Wireless Mics, part 2 of 2
As I said right off the bat in “Wireless Mics, part 1 of 2“, this is an “applications” guide, with proven advice on how to make your wireless system (heretofore referred to as an “RF” system) work as well as possible. Proven advice … not hearsay … not urban legends.
The Parts Of An RF System
A Little Something About Mics (for more help on this, see “Pick A Mic, Any Mic!”)
- Lav (lavaliere or clip-on). For magicians, this is usually attached to clothing, but it can also be “dressed” into the front hairline.
- Headset. Often called a “Madonna” mic.
- Earset or adapted lav. Essentially, this is a lav mic that is part of (or attached to) a small, non-invisible assembly that places the mic very close to the mouth. While this seems to be a small version of a headset mic, it’s not. There are a few very important differences.
- Handheld. This type can also be moved on/off a mic stand with a mic clip.
- Note. Pretty well any lav or headset can be wired to work with pretty well any beltpack transmitter. The mic’s manufacturer can provide wiring instructions to make their mic compatible with any popular transmitter.
When using a lav mic, in order to get the best possible sound quality and acceptable “gain-before-feedback”, microphone placement is very important. Use a high-quality microphone, and place it as close as practical to your mouth. Place it in that location every time.
You may wish to borrow a page from the theatre standard, hiding a lav mic somewhere as close as possible to your mouth. Maybe in front of the ear, on the forehead, etc… Again, getting a lav mic as close as practical to the mouth is extremely important in order to achieve acceptable gain-before-feedback and sound quality.
A Little Something About Transmitters
The microphone choice will usually dictate the transmitter type (handheld or beltpack). A lav or headset requires a beltpack transmitter, whereas a handheld mic has an integrated transmitter.
You might wish to consider whether or not you’ll need your transmitter to have a “mute” switch. That’s not the same as an “on/off” switch. A mute switch leaves the power on, but disables the audio signal. Suffice it to say that, for a few different reasons, if you want to be able to turn your own mic on & off during performance (as opposed to having your audio tech do it according to the script), you are definitely better off using a “mute” switch.
The beltpack’s antenna must be allowed to extend to its proper length for maximum efficiency, and must not be touching anything conductive, including skin. Sweaty skin is even worse.
A “gain pot” or the gain setting in the transmitter’s menu, is also a good feature, because it allows you greater control over the system’s apparent “signal to noise ratio”. We’ll discuss the setting of this control in a minute.
Size & appearance may also be issues for you, but reduced size can mean a lot more money, and, “Hey! Looks aren’t everything!”
A Little Something About Receivers
An excellent feature goes by a different name with each manufacturer (tone-coded squelch, tone-key squelch, auto-squelch, etc…). What it means is that if you turn off the transmitter’s power switch, or if the transmitter “drops out”, or if another RF signal overpowers your transmitter, the receiver will mute its audio circuit so that unwanted noise won’t come blasting through your PA!
A Little Something About “Tunability” or “Frequency Agility”
Generally, you should select a tunable (also called “frequency agile”) system, even if you’re only using one system. If you’re using multiple systems though, I suggest it’s a very bad idea to select non-agile (single frequency) systems.
Make sure all transmitters are at least 1 metre (3 feet) apart from one another, and at least 3 metres (10 feet) from the receivers.
If the transmitter has a “gain pot” or “sensitivity switch”, put the mic in place (see, “Pick A Mic, Any Mic!”), and perform the loudest passage of your show. Adjust the gain pot or sensitivity switch until the transmitter’s peak LED flashes, and then turn it down slightly. If your transmitter doesn’t have a peak LED, then let the receiver’s AF (audio level) meter be your guide. This will ensure the best possible “signal to noise ratio” for your system. Set this properly one time and then leave it alone: Don’t re-set it at every new venue.
For tunable transmitters make sure that the transmitter is set to the same frequency as the receiver.
A beltpack transmitter is usually clipped to a belt or pants waistband, but the antenna must be allowed to extend freely. Unfortunately, clipping a beltpack to a belt or sticking it into a pocket makes it too easy for the beltpack to come free, falling to the ground and smashing into little $100 bills! I know that’d be a cool effect, but it’s an all too common occurrence. It’s real easy to rub up against something or stumble, and drop the beltpack. A very simple solution is to purchase or make a beltpack holder, like the one from Shure. Something like a Velcro closure makes sure the beltpack can’t pop out accidentally, and the use of neoprene also serves to absorb sweat, thereby helping to keep the beltpack dry, extending its life. These belts fit easily under a jacket. Just be sure to let the antenna extend freely. By the way, keeping your beltpack in your pocket also makes it almost impossible to let the antenna extend freely.
No matter how or where you wear your beltpack, a common trick from the world of theatre is to put the beltpack into a non-lubricated condom to help keep sweat from damaging the electronic components. Again, be sure to let the antenna extend freely.
Since your body can get in the way of efficient RF transmission, and an RF beltpack is typically placed up against your body, you’ll have reduced performance every time the transmitter’s antenna can’t “see” (unimpeded line of sight) the receiver’s antennae. In other words, if the transmitter’s on your left hip, and the receiver is off-stage left, then every time you turn to the back of the stage you’ll experience reduced performance which may (or may not) result in dropouts. Therefore, place the transmitters on the side of your body from which it will most often be able to “see” the receiver’s antennae.
Don’t go too close to the aforementioned non-broadcast interference sources.
I know I keep hammering this home, but the transmitter and the receiver should be arranged such that they have the shortest possible unimpeded line of sight. This means that the receiver should be at the stage, and not at the FOH (front of house) mixer position.
As with the transmitter, don’t put the receivers too close to the aforementioned non-broadcast interference sources. Also, don’t place the receiver too close to large metal objects.
As mentioned before, for best results, the receiver antennae should be oriented in the same direction as the transmitting antenna. Typically, in order to find the best possible average, the receiver antennae should be 45º from upright.
For tunable (frequency agile) transmitters make sure that the transmitter is set to the same frequency as the receiver.
Test your RF at the same time that all other production is also running so that you’ll stand the best possible chance of identifying any broadcast and non-broadcast interference sources. I say you’ll “stand the best possible chance”, because, at show time, it’s possible that a source of interference will have been added or taken away. For example, it’s possible that the daytime fluorescents will be turned off at show time, or that security guard two-way radios will be turned on at show time.
First, turn on the receiver but leave the transmitter off. Check the receiver’s RF signal strength meters to see if the receiver is picking up any unwanted signal. If so, change frequencies, and once you’ve found a clear one, be sure to set the transmitter to the matching frequency.
Do a “walking test” to be sure there are no dropouts in your performance area. Remember, dropouts may often happen only within a 7.5cm x 7.5cm (3” x 3”) area(s), so you may just be able to put a “tape spike” (tape marker) that point on the stage as a reminder to avoid it during the show.
After your test, ALWAYS turn transmitters on first, then receivers. While understanding the reason for this is not important, observing the rule is important, so I’ll repeat it. Always turn transmitters on first, then receivers.
Well, there ya go, my friends! Now get out there and go wireless!
By the way, for more in-depth help with troubleshooting RF systems, check out what Tim Vear has to say at the Shure Web site.