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Impedance question

Discussion in 'Recording' started by Guitarfreak, Apr 8, 2009.

  1. Guitarfreak

    Guitarfreak Well-Known Member

    How does the impedance of a microphone impact the sound? I am comparing two mics that are rated 100 and 120 Ohms. Since impedance is a measure of electrical resistance, does this mean that the 100 Ohm model is more sensitive, or that it picks up nuance better, since it takes less force to move the coil?
     
  2. dvdhawk

    dvdhawk Well-Known Member

    Impedance does affect the sound, but what really counts is the interaction between the mic and the resistance the pre-amp is optimized for.

    If it's a dynamic mic lower impedence usually just means it has fewer windings in either the voice coil or the internal transformer. Fewer windings may make it more sensitive in theory, but the resulting electrical impulse the transducer would make would be diminished too. So if your pre's are optimized for 600 ohm loads it will take more gain. Great pres will let you adjust the impedance they work at, which is especially handy for ribbon mics.

    You're a guitar player, so to make a guitar analogy - which has higher output through your guitar amp a humbucker or a single-coil pickup? Humbuckers are higher impedance, but generally speaking louder and arguably less defined.

    Food for thought, it might be an over-simplified way of looking at it.

    Bon-apetit
     
  3. Guitarfreak

    Guitarfreak Well-Known Member

    Hmm, very cool, thanks for the post. So by saying the higher output pickup equals higher impedance (electrical resistance) does this mean that the relationship is symbiotic. I.E. "equal and opposite" higher impedance levels also mean higher outputs and vice versa?
     
  4. Guitarfreak

    Guitarfreak Well-Known Member

    srsly? no one?
     
  5. dvdhawk

    dvdhawk Well-Known Member

    OK I may not be the best one to continue this study in electronic engineering, but since nobody else has chimed in I'll give you what I can.

    It seems logical that adding resistance to a circuit would automatically diminish it's ouput. And it's true that two resistors (or speakers) in series basically adds the two impedances together. But Professor Ohm didn't become famous for 2+2=4.

    You probably know that putting 2 x 8-ohm speakers in parallel in reality drops the total load to 4-ohms. What's up with that? Like virtually everything else involving electricity a resistive load in parallel with another resistive load or circuit is subject to Ohm's law - which I'm not qualified to teach in any detail. But here's how I would explain it. Humans can neither create or destroy energy, but we can transform it. So when you take a resistor or potentiometer across an electrical signal the amperage (current) (or energy) has to stay the same - but the voltage is changed in accordance to Ohm's Law. V=IxR [V oltage = I (current in amperes) x R esistance]

    The resulting output levels and sensitivity you're asking about - in mics and guitars is a combination of resistance and capacitance of the mic and cable along with their interaction with specific voltages. All electronic devices use these relationships to get the optimum levels.

    Again, I'm afraid this is still over-simplifying it, but if you want some independent study there are roughly a million websites that teach Ohm's Law a lot better than I could ever explain it.

    Best of luck. If that doesn't answer your question - you're going to need somebody else to explain it.
     
  6. djmukilteo

    djmukilteo Well-Known Member

    Impedance is not purely resistive. Impedance involves ratio's of AC voltage, Inductors (coils), Capacitance and frequency and only applies to AC circuits.
    Your question about 100ohm or 120ohm "rated" microphones. Microphones are not "rated" in terms of impedance that is the designed impedance value or load they apply to the input of a preamp or amplification stage at a certain voltage over a specified bandwidth of frequency...the more common value for design purposes of microphones is in the range of 150ohms. This is a typical balanced microphone circuit.
    The more important question is matching the input impedance of your microphone to your preamp stage.
    A matched impedance 150 - 150 indicates unity gain with no loss of signal through that particular chain of amplification..
    If you connect a 100ohm impedance microphone to a preamp that has a designed input impedance of 150ohms you will have a mismatch at that particular stage of amplification and there will be a certain amount of gain or loss in your signal...
     
  7. Boswell

    Boswell Moderator Distinguished Member

    I'm sorry to say you are all firing somewhat wide of the mark. The only thing that actually matters is the designed load impedance for a microphone.

    The designer will have created a microphone that acts (at audio frequencies) as a voltage source in series with an impedance. The impedance has both resistive and reactive components, and has to be considered along with the capacitance of the microphone cable. For dynamic microphones (including ribbons), the reactance is usually inductive, and for other microphone types such as condensers (variable capacitance) that have built-in active followers or pre-amps, the reactance is usually capacitative.

    The manufacturer of a good microphone will specify a load impedance or a range of load impedances within which the product will meet its specifications. That doesn't mean to say that it will not work if the load impedance is higher or lower than recommended, but you may get a different sound and/or sensitivity. Dynamic mics may be under-damped if working into too high a load impedance, and the followers in active types may distort or clip if they have to drive high output amplitudes into too low an input impedance.

    So as a rule, you don't need to pay much attention to the internal resistance of a microphone. Instead, look at what load the manufacturer says to drive it into for it to meet its specifications. You can sometimes get special effects by deliberately driving into a wrong impedance, but do that only after you know how to make it work properly.
     
  8. djmukilteo

    djmukilteo Well-Known Member

    I guess I was only trying to clarify some impedance "ratings" misnomers and point out the same facts Boswell did in his reply..different microphones have different sound clarity, different polar patterns, different bandwidths, different applications and use....these range from simple podium mics for voice applications in auditoriums to high end vocal applications in a studio environment to specific acoustic instruments being recorded in certain acoustic spaces.....this is why you have microphone specs.....

    I think we deviated from the original question...Guitarfreak has 2 mics...100ohm and 120ohm....that's all we know...so in order to make some educated statement to answer his question you would need to know what type of microphone each of these mics are, what are there specs, what preamp are they plugging into, what polar pattern do they have (fixed or selectable), is the source placed on axis or off axis, etc. etc.....
    Maybe if Guitarfreak tells us a little more about each of these mics we can discern an answer......
     
  9. Guitarfreak

    Guitarfreak Well-Known Member

    Here you go...

    link removed

    link removed

    So you pretty much need a different preamp for every mic within a certain impedance range? At least in theory. I can't seem to find a mic impedance on my PreSonus FireBox. Bunch of other impedance ratings, but not that particular one.
     
  10. djmukilteo

    djmukilteo Well-Known Member

    Not at all.....your Presonus input impedance is 1.3Kohms on the two front connectors which is plenty high enough to match either of those 2 mics....the 2035 has better S/N and some additional features (low freq roll off, 10db pad etc.) which would make it a better all around choice... depending on what your going to record, guitar, vocals I would assume.....either of those mics will sound good. You might hear a difference between the two sonically
    just because the 2035 has better sensitivity and better dynamic range...the 2020 has a bit more noise floor...so if your doing vocals in a booth the 2035 would be slightly better there also...
     
  11. Guitarfreak

    Guitarfreak Well-Known Member

    How about in front of a guitar amp? I've heard that cheaper condensers actually sound better on this application. I don't have a problem spending the extra money on the 2035, but the only reason I'm considering the 2020 is because of what somebody said about guitar amps. Do you think the 2035 will be better in this case as well?
     
  12. djmukilteo

    djmukilteo Well-Known Member

    I think with the added features of the 2035 (the 10db pad and the freq roll off) you would have more flexibility in setup. The 10 db pad gives you the added SPL and there may be some low frequency harmonics coming from your guitar amp that you might want to get rid of.....that would be worth the extra bucks IMHO.

    I would think you would want to setup a nice clean detailed sound from your guitar amp....setup good levels and mic placement, no clipping...balanced sound levels across your range of play....if that's what your looking for....on the other hand if your just looking for a really loud mushy, mashed distorted guitar sound with less acoustic detail....then any old cheap mic condenser or dynamic will do the job....so the next real question is....
    What kind of sound are you going for?
    Will you be recording this guitar "dry" with no effects?
    Do you want to add effects in the mix?....or will there be effects coming from your amp?
    So many different variables!!

    One thing to remember...the best method is to make a few trial takes of what your going to play with different setups (make a note of each different setup) then do an A/B listen to each track and let your ears decide....listen to it on different speakers, different headphones, different playback devices etc...trust me...you will know which one you like best....
    as far as picking the best of those two mics....go for the 2035!
     
  13. Guitarfreak

    Guitarfreak Well-Known Member

    Guitar recording, at least for me, is a touchy topic because I can't really do it as well as some other people. At least IMO, maybe I'm overcritical.

    My sound...that's debatable, I'm not really able to get the sound I want from my amp even when not mic'd so I try to use techniques to fool the ear into thinking I am getting better sound than I actually am. It doesn't always work out, and most of the time it just doesn't sound that great. At least it sounds better than some people's guitar recordings, but I'm just not getting the clarity and beef that I desire.

    I will be recording dry dry dry. I don't like a lot of extra wiring/stuff in the mix, I run a minimalist setup. Guitar straight into amp, no reverb or onboard effects. Anything else is added via DAW.

    I like a few different sounds and try to emulate them. All pretty modern though. I like warm tones, but one thing about "warm" is that sometimes it lacks clarity. That's something I'm really struggling with at this point, getting a balance between tone and clarity in the recording.

    For low gain pop punk/alternative rock, listen to the rhythm tone of New Declaration by Just Surrender. Sick or Sane by Senses Fail is good also. Good distinguished strat sounds.

    For metal tone listen to The Arms of Sorrow by Killswitch Engage.
     
  14. djmukilteo

    djmukilteo Well-Known Member

    Do you have an example of your own guitar sound that isn't cutting it?
    A simple MP3 track of one with or without effects would be most helpful...
    Maybe if I heard your guitar track I would have a suggestion or there would be some suggestions from the forum....it's not necessarily the mic your using or your guitar amp... could be a lot of things..

    Sounds like your looking for that fast "chunk" style rhythm which is pretty common for that type of punk/rock sound....which does have effects.

    Are you getting a nice fast snappy chunk or is it sustaining a little?
    Hard to know without hearing it!
     
  15. Guitarfreak

    Guitarfreak Well-Known Member

    Let me see if I can hook up my setup right now before I have to go to school. I'm only going to use one mic and record one track. Just so there's no "voodoo" or other things going on. I am going to put my SM57 right in front of the amp perhaps a little to the right depending on how my amp sounds today.

    BTW thanks for helping me man, I really appreciate it.

    OK, it's on my myspace. http://www.myspace.com/chrysalisct
    It's called *Test
     
  16. djmukilteo

    djmukilteo Well-Known Member

    Well a couple things I'm hearing on that Test track.

    You have a lot of sustain going on and that runs together and drones between your chunks.....not going to be very snappy or clean sounding unless you reduce that from happening....seems like some reverb is in there causing that?....not sure..didn't sound all that "dry"..
    Maybe a "gating" effect (which are hard to setup) but sometimes those give you a nice fast snappy sound if you can get them to gate at the right times....the other thing would be for you to stop your strings from "ringing" after the initial strumming....which I think is more of a guitar technique...grab and stop the strings in between your strums..something to try....if you know what I mean....not sure if that's possible..
    The other thing I hear is a scratchy "zzzziizzz" up in the upper frequency region....very crispy in the ear pretty constant and not very tonal...
    I would use an EQ to locate that and cut that down or get it out of there all together....or try to figure out where that is coming from....maybe there's some distortion in your cabinet....
    An EQ will give you the most control over the tone....it really takes some time to find those frequencies that are "warm" sounding and have just the right amount of low end, mid and high frequencies....but the only way to find it is to listen and adjust until you get a nice balance....then when you have what you like then listen to it in the mix...then you add something else to it and change the whole thing again....Hehe....it's a vicious circle of sound....
     
  17. djmukilteo

    djmukilteo Well-Known Member

    BTW I liked the Imagine song....
    I listened to your other songs and some of them are really clean sounding.....but the distortion rhythm sound does seem a bit scratchy and there's alot of crispy high end noise up in there....EQ the top end down a bit and I think it will sound smoother....need to get that "grating" sound back in the mix a bit..
    Do you generally get better sounding results recording your guitar directly into your DAW?
    What audio software are you using?
     
  18. Davedog

    Davedog Distinguished Member

    Is your amp a combo or a separate head and cab? Two things. A combo has more ability to excite the nodes around it due to the open back. The other thing, a head on the cabinet ESPECIALLY with those kind of lows and low mids will cause interaction and vibrations of the tubes creating all sorts of little things you dont suspect until you remove the head from the cabinet.

    Also, isolate the amp from the floor. It should be up in the air no matter what type it is.

    I was also hearing a thump everytime you went to pick the chunks.

    I think this is all technique and a physics thing with the amp and the floor or the room.

    Of course a better amp might be better for you.
     
  19. Guitarfreak

    Guitarfreak Well-Known Member

    Hmm, few things. I heard the high frequency grating on my car stereo on the way to school. It is very annoying and I would slap an EQ on there in a second but I can't hear it on my home stereo. I don't have monitors so at this point I'm shooting in the dark with a lot of the EQ work I do. My amp is a combo, but contrary to what DD said it is closed back. I am working out of Logic Express.

    Sustain? Hmm, that is interesting. I have a pretty thick quilt behind the mic hoping to dispel most ER and reverb from reaching the mic. Also I recorded it in my closet so as to not get a lot of room tone.

    As for amp settings I have the bass at only 3, and I used an EQ to roll off the bass at 130Hz 24 dB/oct, so I am pretty surprised that both of you complained about bassiness/muddyness. How could I get the amp off the floor effectively? I know that seems like a stupid question, but if I put it on a piece of wood it would still transfer quite a lot of vibration. Not cutting the strings off could be me just being sloppy because I literally threw this down in one take while walking out the door. My strings also haven't been changed in a while.

    Thanks for the feedback.

    Would this do?
    link removed

    Or would I be better off with really getting it off the ground?
    link removed
     
  20. djmukilteo

    djmukilteo Well-Known Member

    I don't think you need anything special to move your cabinet off the floor.
    Anything will do....just so long as it's off the floor about 16" or more...the sound wave will bounce off the floor and create a reflection which is delayed and out of phase with the sound directly from the speaker and they beat against each other causing "standing waves" which can make it sound muddy ...
    Maybe DD has an opinion on this but I don't think putting it in a closet helps that much unless you have a really noisy main room. I would think you want some space around the cabinet for the sound field to develop a bit and if you have the mic placed directly in front of the speaker the pattern of that mic has pretty high side rejection. A little room reverb doesn't hurt..but that a whole other issue...Have you tried both off axis and on axis with the mic?. I would experiment further with your amps tone controls also and see if you can get the sound you want if you can't EQ it afterwards in the mix.
     

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