Low Frequency Tone for Speaker Rub

[mrgreen711]

Hey! First time poster here, so be gentle

I have a pair of Bose 501s (I know, I know, just bear with me) that I grabbed for cheap because they look great in our little vintage vinyl shrine, and not surprisingly, the woofers needed to be refoamed. I've successfully refoamed speakers before so I went ahead and did that repair... but whereas last time I used shims under the dust cap, this time I did not (the speaker surround kit didn't recommend it in the instructions). Anyway, long story short, they were not centered as well as they should have been, and I'm stupid for having skipped that step, so now I have two beautifully refoamed speakers that are rubbing (hangs his head in shame).

I'd ideally like to avoid having to replace the surrounds again, especially since the brand new adhesive is going to be a pain to remove, so I'm trying out some last ditch effort solutions before heading down that route. The regularly suggested solution without replacing the surrounds seems to be to shim the voice coil and paint a little bit of acetone on the spider, in hopes that it will soften the glue and reposition itself slightly. I've also read (but not tried) using a low frequency tone to center the voice coil and cone while refoaming speakers, rather than using shims.

So my question is: do you think that using the acetone to loosen up the spider, then using a low frequency tone to center the coil would work the same way as using shims? I don't mind cutting into the dust cap if I absolutely have to, but of course, it would be ideal if I could leave it intact (plus my hands are fairly twitchy due to years of playing piano, so I barely trust myself to be able to cut the dust cap without slipping, despite having done it successfully in the past). I just don't know if using a test tone will do the same job of centering if it's relying on the acetone to loosen up the spider.

In case the question arises, I have tried the other simpler methods - rotating the woofers, tightening/loosening/removing screws, etc. And before anyone posts it, yes, I know these speakers aren't worth the effort, and I could do better buying new ones - but I have already made the commitment and I swear I will get these things functioning if it kills me!!!

Any help would be greatly appreciated!

 

[CopperWizard]

Get the
foam off and start over using the test tone method. Let someone with a steady hand do it using a couple new razor blades to get the glue off the basket and the cone. Don't use the acetone, trying to counter an off center is not the way to go. Start straight, end straight. Start center, end center. It sounds like you used absolutely no center r ing method. Even just some music playing at lower volume with some bass in it is enough to hear if things are centered while drying. Good luck!

 

[mrgreen711]

The instructions for these particular surround recommended just physically centering the cone as the glue dried, but it dried way too quickly for that to be a feasible method (I should have known better though).

my primary concern with removing the surround is that I won't be able to get it off cleanly and will have to replace the foam again - which wouldn't normally be an issue, but frankly I've already poured more money into these speakers than they're worth so I'm hesitant to spend another 30 bucks to replace those. Any particular recommendations for salvaging the current surrounds, or am I s.o.l.?

 

[CopperWizard]

Depending on where the mistake was made, the cone or basket. Can you lift the glue surround connection from the basket with a fresh razor blade? Or is it the cone/surround glue. A picture tells a thousand words and the type of glue would be helpful.

 

[colohiker]

You will probably need to replace the foam. I did a cheap repair on a pair of 501's for a friend using some generic foam and they fit great! Might be an option if you don't want to sink too much more into them. I usually use Aileen's Tacky glue when doing foams with a test tone. Even after doing 30+ refoams, I find that the quick drying glue is difficult to use.

 

[elitopus]

+1 buy new foams and redo it.
Even if you could move the spider, the whole VC assembly would be at an angle then. It might not rub when pushed slightly but it would rub when there was more cone excursion. Not to mention that acetone probably wont dissolve the epoxy that the spider is attached with.

You can buy cheap surrounds for less than 10 bucks. Redo them with some centering method. I prefer using a test tone. I have never shimmed and have not had an issue. Shimming is a good method too though

 

[mrgreen711]

Thanks for all the help everyone!

So based on everyone's recommendations I removed the old surrounds and am ready to try again. Unfortunately I couldn't salvage the old ones, but I am planning on being more cautious this time around.

Before I purchase the new surrounds though, I wanted some feedback in terms of testing the woofers for issues with the voice coil. With the surrounds removed I tested both woofers with a low frequency tone at very low volume to see if there was still distortion (there seemed to be a little tiny bit of rub when I physically manipulated the cone). The one woofer lets out a really beautiful low sub sound, but the other one has some rattle to it when I use the test tone (that dry... "farty" sound, for lack of a better descriptor). Ironically, the woofer that gave more rub physically is the one that has no distortion on the test tone, and the one with less physical rub is the one with the fart noise.

I have heard about these slight rubs occasionally being caused by debris under the dust cap, or potentially some warping of the basket. I don't think the VC is toast based on what I'm hearing; and even if it is, they're definitely not worth the price or effort of THAT repair. Anyone have any thoughts on what my situation likely is?

 

[dc270]

One of the best incestments I made was to purchase a CD test tones with octave ranges, and all sorts of goodies! I think I found it on Amazon. It was Precision Test Signal CD. Now I can accurately measure all kinds of frequencies to check for peaks, drops, etc- also according to what my room is promoting as well! You can find probably any kind of test signal ya need on the net too!
DC

 

[CopperWizard]

I would start with the refoam. Keep things centered and as the Eileens tacky glue dries (you got this I hope) then the centering is checked a final bit by using a test tone, don't take it too literally meaning j u st put on a bass heavy track and lower the volume so the cone is just moving a little. It should tell you where center is.

 

[elitopus]

You can check the VC by laying the speaker on its back a playing a test tone. Even with no surround there should be no VC rub with it on its back. If there is you might have a warped VC or some other issue.

 

[moebuster]

this is what I do and most of the times but not always it does the job-
glue the surround to the cone allow to dry.
glue the surround to the basket and at about 5 minutes into the drying at this stage begin to center the voice coil simply by
listening for rub and shifting the cone/surround til rub goes away.continue checking/pressing the surround onto the basket
listening for rub abd adjusting/shifting thesurround/cone til rub goes away.
most every speaker requires a slightly different amount of attention but you get the idea.

now then-
the amount of glue used will affect the lead in time where you start adjusting the voice coil/surround/cone for no rub.
use all 5 fingers and press just outside the dust cap and listen carefully.

Aleenes is overall about the most forgiving glue to use.
I tend to overapply glus to be certain I'll have solid adhesion and once the glue starts to set i'll take a damp cloth and wipe away the excess.
again it's a learned method. it takes trial and error.