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adding ferro fluid to rcf n350

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matty w View Drop Down
Young Croc
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    Posted: 29 April 2017 at 8:14am
Hey guys ,

I'm considering adding Ferro fluid to a compression driver ,a one inch exit ,1.75" plastic diaphragm ,the RCF N350!

The driver DOESN'T come with Ferro fluid from the factory !

The drivers are mounted on some exponential 3khz solid pine horns that I made ,they actually do there job very well albeit needing some eq !

There is a certain character that needs to be neutralized but can't be acheived with eq , I'm confident the extra damping might just smooth out the resonance that I thinks causing it ,in any case I allways prefer the sound of a compression driver that uses Ferro fluid


Im asking if there is potential to cause damage adding the Ferro fluid ? With adhesives mayb ?.

I plan to fill the gap up about half to two thirds full and go from there !.

Anyone got anything to add to this ?
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madboffin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote madboffin Quote  Post ReplyReply Direct Link To This Post Posted: 29 April 2017 at 4:58pm
This may be a bad idea.

Ferrofluid is incompatible with some glues, and you won't find out if yours is OK until the voice coil eventually falls off in use (or doesn't).

Some ferrofluids dry out after a few years, leaving residue in the gap. A lot of Hi-Fi tweeters have this problem.

Having said that:
If you are aware of the potential problems and are willing to try it as an experiment, and have some measuring kit to evaluate the effect on the frequency and impedance response of the driver, then give it a try.
Experimentation and self-build is what Speakerplans is all about. Please be sure to post the results, whether they are good or bad, for us all to learn from.


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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 11:45am
Thankyou for your advice, a little late I know

So I purchased 900ul of Ferro fluid from Queensland speaker repairs for about $23 aud.
They sell two types ,of differing viscosity, one for woofers and one for tweeters etc .
There's literaly multiple different viscosity fluids available but I guess providing your in the rite ballpark it doesn't matter too much .
Mayb if you had an extremely delicate tweeter or a really heavy duty woofer u may seek something more fine tuned for application or mayb if your replacing fluid as opposed to installing it like I am it would be worth doing some more research as to exactly what you need .

Anyone have any thoughts on this ?

So iv used slightly under half the tube in each voicecoil gap .
When I squeezed it out from the tube , which is quite an odd process as u can barely see it come out due to it's magnetic attraction , the fluid seemed to suspend itself towards the top of the magnet gap !
It's hard to say whether the gap was full or just that the magnetic flux was stronger at the top of the gap .

My gut feeling is that it could potentially comfortably accomodate more fluid   but id rather have not enough than too much considering the nature of the application.

Anyway , comparing one tweeter to the other after one had been filled , it behaved exactly as I expected it to !

I havnt taken any real indicative measurements ,sorry , havnt the facilities to do it

But it was night and day tbf , the driver with the Ferro fluid sounded smoother ,less aggressive and more musical .

It just sounds more damped lol which it is , less resonant ,silkyer .
Don't think it's had a huge difference to frequency response ,it's just it's character that's changed if that makes sense , doesnt sound like your listening to a plastic diaphragm anymore .

Suprisingly , to my ears it seems to have helped with the very high frequency , I thought it would attenuate the very high frequency but without out measurements ,who knows ,it could be a product of reduced distortion allowing the detail in the very high end to seem more prominent !

Anyway . It's been in there for about a month now and the rig has been gigged a few times at war volume plus I use the tops at home ,so has had consistant use and all good so far :)

So watch this space !!
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gen0me View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 12:21pm
Originally posted by matty w matty w wrote:

the fluid seemed to suspend itself towards the top of the magnet gap !
It's hard to say whether the gap was full or just that the magnetic flux was stronger at the top of the gap .

Have you thought about experimenting with demodulating ring? Some machining could be necessary though.

Do you have any demos with them? Before and after?
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 12:46pm
I havnt sorry ,not sure a video from my phone would be acurate enough to show much up but would of been interesting all the same !

I don't really understand what a demodulating ring does tbh , care to explain ?
I'm aware of them, some reading tonight to be done :)

My next project is gonna be , boreing out the back chamber of a community sound m200 compression driver to give it some more gain in the lower regions !
To make full use of some jbl 2360a horns but that's another storey :)
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 12:47pm
I recently built some solid pine horns for the rcf drivers , I'll try an dig out some pics :)
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gen0me View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 4:10pm
http://terpconnect.umd.edu/~wbreslyn/chemistry/is-copper-magnetic.html
They keep the magnetic field in the gap.
Here is picture without demodulating rings:

Out of magnet gap is still magnetic field and as vc moves it moves in that field unsymetrically. Demodulating rings are usually placed where green arrows are but you noticed same behaviour of magnetic field on the top. You could probably figure out some way to add them at the top.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 4:34pm
"Ferrofluid is incompatible with some glues"

+1

I´d get in touch with RCF asap and find out if the glue used on your comps will be ok with the fluid. Otherwise, you´re effectively binning them!  


Earplugs Are For Wimps!
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 6:11pm
It's only 60 dolla for an original replacement diaphragm so I'm not gonna lose sleep over it tbh .

Your rite though I should try and contact RCF, kinda figured they wouldn't wanna give me the information as it involves modifiying there product.

The fluids been in there over a month now ,would of thought it would of saturated the adhesive by now but who knows

I may take one out and have a look ,although I doubt it would show anything .

According to I think it's ferrotec ( will have to check ) it's unusual for there to be an issue , however i guess they would say that .

As I allways like say ... " gotta be in it to win it " aaaand ... "He who dares Rodney ,he who dares " haha
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gen0me View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 6:18pm
Right but you cant get original one with the same glue neither cant get ferrofluid out.
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 6:34pm
Gen0me ,thanks for the diagram and incite , can't quite get my head around the concept atm but it's half one in the morning here ha I understand what it acheives but cant quite understand how it does it to know whether it's diy'able!


Going back to the Ferro fluid , if the adhesive does fail ,I'll be looking for a different driver anyway as they don't make the mark without it so ..

Would like some community sound vhf100 drivers but there just so expensive and I don't know if they will keep up with an m200 on a jbl 2360 high passed at 3khz.
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2017 at 6:39pm
Can't imagine it would be too difficult toget the fluid out ,its a liquid afterall ,it will absorb , the Ferro kits actually come with absorbent strips to get the remaining existing fluid out but could be wrong , all unknown territory for me
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