This "idiot" obviously knows a heck of a lot more about amplifier design than you do. Do you even know what EPDR means? It is a measure of the voltage delivered / current delivered at a given frequency. Why does that matter? .... It matters because that comes into play for power dissipation in an amplifier in the linear region. Keep in mind, we are talking real music here, not continuous pure tones, so low EPDR only increases the dissipation a bit dependent on music material. EPDR raises the power dissipation at the device level, and for BJT devices, that can lead to BJT secondary breakdown. This is from a Toshiba app note.
MOSFETs and Tubes do have secondary breakdown effects, but their safe operating areas and secondary breakdown mechanisms are different and hence they don’t experience failure in the same way a BJT amplifier will from short term thermal events such as those that could be induced by low EPDR. Amplifier power dissipation at a given power output will go up with phase angle (assuming not pure class-A), but you don’t get the catastrophic failure of a BJT amplifier.
EPDR does not mean your amplifier has to delivery higher peak currents. An EPDR of 2 ohms, does not mean the current drawn is higher than an impedance minimum of say 3 ohms. What it means is the amplifier power dissipation is a maximum at the EPDR minimum. It would be rare that it would be at the impedance minimum (if at all), so the impedance minimum does represent the maximum current delivered by the amplifier.
Having a 4 ohm tap isn’t going to make your amplifier more robust to a lower EPDR than the impedance peak. It is quite meaningless within the framework of impedance matching of the amplifier, or the output impedance of an amplifier. EPDR just tells you for a given speaker what the potential maximum power dissipation will be in your amplifier output devices, assuming a particular amplifier architecture.
Secondary breakdown is a failure mode in bipolar transistors in which negative resistance (current concentration) occurs under high-voltage and high-current conditions. Current concentration causes local heating, resulting in a small hotspot. The impedance of the hotspot decreases, causing further current concentration. This cycle called thermal runaway leads to device degradation and destruction.
MOSFETs and Tubes do have secondary breakdown effects, but their safe operating areas and secondary breakdown mechanisms are different and hence they don’t experience failure in the same way a BJT amplifier will from short term thermal events such as those that could be induced by low EPDR. Amplifier power dissipation at a given power output will go up with phase angle (assuming not pure class-A), but you don’t get the catastrophic failure of a BJT amplifier.
EPDR does not mean your amplifier has to delivery higher peak currents. An EPDR of 2 ohms, does not mean the current drawn is higher than an impedance minimum of say 3 ohms. What it means is the amplifier power dissipation is a maximum at the EPDR minimum. It would be rare that it would be at the impedance minimum (if at all), so the impedance minimum does represent the maximum current delivered by the amplifier.
Having a 4 ohm tap isn’t going to make your amplifier more robust to a lower EPDR than the impedance peak. It is quite meaningless within the framework of impedance matching of the amplifier, or the output impedance of an amplifier. EPDR just tells you for a given speaker what the potential maximum power dissipation will be in your amplifier output devices, assuming a particular amplifier architecture.