Help stabilising a tripod

[Randy Sanchez]

Thanks for all the great suggestions.. I still havent started to work on anything yet but i will report back when i do.. I have some things to film in a short while so i will need it sorted in the near future.

[Les Nagy]

The problem with loud sounds is not easily overcome. Adding a sheet of wood into the mix is adding another microphonic element into the mix. The drum beats will be picked up and the sheet will vibrate in sympathy. This is the exact wrong direction to go. (Sorry Chris)

Chris is right in that adding mass and decoupling is needed. One way to do this is to use a foot level spreader or dolly. The three points can be isolated from the floor by just sand bags in some cases, by triangles of wood with three tennis balls glued on and the tennis balls partially cut off, or with small soft rubber things. I am being specifically vague here because each setup and each venue has their own requirements as to what is the best decoupling compliance.

Adding mass to the tripod near the top can help detune the tripod from resonating at the specific frequencies that are upsetting the image. Sometimes putting a sand bag one just one leg can fix all the problems in vibrations. As a general rule, try not to have all the legs have the same mass on them so that they all don't resonate together at the same frequency. Sand bags are your friends.

And one last thing; most image stabilization systems do not like vibration and can make the image look even worse. Make sure that any stabilization is turned off in these kind of environments.

In summary, detune similar parts so they don't have the same resonant frequency, image stabilization off (but it shouldn't be on when using a tripod anyway), do not add sound receiving materials into the mix such as sheets of anything, and decouple the legs from the vibration using any method that works for the situation. This last point means carrying around many different things in your concert kit bag.

[Chris Soucy]

Glad to see you survived the earthquake carnage unscathed.

Back to the chase.

When I was considering the problems faced in the environment that Randy shoots in, I was minded of those aerial video clips from Vietnam, showing the results of high level bombing on jungle areas in high humidities.

Those as can hark back that far will remember the rapidly expanding doghnuts of high pressure "cloud" created by the blast wave travelling at the speed of sound in air (the ground blast travelling considerably faster and clearly visible in some shots.

Mapped to Randy's circumstances, if you consider those big speaker banks as "ground zero", then the first thing the pressure wave is going to do is push that floating wooden floor down vertically, then suck it back up again, creating a vertical pressure wave radiating out from said "ground zero", travelling at some colossal speed, as it is radiating through a (more or less) solid.

This means that to protect the camera support you need to isolate it from that vertical wave. I gave a lot of thought as to how to acheive this isolation and every scenario just led me to the same dead end due to the sheer bulk of individual shock absorbers for each leg and the sandbags required to achieve the necessary inertia.

Being mindfull that sandbags need real estate and must not at any point touch the floor, else they will "short circuit" the isolation, I concluded a platform was really the only way to go.

However...............

Going back to "ground zero" for a moment, we need to look at the second thing that is going to happen with that shock wave. This is, of course, a spherical pressure wave travelling at the speed of sound (much slower than the floor shock wave) which is going to rattle the teeth of anything with a plane cross section parallel to the line of travel.

Compared to the tripod legs, head and camera, the platform has a minute plane cross section in the direction of the shock wave travel, AND, being suspended at some distance above the floor will allow the shock wave to travel both over and under it, cancelling it's effects out to a great extent. There will be some minor attempt to move the platform back and forth but there should be enough inertia imparted by the necessary sandbags to keep that to a minimum.

Thus, although the platform is not ideal, it appears to be the lesser of all the available evils.

(Sorry Les......:)

Of course, this leaves us with the major problem of that airborn pressure wave acting on the above mentioned legs, head and camera. As you have highlighted, Les, this is a real can of worms, and whilst all your suggestions are valid, I can see no perfect solution but to have some sort of rigid, curved barrier which physically prevents the pressure wave from impinging on the exposed elements.

How you contrive such a monster, move and position it etc etc is proving a major stumbling block, tho' as anyone who has sought temporary refuge in a disco from the speaker towers by cowering behind a concrete support pillar can attest, it works.

Nice to see you back, Les!


CS

[Les Nagy]

Thanks Chris!

One has to consider that there isn't a simple single spherical pressure wave expanding from a point. In any real concert environment there are multiple sources and multiple paths for them to be reflected. If the tripod is on a floor that isn't 1 meter of concrete the floor itself can re-radiate stored sound energy. There are many variables to consider that can affect a sheet of plywood sitting a few centimeters from the ground.

The reason I am so emphatic about this is because I ran into this situation and solved it.

The particular situation was one where I was AD on a music video shoot and the camerman had brought along his homemade (but well made) dolly and track system. It tracked smoothly but as soon as the drummer started to kick away at his bass drum the image went wild. The cameraman and the director had no idea what was going on and asked me to look. The dolly was a sheet of plywood straddling two runs of rigid plastic tubing on roller skate wheels. The tripod legs had been placed in sockets that placed the legs at two corners over the wheels, and one over the middle of the board. The only thing that tamed this problem for them while they needed the tracking shot was to sand bag the centre of the board, place a sandbag on the middle of the board leg, and hang a weight from the middle spreader. The floor that all this rolled on was a thick poured concrete base. The camera behaved properly hand held, and on a tripod NOT on the plywood sheet.

As I said, there is no right solution that works for every situation. Each vibration problem must be approached with imagination and the willingness to try whatever works for that one time. Floors will be different, the acoustics and speakers will be different, the camera might be different, and the height of the tripod can change things too.

I did not say what I did in my previous post as a theory, it is from practical experience.

One last thing. A sheet of wood a few centimeters above the ground does not provide a symmetrical area top and bottom to a pressure wave, and it also depends on the wavelength of the sound involved.

[Steven Davis]

I just ran into this tonite at a concert, the base on the drums was so loud, my back camera was bouncing. I think I'm going to get a couple of those foam puzzle pieces and see if I can do some testing. Maybe if I cut sections off, tape them together and put them under the legs............. is there anything gaff tape can't do?