When using a microphone for live sound reinforcement, one of the most common issues is feedback or howling. This occurs when the sound from the speaker is picked up again by the microphone, creating a loop that amplifies itself and results in an unpleasant whistling noise. While this positive feedback phenomenon is well-known, it's not the focus of this discussion. In practice, sound engineers have tried various methods and equipment to tackle this problem, but few solutions are completely effective. Based on my personal experience, here are several approaches you can consider trying:
1. Feedback suppressor: These devices work by detecting and reducing specific frequencies that exceed a set threshold, helping to prevent howling. They can be somewhat effective in fixed setups like conferences, but they often struggle during dynamic stage performances. When performers move around or sing with high dynamics, the suppressor may incorrectly identify normal sounds as feedback and cut important frequencies, which can negatively impact the overall sound quality and performance.
2. Frequency shifter: This tool shifts the microphone signal up or down by a few frequency points to avoid feedback. It works best in controlled environments like meetings, but it’s less suitable for live performances. The frequency shift can make the sound unnatural, confusing both the audience and the performers.
3. Automatic mixing console: These consoles use a noise gate to automatically switch microphones on or off based on the presence of a signal. They’re great for large conference settings or language-based programs, but they aren’t always ideal for music and dance performances. This is because the noise gate might shut off a microphone when a performer speaks softly, causing the sound to disappear unexpectedly.
4. Noise gate: A noise gate turns the microphone signal on or off based on a set threshold. It’s commonly used with drum mics, where it only activates when the drum is hit. This helps prevent feedback between the stage speakers and the drum kit. However, it’s not very effective for vocal performances, especially if the voice is soft and doesn't reach the threshold level.
5. Compressor: A compressor reduces the volume of a signal when it exceeds a certain level, preventing it from becoming too loud and causing feedback. It works well for stage performances, but it can’t address feedback that occurs before the signal reaches the threshold.
6. Graphic equalizer: This device allows you to cut or reduce specific frequencies that cause howling. However, its fixed frequency bands can lead to over-cutting, resulting in a loss of clarity and distortion. It’s best suited for situations where sound quality isn’t a top priority.
7. Parametric equalizer: Unlike a graphic equalizer, a parametric EQ lets you precisely target the exact frequency causing the howling. By adjusting the bandwidth and attenuation, you can eliminate the feedback without affecting the rest of the audio. This makes it highly versatile and ideal for different performance scenarios.
Based on my experience, I recommend using a combination of a parametric equalizer and a compressor on each microphone channel, along with a noise gate for the drum channels. While this setup requires some investment, it offers the best balance of control and sound quality. Always test with the actual microphones you’ll be using, as different models and placements can significantly affect the results.
Another issue to watch out for is feedback from lavalier (clip-on) microphones. These are often omnidirectional, meaning they pick up sound from all directions. If the microphone is placed far from the mouth, it can easily pick up sound from the speakers, leading to feedback. To minimize this, try reducing the gain at the microphone and the mixer. Also, make sure to use a high-quality lavalier designed for live performance, such as a condenser or dynamic model, rather than a small electret type, which can distort or produce more feedback.
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