How to Build A Speaker Box: Make Custom Speaker Boxes: DIY

My brother-in-law is a genius. The reason I'm saying that is because he learns and then makes things all by himself, best of all, what he makes all look like things you can buy off of the shelf. He's not a science person, he's talented in Chinese writing, calligraphy, Chinese seal carving, stuff like that, yet when he has to deal with science and technology, he reads information himself and implements them with common sense, amazingly, he never fails!

Because my sister likes to sing with Karaoke (we simply call it "K song" in Chinese), that is what got my brother-in-law into building his own homemade speaker boxes just so she and other family members could sing anytime they wanted, and it would save money too, just to think of it. So he ended up building several customized speaker boxes several years ago for my sister, they turned out to look and sound fantastic. I thought they were bought from a store at first. He even had brand labels attached to them and that indeed fooled me. Today I'd like to try my best to present how he built those custom speaker boxes.

He happens to have a pair of polypropylene Nanjing dual cone speakers. Although the price isn't high, the quality is very descent, and the voice is so warm, quite ideal for singing Karaoke.

The Calculations:
It all begins with a series of tedious calculations. My brother-in-law is sort of computer illiterate, so instead of using a speaker design software, he has to go through his own silly way of calculation. You can ignore his way if you can find a good speaker design software online. A small calculator with arithmetic functions makes the process not too hard for him, fortunately. This speaker's Q value is 0.6, and other parameters determine it is appropriate to be a closed-box chamber, so he designed the box accordingly.

The next step is to saw a board. He uses the regular medium density plywood sheet due to its consistent physical characteristics and ease of processing. There are tools you need during the entire process.

The next step is to saw a board. He uses the regular medium density plywood sheet due to its consistent physical characteristics and ease of processing. There are tools you need throughout the entire process.

Restricted by the parameters of this speaker, the volume of the box has to be designed as 20 liters which is a bit too large for a 6.5" speaker pot. To avoid increasing the size of the box any further, he only adds an additional 1 liter space to be occupied by the speaker, and eliminates other normally required processes such as rebar and asphalt coating. Now it has to come down to the speaker box strength. Initially he has considered to cut the corners to 45 degrees so the bonded areas will be larger. But considering without rebar, screws can only be tightened on the board, as the result, the strength screws can bear on a 45-degree bonding surface would be a lot less than if it were screwed on a 90-degree bonding surface. So instead of cutting the board 45 degrees, he chose to make it straight 90 degrees.

The board needs to be cut precisely, pay special attention to the corners, make sure they are exactly square everywhere, including the side and ending facets.

Due to the fact that adjustments are needed in later stage, which require repeated demolition of the speaker box and face board, using just regular hex wood screws may result in damaged screw holes on the panel after all. My brother-in-law chooses to use machine hex screws instead, also glues nuts on the back of the panel so extensive demolishing process can be endured. Either building adhesive or white latex glue can be used for this purpose. A wood strip should be used to support the panels before the glue completely dries out.

Four side panels should be glued first, then the top panel on the loudspeaker side, inner treatments inside the box are to follow after. This includes minimum of two coating of glue, asphalt coating and adhere sound absorbing materials. Glue the top panel on the subwoofer side after all these are done. That way, since the hole for subwoofer speaker is much larger, doing the rest of the hand works becomes so much easier and convenient. This is very important to know ahead of time, or the inside treatments would become a hassle.

Initially a kind of stretchable acrylic cotton was picked for sound absorbing. But it turned out this type of material did not seal very well on metal framed speaker cones, so in the end the silicone sealant was chosen.

First, squeeze out a thick layer of sealant into the grooves the same size of the holes for loudspeaker and subwoofer, wait for about 2 hours till the surface solidifies. After that, push the speaker down to pre-determined depth, and then let it stay until the sealant completely dries out. Do it for both speakers. Now you have a perfect matching sound absorbing speaker pad for each of your speaker. The drawback: you need plenty of sealant, but it's not easy to handle the extra amount; also, also this material has a degree of irritations to human body.