How does diaphragm size/polar pattern relate to mic applications?

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I just wanted to welcome h kuhn to the board. I think you'll find some kick-ass infromation here, dude.

Also, while I'm here, we've been using our EV-235a as our harmonica pickup; it was "the leftover mic." The lack of proximity effect changes with this application, because Todd's hands are cupped around it. Together with an' old crappy solid-state Crate w/ lots of chorus and reverb (and gain), you can get a KILLER harmonica tone. Then it's a '57 into the board...

One more thing: I've noticed that cheap electronics often incorporate a condensor mic (remember those old tape recorders?). I figured for the price, they'd just put in dynamics... Are these real condensor-type mics?

(Dragon: interesting reply options. hope to see more interesting threads come of it)
 
Kelly Holdridge said:
I've noticed that cheap electronics often incorporate a condensor mic (remember those old tape recorders?). I figured for the price, they'd just put in dynamics... Are these real condensor-type mics?
Yes, they're small, cheap electret (pre-polarized) mics, usually available from Taiwan for around 15 or 20 cents each. Much easier to mass produce than a dynamic mic.
 
Flat Omnis...

Just another perspective on the flat omnis:

Many people want something that will make their voice or instrument sound "better" than it really sounds ...add "excitement", etc. The flat omnis DON'T do that.

BUT, if you have an instrument that DOES already sound good, the flat-omnis are much better at *capturing* that sound.

So I have come to recognizing the widely varying opinions regarding these as simply representing two different philosophies of recording. Some want the recording chain to be part of the "tone enhancement" system. Others want a transparent "capture system". I tried a lot of "highly recommended" mikes that sounded just horrible to me until I found and settled in with the E-Wks QTC1s.

If you are one of the people who keeps wondering why it is so hard to capture a good sound from an instrument you are happy with, they are definitely worth a try.

Peace,
Rick
 
A few more things to think about

OK, before we get into what mic to use for what purpose, and where to place it, here are a few more things you hafta be aware of. One is called "musical intrument radiation patterns" and the other is "near-field placement vs. far-field placement".

The most common question here is "how do I mic an acoustic guitar?", followed by vocal mic techniques. Let's look at the first question because it's more complex than it appears and it's actually made up of two parts.

Musical intrument radiation patterns

Guitars, violins, stringed instruments, in fact, all instruments radiate notes differently at different frequencies!! Read that again: Guitars, violins, stringed instruments, in fact, all instruments radiate notes differently at different frequencies!!

What does that mean exactly? It means that different parts of the instrument's body are used to produce different notes! Just pointing a mic at a guitar is no guarantee that you'll get what you want. Unless you understand how guitars generate sound, the best you can hope for is to somehow get lucky. Here are two links that show how the guitar top changes with each note:

Chladni guitar top radiation patterns

Radiation patterns

As you can see, different notes come from different places on a guitar, which brings us to the next section:

Near-field placement vs. far-field placement

Ok, so what the hell does that mean? Well, let's do a thought experiment to illustrate this concept:

Think of a tall column of speakers - about 6 feet tall, with woofers on the bottom, midrange speakers in the middle, and tweeters at the top. Now imagine that you walk right up to it and put your ear about 4" away from the system; what will you hear?

If you answered that it depends on whether your ear is near the tweeters, mids, or woofers, you're absolutely right. So where would you hafta stand to hear the whole system evenly balanced? At least 6 feet away is the correct answer - and that 6' away point is the boundry between the "near-field" and the "far-field" in this example. Any closer than 6 feet and you don't hear the whole sound, because you're in the "near field".

Now let's look at a typical acoustic guitar. The body is about 2 feet across. Put a mic any closer than 2 feet and you're in the "near field" of the guitar, and those two links I posted show you that you will be hearing uneven sound, depending on the note being played.

So, the first rule to remember is: "The near field distance is defined as being equal to the length of the longest part of the vibrating section of the istrument."

The second rule to remember is: "Inside the near field of an instrument, the sound will change drastically with different mic placements".

We'll get into mic choices, polar patterns, and mic placements in our next installment, but this "radiation pattern" and "near-field" vs. "far-field" stuff is really important to remember when you're trying to get a good instrumental sound.
 
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I just wanna chime in here and thank Harvey for taking the time to give us all of this information. I'm trying to absorb it all (which is tough, as my brain is fried from this semester in grad. school).

This is really great. I'm especially looking forward to the practical information, though I really appreciate learning the theory behind it. So far my mic placement, etc. has been through guesswork and trial and error, which isn't ALL bad, but I can't wait to have some guiding knowledge to help me know where to start.

Like I said, I just wanted to say thanks for the time and effort. It is VERY much appreciated. :)
 
KaBudokan said:
I just wanna chime in here and thank Harvey for taking the time to give us all of this information. I'm trying to absorb it all (which is tough, as my brain is fried from this semester in grad. school).

This is really great. I'm especially looking forward to the practical information, though I really appreciate learning the theory behind it. So far my mic placement, etc. has been through guesswork and trial and error, which isn't ALL bad, but I can't wait to have some guiding knowledge to help me know where to start.
Believe it or not, all the stuff we've been going over so far will become even more important when we get into mic placement, mic choices, and polar patterns under real operating conditions.

From what we've already learned, we can figure out what kind of mic to use if we want to accurately record that imaginary speaker column we just talked about, where to put the mic, and what the problems are going to be as far as trade-offs are concerned.

It's like learning a magic trick; once you know how and why, it becomes a lot simpler than it looks.
 
rjbutchko said:
Harvey, have you considered shopping around for a book deal?:cool:
Nope, believe it or not, I really like the idea of making all of this information available free to anybody that wants to learn it. When I first started, a lot of great engineers freely shared their knowledge with me - this is my way of paying them all back, by passing on what they taught me.
 
I would also like to chime in here with a huge thanks. Your time and effort are very much apreciated by yet another.

:)
 
Re: A few more things to think about

Harvey Gerst said:


If you answered that it depends on whether your ear is near the tweeters, mids, or woofers, you're absolutely right. So where would you hafta stand to hear the whole system evenly balanced? At least 6 feet away is the correct answer - and that 6' away point is the boundry between the "near-field" and the "far-field" in this example. Any closer than 6 feet and you don't hear the whole sound, because you're in the "near field".

This makes perfect sense, but it also brings up a couple of points for later if I'm understanding you right:

a) the person who is playing the instrument is in the near field, and if they're an accomplished musician it means that they've been practicing for years and years in the near field, which would mean that there's at least a decent chance that the person creating the music doesn't really know what the instrument really sounds like to someone else when they're playing it. And a microphone is the proverbial someone else in this situation. This might explain why many acoustic musicians become so confused/disconcerted when asked to wear phones in the studio....because they are accustomed to hearing only from a certain place in the near field and reacting to that, and all of a sudden someone has moved their "ears" to another location by making them wear headphones. Either that, or I'm making this sh*t up as a rationalization for why I hate recording with phones on.... it makes me feel as if I'm suddenly not playing the same instrument anymore.

b) If you get further away than 6 feet, you might be hearing "the whole sound", but you're also hearing more than that, because the further you move away from the sound source, the more your listening environment (i.e. - room or hall) is coloring your sound with reflections of some sort. So this is why the speakers mounted on either side of the desk in most studios are called "near field monitors", right?

Now let's look at a typical acoustic guitar. The body is about 2 feet across. Put a mic any closer than 2 feet and you're in the "near field" of the guitar, and those two links I posted show you that you will be hearing uneven sound, depending on the note being played.

So, the first rule to remember is: "The near field distance is defined as being equal to the length of the longest part of the vibrating section of the istrument."

A couple of questions related to (a) above:

For stringed instruments of the fretless variety, is the sound of the string vibrating on the fingerboard (i.e. - the "growl" of the low notes on a Double Bass) also part of this "near field distance", or do you only count the length of the body itself? I'm only asking because this would change the length of "near field" somewhat.

For a grand piano, do you count the length of the longest (bass) portion of the soundboard? And how do you decide whether to mic the top or bottom of it?

The second rule to remember is: "Inside the near field of an instrument, the sound will change drastically with different mic placements".


Gotcha. This is making more and more sense. Thanks.

We'll get into mic choices, polar patterns, and mic placements in our next installment, but this "radiation pattern" and "near-field" vs. "far-field" stuff is really important to remember when you're trying to get a good instrumental sound.


So any time you mic in the near field, you're really getting an incomplete sound, and if you use only one mic, or two or more mics placed more that about 5" apart, you're recording an "artificial" or "manufactured" sound since your ears could never pick up that sound in a natural acoustic setting. How would the "polar pattern" of a set of human ears be described using general microphone terminology? Stereo omnidirectional?

Thanks again for your time....this stuff is not only fascinating, but also addictive!
 
Near Field...

C7sus:
There is no sharp dividing line between the "near" and "far" fields. The differences just gradually fade into obscurity. That is why it is somewhat irrelevent what the length of the string is. The entire guitar body is always vibrating, including neck, headstock, strings, and body top, sides, and back..

My experience on acoustic guitar is that omnis sound more natural because they are more similar to the human ear, which is *closer* to omni than cardioid. They are also generally flatter (more accurate) in frequency response. If you move your head around in front of someone playing guitar, the tone does change somewhat, but it is not the same dramatic differences as when you move a cardioid mike around slightly (wild variations in tone).

Even well inside the "near field" (4 - 8 inches) an omni sounds much more natural than a cardioid. Then the S/N ratio problem is solved because the guitar is so much *relatively* louder than any other noise in the room. Having said that though, I keep my mikes about 14-18" out, because it does allow the sound to come together a little better.

An experiment is a very good thing on this phenomenon. Many people (myself included) have been virtually brainwashed into thinking that cardioid is the only way to go. A brief experiment with a good omni will blow your mind !

Rick
 
Wow, what a great thread this is turning out to be. I love to see the little lightbulbs turning on inside people's heads. I just got back from the doctor (I wound up with a very painful pinched sciatic nerve over the weekend), but as soon as the pain goes down, I'll answer each one of these wonderful and insightful posts in detail. Some great questions, gang.

BTW, Al Schmitt called me this morning to let me know he received the Marshall 603s and the V67Gs from Marshall. He's mainly mixing for the next two weeks so he won't have much chance to try them, but he promised he would try them as soon as he had a break and let me know what he thought of them, compared to his beloved Neumanns. He also mentioned that he too thought overall, the AT mics had a little too much hyped top end, which agrees with what I heard when I tried them.
 
Since the post on instrument length and near and far field I have recorded and acoustic guitar and a flute (audition tape for a high school band) with different and pleasant results - not sole ly micing so close to the instrument.

It is easier understanding how just this one little piece of information has helped.

Harvey, thanks so much for this thread and to the others for their questions asked of Harvey too.

Hope your sciatic settles down - mine is a problem too at times and it can sure hurt - good luck and thanks again!!!!

:D
 
Another concideration after looking at the resonance maps...

I would imagine that different instruments resonate differently- obviously- and we can easily here the different timbres of different accoustic instruments. Different guitars can even sound vastly different.

Question is do similar instruments project the same frequencies from the same areas? For example, do ALL guitars tend to sound basey in the same area?

Seems like this would be handy stuff to know when deciding where to start with near-field miking. I can also see that the different mike patterns will interact with different areas of sound projecting from the instrument...

I'm imagining a figure-8 pattern mike placed right between a guitar and a reflective wall that are 4 feet apart with the guitar facing the wall.

This is really neat stuff to think about! I'm looking forward to applying it. ;) (and seeing how well/poorly those ideas work!)

Take care,
Chris Shaeffer
 
Re: Re: A few more things to think about

Damn Chris, you sure do ask a lotta questions! :)

Originally posted by Chris F

Originally posted by Harvey Gerst
If you answered that it depends on whether your ear is near the tweeters, mids, or woofers, you're absolutely right. So where would you hafta stand to hear the whole system evenly balanced? At least 6 feet away is the correct answer - and that 6' away point is the boundry between the "near-field" and the "far-field" in this example. Any closer than 6 feet and you don't hear the whole sound, because you're in the "near field".


This makes perfect sense, but it also brings up a couple of points for later if I'm understanding you right:

a) the person who is playing the instrument is in the near field, and if they're an accomplished musician it means that they've been practicing for years and years in the near field, which would mean that there's at least a decent chance that the person creating the music doesn't really know what the instrument really sounds like to someone else when they're playing it. And a microphone is the proverbial someone else in this situation. This might explain why many acoustic musicians become so confused/disconcerted when asked to wear phones in the studio....because they are accustomed to hearing only from a certain place in the near field and reacting to that, and all of a sudden someone has moved their "ears" to another location by making them wear headphones. Either that, or I'm making this sh*t up as a rationalization for why I hate recording with phones on.... it makes me feel as if I'm suddenly not playing the same instrument anymore.

That's probably a part of it, and it also explains why a lot of guitarists like my over the shoulder technique of guitar miking.

b) If you get further away than 6 feet, you might be hearing "the whole sound", but you're also hearing more than that, because the further you move away from the sound source, the more your listening environment (i.e. - room or hall) is coloring your sound with reflections of some sort. So this is why the speakers mounted on either side of the desk in most studios are called "near field monitors", right?

Yes, as you move further back, more of the room comes into play. That's also when you start changing polar patterns to compensate, or to use more of the room sound (but that's all covered in the next installment). With regards to monitors, yes they are in "your" nearfield so you hear them before you hear any room reflections.

Now let's look at a typical acoustic guitar. The body is about 2 feet across. Put a mic any closer than 2 feet and you're in the "near field" of the guitar, and those two links I posted show you that you will be hearing uneven sound, depending on the note being played.

So, the first rule to remember is: "The near field distance is defined as being equal to the length of the longest part of the vibrating section of the istrument."


A couple of questions related to (a) above:

For stringed instruments of the fretless variety, is the sound of the string vibrating on the fingerboard (i.e. - the "growl" of the low notes on a Double Bass) also part of this "near field distance", or do you only count the length of the body itself? I'm only asking because this would change the length of "near field" somewhat.

Since the body accounts for the bulk of the instrument's radiating energy, I tend to just consider the widest part of the body itself, unless you're close-miking.

For a grand piano, do you count the length of the longest (bass) portion of the soundboard? And how do you decide whether to mic the top or bottom of it?

Piano is one of the hardest instruments to record and I planned to go into that in greater detail later. For now, I consider the widest dimension as the length, and I mic from out front if it's a solo instrument, or in close if it's to sit in a mix.

The second rule to remember is: "Inside the near field of an instrument, the sound will change drastically with different mic placements".

Gotcha. This is making more and more sense. Thanks.

We'll get into mic choices, polar patterns, and mic placements in our next installment, but this "radiation pattern" and "near-field" vs. "far-field" stuff is really important to remember when you're trying to get a good instrumental sound.

So any time you mic in the near field, you're really getting an incomplete sound, and if you use only one mic, or two or more mics placed more that about 5" apart, you're recording an "artificial" or "manufactured" sound since your ears could never pick up that sound in a natural acoustic setting. How would the "polar pattern" of a set of human ears be described using general microphone terminology? Stereo omnidirectional?

Yes, but that "artificial" or "manufactured" sound is not always bad, if it works better in the mix.
Ears are basically pressure transducers with increased directionality at higher frequencies.


Thanks again for your time....this stuff is not only fascinating, but also addictive.

It's a fascinating subject, and the more you learn, the more you realize how much more there is to go.
 
c7sus said:
What I wanna know is why the field of the instrument is the width (length?) of the body and not the length of the string..... which as you play changes constantly.....

Some people do use the whole string length to calculate the near field distance. I don't since the radiating area of the neck isn't bery big once you're out to the body distance. it adds a bit, just not that much, IMO

Now I may be getting way ahead of myself..... but if the field is 2 feet out from the front of my guitar, wouldn't I want to use the tightest pattern possible to capture just the sound of the instrument and not an omni that is gonna pick up the room..... then, since I'm 2 feet from my source, won't I start running into S/N problems......

Maybe time for a little experiment.....
Ahhh, the light is coming on. Yes, when you're out of the nearfield, you start thinking about other mic polar patterns. There's where you might wanna switch to larger diaphragm mics (remember condenser diaphragm size determines ouput level, all else being equal). But you give up some accuracy when you trade off to a larger size.
 
Re: Re: Re: A few more things to think about

Harvey Gerst said:
Damn Chris, you sure do ask a lotta questions! :)

Sorry, I get carried away sometimes....but you might be interested to know that I only do that with good teachers. I'm pretty silent around the crummy ones.


Piano is one of the hardest instruments to record and I planned to go into that in greater detail later. For now, I consider the widest dimension as the length, and I mic from out front if it's a solo instrument, or in close if it's to sit in a mix.

I'm very much looking forward to this, as the piano is a large part of many of the things I'll be recording.

..... "artificial" or "manufactured" sound is not always bad, if it works better in the mix.
Ears are basically pressure transducers with increased directionality at higher frequencies.


So as a musician who's learning to record, I should learn to "hear" from both perspectives. That is to say, I'm used to hearing the acoustic bass from above and slightly behind the body, so one option is to mic it from there (but then where am I gonna put my head???); another option is to experiment with mic placement, find a good sounding setup, and then practice with phones on while listening to what I'll be hearing from the mic's point of view. Hmmm, time for an experiment.

It's a fascinating subject, and the more you learn, the more you realize how much more there is to go.

Which can be said for almost all of life (not including television). I'll try to stick to one or two small questions per post in the future....I figure if you could have handed out the meaning of life in 20 words or less, you'd have done it by now. :cool:

Hope you feel better soon.
 
Chris Shaeffer said:
Another concideration after looking at the resonance maps...

I would imagine that different instruments resonate differently- obviously- and we can easily here the different timbres of different accoustic instruments. Different guitars can even sound vastly different.

Question is do similar instruments project the same frequencies from the same areas? For example, do ALL guitars tend to sound basey in the same area?


No they don't all radiate exactly the same, and that's what makes it so frustrating and individual - everything must be decided on a case by case basis. But there will be some similarities and that can help. Like the bass boom coming from the sound hole.

Seems like this would be handy stuff to know when deciding where to start with near-field miking. I can also see that the different mike patterns will interact with different areas of sound projecting from the instrument...

I'm imagining a figure-8 pattern mike placed right between a guitar and a reflective wall that are 4 feet apart with the guitar facing the wall.

This is really neat stuff to think about! I'm looking forward to applying it. ;) (and seeing how well/poorly those ideas work!)

Take care,
Chris Shaeffer
You hafta be very careful with figure 8 patterns, since it's impossible to predict easily whether the reflections from a hard surface will help or cancel some other critical frequencies. But we'll get into that in the next installment.
 
Chapter 8 - Fortress Of Doom

Ok, one more quick review and we're off into placement and mic choice land:

1. Small mics generally tend to be more accurate than large mics. Large mics are generally more flattering than small mics.

2. Omni mics generally have the greatest accuracy but the smaller most accurate omnis have a higher self-noise level, but they can handle higher SPLs as well.

3. Pressure gradient mics (cardioid, hyper-cardioid, and figure 8) use delayed sound coming into the backside of the diaphragm to create their patterns.

Any mic can be used to record any sound

Think about that for a minute. A mic doesn't care what it's recording, but some mics are better suited for certain things. If you don't have the one "perfect" mic for the job, any mic will work, with some trade-offs in sound quality. Understanding what those "trade-offs" are is the hard part.

How does this part fit into the song?

Does it need to be miked in stereo or will mono work? Is it gonna be an upfront part or does it hafta blend in? Is there another instrument operating in the same frequency range that might cause a conflict? The right choice of mics can help in all these situations, but you hafta make sure BEFORE you set up any mics just exactly what it is that you hope to accomplish. Here is how I think about where a part fits in:

soundstg.gif


Notice there are 3 important elements to this box:

1. Panning (Left to Right) - Very useful for separating instruments that occupy the same frequency range.

2. Level (Front to Back) - In combination with reverb, this creates the illusion of near and far, and can also seperate instruments in the same range.

3. Frequency (Lo to Hi) - the most overlooked aspect of getting a good blend when you're first starting out. Most people solo a track and then work to get a killer sound (bass, guitar, whatever), then move on to the next track. Wrong way to think. Instead, think about the song; which instrument should cover the bottom octave, electric bass or kick drum? If it's the kick, roll off some of the bottom on the electric bass and listen to make sure the two instruments aren't fighting for the same space.

Is the vocal important? Put it in the center, right up front. Are the guitars conflicting with the vocal? Move them out of the way with the pan control.

But what if it's just a solo guitar or piano track? Ahhh, there's where you need to decide if a stereo recording would be best. If it's an acompaniment to a vocal, a stereo recorded guitar or piano can sound very nice contrasted with a mono vocal.

Sorry this has turned into a rambling diatribe, but these are things that people tend to overlook in their haste to record stuff. But it's exactly this stuff that determines what mic, polar pattern, and placement you should be using - before you even plug in the first mic. We'll cover exactly that part next - I promise.
 
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