Speaker tip for rubbing coils.

[walpurgis]

If you have a bass driver that has a rubbing or binding coil, I have a dodge that I've used a number of times.

Find out where the coil is rubbing by applying gentle pressure to the side of the cone inside the chassis, not on the front, all the way round and moving it back and forth slightly. The area most prone to binding will become evident. Mark the chassis at that point with a felt tip pen for reference. Using a hair dryer on hot setting blow into the speaker chassis behind the cone and heat the rear spider all round, that's (normally) the corrugated fabric ring and apply mild pressure to the cone just in front of the spider on the opposite side to that you previously marked, then set the dryer on cold and keep blowing onto the spider. You may need more than one attempt, but it generally works, unless the coil or former is damaged or there is rust or other contamination in the magnetic gap.

The basic principal is that the heat of the dryer relaxes the setting of the spider and allows it to be reset, i.e. fixed in a new alignment.

[awkwardbydesign]

I have some old KEF B139s, polystyrene cones, so heating might upset them! One of them was rubbing, so after working out which side, I used a rubber mallet and tapped the magnet assembley across.
I realise this could easily end in disaster, but on this occasion it worked.

[spendorman]

I have some old KEF B139s, polystyrene cones, so heating might upset them! One of them was rubbing, so after working out which side, I used a rubber mallet and tapped the magnet assembley across.
I realise this could easily end in disaster, but on this occasion it worked.

Some speaker units have the magnet glued into place. Think the B110 and B200 have. Possibly later B139's, but not sure.

[synsei]

Sometimes just rotating the driver by 180 degrees is enough to cure this problem

[spendorman]

Sometimes just rotating the driver by 180 degrees is enough to cure this problem

Often done with Spendor BC1's, have done it with a bass unit in a B&W DM4, was successful.

[synsei]

I can't claim ownership of this particualr tip as it was you Alex who suggested it when I was having a similar problem with one of the bass drivers in my DM2's, so a Brownie point for you as it worked a treat

[spendorman]

I can't claim ownership of this particualr tip as it was you Alex who suggested it when I was having a similar problem with one of the bass drivers in my DM2's, so a Brownie point for you as it worked a treat

Funny thing is that DM2 bass units are not particularly prone to rubbing. Up to recently I had four pairs of DM2's / DM2a's and a spare pair of bass units. None suffered from this. Recently gave a pair of DM2's away.