Magnetic oil in Tweeters is it still relevant ?

[bothu]

Many years back magnetic oil was often used in tweeters, did it make any improvement or was it "snake oil" ?

Bo Thunér, Linköping, Sweden

 

[thewas]

Ferrofluid is still used in many current tweeters mainly to reduce the voice coil temperatures, personally as a loudspeaker collector I am not a great fan of it though as it can deteriorate after some decades.

 

[morillon]

allows you to increase the admissible power..some believe that it would take away the finesse..but many hdg tweeters use it..but in fact it degrades, becomes viscous, over time and must be cleaned and changed after a while. ..(but it can also be observed quite easily when measured)

 

[voodooless]

I think Kef uses ferrofluid in their coaxes. I’m not particularly a fan of the stuff.

 

[morillon]

I think Kef uses ferrofluid in their coaxes. I’m not particularly a fan of the stuff.

if the cutoff is rather low...and rather necessary

 

[DSJR]

allows you to increase the admissible power..some believe that it would take away the finesse..but many hdg tweeters use it..but in fact it degrades, becomes viscous, over time and must be cleaned and changed after a while. ..(but it can also be observed quite easily when measured)

Apparently the tweeters used in Harbeths with ferro-fluod DO NOT degrade over time and apparently measurements on twenty odd year old (or even older) tweeters compared to new ones proved it.

My own experiences do indicate that *some* tweeters do change over time for whatever reason and I have seen pics in the past of tweeters with dried out one-fluid having to be literally picked out of the coil gap.

 

[voodooless]

if the cutoff is rather low...and rather necessary

2.1 kHz isn’t particularly low (LS50 meta) There are plenty of low fs tweeters that manage lower without it.

But maybe not all ferrofluid is made equally…

 

[morillon]

2.1 kHz isn’t particularly low (LS50 meta) There are plenty of low fs tweeters that manage lower without it.

But maybe not all ferrofluid is made equally…

if in cutoff a 2.1k is precisely low enough...you don't understand... that s not compression..no?

 

[voodooless]

if in cutoff a 2.1k is precisely low enough...you don't understand... that s not compression..no?

Indeed, I don’t understand any of what you just said…

 

[Deleted member 21219]

But maybe not all ferrofluid is made equally…

That would be an important point. This Wikipedia entry on ferrofluid in loudspeakers (below) uses the plural, "ferrofluids". I don't know whether that's significant or not, but the whole article mentions different sorts of ferrofluids, although for applications other than loudspeakers.

"Loudspeakers​

Starting in 1973, ferrofluids have been used in loudspeakers to remove heat from the voice coil, and to passively damp the movement of the cone. They reside in what would normally be the air gap around the voice coil, held in place by the speaker's magnet. Since ferrofluids are paramagnetic, they obey Curie's law and thus become less magnetic at higher temperatures. A strong magnet placed near the voice coil (which produces heat) will attract cold ferrofluid more than hot ferrofluid thus pushing the heated ferrofluid away from the electric voice coil and toward a heat sink. This is a relatively efficient cooling method which requires no additional energy input.[14]

Bob Berkowitz of Acoustic Research began studying ferrofluid in 1972, using it to damp resonance of a tweeter. Dana Hathaway of Epicure in Massachusetts was using ferrofluid for tweeter damping in 1974, and he noticed the cooling mechanism. Fred Becker and Lou Melillo of Becker Electronics were also early adopters in 1976, with Melillo joining Ferrofluidics and publishing a paper in 1980.[15] In concert sound, Showco began using ferrofluid in 1979 for cooling woofers.[16] Panasonic was the first Asian manufacturer to put ferrofluid in commercial loudspeakers, in 1979. The field grew rapidly in the early 1980s. Today, some 300 million sound-generating transducers per year are produced with ferrofluid inside, including speakers installed in laptops, cell phones, headphones and earbuds.[17]"


.... from https://en.wikipedia.org/wiki/Ferrofluid

Jim

 

[thewas]

I have talked in the past with few experienced loudspeaker engineers and they said the current ferrofluids cannot be compared with the early ones regarding aging properties, but would be nice to have some objective data for that.

 

[dfuller]

A fair few highly regarded driver manufacturers (Bliesma, among others) have chosen to not use ferrofluid as they feel it takes away from the dynamic abilities of the tweeter. I am not particularly sure why this is, it could be because they feel it overdamps the driver.

 

[ernestcarl]

A fair few highly regarded driver manufacturers (Bliesma, among others) have chosen to not use ferrofluid as they feel it takes away from the dynamic abilities of the tweeter. I am not particularly sure why this is, it could be because they feel it overdamps the driver.

Am I wrong in thinking that many compression drivers also do not use/require ferrofluid like in this HF compression horn?

 

[Thomas_A]

I have talked in the past with few experienced loudspeaker engineers and they said the current ferrofluids cannot be compared with the early ones regarding aging properties, but would be nice to have some objective data for that.

Do you know what age period is equal to current and past ferrofluids?

 

[thewas]

From those past talks I would guesstimate around century, but there can be exceptions in both directions.

 

[sam_adams]

One should be more concerned with the black oil than with magnetic oil.

 

[Ron Texas]

How about liquid nitrogen?

 

[sam_adams]

How about liquid nitrogen?

Not viscous enough.

 

[andrewdrouin]

2.1 kHz isn’t particularly low (LS50 meta) There are plenty of low fs tweeters that manage lower without it.

But maybe not all ferrofluid is made equally…

I operate a small Ferrotec brand ferrofluid distribution Co. in Canada - there are literally dozens of viscosities of ferrofluid available, along with several different carrier liquids.

 

[valerianf]

The problem is that if the ferrofluid is dry, the tweeter need to be opened, cleaned and refilled.
Not all tweeters can easily be disassembled.

I got a pair of tweeters using ferrofluid and after 10 years they are still working.
I may change them in 1 or 2 years, I already bought new ones more performant (I hope).