David Mellor - Mic Polar Patterns Part 1

So, David Mellor, Course Director of Audio Masterclass, how did you first get into audio? Thank you for that. That's Betty, my AI voice synthesized assistant, which shows us how far audio has come since I first got into it a long, long time ago. I'm David Mellor, Course Director of Audio Masterclass, and today I'd like to tell you all about polar patterns, starting with a piece of audio history, Then bring things up to date with audio. I recorded myself in Abbey road studio too. This podcast is part one of two parts. In this part, I'll play you one of my Abbey road demonstrations. Then in part two, I'll play all of them with my close analysis of what you'll hear. Cast your mind back, if you can, to a time before the Beatles had released their third album in the UK, A Hard Day's Night. An older relative of mine had bought a tape recorder. I saw it, heard it, and wanted it. Or one like it. So I invested my savings from my pocket money, best of my parents and grandparents to help out, and bought a Stellaphone ST458 reel to reel. Of course it was reel to reel. Cassettes hadn't been invented. I was hooked, and a few months later, impressed by my Stellaphone, another relative, my uncle, bought a whole hi fi system. No one had hi fi then. The sound of FM radio coming through what then seemed massively large speakers was astounding. And on his tape recorder, the superior, and stereo, Stellaphone ST 459, He would play his set of Emmy Guides, Emmy guides, released by EMI in 1961, which were a set of talks and demonstrations on audio narrated by John Boric, EMI. Electrical and Musical Industries, as you may know, was the owner of Abby Road Studios at the time, EMI, recording studios as they were. John Boric was senior lecturer in recording techniques at the University of Surrey when I started my tone meister degree course. One of these Emmy guide tapes fascinated me particularly, the one where John Borwick demonstrates the polar response of a microphone. Here it is, perhaps a little faded after more than 60 years. I'm standing in front of the ribbon microphone about two feet away, and I'm going to walk around it in a circle so that you can hear how it behaves at different angles. Now I'm moving around to the side, and I'm coming to the edge now, but I'll carry on, of course, until I reach towards the back of the microphone, where I should be at full volume again. Now, keeping on going, you should hear me passing across the other side position, where the microphone is very dead to sounds, and now back to where I started. So, Borek is walking around a ribbon microphone, which, like most ribbon microphones, is sensitive at the front, equally sensitive at the back, but completely insensitive, or rejecting, at the sides. What you hear when he's speaking from the sides is reverberation from the room getting into the front and back. So, if I wanted to identify the one thing that most influenced me to get into audio, this is it. I could go further with my one thing thought. What's the one thing that interests sound engineers and recording engineers most? I think that if I conducted a poll, that microphones would be that one thing. Choosing and using microphones will make more difference to whatever you're doing in audio than anything else. When you have an instrument, vocalist, or band to record or amplify, the first thing you'll do is choose your microphone, or microphones. And it's quite likely that the first thing you'll consider is the polar pattern. I'll just slip in here that most of this podcast will be based on practical issues. Where there's science stuff, I'll be taking as my primary reference the book, The Microphone Book, snappy title, by John Ergel. Unfortunately, the late John Ergel now But I can very much recommend it if you want to dive deeper into some elements of this podcast that I've simplified for practicality. Okay, what is this polar pattern thing? Well, we've heard a demonstration already, but I need to elaborate. The polar pattern of a microphone is its relative sensitivity in different directions. It can be called directional characteristics, directionality, I don't like that one, or maybe pickup pattern. I don't like that one either. Polar pattern or polar response work best for me. I like to think of the two golden rules of microphone positioning. Rule one is point the microphone at the sound source. Rule two, maybe I'll leave that for a future podcast. Rule one is what I'm interested in here. You have a sound source, an instrument or vocalist, point your microphone at it. Well, usually, but I'll get into possible complications later. Rule one nearly always applies. This makes sense because microphone designers and manufacturers optimize their microphones for sound quality. coming in head on. Why wouldn't they? If you have just one instrument or voice, it would make sense then to use a microphone that is only sensitive to the front. Unidirectional. Oh dear, I hate this term. Sure, a well known manufacturer of microphones. Says this, unidirectional microphones are most sensitive to sound arriving from one particular direction. By one particular direction, of course, they mean the front, or on axis. The problem with this, though, is that any reasonable person, who isn't yet familiar with microphones, would take this to mean that a unidirectional microphone is only sensitive to the front. This is just so not so. A unidirectional microphone is most sensitive at the front, but it is still very sensitive at angles, to the sides, to an extent round the back, and only fully rejecting at one or two particular angles. When I say one or two, I mean that literally, as we shall see, and hear. So if we take the cardioid microphone as an example, its sensitivity at 90 degrees to the side is only 6 decibels less than at the front. 6 decibels of off axis rejection, we can call that. Okay, 6 decibels is an audible difference. But in practical use, it absolutely cannot be ignored. 6TB, by the way, is the theory. In practice, of course, this will be an approximation. But both in theory and practice, this microphone is not, literally, unidirectional. Not in my interpretation of the King's English, anyway. So, that's it. Now that I've got that bee out of my bonnet, let's run through the various polar patterns that you'll meet out in the wild. The starting point for me is omnidirectional, which means equally sensitive all round, in theory. At the other end of the spectrum, and polar patterns are a spectrum, is figure of eight. This is sometimes called bi directional, but don't get me started on that. Figure of eight is what it says, and it's like John Borick's ribbon microphone. It's equally sensitive at the front and back. And it is equal in practice, not just theory. And as I said previously, the figure of eight is insensitive at the size with perfect rejection of sound coming from 90 and 270 degrees. If you try to visualize this, sound coming from the front or rear hits the diaphragm square on. Sound coming from the sides is edge on, and it's hardly going to bother a diaphragm that is microscopically thin. In some schools of thought, these are the classically perfect polar patterns. An omnidirectional microphone responds to sound pressure. A figure of eight microphone responds to the difference in pressure, or pressure gradient, between the front of the diaphragm and the back, which are both fully open to the air. We sometimes also hear of a pressure gradient microphone being described as a velocity microphone, because pressure gradient and velocity are proportional. In the Microphone Book, John Urgell describes this as being virtually proportional and at long wavelengths. So, I'll use the term pressure gradient going forward. A quick summary then in the omnidirectional microphone, the diaphragm is open to the air only at the front in the figure of eight microphone, the diaphragm is fully open to the air at both front and back. When I say that these two patterns are the classically perfect patterns, I could put it that the omnidirectional and figure of eight patterns are the pure breads of patterns. Anything else is a cross breeded, a half-blood. I'm sure there's a better way of saying this, but that's all I have for now. So what do we have in the category that I'm calling? crossbreed patterns. Well, I've mentioned cardioid already. So let's look at that. What we're talking about here is a microphone that has an element of pressure sensitivity and an element of pressure gradient sensitivity. In common usage, the cardioid and other crossbreed patterns are called pressure gradient, which technically isn't correct, since only the figure of eight is a true pressure gradient transducer. But it is common usage, so we can probably live with it. To get this balance between pressure and pressure gradient sensitivity, the diaphragm of the cardioid mic is partially open at the back. A cross between an omnidirectional mic where the rear of the diaphragm is fully enclosed, and a figure of eight where both sides are fully open. So in a cardioid microphone, the front, of course, will be fully open, and only some sound is allowed to enter at the back. You'll see this in a cardioid pencil mic, where there are openings behind the diaphragm that look a bit like the gill slits of a fish. There's a lot more theory to this, but once again, I'll refer you to the microphone book. As I hinted earlier, a true cardioid microphone is totally insensitive, or totally rejecting if you like, directly at the back. A polar plot of sensitivity would look like a heart shape, which, thanks to the wonder of the ancient Latin language, is where we get cardioid from. A cardioid microphone is directional in the sense that it's more sensitive at the front than any other angle. But in practical terms, it isn't all that directional. And we might like to have a microphone that's a bit more pointy. And so we have the hypercardioid, where more sound is let in at the back, making it more like the figure of eight. It's more pointy than the cardioid at the front, with the, perhaps, drawback of some pick up at the rear. The hypercardioid is fully rejecting at 110 degrees and 250 degrees, which is information that you'll find hard to make use of in practice. Unless you're doing live sound with those clunky, old fashioned wedge monitors. It's a school of thought that the null of a hypercardioid mic would fairly closely point at the wedge monitors on stage. Getting decent rejection here is important, as the last thing you want is feedback in the monitors. There's also the supercardioid, which is a kind of halfway house between the cardioid and hypercardioid. More pointy than the cardioid, less rear pickup than the hypercardioid. Let me just go back to the terminology pressure gradient for a moment. If you check out what should be authoritative sources, you'll find that some count velocity and pressure gradient as the same. Some don't mention velocity at all. Some mention velocity only in connection with ribbon mics. Some use pressure gradient to mean only figure of eight. Some say pressure gradient is anything other than omni. I'll nail my colours to this particular mast and say that omni is pressure sensitive, figure of eight is pressure gradient, in between patterns such as cardioid are a blend of pressure and pressure gradient. But common usage is often that cardioid, supercardioid, and hypercardioid are pressure gradient, and we can live with that. Now, I have something to tell you. Nothing's perfect. Any real world microphone, whatever its pattern nominally, is only an approximation of its mathematically ideal version. So, let's consider the omnidirectional microphone. It may be almost perfectly omni at 1 kHz, which is a nice frequency for manufacturers to publish their polar response charts, but at higher frequencies, the response usually tightens up and is tending more towards the subcardioid. Ha, I just threw another pattern in there. You can look it up. Similarly, a cardioid microphone may be an almost perfect heart shape But it will tend to be tighter at higher frequencies, and at the same time looser, more omni, at lower frequencies. It may seem that the world would be a better place if microphones could bring practice closer to theory, but every great recording you have ever heard has been made with microphones that don't match up to theory. And in some ways, less than perfect microphones can give you texture to play with. I'll give you an example told to me in person by Gordon Parry, one of the legendary Decca boys, from what some would say was the golden age of classical music recording. Briefly, Decca used a standardised method of recording called the Decca tree, or probably just the tree internally. This had two microphones spaced apart, with a third microphone in front. Left and right panned left and right, centre front panned centre. All of the mics were omni. So, if you read the textbooks and study the diagram, you might think you could get results comparable to Deca using any three omnidirectional mics. All three the same, of course. But, and this is the thing that Gordon Parry told me, the microphones Deca used back then were the Neumann M50, which is nominally omni. But it was the tightening of the polar pattern at high frequencies that really made the tree setup work. Okay, that's a story from the past, but my point is that whatever isn't perfect is texture. And texture is what sound engineers and recording engineers can use to their advantage. In this podcast, and in part two, I'm going to play you some examples demonstrating polar patterns. I have some crazy ideas sometimes, and one of them was to book Abbey Road Studio 2 to do this. Abbey Road Studio 2, where the Beatles made most of their great recordings. So, there I was, with a piece of string, some masking tape, and a large protractor I'd made previously. I marked out a circle with points at every 22. 5 degree increment. I'd like to think that I'm the only person ever to have done this at Abbey Road, but Who knows. For microphones, I use the Sher's Colette series, which I admire greatly. The Colette comes as an amplifier and interchangeable capsules of different polar patterns. So for omnidirectional, I use the MK two H capsule cardio, the MK four SuperCard, MK 41, and figure of eight. MK eight. There isn't unfortunately a HyperCard in this series, but we have enough to work with. In this part one of my two part podcast, I'll duplicate John Borick's demonstration using the figure of eight capsule. I'm going to recite a poem, getting most of the words right, and walk around the mic speaking at 22 and a half degree increments. Like the famous countdown clock, I could cover just the first 180 degrees, and we should learn all we need to know. But polar patterns go all the way around, so I will too. I wandered lonely as a cloud that floats on high o'er dale and hill. When all at once I saw a crowd, a host of golden daffodils. I wandered lonely as a cloud, that floats on high o'er dale and hill. When all at once I saw a crowd, a host of golden daffodils. I wandered lonely as a cloud, that floats on high o'er dale and hill. When all at once I saw a crowd, a host of golden daffodils. I wandered lonely as a cloud, that floats on high o'er dale and hill. When all at once I saw a crowd. A host of Golden DAF Tails. I wanted Lonely as a cloud that floats on high or Dale and Hill. When all at once I saw a crowd, a host of Golden DAF tails. I wanted Lonely as a cloud that floats on high or Dale and Hill. When all at once I saw a crowd, a host of Golden Dils. I wandered lonely as a cloud that floats on high or Dale and Hill. When all at once I saw a crowd. A host of golden daffodils. I wandered lonely as a cloud That floats on high o'er dale and hill When all at once I saw a crowd A host of golden daffodils I wandered lonely as a cloud That floats on high o'er dale and hill When all at once I saw a crowd A host of golden daffodils I wandered lonely as a cloud That floats on high o'er dale and hill When all at once I saw a crowd A host of golden daffodils. I wandered lonely as a cloud, That floats on high o'er dale and hill, When all at once I saw a crowd, A host of golden daffodils. I wandered lonely as a cloud, That floats on high o'er dale and hill, When all at once I saw a crowd, A host of golden daffodils. I wandered lonely as a cloud, of the floats on the line of the tail and tail. When all at once I saw a crowd, a host of golden daffodils. I wandered lonely as a cloud, that floats on high o'er dale and hill. When all at once I saw a crowd, a host of golden daffodils. I wandered lonely as a cloud, that floats on high o'er dale and hill. When all at once I saw a crowd, a host of golden daffodils. I wandered lonely as a cloud, you That floats on high or Darland Hill when all at once I saw a crowd, a host of Golden Daffodils. I wandered lonely as a cloud that floats on high or Dale and Hill, when all at once I saw a crowd, a host of Golden Daffodils. And so my tribute to John Boric confirms precisely his results from 1961. The sound is equally strong up front and rear, and there's nothing at the sides but the reverberation of the room. Total rejection of the direct sound of my voice, quite a rat. Demonstr random. You'll hear my demonstrations of all four polar patterns in part two of this podcast. I'm going to listen closely and tell you precisely what I hear in omnidirectional card, SuperCard, and figure of eight. And I'm also going to demonstrate metallic percussion, which will show you clearly that frequency response can differ a lot between on axis and off. This is the point where I should mention that there are such things as multi pattern microphones. A multi pattern microphone will have two cardioid diaphragms back to back in a dual capsule. I'm going to spare you, and me, the maths, but they can be combined together in various proportions to give any of the polar patterns I've mentioned. I should say that there are other ways to achieve multiple patterns. And if you're interested, you might look up as one example, the AKG C1000, which offers cardioid and hypercardioid patterns using an adapter. Some multi pattern microphones are continuously variable all the way from omni to figure of eight. Which I've already said is a spectrum. So if you can't decide whether to use hypercardioid or supercardioid, you can position the dial, which is usually on the power supply of a valve multi pattern mic, halfway between and get superdupercardioid. I made that up. The word, not the technique. Now that we know all about polar patterns, what are we going to use them for? I think it's fair to say that the most generally useful pattern is the cardioid, pointed at the sound source you want to amplify or record. It's as simple as this, you want to amplify or record an instrument or vocal, and you don't want to pick up anything else. Okay, the cardioid pattern still has a lot of pickup at every angle, other than directly at the rear, but the rejection is usually as good as we need. So the question becomes, why use anything other than the cardioid? One example I have is when I occasionally use my AKG C414EB to record my voice for my YouTube videos. It's a multi pattern microphone that does omni, cardioid, hypercardioid, and figure of eight. I get the least amount of room sound on hypercardioid, so I use that. For instruments or voices in a good acoustic environment, I might use ambience microphones in addition to my other mics. I could choose the omni directional pattern, seeing as ambience comes from all around. Having said that, I could use cardioids and point them away from the sound source. Again, breaking golden rule number one, you. but for the good reason that the balance between direct and reflected is now much more controllable. There is a school of thought that for acoustic instruments and ensembles, then the omnidirectional microphone has the purest sound, although clearly because of the lack of pointiness, if that's a word, it's going to require more skill and care from the engineer. Cardioid microphones are very useful for stereo as a coincident crossed pair, where the diaphragms of the mics are as close together as possible, one point's left and one point's right. Figure of eight microphones are good as a coincident crossed pair, too, although you have to bear in mind that the pair of mics are pointing just as much backwards as they are forwards. That in itself, though, can help in audio drama, as half the cast can be at the rear of the pair, and it will sound to the listener as as though they are in front. A word of warning though, that at the sides of the figure of eight crossed pair, the outputs are out of phase. Don't put anything you want to record there. And try not to worry that the ambience that comes in from the sides will be out of phase. What about the rear lobe of the hypercardioid microphone, or supercardioid to a lesser extent? Well, I used to do classical recording on a small scale with a small set of microphones. When I say small scale, it was usually for concert promoters to give copies to whoever they needed to curry favour with. Small scale in terms of pay, too, but not too bad. One time I found myself in the Royal Festival Hall on the South Bank in London with a small but unusual combination of instruments. I seemed to be one mic short for what I wanted, but then I realised I could use one of my multi pattern mics in hypercardioid, and with careful placing, I could cover two instruments reasonably well. I could have used a figure of eight, but on the day, the hypercardioid pattern gave me the best balance. The nulls of the cardioid and figure of eight patterns. You can point them at what you don't want to pick up. One classic example that's commonly quoted is the singing guitarist, where you can angle two figure of eight microphones so that one points towards the mouth and away from the guitar, and the other points towards the guitar and away from the mouth. Just tell the performer they'll have to be patient while you figure it out. Then of course, and I haven't mentioned this yet, directional microphones simply sound different to Omni when used close to the sound source. This is the proximity effect. I would like to explain why it happens, but seeing as it takes Shure on their website, 783 words and 13 diagrams, I think I'm going to swerve it. But look it up when you're thinking with a very clear head. Anyway, it happens and it's going to make your vocalist sound good because the proximity effect boosts the bass. Richer and smoother. You'd think you could imitate the proximity effect with EQ, but some things, in my opinion, are best captured in the microphone and can't be imitated fully by later tweaking. You might, however, prefer proximity effect less if you have a vocalist who uses microphone technique. Where they bob backwards and forwards according to how loud they're singing. Inevitably, the low frequency content will vary with the change in distance. But if it works, then go for it. Okay, coming to a close now. But I need to mention polar patterns outside of the normal spectrum of omni, cardioid, supercardioid, hypercardioid, and figure of eight. Obviously, there's nothing outside of this spectrum more omni than omni, and nothing more 80 than figure of eight. But microphones can be more directional than any of these, more pointy, to use again a word I've used earlier. What I'm talking about here would be the interference tube microphone and parabolic reflector mic. The parabolic reflector mic is very interesting, but it's probably best for wildlife and sports broadcasting. The interference tube mic, though, is commonly used in television and film. Putting this simply, there's a tube in front of the diaphragm through which on axis sound travels directly. Off axis sound enters through slots in the sides and cancels through interference of the waveforms. I'll direct you to the DPA website where they'll explain this for you in a concise 938 words and 5 diagrams, one of them animated. The great thing about the interference tube microphone is that it is, indeed, very pointy. And the longer the tube, the pointier it is. The drawback is that off axis sounds are not cancelled completely. Unlike the hypercardioid and supercardioid have a lobe of rear sensitivity, the interference tube has lobes. Multiple lobes of sensitivity at different angles. And whatever's coming in through the sides usually doesn't sound all that good. But we compromise. The directionality of the interference tube microphone usually outweighs any issues. And guess what? You're listening to an interference tube mic right now. My Sennheiser MKH416, which is widely used in film and TV production, in news reporting, anything where you really want to focus in on the sound source, and of course in YouTube and podcasting. I'm going to round off part one of my two part podcast with an exception to golden rule number one, which is point the microphone at the sound source. If you remember what I said earlier, microphone designers and manufacturers optimize their products for sound coming in from the front. They want the on axis response to be flat, or flattering. But you may find that you've pointed your favourite mic, or the last mic in your microphone drawer, at your vocalist or instrumentalist, and it doesn't sound quite the way you want it, possibly too bright. Of course, you experiment with positioning and distance, but there's one more trick you can try. And this goes back to a microphone's texture, off axis. Experiment by angling the microphone a little so that the sound is coming in slightly off axis, so that you get a different frequency response. This isn't a trick that will work every time, but it's worth knowing about, and, if you need it, worth a try. As I said, sometimes things are best captured in the microphone, rather than trying to tweak them later. I have a joke for you. Why didn't the Omni ask the Cardioid out on a date? I don't know. Why didn't the Omni ask the Cardioid out on a date? Because it couldn't handle the rejection. I'm David Mellor, course director of Audio Masterclass. Thank you for listening. Part two of this two part podcast coming up soon. Thank you for listening, and be sure to check out the show notes page for this episode, where you'll find further information, along with web links and details of all the other episodes. And just before you go, let me point you to the soundonsound.com/podcasts website page, where you can explore what's playing on our other channels.