Trying Different Methods to Solve Microphone Feedback
When using microphones for live sound reinforcement, microphone feedback (self-sustaining howl due to positive signal feedback - line signal feedback not discussed here) is inevitable. Simply put, it occurs when sound signals output from speakers are picked up again by the microphone, re-amplified by the system, creating signal superposition and positive feedback leading to howling. Audio engineers have long tried various methods and equipment to solve this, often with limited success. Based on my experience, here are several methods to try:
1. Feedback Suppressor: Works by suppressing the level of several significantly prominent frequency points exceeding a preset threshold. This method offers some effect for fixed microphone setups or conference systems but performs poorly or even disrupts stage performances. Stage performers move constantly, making frequency tracking difficult. Moreover, performers (especially rock singers) have high dynamics, causing many frequency points to overload not from feedback, misleading the suppressor to suppress them, causing sound pressure collapse and ruining the performance.
2. Frequency Shifter: Shifts the microphone signal frequency up or down by several or tens of Hz to avoid positive feedback. This method also suits conference systems only. On stage, the frequency shift effect sounds comical and disorienting.
3. Automatic Mixing Console: Uses auto-delay noise gates to mute/unmute microphones based on signal presence, eliminating feedback. This suits conferences with many microphones or stage language programs well, but poorly for song/dance programs (see Noise Gate).
4. Noise Gate: Uses threshold level to mute/unmute microphone signals, eliminating feedback. Commonly used for drum miking (drum triggers excluded). Mics open only when struck, preventing feedback between stage monitors and drum mics. Unsuitable for song/dance programs as soft vocal parts may fall below the threshold, causing "dropout".
5. Compressor: When signal exceeds a set level, it proportionally compresses the signal to prevent further increase and eliminate feedback. Usable for stage song/dance programs but ineffective against initial feedback below the threshold.
6. Graphic Equalizer: Attenuates or cuts specific feedback frequencies. Disadvantages: fixed frequency points vs. variable feedback points (which can fall between them), often requiring adjacent point attenuation. Also, graphic EQs have wide bandwidth; cutting frequencies causes frequency response dips and distortion. Best for less demanding amplification scenarios.
7. Parametric Equalizer: Uses a sweepable filter to locate the feedback frequency, adjusts its bandwidth (Q), then attenuates or cuts it precisely. This addresses feedback while preserving useful signals, making it suitable for various situations.
These are my feedback elimination experiences. Of course, decisions depend on actual conditions, including testing. I recommend testing feedback points with the actual performance microphones, not dedicated test mics, since performers don't sing with test mics. Connection methods also require practice. My typical setup: Parametric EQ + Compressor per microphone input channel (one set per mic), drum channel + Noise Gate. This requires more equipment and investment. Choose methods and devices based on your situation (perhaps better methods exist).
Regarding feedback-prone lavalier mics (lapel mics): This relates to their pickup pattern and gain. Lav mics usually have wide patterns (omnidirectional or cardioid) and are clipped on the chest/lapel far from the mouth, requiring higher gain at both mic and mixer. Hence, feedback risk is higher. If this occurs, slightly reduce gain at both points – balance performance and feedback avoidance. Also, regarding patterns: Some conference/educational lavs use tiny electret mic heads; never use these for stage – they distort vocals and feedback easily. Stage lavs are condenser or dynamic types, offering undistorted sound and less feedback tendency.
1. Feedback Suppressor: Works by suppressing the level of several significantly prominent frequency points exceeding a preset threshold. This method offers some effect for fixed microphone setups or conference systems but performs poorly or even disrupts stage performances. Stage performers move constantly, making frequency tracking difficult. Moreover, performers (especially rock singers) have high dynamics, causing many frequency points to overload not from feedback, misleading the suppressor to suppress them, causing sound pressure collapse and ruining the performance.
2. Frequency Shifter: Shifts the microphone signal frequency up or down by several or tens of Hz to avoid positive feedback. This method also suits conference systems only. On stage, the frequency shift effect sounds comical and disorienting.
3. Automatic Mixing Console: Uses auto-delay noise gates to mute/unmute microphones based on signal presence, eliminating feedback. This suits conferences with many microphones or stage language programs well, but poorly for song/dance programs (see Noise Gate).
4. Noise Gate: Uses threshold level to mute/unmute microphone signals, eliminating feedback. Commonly used for drum miking (drum triggers excluded). Mics open only when struck, preventing feedback between stage monitors and drum mics. Unsuitable for song/dance programs as soft vocal parts may fall below the threshold, causing "dropout".
5. Compressor: When signal exceeds a set level, it proportionally compresses the signal to prevent further increase and eliminate feedback. Usable for stage song/dance programs but ineffective against initial feedback below the threshold.
6. Graphic Equalizer: Attenuates or cuts specific feedback frequencies. Disadvantages: fixed frequency points vs. variable feedback points (which can fall between them), often requiring adjacent point attenuation. Also, graphic EQs have wide bandwidth; cutting frequencies causes frequency response dips and distortion. Best for less demanding amplification scenarios.
7. Parametric Equalizer: Uses a sweepable filter to locate the feedback frequency, adjusts its bandwidth (Q), then attenuates or cuts it precisely. This addresses feedback while preserving useful signals, making it suitable for various situations.
These are my feedback elimination experiences. Of course, decisions depend on actual conditions, including testing. I recommend testing feedback points with the actual performance microphones, not dedicated test mics, since performers don't sing with test mics. Connection methods also require practice. My typical setup: Parametric EQ + Compressor per microphone input channel (one set per mic), drum channel + Noise Gate. This requires more equipment and investment. Choose methods and devices based on your situation (perhaps better methods exist).
Regarding feedback-prone lavalier mics (lapel mics): This relates to their pickup pattern and gain. Lav mics usually have wide patterns (omnidirectional or cardioid) and are clipped on the chest/lapel far from the mouth, requiring higher gain at both mic and mixer. Hence, feedback risk is higher. If this occurs, slightly reduce gain at both points – balance performance and feedback avoidance. Also, regarding patterns: Some conference/educational lavs use tiny electret mic heads; never use these for stage – they distort vocals and feedback easily. Stage lavs are condenser or dynamic types, offering undistorted sound and less feedback tendency.