Speaker Measures Open Curcuit

[BoogieMKIIA]

Was getting ready to play the last song of the first set and my rig went dead. Checked cables (direct to amp with two good cables), the discovered no cone movement with a battery test. Measuring at home today with a multi-meter, open circuit right at the terminals.

Any suggestions what else to look for? Will be removing it from the combo to see if the leads from the terminals to the cone/voice coil. This is a Mesa Boogie MS12 which has been long out of production, not sure if there are parts to fix. I will check with Eminence, they made these.

Was able to make it through the gig with a Quilter Superblock US, DI to the board. We had our in ears, thank goodness. Be prepared.

[HSB0531]

17 minutes ago, BoogieMKIIA said:

Was getting ready to play the last song of the first set and my rig went dead. Checked cables (direct to amp with two good cables), the discovered no cone movement with a battery test. Measuring at home today with a multi-meter, open circuit right at the terminals.

Any suggestions what else to look for? Will be removing it from the combo to see if the leads from the terminals to the cone/voice coil. This is a Mesa Boogie MS12 which has been long out of production, not sure if there are parts to fix. I will check with Eminence, they made these.

Was able to make it through the gig with a Quilter Superblock US, DI to the board. We had our in ears, thank goodness. Be prepared.

I repaired a JBL speaker once.  The speaker lead between the terminal and the cone had come off right at the terminal.  I was able to resolder it.

Check those leads. You can connect your multimeter at the terminal and at the wire lead where it connects to the cone.  Test both leads.  If you have continuity, it's a break in the voice coil, which means you will need a recone.

[BoogieMKIIA]

Maybe the connection of the cone wire to the terminal was intermittent. Got a reading with some wire wiggle behind the terminal. Flowed some solder and seems good now. Will need to play it a bit to build confidence.

I wouldn’t think the voice coil of a 150W speaker could be burnt out with a 60W amp.

[JGale]

I had that happen to a Fuchs Fat S-1, an Eminence Delta Pro. I had to recone it. Anyone need a big heavy speaker? 

[HSB0531]

On 3/31/2024 at 7:52 PM, BoogieMKIIA said:

Maybe the connection of the cone wire to the terminal was intermittent. Got a reading with some wire wiggle behind the terminal. Flowed some solder and seems good now. Will need to play it a bit to build confidence.

I wouldn’t think the voice coil of a 150W speaker could be burnt out with a 60W amp.

I'm glad it was just the poor connection and you were able to solder it.

Regarding a 150w speaker and a 60 watt amp, yes, you can burn a voice coil with an underpowered amp providing it's sending a very clipped signal.  A square wave will kill speakers ( severe clipping ).

I did it to a JBL K145 15" speaker when I powered it with a Kent 50w bass head (awful distortion).  

Correction:  I fried an Altec 418B 15" speaker with that head.

I blew the K140 with my Acoustic 140 bass head.

[BoogieMKIIA]

I blew the speaker in my Princeton Reverb using a Lafayette fuzz... many years ago.

I had distortion and wah running when it happened, but below 2 on the master volume. Will see if re-soldering holds up.

[HSB0531]

On 3/31/2024 at 7:52 PM, BoogieMKIIA said:

Maybe the connection of the cone wire to the terminal was intermittent. Got a reading with some wire wiggle behind the terminal. Flowed some solder and seems good now. Will need to play it a bit to build confidence.

I wouldn’t think the voice coil of a 150W speaker could be burnt out with a 60W amp.

Good point to make about wiggling the wire.

The 2 main causes for a blown speaker are over excursion of the cone, where the voice coil/former assembly moves out of the pole piece and does not return into the gap in a linear fashion (mechanical destruction of the coil/former), and overheating and/or burning of the voice coil.

Overpowering can cause both to happen, whereas underpowering and sending high distortion into the speaker will cause burns and rubbing of the coil in the gap, and/or shorts or opens in the coil.

DJ's usually cause mechanical failures (sorry if I offend), and a highly clipped guitar amp with lots of harmonics (power chords) usually causes overheating.

Most guitar speakers have voice coils that are only 1.5" to 3" in diameter, and those with aluminum coils overheat even faster.