No announcement yet.

Choose ferrofluid for my tweeter

  • Filter
  • Time
  • Show
Clear All
new posts

  • Choose ferrofluid for my tweeter


    I have just reshaped a fully pushed dome in my old KEF Q5 speaker. Huge difference! I know a creased one is not like a new one, but I'm happy enough.
    The point is that when I separated the magnet and the dome I found some ferrofluid drops inside the dome. I guess that it went out due to the force needed to separate them.
    In the tweeter apparently there is some FF and around the voice coil as well. But I am not sure if this enough. Not 3/4 in any case.

    It would be an easy operation to refill the FF but my problem is get a correct FF. I know that Part express sells a recommended one, but unfortunately an international shipping is way too expensive...

    I have found a shop in my country (Spain) that sells FF for tweeters but its specifications are not exactly the same as Ferrotec recommends for this application:

    Specifications and Physical Properties:
    Material: Hydrocarbon Oil
    Sat.Mag. 280Gss (SI: 28mT)
    Viscosity t.Amb: 120cP (SI: 120 mPa)
    Density t.Amb: 1.10g / ml (SI: 1.11 g / cm3)
    T. Work: -10º ~ 140º cent.
    Cong point. -45º cent.
    Umb. Boiling: 233º cent.
    Flash point: 182º cent.

    Ferrotec on the other hand says:

    Ms value (mT)
    Tweeter, headphone, high frequency compression driver, multimedia

    Midrange, full range, midrange compression driver, siren driver

    Woofer, subwoofer, siren driver


    The viscosity value of the ferrofluid should be selected with respect to the desired amount of damping at the speaker’s resonant frequency. Typically, values of less than 200 mPa·s provide light damping, values in the 200–1000 mPa·s range provide moderate damping and values over 1000 mPa·s provide heavy damping.

    So this FF would have more mT (28 vs 22) and low viscosity (although I don't know what is the effect)

    On the other hand I'm not sure if my tweeter has enough FF right now. Maybe it is ok and don't need to replace. I would replace it if I could have the same FF but it seems that this is not guaranteed.
    What do you think? Will it work? Or I should stay away?


    PS: I attach a couple of photos of the dome with FF drops and the magnet...

  • #2
    Hi again

    I have found more details about the typical ferrotec kit:

    So its characteristics are:
    Saturation Magnetization (Ms) 220 Gauss 22 mT
    Viscosity @27°C 200 cP 200 mPa·s
    Density @25°C 1.16 g/cc 1.16 103 kg/m3
    Pour Point -35 °C -35 °C
    Flash Point >200 °C >200 °C
    Thermal Conductivity @38°C 150 mW/(m·K) 150 mW/(m·K)
    Surface Tension @25°C 32 dynes/cm 32 mN/m
    Coefficient of Thermal Expansion 7.5 x 10-4 ml/ml°C 7.5 x 10-4 /K

    Main differences with the one I can easily buy;

    Ms 22 vs 28
    Viscosity: 200 vs 120
    synthetic ester oil vs Hydrocarbon Oil

    Is this enough to discard it?


    • #3
      I've used plenty of ferrofluid, I never worried if it was correct or not, I'd say use whatever you can get. Dispensing the correct amount is the more difficult part, because to do it right you need to run an impedance curve, this may necessitate opening the tweeter several times and adding or subtracting more fluid.