All,
everyone puts a very large emphasis on protecting speakers via some DC blocking mechanism (be it a DC detection circuit and a relay or a DC blocking cap).
I am trying to avoid either for simplicity and wonder this:
1. If I have 100W RMS speakers (around 150W peak), my power supplies can deliver at most 24V and my speakers are 8 Ohm nominal (i.e. DC impedance), than I do not see why I cannot simply say that the maximum current is 24/8 = 3Amps. Power = (3^2)*8 = 72W < 100W.
So my question is, can I not oversize my speakers a bit to avoid having to introduce any DC protection mechanism? I realize some of that 100W is going into the high end drivers, however I consider that to be a minimal amount of power compared to the low end drivers (the ones who will see the DC and the ones who contain most of the power rating).
Regards,
James
everyone puts a very large emphasis on protecting speakers via some DC blocking mechanism (be it a DC detection circuit and a relay or a DC blocking cap).
I am trying to avoid either for simplicity and wonder this:
1. If I have 100W RMS speakers (around 150W peak), my power supplies can deliver at most 24V and my speakers are 8 Ohm nominal (i.e. DC impedance), than I do not see why I cannot simply say that the maximum current is 24/8 = 3Amps. Power = (3^2)*8 = 72W < 100W.
So my question is, can I not oversize my speakers a bit to avoid having to introduce any DC protection mechanism? I realize some of that 100W is going into the high end drivers, however I consider that to be a minimal amount of power compared to the low end drivers (the ones who will see the DC and the ones who contain most of the power rating).
Regards,
James
It seems your perspective is based entirely upon a DC world. Impedance relates to AC (I believe "DC Impedance" is an oxymoron), and the impedance of a speaker driver varies dependent on the frequency of the AC imposed upon it. Around the driver's resonant frequency the impedance is highest. A nominally 8-ohm woofer, let's say, probably has a DC resistance of under 2 ohms. It may have as high an impedance as 15 or 20 ohms at its resonant frequency (say, 45 Hz), and as low as 3-ohms at, say, 20 Hz. Like @Saturnus, I think you should avoid DC at all costs, as even if the voice coils aren't melting you're pushing the driver into non-linearity.
The DC resistance of nearly all 8 ohm woofers is between 5 and 7 ohms.
Some DC can actually improve or degrade linearity depending on driver design.
DC protection is intended to prevent speaker damage when the amplifier fails resulting in the output sticking to one rail and you are not there to turn it off quick enough. A basic DC protection would just cut power to the amplifier in case a few volts of DC are detected. Actually, the criteria used to design it is usually the opposite, to allow full output down to 20Hz without activation (and to require a few volts, like >3V, because less DC is not that dangerous).
Some DC can actually improve or degrade linearity depending on driver design.
DC protection is intended to prevent speaker damage when the amplifier fails resulting in the output sticking to one rail and you are not there to turn it off quick enough. A basic DC protection would just cut power to the amplifier in case a few volts of DC are detected. Actually, the criteria used to design it is usually the opposite, to allow full output down to 20Hz without activation (and to require a few volts, like >3V, because less DC is not that dangerous).
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