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The physics of microphone placement

Discussion in 'Amps, Mics & Pickups [DB]' started by martinc, Feb 17, 2014.

  1. Anyone know, from a physics/acoustical engineering perspective, what the best place on the bass would be for a microphone?
    I see photos that indicate four places that seem to be favoured:
    - between the legs of the bridge
    - somewhere near the upper f-hole on the treble side
    - slightly under the treble side bridge foot.
    - near the end of the fingerboard

    I have tried all of these locations on my ply bass. Neither one seems to stand out. But if I knew from a purely technical point of view which would the best, I could spend more time experimenting with a mic in that specific area. I am leaving the type of mic, and that I go straight into the PA through a tube preamp, out of this query to avoid further confusion for myself.
    Has anyone seen a graph or sound wave dispersal chart of a bass top that would show where the strongest vibration is? Is it close to the sound post? Between the bass bar and the soundpost? Under a bridge foot? Near an f-hole?
    Is the strongest point of top vibration always the best place to mic a double bass?
    Would a ply bass react differently to a carved top and be more difficult to mic?
    Or does any of this really matter...and should I go back to stuffing my SM58 under the tailpiece?:confused:
  2. Arjank


    Oct 9, 2007
    Above Amsterdam
    IMO one would get the best results with a combination of a mic and a piezo transducer underneath the foot of the bridge.

    The placement of the mic is also very dependent on the position of the instrument in that particular room/venue. If you want to capture the fundamental of the uprightbass it's nearly impossible to get it right with a mic because of the room nodes and room/instrument interaction. Therefore it would be best to use both a piezo and mic. The piezo will faithfully transfer the fundamental whereas the mic will nicely capture the instrument/room acoustics.
  3. What microphone are you using?

    There really aren't rules when you are close mixing as the pinpoint locations for optimum sound are scattered across the bass. I would suggest a hclamp though for ease of movement of the instrument as you play. As stated above, blending a piezo with a mic lends to a little easier mic placement as the mic can solely be used for the "air" of your overall sound.

    Let us know what mic you are using.
  4. Champagne: In the small restaurant where I play regularly I have been experimenting and found that my SM 58 on an H clamp between the legs of the bridge works quite well. However I am looking for a mic with more gain, more sensitivity and more directional eg Super/Hyper Cardioid, side address etc. But before I spend bigger $$ I would like to know if research has been done on the structure of the double bass indicating the "hot spot" area of the top.
    Maybe I have already found it and not realized it so I am looking for data so I can concentrate on finding a mic which will respond well to that. I am trying to avoid randomly trying microphones as much as possible.
    Over the past 15 years, I have previously owned: Shure SM57, Audix D2 and a D4, Peavey 45i and Sennheiser E609. They are all fine microphones but for some reason on my Eberle ply, the 58 sounds better than all of them.
    For pickups I have a Bass Max, Rev Solo2 and a Schatten RB-1.
    I have tried mixing mic's with all of these pickups using a 2 channel Ultrasound DI Max...but it's pain setting up on the job.
    I prefer the sound of the SM58 (and most of the other mics I have tried) to all of my pickups which is why I am searching for more information of how a bass responds.
    Arjank's comment about the room having an effect on the mic placement is intriguing. That is not something I have taken into consideration.......and could eliminate my need for research on the response of a bass top. That could mean I would have to change the location of the mic each time I play at a different location.
    And maybe mic placement IS just random regardless.
    Normally my life is not this complicated.:meh:
  5. Martin,

    There is no doubt it is a crapshoot, and I am a recording engineer by trade! Every instrument has its sweet spot, sometimes many spots. Also, every microphone, preamp and amp have a response curves. Knowing how they respond and act in situations leads to choices in areas of placement. Heck, I have over 30 mics in my closet to approach instruments. The difference here in this thread is that we are talking about a live situation where the mic would usually have to be closer to the instrument to have greater signal to noise/bleed/room/etc. I wouldn't poopoo the 58 by any means. A lot of folks achieve great success with that mic in live environments.

    As far as hot spots on a DB, where you have had success (bridge feet) is something I see a lot. Grazing a ff is another, under the tailpiece, under the fingerboard. Being such a complex and large instrument along with a pleathora of different sounding basses, I don't think you will ever find a science other than "where is sounds best" while taking into considerations the environment (overall levels on stage, bleed from other instruments, location of amp, context of the rest of the band where you are sitting your bass' "SOUND" into, the room...). Knowing what areas of the bass add to the mic is another. For instance, you know if you point the mic on-axis into a ff, the bass response will go through the roof, but if you take it off axis and play with the proximity, you can use it to your advantage. This is something you'll have to figure out.

    A week or few ago I bought a mic for live usage with my DB. I got a atm450. I compared it with a lot of what I have in my closet that I would CONSIDER using on stage along with a heil pr40 and kept the 450. It's a dynamite little mic. What I found close micing is that there are sweet spots galore. Not just one. Now, my bass is an old carved german and that may have to do with all the different sounds I found all across the instrument close micing but I think the same, but maybe to a lesser degree?, you will find with a plywood bass. There are structural pieces such as the bass bar, sound post, bridge feet, neck, block areas... that will alter the sound of the top and the organic interrelationship of those things bring out the musicality of the top and instrument as a whole.

    I guess my long-winded writing here is basically saying you will have to find your sweet spot. Every single instrument I have ever recorded has one though there are some goto spots like I mentioned here for the double bass.

    So, according to you, you have found the sweet spot on your bass for your sm58. A different mic may reveal the same or a new. When comparing mics, look at there frequency plots and compare them to the sm58. Also compare their sensitivity level. This will give you a little idea of how they will sound different in the same location on your bass though it will not be absolute.
  6. Champagne:

    Thanks a million for the info-packed response.
    It's not what I wanted to hear...I was hoping for an easy answer!:crying::D Just kidding.
    What you are saying does make perfect sense. Double basses are unpredictable in other areas such as strings and pickups because of their size.
    I seem to recall several years ago seeing a picture on a blog or website of a bass top from underneath with sound patterns superimposed. That's what got me thinking that science might come to the rescue.
    I also appreciate your advice (even after 30 years in broadcasting!) re the plotting of mics. I am looking at a tom mic with a supercardioid pattern and a frequency response of 20hz -12,500hz. It has a sensitivity rating of 2.2mv v 1.85mv for the SM58 at approx the same dBV.
    So....back to the same old. On the job experimentation. I'll start out where the SM58 normally is (feedback has not been a problem) and hope there is an improvement. Then try other locations. If there is no improvement, then I will also have learned that the good 'ol SM58 may not be so bad after all. No matter where it is on the bass.
  7. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Champagne is dead on target. Certainly different close mic locations yield different tonal characteristics. The sound of the bass we want is really captured several feet in front of it. So, one would want to place a mic somewhat removed as one can do in a studio but not on a live gig. Add to that the potential for "proximity effects" (see here) resulting from different response patterns. Thus, the crapshoot.
  8. MR PC

    MR PC

    Dec 1, 2007
    Tough, playing live, to place a full size mic like the 58 in any places but stuffed under the tail, stuffed with foam between the bridge feet, or stuffing it thru the after lengths pointed down at the top. On a Ply bass especially, those spots all sound good for different live playing applications, so I think it's good to get familiar with the plus and minuses of each. And I think it's good to have a mic preamp, even a cheapie like the ART before sending the signal to whatever you are using to get the sound to the house, be it amp or PA, or even both. The 58 is great, you can hammer nails with that thing, and it always sounds good.
  9. DRURB: I was hoping you would eventually chime in on this Doc! Thanks.
    I think one reason the SM 58 works OK is because of the proximity effect. I have the windscreen right up against the top.
    Have you ever seen that sound pattern diagram showing how the sound emanates across the top when a string is activated?
  10. Mr PC: Yeah.... on what you said. Thanks.
    I use an ART Project Series Tube MP pre-amp...with a very much improved old tube (Garnet pre-amp by Mullard). That's why I want to stick with a dynamic mic unless it's absolutely necessary to use a pickup.
  11. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    The proximity effect will, depending on the mic, exaggerate the mower mid/bass. Hey, if it works for you, then great!
    Which pattern? Chladni patterns?
  12. Doc: What I vaguely remember (probably 8 years or so ago) was similar research done by someone in Europe specifically on a double bass. At the time I found it interesting.... but not interesting enough to figure out the possibilities of using the information to see if it would help in microphone placement.
    I remember reading your posts about your Ehrlund and how a small shift can make a huge sound. Why is this? Would a dynamic mic be in an optimum position in the same place? Or does the way you attach the Ehrlund affect it's location because of damping?
    I would love to see if the Chladni patterns could be used to locate the best spot for a mic. Perhaps the violin measurements could be applied to the double bass. Maybe I should contact the University of New South Wales.
    Or maybe it would be more rational to just experiment on my own with the mic , go with my ears.... and to heck with science.:D
  13. JeffKissell

    JeffKissell Supporting Member

    Nov 21, 2004
    Soquel, CA
    I think the idea of adding clean gain to a pleasant sounding dynamic mic is a good thing to explore. I ended up with a FEThead for my ribbon mic but it boosts the signal on a 58 in a really musical way too. If you like the sound of the 58 then Senior Piece's suggestion of experimenting with mic pre-amps is a sound one... ;)

  14. I would go with your last statement. :) Science can only get you so far with this instrument.

    I have an Ehrlund too. I use it with a rs mic and/or with the 450. It just is what it is and the Ehrlund was a real pain to find the sweet spot. As I wrote above, you have a lot of structural components and changing densities that create variable tension, compression and torsion all over the bass when strung up and played. Different spots will just resonate differently as a result. It's not limited to the top or the DB as a whole either. The weight and tension of the strings along with the plucker person's approach or puller person's draw of the bow have dramatic impacts on what the bass does in response too. It is nutty and it it is awesome. Science can provide a framework, but there are way too many variables with an instrument and player.

    I was admiring on sunday how much sympathetic resonation that just my tailpiece adds. I threw my cleaning rag between it and the top so the line I was playing would sound cleaner. If I was a better player and if my bass wasn't so tender I could have probably avoided the rag stuffin! Oh, BTW, I think there is a science to afterlength tuning :p:bag:
  15. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    I think you have the right idea. When you move the Ehrlund a small distance and get a substantial change in the sound, then, by definition, the vibrational pattern of the table must be substantially different at that point. Now, I doubt that a mic placed at the same position would be in its optimal position. This would be because:
    1. The acoustic energy radiating from the top that converges on the mic will not necessarily correspond to the vibrational energy at a point on the top.
    2. The transfer function of the mic is not the same as that of the Ehrlund. So, even given the same "input," they will sound different.
    I'd love to see those DB vibration patterns if you can find them.

    When I first saw this thread about predicting the optimal mic location, I thought, "Wow, that's a complex problem!" Many here have touched on why. Different mics, room reflections, etc.

    I think this really is one of those cases in which the most efficient and satisfying process is trial and error while using your ears. :)
  16. seamonkey


    Aug 6, 2004
    Don't dismiss omni, they can be a good choice. Lot's of good advice here from a mic maker

    but then they do push a hyper cardioid.

    Studies, of the top.


    i.e. maybe an omni is better for some because as you're standing there you hear front and back, and all over the bass.
  17. Seamonkey:
    Thanks so much. You have struck gold here!
    This is not the study I was thinking of but it addresses the issue much better.
    I need some time to absorb all this...and the roundback images. But it appears to confirm scientifically what we all have found out by ear ie. that several areas of the bass can yield a good response on the top. And although the sound emanates from the point where the soundpost meets to top (and back), there may be no one single location that would be the"best". But how can you argue that the placement of the DPA 4099 in your other link is wong!
    This study also notes that much depends also on the rigidity of the bracing too.
    Interesting to see the differences between the roundback bass response v the flatback.
    In terms of my own situation, I need to spend a lot longer trying out different placements on my bass.
    I hope other TBers will also weigh in on this study. It goes to the core of how our basses work.
  18. MR PC

    MR PC

    Dec 1, 2007
    Some how I think that the graph could pretty accurate for a static environment like a sound lab. But in a real life situations where things like room position of the player, room size and accompanying acoustics, temperature and humidity, all effect the sound it couldn't be very accurate. Add to that the distance of the mic, the proximity effect and phase issues that go with that territory...you can waste a lot of time placing the mic in a spot where it's supposed to sound good. But often it doesn't. I've had engineers getting out the tape measure to place a mic and all that kind of thing....I just wait to see what it sounds like and only comment if it really sounds bad. It's sorta entertaining to watch them go through the motions after I try to tell them which mic I prefer, and where I like it on the instrument.:)
  19. seamonkey


    Aug 6, 2004
  20. Mr PC: I agree....and that has always the way I have seen things. I think one reason my SM58 (a cardioid) worked so well was the proximity effect. I will be trying a supercardioid with a 20Hz low end frequency response to see if it is an improvement. If not...well there's always the classifieds on this website. I would love a DPA but would like to check out one more dynamic mic before looking at condensers.

    Over the weekend when I started this thread I was thinking about a new mic...it was cold as hell outside...so it was either start packing for a move or navel gaze about possible new microphones. That's when I remembered seeing the graph of sound waves on a bass top. So I decided that airing my curiosity about the subject was infinately preferable to packing. However I have now used up all my allowable procrastination time and frequent glares from my good lady when she was packing her crystal stuff mean I will have to spend a lot less time on Talkbass over the next month.:meh:
    I really appeciate the response from all of you. It's been very helpful.