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Proper placement for body-worn microphones Eddy B Brixen, audio specialist at DPA Microphones, discusses FOR THOSE LISTENING TO AN amplification or a recording of a person speaking, the ability to understand what is being said – or sung – depends on several factors. This includes the quality of the recording, including the microphones, the playback system, the acoustics of the room and background noise, among other things. When the voice is amplified or recorded and then later played back, there is a risk that some essential information in the audio is lost along the way. With microphones,
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it’s not just the “what type” that needs to be considered, but also the placement of the equipment.
The voice is most commonly picked up from in front of the person speaking. In “normal” conversation, this would require a placement distance of no more than 1m from the speaker. The sound of the voice varies a lot depending on the position of the listener or the microphone used to pick up the sound of the voice. Moving below or behind the speaker changes the sound and compromises intelligibility. The same is true of microphones used to amplify the spoken word. While it should be clear to everyone that positioning behind the person talking is not ideal, even positions below the mouth – such as on the chest – will introduce some intelligibility challenges. This is because the frequency range between 2–4kHz – where the important consonants are predominant – is suppressed in that position on the chest. As a result, the sound is often perceived as if it was generated from the chest, but that is actually not the case. This phenomenon, known
as “chest sound”, is due to body absorption and head shape. The sound is generated from the vocal cords and is louder than the sound generated by the (small) vibrations in the chest. With so many factors to consider with increasing speech intelligibility, proper microphone positioning is an easy one to address without the need for purchasing new equipment. Of course, mic placement will also depend on the benefits and consequences of each different miniature, body-worn microphone. To evaluate ideal positioning, we first began by placing a single reference microphone 1m in front of the test subject. This enabled us to collect a reference source: the normal vocal and tonal aspects of their voice. We then positioned several identical miniature omnidirectional pressure microphones around the person speaking and analysed the differences between those recordings and the reference microphone recordings. We did this with the mic positioned on the forehead, over the ear, on the neck and on the chest, etc.
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