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Re-Magnetizing the Ferrite Magnet of Vintage Philips Drivers

Wharfedale Speakers

Hari Iyer

Well-Known Member
Joined
Feb 8, 2010
Messages
3,168
Points
113
Location
Mumbai
This vintage Philips drivers were gifted to me by FM Shafic and due to age i believe the magnetic flux density have reduced considerably. Due to this the TS parameter calls for a larger box size which is not practically possible. The main culprit was the bigger Qts (total Q) which was as high as 1.9. Also the BI was around 3 Tesla which cause an early roll-off of the lows.

I googled many approaches to bring back the lost power of this ferrite magnet and finally narrowed to the easy CD method (Capacitive Discharge) method to power the magnet back to strength.

I did not have high value electrolytic capacitors and tried magnetizing the drivers with this method. I had a total capacitor value of around 1400 microfarads (Electrolytic) and a simple 5V power supply from my mobile charger. i manually charged and discharged the drivers alternatively for around 20 rounds (15 minutes) or so. I then measured the TS parameter of the driver and to my amazement found the flux density to increase from 3Tesla to 5.1Tesla. Also the Qts dropped from 1.9 to 1.35. I repeated measurements twice to confirm this and this was correct.

After i return to Mumbai am planning to redo this with a 40,000 + capacitance discharge to the drivers. I want the flux density to increase to atleast 6 to 7 to reduce the cabinet size and reduce the total Q of the driver.

Suprisingly also the Vas reduced marginally for the driver making it even more better for a smaller box.
 
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