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Dried out ferrofluid ?

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Saw a post over on Audiogon for rebuilding tweeters with dried-out ferrofluid and was wondering if any of the AR series is having this problem like the AR-11, etc?

Roger

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According to KEF ferrofluid in drive units has a life expectancy of 20-25 years. Here is good discussion about rebuild issues of T33 tweeter.

http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=1304&highlight=ferrofluid

Ferrotec has made ferrofluid for many speaker companies, and there are more than 50 different fluids available to OEM speaker manufacturers and many fluids are obsolete now. Very few fluids for audio are available as refill kits. Life expectancy of different fluids might vary.

https://ferrofluid.ferrotec.com/products/ferrofluid/audio/

Many fluids on e-bay are for educational purposes, say for showing how magnetism works... ie not for speakers.

Best Regards

Kimmo

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According to KEF ferrofluid in drive units has a life expectancy of 20-25 years. Here is good discussion about rebuild issues of T33 tweeter.

http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=1304&highlight=ferrofluid

Ferrotec has made ferrofluid for many speaker companies, and there are more than 50 different fluids available to OEM speaker manufacturers and many fluids are obsolete now. Very few fluids for audio are available as refill kits. Life expectancy of different fluids might vary.

https://ferrofluid.ferrotec.com/products/ferrofluid/audio/

Many fluids on e-bay are for educational purposes, say for showing how magnetism works... ie not for speakers.

Best Regards

Kimmo

Kimmo,

I see you've been working on this already. Looks like some ferrofluid AR tweeters are or have exceeded their life-expectancy rating.

I notice Simply Speakers is offering single repair quantities on ferrofluid for die-hards.

Roger

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Dear Roger

Simply Speakers refill kit should be close enough. When I made inquiry to Ferrotec Europe, they were able to offer close replacement for the original fluid after Ric Cecconi (Kef Engineer from 70´s-90´s) told which fluid was used in the original T33. tweeter. Fluid was available from Ferrotec in quantities of something like 0,2 litres... for thousands tweeters.

My Kef P60 project is not finished yet. Tweeter rebuild was necessary for 20 year old speakers as hf was certainly too grainy. I was able to source replacement for the original fluid, but tweeter rebuild is not finished yet. I learned that ferrofluid is nice feature to peoples who buy new speakers... but pain in the ass for anyone who will like speakers older than 10 years.

Best Regards

Kimmo

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I was wondering exactly the same thing!

I have a few pairs of ARs and my main speakers are AR90.

They seem OK to me, but maybe I'm missing something?

How do we know for sure if something is wrong?

What are your experiences?

How would you describe the sound of AR9/90/91/92 speakers with UMR drivers and tweeters with bad ferro fluid?

.

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My main speakers are AR-9's. I'm the third owner (had them since 2010). The second owner (an MIT Elec Eng grad) had them for about 15 years and re-capped the x-o's and re-foamed the 12's and the 8's. Except for a missing plastic insert in one of the level switch wells and a slightly cracked woofer grille frame on one of the four woofer grilles, they are in nice cosmetic shape.

(Well, as "nice" as that incredibly ugly/strange industrial design, with their pathetically mediocre vinyl veneer sides, can look. No excuse for their horrendous as-designed appearance. The ADS 1590--in the same general time period and with the same general driver complement and retail price-- was an absolutely beautiful speaker, so the 9 didn't have to be as dog-ugly as it was.)

But the 9, to my ears, is still a great-sounding speaker, even by today's standards. Now, I'm sure my ears are not what they were 30 years ago, but I still hear pretty well. I never was a hard-core heavy-metal rocker, and I never worked contruction nor was I in a profession around jet aircraft. To my still-respectable ears, my 9's sound fine. The UMR's and tweets are operating just fine. Lots of sheen, lots of sparkle, lots of detail.

The dried FF issue is less of a concern to me than actually blowing a driver and then not being able to find a genuine NOS replacement. I figure I will have to buy one more set of so-called "good" speakers in my lifetime, and the hunt has started. The Legacy Signature SE is a prime contender. Legacy designer/founder Bill Duddleston cites the AR-9 as one of his favorite designs from the past, and he freely admits to using many of the 9's design precepts as a guide in his designs.

But as far as dried FF--I think we've got more pressing issues, like the rapidly-dwindling availability of replacement parts for pre-1980 AR's.

Steve F.

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My main speakers are AR-9's. I'm the third owner (had them since 2010). The second owner (an MIT Elec Eng grad) had them for about 15 years and re-capped the x-o's and re-foamed the 12's and the 8's. Except for a missing plastic insert in one of the level switch wells and a slightly cracked woofer grille frame on one of the four woofer grilles, they are in nice cosmetic shape.

(Well, as "nice" as that incredibly ugly/strange industrial design, with their pathetically mediocre vinyl veneer sides, can look. No excuse for their horrendous as-designed appearance. The ADS 1590--in the same general time period and with the same general driver complement and retail price-- was an absolutely beautiful speaker, so the 9 didn't have to be as dog-ugly as it was.)

But the 9, to my ears, is still a great-sounding speaker, even by today's standards. Now, I'm sure my ears are not what they were 30 years ago, but I still hear pretty well. I never was a hard-core heavy-metal rocker, and I never worked contruction nor was I in a profession around jet aircraft. To my still-respectable ears, my 9's sound fine. The UMR's and tweets are operating just fine. Lots of sheen, lots of sparkle, lots of detail.

The dried FF issue is less of a concern to me than actually blowing a driver and then not being able to find a genuine NOS replacement. I figure I will have to buy one more set of so-called "good" speakers in my lifetime, and the hunt has started. The Legacy Signature SE is a prime contender. Legacy designer/founder Bill Duddleston cites the AR-9 as one of his favorite designs from the past, and he freely admits to using many of the 9's design precepts as a guide in his designs.

But as far as dried FF--I think we've got more pressing issues, like the rapidly-dwindling availability of replacement parts for pre-1980 AR's.

Steve F.

Steve,

I don't have any way to do testing so I just threw the question out there. Glad to see you don't think it is a big issue. Those Legacy's look very fine indeed.

Roger

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Quick correction to my post--the AR-9 didn't have vinyl veneer sides, of course; it was real walnut veneer. Really poor walnut veneer. That caliber of finish may have looked passable on a 2ax or 3a (especially if they were buried in a bookshelf), but on the huge expanse of exposed slab sides of the 9, it was inexcusable.

Good thing it sounded so good.

Steve F.

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On 9/29/2014 at 3:34 PM, Steve F said:
......................................................................................................................................................................................................................................

(Well, as "nice" as that incredibly ugly/strange industrial design, with their pathetically mediocre vinyl veneer sides, can look. No excuse for their horrendous as-designed appearance. The ADS 1590--in the same general time period and with the same general driver complement and retail price-- was an absolutely beautiful speaker, so the 9 didn't have to be as dog-ugly as itwas.)..............................................................................................................

Steve F.

I'd choose performance over looks any day. The woofer design of the 9 enabled them to produce better bass response IMO. I don't think the Wilson speakers look very nice but they sound wonderful. They remind me of the old rock'em sock'em robots game from the 70's.

Listen to the music.

71AGZyPABaL._SL1500_.jpg

wilson-lifestyle3.jpg

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How do we know for sure if something is wrong?

I think our experts will have better idea how much dried ferrofluid will degrade AR90 or AR9 performance. But... they must face similar problem that I had with Kef P60:s... It is impossible to make comparison to new unit, as ferrofluid has dried also in NOS units, unless they have been rebuilt recently.

There are at least two reasons why ferrofluid has been used. The first thing was to provide better time constant for thermal capability. Fluid will conduct heat to magnet assembly more efficiently than air in the VC gap, so tweeters will not blow so easily during short overload situation. This feature will also improve linearity as DCR of VC will not change during louder passages, consequently crossover parameters stay closer to targeted ones.

Second bonus that fluid will provide is mechanical damping of VC. If you look impedance curve of ferrofluid cooled tweeter, you should note that Q at resonance is usually quite much smaller compared to non cooled tweeter. This makes it easier to use low order crossovers and less impedance compensation is needed to stay within targeted acoustical slopes close to crossover.

When ferrofluid dries you will loose both features. If you are not using too much power thermal issue should not be problem. When you loose mechanical damping, crossover design will effect how far you are from targeted slopes. In 2-way design when fs might be 1 octave from crossover frequency, difference might be considerable. In designs like AR9 where upper crossover is quite far from fs, loss of damping is not big issue from this view point... but mid might be working closer to fs...

When fluid dries in magnetic gap, only volatile parts of fluid will not contaminate the gap. Other parts of fluid will stay adhered in the gap and coil former. If weight of moving assembly will increase fs will decrease, sensitivity will decrease. Other things may also happen, but our experts might have better understanding for this. Contamination on gap surface might not trouble at all, unless gunk developed will not make contact to VC... and this certainly is not good thing.

I usually try to be optimistic... but as you can see, this ferrofluid issue makes me think at least tree times before going any further.

Best Regards

Kimmo

.

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Thanks!

If weight of moving assembly will increase fs will decrease, sensitivity will decrease.


If I understood this correctly, output from UMR drivers and tweeters can (only?) be reduced if the ferro fluid is dried out?


This is certainly not the case with my AR90s.

After recapping with modern poly caps, I had to permanently reduce the UMR drivers output by 3dB

...and they still can sound unpleasant and shrill on poorly produced recordings.

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Damping (friction in fluid) will also consume some power. So gap without fluid can produce similar SPL even with increased mass of VC. It might be impossible to give universal formula to this issue, things can be different with different drive units.

If good efficiency has not been prime issue, wide gap might mean that drive units are less prone to deterioration.

Best Regards

Kimmo

PS picture does not look too good

post-126436-0-95485600-1412089077_thumb.

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"I'd choose performance over looks any day."

So would I, if I have to choose. I'm just at that point in my life where I'm light years beyond cinder block/wood shelf "equipment stands" and speakers sitting on plastic milk crates. That was fun in college, but our house has no place for that. Even my so-called "music room" is beautifully decorated, nicely finished. The 9's are the worst-looking things in the room. As I said, it's a good thing they sound so good.

These days, it's less likely to have to make that 'looks vs. sound' choice. Legacy, Aerial, Vienna Acoustics, most of the B&W's, etc are pretty decent-looking speakers.

Steve F.

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Damping (friction in fluid) will also consume some power. So gap without fluid can produce similar SPL even with increased mass of VC. It might be impossible to give universal formula to this issue, things can be different with different drive units.

If good efficiency has not been prime issue, wide gap might mean that drive units are less prone to deterioration.

Thanks!

I still can't figure out if some sonic "quality" exists that is specific to drivers with bad ferro fluid...

How to figure out if my AR90 drivers need servicing just by listening, without having to cut them open? :)

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...

But as far as dried FF--I think we've got more pressing issues, like the rapidly-dwindling availability of replacement parts for pre-1980 AR's.

Steve F.

Steve F,

Enjoy those old classic ARs why they last. After our generation they will all be in the landfill. Like RoyC says: There are plenty of better sounding speakers out there. ARs rise to fame was because of the middle class which is rapidly dwindling these days. I suspect in a hundred years people will be listening to cochlear implants ala Star Trek's Borg and you will be able to dial in the sound of any vintage speaker you desire :)

Besides they are not exactly rocket science at any rate. I'm sure a dedicated individual could totally remanufacture the early AR dome tweeters. A visiteing friend who spends summers in Alaska and winters in Hawaii was in turn paid a visit by one of his brothers here last year. For show and tell, he had a steam engine in the back of his pickup that he had built from scratch. It was a marvel of machine work and was featured a national magazine. So, got the desire and the man hours? I'm sure if Bill Gates wanted to hear a brand new AR-3 he could have one cranked out for under a quarter mil ;)

Roger

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Enjoy those old classic ARs why they last. After our generation they will all be in the landfill.

Roger +1

There is surely some Smart Alec selling canned 50´s air to fill spare tyre of Buick Roadmaster... But if AR decided to use ferrofluid in their drive units there was good reason for this and without this fluid they are not performing as designed. Same is true to hard dome tweeters in my 2ax, 5 and 3aImproveds. Deteriorating damping material behind dome is compromising performance among other things. Rebuild is not impossible, but at least difficult or expensive and would not be my first choice. Even I did know this, I wanted to make trip to 70´s to see how things were these days and use AR:s for maybe 2, 5 or even 15 years.

Maybe someone is willing to make correct replacements some day. There is reproduction unit available for discontiuned JBL LE25, Falcon Acoustics has tooled new production Kef T27 and B110 with Malcom Jones who designed these units in 1960`s. Falcon units are made in Great Britain are not too expensive, considering limited production. Falcon even got licence from BBC to build new LS3/5A. http://www.falconacoustics.co.uk/ls3-5a.html I do not know how good LE25 copy or Falcon T27 and B110 are... but all faith to receive some good news is not lost.

Steve F... I had AR9 pair in early to mid 80´s and do not recall that veneer was so bad... but of course, I was young and these speakers were out of space these days

Best Regards

Kimmo

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I remember in the 70's when FF was new, a speaker rep took his samples into the dealer's showroom to play them during a sales presentation.

The speakers sounded lousy and the dealer rejected them.

It was winter. The speakers had been sitting in a cold car trunk for a long drive, and the FF had thickened. Once the speakers got back to room temp (and the VC's got heated by being played), the tweets came back to life and they sounded good again.

Amusing--but true--story.

Steve F.

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