Physical speaker problem undiagnosed

[loninappleton]

I've been playing around with a pair of old RS 1197's.

One of them has a 'vibration problem.' What causes this?

In playing test tones (or music as well) the cone seems to be
touching on something but I can't find out where it is. No dirt seems to be in there around the magnet where I removed the dustcap to
experiment with some homebrew phase plugs.

This vibration sound occurs with or without the plug installed.

The only thing I can see is to dump the pair because the one is
unusable.


Pressing down on the surround can make the vibrating sound go away
but that is of little help. The wiring should be in phase and I cannot
see that as a problem. The wiring to the cone vibrates as the cone moves but that is just part of the way it works. I've seen no broken contacts or anything else visually down in the spider or elsewhere.

This is a sound that electric razors pick up over time.

Is the speaker just shot?

[Cal Weldon]

When the speaker is unplugged and you push down on different locations of the cone do you get any rubbing/scratching sounds?

[loninappleton]

Yes.

With phase plug removed I can hear and feel rubbing.


I did this test before writing in here but maybe it's not the motor.

I can't see where it's coming from. Everything down in there looks clean.

Thanks Cal.

[Cal Weldon]

Turn the speaker so it's face down and run a low frequency signal through it or tap with your finger. It may be that something you can't see has got in there. Hopefully it's not iron based and will come out with a little jiggling. It may also be that the last winding of the coil has lost it's adhesive and is sagging or dislodged. In that case you're hooped. What is the former made of?

[loninappleton]

Originally posted by Cal Weldon
Turn the speaker so it's face down and run a low frequency signal through it or tap with your finger. It may be that something you can't see has got in there. Hopefully it's not iron based and will come out with a little jiggling. It may also be that the last winding of the coil has lost it's adhesive and is sagging or dislodged. In that case you're hooped. What is the former made of?

You mean the former as opposed to the latter?



I just went to my Speakerbuilding 201 book and couldn't find it in the index. I've heard the term but only in forums I guess. No engineering background on my part.


Old timers who've used the Radio Shack 1197 prob'ly know this.

[GM]

The former is the cylinder the VC is wrapped around and glued to the diaphragm.

GM

[loninappleton]

Originally posted by GM
The former is the cylinder the VC is wrapped around and glued to the diaphragm.

GM

That is paper as I thought they all were.

For full disclosure:

When cutting off the dust cap, I attempted to smooth the edge with some sand paper so that the plug would not touch the sides.

In doing these tests I had better luck with the 50 cent pioneers than
I did with the old RS 1197's. The diameter of the former might be a
bit smaller.

But if this kind of problem is unavoidable, I'd not want to doctor my FE127e's in this way.

Plus there's the fact that I have made my phase plugs from found objects-- not lathe-turned.

Are dimensions given for the phase plugs anywhere? I have seen some pictures of the ones for sale but that's all I know. I got myself an inexpensive caliper to measure things if it comes to that.

[GM]

No, paper formers can't handle much power, so mylar and other materials are used for higher power ratings.

Hmm, I see no way to guarantee no sanding debris getting into the gap unless possibly with the driver held over your head with someone holding a vacuum hose nearby, so if dust got in the gap it could get embedded in the VC's windings if heated up. If this happens, then it becomes a paperweight/'clay pigeon'/whatever.

No phase plug dims published AFAIK, but they need to be a close tolerance fit to keep airborne particles from accumulating in the gap such as a single layer of Scotch tape.

For small drivers I'm surprised someone isn't carving them out of rigid foam and just gluing them to the diaphragm as a DC replacement.

GM

[loninappleton]

Originally posted by GM
No, paper formers can't handle much power, so mylar and other materials are used for higher power ratings.

Hmm, I see no way to guarantee no sanding debris getting into the gap unless possibly with the driver held over your head with someone holding a vacuum hose nearby, so if dust got in the gap it could get embedded in the VC's windings if heated up. If this happens, then it becomes a paperweight/'clay pigeon'/whatever.

No phase plug dims published AFAIK, but they need to be a close tolerance fit to keep airborne particles from accumulating in the gap such as a single layer of Scotch tape.

For small drivers I'm surprised someone isn't carving them out of rigid foam and just gluing them to the diaphragm as a DC replacement.

GM

I too think there are things in 'the natural world' that could be used for this.

I first looked for the right size and shape of plastic eggs at Easter a couple years ago. Then I found the right size and shape of egg in wood sold in craft stores. The shaft is a piece of 3/4 in dowel.

Some sort of cap over the Dust Cap of lightweight material might be the answer to all these cutting problems.

A kids toy prob'ly has what is needed in some form. Or a disposable container. The egg that Silly Putty comes in is too big. Thats all i can think off. Maybe there are party favors at a party store that
would work? There's plastic everything and something is waiting to be found for this. Hard celophane containers that hold small objects
maybe-- like the tubes that cigars come in. Or Jobes tubes that are used to hold water for single flowers.


Maybe someone else has some ideas.

[loninappleton]

Custom valve caps:

http://www.kustoms.com.au/catalogue/valvecapacc.html

Prob'ly the wrong size and material but an idea starter. See previous.