Apparently my speakers survived 300mV (!) worth of it. The other channel had around 90mV. This is coming from a cheap small Chinese ebay amp that hums like crazy. 
So I was calculating, at 0.3V, the heating power would be, assuming 6 ohms for DC current, 0.015W, which appears to be able to generate less temperature difference than living in the tropics, which I do.
Do we need to be paranoid about speakers frying from such (huge?) amount of offset?
So I was calculating, at 0.3V, the heating power would be, assuming 6 ohms for DC current, 0.015W, which appears to be able to generate less temperature difference than living in the tropics, which I do.
Do we need to be paranoid about speakers frying from such (huge?) amount of offset?
Had a DCX2496 leave 1V DC on one of its outputs(it was faulty) into a Zapsolute mk2. It's DC servo probably saved things but even that ran out of range.
Peerless HDS164 (850438) got HOT!
I first detected a smell out of the BR port and turned things off quickly. It was on for a minute or so, maybe two.
The phaseplug was nearly untouchable and the cage was nearly as hot.
The driver works fine and I can not detect any differences or bad sound compared to the non heated one.
So it depends on the driver. The thermal design is important and they certainly held up in that department.
Personally, anything above 50mV is a no no. Prefer it to be under 20mV.
More due to principle than damage potential.
Peerless HDS164 (850438) got HOT!
I first detected a smell out of the BR port and turned things off quickly. It was on for a minute or so, maybe two.
The phaseplug was nearly untouchable and the cage was nearly as hot.
The driver works fine and I can not detect any differences or bad sound compared to the non heated one.
So it depends on the driver. The thermal design is important and they certainly held up in that department.
Personally, anything above 50mV is a no no. Prefer it to be under 20mV.
More due to principle than damage potential.
Loudspeaker and DC Offset
Hi,
I readed some very short about this here:
B&C SPEAKERS
But I would like to find something more specific(theorical analysis I mean!) for that....Do somebody know where I can find something like that???
Thanks
Opacheco.
Hi,
I readed some very short about this here:
B&C SPEAKERS
But I would like to find something more specific(theorical analysis I mean!) for that....Do somebody know where I can find something like that???
Thanks
Opacheco.
The B&C paper refers to DC offset caused when driven with heavy bass content. That is, it is about the temporary shift of the mean position that comes with strong LF drive. This "DC rectification" is due to nonlinearities in the woofer such as inductance changing with postion.
I think the primary concern with DC is heating of the voice coil and loss of excursion from shift of the mean position. If both are minor then it isn't a real issue. The OP calculations show a minor amount in this case.
I have seen (and conducted) tests where some DC offset is intentionally applied to find the lowest distortion point on a particular woofer. You can generally null out even harmonics (at least at a particular drive level) by applying a little positive or negative DC offset. This can vary from sample to sample of a given design due to the difficulty of getting the voice coil height exact.
In extreme cases of offset the coil will come out of the gap and the cooling effect of adjacent metal parts will be gone. The coil can then fry in short order. Upon disection you may see one end or the other of the coil charred, while the other end is fine.
David S.
I think the primary concern with DC is heating of the voice coil and loss of excursion from shift of the mean position. If both are minor then it isn't a real issue. The OP calculations show a minor amount in this case.
I have seen (and conducted) tests where some DC offset is intentionally applied to find the lowest distortion point on a particular woofer. You can generally null out even harmonics (at least at a particular drive level) by applying a little positive or negative DC offset. This can vary from sample to sample of a given design due to the difficulty of getting the voice coil height exact.
In extreme cases of offset the coil will come out of the gap and the cooling effect of adjacent metal parts will be gone. The coil can then fry in short order. Upon disection you may see one end or the other of the coil charred, while the other end is fine.
David S.
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