How to build a Foley pit

Base flooring

One of the key factors in how any Foley pit will sound is what floor it will be installed on.

What do I mean?

Imagine that your Foley room will be located on the second floor of a multi-story building, or, worse, in the upstairs of a house with flooring laid across suspended timber joists. In both cases, the likelihood that resonances from the floor structures will be translated to your Foley footsteps is extremely high. The resonances will be especially audible on the recordings of dynamic steps, where the entire body weight of the Foley artist is used during the performance. A concrete slab floor in a multi-story building will almost always resonate as well as a timber joist floor. You may not be aware of it, but try to record active jumping on such flooring into a mic.

I see Foley artists who continue to work in these difficult conditions, trying to decrease resonances by reducing the performance dynamics, putting less energy in their footsteps, and placing the microphone close to the source. But this is, perhaps, another topic for another article.

What is the best?

Ideally, Foley pits are placed on a massive concrete slab with sand or ground underneath. Moreover, such a slab should be a mixture of cement and sand where the cement content is greater than the sand content. The thickness of a monolithic foundation slab should not be less than 30 centimeters. I cannot speak for everybody, but here in Russia, the use of monolithic foundation slabs in building construction is widespread. Unlike a pile foundation, a cement slab practically does not have any resonances since it is damped by the dense layer of sand on which it lies.

I know a Foley studio where the concrete surface is a free-standing monolithic cement slab, 80 centimeters deep, integrated into the ground. This surface sounds as solid as possible. This is a great solution. But it's worth mentioning that the cost of building this Foley theater was over $1 million.

Base flooring in Foley First

Here at Foley First, we have a 35 centimeter monolithic cement slab laying on a thick layer of dense sand.

The only, but significant and undesirable, difference is that in our case, on top of the foundation slab there are also 2 leveling layers of expanded clay, or LECA, and levelcrete. This was originally installed for thermal insulation and for leveling the floor.

Before building the Foley pit, it was essential to dismantle both of these layers since the air cavities in the LECA layer and the levelcrete (with a high sand content) inevitably translate resonances in the range of 80-200 Hz. As I said, if a concrete Foley pit or any other Foley surface is erected on such a base flooring, then one way or another, the resonances of the original floor will be audible in your Foley recordings. So the main
goal was to get to the foundation concrete slab.

Foley pit construction

Materials

As you can see in the picture above, my Foley pit framing is built from cement. I am totally against using wood framing for Foley pits since the wood does not have sufficient density and weight, and as a result, it translates low-mid/mid frequency resonances. But wait. We’ll still need wood to build the Foley pit.

Before building the Foley pit, it is a good idea to first decide on its dimensions. In my case, the dimensions were determined by the room itself and the space available since the new Foley pit is not the only one on our Foley stage. A Foley artist himself should choose the dimensions of each surface on which he has to work, but for me, I wouldn’t advise building a structure with a usable area of less than 0.8 sq. meters. At any smaller than this size, the Foley artist will be severely limited in artistically performing his footsteps (unless he is performing Foley sitting down). Dimensions of 1.2 x 1 meter are optimal for me. Bigger is better.

The materials we used are:

1. Ready-to-use sand mix
2. Concrete
3. Wood, 190x20x3000 mm, or about ten feet of 1x8 boards (used for framing)
4. Rebar

To make the sand mix stiffer, we added 1/3 concrete to it.

Step 1: wood framing and its size

After we dismantled the layer of levelcrete and LECA and prepared the surface, the first step was to erect the form for pouring the cement for the Foley pit’s frame.

Coming back to the question of dimensions, I would say that the thickness of the Foley pit’s concrete framing on all sides should be at least 70 millimeters. Personally, I prefer a thickness of 100 mm. This is enough to obtain a solid and splinter-resistant construction.

The height of the structure itself can vary depending on the function of the Foley pit and the preferences of the Foley artist. Depending on what texture is planned to fill the framing, its height can range from 50 millimeters to 1 meter (if we are talking about a water tank).

Also, I should mention the internal shape that the concrete Foley pit should take. If you plan to erect a universal pit that is fairly deep, say 30 cm, and the depth of the bulk material used for your Foley footsteps will vary from 5 cm to 10 cm, then I recommend that the concrete framing forms a trapezoid or otherwise abandons a regular shape with parallel walls. This will eliminate unwanted standing waves inside the structure if the depth of the bulk material is too low. With parallel walls and a low level of bulk material, the internal space of the Foley pit starts to reflect sound, which translates to resonances. This is especially true for the water tank.

To keep the inner walls of the Foley pit neat, we use a simple method of covering the wood framing in polyethylene plastic sheeting before pouring the cement. In this case, after drying, the cement will not stick to the boards and will have a smooth surface.

Step 2: reinforcement of concrete

I would recommend using rebar to reinforce the concrete. This will stiffen the structure and allow it to bond to the base concrete slab.

In my case, reinforcement of the concrete consists of two rebar rods around the entire inner perimeter of wood framing and several metal rods integrated into the base concrete plate to a depth of 10 centimeters. (See the picture for the arrangement.)

Step 3: pouring the cement

There are no tricks here, and I'm sure any worker knows how the pouring process works. If you choose to do it yourself and have no experience, you should consult with experts before you start because it is important to use the correct proportions of cement, sand, and water.

Result

This is how the finished Foley pit looks in our Foley stage. The whole process of erecting such a structure can be done within a day, but it will require construction skills from you if you have never worked with cement and do not have professional tools.

I hope this short article was useful to you and answered many important questions.

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Thanks for reading!

Text edited by Rebecca Wilson Jones