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Foam under pickups

Discussion in 'Pickups & Electronics [BG]' started by gimmeagig, Jan 25, 2012.

  1. I know a guitar tech who places cork in the cavity underneath the pickups and then a very thin piece of foam under pickups for adjustment. His theory was that the less foam you use, the more solid the connection to the instrument,the better the tone from the pickups.
    Is there anything to that or is that sort of over the top, waste of time kind of stuff?
  2. f.c.geil


    May 12, 2011
    It's over the top, waste time kind of stuff. Pickups pick up the actual vibrations of the strings. The woods and hardware change the way the strings vibrate, which changes the tone. Wood, cork, and foam are not magnetic, but the pups are...
  3. parsons


    Feb 22, 2008
    I can see the logic but I have a slight issue.

    I am by no means an authority... but I like the idea of pickups sucking their tone from what I am doing with the strings above them, not picking vibrations or overtones that may not be pleasant from the body that I have no control of with my hands. These also would be almost inaudible. Ever take a Precision bass and put the pickup to your mouth and hum really hard on it? It will hardly come through your amp. My mouth is vibrating a bit "harder" than any of my basses do when playing them.
  4. packhowitzer

    packhowitzer 155mm of pure destruction

    Apr 20, 2011
    I think this should be a standard part of the setup process for all basses at GC. :D
  5. This is essentially the "pickup rings versus direct mounting" debate that goes on on guitar forums.

    Pickups respond to disturbances in their magnetic field. If you are getting significant vibration from the body, the pickups are microphonic.

    In any case, I certainly DON'T want to hear nasty body vibrations. I suppose it's not bad on hardtail basses, but bang on any tremolo equipped guitar and you will hear the trem springs.
  6. michael_atw


    Feb 28, 2009
    Jamestown, NY
    Over the top. The pickup isn't losing any of it's potency with foam under it. The pickups could be suspended in the air and it would sound just the same. "Solidifying" the connection with the wood does nothing.

    I'm not a proponent of wood type or fingerboard type doing anything significant to tone either, so that's where I'm coming from personally.
  7. michael_atw


    Feb 28, 2009
    Jamestown, NY
    That's a bridge issue, not a pickup issue of course.
  8. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    You don't want the pickups to vibrate, since they may vibrate out of phase from the strings, which would cause some kind of comb filtering. Having aid that, I've never heard a problem from it, except for the occasional squealing if you get too close to the amp.

    The way Gibson style guitar humbuckers is mounted is dumb, because they can move around too much. So in that case, screwing them to the wood is better, but then they are hard to adjust.

    But the pickups don't get any sound from the body directly, so being solidly mounted doesn't really matter. The wood of the body and neck do filter the vibrations of the strings, but the pickups are just sensing the string's disturbance of the magnetic field, as has been already stated.

    So good stiff foam is fine. As long as the pickups are not wobbly you are good to go. There's nothing wrong with the way he's mounting them, but it does make them harder to adjust.
  9. darkstorm


    Oct 13, 2009
    All foam is much better if the pups adjustment screws dont have springs on them to keep them still and not wobbly etc. It lets you adjust the pups better. You dont want wobbly cause then their not staying at the surface angle to strings you want. And if too loose could vibrate causing the problem another noted.
  10. khutch

    khutch Praise Harp

    Aug 20, 2011
    suburban Chicago
    No it is not over the top. What a pickup really senses is the relative motion between the pickup and the string. It senses that by means of the magnetic coupling between the two but it is the relative motion between the two that causes the magnetic coupling to change. So, if the pickup as well as the string is moving the relative motion between the two is changed and that may change the tone.

    Think about all the debates here concerning "tonewoods", bridges, and other construction features and their effects on tone. How can these things possibly change the tone? Well the strings are tied to the body of the bass at two points, the nut and the bridge. These attachment points and therefore the structural details of the bass itself define the "boundary conditions" for the equations that describe the string vibration and so they may have some (but likely to be quite small) effect on the attack, decay, and harmonic content of the string vibrations, ie the things that determine what we perceive to be the "tone". In addition some of the strings' vibrational energy is coupled to the pickup location by the structure of the bass and also affects the relative motion between the pickups and the strings.

    There is a strong potential here for the pickup mounting system to have as much effect on the tone of the bass as all the other things that feature so prominently in the tone wars. A cruel irony, eh? The fact that virtually no one here mentions or worries about this is another nail in the tonewood coffin, I think. If those other things have any significant effect on the tone of the bass then surely the pickup mounting details do too.

    The "tone foam" debates will start at 1:23:57 this afternoon, US CST....

    Ken :D
  11. Of course i would need a little bit of foam even if I put some type of cork or wood shim underneath. What I like to use is mouse pad strips and currently I have a long piece with a shorter one ( as long as the distance between the mounting screws) on top of it.
    I wouldn't expect to hear a significant difference but iit might still be fun to do it. After all who in the audience or even fellow musicians would notice the difference between a stock bridge or a Badass, Nordies vs Lindy Fralins, Aguilar vs Bartolini preamp....? But we still mess with that stuff all the time and to us the difference can be huge.
  12. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    In order of magnatude, the platform in which the strings is mounted overwhelms the mounting system of the pickup, mainly because all of the mounting systems are similar enough as to not matter much. As long as the pickup is held stationary under the strings it will work the same, no matter if it's screwed into the wood, or mounted from a pickguard.

    I often do quick tests on pickups by holding them over the strings with my hands! They aren't even mounted to the bass.

    As I mentioned previously, what you don't want is it bouncing around. But even on guitars with wobbly pickups, the most detrimental affect is feedback. You might hear a difference if you really listen carefully, but it would be slight.

    The wood the bass is made from on the other hand makes a big impact on the tone because that's what the bass is made from. Even fingerboard woods. All you have to do is build a few basses of the same design with different woods to hear it. And then, even two basses from the same boards might sound a little different.
  13. Ok, I'm convinced and I'll leave the bass alone.Thanks for the responses!
  14. khutch

    khutch Praise Harp

    Aug 20, 2011
    suburban Chicago
    This is exactly what I said so I agree. However no pickup mounted on a bass is exactly stationary under the strings. It could only be stationary if the structure of the bass were perfectly rigid, which it is not.

    This neither surprises me nor disproves what I am trying to convey. Your hand does move with respect to the strings and your hand movements both modulate the amplitude of the string sound which you can and do hear as well as add an audio component of their own to the bass signal which you cannot hear because it is at too low a frequency for you to hear or for your amplifier to reproduce. When you mount pickups on your bass the vibrations transmitted to the pickups from the string are at the same frequencies as the string produces and they are at some random phase determined by the minute details of the bass construction. These vibrations can indeed have an effect on the tone and without an mathematical analysis that can establish their contribution to a far greater level of certainty than anything I have yet to see done on TB they may in fact be the primary means by which a tonewood colors the bass's tone.

    I have an open mind about the tonewood question even though the best, most "scientific", attempts on TB to establish its existence have had rather unsympathetic results. But I can tell you this, if tonewoods have any effect whatsoever it can only be because they move. If the wood of the bass moves and "resonates" as is so often claimed then the pickup attachment points also move. This is one of the more direct and obvious ways for tonewoods to have an effect on the tone. The relative motion between string and pickup is the only thing that makes electrons move back and forth to eventually produce sound.

    Here's a real problem I have with the tonewood argument and one that I never saw until I just now realized I had overlooked something in my previous post in this thread. I said the string vibration details were determined in part by the boundary conditions at the bridge and the nut. See the issue yet? Even the most dedicated, drop tuned, metalhead does not play only open strings! So, a very great deal of the time the boundary condition at one end of the string is determined by by what is happening at a fret, not the nut. And that points out something that has always been missing in this debate. The boundary conditions for a bass string, one of only two ways a tonewood can have an effect, are not determined by the tonewood or bass construction alone. They are also set by the fretting hand, the strap connections, and the pressure of the back of the bass against your body. Do you get the same response from a drum when you hold your hand against the membrane as when you play it normally? NOPE! But that is what you do to your precious tonewood when you hold your bass....


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