KnowHOW: Proper placement for body-worn microphones
KnowHOW: 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, 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.
This experiment was caried out in an anechoic chamber with no reverb or reflections from the surrounding, to focus on the placement differences. The tonal difference between the reference mic (1m away) and the microphone on the body was recorded.
Used most commonly in theatre applications, forehead placement is generally not found in houses of worships. However, there is something to be said for using this style. In our experiment, we found that the recording with an omnidirectional microphone from the forehead placement was similar to the reference recording. This means that the sonic character of the voice captured with a forehead microphone is almost identical to the voice that we normally hear from the speaker. There was a small peak around 800Hz and a small valley right after around 1.5kHz but, overall, there was a similar frequency response and the consonants were preserved. For churches that have omnidirectional lavalier microphones, it might be worthwhile to use them in a hairline application, especially for vocal performances.
While not a common mic position, we also compared over-the-ear omnidirectional microphones during our experiment. We found that this placement, which positions the microphone behind the mouth, degrades the higher frequencies of the person speaking. We still saw the peak around 800Hz but the range from 1kHz and up is lost, which means most of the important consonants are lost. Generally speaking, it might be best to avoid this placement in HOW applications. If over-the-ear is the speaker’s preferred way to wear a microphone, it would be worthwhile to invest in a directional/cardioid solution, which will provide tonal improvements to the voice.
Headset microphones are perhaps the most popular solution for HOWs these days, and for good reason. Placed at the corner of a person’s smile, headset microphones are excellent for decluttering a stage and encouraging mobility of the pastor. Plus, the intelligibility of omnidirectional headset mics is an improvement to the over-the-ear position. In our experiment, we found better preservation of the 1–2kHz range, which allows consonants to sound more natural and improves speech intelligibility. With most headset microphones, placement still ends up a bit behind the sound source and therefore loses some of the extremely high frequencies. It is not as good as the forehead position.
To avoid this and still ensure the singer or speaker’s voice sounds great, opt instead for a directional headset mic. Compared to an omnidirectional mic, the cardioid design of a directional mic will pick up only half the amount of the background sound. Furthermore, the low-frequency sounds from loudspeakers, drums or organ will be reduced to 1⁄10 or less. For venues that prefer using an omnidirectional microphone – perhaps to help reduce the need to mic other areas of the stage – we recommend selecting a design with an adjustable boom height and length.
Chest and neck
Omnidirectional mics placed in the neckline area, such as on a tie clip or along a shirt collar, are the most challenging for speech intelligibility because the microphone is placed below and behind the sound source. This means that all the higher frequencies are almost gone. The worst position is below the chin, on the neck, because it is the furthest behind the mouth. The biggest challenge for this omnidirectional microphone is that the range between 2–4kHz is practically removed from the sound spectrum, which results in poor speech intelligibility. In a similar fashion to the ear and headset mics, selecting a directional or cardioid lavalier would be better suited for these applications. As mentioned above, churches that already have omnidirectional lavaliers could choose to affix the microphone to the hairline to improve intelligibility.
Another factor to consider when mic’ing a pastor is the pattern of their speech. When we raise our voices, we add energy and level to the entire word. While we are not able to add much level or energy to the consonants, we can easily add energy to the vowels. By raising our voices to increase intelligibility, the level differences between the weaker consonants and the louder vowels increases and eventually ruins speech intelligibility. The consonants become masked or drowned behind the vowels. When we whisper, the opposite happens the vowels drown. To maximise intelligibility, keep your voice at a consistent speaking level whenever possible.
Microphone type and position are the most important factors to consider in any spoken word setting. With most applications, the microphone will be placed below or behind the mouth. In these cases, you must compensate for the placement with an EQ, otherwise speech intelligibility will be compromised. No matter the microphone selected or currently in place, the best solution for capturing or amplifying a voice in as natural a way as possible is to use a natural sounding microphone. Additionally, one positioned on the forehead would need the least amount of live EQ or postproduction work.
This feature appears in the September-October edition of Worship AVL.