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Vibration Isolation Question

  1. May 2, 2010 #1
    Im new here and im not an engineer but i have a question hopefully someone can offer their thoughts on..

    I film and record bands live and i want to run a video camera at concerts that are often very loud.. At times I also need to position the camera in front of the PA speakers and this combined with lots of bass frequencies and an unstable floor creates lots of vibration which affects the camera..

    So id like to design a small platform to place the tripod on that would absorb the vibration .. I have seen some examples of vibration and shock absorbant items but im not sure how to tackle the problem exactly.. I cant afford to spend too much on this, i was hoping to do something for $200 or less..

    I thought of a semi inflated inner tube from a traktor under a a 4 foot square piece of timber.. I wasnt sure how well this would dampen the vibrations though ? I thought the different levels of inflation may make it better or worse. But how would you know how to determine whats best ?

    The bass guitar usually creates consistant vibration (of varying degrees depending on the notes being played) and then it is amplified when the bass drum hits also so its a two fold problem really, constant vibration plus transients.. Its also affected by the different venues and their acoustic properties..

    Ive looked on this site and seen some things which may help but id like to hear from anyone who has any info they would care to offer as im not really educated on these things.

    http://www.vibrationmounts.com/Products1.htm

    Appreciate any help.
     
  2. jcsd
  3. May 2, 2010 #2

    minger

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    Damping products in my personal experience are categorized in two types. The first are types that damp a specific frequency. These materials typically have damping and stiffness properties that are "tuned" to a system.

    The other type are shock absorbers basically. They work best at damping sudden and unpredictable responses.

    Now, there are some polymer companies that have off-the-shelf materials that you can probably purchase. You can either get pre-formed stuff, like in pads and sheets, or sometimes you can get some pourable stuff. I've worked with GE Silicones, Lord Corporation, and Du Pont. They all have really good people and great materials that you can buy.

    Also, I recently had a project which involved vibration damping and I went to a company called Sorbothane. They basically only do vibration damping. For our purposes we had them mold us some parts, but they sell pre-fab sheets and stuff too. What is REALLY nice is that they publish their damping properties on their website.

    You can also just try something like the McMaster-Carr catalog. They sell vibration mounts, pads, and pourable polymer stuff too. I tested some of their pourable silicone (can't remember the kind, although it was blue) and it had fairly good damping properties.
     
  4. May 3, 2010 #3
    Thanks for the response...

    Ive seen some of the products out there, but would you have any recommendation on what product would work best with live music ? I was hoping to hear from someone with direct exposure to my type of situation before i go spending money as i dont want to end up buying the wrong things..

    At times there is a consistent lower level vibration from the bass guitar but it changes when the notes being played change, and is worse obviously when it nears a resonant frequency.. But then also when the bass drum is played every second or two it creates a spike which is actually the worst part of the problem, you can usually see the picture shake in time with the music as each bass drum is played.. But it also swells up if the song has louder dynamics in various spots..

    So im wondering if theres any recommendations on what would tackle this as best as possible ? i just want to try and do the best i can on the limited budget i have for it..

    Also its an unsual problem because sometimes you will be there and the PA will be REALLY loud and you will be near a speaker but it just doesnt affect you that much, then other times you can be in a similar situation and it can vibrate so bad its almost not worth filming.. i want to try and understand it better and learn which products are best suited so im not just flying blind as i currently am.
     
  5. May 3, 2010 #4

    minger

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    Without sounding like a spokesman, I would first try to get my hands on the Sorbothane, only because I've personally used it with great success. The problem there might by finding a vendor or being able to order a small enough quantity from the factory.

    My next step would be to just go through the McMaster-Carr catalog
    http://www.mcmaster.com/#vibration-damping-mounts/=6xg2zx
    http://www.mcmaster.com/#vibration-isolators/=6xg3a2

    Items there are super cheap, you'll be able to get whatever you want and just play around with it.

    I wonder if anything like a microphone pop-filter would help at all with the bass drum hits. Probably not, but perhaps you could rig something with foam around the camera as well??? Just guessing here though.
     
  6. May 3, 2010 #5
    i have heard good things about Sorbothane also so i will dedinately look into it..

    I just checked the links you listed and there are some good options on there.. They seem to have air springs very cheap compared to what i have seen.. if im reading it right they appear to be $10.24 each ? Im not totally sure but something tells me they might be a good option also... I could maybe put some air springs under the platform and then some sorbothane on the top of the platform under the tripod legs.. I'll email them and see what they say..

    I never thought of the pop filter idea.. Thats worth a shot also..

    have you bought from McMaster before ? Are they good to deal with ?
     
  7. May 3, 2010 #6
    You could also try to shield the camera from the direct output of the speaker with something like foam. To test it before you spend any money, just try holding up a couch cushion. If you are too close to the speaker this could end up making the output sound muffled to the rest of the room and you might have to try something more advanced like is being suggested here.

    As ugly as it looks, you could try using egg cartons around the camera. These work great because the sound hits the surface at different times which really helps damp the sound waves.
     
  8. May 3, 2010 #7
    the problem is more the vibration off the floor than the direct sound hitting the camera.. At least im pretty sure it is.. If i take it off the tripod it doesnt happen so i dont think any of the vibration is just the volume through the air..
     
  9. May 3, 2010 #8

    minger

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    Sounds like a good idea to me.

    They're great. One of the best places to buy hardware of any kind from. Super easy to get a hold of an actual person on the phone too!
     
  10. May 3, 2010 #9
    Minger... I emailed McMaster but they are unable to send to Sydney (where i live) I have a friend in USA that could maybe send things on to me but i was wondering do you know any other places like McMaster that might sell similar items ? I have been looking in google searches and not having much luck.

    EDIT: Also ive been speaking with our local distributor of sorbothane and he was in high praise of its ability.. I wasnt sure if it was just good salesmanship or genuine adivce though.. Were you happy with sorbothane for your application ?
     
    Last edited: May 3, 2010
  11. May 3, 2010 #10
    I used to buy Sorbothane as running shoe inserts (~US $20/pair). Personally, I think it's far too dense for your needs - you've got long, bass audio vibes, not high-freq micro-vibes.

    I'd hang two or more uneven-length rubber bands/belts from a floor-based frame made of uneven lengths of EMT tubing, then hang a camera from the belts. Try changing the angles or resiliency of the bands, with weighty deadeners in their middle or on the camera, etc.

    Add uneven lengths of stiff material, off-center, in three or more axes to the camera, with none perpendicular to a speaker's output to semi-randomly, poorly resonate, thus deadening vibes.

    Try a 'shake-free' video camera. Some use software tricks, some use tiny motors.

    Paint everything black to seem less obvious to the audience, or dress it up to look interesting.
     
  12. May 4, 2010 #11
    If you just want to use the tripod, drill a hole off-center (try different spots) in a strip of metal or plastic and bolt it down. Hang the camera off to one side using the materials I just mentioned (above). Shake-free cam may still be your best bet.
     
  13. May 4, 2010 #12

    minger

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    I'm not sure of any other international suppliers like that; McMaster-Carr is pretty huge here in the states. As far as the Sorbothane stuff, Chazz is right, they do make shoe inserts, which will not be what you want.

    They make several different mixes of the stuff, with a range of hardnesses. I was thoroughly impressed with their stuff. Our other option was going to someone like Lord Corporation, or Enidine. They were going to charge us tens of thousands of dollars for a material development program, whereas the Sorbothane stuff we used was essentially off-the-shelf and performed almost as good as the custom stuff would have.

    Try asking for a sample. I would ask for their softest stuff, and just see if you can get a few square inches of a pad. That should be enough to mount your tripod on. Test it out, if it doesn't work, then try getting some of the damping mounts from a place like McMaster-Carr.
     
  14. May 4, 2010 #13
    im not totally sure but i think the guy i spoke to was talking about some sorthbothane thats different from the shoe inserts.. he seemed to think it would be very effective at what im trying to do and said i wouldnt need much.. But i wasnt sure if it was just good sales or he was really accurate and knew what i would need.

    Unfortunately mcMaster Carr wont sell to me in Australia otherwise id be keen to get something through them.. I'll try the sorbothane and see how it goes.. I think it will cost me around $120 AUD for the small amount that i need.. He suggested i put it in between two pieces of plywood to use as the platform to mount the tripod on.. So i could always add the inner tube underneath that i suppose and maybe even something on top also (was thinking of some carpet underlay and carpet on top)

    Another person i spoke to said a cheap alternative might be some squash balls under the wooden platform. Im not sure how id go mounting them though ? Something tells me the inner tube may be better as i could raise and lower its air pressure ? But i wasnt sure if it would make more sense to have one large air filled device or a number of smaller ones..
     
  15. May 4, 2010 #14
    A cheap fix might be to try some homemade pads for under the feet of your tripod and skip a bulky platform. Maybe something like stacks of neoprene (you can get pieces from surf shops for wetsuit repair), or talk to a local contractor and see if they have any scrap sound insulation around (the kind they use between apartment walls - I think that stuff is designed for low end). Maybe even play around with layered stacks - couple layers of neoprene (or shoe inserts) with a couple layer of heavy vinyl sound proofing, etc...
     
  16. May 4, 2010 #15

    minger

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    Agreed, I had no idea a single pad would cost you $120; that seems a little ridiculous. Either way, I would certainly not sandwich them between two pieces of plywood. That will transmit response from one leg to the others, along with reducing the effective form factor of the pad.

    mapache I think it on the right track. Just get some cheap foam, or soft elastomer and put some under each leg. Do you have a PA available that you could do some testing, or would you have to wait until the next gig?
     
  17. May 4, 2010 #16
    In Australia things are always expensive for some unknown reason, if i can order via USA and the companies will ship to me its usually a lot cheaper.. I guess i can try the cheap options first and see how they go, then work my way up if its not working..

    Wouldnt the distribution of weight across a larger panel of wood be better for the absoring material than the smaller tripod feet ? To my understanding if something is small and pointed (like a pin) its easy to puncture something, so something flat and blunt distributes the force wider ? So wouldnt the platform be better at isolating the vibrations ?

    The tripod is really tall and fairly heavy also so the feet would squash down most foam fairly easily, not saying im not willing to give it a go just might need to find the right foam, or maybe add some rubber on the top..

    I dont have a PA which is anywhere near the size that creates the bass problems.. What i can do though is build something and then go to a gig i expect to be loud and test.. Hopefully i can iron out the bugs on gigs where its just me and there is no expectation to get it right.
     
  18. May 4, 2010 #17
    Good point - you should use rigid toppers like pieces of plywood or something if you go that route.
     
  19. May 5, 2010 #18

    minger

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    I still don't agree with sandwiching the damping material. One of the big problems with the elastomers is that they are nearly incompressible. They often times have Poisson ratios of 0.499 or higher. What this means, is that if you push down on one side, it will pop up the other side.

    In other words, you need to give the material room to expand, otherwise the material can act very very stiff. By constraining the material with plywood on both the top and bottom, you're hindering the materials ability to damp. If you need to go that route, either because the tripod is too heavy and you just need additional area, or whatever, then make sure that each leg has its own independent piece to sit on.
     
  20. May 5, 2010 #19
    What you are saying makes sense minger.. I will experiement with a few setups and see how i go.. Theres lots of varying opinions so i think its going to come down to actual practise and seeing what works..

    The thing that i keep wondering about beyond how to attach and stabilise the setup is if i can manage to dampen the platform in the correct frequency range.. im realising the only way i'll find out is by trying. Im going to start with the inner tube idea cause it will only cost me a small amount for the tube, i might even be able to find an old one at the auto wreckers.. I'll prgress from there if its not effective at all..
     
  21. May 5, 2010 #20

    minger

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    Sure, perhaps with some software stabilization that might be enough. Good luck!
     
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