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Did Fleetwood Mac's "The Chain" blow up my woofer?

System: Ortofon 2M Red > Musical Surrounding Phonomena II > PS Audio Stellar preamp > M700 monoblocks > Buchardt S400 

Phonomena is set to 46db of gain, 200pF capacitive, 50k Ohms resistive

The other day I was playing "The Chain" off of Rumors, and one of the woofers stopped entirely during the bass guitar interlude. It just went completely silent, no pops, crackles or distortion. The tweeter is fine, and I reversed the L and R channels to confirm this problem is in the right woofer. The volume level was a "strong" listening level (30 out of 100 on the Stellar), but not loud. We were still able to converse just fine without raising our voices much at all. I have certainly listened to these speakers much louder with other sources.

I understand the power amps are overkill, but I figured my ears would bleed far before I was in danger of blowing anything up. Was this distortion? Subsonics? Woofer pumping due to poor TT isolation? Or a simple defect in the driver?


jayy42
jayy42 OP
4 posts
 
I suspect woofer pumping is the culprit here, but I am seeking advice. Right now the components are stacked on the floor while I wait for my new media console. 

I didn't see any burn marks on the woofer or the stuffing around the crossover. I have a new woofer unit on the way. 

I am thinking about a maple shelf with sorbothane feet on which to place the TT along with a KAB RF-1 filter. Hoping that will eliminate the potential for rumble/pumping in the future. I already have sorbothane pucks between the speakers and the stands. 
rocknss
130 posts
 
Fortunately, resistors in a crossover that go bad tend to turn black, along with nearby parts suffering from too much heat, so a visual inspection is often helpful.
These are large ceramic power resistors. I don't think that they usually turn black, at least I know that I have seen them when they didn't.

Doesn't look like these speakers have any fuses, so hopefully they designed them with at least one of these fuses as the weak link.
stevecham
3,340 posts
 
Well you "blew up" one and not both so that points to defective woofer or crossover in the one that blew. Talk to the manufacturer and see if they can replace. Or you can take the problematic woofer out of the enclosure and use a 9 volt battery briefly touched to the terminals to see if the cone will move. That will tell you if the coil is burned or if it's a crossover problem.
kcleveland
15 posts
 
You could also measure the woofer with an ohm meter. Should be around 8 ohms (typical). I've found the best solution for TT isolation is a wall shelf. Rega sells one for not huge money and you can buy or build a simple plywood shelf to sit on this if your TT is not a Rega.
Good Luck.
mulveling's avatar
mulveling
1,895 posts
 
This happened to one of my big Tannoys a year ago. Turns out a lead wire to the woofer became disconnected. Most likely the lead came from the factory with a marginal physical connection, and the large amounts of energy thrown around the cabinet during loud listening  (96 dB/ Watt efficient and 15" woofer) eventually shook it loose. Simple to resolve; my tech fixed it easily, and it's worked perfectly since then. No permanent damage to the woofer.

As noted by others, you'll want to make sure you don't have a rumble issue (my current system has absolutely no rumble or woofer flapping). That's extra energy that can only have deleterious effect. 
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