We hate it because it sounds bad, causes feedback, and makes our job harder.
The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.
I recently posted something on my personal Facebook feed. That something was this:
A number of people found it funny.
When you really get down to it, though. It’s an “in joke.” The folks who get it have lived through a cupped-mic situation or two, and probably know why it’s a bad idea. For other folks, especially those who have been surprised by being chewed on by an irate sound-craftsperson, the whole thing might not make sense. Why would an audio human get so irritated about how a performer holds a mic? Why is it such a big deal? Why are jokes about mics being cupped such a perennial feature of live-sound forums?
The short answer is that cupped mics sound awful and tend to be feedback monsters. The long answer has to do with why.
The Physics Of How Looking Cool Sounds Bad
Microphones are curious creatures. It might sound counter-intuitive, but creating an omnidirectional mic (a mic that has essentially equal sensitivity at all angles around the element) is actually quite simple. Seal the element in a container that’s closed at the back and sides, and…there you go. Your mic is omni.
Making a directional mic is rather more involved. Directional mics require that the element NOT be housed in a box that’s sealed at the back and sides. Sound actually has to be able to arrive at the rear of the diaphragm, and it has to arrive at such a time that the combination of front and rear pressures causes cancellation. Getting this all to work, and work in a way that sounds decent, is a bear of a problem. It’s such a bear of a problem that you can’t even count on a microphone patent to tell you how it’s done. The details are kept secret – at least, if you’re asking a company like Shure.
But, anyway, the point is that a directional mic is directional because sound can reach the rear of the element. Close off the porting which allows this to happen, and the mic suddenly becomes much more omnidirectional than it was just moments before. Wrapping a hand around the head of the mic is a very efficient way of preventing certain sounds from reaching the back of the capsule, and thus, it’s a very quick way to cause a number of problems.
Fighting feedback meaningfully requires that mics be as directional as is practical. The more “screamin’ loud” the monitors and FOH have to get, the more important that directionality becomes. When setting up the show, an audio human inevitably finds a workable equilibrium ratio of gain to feedback. A highly directional mic has much lower gain in the non-sensitive directions than in the sensitive ones. This allows the sound tech to apply more gain in downstream stages (mic pres, monitor sends, FOH faders), as long as those devices result in output that the mic experiences in the “lower-gain detection arc.” At some point, a solution is arrived at – but that solution’s validity requires the gain of all devices to remain the same.
When a mic is cupped such that it becomes more omnidirectional, the established equilibrium is upset. The existing solution is invalidated, because the effective gain of the microphone itself suddenly increases. For instance, a microphone that had a gain of -10 dB at 2 kHz at 180 degrees (degrees from the mic’s front) might now have a gain of -3 dB at 2 kHz at 180 degrees. Although what I’m talking about is frequency specific, the overall result really is not fundamentally different from me reaching up to the mic-pre and adding 7 dB of gain.
Especially for a high-gain show, where the established equilibrium is already hovering close to disaster, cupping the mic will probably push us off the cliff.
Intentionally omnidirectional mics can be made to sound very natural and uncolored. They don’t rely on resonance tricks to work, so very smooth and extended response is entirely achievable with due care.
Problems arise, however, when a mic becomes unintentionally omnidirectional. Directional mics are carefully tuned – intentionally “colored” – so that the resulting output is pleasant and useful for certain applications. The coloration can even be engineered so that the response is quite flat…as long as the mic element receives sound from the rear in the intended way. Much like the feedback problem I described earlier, the whole thing is a carefully crafted solution that requires the system parameters to remain in their predicted state.
A cupped microphone has its intended tuning disrupted. The mic system’s own resonant solution (which is now invalid), coupled with the resonant chamber formed by the hand around the mic, results in output which is band-limited and “peaky.” Low-frequency information tends to get lost, and the midrange can develop severe “honk” or “quack,” depending on how things shake out. At the high volumes associated with live shows, these narrow peaks of frequencies can range from merely annoying to downright painful. Vocal intelligibility can be wrecked like a ship that’s been dashed on the rocky shores of Maine.
An added bit of irony is that plenty of folks who cup microphones want a rich, powerful vocal sound…and what they end up with is something that resembles the tone of a dollar store clock-radio.
Reduced Output In Severe Cases
The worst-case scenario is when a mic is held so that the ports are obstructed, and the frontside path is ALSO obstructed. This occurs when the person using the mic wraps their whole hand around the grill, and then puts their thumb in the way of their mouth. Along with everything described above, the intervening thumb absorbs enough high-frequency content to make the mic noticeably quieter at frequencies helpful for intelligibility.
So the mic sounds bad, the singer can’t hear it, the whole mess is ready to feedback, the singer wants more monitor, and FOH needs more level.
I think you can see why sound techs get so riled by mic-cuppers. Holding a mic that way is fine if the whole performance is a pantomime. In other situations, though, it’s just bad.