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Lowther Maintenance
Do you have problems with your Lowther driver? Here is how we maintain them. Make sure that you have a clean work environment. Do not have steel tools or metal dust lying around. Always keep the very large magnetic force in mind. The magnet can pull a tool from your hand and into the cone, or any small metal shavings into the voice coilgap. The most common problem with Lowther drivers is voice coil rubbing. This can be caused by any of the following:
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The diaphragm assembly does not sit square on the magnet and the coil rubs inside the magnet cap.
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The driver could have been jogged in transport or maybe the coil is not quite round. The air gap width of the magnet is less than 1mm so small misalignments are critical.
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Foreign matter has entered the gap and is causing the cone to rub.
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Your driver may be so old that the foam surround has perished. The required tools for maintenance are:
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A 5/16mm wrench, it should be as "thin" as possible. Stainless steel is preferred, but not necessary.
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A roll of aluminum foil tape with an acrylic glue on one side. You can also use a business card with tape wrapped around the outside, sticky side out. This is what you need for those iron filings stuck in the air gap.
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1.5” diameter pipe will be required if the former is not round.
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A test CD or frequency generator for 20-50Hz notes. Connect the driver to an amplifier which is being fed a 20 hz. note. Raise the volume very slowly until the cone moves about 1/8”. There is often a slight clicking noise from the flexible wires connecting the post to the cone, ignore this. If you do not hear any scraping noises the cone is properly centered & the voice coil gap is clean. If there is a scraping noise then continue on. At times something gets caught in the voice coil so that sometimes it rubs, and sometimes it does not. If you have this problem you must go disassemble the driver and clean out the voice coil gap. If you can see that the voice coil is not properly centered, you probably just need to realign the cone. Place the driver onto a table and connect to your test system. Loosen the bolts holding the cone basket to the magnet. “DX” drivers have four bolts, “A” drivers have 3. You want these mildly tight to prevent easy movement of the cone, but not so tight that you cannot adjust the cone position.