Get a cheap sub and make a premium box for that speaker

How much an enclosure matters in an audio system? Well, we’re about to find out. I’m going to buy a cheap sub. The cheapest 12″ subwoofer we find available on the known DIY Audio websites and build the best box (within reason) we can for that particular sub. In our case, the subwoofer is a GRS 12SW-4 and the enclosure we will build for it is a 4th order bandpass box. Go ahead and watch the YouTube video for detailed instructions, but read the article as well for all the parts, dimensions and maybe tips I forgot to mention in the video.

Parts list

Here are all the parts you will need for this build. Except for the box material. You can use whatever you have available: MDF, plywood etc. Here are the links for the parts, from the most known web sites.

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Loudspeaker engineering : How to design speaker crossovers

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Box dimensions

We got all the parts that we need, including the cheap sub, now we have to make the box. The material I’m going to use is 18 mm thick MDF. Plywood works as well. Now, I’m going to list the panel dimensions for 18 mm thickness but I’m also going to list for 19 mm thickness. As I’m told 18mm thick MDF/Plywood is very difficult to find in the US, therefore, to keep your math to a minimum, I’m going to list the 19 mm thick panels as well.

cheap sub premium box GRS BP4 subwoofer

Now these sketches serve both types of thicknesses. The cutout for the speaker is done in the middle of the baffle panel and the diameter is 11″ and 6/16″ or 289 mm. The brace is just a random widow frame.

18 mm thick

Panels sizes:

  • Front / back = 400 x 544 x 18 mm (2 pcs)
  • Top / bottom = 414 x 544 x 18 mm (2 pcs)
  • Sides = 450 x 400 x 18 mm (2 pcs)
  • Baffle / Brace = 414 x 364 x 18 mm (2 pcs)

BP4 enclosure GRS 12" subwoofer

The pics should be self explanatory.

19 mm thick

Panels sizes:

  • Front / back = 400 x 551 x 19 mm (2 pcs)
  • Top / bottom = 412 x 551 x 19 mm (2 pcs)
  • Sides = 450 x 400 x 19 mm (2 pcs)
  • Baffle / Brace = 412 x 362 x 19 mm (2 pcs)

cheap sub expensive box


bass reflex port

Bass reflex port

The port is made out of 3 parts: 2 flares and 1 tube. The tube needs to be cut to size. Using some sort of manual saw and some patience will do. You can use some sanding paper if your cut was not perfectly straight. Gluing the parts together with some PVC glue is a very good idea. Also, placing some blu-tack between the port and the box is highly recommended. Forgot to say the dimensions of the tube: 60 mm. This is the dimension of the straight tube only (without the inner and outer flare).

Damping material

For this box, damping material is used in both the sealed chamber and the ported chamber. Use some poly fill to fill the sealed chamber 50-75%. That stuff is fluffy, so make sure you press it in somewhat. For the ported chamber line the walls with some dense speaker damping. In the parts list, the Amazon link contains some thin insulation material (only 5 mm thick). If you plan in using that, make sure you use 2-3 layers of that stuff. If you get the Parts Express or Sound Imports damping mats, 1 layer is enough. The ported chamber damping material is to absorb some higher frequency resonances. If you plan in using an aggressive low pass filter (60 Hz maybe), you won’t hear those resonances anyway. As a result, you could say that in some cases the ported chamber damping material is optional.

Cheap Sub Premium Box

I like this idea of a cheap sub and little-to-no-compromise box. However, don’t have huge expectations of this subwoofer. It’s still a cheap 100W sub. Although, if you factor in all its shortcomings, it’s quite impressive when it’s paired with a great box.