This page explains the cause of the feedback and how to resolve it.
Mechanism of feedback generation
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Feedback is caused by acoustic loop in which the sound output from the speaker (SP) is input again to the microphone (MIC), where it is amplified again and output from the SP. In other words, feedback may occur if the MIC and SP are in the same location. The problem with feedback is that it produces a very loud sound that can destroy the ears of any equipment or audience on the loop.
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Note that feedback is also called "howling" in some regions. Also, the onomatopoeic expression is "keen" , "peen", "hyeen" or "boh",...
but it differs depending on frequency of occurrence and also depending on the language culture. There may be some cultures that do not use onomatopoeic expressions very often. Also, various noises are often called "feedback", but if the MIC and the SP connected to it are not in the same location, the noise is not feedback.
but it differs depending on frequency of occurrence and also depending on the language culture. There may be some cultures that do not use onomatopoeic expressions very often. Also, various noises are often called "feedback", but if the MIC and the SP connected to it are not in the same location, the noise is not feedback.
So, does feedback always occur if the MIC and SP are in the same location? This is not the case. A well-designed system will output enough sound from the SP, but will not cause feedback.
Feedback occurs when the sound coming back to the MIC is too loud.
So why is it too loud?
There are several cases for this.
Many of these are caused by poor system design. If this problem has already occurred in the field, it will be difficult to resolve it. This means that design is important.
So why is it too loud?
There are several cases for this.
Many of these are caused by poor system design. If this problem has already occurred in the field, it will be difficult to resolve it. This means that design is important.
As mentioned above, the cause of feedback gain is excessive input sound to the MIC, but the figure below breaks down the reasons why this occurs.
The system designer cannot change the structure of the room or the user's operations. However, there are many points that system designers can solve, such as the number of SPs and their location.
Solution in Design
Some causes and design solutions are discussed below.
Cause: Wide Directivity
When MIC has high sensitivity and wide directivity, and SP has wide directivity
It's easy to think of it this way: SP has wide directivity, so it spreads sound close to the MIC, and the MIC collects sound from a wide range.
Solution
Move the MIC away from the SP coverage area.
If possible, choose a MIC with low sensitivity, such as a handheld dynamic MIC.
See this page for information on MIC sensitivity.
When MIC has high sensitivity and wide directivity, and SP has wide directivity
It's easy to think of it this way: SP has wide directivity, so it spreads sound close to the MIC, and the MIC collects sound from a wide range.
Solution
Move the MIC away from the SP coverage area.
If possible, choose a MIC with low sensitivity, such as a handheld dynamic MIC.
See this page for information on MIC sensitivity.
Cause: Strong reverberation (long reverberation time)
If the reverberation is strong, a lot of sound will return to the MIC.
Solution
Please see this page about reverberation.
If the reverberation is strong, a lot of sound will return to the MIC.
Solution
Please see this page about reverberation.
Cause: Sound pressure distribution is not uniform
This secondarily causes feedback.
The fact that the sound pressure distribution is not uniform means that there are places where the volume is sufficient and places where it is not loud enough. If you turn up the volume on your system for areas where the volume is insufficient, the volume will become too loud in areas where the sound was sufficient. Then, the volume that returns from the SP to the MIC increases, causing feedback.
Solution
Please see this page about volume insufficient.
This secondarily causes feedback.
The fact that the sound pressure distribution is not uniform means that there are places where the volume is sufficient and places where it is not loud enough. If you turn up the volume on your system for areas where the volume is insufficient, the volume will become too loud in areas where the sound was sufficient. Then, the volume that returns from the SP to the MIC increases, causing feedback.
Solution
Please see this page about volume insufficient.
Cause: Frequency characteristics are not flat
Microphones and speakers often do not have a flat frequency response. The room itself may also raise the level of certain frequencies excessively.
In these cases, feedback is likely to occur at that frequency, as shown in the figure below. That's because each time it goes through a loop, that frequency is boosted too much.
Microphones and speakers often do not have a flat frequency response. The room itself may also raise the level of certain frequencies excessively.
In these cases, feedback is likely to occur at that frequency, as shown in the figure below. That's because each time it goes through a loop, that frequency is boosted too much.
This diagram attempts to explain the mechanism by which feedback occurs. If a system or room has a light blue frequency response, the volume will increase each time it passes through a loop, so the frequency response will increase in level as shown by the green dashed line each time it passes through a loop. Then, certain frequencies, which are originally higher in level than the surroundings, reach a level where feedback occurs.
*Of course, since it is the sound that actually causes feedback, the occurrence of feedback also depends on the frequency content of the input sound.
*Of course, since it is the sound that actually causes feedback, the occurrence of feedback also depends on the frequency content of the input sound.
Solution
Choose a device with an equalizer. By setting the equalizer to a frequency characteristic that is the opposite of the system's characteristics and the room's characteristics, an overall flat characteristic is achieved.
Choose a device with an equalizer. By setting the equalizer to a frequency characteristic that is the opposite of the system's characteristics and the room's characteristics, an overall flat characteristic is achieved.
In summary, the design requires the following:
- Preparation of equipment that creates flat frequency characteristics
- Sufficient number and location of SPs for sufficient and uniform sound pressure distribution
- Proper SP installation to ensure clarity and avoid reverberation as much as possible
>> For proper SP installation, please click on the image below to visit these pages.
CeilingSP location
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Sound SP location
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A feedback suppressor is also useful for removing feedback, but it is a device that removes feedback that has occurred and does not prevent it from occurring. Unless the above requirements are met, feedback is likely to occur.
On-site solution
If feedback has already occurred in the field, it is difficult to eliminate the root cause. But there are some urgent ways to avoid it.
- First, turn off the MIC.
If the system has a lot of MICs, turn off the AMP. Feedback immediately disappears because the loop is broken. - Reduce volume
Increase the volume little by little and find the highest volume without causing feedback. Please confirm that this volume is really insufficient for operation. - Move MIC away from SP
Change the MIC position to reduce the volume that goes into the MIC from the SP. - Check the orientation of SP
Make sure that the SP is not facing towards the MIC or towards the ceiling or wall above which will cause reverberation. Pointing the SP at the audience improves the clarity of the voice emitted, making it easier for the audience to feel that the volume is sufficient, even at low volumes. The lower the volume, the less likely feedback will occur.
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The following assumes that the equipment has been installed in advance.
- Suppressing frequencies that cause feedback with an equalizer
- Turn on feedback suppressor
Also, this requires a request from the user,
- Avoid holding the MIC head
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When a MIC's head is gripped, it loses its directivity and picks up a wide range of sounds. In other words, it is more likely to trigger feedback.
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Summary,
First, to protect your equipment and audience, turn off the MIC or amplifier to stop feedback.
Then turn down the volume.
There are few effective measures that can be taken in the field. After all, design is important.
