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MICROPHONE TYPES AND A CLASSIC LIVE BED TRACKS MIC PLAN

 

Neumann KM184 matched pair of small-diaphragm condensers

Neumann KM184 matched pair of small-diaphragm condensers

 

Microphones are awesome.  I love them!  There are quite a few microphone types to get familiar with if you want to know all the options out there.  A quick history tour and a few fun facts, and then I’ll give you relatively cheap options in a cheat-sheet format for miking most of the things you want to record in a home studio setting.

Alexander Graham Bell invented both the microphone and the speaker when he invented the telephone in 1875, filing his patent on January 14, 1876.  Way to go, Alexander!

In an amazing quirk of fate, the co-founder of Western Electric, one Elisha Gray, filed a patent for the same invention in a subtly different form on the exact same day as Bell filed his patent.  Bell’s patent application went in a few hours ahead of Gray’s, and so, some ten years later, Bell was granted free title to the patent.  By then, funnily enough, the Bell Telephone Company had bought a controlling interest in Western Electric anyway so it was a moot point financially to Bell.   More importantly, the history books now remember Bell for the invention of the microphone, the speaker, and the telephone.

Less than a decade later, Thomas Alva Edison invented the vacuum tube amplifier and all things audio were ready to begin moving along nicely.

Let’s see what microphones actually do.

Microphones are transducers.  Their job is simply to turn acoustic energy in the form of soundwaves into electrical energy in the form of an oscillating voltage.

They are a mirror image of the process performed at the speakers, at which time that oscillating electrical energy the microphone supplied is changed to kinetic energy (the motion of the speaker moving in and out), which of course generates acoustic energy in the form of the sound waves radiating outwards from the speakers.

There are three microphone transducer designs, but a larger number of ways of applying them.

There are also several types of pickup pattern, or polar pattern.  You may find cardioid (heart-shaped) patterns, bi-directional (figure-8) patterns and omnidirectional patterns.   The type of pattern you select on your microphones (at least, those that allow a choice of pattern) will help you to exclude unwanted sounds as well as aim towards sounds you wish to capture.  The aiming directions of both ends, the front and rear and sides, of many types of mics are very important in careful positioning.

In fact, there are a great many styles of application, especially in the area of stereo miking.

DYNAMIC MICS

There are two types of mic you’ll see most often, namely the dynamic mics (also called moving-coil mics) and the condenser mics (also called capacitor mics).

Two Shure classics - the SM58 (with the windscreen) and an SM57 (without)

Two Shure classics – the SM58 (with the windscreen) and an SM57 (without)

The dynamic mics (or moving-coil) types can take a lot of sound pressure levels without complaint, and are normally robust and rugged mics.

Examples are the Shure SM58, the Shure SM57, the Electro-Voice RE-20 or the AKG D112.

The latter two are large-diaphragm types, and the Shure SM57 and SM58 mics are small-diaphragm types, but they are all dynamic mics in operating principle.

The other type you’ll see a lot of are the condenser mics.  These are excellent for speech and vocals, and cymbals and sources with a lot of high end detail, such as a mandolin or fiddle.  Delicate instruments are well suited to condenser microphones, but generally not suited to dynamic mics which can be hard and edgy-sounding in the midrange in comparison.

A smaller subset of condensers exists called Lavalier mics, and you probably won’t use them in the studio, although they can be helpful with fiddles and the like that have no internal pickups.  These are the little clip-on mics (with a condenser capsule type) that you see on television and in theatres used for actors, comperes, TV presenters and interviewees and so on.

Their tiny visual footprint makes them ideal for applications where you don’t want to reveal the microphone to the audience, or must minimize awareness of the presence of microphones at the least.  This can be critical to suspending disbelief in the theatre, when, for instance, you are miking an actor in a period costume in an Elizabethan drama, where an audience seeing a microphone onstage would clearly be incongruous to say the least.

They don’t get used in recording a lot because they are susceptible to clothing rustle and similarly annoying unwanted audio incidents, but they can help with unusual delicate instruments with no pickups of their own because they are small, discreet and tend not to obstruct playing actions or damage instruments when clipped on somewhere sensible (perhaps with a protecting cloth that won’t rustle or move between the mic and the instrument body).

Another more common subset of condensers are the electret-condensers.  These carry an effectively permanent charge of static electricity that powers the capacitance.

Voltage is not needed to power the capsule of an electret condenser type of condenser, as it happens, but there is an internal preamplifier in the microphone, after the capsule, and that needs juice if you expect it to output a signal to the mixer or DAW interface.

Over time, there is a really slow and small drop in the sensitivity of electret capsules since there is no such thing as a really permanent charge, but we’re talking decades, not days, and mine are still working fine after several decades of use.   You can’t change the laws of physics, Jim.

LARGE OR SMALL DIAPHRAGMS

The biggest thing to watch out for with dynamics or with condensers (other than vast price differences in either type of mics) is whether it’s a large or a small diaphragm mic.  Both condensers and dynamics can have large or small diaphragms.

A nice solid Rode mic, the NT-4, which lets you record in stereo using a special cable.  The X-Y mic positions of the capsules give you great phase coherence since they are so close together that all soundwaves (except extremely high ones)  arrive completely in phase at one capsule relative to when they arrive at the other mic capsule.

A nice solid Rode mic, the NT-4, which lets you record in stereo using a special cable. The X-Y mic positions of the capsules give you great phase coherence since they are so close together that all soundwaves (except extremely high ones) arrive completely in phase at one capsule relative to when they arrive at the other mic capsule.

 

 

The small diaphragm mics will have better frequency response, and will sound more natural when they are aimed indirectly into the path of a sound (off-axis to the sound source rather than perpendicular to it), compared to the large-diaphragm mics.

Sounds that have plenty of lows do well with large-diaphragm mics, since the waveforms of low notes are dramatically longer, physically, than the high frequencies, which may only be a few millimetres across.   The large diaphragm mics have a full sound with character and body, and the midrange will be firm.

Another big difference is that condensers require electricity to work and dynamics don’t.  All condensers require electricity to be supplied, either from a battery or from a phantom power supply of 48 volts (sometimes just called PP48 on equipment markings).

Dynamics don’t need power to work, they just do.  They usually don’t mind if the power is on at the console or preamp you connect them to, but ideally you will only apply phantom power to condenser microphones since they won’t work without it.  It’s a very small current, nothing to be concerned about at all.  Unpowered ribbon-type microphones don’t like it (they are not condensers), but it won’t hurt you or any dynamic mics.

The 48 volts is a current that travels down the mic cable in the opposite direction to the sound entering the mic, powering the microphone from the connected device.  A console’s mic input  channels will always feature a preamp, usually shown by the presence of a MIC/LINE toggle switch and an XLR 3-hole input socket or 1/4″ TRS jack input socket or XLR/jack combo that allows either XLR or jack inputs.  Set to MIC for any microphone signal, of course.

When you have plugged in your condenser mic, you turn on the PP48v switch, either one mic channel at a time or using a single switch globally operating it for all channels at once on your mixer or multi-channel interface.  If you have mic inputs on your DAW interface, you will have a PP48v switch for condensers.   They have great high frequency response and sound relatively natural, compared to the harder, more brutal sounding dynamic mics.

Condenser mics are great for speech because they capture the high end so very well, giving an airy, detailed sound that brings out the lip smacks and mouth noises a little more for added realism and intimacy on a vocal, or the swish of a light cymbal wash floating above the drums.

A condenser mic contains a thin strip of plastic or Mylar diaphragm positioned right next to a fixed backplate, maybe a thousandth of an inch away.

The diaphragm has been sprayed, typically with nickel or gold particles, to create a coating that can get the capacitance going that fluctuates according to the pressure the sound waves apply to the diaphragm, provided the backplate receives a polarizing voltage (phantom 48v or battery).

RIBBON MICS

A third category, ribbon mics, fell out of favour in the 1960’s due to fragility, but better designs for ribbon mics have led to their recent renaissance over the last fifteen years or so, mostly thanks to Royer Labs and their R121 pencil ribbon.

They originally appeared in the 1930’s or possibly late 1920’s, revolutionizing microphone technology.  The RCA 77DX is the classic studio microphone from pictures of the day, and offered vast improvement on the earlier wire equipment available.  At last, one could capture sounds all the way up to 10kHz, which, of course, left another 10kHz of frequencies above that (and audible to humans) still not recordable.  Still, it was a big step forward.

They have become pretty common in recording set-ups once again, in part because they are not so easy to break now and also because there are ribbon mics that use phantom power now, where previously that was not possible and they could be damaged by it.

AEA R84 passive ribbon mic - and it's handy padded protection cover, for when it's not needed.

AEA R84 passive ribbon mic – and it’s handy padded protection cover, for when it’s not needed.

 

They are quite a bit less fragile these days, but still susceptible to strong blasts of air damaging them, and therefore they are rarely used for live shows.

Be careful not to slam any doors around them, and don’t put them too close to a kick drum’s mighty blasts of air, even if your new ribbon mic does sound as warm, dark and velvety as a late-night cup of hot chocolate.

It’s the differences in pressure between the front and back sides of the ribbon that cause the voltage fluctuations representing the sound.  Sometimes it will be called a pressure-gradient microphone, due to this.

Some ribbons have equally sensitivity from front and rear sides, so they have the rear produce an opposite-phase signal, at 180 degrees phase to the front side.  This gives a figure-eight pattern, equally strong front and back, with no output at all on the sides.   Great for background vocals from two singers, one either side of the same mic facing each other as they sing.  Great for performance, great for sound.

Just watch those blasts of air (stay a good few feet back from any brass instruments, and point them off-axis to the source a little bit).  Use pop shields or windscreens – you can even use nylon stockings over a coat-hanger at a pinch, if you have to go old-school.

Some modern ribbons have internal preamps that require power.

Ribbons are smooth and warm sounding.  Silky and cool.   Try them!

BOUNDARY LAYER MICS or PZM MICS

A more unusual type of mic is the PZM mic.  PZM stands for Pressure Zone Microphone, but that’s really a corporate trademark, referencing the Crown PZM, a mic that was very popular in the 1970’s.

The technical name for this type of mic is the Boundary Layer mic.   Where a Crown PZM was very low-cost, being tens of dollars rather than hundreds, and available from Radio Shack (now called The Source, at least in Canada), you can actually pay an awful lot of money for a world-class Boundary Layer mic.

Boundary layer mics can range from under a hundred dollars to several thousand dollars.

Neumann GFM132 Boundary Layer mic (a.k.a. PZM mic) in it's box - the mic is the big triangle, with a cm ruler for scale

Neumann GFM132 Boundary Layer mic (a.k.a. PZM mic) in it’s box – the mic is the big triangle, with a cm ruler for scale

 

They work by placing the capsule directly beside a boundary, in this case a large metal plate that is part of the mic.  The GFM132 pictured is a triangular flat plate with a tiny capsule housing attached right beside it.

The body is about four or five inches across due to the plate that forms the major part of the microphone body, often square, but in the GFM132 it’s a triangle.  The capsule housing mounted at the plate is tiny in comparison.

Being placed at a reflecting boundary (the plate), there are no reflections to speak of, since the distance to the boundary is smaller than even really high frequency waveforms.  This is the whole point of the design, and why it’s called a boundary layer mic.  It’s mounted at an acoustic boundary by design, bringing it’s own boundary as part of the mic.  You place the mic on a much bigger boundary, ideally at least four or five feet across.  It won’t provide useful audio without being mounted on a pretty large boundary like a wall or a ceiling or a very big tabletop.

You place them on a large flat surface that can vibrate, such as a large piece of wood (perhaps a ceiling) or the underside of a piano lid.  The lowest frequency you can pick up is determined by the size of the boundary you place the microphone onto.   Being a function of the dimensions of the houndary, this means you won’t get much below 600Hz if you mount the mic in a piano.

On a ceiling, you may get a lot more mileage, but bear in mind people may be walking about on the other side of the ceiling.  Not ideal.  Generally, the sound will be rather hollow, and “middly” sounding.

The Neumann GFM132 is very costly, and that still sounds a touch hollow, so I don’t think I can recommend PZMs for home studios with only four or five mics in their collections, although a cheap one out a few feet on the floor in front of a drumkit can make for reasonably listenable recordings, but often with very little bass or even low mid frequencies captured.  You may well find it impossible to even capture sounds below 1kHz when you mount a PZM on a tabletop.

The great trick about the PZM design is that they have a very even frequency response,which, uniquely, is pretty much irrespective of distance.

The tone won’t really seem to change whether the sound source is fifteen feet away, or two feet away.  This makes for good balances with drumkits or bands, for example, when recording a live gig in mono for your own reference, but the tone is a bit hollow and “live” sounding for most uses.

SHOTGUN MICS

A particular type of condenser called a shotgun mic works by having really, really long ports (often a foot or more) on the body of the mic to let sound in.  These things are pointed at a distant source, focusing in on sound from that spot, and are very directional.   Aiming them carefully is very important to what you pick up.  They reject sound that arrives to the sides and rear of the mic, a useful trait in many ways.

Apex 176 shotgun mic and an SM58 dynamic mic for scale

Apex 176 shotgun mic and an SM58 dynamic mic for scale

They crop up on movie sets all the time for obvious reasons (they can be kept out of the camera’s view easily by being a long way away from the actors) and they are popular for miking a school play at a distance from the stage so as not to frighten little kids or distract them unduly.

A CLASSIC LIVE BED TRACKS MIC PLAN

Here’s a quick rundown on a handful of cheaper mics (and one or two slightly more costly classics if you have a rental or purchasing budget).  These will get you through a bed tracks session with decent results for not much outlay.  I’ll assume for simplicity here that it’s a bass guitar or upright bass, with drums, and electric guitars bed track, maybe with a guide vocal, all performed simultaneously.

To capture a drummer’s performance with a few microphones, say five, you would usually use dynamic mics and condenser mics in combination.

The condensers give you the highs of the cymbals, and the distant details of room sound, whereas the Kick, Snare and Toms can easily be captured with dynamic mics, which can take very high SPLs (Sound Pressure Levels) without being damaged.  Placement is a skill that takes time, and there are several good books on drum recording that I will mention in my Recommended Reading post at the end of June.

A reasonable budget drum mic selection you could slowly assemble over time on a low budget might be as follows:

An all-in-one “Drum Miking” solution in one box is one way to go, or, for more fun and education, you can try various brands on each part of the kit.

AKG D112 in it's box

AKG D112 in it’s box

 

KICK DRUM: AKG D112 or EV RE-20 are two of the lower-budget classics, but virtually any large-diaphragm dynamic mic will do, provided it can go at least as low as 40Hz.   Don’t try ribbons on a bass drum unless they are six feet away in front of the kit, and then they will pick up the whole kit anyway.  Dynamics are best here, though condensers are jazzy too.

SNARE DRUM: Shure SM57 is great, and there are lots of other choices of dynamic or condenser.  Again, no ribbons up close to be safe here.

HI-HATS: Shure SM81 is silky and quality at a fair price, or use an AKG C1000 for bright and smooth on a budget (or even SM57 dynamic for a harder, clankier sound).  Avoid dynamics completely if you want silky results.

OVERHEADS:  The popular choice in bigger studios might be a pair of Neumann KM184 – or two KM84 mics if you’re really lucky.   Many other contenders are out there, such as the Rode NT-3,  Shure KSM44, AKG C414, and numerous others.  On a sensible budget at home, try any pair of small “pencil” condenser mics, maybe Rode NT-3’s, and ideally a “matched pair” (a pair picked out and sold as a matched frequency response pair by the manufacturer).   Small is often better for overheads, for various reasons.

These small condensers can be used as overheads (pointing at the kit from above about 3 to 6 feet away, to capture the image of the entire drumkit as one sound, but mostly picking up cymbals due to being above the kit.  You could get away with two of the AKG C1000’s if you are trying to keep it very inexpensive, but it’s harder to accurately position them to avoid phase issues due to their larger size.  They certainly have a bright sound, but it’s a bit harsh for my ears most of the time.  I’ll cover drum mic placement in a couple of days in this blog series.

It’s easier to work with small-diaphragm mics on overheads but large-diaphragms do sound full.

TOMS – Dynamics are great here, due to their hard, clean sound and their ability to take high pressure levels.  Condensers are also really cool here, but can be more trouble to work with safely.  Drummers tend to whack mics on their kit by accident, so bear that in mind.  Even SM57s will get you by on toms very nicely, although there are lots of better choices if you can spend a few hundred dollars.  How many toms are there?  You can share a mic on two high/mid toms a lot of the time.  Try not to point it at the snare or hat.

FLOOR TOM – For floor tom, a large dynamic is often best, like an AKG D112 or EV RE-20, as on the bass drum.  Condensers can be good too.

CRASHES & RIDES – pick them up with condenser-type overheads a few feet above the cymbals.  Don’t use too many mics at once on a kit if you want to avoid phase issues.

FRONT MIC – You can safely put a mic about three feet up in the air and about three to six feet in front of the kit and it will pick up a representative picture of the entire instrument.  It can be hard to “reassemble” the kit in the mix so that it seems like a single instrument.  This front mic may help mixed in low, if the inevitable phase issues can be ironed out, because it will also give you phase issues to deal with.  Be cautious in using it, and check in mono on a small speaker when mixing.  If you throw out all the other mic recordings of the kit and only use the one front mic, you can actually get an interesting sound, but it won’t be a normal drum sound with the tone and balance you expect on 99% of records.

BASS GUITAR – mic an amp with a large-diaphragm dynamic or condenser, witht he AKG D112 again being very popular.  You can also simply record a bass with a DI (direct injection) method straight into your DAW interface, preamp or mixer’s Instrument Input, not bothering with a mic at all.  In many cases, this is the best option anyway, especially with less aggressive types of music.  High sound pressure levels mean dynamics are usually the best choice.

UPRIGHT ACOUSTIC BASS – You could perhaps grab an upright bass track instead of a bass guitar DI, but it’s a bit harder to do since any nearby drums will easily “bleed” into the bass mic.  If you can use a pickup from the acoustic bass, do so!  It will be much simpler.  Most players have a pickup and will have an opinion about the sound they want.  Make a point of listening to them AND their instrument!  Even an SM57 dynamic can give you a pretty good bass sound (with not much low end, obviously) on smaller speakers, but it won’t give you any serious lows, so on bigger speakers it’s a less useful sound.  The first harmonics of all the acoustic bass range of notes should get picked up by an SM57, at least, though a few of the lowest fundamentals will get missed.   In big studios, they tend to use large-diaphragm condensers.  A vintage U47 is always quoted in books, but you try finding one.  Try finding two that sound the same, even.  And they would cost you a small fortune!  I’ve had great results from a modern Telefunken AK47, but they cost four figures themselves, so they are hardly typical home-studio fare.  Maybe a large condenser from Shure or ATK would be great, but I haven’t tried them.  A Rode NT-5 worked well for me the one time I tried one on acoustic bass.  They are small-diaphragm condensers, so they have great response, and are less touchy about off-axis sounds, but they aren’t as full-bodied as a large diaphragm might be.

GUITAR AMPS – Use SM57s or modern ribbons that use phantom power for a darker sound.  There are lots of other mics you could try, and almost all of them will sound cool on a guitar amp.  The sound pressure levels can get intense, so I wouldn’t use older “passive” ribbons.

ACOUSTIC GUITARS - I recommend tracking these later, after drums.  If you must play too, isolate yourself as best you can, and use a small diaphragm condenser 5 or 6 inches from the 12th fret, angled a little off-axis from the strings, and please don’t point at the soundhole, which is normally way too boomy.  The mic is a bit far away, so it might pick up lots of unwanted other instruments playing near you.

ACOUSTIC PIANO - A pair of condensers is typical, since stereo is helpful with a wide instrument like piano.  It’s also very cool to have a narrow point source of piano, in mono, panned to a spot in your stereo image where it sounds best and is not sharing the spotlight with any other sounds at that panning position.  Shure KSM44s are nice, and so are Neumann KM184s, and so are Rode or AKG or Sennheiser mics.  In a budget squeeze,  perhaps one or two AKG C1000 mics will help if you don’t need big lows in the sound.

Pianos sound great in various miking schemes, but obviously the further the instrument is from the mic, the more complete the instrument appears.  At the same time, more and more room sound and spill from other instruments appears.  So, it’s a trade-off.  I like the jazzy warm sound of a half-open lid on a baby grand, but you may well have an upright.  The bird-cage style of upright is hell to tune, and should be avoided.  Stick a mic or mics in the lid from the top, or at the back of the piano.  Watch out for pedal noises when placing mics.

GUIDE VOCAL – This is a nightmare if the drums leak in and you want to keep any of the guide.  It’s also a nightmare if the guide vocal leaks onto the other microphones and you are redoing the vocal later.  If possible, put the singer in another room where they can’t be heard except over the headphones.  The big problem here is that they generally need to see the drummer or at least one band member and vice versa for the band to see the singer go through the song.

Webcams, video cameras, tablets  and CCTV spring to mind as solutions for having to isolate performers in distant spaces that don’t view the studio floor area (your living room or basement, perhaps).  Blankets, quilts, gobos (homemade isolation dividers) can be handy in these situations.

A FEW LAST THOUGHTS

Phase problems arise with multi-miked drum recordings very readily, especially if you don’t consider microphone placement very carefully, in relation to other mics already placed.

The tips on this will be in my imminent post on Recording Drums.  As a rule of thumb, try to align mics to point mostly parallel to each other.

Another very helpful rule to follow is the 3:1 rule.  Keep mics picking up the same thing at least three times as far apart from each other as they are  distant from the source.  This rule prevents unwanted phase cancellations occurring between those mic signals when they are combined in a mix that is then collapsed to mono at some point and this rule saves you a lot of time later when you’re mixing.

More on all this soon.  Tomorrow I will discuss DI Boxes, Preamps and Line Conditioners before going into details on the various popular instruments one by one.  I’ll cover mic pickup patterns (polar patterns) as I go along in discussing placements.

See you tomorrow!

 

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