Ferrofluid tweeters

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An easy way to check is to listen to them. If the highs sound sluggish, like soft and loud, chances are it's the ferrofluid.

But I seriously doubt your Scanspeak tweeters ferrofluid will give problems. Two years is very short. I've got some vintage Vifa tweeters that are 10-20 yrs old and their ferrofluid are still good.

I also have the Peerless tweeter that are made in China nowadays. Some of the models do have ferrofluid issues. And they are brand new.
 
I seem to recall that it was non-working SEAS 19TAF/G tweeters that first brought me to this wretched place. :D

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Ferrofluid is vastly overrated, IMO. No evidence that it improves things at all. You can buy it cheaply enough at Blue Aran, UK or at Parts Express, US at slightly silly prices. Mr. Troels Gravesen is keen to strip it out at the first opportunity.

Thing is, back in the day tweeters seemed to mostly survive party abuse without it. To quote the figures, a SEAS tweeter can survive 70W momentary without it, or 110W with it. Might matter in a dogfight, but the rest of us shouldn't really care. :)

I suspect the SEAS tweeters failed relatively rapidly because of their lack of air seal when exposed to boiling heat.

All these years I been thinking Michael Chua is French. Suddenly I realise he lives in the spooky state of Maine, US. Gotta say The Starling was a moment of enlightenment for me.
 
Ferrofluid is vastly overrated, IMO. No evidence that it improves things at all.
It can partially damp some dome resonances, leading to a bit smoother frequency response. It dramatically changes the damping at Fs which leads to lower Q, changing the roll-off on the low end and makes the impedance peak at Fs smaller which can arguably make designing the crossover easier. Some tweeters can rely on it to centre the voicecoil and prevent rubbing.
 
It can partially damp some dome resonances, leading to a bit smoother frequency response. It dramatically changes the damping at Fs which leads to lower Q, changing the roll-off on the low end and makes the impedance peak at Fs smaller which can arguably make designing the crossover easier. Some tweeters can rely on it to centre the voicecoil and prevent rubbing.
You are not telling me anything I don't already know. In fact, I think I mentioned centreing the voicecoil and the impedance peak before anyone else.

Ferrofluid is a gooey damping material. It also wicks away spare heat. But actually, there is a great deal of evidence that mechanical loss is about the most non-linear thing around.

Far better to do it electrically, IMO.

Since you are the self-professed TMM, let me tell you why TMM is totally wrong.

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This is actually a MTTM. Dispersion is more cylindrical than inverse square. It happens to sound way better than most speakers I have heard. I won't go into the technical details of implementation.

Another valid solution is the Classic 3 way. A good friend of mine likes the Celestion 22:

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TBH, I think ferrofluid is a cheap fix that increases profits for speaker makers. Bit like soaking Salmonella infected chickens in bleach before selling an obviously sub-standard product. Think about it. :cool:
 
Is there a way to test / check ferrofluid performance? I have a pair of ScanSpeak D2905/970000 that have been sitting for two years, still boxed.
I am almost certain that the D2905/970000 is NOT ferrofluid damped. I have used this tweeter in quite few projects precisely because it does not use ferro-fluid. The D2905/950000 on the other hand does use ferro-fluid. You might want to check this though. BTW it is my first choice for consistent good performance. I have blown a couple though with switch on/off transients from less than perfect electronics, so it might be considered fragile. It is also relatively pricey compared to SB Acoustics alternatives, but it does deliver the goods.
 
You are quite right, Bon:

• D2905/9500: This Scan-Speak tweeter is a combination of the 9300 dome assembly, front plate, and Ferrofluid damping, combined with the 9900 aerodynamic non-resonant rear chamber. Since I have a few reservations about the sonics of the 9900, that makes this the best all-around choice for the Ariel and ME2. The reports from the Ariel Builders Club all agree: this is their favorite tweeter ... guess I better replace my old sticky-dome 9000's with the 9500's one of these days.


• D2905/9700: A 9900 with a flat faceplate. I've heard a rumor that Siegfried Linkwitz commissioned this tweeter for the Audio Artistry line of speakers. He wanted all the features of a 9900 without the shallow horn, thus the 9700. No question about it, they sound very good in the Audio Artistry speakers - with Linkwitz as the designer, they should!

The 9700, along with the 9900, do not use any Ferrofluid in the voice-coil gap. (A very unusual feature in any tweeter these days.) That creates a large peak in the impedance curve at the tweeter resonance of 600Hz, thus requiring a precisely tuned notch filter in the crossover. More significantly, this also means the tweeter portion of the Ariel and ME2 crossover requires a complete redesign for the 9700 - if you use the "stock" crossover there is a real possibility of damaging the tweeter and the certainty of very high IM distortion as the result of uncontrolled excursion at the tweeter resonance.

What a complete waste of time this thread is! The Ariel, Part I
 
smoother frequency response and flatter impedance is not considered improving things in anyone's eyes? That's the first i've heard of it! Of course there are drawbacks to any design element, otherwise someone would have designed the perfect loudspeaker already. Afaik ferrofluid doesn't introduce the same amount of non-linearity that spiders and surrounds do.

Since you are the self-professed TMM, let me tell you why TMM is totally wrong.
Very funny. My current speakers are a 3-way haha.
 
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I built an active DSP 3-way with D220TI's on top and about halfway through optimization decided to take the tweeter drivers apart. The datasheet or somewhere mentioned ferrofluid but there was none in there. I had some particular grade (there are many) in a bottle from 30 years ago and decided to put some in. Ever since that I've never been able to get the high end to sound as good as I swear it once did. I tried all sorts of electronic / processing remedies, but the sound is pretty vague and honestly, weird. Sometime soon I'll get around to cleaning out the gaps and coils to see what happens. There's no chance I'll ever end up with power handling problems so.. After decades of experience I think I've come to recognize a certain sound that ferrofluid tweeters make and it's not too impressive. I can think of all sorts of reasons for it but I really don't know why.
 
From the Scanspeak site
http://www.scan-speak.dk/datasheet/pdf/d2905-950000.pdf
http://www.scan-speak.dk/datasheet/pdf/d2905-970000.pdf
Reading the key features, the 950000 clearly mentions ferro-fluid whereas the 970000 does not. It is reasonable to infer that the 970000 is ferro-fluid free. Wilmslow would appear to have it incorrect on their page.
 
From the Scanspeak site
http://www.scan-speak.dk/datasheet/pdf/d2905-950000.pdf
http://www.scan-speak.dk/datasheet/pdf/d2905-970000.pdf
Reading the key features, the 950000 clearly mentions ferro-fluid whereas the 970000 does not. It is reasonable to infer that the 970000 is ferro-fluid free. Wilmslow would appear to have it incorrect on their page.

Hi Bon, yes I see now. Out of interest, what does the schematic at the bottom refer to? Also a second order Butterworth is highlighted with an asterisk. I have been attempting to design a a two way Butterworth third order crossover(driver is a volt BM220.8). Would I be better off opting for two separate filters, starting with a second order Butterworth for the ScanSpeak?
 
Out of interest, what does the schematic at the bottom refer to? Also a second order Butterworth is highlighted with an asterisk. I have been attempting to design a a two way Butterworth third order crossover(driver is a volt BM220.8). Would I be better off opting for two separate filters, starting with a second order Butterworth for the ScanSpeak?
The schematic is the electro-mechanical model for the driver. The data values unfortunately is not listed, but it is not really of practical use for crossover design. The mention of the second order Butterworth high pass filter is stating the conditions under which the power handling is measured. It is only a guide for typical operating conditions. In my projects, I usually set the tweeter high pass around 2.4-2.5 kHz. It depends greatly on the performance of the chosen mid-range in the crossover region and just above.
 
The schematic is the electro-mechanical model for the driver. The data values unfortunately is not listed, but it is not really of practical use for crossover design. The mention of the second order Butterworth high pass filter is stating the conditions under which the power handling is measured. It is only a guide for typical operating conditions. In my projects, I usually set the tweeter high pass around 2.4-2.5 kHz. It depends greatly on the performance of the chosen mid-range in the crossover region and just above.

Thanks for your advice
 
I purchased years ago a pair of expensive Morel Supreme tweeters that supposedly made use of ferrofluid.

As the drivers did not behave as expected, i decided to open one of them and then discovered slight spots of ferrofluid on the voice coil and almost nothing in the gap...

This drove me to the conclusion that some "wise" guy purchased these drivers before me, removed the ferrofluid from it as explained is so many youtube videos in search of some "improvement" on the cheap, was not quite happy with the results and then decided to return the units to the dealer...

I then bought the Morel item and was then sent this pair without knowing its whole story and thus say :

F... the tweakers! :mad:
 
I heard the same thing with my Peerless H26TG45-06 horn tweeter. The highs disappeared and the entire speaker sounded like out of sync. I eventually removed all the ferrofluid and the H26TG came alive.

Here's how to remove the ferrofluid from the H26TG45-06.

Especially with horn loaded compression drivers running far in-band of the horn and at very low listening levels, I think we can rule out pure hydrodynamics relative to voice coil motion. Since the degradation in sound is so similar with these and anything else all the way down to the ubiquitous Audax knock-off 1/2" plastic hard domes, I think something magnetic (and bad) is going on with ferrofluid drivers.
 
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