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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: Phase Angle posted by Mechans on November 24, 2010 at 09:44:04:
The simplest AC voltage has a wave form described by the sine function. This is a pure tone at a single frequency. Your AC power voltage should be a pure sine wave of 60 or 50 Hz, depending on where you live.If this voltage is connected to a pure resistor, the current that flows will also have the form of a sine wave. It will be zero when the voltage crosses zero and maximum when the voltage reaches its positive or negative peak.
If the load has some capacitance or inductance, the current will not match the voltage in time. The current will not be zero when the voltage crosses zero, and it will not reach its maximum when the voltage reaches its maximum. It will still have the shape of the voltage wave form, but be shifted in time ahead or behind the voltage.
"Phase angle" is the way we measure the amount of time shift. This comes from the observation that a sine wave is generated by measuring the displacement from horizontal of a stick that is rotating smoothly around a fixed point at one end, like a clock hand. The moving end of the stick describes a circle, which is conventionally divided into 360 degrees or 2 Pi radians. In mathematical terms, sine (x) is equal to sine (x + 2 Pi).
Thus, a small phase shift of a few degrees means the load is mostly resistive but has a little capacitance or inductance. A shift of 90 degrees means the load is a pure capacitor or inductor with no resistance. A shift greater than 90 degrees means energy is being stored and released with some delay time, and the load is not a simple network.
This matters for amps and speakers because amps may not avoid distortion or even destruction if they have to deal with currents that are too far away from the voltage in terms of time displacement. Amps have their own internal phase angles [considering the time relationship of output to input voltages]. If the load adds enough to the amp's voltage phase angle at a frequency where the amp has gain, the feedback loop may go from negative to positive. The amp may go into oscillation and burn up.
Most speakers these days and most amps are behaved well enough to avoid this drama. However, a difficult speaker may cause some amps to deliver more distortion than others, so that it does not sound good with some amp combinations.
Edits: 11/25/10
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Follow Ups
- Relationship of voltage and current. - Al Sekela 15:29:45 11/24/10 (0)
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