The idea of the 'human mic' was one born out of a practical necessity, the police prevented the first OWS protests from having electronic amplification so to compensate the mechanism of the HM emerged, where the person currently with the 'mic' would say a short phrase of their statement, which those around them would shout, before the speaker moved onto the next phase and so on - there's a good example here:
In addition to solving the initial amplification problem Mark Lance and Sydney Levy at theNew APPS blog point out that this has some quite interesting effects on the nature of discourse through the HMs:
What is most interesting about the HM is the way that it shapes the time and space of a discourse. Of course the most obvious feature is that it slows things down. Everything is said twice. This is a mixed blessing, no doubt, stretching out already long consensus meetings. But at the same time, we must remember that we are dealing with a huge, diverse crowd of people, many of whom are completely new to the very idea of directly democratic decision-making, and none of whom have much experience with this group. So slowing things down and repeating everything that is said before it is possible to respond also functions to draw people in and lends an air of seriousness to the comments of others.
Similarly, the practice eliminates side-conversations. If you participate in the HM, you have to listen so that you can repeat. You can't be chatting snarkily with your neighbor, or even focusing on a text. Neither can folks talk over one another as they could if, say, everyone was mic-ed electronically. The HM can only repeat one thing at a time. So there is a built in technological imperative of waiting one's turn.
HM as a practice seems to function to "decenter" conversation in large groups. You don't have to be on the stage, at the mic, or in front to be a part of the conversation of the whole. And even in the most inclusive groups, the process of coming up to the front will be disproportionate intimidating to some and, in the case of some disabilities, physically difficult.
HMs on the face of it seems to address the classic problem that people aren't really listening if they're working out what they're going to say next by keeping the audience tasked on repeating the current message. While someone with an electronic mic is addressing a passive (and non-tasked) audience, they might disengage and begin side-conversations if they find the speaker uninteresting, or challenge the speaker for control of the sound-space by shouting or booing. A tasked crowd is less able to do these things[1. Another possible factor is that HMs are imperfect methods of amplification and so can't tolerate as much other noise, and so people are obliged to be quieter to let it work at all]. This raises a question: as the form of the human mic requires people to take part in other people's words, what do people do when they disagree with the message? Dan Kervick gives a possible answer:
At least at the GA I attended, it seemed to be understood that you would try to repeat even those words you disagreed with. People were repeating words even as they were giving down twinkles of disapproval. However, even while repeating the words, you might not say them with much enthusiasm. Sometimes people would repeat the words fully, but in a "yada, yada, yada ..." tone of voice. The force and enthusiasm element of the repeated words seems itself to be part of the consensus-building aspect of the assembly discourse. The speaker's rhetorical direction is influenced in some directions and away from others by the audible and continuous rising and falling of the assembly's support, and by the twinkles. [...] one guy got very vulgar and self-indulgent, and the repetition flagged in energy and took on a tone of "C'mon man, stop being an ass."
This might not be universal but in this case rather than cancelling or drowning out the original speaker, people who are part of the microphone instead modulated the original voice to express their opinion- the message and dissent to the message become one and the same thing. This means it isn't content-neutral as a medium, but also that people calling it "the people's mic" aren't being entirely silly, as there's an extent to which the crowd can imbue a statement with their own feelings about that statement (although it clearly can't apply past the people taking part).
In addition to the decentering point made above somein the comments at APPS make the point that this is a form of amplification that's slower and so friendlier to those who might not otherwise want to step up and speak, but at Occupy Patriarchy Lucinda Marshall argues that the human mic isn't necessarily that empowering:
Listening to people yell, “Mic Check!” at Occupy locations throughout the country, it is hard not to observe that those with the loudest voices are the ones who really get heard with this system, and those voices usually are male baritones. Talking to women here in Washington and also reading reports from elsewhere, it is clear that many women find this system of having to yell at the top of your lungs to be one that is an uncomfortable way to communicate and participate. Some women report being harassed when they speak, and even of mics being grabbed from them.
This doesn't seem to be a universal experience but it's a problem that should qualify descriptions of HM's democratic virtue - for all its merits it is as heart a means of amplification and that leaves it vulnerable to existing disparities in voice. Still, it's a method that has potential to enhance the deliberativeness of public conversation and open up and democratize (to some extent) the sound-space, and so is far more than the simple yelling it might appear to be at first.
Given this understanding of what the HMs are supposed to do, it becomes clear that some groups aren't really using them correctly. Case in point, a group of protesters at Cambridge University used what they claimed was a "people's mic" to shut-down a David Willetts event, but if it was it's a much poorer conception of the mic than the one emerging as their aim wasn't to conduct discussion but to close it down, not opening up the sound-space but filling with white noise to make it unusable. As the form of the human mic becomes better established it'll be interesting to see if it keeps its original deliberative spirit.