A diaphragm is the heart of a high frequency driver. It sits inside the magnet assembly and moves in response to the electrical impulses from an amplifier. it's the part that breaks when the driver stops working. Replacement diaphragms are available for many JBL drivers to repair them in the field. Since most of us do our audio jobs in the field, it's reasonable to assume that somewhere along the line we will be required to replace a diaphragm without anything more than ordinary tools and our wits. After all...the show must go on! Replacing the diaphragm is not rocket science, but it does require a steady hand, a clean workplace, some common tools and patience. If you can't take the time to clean the magnet assembly before installing the new diaphragm, then you will probably be disappointed in the results.
We are using the JBL 2408 High Frequency Driver as our example. Your driver may look really different and you should examine it carefully as you take it apart, but the gap still has to be cleaned completely before installing a replacement diaphragm.
Picture A = Here I am marking the outside of the driver at the + lug. I like to use red for "hot" but it doesn't matter. I do this to help orient the new diaphragm to the same position.
Picture 1= This shows the driver after the flange has been removed. The diaphragm has been pulled up out of the driver. The driver body remains below exposing the voice coil gap. The part on the inside of the gap is called the polepiece. Both the driver body and the polepiece are magnetic.
Picture 2=This side of the diaphragm exposes the voice coil which is just fine wire wound on a coil form and suspended from the diaphragm frame. The bright orange rubber shown in this picture is a damper to isolate internal vibration. It is uncommon and only used on a few JBL drivers. Your driver may not have this damper. Put the old diaphragm aside and move on to cleaning the gap in the driver body. Leave the new diaphragm in its box until the last minute.
Picture 3= Before you can install the new diaphragm you must clean the voice coil gap. You do this with something sticky pushed down against the outside and then against the inside of the voice coil gap. The tape shown here is standard Electrical Tape which you can purchase at many locations in a variety of colors. Choose a color that makes it easy to see the junk you take out of the gap. You push a fresh piece of tape down into the gap, bent into a gentle curve to match the curve of the gap and against the side of the gap and begin to go all the way around the driver so that the sticky tape touches all the surfaces around the outside of the gap and then you do it again to the inside of the gap against the polepiece. Keep using fresh pieces of sticky tape until the tape comes out clean for both sides of the gap. You get the idea? You keep sticking clean tape into the gap, rotate the driver body to clean all the way around the inside of the gap and the outside of the gap and don't stop until the tape comes out clean. The gap can have all kinds of stuff inside and some particles will be magnetic, but don't use anything but sticky tape to clean the gap. Don't blow into the gap and don't use high pressure air which can contain moisture.
Picture 4=You don't have to use electrical tape...just don't use a tape like scotch tape or duct tape or masking tape...too many chances of the tape breaking or leaving a sticky residue. Here we are using the gummy part from a "post-it" note. This sticky paper tape works really well and the "post-it" note is usually easier to find around the house.
Picture 5= Use the sticky paper the same way as the electrical tape...bend it to conform to the curve of the voice coil gap and run it all the way around pulling off any debris that is stuck to the inside and then the outside of the gap
Picture6=when the gummy side gets full, just trim that part off and continue. You have to keep doing this until the sticky side comes out clean all the way around.
Picture 7=As soon as the gap is clean, put the new diaphragm in place immediately, but don't be in a hurry. Carefully center the diaphragm over the driver body and lower it gently down into the gap. The voice coil can be damaged easily. The diaphragm is designed to help keep the voice coil centered, but the task is really up to you and you must be very very careful. The 2408 type diaphragm shown here will kind of float on the orange damper plug. Other diaphragms seat directly into the driver body. Rotate the diaphragm carefully until the spade lugs are properly oriented (+ towards the plus markings you made on the driver body) and the screw holes are lined up. Place the driver flange over the diaphragm making sure the + sign is properly placed.
Picture 8=With the flange in place and all holes lined up you can begin to put in the screws that hold the assembly in place. In the case of the 2408 style driver you will have to push straight down on the flange to compress orange damper plug making the diaphragm "sandwiched" between the driver body and the flange. On other drivers the diaphragm will mount with one set of screws and the flange or a cover will mount with a second set of screws.
Picture 9=In all cases, tighten the screws gently and evenly so the diaphragm is not allowed to "tilt" and do not overtighten the screws...just snug+ is OK.