Design/mechanics question about condenser mics

[Harvey Gerst]

I'm not entirely sure, I can't base an answer on experience as I've never done anything like that before.

Based on my "scientific knowledge", I would assume that as the bass boom is mainly coming from the body (rear and behind the mic), it shouldn't really be picked up.

You want the string sound, so I'm guessing by pointing the mic at the strings, it should pick up just that (being cardioid).

Okay, everybody take a deep breath and let's think this thing through. Go to Shure's website and take a careful look at the first polar response chart for the SM57 or 58. Find the line that represents 125 Hz and notice the rear level is only down about 10 or 11 dB compared to the front level. Now, think about this:

How loud would the string be if it was fastened to a log and plucked? Next, how loud is the sound coming out of the sound hole (when the whole top of the guitar is moving at that note and forcing air out of the whole chamber)? Think the string by itself is only 11 dB from the sound hole level? If so, you would still get equal levels into the mic. News flash: The output of the string by itself is far lower than that.

Bottom line: the string output is far smaller than the output of the guitar top or the guitar sound hole. That's why acoustic guitars need that big top and the large internal air volume.

 

[philbagg]

Bottom line: the string output is far smaller than the output of the guitar top or the guitar sound hole. That's why acoustic guitars need that big top and the large internal air volume.

Listen to this guy, forget what I said
Never looked at it like that, nice work

EDIT: On second thought, the body is amplifying the string sound yes?
I know it also adds some undertones etc. But (just a thought), if you're just
going for the strings on their own, can they not be artificially amplified once
recorded?

Or how would it work to put an omnidirectional mic in there? No proximity
effect?

 

[Tuneful]

Okay, everybody take a deep breath and let's think this thing through. Go to Shure's website and take a careful look at the first polar response chart for the SM57 or 58. Find the line that represents 125 Hz and notice the rear level is only down about 10 or 11 dB compared to the front level. Now, think about this:

How loud would the string be if it was fastened to a log and plucked? Next, how loud is the sound coming out of the sound hole (when the whole top of the guitar is moving at that note and forcing air out of the whole chamber)? Think the string by itself is only 11 dB from the sound hole level? If so, you would still get equal levels into the mic. News flash: The output of the string by itself is far lower than that.

Bottom line: the string output is far smaller than the output of the guitar top or the guitar sound hole. That's why acoustic guitars need that big top and the large internal air volume.

I bet if you made a small foam cover, slightly wider than the fretboard and the full length of the strings, then strummed the strings and put it over them, you would hear nothing even resembling the sound that normally comes off of the guitar.

The body gives you mostly bass, the strings give you the treble and bass.

The soundhole on a guitar is tuned, much like a speaker port is, to a very low frequency.

 

[Tuneful]

Listen to this guy, forget what I said
Never looked at it like that, nice work

EDIT: On second thought, the body is amplifying the string sound yes?
I know it also adds some undertones etc. But (just a thought), if you're just
going for the strings on their own, can they not be artificially amplified once
recorded?

Or how would it work to put an omnidirectional mic in there? No proximity
effect?

Well i'm definitely going to go with omni mics now that I know how the cardioid mic would work in that situation.

 

[Harvey Gerst]

I bet if you made a small foam cover, slightly wider than the fretboard and the full length of the strings, then strummed the strings and put it over them, you would hear nothing even resembling the sound that normally comes off of the guitar.

The body gives you mostly bass, the strings give you the treble and bass.

The soundhole on a guitar is tuned, much like a speaker port is, to a very low frequency.

You really still don't get it, do you?

The strings are like a voice coil, moving back and forth, but producing very little sound on their own. It's only when the strings are connected to to the flexible top of the guitar and transmitting those vibrations into the top, through the bridge, that you actually hear the sounds at a reasonable volume. Both highs and lows.

Yes, the cavity and port are used to boost the bottom end, but it's the vibrating top you hear that is producing the sound, like adding a cone to the voice coil.

 

[Tuneful]

You really still don't get it, do you?

The strings are like a voice coil, moving back and forth, but producing very little sound on their own. It's only when the strings are connected to to the flexible top of the guitar and transmitting those vibrations into the top, through the bridge, that you actually hear the sounds at a reasonable volume. Both highs and lows.

Yes, the cavity and port are used to boost the bottom end, but it's the vibrating top you hear that is producing the sound, like adding a cone to the voice coil.

Rubbish.

The strings in fact, put out plenty of sound by themselves.
If you had ever heard one of the neck-only practice guitars, you would know this.
And it's not the "vibrating top" that produces the highs, it's the wave form that forms "across" the top that when added to the direct sound of the strings gives you all your highs.
It's an entirely distinct difference between vibrating top, and a wave form across the top.
There's a reason that a tweeter diaphragm is only a couple of grams or less. It's because it wouldn't be capable of producing the highs otherwise.
And neither is the vibrations in the wood of the acoustic body or top.

Everyone seems to accept the example that by putting your hand on the soundboard and hearing less sound that you in fact prove that's where all the sound comes from.
But the obvious example, that covering up the strings will do much more harm to the sound isn't valid?

 

[mshilarious]

Rubbish.

Tomorrow I will take a drill press to one of my guitars and mount microphones in and around it. That will take me less time (probably a half hour) than you've wasted of all of ours being apparently incapable of performing the experiment yourself.

 

[Tuneful]

Tomorrow I will take a drill press to one of my guitars and mount microphones in and around it. That will take me less time (probably a half hour) than you've wasted of all of ours being apparently incapable of performing the experiment yourself.

But if you want to do an experiment that is going to any statistical validity, you need to mount a set of strings to a bridge and nut that are mounted to a piece of granite, the exact same size as a guitar.

From that signal source, you would have to do a frequency analysis as well as sound level.

Then and only then would you know the bulk of high frequencies come from the surface of the guitar along with the direct radiated sound from the strings.

I would love to see this ran by a Joseph D'Applito.
Joe would no doubt want to use tone woods for the tweeter diaphragms of his next speaker design.

 

[Chili]

The strings in fact, put out plenty of sound by themselves.

So, why doesn't electric guitars put out much sound when unplugged from an amp? I'm strumming on mine right now. It ain't very loud.

 

[Tuneful]

In all seriousness, I think there's not a single person making your argument that has any sense of frequency at all.

What passes for midrange by the numbers, is in fact fairly high frequencies.

Get a tone generator, and play the relatively low tone of 800hz.
I'm guessing that many of you will be surprised at how high that tone is.

In short, you would realize that the volume that actually comes from the soundhole as well as the actual vibrations in the wood of the body, are quite simply the lower register that the guitar produces.

If you looked at this from a logical point of view, you would realize that that is the beauty of the balance in an acoustic guitar.

 

[Tuneful]

So, why doesn't electric guitars put out much sound when unplugged from an amp? I'm strumming on mine right now. It ain't very loud.

You mean it ain't very loud in the lower registers.

I never said the acoustic body doesn't produce volume. Only that it doesn't produce much highs.
There's some bass that's produced by the strings, and there's some highs produces by the body cavity.

 

[mshilarious]

In all seriousness, I think there's not a single person making your argument that has any sense of frequency at all.

Why don't you look into the people who were (past tense) trying to help you? You might be surprised at what they know. Did you think I was kidding when I pointed out my experience with microphones? How about Harvey, why don't you Google him? Or just read his big thread; had you done that you could have spared us most of this thread.

What passes for midrange by the numbers, is in fact fairly high frequencies.

That's a nonsensical statement. High frequency is >8kHz. Midrange is say 200Hz to 2kHz--the fundamental tones and first overtones of a normal melodic range. Between the two is usually considered "presence". Sure, plenty of high frequencies come from the strings, but that's hardly a balanced tone because it lacks the fundamentals and low overtones in the ratio that the guitar naturally produces. I have never argued otherwise.

Ask yourself this: why is the standard studio technique for stereo micing an acoustic guitar to put one mic at the 12th fret AND one mic at the lower bout? Why is the soundhole almost never selected?

Get a tone generator, and play the relatively low tone of 800hz.
I'm guessing that many of you will be surprised at how high that tone is.

I'm guessing you're wrong, because I listen to test tones nearly every day.

In short, you would realize that the volume that actually comes from the soundhole as well as the actual vibrations in the wood of the body, are quite simply the lower register that the guitar produces.

Please answer this question: have you performed the very simple experiments I have repeatedly mentioned in this thread (regarding putting your ear at various places on your guitar, never mind the cardioid microphone demonstration I had to do for you)? Please answer that question directly and honestly with a yes or no. If you cannot answer that question in your next post, then my post with the results of the microphone experiment will be my last post in this thread.

Again, an experiment: playing an open high E string while moving your ear at a distance of 1" from the guitar from the 7th fret down to the soundhole and then to the bridge and finally the endpin. Where is the sound loudest and most balanced?

If you looked at this from a logical point of view, you would realize that that is the beauty of the balance in an acoustic guitar.

Yes, and you wish to ignore that balance by close-micing the strings and soundhole.

You see, there is "logic", which you take to mean thinking normatively without respect to evidence, and then there is science, which involves testing your hypotheses in a controlled experiment. You're a bit weak on the latter, and your logic is compromised by faulty major premises which cause your deductive reasoning to fail.

 

[XLR]

In all seriousness, I think there's not a single person making your argument that has any sense of frequency at all.

What passes for midrange by the numbers, is in fact fairly high frequencies.

Get a tone generator, and play the relatively low tone of 800hz.
I'm guessing that many of you will be surprised at how high that tone is.

In short, you would realize that...

Wow, I can't even remember the last time I gave negative rep.

 

[Harvey Gerst]

Rubbish.

The strings in fact, put out plenty of sound by themselves.
If you had ever heard one of the neck-only practice guitars, you would know this.
And it's not the "vibrating top" that produces the highs, it's the wave form that forms "across" the top that when added to the direct sound of the strings gives you all your highs.
It's an entirely distinct difference between vibrating top, and a wave form across the top.
There's a reason that a tweeter diaphragm is only a couple of grams or less. It's because it wouldn't be capable of producing the highs otherwise.
And neither is the vibrations in the wood of the acoustic body or top.

Everyone seems to accept the example that by putting your hand on the soundboard and hearing less sound that you in fact prove that's where all the sound comes from.
But the obvious example, that covering up the strings will do much more harm to the sound isn't valid?

I can see that you've pretty well made up your mind on this subject, so any further arguments I might make will go unheeded, or challenged. It's pointless for me to continue in this thread. Sorry to have interrupted the thread with my "speculations".

But, I would be curious to hear the "wave form that forms across the top" of a piece of 3 foot, 1" thick granite and the strings.

 

[PhilGood]

Rubbish.

The strings in fact, put out plenty of sound by themselves.
If you had ever heard one of the neck-only practice guitars, you would know this.
And it's not the "vibrating top" that produces the highs, it's the wave form that forms "across" the top that when added to the direct sound of the strings gives you all your highs.
It's an entirely distinct difference between vibrating top, and a wave form across the top.
There's a reason that a tweeter diaphragm is only a couple of grams or less. It's because it wouldn't be capable of producing the highs otherwise.
And neither is the vibrations in the wood of the acoustic body or top.

Everyone seems to accept the example that by putting your hand on the soundboard and hearing less sound that you in fact prove that's where all the sound comes from.
But the obvious example, that covering up the strings will do much more harm to the sound isn't valid?

WHAT?!


Oh my God!! Where did you pull that out of?

 

[darrin_h2000]

I was wondering why my Bow and arrow was so loud it scared every animal in the forest

 

[Tuneful]

Why don't you look into the people who were (past tense) trying to help you? You might be surprised at what they know. Did you think I was kidding when I pointed out my experience with microphones? How about Harvey, why don't you Google him? Or just read his big thread; had you done that you could have spared us most of this thread.



That's a nonsensical statement. High frequency is >8kHz. Midrange is say 200Hz to 2kHz--the fundamental tones and first overtones of a normal melodic range. Between the two is usually considered "presence". Sure, plenty of high frequencies come from the strings, but that's hardly a balanced tone because it lacks the fundamentals and low overtones in the ratio that the guitar naturally produces. I have never argued otherwise.

Ask yourself this: why is the standard studio technique for stereo micing an acoustic guitar to put one mic at the 12th fret AND one mic at the lower bout? Why is the soundhole almost never selected?



I'm guessing you're wrong, because I listen to test tones nearly every day.



Please answer this question: have you performed the very simple experiments I have repeatedly mentioned in this thread (regarding putting your ear at various places on your guitar, never mind the cardioid microphone demonstration I had to do for you)? Please answer that question directly and honestly with a yes or no. If you cannot answer that question in your next post, then my post with the results of the microphone experiment will be my last post in this thread.

Again, an experiment: playing an open high E string while moving your ear at a distance of 1" from the guitar from the 7th fret down to the soundhole and then to the bridge and finally the endpin. Where is the sound loudest and most balanced?



Yes, and you wish to ignore that balance by close-micing the strings and soundhole.

You see, there is "logic", which you take to mean thinking normatively without respect to evidence, and then there is science, which involves testing your hypotheses in a controlled experiment. You're a bit weak on the latter, and your logic is compromised by faulty major premises which cause your deductive reasoning to fail.

See, now you're the one who doesn't get it.
I know what midrange is by the numbers.
What i'm telling you, and you clearly and absolutely do not get, is that an 800hz tone is actually a fairly high frequency. Why don't you be the person in this instance that tries what I said to.

I don't know whatever gave you the idea that I've never put my hand over a soundhole, or pushed on the bridge, or soundboard, but that's not even acoustics 101. That's kindergarten. And it's insulting the way you guys seem to think you know more about acoustics than I do.
Because you clearly don't. You know one hell of a lot about microphone capsules, and electronics in general. That's fairly obvious.
But I freaking OWN acoustics. PERIOD.

Take a goddam set of acoustic strings and put it on a freaking stick and strum it.
It will be louder than any of you knuckleheads thought it would be.
The example of electric guitar strings not being very loud only proves that electric guitar strings are not very loud.
Put an .012 set of Martin acoustic strings on that guitar and then do it.
I'VE DONE THAT.

Every single person who's arguing this mumbo jubmo about the body producing highs, needs to quit while they're behind, because by now you should all be embarrassed about saying such retarded things.

Can you put a mic in the dead center space of air underneath the soundboard and measure highs? Yeah. Duh. The strings are sitting right on top of a big hole in the soundboard, so the highs are going to get inside the body.

But does the body itself vibrate fast enough to produce the highs that you actually hear?
Not a chance.

Now at this point it almost seems like you people are pulling my chain, because no one with any clue whatsoever of acoustics, would make such moronic claims.

Enjoy your retarded board.

 

[XLR]

A prayer...

God, please grant me the ability to give neg rep to someone twice in a row.

/tries again/

Damn.

 

[mshilarious]

See, now you're the one who doesn't get it.
I know what midrange is by the numbers.
What i'm telling you, and you clearly and absolutely do not get, is that an 800hz tone is actually a fairly high frequency. Why don't you be the person in this instance that tries what I said to.

BECAUSE I LISTEN TO 1KHZ (and several other frequencies) TONES NEARLY EVERY DAY OF MY LIFE, BECAUSE I DESIGN AND SELL MICROPHONES (and amplifiers) FOR A LIVING.

There, shouting felt good

I don't know whatever gave you the idea that I've never put my hand over a soundhole, or pushed on the bridge, or soundboard, but that's not even acoustics 101. That's kindergarten.

Not your hand, YOUR EAR. Listen!

And it's insulting the way you guys seem to think you know more about acoustics than I do.

I only know the basics of acoustics. Harvey knows more than you do. So does muttley. You are unfortunate muttley hasn't visited this thread, because he builds guitars for a living and also lectures in physics. He can tell you at a very detailed level how guitar acoustics work.

But this issue is so, so, simple that a PhD in physics is not required to grasp it. Just a simple experiment. I have already drilled the hole; I need to build a couple more mics. I have a lot of other work to do, so it will probably be later tonight.

The bottom line is you have a board full of subject-matter experts that you choose to ignore because our considered advice doesn't fit the foreordained conclusion you have drawn.

Remember my basic advice: you don't want three microphones when one will do. Sound reinforcement 101. You don't want to mic a soundhole; it's too bassy. You don't want to only mic the strings, that is not the full-range tone of the guitar. The best place to put a single microphone is on the soundboard of the guitar. It doesn't have to be close to the strings, although it can be moved around to taste.

Will a soundhole or string mic work? Yes, but they will require substantial EQ correction and still sound less natural than a soundboard mic (which would only require EQ to the extent that stage volume demands ringing out). Does it make a difference to a live audience? Of course not, they couldn't care less if you only used a piezo. But by that token, neither is there a need to create a three-capsule system.

You know one hell of a lot about microphone capsules, and electronics in general. That's fairly obvious.

Actually I only know enough to get by. A talented EE or simply seasoned circuit designer can run rings around me. But I could build your circuit in less than an hour, it's child's play really. Basic buffers, single or double pole filters, summing amplifiers.

But I freaking OWN acoustics. PERIOD.

That's laughable.

Take a goddam set of acoustic strings and put it on a freaking stick and strum it.
It will be louder than any of you knuckleheads thought it would be.

No, it will be as quiet as I think it will be, because I've already done my listening experiment. When I put my ear near the seventh fret and strum all open strings, nearly all of the sound I perceive comes from the body of the guitar and none from the neck. Therefore I know that the sound from the strings must be at least 10dB quieter than the sound from the top. This I can and will verify with measurement later tonight.

The example of electric guitar strings not being very loud only proves that electric guitar strings are not very loud.
Put an .012 set of Martin acoustic strings on that guitar and then do it.
I'VE DONE THAT.

The difference is an increase in tension. muttley could give exacts, but I'll bet the difference is not 10dB (which is a mere factor of 3-ish). It should not be a material difference; akin to tuning up a step which does not produce a 10dB increase in volume. That's just my guess though. How loud have you measured the difference in volume?

Enjoy your retarded board.

I shall!

 

[Harvey Gerst]

Deleted, sorry.