OMNI vs CARDIOID: WHICH LAVALIER IS RIGHT FOR YOU
Wireless microphones have become commonplace in today’s houses of worship, and wireless lavalier systems are unquestionably the most popular for the presentation of the spoken word. These inconspicuous little microphones consistently accomplish the task of concealment quite well, however there are variables that influence how successfully they perform with a sound reinforcement system. Lavaliers are available in a variety of polar patterns, and understanding how these pickup characteristics incorporate into the environmental elements of a room will help guide you in choosing the right one for your application.
Polar patterns can be thought of as the field of vision of a microphone where there’s a combination of both width of panorama and depth of field. Examining the polar pattern graph of a microphone might be perplexing without a point of reference. Typically, a polar plot indicates the relative sensitivity of the microphone diaphragm to sounds arriving from an infinite field of 360. The 0 point represents the measured source sound arriving at, and perpendicular to the diaphragm. Conversely, the 180 point represents the measurement of sounds arriving from the opposite direction. It might help to think in terms of a round face clock where 0 is at 12 o’clock and 180 is at 6 o’clock.
An omnidirectional pattern microphone has a fairly unlimited field of vision. Their width of panorama is spherical allowing them equal sensitivity to sounds arriving from any direction, and their depth of field is extended due to their liberal sensitivity to sound sources. Delivering a natural openness due to the perceived low ratio of close to distant sounds, omnidirectional lavaliers have a reputation of sounding true-to-life even when attached to clothing very near the mouth.
A cardioid pattern microphone has a limited field of vision. Their width of panorama is generous at the front of the diaphragm, limited at the sides, non-existent at the rear, and their depth of field is somewhat shallow and is dependent on the angular orientation of the sound source to the diaphragm. Delivering an up-close sound due to the perceived high ratio of close to distant sounds, cardioid lavaliers have a reputation of sounding dry due to the lack of ambience. Due to the nature of the pattern, there’s a low frequency boost when the microphone is positioned very close to the sound source. This proximity effect is an attractive characteristic of a handheld vocal microphone but it can be problematic with lavaliers.
The next element to consider when evaluating a wireless lavalier in presentation-style applications is the nature of the performance. Wireless lavaliers afford the speaker the freedom to roam about the venue and to perform with all of the animation required to get the message across. Consider the amount of gestures, head turns and overall body movements a pastor makes during a sermon, and how the different polar pattern characteristics will react to these changes in sound pressure. Lavaliers are generally clipped to the tie or lapel at a distance of 5 – 7 inches below the chin and aimed upward towards the mouth. The omnidirectional lavalier will respond favorably to head turns as its field of vision is quite broad, and changes in vocal amplitude are relatively unnoticeable. Conversely, head turns will be quite noticeable with cardioid lavaliers. As the position of the mouth enters and leaves the microphone’s zone of highest sensitivity, the changes in vocal amplitude and tone will be pronounced. This can be distracting to the listener, especially if the presentation is being recorded either on audio or video tape. The general rule of thumb is that if a performance is for broadcast, video or audio recording, omnidirectional lavaliers will render the best results.
SOUND SYSTEM CONSIDERATIONS
Room geometry, cubic area and loudspeaker positions are unique in any venue, and their relationship to any microphone plays a great role in overall system performance. Sound reinforcement systems are designed to lend amplification to sound sources and provide even distribution to the listeners. The amount of sound reinforcement required for even distribution is dependent on two factors; the cubic area of the room, and the positioning of the loudspeakers. Lower cubic areas require less gain, and larger cubic areas require higher gain. The objective of any sound system is to amplify microphone signals to adequate levels without feedback.
Feedback is caused when the input to a microphone is heavily weighted with the output from a loudspeaker that is amplifying that microphone’s signal. The number-one cause of feedback is a speaker placement that is directed towards the microphone diaphragm. The second most common cause is poor microphone choice or placement that requires abnormally high gain for the desired sound level. Suffice it to say that any microphone/sound system combination will feedback if the gain of the microphone is raised too high. Positioning the microphone closer to the sound source and away from the radiating pattern of a loudspeaker generally improves gain before feedback problems.
Choosing the right lavalier involves understanding the aforementioned sound reinforcement criteria, as well as the gain before feedback characteristics of the different polar patterns. Because of their limited field of vision, cardioid lavaliers have a high gain feedback characteristic and are generally chosen when high levels of sound reinforcement in a large space are required or when the speaker placement is problematic in medium and smaller spaces with high sound level requirements. Conversely, due to their unlimited field of vision, omnidirectional lavaliers have a lower gain before feedback characteristic and are generally chosen when lower levels of sound reinforcement are required, or when the performance is being recorded for broadcast or reproduction.
POSITIONING LAVALIERS FOR BEST PERFORMANCE
As with any microphone, placing a lavalier closer to the sound source increases its gain, and in turn lessens the amount of gain required through amplification.
Because of their polar characteristics, cardioid lavaliers have what some users might call a sweet spot. That is, a distance from the sound source that renders the most uniform pickup and tonal performance. Remembering that cardioids have proximity effect, and this can be an advantage if positioned properly, there is a fine line between too close, just right, and too far. There is a considerable increase in low frequency response when the cardioid lavalier is placed within a few inches of the throat, and this diminished as it is moved farther away. Having the lavalier this close poses some field of vision issues because at that distance, the pickup pattern is quite narrow, and the tonal and amplitude shifts caused by head turns are quite pronounced. It is never recommended to place any lavalier more than 5 – 7 inches below the chin. This distance usually allows an adequate margin for the directional nature of cardioids, while not being too far away causing the sound to be thin. Although the perceived pattern widens the farther below the chin a cardioid is placed, the tone will thin out and the microphone will require more gain, which in turn increases the chances of feedback.
Omnidirectionals are a bit easier to place for best performance. There is no proximity effect to contend with, so in high gain situations placing it near the sound source poses no tonal complications and the insensitivity to head turns is not diminished. Obviously, placing more distance between the sound source and the omni widens the perceived spaciousness of the sound, but following the 5 – 7 inch rule applies as well.
Choosing the right wireless lavalier for your needs involves understanding the nature of polar patterns, loudspeaker system placement, the cubic volume of a room and the required level of gain to fill it. Omnidirectional lavaliers sound natural, are less sensitive to head turns and are the best choice if the signal will be recorded or broadcast. They have a lower gain before feedback characteristic because of their wide field of vision, however placing an omni closer to the sound source can improve the gain before feedback problem in high gain situations. Cardioid lavaliers have a narrow field of vision and a high gain before feedback characteristic. Cardioids are sensitive to head turns, and the closer to the sound source, the more pronounced this selectivity becomes. Cardioid lavaliers are generally the chosen tool in high volume situations where gain before feedback is a problem and properly-positioned omnidirectional lavaliers feed back.