You Don’t Have to See it To Believe It

When assessing how best to outfit a conference room with technology, some decisions are fairly straightforward. A 90” display is larger than a 70” display, and thus allows viewers further away from the TV to see content. A 6,000 lumens projector is brighter than a 3,000 lumens projector, meaning the lights may not need to be turned off in order to see what’s on the screen. These concepts make sense, regardless of whether or not you have a background in AV.

Not every decision, however, is quite as intuitive. Boardrooms, meeting rooms, and huddle rooms can feature many different styles of microphones to capture in-room audio. Mics can be wired or wireless; table-mounted or ceiling-mounted; large or small; omni-directional or uni-directional (more commonly known as cardioid). And as is the case in the world of audio, you can’t actually see the difference in sound quality between your various choices. So how do you decide which path to choose? There isn’t one magic answer – each room is different and requires individual consideration from a professional. But there is some basic information that anyone considering this type of decision should know. This article will break down the typical conference room microphone choices, and examine the ins and outs of each.

A variety of conference room microphone styles

The Basics

Before getting into the specific styles, it is important to understand why microphones are so often a necessity. Microphones are usually installed in a conference room for one of three scenarios. The first – and most common – is a room with integrated conferencing (either audio teleconferencing, video teleconferencing, or both). Audio teleconferencing is simply a phone call, but with a room full of people on one or both ends of the call. In these situations, the low audio quality and lack of processing provided by a speakerphone won’t cut it. The solution is to install microphones, loudspeakers, and a digital signal processor into the room – the microphones capture the near end of the call, the loudspeakers play the far end, and the DSP processes the signals, provides noise cancellation, and eliminates echo. This type of audio system is also used for video teleconferencing, augmented with a camera and a display.

The second scenario where mics are necessary is in a larger room that is in need of “voice lift.” Voice lift takes the same signal from the microphone, but instead of sending it to the other end of a call, it sends it to in-room loudspeakers, allowing everyone in the large room to hear the person who is talking. The third scenario is a recording system – audio from the mics is captured and sent to a dedicated device that records and saves the files.

Microphone Styles

When evaluating microphone styles, there are four main categories of information to consider: pickup pattern, location of microphone in relation to the person talking, form factor, and wired vs. wireless. Different combinations within these categories can lead to a lot of different possibilities, and indeed, there are many different styles of microphones. It’s fair to wonder: if the simple goal is the best sound quality possible, then why are there so many different variations? Aesthetics, furniture style, cable pathways, and seating plans are some of the many factors that necessitate these varieties, and a good AV designer will consider all of these when choosing microphones. This article will examine four common styles in detail:

1. Table-Mounted Boundary Button Microphones

The single most important concept to keep in mind with regard to mic choices is a simple one: the closer the microphone is to the person speaking, the better he or she is going to sound to those hearing it. For that reason, the conference table is a natural place to install a microphone. Some have a problem with the aesthetics of a microphone on the table – it’s permanently installed, it takes up space that can be used for laptops, and it obscures the flat surface sometimes used for laying out large sheets of paper. But as far as sound quality for an installed mic goes, it’s usually the best option. The video at the end of this post shows what a table-mounted microphone sounds like.

Table-mounted microphones exist in a variety of form factors, but due to the aesthetic concern and the importance of tabletop real estate, the most common style is the button microphone. A sub-classification of the boundary microphone (or one that is designed to be installed onto a hard surface), the button mic is about as small as it gets, typically at around an inch in diameter. Gooseneck microphones are a very good option too, as they get the mic even closer to the talker, but these usually are ruled out for aesthetic reasons.

Table-mounted boundary button microphone

1A. Omni-Directional

Table-mounted button microphones typically come with one of two different pick up patterns: cardioid or omni-directional. Cardioid mics pick up roughly 120 degrees in front of them (see pickup graph below), and omni mics pick up a full 360 degrees around them. Because of this, microphone counts can double or triple when comparing cardioid to omni-directional. So, off the bat, it sounds like omni-directional mics are the way to go. And indeed, many inexperienced AV designers go down this route – the picture of a conference table with a couple omni-directional mics down the center is something everyone in the AV industry has seen. End users are often quick to bite on this strategy: three mics on the table cost less and take up less space than eight, right?

This strategy, however, can lead to calls with more ambient noise and less intelligibility. Omni-directional mics pick up everything around them, including HVAC noise, whispers, or other ambient noise. Since the goal of an omni-directional mic is to capture 360 degrees of audio, there is little ability to differentiate from the sound you are trying to capture (the talker) and the undesirable room noise. This greatly limits what audio engineers can program the conferencing processor to do – if you turn up the talker, you’re turning up the HVAC noise along with it. According to Polycom, one of the video conferencing industry leaders, while some systems “achieve lower prices using less-expensive ‘omni- directional’ (non-directional) microphones, they also pick up all of the room noise and room echo the entire time, which is extremely distracting and makes it hard to understand what is being said. Such systems should be avoided.”

1B. Cardioid

Cardioid microphones provide something much different. Very little outside of the mic’s coverage area (also outlined in the below graph) is captured, greatly reducing ambient and unintended noise. In turn, each mic is only responsible for one or two seats at the table. This directionality means that the difference between speech and unintended audio – or the “signal to noise ratio” – is much starker than that of an omni-directional mic. A higher signal-to-noise ratio allows programmers to put a “gate,” or a bottom threshold, on the entire system. Only audio that comes in above the threshold is let through, which eliminates most non-speech.

In sum, cardioid mics provide the individualized pick-up areas that allow programmers to fine-tune the system, amplifying speech and cancelling out unintended audio. Omni-directional mics do not allow this flexibility.

                                         

              Cardioid pickup pattern                                                                Omni-directional pickup pattern

2. Ceiling-Mounted Microphones

So far, we’ve established that cardioid microphones provide better sound quality than omni-directional microphones when mounted on a table. But what if a C-level executive cannot abide by the aesthetics of microphones on the table? What if the table is modular and re-configurable? Or what if the client is an architect who uses the table to lay out large drawing sets that might cover the microphones?

These situations are when AV designers – begrudgingly – turn to ceiling microphones. Ceiling mics occupy otherwise unused space, and newer models are visually less obtrusive as well. But when held against the key philosophy mentioned earlier – the closer the mic to the talker, the better – they don’t fare so well. According to the ClearOne publication Optimal Audio for Conference Rooms, ceiling mics “add unnecessary ambient noise and because they are further away from the participants they may make it more difficult to pick up all audio.” Shure, a highly respected microphone manufacturer, puts it even more blatantly in a bulletin: “Shure feels strongly about not placing microphones in the ceiling.” The comparison video below shows what most ceiling microphones sound like.

Many of the key characteristics of ceiling mics are influenced by the long pickup distances they have to cover. They’re typically cardioid mics, as an omni-directional ceiling mic would pick up far too much unwanted noise. They also often hang down from the ceiling in order to “cheat” twelve inches or so towards the talker. To reduce the amount of microphones necessary, ceiling mics often come as “arrays” – multi-element units that point a variety of cardioid mic elements in different directions, all under the same grille. Three-element microphone arrays are the most common, however there are new products out such as ClearOne’s 24-element Beamforming array that will be major players in ceiling microphone solutions moving forward.

A typical ceiling microphone array

Ceiling microphones aren’t going to sound as good as table microphones. They can, however, get the job done in some situations. The main thing to keep in mind is that, because of the amount of reflections they pick up from around the room, if you do have ceiling mics, you are at the mercy of the acoustics of your space. And indeed, audio industry leader BiAmp lists “considering room acoustics” as its number one “Ceiling Mic Best Practice.” A ceiling mic in a room with a dropped tile ceiling, a carpet, and acoustic tiles might very well sound decent. A ceiling mic in a room with ten-foot ceilings, glass walls, and a wood floor is not going to provide acceptable audio. It will simply pick up too much reflected sound. If ceiling microphones, for one reason or another, are the way you’re going to go – do everything you can to improve the acoustics in your room. Start by adding acoustical tiles to the walls – they are inexpensive, they can be hung artistically, and they will help your sound quality significantly. Dropped ceilings, window curtains, carpets, and any other soft, absorptive surface helps as well.

Typical sound reflections in a conference room

3. Wireless Microphones

Every microphone mentioned thus far is a wired microphone. Put simply, wired mics are more reliable than their wireless counterparts. Wired microphones rely on tried-and-true analog cabling, whereas wireless mics transmit their signals as radio waves. Thus, they are subject to interference and the politics of the ever-changing RF spectrum allocation (see the below chart). This is a real issue – according to InfoComm, in 2015, the FCC will put a large portion of the 600 MHz range up for auction. The 600 MHZ range also happens to be where most professional wireless systems reside. This would force users to re-invest entirely in a new system that occupies a different frequency range.

Beyond this, wireless systems are also subject to dropouts, distance limitations, and channel count limitations within a system. All this is to say: the most expensive wireless system out there is almost as good as a regular old mic and cable. Sound quality for wireless mics is less of an issue – they’re typically positioned close to the talker since there is no cabling to worry about – but their reliability and longevity vis-à-vis RF allocation are the main concerns.

The US Radio Frequency Allocation Spectrum… It’s Crowded

This does not, however, mean that there aren’t situations where wireless mics make a lot of sense. In many ways, they are an extremely compelling option. Not every conference room is outfitted with AV during construction – many projects in the industry are retrofits and do not offer any opportunity to run cabling. Wireless table mics work extremely well in this scenario, as they can be installed at any time. Trainers often need to walk around the room with both hands free – wireless earworn or lapel mics make sense here. Larger meeting rooms feature question and answer sessions – passing around a wireless handheld mic is a reasonable solution in these cases. Cabling is one of the biggest challenges in an AV installation, and a wireless microphone system takes that worry out of the picture entirely.

The main thing to keep in mind with wireless microphones is this: they require managing. If you’re going to invest in wireless mics (they are also much more expensive than wired ones), make it part of someone’s job description to look after them. These mics either require new alkaline batteries every six or so hours of use, or need to be charged on a stand. Either way, someone needs to closely monitor their usage so that they don’t cut out mid-meeting. Someone should be able to instruct users which way wireless table mics are supposed to face. And someone needs to make sure that the mics don’t get lost or stolen. Anything in the AV world that isn’t permanently installed is going to be less reliable – so if you do go wireless, make it someone’s job to manage the mics.

A multi-channel wireless microphone system

Moving Forward

Microphones aren’t an easy topic – that’s why professionals like PPI’s Account Managers are there to help you through it (and why this blog post is at 1900 words and counting). In all seriousness, it is always wise to be as informed as possible on your decision. Keep what you’ve learned in this article on cardioid table mics, omni-directional table mics, ceiling mics, and wireless mics in mind, and you’ll be well on your way to making an informed decision. Contact an Account Manager today to user your new knowledge and to take the conversation to the next level. Please also check out the video below for a demonstration of what was covered in this post.