Refoam? Recone? Replace?
October 14, 2020 10:39 AM   Subscribe

Come into possession of some v elderly Mission 700 speakers. One woofer sounds "blown". What now?

I'm based in the UK.

The speakers look like this. That's not my photo - the foam on mine is damaged, but not by quite that much - otherwise everything else is identical including logo.

The foam around the biggest circle (woofer?) on both speakers is v elderly and cracked, and one speaker has holes in the foam that you could probably get a finger through. However, that speaker sounds fine. The other has 10-12 narrow cracks extending through the foam from the cone to the part that screws into the cabinet. That woofer is making a distinctive "blown" noise / buzz when music is played through.

Both cones look ok. In both cases the bump in the centre of the cone has been dented inwards.

1) Are these rescue-able?

2) If so, is it worth it?

3) If so, do I need a new woofer, or new cone, or new foam?

4) And if I need replacement parts, how do I know which Mission 700 line these speakers are from? E.g. replacement foam from here shows different foam rings for various types of Mission 700 speaker.

Thanks!!
posted by chappell, ambrose to Technology (5 answers total) 2 users marked this as a favorite
 
1) Are these rescue-able?
Most probably.

2) If so, is it worth it?
It depends on what 'worth it' means to you. Are you doing this as a fun project? Are you looking to resell them? How much are you looking to spend? Quick cursory search shows them selling for about $100 here in the states? I wouldn't likely dump more than that into them, as they're pretty good but not like, necessarily amazing speakers to begin with. Unless you're just wanting to dick around with them as a hobby. Hell knows I've spent more money than sense on projects for shits and giggles. That's fine too.

3) If so, do I need a new woofer, or new cone, or new foam?
It is hard to tell without pictures of your exact speakers and the damage they have, but when I've done work on speakers in the past, I typically just consider it good practice to replace whatever I can if I'm digging into something like that. I tend towards 'full restoration' when multiple things are wrong or broken, because I've been in the situation so many times where I just replace things piecemeal, and now I spend all my time replacing little odds and ends on a Thing forever. I would go whole hog and replace whatever is even remotely questionable.

4) And if I need replacement parts, how do I know which Mission 700 line these speakers are from? E.g. replacement foam from here shows different foam rings for various types of Mission 700 speaker.
Is there a serial number that you can reference? I would call/email whoever you are planning on ordering parts through and ask them directly. I have a good audio shop in my world that's more than willing to help order parts (and I tip them well when I just order parts through them and don't use their labor).
posted by furnace.heart at 11:16 AM on October 14, 2020 [3 favorites]


That woofer is making a distinctive "blown" noise / buzz when music is played through.

That 'buzzing' sound tends to be caused by the voice coil being damaged or distorted, and rubbing against the magnet or the pole piece. Here is a cross-cut drawing of a speaker like the woofers in your Mission 700's (wonderful speakers, by the way).

The way I check for that kind of problem is by VERY gently pushing on the dome (dust cap in that drawing) to move the cone inwards. If you notice a scraping sound and/or a difference in (mechanical) resistance to this pushing compared to the other unit, the voice coil is damaged or the pole piece has shifted and you're basically looking at replacing the unit. It's also possible that some kind of debris has entered the gap the voice coil sits in, but given that that gap is enclosed by the magnet and the spider, that is as good as impossible except when the spider is damaged and, again, you're looking at replacing the unit. The domes being dented doesn't matter as such, as long as they're intact.
posted by Stoneshop at 2:38 PM on October 14, 2020 [3 favorites]


Thanks Stoneshop, I think this might be the issue.

Gentle pushing on the dustcap in the centre of both speakers doesn't seem to show much difference, but gentle pushing around the cone in different places suggests that the problem speaker is "stuck" at the bottom completely, and mostly stuck on the right hand side as well, whereas the good speaker shows the same resistance to pushing in every location.

What a shame! But definitely worth knowing not to sink money into trying to fix them in that case.
posted by chappell, ambrose at 4:22 AM on October 15, 2020


Only a cosmetic thing, going by Stoneshop’s knowledge, but I’ve successfully un-dented the central dome in a speaker by using blu-tack or double-sided tape to pull it out into shape again.
posted by fabius at 5:33 AM on October 15, 2020


the problem speaker is "stuck" at the bottom completely, and mostly stuck on the right hand side as well

Hmm. This sounds (hah) like something's gotten loose inside the box, or has gotten in via the bass port (the hole just over the lettering), and it's now wedged between the driver's frame and its cone ("driver" is any individual speaker unit fitted to a box; naming it thusly distinguishes it from what people often call a speaker, being the entire box).

Undoing the screws may or may not be sufficient to get the driver out as there may be sealant between the driver frame and the front panel, but gently levering the unit out should take care of that.
posted by Stoneshop at 7:56 AM on October 15, 2020


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