Design/mechanics question about condenser mics

[Tuneful]

Having dabbled a bit myself in speaker design and building, I agree that the subject of speaker building is not related to your questions, but the concepts I quoted are. The sound of a guitar comes from two places:

1. A specific area of the guitar top, depending on the note frequency.
2. The body volume and port, which acts like an amplifier for low frequencies.

Speaker cabinets are generally designed for stiffness and freedom from spurious resonances, caused by vibrating cabinet walls. Only the speaker should move, and the air inside the cabinet, tuned by the port.

The strings are most similar to a speaker voice coil, while the guitar top would be more accurately compared to the function of a speaker cone. Removing the speaker cone and just miking the output of a voice coil wouldn't be too useful.

Let me correct where I was coming from in my statement, as I can see how it came across.

It's not that acoustics themselves do not pertain here. This is quite precisely all about acoustics.
But I do understand fairly well how a wave form develops, and so having the mics in the center of that would actually be quite sound, no pun intended.

And look, I did mention that i'm open to suggestions.

What I hoped for out of this thread was to find out one thing and one thing only. Could a cardioid capsule in between two omnis, become overwhelmed with boominess if place in the center edge of the soundhole.

I'm stubborn about the idea being sound, but not necessarily about it being the best idea to run with.

Believe it or not, lol, I actually fantasized about this being a two response thread, and I was going to start my next thread about getting suggestions.

 

[mshilarious]

Having dabbled a bit myself in speaker design and building

Classic I love Harvey!

 

[Tuneful]

Yeah? You ever design a speaker that Hendrix used?

Seriously, I don't get you. Sure, an electret capsule costs $0.25, but not at Radio Shack, they charge $2.99. The better capsules cost $1-$2 in quantities of 500, but you probably don't want 500, so figure $2-$3. For your purpose, I would try Panasonic WM64PNT, which would be relatively easy to flush-mount in a fingerboard. I would further load it with the high-shelf cut circuit I drew, because otherwise it will be way too bright.

So if you want to save money on the capsule, why buy a commercial preamp? Markup is the same there. The difference is the engineering of the circuit which was probably done with the limitations of the capsule and the placement in mind.

Anyway, enjoy your project, however it turns out you will probably declare it a success irrespective of how it actually sounds. You have to understand that Baggs' market is based more upon appearance and convenience than the best possible quality sound. And I think your goal of avoiding EQ is very naive. The simple filter circuits I dropped in that schemo are likely not even close to sufficient, just enough to not totally sound like poo.

Again, take your RS capsule and tape it to your soundboard. Try to beat the quality of that sound with whatever other arrangement you can think of. My money's on RS.

My only issue with building the pre-amp will be time.
My last project that I built was a pair of Dynaudio monitors, maybe 5 years ago. I'm rusty. I can follow a schematic, but I know how slow i'll be.

So depending on the price point...

Let me put this another way... Say I logon to the Baggs site today, or Shadow, or Graphtech, however. And they got a new mic setup that is 3 small condensors, all black powder coated and looking awesome. With a set of Piezo saddles. With the pre-amp, made to balance everything nice and easy. And say that setup was $200. I'd probably whip out the credit card.
The problem is, that all of this stuff would be much more than that.
So that's the break point to me. Too much and i'll build it myself. Right at the maximum of my budget though, and I'll go with it.

And this brings up another question that I appreciate if you'll advise me on, that i'll post separately in a minute.

 

[mshilarious]

Let me correct where I was coming from in my statement, as I can see how it came across.

It's not that acoustics themselves do not pertain here. This is quite precisely all about acoustics.
But I do understand fairly well how a wave form develops, and so having the mics in the center of that would actually be quite sound, no pun intended.

Neither the fingerboard nor the soundhole is the center of where the sound develops. You keep thinking a guitar is a point source; I have no idea why. Did you do the experiment with putting your ear different places and listening? Where does the guitar sound best? That's where you put the microphone. Anywhere else is suboptimal and will require a capsule design with an offsetting frequency response or a filter circuit.

 

[darrin_h2000]

You never say you love me

I wanna go out on a limb and explore the possiblity of trying a nice SDC mounted below the bridge and hard wired into the instruments preamp...then tell us what you think it sounds like.

 

[Harvey Gerst]

What I hoped for out of this thread was to find out one thing and one thing only. Could a cardioid capsule in between two omnis, become overwhelmed with boominess if place in the center edge of the soundhole.

An omni mic is a pure pressure device and responds ONLY to changes in air pressure. A cardioid mic is a "pressure gradient" mic and responds more to velocity up close. Strings alone don't move much air (either in terms of pressure or velocity), so where do you think the sound in a port would fit into this equation?

So the answer is yes, a cardioid capsule placed between two omnis, would become overwhelmed with boominess if place in the center edge of the soundhole.

 

[Tuneful]

When it comes to the mic capsules, I did a lot of digging around for different sizes, types, etc.

One thing I found was that say you look at this one here, it seems to have some really fantastic specs.
But I never seem to find the capsules separately from anyone, with specs as good as that.

What's the real deal with that? Do the companies like Takstar simply fudge the numbers? Or is it maybe that they use better capsules?

Now I've read plenty about now the RS capsules are actually really decent.
And in my own experience, I got a lapel mic from them, plugged it into my soundcard and was pleasantly surprised at how good the sound was. So yeah, I can see where they really are decent. But if i'm going to go through all this trouble, I like to take into consideration every option I have.

 

[Tuneful]

Neither the fingerboard nor the soundhole is the center of where the sound develops. You keep thinking a guitar is a point source; I have no idea why. Did you do the experiment with putting your ear different places and listening? Where does the guitar sound best? That's where you put the microphone. Anywhere else is suboptimal and will require a capsule design with an offsetting frequency response or a filter circuit.

I think I did point out why I was doing that. It's to add a through-the-mic string sound to the piezos. Eq the top off of the piezos and blend in the electrets.
So therefore, the best spot for the electrets to get the string sound is right near the strings, no?
For one thing, I can use less gain with less chance of feedback that way.

 

[Harvey Gerst]

With the single exception of a single diaphragm, small size omni mics, all other mic capsule designs depend greatly on the overall effect of the grill housing and many other factors. A measurement of just the capsule in those designs would be meaningless, except to a microphone designer.

 

[Tuneful]

You never say you love me

I wanna go out on a limb and explore the possiblity of trying a nice SDC mounted below the bridge and hard wired into the instruments preamp...then tell us what you think it sounds like.

I originally wanted to do that, but read a few comments about that not being so hot. I dunno. It made perfect sense to me.
I was actually going to just get a pair of goosenecks and put one under the bridge, and one up in the corner of the upper bout. (edit* attached to the rear bracing so as to not effect the soundboard vibrations)

 

[mshilarious]

When it comes to the mic capsules, I did a lot of digging around for different sizes, types, etc.

One thing I found was that say you look at this one here, it seems to have some really fantastic specs.
But I never seem to find the capsules separately from anyone, with specs as good as that.

What's the real deal with that? Do the companies like Takstar simply fudge the numbers? Or is it maybe that they use better capsules?

What specs are you referring to? More importantly, what specs do you think you need? Capsule quality doesn't show up in a spec.

When you are talking tiny capsules, Panasonic makes the best commonly available. They don't make a huge variety, but you don't really need anything unusual.

I assume you aren't talking 1/2" cardioid capsules like you'd find on Takstar and those types. Many of those aren't even electret, so you'd need a high-voltage bias source.

 

[Tuneful]

An omni mic is a pure pressure device and responds ONLY to changes in air pressure. A cardioid mic is a "pressure gradient" mic and responds more to velocity up close. Strings alone don't move much air (either in terms of pressure or velocity), so where do you think the sound in a port would fit into this equation?

So the answer is yes, a cardioid capsule placed between two omnis, would become overwhelmed with boominess if place in the center edge of the soundhole.

Right. That's why (I think) we're all talking about omnis now.

 

[Tuneful]

What specs are you referring to? More importantly, what specs do you think you need? Capsule quality doesn't show up in a spec.

When you are talking tiny capsules, Panasonic makes the best commonly available. They don't make a huge variety, but you don't really need anything unusual.

I assume you aren't talking 1/2" cardioid capsules like you'd find on Takstar and those types. Many of those aren't even electret, so you'd need a high-voltage bias source.

Well like the self noise, frequency response, dynamic range, that sort of thing. The separates seem to list fairly toned down specs.

And to make matters worse, if you go to the Panasonic website, their own specs are modest in comparison to what other people attribute to those capsules.
Panasonic lists them as something like 50hz to 16k.
But i've seen literature on other websites claiming 20-20k.

That's the sort of thing that can mess with the process of choosing the best option.

But if you say the Panasonics are really supposed to be that good, then maybe i'll just run with that then.

 

[mshilarious]

I originally wanted to do that, but read a few comments about that not being so hot. I dunno. It made perfect sense to me.
I was actually going to just get a pair of goosenecks and put one under the bridge, and one up in the corner of the upper bout.

*On* the soundboard, not on a gooseneck above it. You need to be very close to a surface for boundary effect, and you want boundary effect.

I don't know where you read that a mic mounted on a soundboard was worse than a mic mounted in a soundhole. That sort of statement would have to come from someone who had never tried both.

The only downside to a mic on the soundboard is there is a mic on the soundboard. People don't like that look. If you are into guitar construction, mount a capsule inside a bridge and route the wire into the guitar body. Don't even aim it at the strings, aim it at the endpin.

Hmmm, that's actually a pretty good idea, I should try that . . .

 

[Tuneful]

With the single exception of a single diaphragm, small size omni mics, all other mic capsule designs depend greatly on the overall effect of the grill housing and many other factors. A measurement of just the capsule in those designs would be meaningless, except to a microphone designer.

I can understand that. Damping materials, reflective edges, surfaces, chamber volume, etc.

And yet, it seems to me that a carefully crafted enclosure that was mindful of the typical issues like vibration, damping, etc, might likely allow for a nice big fat condensor capsule that could sit in the sweet spot inside the guitar. I'd almost want to try that one first. But i've got pretty big hands that won't fit inside the soundhole, so anything I try to do inside is going to be a major chore for me.

 

[mshilarious]

Well like the self noise, frequency response, dynamic range, that sort of thing. The separates seem to list fairly toned down specs.

And to make matters worse, if you go to the Panasonic website, their own specs are modest in comparison to what other people attribute to those capsules.

Panasonic lists them as something like 50hz to 16k.

Which capsule? The frequency response varies according to model. That range is probably correct for WM55. Cardioids generally have a "worse" spec for frequency response than omnis, but what a "better" frequency response is for a particular application is open to question. The omnis go lower, but you don't care, because the lowest fundamental of a guitar is 80Hz. And for live sound you don't particularly care about much over 12kHz.

You also need to consider that the capsules are measured for their unmounted response; when you install them in an enclosure their high-frequency response will change according to the size and type of enclosure.

Self-noise and dynamic range are two ways of expressing the same thing. The capsule manufacturers tend to spec unweighted noise while microphone manufacturers will spec A-weighted noise. The test circuit for the capsules used by the capsule manufacturers is also suboptimal. Further, you must always consider diaphragm size when comparing self-noise. A large-diaphragm condenser will have much lower self-noise than your RS capsule, but you probably don't want to drill a hole that big in your guitar. In your application, self-noise is not particularly important.

And yes, if a $10 Chinese cardioid microphone is spec'ed as 20Hz-20kHz, let's say that is probably an exaggeration

But if you say the Panasonics are really supposed to be that good, then maybe i'll just run with that then.

I don't suppose anything; I have used something like 4,000 of them. I have also used capsules from most of the other common brands in the hundreds.

 

[Tuneful]

*On* the soundboard, not on a gooseneck above it. You need to be very close to a surface for boundary effect, and you want boundary effect.

I don't know where you read that a mic mounted on a soundboard was worse than a mic mounted in a soundhole. That sort of statement would have to come from someone who had never tried both.

The only downside to a mic on the soundboard is there is a mic on the soundboard. People don't like that look. If you are into guitar construction, mount a capsule inside a bridge and route the wire into the guitar body. Don't even aim it at the strings, aim it at the endpin.

Hmmm, that's actually a pretty good idea, I should try that . . .

I'm pretty sure that he was talking about the mic being inside the guitar, located directly under the bridge.
That's the one I meant when I said i've read some comments about it.
And I seem to remember it was in the context of reviews, saying that it was not as good as other methods.

If that's wrong, I wouldn't be against changing my game plan and putting a single mic under the bridge.

I actually like that idea, anyway.

 

[Tuneful]

Well like the self noise, frequency response, dynamic range, that sort of thing. The separates seem to list fairly toned down specs.

And to make matters worse, if you go to the Panasonic website, their own specs are modest in comparison to what other people attribute to those capsules.


Which capsule? The frequency response varies according to model. That range is probably correct for WM55. Cardioids generally have a "worse" spec for frequency response than omnis, but what a "better" frequency response is for a particular application is open to question. The omnis go lower, but you don't care, because the lowest fundamental of a guitar is 80Hz. And for live sound you don't particularly care about much over 12kHz.

You also need to consider that the capsules are measured for their unmounted response; when you install them in an enclosure their high-frequency response will change according to the size and type of enclosure.

Self-noise and dynamic range are two ways of expressing the same thing. The capsule manufacturers tend to spec unweighted noise while microphone manufacturers will spec A-weighted noise. The test circuit for the capsules used by the capsule manufacturers is also suboptimal. Further, you must always consider diaphragm size when comparing self-noise. A large-diaphragm condenser will have much lower self-noise than your RS capsule, but you probably don't want to drill a hole that big in your guitar. In your application, self-noise is not particularly important.

And yes, if a $10 Chinese cardioid microphone is spec'ed as 20Hz-20kHz, let's say that is probably an exaggeration




I don't suppose anything; I have used something like 4,000 of them. I have also used capsules from most of the other common brands in the hundreds.

I'm always careful to compare apples to apples, so when i've spotted a statistic (and I just did this the other night with a dozen open tabs), I make sure it's the same measurement method being used.

And I do get that I don't need 20-20k. But if I've got two equal quality capsules that are 50-16k and 20-20k, i'd probably use the 20-20k one.

Sound quality, trust me on this, was always going to be something I asked plenty of questions on.

I mean, this board is great. I expected to have to make a bunch of threads to get this much information.
I seriously appreciate the time you guys are putting into this for me.

 

[Tuneful]

Oh yeah, you asked which capsule. I found a link to all of the Panasonic electrets.
It was pretty handy, you click on the picture and you get the specs. Pretty much, they're nearly identical. Any variations between the capsules were fairly minor.


edit* here it is.
http://www.panasonic.com/industrial/components/audio/aud_mic.htm

 

[philbagg]

So with the mic facing out of the soundhole, wouldn't that make it less likely that the bass from the cavity would get added to the mic?

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).

If all else fails, try either a different approach or see how you get on with doing a recording and working some EQ/multi-band compression on the low-end to reduce any boom.

Hope this helps