Off center subwoofer magnets

I have been given a Definitive Tech 8 inch subwoofer driver that was thought to be blown, but it turns out that the magnets have slipped at one point or another. The coil reads 4 ohms with a multimeter so it is for sure not blown. As far as I can tell, they are still glued together, although one magnet is significantly off center, and the backplate is entered on that magnet. I have looked for videos and forum posts about this but everything only is for getting the magnet back on.
Thanks,
Micah
P.S. here is a picture of the sub, looks to be a quality unit with double stacked magnets and a 1.5 inch coil.
q3zgmvyebgk8.jpg
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2 channel
Speakers: Mission 770 Freedoms
Integrated amp: Technics SU-v75 and matching tuner
CDP: Technics SL-PC20
Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
TT: Technics SL-3200, direct drive
Cartridge: Shure M97xE

Pc gaming setup
Receiver/amp: Yamaha RX-V665
Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
Speakers: Boston Acoustics CR75s

Random equipment on standby:
Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
txcoastal1 wrote: »

You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
Seen somewhere on AudioKarma (I think)

Comments

  • FestYboyFestYboy Posts: 2,326
    To repair it, the motor has to come apart for surface prep before reassembly.
  • pitdogg2pitdogg2 Posts: 9,831
    edited May 5
    Is it scratchy when pushing on the cone? Is the cone locked up? To be honest just because they're off center doesn't mean they slipped. When speakers are made the magnets are not magnets yet. They build and glue THEN they are put in the inductor to be magnetized.
    I've seen many off center magnets and the woofer was just fine
    Post edited by pitdogg2 on
  • mlistens03mlistens03 Posts: 990
    edited May 5
    It is not quite locked up, it will go out just fine, and with a little bit of pressure it will go in (I only did this once when I thought it was cooked, haven’t done it again). I assumed that they slipped because I honestly don’t know what else could have happened. They came out of a working cabinet that the amp had died on (my guess was momentary short because of the coil rubbing, scratches off the lacquer, boom dead amp). It wasn’t driven hard, it was my great grandmas and she never used her TV.
    I also believe I have identified the driver, I think it is a DefTech Pro Sub 80, which is very well reviewed and is still being sold today for ~$500, so it’s worth fixing methinks. I’ll build a nice little cabinet for it and buy an amp, fun project.
    Post edited by mlistens03 on
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
  • mlistens03mlistens03 Posts: 990
    edited May 5
    Also I do know the driver works, I am gonna test it in a minute just to see if it’s produces sound and if it doesn’t, I’m screwed :wink:
    Do you think I should try to remove the dustcap so I can see if anything’s amiss in there?
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
  • pitdogg2pitdogg2 Posts: 9,831
    If it don't freely move its toast.
  • mlistens03mlistens03 Posts: 990
    Can’t I just somehow remove the magnet and center the pole-piece? The coil reads good and it can move, but it takes a little pressure. This sub was my great Grandma’s before she got a soundbar and she never used it, for the first 3 years of her ownership it wasn’t even turned on. It has never taken any kind of abuse, or anything, just this. I don’t know what cause this, but I find it hard to believe that it just burned up even though nothing happened to it. If it’s locked up, does that mean the coil is deformed?
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
  • mlistens03mlistens03 Posts: 990
    By the way, I’m not saying you are wrong, I’m asking for explanation for why it’s toast.
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
  • FestYboyFestYboy Posts: 2,326
    If the coil tests good and the cone still moves a bit, it's not toast.

    If you want to fix it properly, the pole plate must be removed from the magnet. then ideally the magnet should be separated from the basket base plate, all surfaces cleaned and then center the magnet to the voice coil and affix with red Loctite. Allow to dry over night at least, before affixing the pole plate in the same manner. I recommend that prior to all this, you find a piece of PVC that fits around the magnet so that a jig can be made to center the pole plate. The fresh Loctite will allow you to position the plate before it cures. Have an amp ready with a sine wave generator app on your phone and sweep between 5 and 20Hz making adjustments untill there is no noise after getting a rough positioning using your hands to manipulate the cone until it moves freely.

    There's a post with pics that explains it better somewhere 'round here.
  • mlistens03mlistens03 Posts: 990
    How should I get the magnet off? The glue didn’t fail, I think that it may have just been a defective unit or something, so the glue is still there.
    Where can I buy Red Loctite? I don’t think we have any, but I think we have some Blue Loctite in the garage, would that work?
    My tone generator only goes down to 10 hertz, and I can’t make it sweep back and forth, so do you know of one that is free and can do the sweep? I don’t think my equipment will let me play down to 5 hertz anyway, I believe there is a crossover in the Yamaha to cut that out.
    Thanks,
    Micah
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
  • pitdogg2pitdogg2 Posts: 9,831
    Blue loctite will not work. Blue is not a permanent glue like Red is.
  • mlistens03mlistens03 Posts: 990
    pitdogg2 wrote: »
    Blue loctite will not work. Blue is not a permanent glue like Red is.

    Ok, good to know, thanks. :smile:
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
  • mlistens03mlistens03 Posts: 990
    I pulled the dustcap off, and it smells a little like cooked voice coils, although I can see the coil through the spider, it doesn’t look cooked. Here’s a pic w/out the dustcap:
    j8cnt7ey05rl.jpg
    Definitely was not the cleanest speaker surgery I’ve ever done, but it looks like the pole piece is a little off center, so I think that is the culprit. And today it is much smoother throughout the excursion by the way, it doesn’t get locked anywhere throughout.
    So what do you suggest I do at this point?
    Thanks,
    Micah
    2 channel
    Speakers: Mission 770 Freedoms
    Integrated amp: Technics SU-v75 and matching tuner
    CDP: Technics SL-PC20
    Cables: Monoprice, Monster, Acoustic Research, and a few generic ones
    TT: Technics SL-3200, direct drive
    Cartridge: Shure M97xE

    Pc gaming setup
    Receiver/amp: Yamaha RX-V665
    Computer: Lenovo g50 (soon to be upgraded to a Dell Precision 690 which is far from stock!!)
    Interconnects: Amazon basics HDMI, Acoustic Research HDMI, Monoprice speaker cables
    Speakers: Boston Acoustics CR75s

    Random equipment on standby:
    Onkyo TX-v940, JBL woofers and tweeters, single Klipsch KG .5, Yamaha guitar amplifier, Peavey Rage 158 guitar amplifier, Kicker comp 12” subwoofer, single Bose 802 series II, a whole bunch of 1”-3” full range drivers, Infinity Crescendo 3007s (on sale), Polk LSi25s
    txcoastal1 wrote: »

    You don't tell her you read the manual, and you tell her you know what the problem is, and you fixed it, because that what men do, fix things
    sure it has a flat response, and sure it has a lot of detail, and yes, it has good and clear lows. But is it enjoyable to listen to? Does it make you grin ear to ear? That’s what really matters.
    Seen somewhere on AudioKarma (I think)
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