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Observation on micing electric guitar cabinets.

Discussion in 'Guitars' started by jm2, Nov 30, 2008.

  1. jm2

    jm2 Active Member

    A short time ago, I posted a question about the necessity of recording electric guitar at high SPL (something I had read many times). The responses were in agreement, and several reasons were given as to why a miced guitar amp records better at loud volumes, including the stress of maxed out speakers and tubes.

    The explanations were comprehensible, however, another question recently popped into view. How much of the equation is governed by the microphone? Theoretically (and remember, it is just conjecture for the sake of discussion), the microphone under greater stress might be accounting for the benefit of recording at high SPL's, rather than the gear itself.

    Further, how could one separate cause and effect when trying to determine where the benefit is really coming from?
     
  2. Greener

    Greener Guest

    "Further, how could one separate cause and effect when trying to determine where the benefit is really coming from?"

    By testing and changing variables in small increments.

    The high SPL low SPL discussion is an odd one. Alot of good effects come from overdriving amps and speakers.
    However you do not need to move air to get a good sound. A very light very small cone driven balls to the wall by a tiny tube amp that's glowing and humming sounds like a tiny little box in the room but shove a mic up in the grill and suddenly it (can) translate into something massive through the monitors. However a massive amp that has ear splitting mids and back melting bass just puts tons of energy into creating mud in the room... You record the mud and on playback the phase cancelation causes holes in the sound and (can) make for a thin translation...

    How you arrive at a good tone takes time, no matter who you are. So you have to spend alot of time playing with different amps and different mic choices and positions.
     
  3. jm2

    jm2 Active Member

    Thanks for the reply. There are three reasons I feel compelled to try to find a way to get good guitar sound from recording at low to moderate levels, although I fully trust what you are saying about micing a small amp, or overdriving, etc.

    The first is just sheer caprice. The second is that I want to try to capture the particular sound in the room that I enjoy playing and listening to, which is more modest in level. I am not a great player with the kind of skill or discipline found in studio musicians. It will be easier for me to capture the best musicality I can muster if it is captured without greatly altering what I am hearing (which would not be the case with rigging up a seriously loaded small speaker). Even headphones seem to reduce my ability to play clean and articulate musical ideas the way I want, as it is a disconnect with the instrument.

    The third reason is that my early attempts at getting respectable sound from modest volume have been well, respectable, which tells me the louder equals better formula may have a small loophole. I am trying to understand if the loophole exists, and how to best exploit it.

    What prompted this particular question about mics, is after loading the mic very close to the speaker, the sound I recorded with modest loudness was quite nice. Granted, my listening skills in the context of recording may be way off, and maybe the sound would not be considered great by an actual engineer, but for the time being, I will have to trust my ear.

    So, moving the mic really close to the speaker is going to increase the displacement of the microphone’s diaphram, and again, I am just wondering aloud as to how much of a factor this particular component is. My guess is that it is an important component, and one that I have not seen mentioned when discussing the benefits of high SPL’s when recording.
     
  4. Davedog

    Davedog Distinguished Member

    Take into cosideration the makeup or construction of a microphone if you will.

    The 'diaphram' is in all actuality a very small speaker. In essence only but a very real aspect.

    A primer on mic construction will clue you into this aspect and give you a more complete answer to your question.

    The short of it is, in most cases where using a mic capable of high spl's, the only thing that really gets distorted is probably the mics preamp circuit.

    The diaphram is usually tensioned so high that actual distortion from a 'distorted' movement of this caused by a high spl is unlikely.
     
  5. GeckoMusic

    GeckoMusic Guest

    Where was that thread? The general consensus on the board here seems to be that lower SPL is better. And that driving a small amp hard as Greener mentioned is generally better than trying to drive a large amp at high SPL.

    Playing with headphones is a different experience than playing live. If you continue to practice playing with headphones on your skills when wearing them will improve.

    I've never heard the "louder equals better" formula. In my experience louder equals muddy with a combed out high end. Of cource one mans loud may be anothers average level. What dB level are we talking and how big is your room?

    If you use a dynamic microphone rated for high SPL, then the distortion of the diaphragm should be minimal. Dynamic microphones do not have active circuitry so they generally do not overload as easily as a condenser. Although you may get some interesting results from putting an LDC touching the grill. To find out what effect the LDC has simply record the same passage with both and LDC and SM57 at the same time and listen to the results.
     
  6. jm2

    jm2 Active Member

    Well, perhaps there is confusion in term or definition. Even a small amp driven hard will be "loud", at the very close proximity of where a mic would be. I think it is possible for two different speakers to produce identical loudness at the cone surface and yet different loudness out in the field (although I will test this idea shortly). So I must confess that it is me who has made the loudness equals better generalization based on the fact that a little amp will be quite loud very close up.

    The room is 13 x 16.5, and fairly dry. I am recording a 2 X 12 cabinet at about 80dB at 3 feet. I am not sure how others would percieve that as far as loudness goes.
     
  7. GeckoMusic

    GeckoMusic Guest

    "Loud" is a pretty straight forward term in itself. Use of the term can be confusing. It roughly defines the sound pressure level. When I hear the term "loud" I think about holding a sound pressure meter in a normal listening position and seeing numbers 90 or above.

    I see where you get the "louder = better" now. It might be clearer to say "higher signal = better" Loud is normally what you hear, signal is what the microphone picks up.

    You cannot have "two different speakers produce identical loudness at the cone surface and yet different loudness out in the field." Sound level is proportional to one over the distance squared. This assumes you are comparing one speaker to one speaker. If you compare a 1x8 to a 8x8 cabinet you will see that the 8x8 is louder "in the field" than the 1x8 with the same displacement measured at one cone.

    The room size, volume and cabinet should be fine if the room is well damped and you keep a dynamic microphone close. You may get a better tone by disconnecting one speaker and keeping the volume in the same place. You may need a load in place of the removed speaker. (Don't try it unless you know what you are doing.)
     
  8. jm2

    jm2 Active Member

    Thanks for the reply and useful tips. In theory, I agree when you say You cannot have "two different speakers produce identical loudness at the cone surface and yet different loudness out in the field." however, in practise, something is still telling me that a 3" speaker producing 85dB at the closest possible micing distance and a 15" speaker producing 85dB at the same mic distance will produce different loudness readings well out in the field, due to the additional area of energy radiating surface presented by the larger speaker. The 1x8 vs. 8x8 analogy is a good one, and I think the same principle applies, but the conceptual obstacle is merely in thinking of a 15" speaker as a multiple of many 3" speakers.

    I am going to test this idea soon, perhaps this evening.
     
  9. GeckoMusic

    GeckoMusic Guest

    My discounting of your theory may come from a lack of understanding of what you are trying to prove. Can you clarify your hypothesis?

    For starters, what do you mean by "loudness at the cone surface" Do you mean the amount of air displaced by the cone? Or the SPL measured with a meter as close as possible to the cone? Is that the center or the edge? As measured at a distance equal to that of the diameter of the largest cone in order to capture most all of the air moved by the speaker?
     
  10. jm2

    jm2 Active Member

    Hmmm.. It will take me a bit of thought to clarify what I think my hypotheses are (post to follow), but by loudness, I am thinking of the measurement given by a SPL meter as close to the loudest region of a given speaker.

    But briefly, I am merely thinking that two different speakers could produce identical SPL at the closest and loudest possible point of measurement and yet produce different loudness (or SPL measurement) at greater distances. I have somewhat lost track of how that fit in with my initial question, but again I will think about it for a time.
     
  11. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    I'm wondering if this whole thing isn't a confusion between the idea of "a small amp cranked loud" being better than a large amp cranked, or not?

    Are you sure you didn't misinterpret that? Tube amps, especially, generally sound better cranked. That's where you get all the factors involved in rock'n'roll overdrive involved. You have preamp tubes pushed more, pumping the power tubes harder, maybe more transformer sag, and speaker breakup...all of which helps cause a natural compression that give a cranked amp its sound. It's a BUNCH of things.

    A smaller amp, cranked, is generally easier to record because it's throwing out less sound that bounces off everything to reflect back to be picked up by a mic. A loud amp may be harder to record because it's filling up the room with more resonances that bounce around, and may cancel, or reinforce some frequencies after the mic picks those up. You could get all kinds of weird things from sounds at different frequencies arriving back at different times. Mainly...mush.

    Of course, all that has to do with the room itself, mic placement, volume, etc., as was said already. A Marshall Major may sound just fine in a certain room...dimed. It may sound like Mississippi mud in another.

    So, I'm just wondering if you aren't thinking "cranked, smaller amp", as opposed to "loud amp", which makes moot most of the SPL and other argument?

    Kapt.Krunch
     
  12. GeckoMusic

    GeckoMusic Guest

    Well put Kaptain. Thanks for bringing it back to the OP.
     
  13. jm2

    jm2 Active Member

    To be clear, I am not disputing the small cranked amp theory, and for all of the reasons described here and in the other thread. Indeed, it would be ridiculous for me to try to argue otherwise since I am a novice recording aficionado in every sense of the word.

    I merely wondered aloud if the microphone itself was a factor, i.e., that it too -like tubes and speakers- is best able to manifest some kind of extra sonic energy if driven harder rather than softer, although it would also appear to be difficult to prove since it cannot be isolated and examined in the audio chain easily.

    The only clue I had about mic loads was the great improvement in sound when I moved the mic very close to the cone, but granted even here other factors may be involved.

    However, I am still wondering if the generality about saturated amps and speakers has loopholes, or rather, if it is possible to capture good sound without going through this stage. I mean there are amps that are capable of producing good sound without being maxed out. There is a simple way to answer the question, and that would be to record guitar from moderate amp levels that sounds great (to qualified ears) and as if recorded by more traditional methods.

    I think I will pursue this avenue for a short time just to better understand things, or at least to better understand the saturation factor. Thanks for the interesting replies. It is all just discussion for the sake of discussion.
     
  14. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Davedog pretty much answered that part. "Overloaded" mics of any kind are not very pleasant to listen to. And, most mics that are used to record amps are chosen for their particular characteristics...including the ability to handle the SPLs that are thrown at them. Since they are designed to handle those high SPLs, they are unlikely to distort much. It's more likely some proximity effect that can fatten or thin a sound out, and not the increased pressure on the diaphragm.

    When moving a mic closer or farther from a speaker, you are changing the input volume to the mic, AND you are changing its tonality, depending on where it is toward the center or edge of a cone. This increased volume may also allow stronger signal through the chain, meaning you may get an approximately same level of volume to the recorder with less gain through the preamp.

    That may change the tonality, since most preamps have some kind of "sound" of their own, depending on how hard they are pushed.

    As you've suggested, there are so many things that affect it, that it would be hard to test to see if, in fact, a mic on the "edge of breakup", imparts its own flavor. I suspect it's a case where it pretty much takes a pummelling until a certain point, and then it's bad. And, I suspect that getting it "JUST" below its bad point will not impart a more pleasant sound, but instead, sound like it's about to go bad?

    Obviously, if you were to just set a mic in front of an amp and kept inching the amp up bit by bit to record to test...you're going to have to compensate somwhere along the line to get any useable recorded signals. The compensations in themselves will render the test useless.

    So, I see what you are getting at. And I'm not sure of the answer, either. I just wrote this to continue the discussion, see if anyone can pick apart my theories, and maybe learn along with you. :wink:

    Anyone?

    Kapt.Krunch
     
  15. Davedog

    Davedog Distinguished Member

    In my experience, mics will approach the 'breaking' point of overload, but again, it is more the function of the internal mic amp than the diaphram getting all out of shape due to the large amounts of spl's being thrown at it.

    This is mostly in reference to dynamic mics and a lot of condensers. Ribbon mics, however, are another matter entirely and should NOT be subjected to high spl's as they WILL without fail, fail due to over exposure to high and especially plosive bursts.

    On average, any mic you place in front of a guitar cabinet will attempt to reproduce the sound hitting its diaphram and then, being routed through its innards to the device amplifying it to a usable signal going into a recording device of some such, will become unusable at a certain level.

    Again, its mostly the mic's own transformer, preamp, etc that will be overloading FIRST....way way before the diaphram could possibly distort due to high spl's.

    In short, you will NEVER get your theory to test properly unless mic amp distortion is what you're looking for.

    And really, this isnt a very nice sounding distortion at all.

    You're better off looking for ways to distort , in a controlled way, the mic preamp downstream from the mic itself and rely on much larger components capable of delivering a better sort of distortion while retaining a clarity that makes it usable.
     

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