Subwoofer Box Designs; Can You Build them?

Many theories exist related to speaker cabinets.

It is widely understood that well engineered speaker boxes will support the speaker drivers without contributing any vibration themselves.

In other words, the DIY speaker cabinet should not move or vibrate as the speaker cone is moving and making music or recreating the electrical signal.

Why is the speaker cabinet so important?

A speaker driver is designed to operate with the lowest distortion possible. In order to do this it must have a solid platform from which to launch. The movement of the cone should be the only movement occurring so that it is the only movement that is being measured. You aren’t likely to find a well-made cabinet on discount speakers.

If a wood panel is also moving this movement will be making a sound of its own which will also be heard. We often are not aware that the speaker cabinet it contributing its own sound to the overall acoustical output because the two sounds are blended together. This could be described as output summing. What it often sounds like is a coloration of the sound; A higher response in a certain area of the frequency response.

A cabinet that is vibrating will also cause phase problems as it moves opposite of the speaker drivers.

Typically, this resonance of panels is unpleasant because it is usually located higher in volume at certain frequencies than others. This is what contributes to a colored sound. And this is what a good speaker cabinet should try to avoid. You should especially use this method when building custom subwoofer boxes.

Making a good speaker cabinet is not easy though.

The usual deterrents of good cabinet design are as follows:

1. Shipping weight – well-made speaker cabinets are going to be very heavy because of the quantity of parts necessary to build them.

2. Shipping costs – also a natural component of shipping weight. This will drive up expenses for the manufacturing company and this cost must be passed onto the consumer. Another reason to try your own DIY speaker projects

3. Labor – building heavy, extremely well braced speakers will take either large amounts of man hours or machine time or both to build a speaker box.

4. Parts – well braced cabinets will need a larger quantity of materials than a typical flimsy retail speaker offering. The large number of parts is also what contributes to the overall weight of the design.

5. Design time and expertise – sufficient thought and expertise must be part of the process. This is a bit like building a bridge. You don’t design it to fail at its maximum payload or output. Both bridges and speakers should be designed to operate well above their maximum limits. This is also called “margin of error”, like placing trucks back to back with maximum payloads -all on the bridge at the same time. Example: Your son’s friends cranking up the volume level 50% higher than necessary, causing you to buy speakers for replacement.

A speaker design should be built to last and over built like a bridge for added measure. This is especially true of bass systems and subwoofer box designs.

6. Science and Geometry – using some basic acoustic theory and geometry skills is a must for a good speaker cabinet design. Ignoring either of these will result in substandard results. (example; trying to build a cabinet that will cost little to ship to maximize company profits.)

Building lightweight cabinets is fine if your only concern is profit. But most consumers would like to have the choice of higher quality if given the option. Because of stiff competition and cheap prices this often is not possible.

Companies just produce a product that will get the job done as light weight as possible while keeping profits in check. And who can blame them? They are running a business. But this does little to improve the performance of any given speaker design. The DIY speaker box has the advantage here as well.

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