Is it possible for LP rumble to destroy woofers? My mother in law has blown 3 Scanspeak 18W/8545K woofers and I'm trying to find out why. I've checked her amp, but it seems to be working fine (I've run it up to clipping with a load and seems no ill effects + very little DC on the output). She does play some LPs so my current thought is if she if playing these at moderate volume the subsonic rumble may be causing them to exceed maximum excursion.
Any thoughts?
Any thoughts?
Rumble causes damage to the cone surround mainly... particularly on old foam surrounds that are disintegrating. To burn a VC out would take some doing I would have thought.
Can you see excessive cone movement playing a record ? If the cone hits the end stops the distortion is obvious.
Is it always the same channel that fails ?
Can you see excessive cone movement playing a record ? If the cone hits the end stops the distortion is obvious.
Is it always the same channel that fails ?
I'd agree that rumble damages the surround, but I expect it would cook the voice coil, if the level has high enough.
When the voice coil leaves the magnetic gap, its inductance changes dramatically (I think it goes down, but I'm not sure). So, if a rumble came along that made the coil leave the gap, the inductance would drop, huge current through the coil, cooked.
So, looks like a rumble filter is on order.
When the voice coil leaves the magnetic gap, its inductance changes dramatically (I think it goes down, but I'm not sure). So, if a rumble came along that made the coil leave the gap, the inductance would drop, huge current through the coil, cooked.
So, looks like a rumble filter is on order.
The inductance change will not significantly affect the VC current. VC inductance is only significant at high frequencies, usually above the operating range of the driver. At low frequencies, the VC current is set by two factors:
1- The DC resistance of the voice coil.
2- The impedance peaks at the system resonance(s).
Most bass driver systems (driver/enclosure) are designed to be excursion limited, not power limited. That is, in most cases, at the lowest frequencies the driver will reach its excursion limits before reaching its heat limits.
For the current scenario, I guess we wait for the results of the failed driver post-mortem examination to decide the cause.
). (/she uses drums to communicate!) Curious.
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You haven't accounted for the changes of impedance when the cone actually moves somewhere.
Get a meter, put it across a woofer. Push the cone in (or out).
Chris
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