I have been restoring a speaker and discovered a felt annulus between the magnet plate of the electromagnet and the bottom of the speaker basket, under the voice coil centreing spider support. I've sent in a photo with its remnants in place.

The original felt is disintegrating and needs to be replaced.

My guesses as to the felt's purpose is a damper for the speaker or to keep dust out of the speaker coil gap, ie a gasket under the spider support.

Any other ideas?

As the speaker was designed the voice coil was centred by a spider made from stiffened paper. So air could circulate through this and possibly carry dust into the voice coil gap. So it seems more likely the felt is there as a damper.

The spider was broken in a couple of places when I received the radio in 1988, and was glued up with superglue. That served for 35 years but failed again. I decided to replace it with the corrugated type, mounted on the same support as the original spider.

The corrugated spider does not pass air so would keeep out the dust, but would present more resistance to movement than the original spider, and perhaps more damping of cone movement.

So that leads to the question, would the cone be overdamped with both the corrugated spider, and felt gasket in place? I thought I would ask these questions before irrevocably assembling the parts.

The cone was also passed it, with a vibration I could not solve so I found a replacement. Photos of the various original and replacement parts will also be submitted, including a new voicecoil I made, and the new black felt gasket in place.

Air will still be vented even if the dust cover is solid, or porous. The speaker will sound horrid if its poling, where the voice coil tube rubs on the edges of the magnet. Normal cause is "off" centre due to the spider being damaged.

There are two types of spider. One is external under the cone an the other is a spiral of three arms in the come & usually screwed to the pole. If either of them gets out of alignment it will pole.

Damage, like rips badly repaired, water damage, or the cone coming loose at the rim; will also cause issues.

In the case of speakers running with DC. Like in series with a transistors collector, or source. The cone should jump out when polarised correctly and I have seen them destroyed by being pulled into the back of the VC cavity.

The best way of testing hard to find rattles is using mono tones, from say a function generator.

My intention is to fix the new corrugated spider to its support and the voice coil, then connect the speaker to the radio and apply just enough volume to make sure everything is nicely centred. And then fit the cone. Hopefully this will avoid poling.

But at this stage I want to know if sealing up the space under the new corrugated spider will overdamp the speaker, since the original under the cone was the three legged type which didn't impede air flow.

Photos will make it all clearer.

The first photo shows the remnants of the felt annulus sitting on the magnet plate. The last photo shows the new annulus in place sitting between the magnet plate and the spider support. Various other photos showing the original spider and voice coil arrangement and new cone, voice coil, corrugated spider and tinsel connecting wire.

I have found PVA woodworking glue to be the best glue to use on speaker cones and related parts.

Just by the way.

I don't think sealing that area would make any noticeable difference. The voice coil and gap are not airtight anyway.

I saw online someone use silicone for broken speaker cones

Actually PVA is a better match in terms of flexibility and it's much easier to work with. And it dries clear.

You then paint it with tyre black and it looks and works like new.

I was up until recently using Acrylic based QuickGrip often in conjunction with medical Micropore (non woven) for many tears & holes. However, it appears that it has disappeared. The Acrylic never really dries rigid (and I have made several tons of it).

If you use a rigid binder on the periphery and convolutions, it is liable to tear holes, which I have seen several examples of.

I intend to try a latex glue that is used to bind abrasive disks to the grinding disks used for sharpening shearing combs & cutters.

For glues & binders that remain tacky, dust with talcum powder. N.B. The scented stuff does not improve music that stinks.

I already have some PVA craft glue which is acid free and claims to be repositionable which should suit for getting things nicely lined up.

With the felt in place and with the corrugated spider the space under the spider is essentially sealed off. There would be leakage through the voice coi gap but that will be sealed off with the dust cap on the voice coil.

I agree, I don't think it should matter as there are plenty of speakers with that space sealed up. I have also thought of using polyester sound absorbing material instaed of felt.

Sealing the inside of the cone may restrict airflow but not stop it. The cone will actually be akin to a bellows. As the cone descends air will be be expelled via the outside of the voice coil and drawn back in as the cone is repelled, via the outside of the voice coil, which is not sealed.

This would also help cool the voice coil.

Photos uploaded to Post 3.

I had thought that cooling of the voice coil would be by convection into the magnet pole and plate and not to the outside atmosphere. But something to bear in mind. Good airflow cannot hurt as far as cooling is concerned.

Have added explanations of the photos to Post #3.

When doing repairs, I use PVA on the cone and silicone sealant on the flexible suspension bits. If the whole suspension has disintegrated, I've been known to replace only the outer half of the cone so as to not disturb the voice coil any more than needed. I have some scraps of old film (blank negatives) to use to 'centre' the voice coil if it has been poling on the magnet.

When restoring the cone this time I decided to spray the cone with paint to deter something chewing on it, presumably silverfish. Even though I tried to so this evenly, the cone when dried had a rattle I could not eliminate. I think the painting caused distortion which pulled the voicecoil out of line. I tried to recover the voice coil but it didn't survive being removed from the cone. So a total rebuild resulted, as the spider couldn't be repaired as I had done in 1989.

I'll use PVA for the cone suspension. I have used a high temperature epoxy (white) making the voice coil, and will use normal epoxy to attach it to the spider and cone. The normal epoxy comes in a dispenser which mixes as it dispenses and should be able to be applied straight to the joint. Time will tell.

Voicecoil centreing has been done in trial runs using plastic cut from a foolscap document envelope.

All fun and games, don't think I will do it again!

I do not like any glue that sets rigid, that is likely to cause tearing if used on the convoluted rim. For some unknown reason Acrylic "Quick Grip" has disappeared. It remained flexible and tacky, so needed talc on it if exposed.

I am considering Latex. As a reinforcement for decades I have used medical "Micropore" (Non woven fabric). As I fix I have seen a lot of damaged cones.

You cannot have convection with a speaker as the cone is moving. It has to be an air pump to affect cooling.