Howdy SEA Fans, its tuesday and we have come up with another article related to sound engineering and it seems to be an another interesting piece of information which you can use.
For the past couple of week we have been talking about location recording and mobile audio recording and this week we are back with a core topic related to the field of Audio Recording.
It is “Acoustic Feedback“.
In the general perception which belong to the sound reinforcement technique, in many films they are placed at the beginning of a “live music scene” and that will help you to better understand what is acoustic feedback in the real world.
Fortunately, there are some ways to effectively avoid feedback under normal conditions.
In this article we are sharing information on
What is acoustic feedback and how can you prevent it?
And how does it arise at all on the stage and in the pro-space?
Here you will find all the tested means to avoid audio feedback.
As mentioned above first off all let us start with what is acoustic feedback.
Acoustic feedback is generated by a closed circuit consisting of microphone, amplification and playback via a loudspeaker whose sound is then again captured by the same microphone. Feedback from a certain volume inevitably occurs as long as microphones, loudspeakers and sound meet. Inadvertently, it is quite annoying – or even create a real danger to the hearing of artists or audience.
How does it sound?
The acoustic feedback (feedback) leads to an effect, which is expressed in an unpleasant, penetrating pipe. It is generated when the signal recorded by a microphone is amplified and reproduced in such a way that the sound is recorded again by the microphone, then is reproduced again, and so on.
In practice, this usually happens on the stage in the interplay of … Microphone – Sound conversion into an electrical signal Mixing console – Amplification of the signal Monitor loudspeaker – Back conversion of the signal in sound waves.
This creates a closed circuit in which the signal by the acoustic feedback is always more. The result is an intense, very unpleasant whistle, which can occur at different pitches, especially in live sound reinforcement. The audio technology involved becomes almost an oscillator.
Avoid acoustic feedback – What to do?
For feedback, you can take the following things to heart.
Combine several measures to prevent acoustic feedback.
Provided below are some of the key points you will find detailed explanations of each topic below
Keep the distance between the sound source and the mic as low as possible.
Microphone with directional characteristic use kidney or super- / hyperniere.
Use another microphone with directivity.
Align the stage monitor with the microphone.
Graphic EQ for attenuating.
Use feedback suppressors.
Guitar & Bass directly feed.
In-ear monitoring instead of stage speakers.
Increase the separation between PA speaker and microphone.
Thick curtain or similar. As a silencer on the back wall.
Being discussed in detail about the methods to avoid acoustic feedback.
Keep the distance between the sound source and the microphone as low as possible
Even if the voice is not very strong: Say, sing or play as close as possible to the microphone capsule. Then the FOH technician does not have to preamp the signal at the mixer so strongly, which reduces the feedback probability.
Use a microphone with a kidney characteristic
The sensitivity of microphones with a directional effect (short: directional microphones) varies according to the angle of the incident sound. This can be used in conjunction with the room acoustics and the orientation of the monitor boxes. If you use a microphone with spherical characteristics, the feedback risk is greatest. Here, the sound from all directions around the microphone capsule is recorded uniformly.
Why use another microphone?
Two microphones of the same type – e.g. From the Dynamic Microphone Division with a renaissance characteristic – can be differently susceptible to feedback. On average, higher-quality microphones (from ~ 100 euros) are better equipped. It is also recommended to rely on established brands such as Shure, EV, AKG etc.
How can the stage monitor be aligned with the microphone?
Align the stage monitor exactly so that it is aimed at the most sensitive point in the directional characteristics of the microphone in the tripod. Or better: Wink the micro accordingly – with the joint of the clip on the microphone stand is simply possible.
For a microphone with a renaissance characteristic, the handle must be positioned exactly perpendicular to the surface of the stage monitor. In a microphone with super- or hyperniere, but precisely at this angle still a certain sensitivity is present. Therefore, you have to align the micro more or less horizontally to the stage floor, as long as the stage monitor radiates the sound in a classic 45-degree angle to you.
What to do against certain feedback frequencies?
Generally, when an equalizer is turned up, the feedback probability increases as the volume is increased in a certain frequency range. If microphones and / or loudspeakers with clearly accentuated frequency ranges are used (especially in the upper mids and highs), the danger for acoustic feedback also increases. In this case, an EQ could be useful, and it can also be used to attenuate over-emphasized (feedback) frequencies. However, a separate graphical EQ is usually required, since it offers the necessary number of adjustable frequency bands (typically 31 bands) for targeted interventions.
Using a feedback controller
This audio device is designed to automatically prevent acoustic feedback. It is switched between the output of the mixing console and the PA system. The setup is as follows: With the Soundcheck, the microphone pre-amplification is fully turned on until feedback comes. At this moment, the device measures the feedback frequency and creates a corresponding filter to attenuate the signal at exactly that frequency. The filters are so narrow that they have little influence on the character of the music.
Especially in the amateur sector or the semiprofessional area, feedback controllers are often used to suppress acoustic feedback. Particularly with changing vocalists during a performance and / or when moving the microphone on stage, they can provide useful services. They are also called “feedback killer”, “feedback eliminator” or “feedback destroyer”.
Guitar & Bass directly feed
(Via DI box or Hi-Z input) an additional microphone in the Rig is a potentiometer for feedback, why not give up on one or two microphones? At least in the E-bass should be the least problem – here the DI-acceptance of the signal is a musically accepted, established alternative to the microphone of a bassbox.
In-Ear Monitoring Instead of Using Loudspeakers
In-ear headphones have become a real alternative to monitor speakers (“wedges”). They eliminate one of the main sources for acoustic feedback on the stage and in the pro space. This presupposes a certain open-mindedness – the direct, near sound of earphones (in conjunction with a certain foreclosure from the room) can be very habituated.
Increase the distance between PA speakers and microphone
The PA speakers should be as far as possible before the microphone. In other words, as close to the audience as possible. In addition, they should be rotated in such a way that the greatest possible part of the radiation angle of the speakers is aimed precisely at the listeners. This reduces the sound reflections of walls and ceiling, which are thrown back to the microphone.
Use a thick curtain or similar.
As a provisional silencer in the back A more or less smooth, solid wall just behind the band reflects the sound particularly strongly into the room. And thus also in the direction of the microphone. There is a big, heavier and thick curtain.
For safety, a basic tip, which unfortunately is not often noticed: before inserting a microphone or instrument always ensure that the corresponding channel is muted in the mixing console. Afterwards, first check how the channel’s gain looks like and to which monitors the channel is sent before you “unlock” it …
Hope the information provide above has been useful for you and appreciate to express your valuable thoughts / updates about the topic in the comment box below.
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