DRIVE UNITS BY MANUFACTURER:
FFAPG O87
APG O87, an ester based fluid with a saturation of 250 Gauss and a viscosity of 750 centipoise. Manufactured by Ferrotec USA .
Other available formulations, contact us for details:
CDF 2250 (Ester based): 220 Gauss, 500 cP
APG 1134 (Hydrocarbon): 220 Gauss, 1000 cP
There is over 100 grades of ferrofluid; the above are the most common specific fluids used by major drive unit manufacturers
Beware: some unscrupulous sellers are offering the cheap, commonly available science project type ferrofluid as an audio product. This results in an unpredictable / overdamped output and can soften drive unit adhesive - always double check the origin and the specification.
Ferrofluid is a cooling / damping compound used in the magnetic gap of many tweeters to increase power handling and smooth out the frequency response; it has a tendency to thicken with age, gradually reducing tweeter output to zero. Many old tweeters from the 1980s/90s can be restored to perfect working order by carefully dismantling and cleaning out the old coagulated fluid then replacing with fresh.
This refill kit comprises a high accuracy syringe pre-filled with Ferrofluid specifically formulated for high fidelity tweeter application. There is sufficient in the syringe for 2 tweeters & a micro applicator nozzle is supplied.
Willys-Hifi Ltd, the UK speaker specialist.
Helpline 01702 523999
Very easy to do on this model speaker as no soldering is required. Made a noticeable improvement. Well worth the effort and cost.
Has fixed the slight grainy sound on my old Mission 771s. The tweeter had a stain on the back suggesting the fluid had escaped. Make sure you release(unsolder) the coil wires before splitting the tweeter. Audax have replacement tweeters TM025C1 albeit 8 ohm which is another way to go.
Thanks for the review John!
Will & Caroline
Delivered quickly. 0.5ml is more than enough for two tweeters and the syringe is essential in order not to over-fill the gap. Well worth it - this has brought a pair of Mission 752 Freedoms back to life.
Thanks for the review Pete !
Will & Caroline
Friendly technical support
40+ years in the trade
UK family run business
Excellent customer service
Quick dispatch
A quick delivery and the tweeters are perfect on my mission 753 freedom speakers. Easy to fit . Highly recommend.
I’m no expert when it comes to speakers, but after some research (and a strong recommendation from ChatGPT), I went with the SB Acoustics SB65WBAC25-4 as a reference full-range speaker in this size range.
Having now tested them, I can confidently say they’re probably the best speakers I’ve ever owned. The clarity is outstanding—every detail comes through with incredible precision. The bass is surprisingly full and punchy for a speaker this size, and they handle power impressively well. For anyone looking for a high-performance compact full-range driver, these are hard to beat.
Item as described and arrived quickly - and did the job. However, I suggested that anyone replacing speaker foam makes sure they have a very large pair of sharp dressmaking scissors as it was not easy cutting to size without producing a ragged edge (which I managed to hide short of a close inspection)!
Great service as always quick delivery
Thanks
Ordered two of these tweeters on Friday afternoon NZ time, amazingly they had arrived in Auckland the following Tuesday morning, arrived in my home town of Christchurch couple of days later and were promptly installed. Seem to be doing and sound as they should, thank you for your service!