Tweeter expiration date

[rdenney]

The tweeters in my Advent NLA's are a lot more than 6 months old. Maybe even more than 15 years old

And it may be that they can't do anything above 16 KHz any more (neither can my ears). But if the ferrofluid had hardened, the tweeters wouldn't work at all, it seems to me. And they definitely do still work. Is it doing everything it's supposed to? Here's an RTA display from prolly half a dozen years ago of my system playing pink noise. The system at that time was an SAE preamp, a B&K amp, and Advent NLA's. The RTA app is more toy than tool, but it's still data and it does apply at least broad corrections to the internal microphone.

The level shows low but the level was not calibrated. The pink noise was playing fairly loudly--maybe more like 75-80 dB SPL. Also note that the app shows the dB with A weighting in the upper right, but the display is unweighted.

The RTA graph may not show the effects of degraded ferrofluid, but the tweeters are definitely working. Those tweeters haven't been out of those cabinets since the speakers were made, and at the time of this test they were 40 years old.

One tweeter subsequently developed a tear because of a dent in the "protective" screen, and I replaced it with one someone pulled from their old Advents that probably had rotted surrounds on the woofers and were going into the landfill. (I've replaced the foam woofer surrounds on these speakers twice.)

This REW trace from after that repair shows stacked Advents (read: two pairs) being run by two identical B&K amps. No, the display isn't what we want to see in terms of scaling, but it's still illustrative--the tweeters are definitely working.

Rick "thinking the base viscous oil will have a lot to do with it" Denney

 

[respice finem]

...if the ferrofluid had hardened, the tweeters wouldn't work at all, it seems to me...

In the "final stage", yes, but it's a gradual process (which took more than a decade to become audible for me with my B&W tweeters).
They seem to deteriorate from the highest frequencies down.

 

[levimax]

The tweeters in my Advent NLA's are a lot more than 6 months old. Maybe even more than 15 years old

And it may be that they can't do anything above 16 KHz any more (neither can my ears). But if the ferrofluid had hardened, the tweeters wouldn't work at all, it seems to me. And they definitely do still work. Is it doing everything it's supposed to? Here's an RTA display from prolly half a dozen years ago of my system playing pink noise. The system at that time was an SAE preamp, a B&K amp, and Advent NLA's. The RTA app is more toy than tool, but it's still data and it does apply at least broad corrections to the internal microphone.

The level shows low but the level was not calibrated. The pink noise was playing fairly loudly--maybe more like 75-80 dB SPL. Also note that the app shows the dB with A weighting in the upper right, but the display is unweighted.

The RTA graph may not show the effects of degraded ferrofluid, but the tweeters are definitely working. Those tweeters haven't been out of those cabinets since the speakers were made, and at the time of this test they were 40 years old.

One tweeter subsequently developed a tear because of a dent in the "protective" screen, and I replaced it with one someone pulled from their old Advents that probably had rotted surrounds on the woofers and were going into the landfill. (I've replaced the foam woofer surrounds on these speakers twice.)

This REW trace from after that repair shows stacked Advents (read: two pairs) being run by two identical B&K amps. No, the display isn't what we want to see in terms of scaling, but it's still illustrative--the tweeters are definitely working.

Rick "thinking the base viscous oil will have a lot to do with it" Denney

Ferrofluid degrading does not stop tweeters from working but just slowly changes their response over time. Are you sure your 40 year old tweeters even have ferrofluid? I have measured loss of HF response and linearity and then changed the ferrofluid (the old stuff was quite dry and sticky compared to the replacement fluid) and there were noticeable changes in the measurements for the better / back to original specs. I also have some 30+ year old speakers without ferrofluid and the HF response looks the same now as 10 year old measurements and as the 30+ year old measurements from a magazine. It is an interesting topic I don't see talked about but if I had or was considering purchasing speakers over 10 years old and they have ferrofluid in the tweeters I would want to check to make sure the tweeters are working to spec. To me the process of replacing the ferrofluid is a little dicey, often requiring the drilling of rivets which creates metal shavings which then get into the magnetic voice coil gap, and then how much ferrofluid to you use and dealing with very delicate parts. For valuable old speakers I would like to know if replacement ferrofluid tweeters were available before I purchased them.

 

[rdenney]

The Advent NLA’s famously used ferrofluid tweeters.

Rick “not sure they were ever really flat to 20KHz” Denney

 

[TheMadcap]

Thank you,
See the photo of the original box. I think it's best to keep it inside.
Where I live (Sao Paulo/Brazil), the humidity is very good, always around 40 to 50%.
So I think keeping it in a dark, humidity-free cabinet is a good idea.

Maybe you can put a desiccant (silica gel) in it as well.

 

[Naqus]

Long-term storage of tweeters will not usually cause damage if they have been kept in normal conditions. The membrane may lose flexibility over time, but this requires many years of non-use. It is better to turn them on periodically to keep them in working order. If the tweeters sound normal, then they are fine.

 

[levimax]

The Advent NLA’s famously used ferrofluid tweeters.

Rick “not sure they were ever really flat to 20KHz” Denney

The lifespan of ferrofluid must be a combination of the quality of the ferrofluid and the environment it is exposed to with heat most likely being one of the biggest issues. The tweeters that I had where the ferrofluid went bad in less than 10 years were medium range Morel tweeters in DIY speakers. I didn't think I was running them "hot" but they were used often and sometimes a little loud. The 30+ year old tweeters are in some Sonus Faber speakers and looking online they also appear to use ferrofluid. They had a similar use pattern and are currently used daily for TV/ movie duty. I guess like a lot of things pertaining to older Hi-Fi gear there are no hard or fast rules unfortunately.

 

[MAB]

Here is a good discussion from Archimago on dried ferrofluid, with measurements before and after replacement.

DIY: Tweeter Ferrofluid Change - with pre- and post- frequency & distortion changes. And on-line amiability among hobbyists.

A blog for audiophiles about more objective topics. Measurements of audio gear. Reasonable, realistic, no snakeoil assessment of sound, and equipment.

archimago.blogspot.com

Dried ferrofluid doesn't typically stop a speaker from operating, although I guess it could under the right circumstances. Also, it typically affects the lower frequencies of the driver's operation more than the upper, as shown:

I have old Seas tweeters with dried ferrofluid, likely assisted by the use of a very low crossover point, they worked even though the fluid was dried like hardened lacquer. They had dramatic reduction in output at low frequency (similar to Archimago's example) and lots of distortion from the voice coil operating in a grove of hardened varnish, even though the HF operation wasn't affected too much. The ferrofluid in these tweeters was so dried I was never able to dissolve the varnish and replace the ferrofluid. This is an extreme example. Less extreme examples have measurable changes in response, primarily at low frequency which makes sense if you consider the excursion of the driver in the groove of varnish that forms as the fluid dries.

I've never heard of ferrofluid drying out while in storage. I guess it could happen, some manufacturers used ferrofluid that was prone to drying (the Seas tweeter I have is one such example), but I would be surprised if it aged dramatically while in storage.

 

[Abdo]

Thank you. A technician told me that since only the diaphragm was repaired, this difference is normal for an original. The original would be 2.8, while replacing the diaphragm alone would raise the signal to 3.8, but it would be very difficult to notice a difference. To get it to the same value as the factory 2.8, the coil would have to be replaced. But the technician doesn't think it's worth it. What do you think? Thank you.

 

[levimax]

I was listening to my main system with new speakers and then a few minutes later listened to some music on another system with some 30+ year old Sonus Farber speakers and it didn't sound right and this thread came to mind. I did a quick MMM measurement and sure enough it looked like the tweeter output was way down. I got replacement tweeters and installed them and it sounds and measures much better and as expected. This is the second time this has happened to me now (that I noticed.... slow tweeter deterioration is not apparent in many cases) so I would say this is a big concern for older speakers and since replacement tweeter are often not available and ferro fluid replacement can be dicey definitely something to take into account when buying older used speakers. Graph below green original, red replacement.

 

[Abdo]

I discovered that two of them here broke down after 17 years, but in my case it was very strange, as both stopped at the same time. I believe it might have been a problem with switching them on and off, a power outage, or some kind of sound feedback. I ended up having them repaired here in Brazil; to my ears, they sound good. But since I don't know how to measure using graphs, I don't know if they're entirely accurate. However, on my last trip to Florida (Winter Garden), I ended up buying two new ones that are stored here in the box; I only plugged them in, tested them, and then took them out. I'll keep them stored as a spare.

 

[dlaloum]

Anyone have any idea of the expected life of the Gallo CDT tweeters?

" CDT uses a piezoelectric diaphragm made of a film-like material (Kynar) that expands and contracts with an electrical signal to produce sound."

Mine are around 16 years old now...

Worth discussing also is the expected life of ribbons, planar magnetics and ESL's....

Also:

I've oft recommended the 1980's Boston Acoustics A400 down to A60 speakers - which I particularly liked the sound of back in the dim dark 80's... Yes their woofers almost invariably need a surround replacement - but their rather nice soft dome tweeter was a ferrofluid cooled device... so would they be serviceable? (are replacement units even available?)

This might mean that some excellent vintage designs are no longer worth recommending?

 

[DVDdoug]

I believe piezos are stable.