Forte II tweeter diaphragms

[Krispy Kirk]

I blew a tweeter a few weeks ago on one of my beloved '89 Forte IIs and, after my replacement diaphragms arrived in the mail, I noticed that they are not made of the same material as the originals.

The stock diaphragms have a dome that appears woven out of a brown material covered in an clear amber coating (phenolic?) They are not "sticky."

The new replacements are black (polymer?) and are quite sticky (they arrived peppered with small flecks of cardboard "dust" from the packaging.

My question is:

Why are these diaphragms different? Are the new diaphragms superior in any way? How do I clean the crud off them (if necessary) ?

Thanks in advance for your responses!

[WMcD]

Dear KK,

I bought a pair of Quartets off e-bay. One tweeter was advertized as bad. When they arrived, both were bad. I bought new diaphragms, replaced them, and kept the old ones.

These are pretty much the same as your Forte II I'd think.

In any event, looking at the old ones, they are black. I can see a pattern of woven material through the black. And there is a speck of dust on one. A finger swipe removed it.

I don't recall the new ones being much different. So somewhere in the production runs, at least the coating changed. Maybe more than once. It may just be the color of the coating. Or maybe something more substantial about the coating itself.

As you can imagine this is a type of composite, like fiberglass. Part fabric and part plastic.

I wouldn't worry.

As you might know, the mass and strength of a diaphragm is a major item in driver design. This arises from the fact that high frequencies equate to high accelleration (sp).

F = M*A. The motor has only so much F, so A is best when M is low. And you also need a strong structure to keep the shape. But structures are made strong by more more material, which is more mass.

Tom Brennan has reported that some poor performance in the T-35 tweeter (the best of the production runs were used in the Heritage as a K-77) was because of problems with the diaphragm QC. Probably too much coating and therefore mass.

By extension, it may be that Klipsch and its suppliers have been using various materials to get the most consistent results of mass and strength. Therefore they look different.

I don't see any problem with dust. Maybe it is packing material stuck there by static electricity and a gentle wipe will remove it.

Gil

[BEC]

I don't have any official knowledge on this diaphrgm subject but I do have quite a bit of experience in replacing the diaphragms. This diaphragm that you are working with has changed a lot from the time it was originally used. The earliest ones are a phenolic dome attached to a plastic gasket. The phenolic domes on those are exactly (it seems) the same as the phenolic ones still used in the K-77 tweeters. At some time those domes changed to a cloth impregnated poly dome that was still pretty stiff like the older phenolic. For a brief time that dome even became a metal one. I have one of those still in its original Klipsch box. Later and now all that is available for these diaphragms is the soft poly dome type that you have described. It is very different from the oldest diaphragms that were very stiff. The new ones are almost as soft as a medical exam glove and it seems quite sticky in that everything seems to just cling to them and sometimes is even impossible to remove lint or whatever that is stuck to them.

OK, what you really want to know is what will the different replacement sound like. The answer seems to be a bit lower output for the new diaphragms compared to the original ones if they were phenolic.

Bob Crites

[Krispy Kirk]

Thanks for the info guys! I've had my new diaphragms in for about a week now and my speakers sound like they did the day I brought them home. I'd have a difficult time picking out the new diaphragm material from the old in a listening test (they sound identical to me.)

I didn't know what to do with the two little plugs of cotton(?) damping material that were behind the old diaphragms so I just reinstalled them behind the new ones. Perhaps this cancelled out any potential sonic differences between the two designs?

[sire]

My stupid question

How exactly can I tell if my Forte II tweeter is blown?

When using Avia or other cd to check my sub xover point, I hear strange noise coming from my rh tweeter, hear it a little from the left. It happens as the tone drops to 20hz. Hard to describe but does not sound like it should be there.

Mike