# Understanding Low Impedance & EMI/RFI in Audio

• cda
In summary: So, high impedance circuits are more susceptible to EMI.In summary, a low impedance audio system is less susceptible to EMI and RFI because terminating the audio cable with a low impedance reduces its efficiency as an antenna and decreases the potential divider action, resulting in a lower voltage induced by the interfering field. However, this may not be effective for magnetic fields. On the other hand, high impedance circuits are more susceptible to EMI because they have a higher voltage for a given current induced by the interfering field.
cda
Question in relation to audio.

I read online that a low impedance system is less susceptible to EMI and RFI than high impedance. How? I thought that high impedance = high resistance, therefore higher resistance to EMI and RFI. Would love to be updated with the explanation.

Thanks.

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cda said:
Question in relation to audio.

I read online that a low impedance system is less susceptible to EMI and RFI than high impedance. How? I thought that high impedance = high resistance, therefore higher resistance to EMI and RFI. Would love to be updated with the explanation.

Thanks.
This is the case when the interferer has mainly an electric field. For instance, the AC mains supply, or maybe a computer. The audio cable acts as an antenna, and develops a voltage as a result of the interfering field. If we terminate the "antenna " with a low impedance, its efficiency as an antenna is greatly reduced. We can choose what impedance we use for our wanted audio, so it makes sense to make it low.
In more detail, a few metres of wire acting as an antenna at audio frequencies is like a small capacitor, so it has a very high impedance (a high capacitive reactance). If we terminate it with a low value resistor, there is potential divider action and the interfering voltage is greatly reduced.
In some cases, magnetic fields are a problem, and using a low impedance will not then be effective as a cure.

To say it another way:
The EMI fields can only induce a small current. If the circuit is high impedance, that means a high voltage, and vice versa.

## 1. What is impedance in audio?

Impedance in audio refers to the measure of resistance that an audio signal encounters when traveling through a circuit. It is typically measured in ohms and can affect the quality and strength of the audio signal.

## 2. How does low impedance affect audio quality?

Low impedance in audio can cause a decrease in signal strength and can also result in distortion and noise. This can lead to a decrease in overall audio quality.

## 3. What is EMI/RFI in audio?

EMI (electromagnetic interference) and RFI (radio frequency interference) are types of electrical interference that can affect audio signals. EMI/RFI can come from sources such as power lines, electronic devices, and radio signals, and can cause unwanted noise or distortion in audio signals.

## 4. How can low impedance and EMI/RFI be mitigated in audio?

To mitigate low impedance and EMI/RFI in audio, it is important to use high-quality cables with proper shielding and grounding. Additionally, using balanced connections and placing audio equipment away from potential sources of interference can help reduce their impact on audio quality.

## 5. What are some common symptoms of low impedance and EMI/RFI in audio?

Some common symptoms of low impedance and EMI/RFI in audio include a decrease in overall volume, distortion, and unwanted noise such as buzzing or humming. These issues can be especially noticeable in high-frequency sounds.

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