBC4 iPlayer:
Yesterday's lecture (Why Can't Elephants Dance?) - http://www.bbc.co.uk/iplayer/episode/b00x1v7l/Royal_Institution_Christmas_Lectures_2010_Why_Elep hants_Cant_Dance/

Tonight's lecture (Why Chocolate Melts & Jet Engines Don't) -
http://www.bbc.co.uk/iplayer/episode/b00x1ygp/Royal_Institution_Christmas_Lectures_2010_Why_Choc olate_Melts_and_Jet_Engines_Dont/

[retro]

The first time I heard of the ferrofluid was late eighties and I think the Dynaudio was first company that has started to use it in tweeters.Price was over 1000 dollars per liter.:scratch:
After tens of years,ferrofluid is no so liquid so it must be cleaned

[DSJR]

My speakers pre-date ferrofluid...

[The Grand Wazoo]

Remind me what they are and when they date from, would you please, Dave?

[hifi_dave]

The first time I was aware of Ferofluid was with certain ProAc speakers in the mid 80's IIRC. They used it to increase the heat disippation and therefore, power handling of the tweeters. It was applied by syringe.

Whilst having the desired effect it also tended to 'deaden' the HF, removing some life and sparkle in the process. It also dries out with age, which might not be desirable.

[The Grand Wazoo]

OK, so there is a downside. Do we know how commonly it's used?

[Alex_UK]

I have a habit of being enthralled every year by the Royal Institution Christmas Lectures

Me too! Not watched this years yet. Good Reminder! :)