Feedback / Microphone: Difference between revisions

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Feedback occurs when the sound from the loudspeaker (or loudspeakers if a microphone is connected to more than one) is louder at the microphone than the sound of the voice.

This fundamental fact is shown in the figure below.

This fundamental fact is shown in the figure below. Note that in the diagram an L1 system is shown but the same fundamental fact is true for ANY loudspeaker.

[[Image:Feedback fig 1.jpg|800px|Microphone Feedback]]

If you understand this diagram, it is relatively easy to understand how changes in an amplification system and room can contribute to either increasing or decreasing the likelihood of feedback.

== Techniques For Reducing Feedback ==

=== Gain Staging ===

~~If you are having issues~~ with ~~feedback, check your~~ gain staging~~. This is critical to getting sufficient [[Gain Before Feedback|gain before feedback]] in live performance applications~~.

Your setup should always begin with good gain staging.

Take two minutes to watch this video by clicking on the picture below.

* If you are using an {{Classic}} or {{Model I}} follow the instructions exactly as shown in the video.

* If you are using the {{T1}}, the principles are the same as shown on the video: simply substitute the [[T1_ToneMatch%C2%AE_Audio_Engine#Set_Input_Trim|trim]] on the {{T1r}} for the trim on the Classic or Model I. {{T1 icon}}

=== Close Microphone Technique ===

'''Get close to the microphone''' when you want to be loud. No other technique has a big an impact on feedback. Each halving of distance is approximately another 6 dB of [[Gain Before Feedback|gain before feedback]]. This relationship in physics is known as the [[Inverse Square Law]]. This means that the difference between working a microphone at 2 inches, and 1/4 inch is 18 dB, which is more than twice as loud. While good mic technique often involves "working" the microphone at different distances, singers must be mindful of the fact that small changes in distance from the mouth result in very dramatic changes in sound level.

In the feedback diagram at the top, getting close to the microphone means getting more <font color="blue">sound from voice</font> which translates to more gain without feedback.

[[Image:Ferrin_eat_mic.jpg|Charlie Ferrin at Bose: Nov. 9, 2007]]

=== Directional Microphones ===

Use a directional microphone. [[Microphone Directionality#Supercardioid_/_Hypercardioid|Hypercardioid]] is better than [[Microphone Directionality#Cardioid|cardioid]], which is better than [[Microphone Directionality#Omnidirectional Microphone|omnidirectional]]. All sound waves impinging on the microphone from a direction other than the intended signal is "noise" and will lower the threshold of feedback.

In the feedback diagram at the top, using a directional microphone, tilted up, means getting less <font color="red">sound from speaker</font> which translates to more gain without feedback.

=== Effects ===

@@ Line 12: / Line 12: @@
 Feedback occurs when the sound from the loudspeaker (or loudspeakers if a microphone is connected to more than one) is louder at the microphone than the sound of the voice.
-This fundamental fact is shown in the figure below.
+This fundamental fact is shown in the figure below. Note that in the diagram an L1 system is shown but the same fundamental fact is true for ANY loudspeaker.
 [[Image:Feedback fig 1.jpg|800px|Microphone Feedback]]
+If you understand this diagram, it is relatively easy to understand how changes in an amplification system and room can contribute to either increasing or decreasing the likelihood of feedback.
 == Techniques For Reducing Feedback ==
 === Gain Staging ===
-If you are having issues with feedback, check your gain staging.  This is critical to getting sufficient [[Gain Before Feedback|gain before feedback]] in live performance applications.
+Your setup should always begin with good gain staging.
 Take two minutes to watch this video by clicking on the picture below.
 {{Get Plugged In Microphone}}
 * If you are using an {{Classic}} or {{Model I}} follow the instructions exactly as shown in the video.
 * If you are using the {{T1}}, the principles are the same as shown on the video: simply substitute the [[T1_ToneMatch%C2%AE_Audio_Engine#Set_Input_Trim|trim]] on the {{T1r}} for the trim on the Classic or Model I. {{T1 icon}}
 === Close Microphone Technique ===
 '''Get close to the microphone''' when you want to be loud. No other technique has a big an impact on feedback. Each halving of distance is approximately another 6 dB of [[Gain Before Feedback|gain before feedback]]. This relationship in physics is known as the [[Inverse Square Law]]. This means that the difference between working a microphone at 2 inches, and 1/4 inch is 18 dB, which is more than twice as loud. While good mic technique often involves "working" the microphone at different distances, singers must be mindful of the fact that small changes in distance from the mouth result in very dramatic changes in sound level.
+In the feedback diagram at the top, getting close to the microphone means getting more <font color="blue">sound from voice</font> which translates to more gain without feedback.
 [[Image:Ferrin_eat_mic.jpg|Charlie Ferrin at Bose: Nov. 9, 2007]]
 === Directional Microphones ===
 Use a directional microphone. [[Microphone Directionality#Supercardioid_/_Hypercardioid|Hypercardioid]] is better than [[Microphone Directionality#Cardioid|cardioid]], which is better than [[Microphone Directionality#Omnidirectional Microphone|omnidirectional]]. All sound waves impinging on the microphone from a direction other than the intended signal is "noise" and will lower the threshold of feedback.
+In the feedback diagram at the top, using a directional microphone, tilted up, means getting less <font color="red">sound from speaker</font> which translates to more gain without feedback.
 === Effects ===