How to Build the Best Subwoofer Design

If only subwoofer design were simple…

Many DIY speaker builders think that building a sub is as easy as making a box and sticking a subwoofer driver into a basic box… don’t waste your time.


Things to watch out for

Cabinet bracing; integral to the best subwoofer design…

Just stick that driver in any old box right? Bad idea… The speaker box is a great way to get maximum performance out of your speaker drivers and subwoofer plans. A well-built and braced speaker enclosure design can make a huge improvement over a thin, flimsy, and lightweight speaker box or subwoofer design. Don’t cut corners.

Build the best subwoofer design you can afford.

This might mean using twice as many braces as you originally planned. It also may mean making the outside dimensions larger to keep the internal volume that you need for the driver you choose. It might mean your sub will weigh twice as much as you thought it would.

I don’t mean to be rude, but most speaker designers don’t have a clue what it takes to design, construct and execute an excellent subwoofer design.

You really need to think big, think heavy, and get rid of any ideas that overbuilding a box and overbuilding a design won’t make a huge difference. Detail is very important here, and most subwoofer manufacturers just don’t bother to invest the time and materials to building truly remarkable sub. (Exception; The JL Audio Fathom and Velodyne DD1812 are both excellent)

Best subwoofer design

Driver T/S parameters and subwoofer kits

Driver suitability of a sub driver to the box type, sealed, ported, band pass;

Not all drivers will work well in all boxes or subwoofer designs. You need to know thy type of box you want to begin with then find a suitable driver to place into it.

Or find the driver you want and build the correct box for it. In either case sometimes you can have multiple options. There are many different ways to sub design and box building.

There are times to use a low Q design, as well as times to use a high Q design. It all depends on what you are trying to achieve.

Some practical Help

When choosing your speaker driver, first know the type of box you want to place it in. Here are some helpful tips;

Sealed subwoofer box:

Look for drivers with a high Qts and Qes of between .40 to .70. Drivers that have between .20 to .40 are better suited for ported sub woofer boxes. This is a good place to start.

Driver volume: you can get a good idea of the amount of air a driver needs by looking at the VAS numbers. Do not use this number exclusively as to determine the amount of volume you need in the box. The VAS number is just a place to start. It can give you a general idea of the size of the box. We will get more accurate numbers later using the calculators at the bottom of this page.

Pay attention if the figure is listed in cubic feet or cubic liters. You will get a high Q if placing a VAS 4.5 cubic foot driver into a .5 cu.ft. enclosure. High Q is fine if you designed it for a specific reason, but it might mean you have no bass in the 20Hz region also.

Use a calculator to help you determine your ports and best box volume sizes. If using a sealed box you have more leeway here as sealed boxes are not quite as picky as ported boxes for achieving good results. However, you can still get the best performance by using an understanding of the specific driver and the box volume to your benefit. A small box volume will yield a higher Q than a lower box volume if using the same driver. Both can be used successfully if you know what and why you have chosen the specific design.

Example – understanding the sealed box:

You can increase the power handling of a driver by placing it into a smaller box than ideal. The added back pressure of a small box will keep a driver from bottoming as easily allowing for higher SPL. This will also raise your F3 or 3db down point of the lowest frequency also.

This is considered a high Q system; the lower box volume presents less expandable air to the back of the speaker driver raising the Q. You can push more power to the driver without bottoming, but it will not play as low in frequency.

The inverse is true as well; more cabinet volume will decrease the Q offering more low bass extension but the cone will bottom easier lowering the power handling.

If you have ever seen very small subwoofers they are built with a driver that has a very low VAS so that they can be used in a small box and also need lots of amplifier power to reach really deep. The limited air volume keeps them from bottoming out easily, more power is needed to reach the lowest frequencies. Use a calculator to make it easy.

Go to sealed subwoofer box calculator.

Go to ported subwoofer box calculator.

Understanding the ported box:

Ported boxes must be calculated accurately.

The volume of the box can be changed within a certain range. Depending on the volume and driver you choose will change the size and length of port you will need.

Start with a driver that has Qts and Qes Thiele Smal parameters of .20 to .40. Example; Qts .35 Qes .32, these would work well in a ported cabinet.

Next, what is the VAS? This is the compliance of the driver which is the same as if sealed in a chamber of air. It moves as easily in x amount of air as it does in free air. It is the compliance of the driver and it helps us determine the type of box it should be placed in. Higher numbers will need larger boxes; lower numbers, smaller boxes.

This number will be a rough idea of how large your box should be. Your cabinet will likely be slightly smaller in volume than the VAS number of the driver.

Use a calculator to figure your best volume, box dimensions, and port dimensions. I use these links often.

Go to ported box calculator.

Go to sealed subwoofer box calculator.

Plug your specific driver T/S parameters into the calculator to arrive at the desired results. If you need help figuring out your volume, this page is helpful as well.

Go to enclosure volume calculator.

Amplifier Power needed for your subwoofer plans:

This is where things get really dicey. There are formulas for how much power you need. But what they don’t take into account is the listener; the individual that is using the subwoofer design is missed. So only you can choose how much power is enough. Often, the budget is another factor as more powerful amplifiers usually cost more than their low power counterparts. Also features are a factor. Do you need a phase adjustment? Bass boost?

It might seem silly but especially when building a sealed subwoofer the bass boost is handy to overcome some of the natural roll off of the sealed cabinet.

EQ functions are also very helpful in getting the best performance out of your sub. Here, you really get what you pay for. The higher priced subwoofer amplifiers will have more power and more features than lower priced, low power units.

A word about the ELA-5 subwoofer

We take these same theories and apply them to our own subwoofers. If you are not interested in building your own sub, we can do it for you.

The ELA-5 is truly remarkable. It uses birch ply construction. This is not a conventional box folks. The inner chamber is very well braced. The driver is top notch too. Read more about it at subwoofer diagram of the ELA-5 sub.

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