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Subwoofer dust protection


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this story is weird. i have pics for those who say it cant be so.

my system sat dormant for 18 months due to the cv19 nonsense. i recently fired it up and ran it one night, the next night all my 18"s were locked up, cant push them in and out by hand, very little sound. distorted too. i was 15db below the DSP limiters when this happened.

 

speakers are 1992 peavey 1801-8, original in HDH3 subs. i am only running 2 double 18's but i have 4.

 

i took them apart, removed the magnets and was greeted by perfectly brand new golden orange voice coils. looked deeper and the foam covering the inside of the screen on the back of the magnets had mostly reverted back to petroleum instead of foam. it melted down inbetween the former and the inside of the magnet gap and burned into it, solidifying the whole thing on all 4 drivers.

i was able to get the gunk off with some simple green and labor, cleaned the magnet gaps very well. took about 7 hours to do 4 drivers. it was stuck on crusty goo.

they all worked great except for one driver rattled and distorted. never did figure it out, the magnet had cracked in 2 spots so i swapped the magnet with a different used one from 1995 and its fine. magnet is different shape on the back and has smaller vent though.

 

they all work again, but i have nothing covering the vents on the magnets. wide open screen.

should i try and do something about the lack of foam over the vent?

 

 

 

 

 

 

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That is quite common with these. The foam does rot. The magnet in the upper right is designed for a 250 watt basket which if I remember right is not as deep as the 350 watt ones. Not sure if the basket voice coil you have on it will bottom out or not but something to think about. Also the larger hole will help vent more heat for the higher power handling so that should be considered as well.  Any foam that is not too hard to blow though will work. You'll want foam that is not too tightly packed so you can't blow through it yet it's not so open cell that it won't stop dust.  Cut the foam slightly larger than is needed around. Put glue around the sides but not where the air blows though. Try a few different glues to see how it reacts to a spare piece of the foam to make sure it doesn't just eat it and leave you with another mess down the road. As far as the one scraping. Sometimes the voice coil going though repeated heating and cooling will become slightly not round. Also the voice coil gap is not perfect either. If you want to try you can do this. Put the basket back on the correct magnet and bolt down. With a marker put a line on the basket and magnet to it's current location.  Gently push the cone around the dust cap trying to push the speaker in at an even amount. See if you hear or feel scraping. If you do try pushing on just one area of the cone so it goes in slightly uneven. See if you get a different scraping sound in different locations. With this done take the bolts out and turn the magnet 1/3 of a turn and try again. See if it is better or worse. If still not better try the last spot. Sometimes just by turning the magnet like this you will find a location that will work.  Last if not any of these locations work try loosing only 1 bolt slightly and see how it effects things. I had a very difficult one that I ended up only using 2 bolts and the last I heard it is still going strong today. Go figure.  One last thing to look for is the spider itself. ( the sort of orange folded circle keeping the voice coil straight going up/down ) I've seen the spider come unglued where it is connected to the basket and make flapping / scraping sound itself. I used super glue "gel" kind of stuff. I picked up the unglued spider with tooth picks and put glue in that way before. Hope this helps. Doug

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