Getting The Best From Radio Microphones

Getting The Best From Radio Microphones

Radio microphones have the huge advantage of having no cable to worry about giving you the freedom, up to a point, to roam around as you please unhindered by an annoying lead. This may well be of considerable benefit but there are certain problems and limitations with radio mics that it pays to know about.

They all have a limited range and this varies considerably depending to some extent on frequency but also the performance of individual microphones both in terms of quality characteristics and brand name in a particular environment.

There is no way of telling what sort of range you will get in advance of using it in a given location. It is a question of trying it out to learn how well they will perform, 50 metres is good but some will only allow you 10 or so metres while some may even do several hundred metres range. Steel beams or RSJs used in building construction are notorious for causing problems with range and drop out. All you can do is change the frequency assuming you can and try again.

Line Of Sight:

"Line of Sight" is how well the transmitter can see the receiver’s antenna. The easier it is for the two antennas to "see" each other without any physical intrusions in between, the better the performance will be as far as range goes. If you can set up the receiver on the side of the stage you will get far better reliability than if you place it further down the venue, say alongside the mixer. If you can set up a trestle and place the receivers on it in a line above floor level if possible, then you can't do better than this. If you have people walking in front of the receiver's aerial this may cause you problems if they completely block the two antennas with a lot of body mass but sometimes it is impossible to avoid this so you may have to change it. This is why it is a good idea to get the receivers up off the ground as far as possible. There is no way of knowing in advance how body mass will affect the behaviour of a radio mic or what combinations of bodies and placement alterations will do. It is a question of try it and sees what happens.

High Frequency Suckout:

This is another problem you need to be aware of.  The result of "suck out" is a serious number of dead spots where the mic simply will not work leaving you speaking or singing but with no audio coming from the PA. This means that you will need to change the frequency you are using or the microphone system itself.  If you are not able to do this you will need to place masking tape crosses on the floor to mark the area where the drop out is occurring so the performer using the mic knows to avoid that particular area. Many modern cordless mics have a frequency selector switch that allows the user to try other frequencies if dropout is causing problems. Moving the receiver to another position can often make a difference but this is a case of trial and error. Placing the receiver's antenna in a different position can sometimes fix the problem also.

Dropout: The Number One Enemy.

Dropout is the major worry with radio mics but it can be controlled if you understand what is going on. Apart from the above it is usually caused by body mass between the two antennas. Reposition the receiver and try to raise it upwards. Keep people away from the receivers because they can block the signal. Spread the antenna apart. Keep the batteries fresh. Change the frequency if you can. Do not stack the receivers on top of each other. Keep a gap between them if you have room. Sometimes the receiver's RF. can interfere with the one alongside it. Keep the antenna clear of cables. If none of these things resolve the problem then the microphone either has a week transmission signal or the receiver sensitivity is very low. Take it to a reputable radio mic service technician for realignment or drop it off at Stage Sound.

Dynamic Range.

This is a microphones sound pressure input level limitation. If this is exceeded the mic will overload and "clip" or "distort", sometimes quite badly. The microphone that is plugged into it can affect the dynamic range of a belt pack. If say a lapel were to be used it may not have any overload problems at all but if a headmic were to be used without any attenuator (pad) changes then it may severely distort the signal.

Using the Pad.

The pad is a small switch or potentiometer that is often concealed in the body of the pack and is adjustable either through a small screwdriver hole or it is located inside the battery compartment. The idea is to yell into the mic and turn the level down until you hear no overload present.

Sometimes belt packs are also used with musical instruments such as guitars or keyboards. The same thing applies with these as well. You must adjust the pad to find the optimum level setting if you wish to get a good result. If you are using a hand held mic the level needed is closely associated with the kind of music. The most demanding being Hip Hop. These guys tend to literally gobble their mics so they need special attention.

Battery Life:

Battery life varies from brand to brand and it is important in the case of a drama or musical production to have some margin available. Having a mic stop in the middle of a performance is not a good idea. In most cases a 9 volt battery will last from 4 to 6 hours but it can be as long as 15 with certain brands. Battery shelf life is another consideration. When you purchase batteries it is not always possible to know how long they have been sitting on the shelf for so they could be flat even before you use them. Endeavour to buy them from a retailer that is likely to have a fast stock turnover. I have had mics that use a single AAA battery do well over 10 hours and others that did not last ten minutes. The quality of the batteries can also make a big difference and remember rechargeable batteries tend to have a longer life than non-rechargeable do. We highly recommend using rechargeable batteries if it is possible both for the sake of the eco system and battery longevity.

Transmitter Placement:

One of the advantages of having no cable means radio mics can be placed in all sorts of convenient places where they will be able to deliver a good lift in volume. You can tape one to the end of a broom or hide one on a shelf or prop. All you need to do is have the performers close enough to get some good lift in volume. This can work especially effectively with lapels if they are Omni directional because they are often very small and easy to conceal.  Don’t hesitate to try this out and experiment with different positions to see if you can get the result you need. Keep feedback in mind though.

Be careful when you place lapel mics on a performer. Do not allow the mic to come into contact with rough clothing or items such as beads or chains etc that can cause severe noise by rubbing or movement. Keep them high up on the body if possible and not blocked by clothing or wearable props. Use tape, blue tack or safety pins to run the cable in a concealed manner so flaying arms cannot damage or break it. Most important!

Whisker Microphones:

This new technology is a god send for MDs producing stage shows as they are almost undetectable on the performers face. They are not cheap but I have heard some great sounding ones and you would think a normal hand help mic was in use. Most are skin coloured and thinner than a straw and nearly invisible to the audience. I think its money well spent.

Working With Headmics.

Headmics have pluses and minuses. One hand they remove the need for good mic technique while on the other they mean the singer cannot use it to control dynamic range. This means loud notes and can cause overload and quiet notes may not be heard very well. This problem can be rectified if the operator has the ability to "sit on the faders" meaning the mixers fader must be adjusted to correct for changes in the singer’s voice levels as they occur. Headmic's can be painted skin colour to make them less obvious. A paint matching company will do this using car lacquer which I found to work very well and it dries quickly. Be careful when you are setting up headmic's that they are set clear of breath flow or you will hear a rushing sound as the performer exhales. It is sometimes necessary to reshape the headband to suit the wearer and make them comfortable. If you feel the headmic is overloading the transmitter you can adjust the boom so that the mic capsule sits further away from the singer's mouth to overcome this problem. They should be lined up with the corner of the mouth but slightly forward. Setup prior to an actor going on stage is very important because once they are out there in front of the audience there is nothing you can do about a badly setup mic.

Things To Watch Out For.

Battery clips can work loose over time and spring lugs can compress against the case and this can cause severe crackling or complete failure during a performance. Another cause of severe breakup is a faulty cable on a lapel mic. Aerials can come lose due to wear and tear on the mounting screws. These need to be checked and tightened regularly. Power supply wall packs can give problems with their plugs and cables fracturing as they age. RF choke alignment is another problem area. This needs to be done by a competent service technician every so often to ensure reliability and good range.

For any further information on this or other blog topics please call Paul Johansen on Ph: 444 8776


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