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I am planning to build a "shooting room". I explain myself: I want to reuse a half of an old animal shelter to build a small room (3.5 square meters, 1.7-1.8m height) to store all the weapons, reloading materials (powder, cartridges), etc but also, to be able to shoot a few cartridges sporadically (measuring the FPS and that the reloading process is correct). The room should have two objectives: 1) stabilize the temperature and humidity (to preserve correctly the weapons, powder and cartridges) 2) silence the gunfires outside the room (to avoid disturbing the neighborhood, animals and people).

The first part is quite common and well known. The second part is something I am completely lost and I ask for some help now that I am planning to buy materials and I can design from scratch the whole room (walls, ceiling and floor).

Currently, it has:

  • 10cm Concrete floor

  • 30cm Large rock (cement between them) walls the first 0-50cm.

  • 0.5cm thin wood boards from the end of the rock walls to the roof (50cm to 180-200cm)

  • 4 10x10cm vertical wood beams (corners)

  • Roof: 0.4cm rubber (external) + 0.7cm wood boards (internal) + 2 10x10cm wood beams. The roof has a slope of around 10-15º.

I am planning to build my own walls in the inner part, that is, preserve the externals (thin wood boards) and build new walls inside them. Externally the shelter will be quite similar.

Also, I am open to build over the rock walls, or even build inside them.

So, first, I thought, what are the characteristics of a rifle gunfire?

I found that it has a peak of 140-165 dB (based on my calibers, near to 165dB) and frequencies from 16 to 2500 Hz. I don't know if that is precise or I should know more important features.

https://pubmed.ncbi.nlm.nih.gov/7761796/

https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1808-86942011000200005

https://www.physicsforums.com/threads/gun-sound-frequency-analysis.898882/

Then, since there are many types of materials and the room configuration can be designed from scratch, I thought about studying it with a simulator, trying to get the best quality/budget materials for my purpose, but it is not an easy task.

I found "pyroomacoustics", and my purpose was to get 2 values: peak dB and dB/time since the shot happened, both inside the room (I don't know if "the dB will be magnified due to the room characteristics") and outside (in different positions), that is where I want the sound reduced. I am still evaluating the tool, but it seems it does not allow to use layers of materials in the same wall (what I was willing to do: e.g. half wall with brickwork+rockwool, another with rock+cement+brickwork), so, maybe I can get only an approximation. I can see this table of materials and their absorption coefficients:

https://pyroomacoustics.readthedocs.io/en/pypi-release/pyroomacoustics.materials.database.html

If I understand the table correctly, the higher the number the more absorption will have that material regarding the sound, that is, less sound will be heard on the other side of the material. Also, the interesting coefficients for my case are from 125 Hz to 2 kHz, since those are the nearest to my 16-2500 Hz.

So, concrete, ceramic tiles or painted brickwork will provide really low absorption coeffs (0.01-0.05). On the other side, 50mm of rockwool (80kg/m3) or Mineral Fibre absorber have good coeffs (0.2-0.6-0.8). But there are many materials and with a variety of coeffs/freq, and those values could not be shared by the product that can be found in my local store.

If I filter by "acoustic isolation", I can find around 30 products in a local warehouse where I can buy. Some interesting to use involve:

  1. Brick block termobrick acoustic and thermal. They are too thick (19cm), I could try to cut in half. 0.69€/unit (https://www.bricomart.es/bloque-ladrillo-termobrick-30x19x24-cm.html)

  2. Semi-rigid agglomerated polyurethane foam panel designed for thermal and acoustic insulation in low-thickness backgrounds. 80 kg/m3. 40 mm thickness. 6.58€/square meter. (https://www.bricomart.es/panel-poliuretano-80-kg-m3-multiaislante-200x100-cm-4cm-espesor.html)

  3. Agglomerated polyurethane foam. Use: acoustic insulation in vertical walls. d = 80 kg/m3. Fire resistance: Euroclass F. 80 mm thickness. 12.58€/square meter. (https://www.bricomart.es/panel-poliuretano-80-kg-m3-multiaislante-200x100-cm-8cm-espesor.html)

  4. Roll of Ultracoustic R glass fibre wool intended for thermal and acoustic insulation in vertical walls. Package of 2 rolls. Thermal resistance (R: 1.35 m2.K/w). Lambda (0.037 w/mK) kg/m3. 50 mm thickness. 1.68€/square meter (https://www.bricomart.es/rollo-lana-mineral-ultracoustic-r-1440x60-cm-5-cm-espesor-2-uds.html)

  5. DANOFON sheet made of recycled fibre blankets and high density bituminous sheet. Indicated for acoustic insulation in low, medium and high frequencies. 275 kg/m3. 28 mm thickness. 11.50€/square meter. (https://www.bricomart.es/lamina-multicapa-danosa-danofon-600x100-cm.html)

  6. 133 rock wool covered by aluminium foil. Designed for thermal and acoustic insulation of ventilation ducts, boilers, pipes. 37 kg/m3. Thermal resistance (R: 0.81 m2.K/w). Lambda (0.037 w/mK). 30 mm thickness. 6.60€/square meter (https://www.bricomart.es/rollo-lana-de-roca-con-aluminio-133-800x100-cm-3-cm-espesor.html)

  7. Pyramid-shaped self-adhesive polyurethane acoustic panel designed to reduce reverberant noise in machine rooms. 25 kg/m3. 43 mm thickness. (https://www.bricomart.es/panel-poliuretano-absorbente-chova-piramide-autoadhesivo-45x45-cm-4-3-cm-espesor.html)

  8. TRIACUSTIC 35 multilayer film made up of polyethylene film attached to high-density viscoelastic film. Airborne sound and ground impact insulation. 7 mm thickness. 5.98€/square meter. (https://www.bricomart.es/lamina-multicapa-chova-triacustic-35-800x100-cm.html)

  9. Only for roof: ROCKFON EKLA ACOUSTIC CEILING TILE 60X60X2 CM. Smooth white finished rock wool. Acoustic absorption coefficient: 1. Improves acoustic comfort. Thermal insulation R= 1,25 m²k/w. Very white. 10.64€/square meter (https://www.bricomart.es/placa-techo-acustico-rockfon-ekla-recto-a-60x60x2-cm.html)

My questions:

a) Do you know any realistic simulator I could provide my own designs with 3d objects (STL/OBJ) of the walls/roof/floor and multi-layer materials to simulate what I am looking for? I could answer many questions using those.

b) From the 9 materials exposed above, what is your recommendation for the walls and ceiling? maybe other materials? If I feel paranoic, I can buy pyramid-shaped polyurethane + rockwool for every wall. Is it too much? Or still not enough?

c) The shelter only has soil underneath it, and a thin layer of concrete/cement (eg. 5-10cm). Would you recommend that I create a wood structure with poolwood (or any other material from the list above) and then over it to use PVC paviment/gres for the floor? Or that is overkill, and with just the concrete/cement + PVC paviment/gres is enough? I am thinking about vibrations.

d) A friend recommend me to put fixed windows to avoid using only artificial light, and I thought about "glass brick" (80mm thickness; translucent: https://www.bricomart.es/bloque-vidrio-incoloro-19x19x8-cm.html) but I don't know if that would be bad against acoustic absorption (the glass has low coefficient). I was thinking just to use a couple of rows in one wall, enough to provide a bit of light inside. If it will "destroy" the whole design of the room regarding acoustic absorption, I can forget about providing small fixed windows (alternatively, I have nethacrylate). What do you think?

I attach an scheme of the current state, and the different "ideas" for the walls, floor and ceiling.

https://imgur.com/a/EKrZnCz

The shooting wall would have a pipe (20x20cm) directly towards a huge amount of ground/soil, avoiding bouncing. The hole is not designed because it will be performed in the future, after the whole room is built. That hole/pipe will have almost the same design and materials as the room, but with walls of concrete/pure ground. The purpose is not to practice shooting/aiming, but just to measure the FPS after doing the reloading of cartridges. But I have omitted this hole for the room design. I can do it in the future.

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Do not attempt to soundproof the whole room, just use a drain type pipe, as heavy walled as possible, insert your arm full length into one end to shoot, your body will partially block that end, put some sandbags against theother end, both to absorb sound and to catch projectile. You can cut two opposite windows(or maybe just one) for your FPS meter. Cover hole with glass or acrylic since meters are optical.

Nothing will reduce shot noise to zero but may turn it from a 911 call to "oh, Mike is trying his new handgun"

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