Mics and Myths

When you understand how microphones actually work it is difficult to see how a mic is supposed to work well in one application and yet not so well in another. While there is some truth in this statement it is often misrepresented in the extreme. In this article I will attempt to clarify the situation and show that microphones are actually far more flexible than is commonly realised.

The two main types of mic in modern day use are the dynamic and the condenser types. Well made mics in either category work very well indeed and can often be substituted for each other with little if any compromise in performance. This is a fact and not a myth and both types definitely cross over in their various uses.

Microphones are used to pick up sound vibrations and feed the resultant electrical AC voltage to a mic pre amp. Microphones vary greatly in their physical dimensions but all act as an interface between a noise source and the pre amp. Sound vibrations in and electrical AC voltage out.

The largest microphones at least in length are called shotgun mics and the smallest are called lapel and or bug mics. The shotgun has to be long to ensure good directivity and the lapel mic needs to be small to ensure its convenience. A shotgun mic is usually used to receive the sound from a source that is located at a distance while a lapel mic is worn clipped to a jacket or shirt to bring it in close to the mouth. Could we swap one for the other? Not very well in this case because apart from the fact that it would look ridiculous the extremes in their design differences would mean a substantial compromise in the end performance.

Here is another example but far less extreme. Shore make a mic called a Beta 52A that is designed for mincing up a kick drum. It is described as a super cardioids large diaphragm percussion mic. They also make a very well known microphone called the SM58 described as a cardioids dynamic vocal mic. What would happen if we swapped these two? In actual fact very little although some so called sound men would react as though the entire show would turn to custard if I did this. Just a few slight tweaks on the mixers channel equaliser and apart from the visual aspects of this swap I would bet money that no average person could tell by listening to the resulting sound that I had committed this terrible crime.

A lot of design differences in mics are well motivated and make life easier for the user but there are also a lot of silly misconceptions. I had a singer once tell me he had to have a Sennhieser 441 which I could not supply. When he found this out and after I offered him a Shore SM 58 he almost refused to perform. He really believed his performance would have been seriously impaired had he used the alternative. This is an example of just how dangerous this kind of misconception can be. In my opinion it would have been almost impossible for anyone but the most critical of listeners to have detected any difference but there you have it.

Small diaphragm condenser mics have a very good high frequency response and are characteristically very flat.  The light weight of the capsule makes them rather difficult to shock mount making some models subject to bad handling noise because the capsule is joined to the outer case. These mics are commonly used as drum overheads or for mincing up instruments because they are accurate and always sit in a clip on a stand in these situations. If you put a wind filter on one and use it as a vocal mic however they are superb as long as they are not hand held. There is no audible compromise only a mechanical limitation.

AKG make a mic called a D22XLR they recommend for tom toms. It is a typical cardioids dynamic mic with a built in stand adaptor which is nice and convenient when you are in a hurry. I have tried all manner of mics on tom toms and I have found it more or less impossible to hear any difference between them. I am not saying that differences don’t exist only that they are not really audible in this mid / low frequency application.

Lapel mics vary radically in sound quality as they are very small and designers need to go to great trouble to get them to sound good with this severe size restriction. Prices for these vary greatly also, some cheaper ones sound surprisingly good but may will suffer from other aberrations such as wind or breathe noise so careful testing is needed before making a purchasing decision with these.

Dynamic range is another issue. This is a mics ability or otherwise to withstand high SPLs in close to the mouth or an instrument. It is also hard to make a mic breath resistant and very compact at the same time. Whisker mics as they are called are becoming very popular for operatic use and some of these products are so small they are almost invisible on the wearer. Some of these tiny mics cost well over $600. Designers of these mics get around the wind rush problem by mounting them on the head set so they are worn side on to the mouth and out of the breath path. As they move with the head breath is not really a problem but careful positioning is still very important.

Mics that have a large golf ball type pop filter as it is called have the driven element mounted quite a long way back from the front to allow a large air gap. This gap greatly reduces the effect of severe breath noises especially at low frequencies caused by a vocalist who is in very close to the mic. Mics that have no or only a very small filter interface suffers badly from proximity effect which tends to be a double edged sword. On one hand it can help make a thin voice sound fatter but on the other it can cause overload and distortion if not handled carefully by the sound engineer. Some singers know how to use this to good effect and it can enhance the dynamics of a song if used tastefully.

As far as mincing up instruments go I don’t believe either type has any perceptible advantage over the other.

Some mics have a deliberate frequency response aberration known as a presence peak. This is intended to freshen up the high midst with the intention of making vocals sound more appealing. Obviously this is a matter of taste and some engineers do not like this compulsory equalisation and it obviously does nothing for musical instruments. A presence peak therefore has nothing to do with accuracy.

Omni -directional mics pick up the sound equally from any angle. It is a common myth that these are better recording mics than directional mics. Their big problem is that they are more affected by reverberation than unit directional mics are. The upside is that they will pick up sound from a group of voices or instruments at an equal volume if the circular distances are constant.

The idea that some mics seem to pick up sound from further away than others is another myth unless they are highly directional in design. There is very little difference in the so-called 'reach' of microphones.

The colour or the look of a hand held microphone has no affect on how it performs but may have a major affect on its desirability from a marketing point of view. Don’t be fooled by the look of a mic, focus your attention on its sound quality and its ability to withstand high SPLs. Listen to its handling noise when you move it around and try to find out if it is robust enough to withstand the rigors of what you intend to do with it. A mic does need to feel good in your hand. If you are a vocalist it will become your friend and companion but you should never become so addicted to it that you can't live without it, as this kind of silly attachment is yet another myth.