crescendo rub?

[hohohiwatter]

right then boys, managed to acquire myself a pair of crescendo 'A'

not a matched pair unfortunately but the real deal nonetheless, 1's a 72 and the other a '71.
they both sound MASSIVE brilliantly clear an all the usual phrases etc, but small prob with the '71 which has a slight distortion/buzz to it.
HELP!
with the amp at real low vol u cant hear it but turn it up slightly an u can hear it creeping in esp on a low open E chord, u can still hear the clean guitar same as the other speaker, but it has this slight distortion in the back ground.
this 1 has a slightly lower ohm rating than the other at 13.1 compered to 14.1
i have taken it out of enclosure in case it was that, nope still doing it.
there is no damage to it at all, but I'm thinking the voice coil might of got a bit nudged during transit (it was packed properly an everything) or it was already out of centre & the seller dint no or dint mention. after suspecting coil rub i had a look around on the site an i reckon that's what it is, unless any 1 thinks different?
i have equally pressed down on the cone sides an it does grate a little but only when pressed quite far down.
had a look at the doc voice coil rub fix, is that the only way to fix this prob? i really dont want to cut away the lovely alu dust cover! is there another way?
is there a way of maybe loosening the mag screws an I've read somewhere putting a little acetone/nail varnish remover on the spider, leave it a bit to reset then tighten up?
i know its often very hard to diagnose problems over the internet but hopefully there r some experts out there that know exactly what it is.
thanks

[OldSchoolDave]

First of all, congratulations on scoring two original Crescendos - AND having them arrive intact!

Take some time to review this thread: viewtopic.php?f=5&t=22

It details Dr.Hiwatt's procedure for recentering voicecoils (using my Sound City Fanes as test subjects). Before you engage in this process, though, try rotating the speaker in the cabinet. Sometimes, just the weight of the basket - over time - leads to a bit of a sag in the support. Hanging it "upside down" may reverse the effects.

If the scratching continues, best take more invasive action. Rubbing the windings off a vintage Fane voicecoil should be avoided at all costs!

Dave

[Dr.HI-TONE]

there is only one way to access the VC in order to shim it in and achieve an even spacing around the cylinder. unfortunately the dust cap is the gateway.

Try Dave's idea first and hope for the best!

[hohohiwatter]

thanks guys,

well at the moment its on its mag out the cab on the floor. cant remember which way up it was in the cab. will that help recenter if i leave it for a few days, cant hurt i suppose!
Hanging it "upside down" may reverse the effects. if it took 35 yrs to get in this state then waiting 1/2 that for it to return to normal is a bit of long time, even for me!

i have read - viewtopic.php?f=5&t=22 and was hoping there was something else i could try before i cut the lovely alu dust cap (which must do something to the sound cause it has a little cloth coverd hole in the middle) very reluctant to do that. is there any way of reusing it?

so u reckon defo voice coil rub?
u not liking the idea of loosening the mag screws an putting stuff on the spider? which i read somewhere.

bah! nothing is ever as simple as it should be esp with vintage gear, but i suppose thats 1/2 the fun!

[Dr.HI-TONE]

you are guaranteed to have a worse sounding speaker if you loosen the magnet without spacers/shims to center the VC.

The Aluminium DC will be destroyed in the process of removing it.

[hohohiwatter]

can i get a replacement alu dust cap with the hole, so it looks the same?

[OldSchoolDave]

...was hoping there was something else i could try before i cut the lovely alu dust cap (which must do something to the sound cause it has a little cloth coverd hole in the middle) very reluctant to do that. is there any way of reusing it?

I've not discovered a way - the dust cover gets sacrificed in the process of saving the speaker . My fear would be anything that would disolve the dust cover glue might harm the other components. If you figure something out, do let us know.

In my experience, Fanes seem more susceptible to gathering gunk in the gap than other vintage speakers. Not sure why, but I've run into my fair share of scratchy coils. It's one of the things that must be checked/verified when purchasing.

Dave

[Stelle79]

Have you checked the dust cap thoroughly for cracks? Alu caps can have tiny almost invisible cracks that cause buzzing.

[hohohiwatter]

how do u check that? by sight or tapping?

[OldSchoolDave]

Have you checked the dust cap thoroughly for cracks? Alu caps can have tiny almost invisible cracks that cause buzzing.

Good call - but I've found the sound of a cracked Aluminum dust cap to be more of a "creak" upon cone excursion and a "chirp" when playing certain frequencies.

A visual inspection may reveal such cracks, but they're usually easier to hear than to see.

Dave

[hohohiwatter]

yeh defo not cracks in alu cover. cant see or feel any an it doesnt chirp, its kinda like having a fuzz box with a mind of its own on at low vols under the clean sound of my chords. cant really hear it on single notes tho.

so on the diy vc rub fix last pics says

Let sit over night. Place something clean over the VC to keep debris out.

to be continued...

what happens next?

[hohohiwatter]

this off the weber site

From: Rich Santucci

Does having an aluminum voice coil cover affect frequency response?
I've always been told that it adds high end. Is this true?

Rich, let's look at the history of the voice coil cover, or 'dustcap'. At first, its only purpose was to keep dust and debris out of the voice coil gap. If you look at any speaker made in the early years, like a Jensen P12R, it had a simple flat felt dustcap about the size of a quarter. Then, as research on the perfect speaker proceeded, it was discovered that if you use a domed dustcap made out of the same material as the cone, you could change or smooth out some of the peaks and dips in the frequency response of the speaker. Next came a combination marketing/engineering idea. A big aluminum dustcap would certainly look cool, and since aluminum has high thermal capacitance, it would suck heat out of the area around the voice coil and radiate it into the air. It's a win-win-win. Cool look, adjust the frequency response, and get heat out of the voice coil. So, to answer your original question, yes, by sizing the dustcap appropriately, within reason, you can affect the frequency response dramatically, including extending the highs.

[hohohiwatter]

whats the best glue to use for alu dust covers?
someone suggested copydex but wouldnt that be best for cloth dust covers?

[OldSchoolDave]

whats the best glue to use for alu dust covers?

The good folks over at the JBL Heritage forum recommended a poly isoanurate (sp?) glue, in medium strength.

I found some at Rockler, a woodworking supply store in the U.S.. It's a two part process - apply the glue and then spray with the fixative (do not store the two anywhere near each other!).

Dave

[hohohiwatter]

what can i get in the uk? will arldite or bosick do?
i wood imagine it just needs to be a glue that doesnt set hard?
i dont even no what poly isoanurate (sp?) glue is!