jouyang3
New Head-Fier
- Joined
- Nov 28, 2014
- Posts
- 1
- Likes
- 0
In electrical engineering, if circuit is constructed for envelop detection, then it is reasonable to assume that it is a RC circuit.
Generally modulated signals, music, especially those from AM radio come will be envelope detected. A modulated signal is usually the sound wave itself multiplied by a cosine of a different frequency. The resulting waveform is a wave that has an envelope resembling the original signal while encapsulating the cosine that the original signal multiplied. Envelop detection can now be used to detect the envelope of this resulting waveform so then it actually is able to reproduce the original signal.
The circuit to construct this envelop detector is usually consisted of RC circuit in combination with diodes for rectification. RC circuits has two stages, 1. it charges the capacitor up. 2. it discharges the capacitor. When the modulated waveform passes through, any rising cosine component will quickly charge the capacitor up and when the cosine drops, the capacitor slowly drops. The capacitor will immediately be charging again when the cosine raises again. As a result, you will have an approximation of the original signal.
Another info: parallel impedance/resistance can be computed with the following equation:
Rout = 1/(1/R1 + 1/R2 + ... 1/Rn)
Now, after the context, we can jump into the question: why do we use high impedance headphones?
Two reasons: 1. RC circuit. If a low-impedance headset is hooked directly across the resistance of the RC circuit, the resulting impedance (resistance) drops, making the time constant be much smaller. This will result in the capacitor discharge much faster and hence the envelope detector will lower in accuracy.
2. Parallel headset: every headset has its resistance/impedance value (just like any circuit). Generally speaking, audio systems require high output impedances for better quality. If you hook multiple headset together with low impedance, it will lower the output value. Even if you hook a couple high impedance headset and then in parallel with a low impedance headset, given the impedance of the "low impedance headset" is small enough, it can actually lower the overall output impedance of the circuit (refer to the equation above).
I haven't been working in this field, I am merely a college student, correct me if I am wrong, but I hope this might answers your question.
Generally modulated signals, music, especially those from AM radio come will be envelope detected. A modulated signal is usually the sound wave itself multiplied by a cosine of a different frequency. The resulting waveform is a wave that has an envelope resembling the original signal while encapsulating the cosine that the original signal multiplied. Envelop detection can now be used to detect the envelope of this resulting waveform so then it actually is able to reproduce the original signal.
The circuit to construct this envelop detector is usually consisted of RC circuit in combination with diodes for rectification. RC circuits has two stages, 1. it charges the capacitor up. 2. it discharges the capacitor. When the modulated waveform passes through, any rising cosine component will quickly charge the capacitor up and when the cosine drops, the capacitor slowly drops. The capacitor will immediately be charging again when the cosine raises again. As a result, you will have an approximation of the original signal.
Another info: parallel impedance/resistance can be computed with the following equation:
Rout = 1/(1/R1 + 1/R2 + ... 1/Rn)
Now, after the context, we can jump into the question: why do we use high impedance headphones?
Two reasons: 1. RC circuit. If a low-impedance headset is hooked directly across the resistance of the RC circuit, the resulting impedance (resistance) drops, making the time constant be much smaller. This will result in the capacitor discharge much faster and hence the envelope detector will lower in accuracy.
2. Parallel headset: every headset has its resistance/impedance value (just like any circuit). Generally speaking, audio systems require high output impedances for better quality. If you hook multiple headset together with low impedance, it will lower the output value. Even if you hook a couple high impedance headset and then in parallel with a low impedance headset, given the impedance of the "low impedance headset" is small enough, it can actually lower the overall output impedance of the circuit (refer to the equation above).
I haven't been working in this field, I am merely a college student, correct me if I am wrong, but I hope this might answers your question.
