Advice from Beauhorn...

REHABILITATING LOWTHER DRIVERS

Cleaning your Lowther driver air-gap and re-aligning it

Because of our experience of using Lowther drivers, Beauhorn gets a number of pleas each year from DIYers (and owners of other brands of Lowther-driven speaker) for help and advice when their speakers start making strange noises. I have put together the following notes which may help to resolve some problems:

Lowther drive units have long been aclaimed around the world as very fine wideband drivers. In part, their phenominal clarity and sensitivity is the result of the very small clearance between the voicecoil and the magnet pole pieces. We are talking tenths of a millimetre here.

As a result of this, very great care must be taken to protect the units from dust and, in particular, from ferrous particles. These, as Lowther themselves warn, may be attracted by the very powerful magnets from 'seemingly impossible' distances.

In the nature of things, however, accidents happen. Very occasionally, a Lowther user may become aware of a distortion or low frequency buzz or grating sound from one channel.

Buzzing driver

There are just three causes of buzzing:

a. dirt in the air gap

b. misalignment of the cone and voice coil in the air gap

c. distortion of the voice coil due to accidental overload (sometimes
caused by actions like changing interconnects while power amplifiers are on
and volume is turned up).

Most frequently it will be 'a.' causing the problem, particularly if it seems to be intermittent.

While exchange drive units are readily available there is some expense involved and it might be sensible to try and rectify the problem yourself. You have little to loose, it sounds more difficult than it is and if you succeed, as you should, you can give yourself a pat on the back.

Fix-it-Yourself

In the following process, you will, of course, observe the need for scrupulous cleanliness. No dust, dirt or metallic particles must get anywhere near your drive unit.

You will need a metric 8M open ended spanner (wrench) for this, although there is probably an AF size that will also fit - it needs to be 8mm (0.315 in) across the jaws, plus clearance.

Remove (unscrew) the phase plug. Undo the four cap screws securing the driver and carefully remove the internal connections, the red (signal) terminal is on the right as you look across the frame, note.

You need to put the driver on a table on something like a pile of books so that you can see under the cone comfortably. It's probably a good idea to mark the cone assembly frame and the magnet so that you reassemble them with the same orientation.

Separating the magnet/cone assembly

Taking care not to let the magnet grab the 8M spanner from you, remove the four bolts holding the basket that supports the cone to the magnet. You can now gently lift the cone assembly away from the magnet.

Use a soft paintbrush (artistic kind) to wipe round the voice coil on both sides. Examine the magnet air gap for signs of foreign matter. Any particles of a ferrous nature can be very difficult to remove. If I see any, I stick them with Scotch tape and drag them out, Lowthers use a high pressure air line. (Not recommended with the cone in place!)

Refit the basket to the magnet, with care to avoid too much scraping of the voice coil, and insert the four securing bolts, but do not tighten them yet. You need to be able to adjust the position of the basket at this point.

Re-alignment

We come to the tricky bit, which is to align the basket so that the cone can move freely in and out without touching the magnet. If you have a test CD with sinewave tones on it that can be a big help (connect to driver and set to repeat sweep tone), otherwise you will need to use your
fingertips on the inner cone to test this.

I find it better to use three equispaced fingertips to do this, and I recommend that you try gently on your good driver to get an idea of what it should feel like - apply equal pressure at each point not to move it sideways. Actual cone movements in use are very small, so don't overdo the pushing - about 1 mm (say, one twentieth of an inch) is all you'll need.

Centre the voice coil and delicately tighten two opposing bolts and check again. It may take some patience to get this right, as it's easy to move the basket as you tighten the screws. But it can be done.

I hope that you can then reassemble your driver and enjoy your music undisturbed.

This all sounds very daunting, I'm sure, but it's not really as bad as it sounds. The first time is definitely the worst.

Good luck, Eric Thomas

PLEASE NOTE: These instructions are intended for the guidance of those reasonably confident of their competence to carry them out; for others, there is the Lowther exchange unit scheme. We do not accept any liability resulting from failure to carry out the instructions successfully.