Recently, a number of people have been asking me about this design. Even though it is not new, many are taking a recent interest in it. I have decided to put up this page so that way people everywhere can satisfy their curiosity. I will not put it in any search engines so spread the word to anybody who is interested so that they may use the information they need. My image really sucks, I know but I don't have three hours to spare to make it perfect. The big hole is for the driver, the two smaller hole are for the ports tuning those chambers. The dotted line is the partition between the chambers and the dotted cylinder is the third port joining the two chambers. Note that the placement is not critical as long as there is a 3 inch gap between any port opening and a surface.

Although the double-chamber reflex was suggested first as a design that could be used with woofers of various specifications, you can apply Thiele data to it as well as to single-chamber boxes. Here is how to do it in a four-step procedure:

- Choose your woofer. Use it's specifications to find the optimum volume. In other words, the Vb of a simple ported box.

- Set the lower frequency of resonance for the box. This frequency should be equal or lower than the calculated fb for your box. Note that there will be another box resonance at twice the frequency of the lower one. This is caused by the second chamber being half the size but the port the same size.

- Choose a port area. Don't make it too large because you will have to get creative to be able to fit it well inside the box. Remember that the port area of a single tube must be multiplied by 2 to measure the total vent area that interacts with room air. Ex: a port diameter of 3" will be as effective as a single 4" port due to the fact that there will be two 3" ports. A 3" port should be fine for a 10" or 12" speaker. A 4" port for a 15" and a 5" port for a 18" speaker.

- Use the total cubic volume and twice the area of one tube to find the duct length using the program or a chart. I prefer the program. This length will apply to all three tubes. Remember that you must divide the total volume so that one chamber has twice the cubic volume of the other. This does not apply to you if you use the program. If you do use this method just multiply the total volume by 1/3 and 2/3. Duh!

The double-chamber reflex has some advantages over single-chamber boxes, particularly in some situations. For example, suppose you want to build a tall, narrow speaker. If you made it a single-chamber box, you might exceed the useful length-to-width or depth ratio, making the enclosure act like a resonant pipe. A double-chamber box can prevent such resonances if one chamber is placed above the other, increasing the height.

The excursion plot of a double-chamber reflex is lower in the since that it has two dips instead of just one. It will unload at infrasonic frequencies just like a simple reflex enclosure. One disadvantage other than the complexity of the design is the complexity of impedance equalization circuits. It has three impedance peaks.

I hope this tutorial has been of great help. If you have any questions about the design you can e-mail me. If you have any other questions related to subwoofers I suggest you visit the subwoofer discussion forum at http://www.spiceisle.com/audiodiy/talkshop/.

Here's the almighty program that you're all drooling to get your hands on.

If you want the original 80 KB program that has 21 functions, most of them useless, use this incredible link. Loudspeaker design program. DON'T FORGET TO USE CAPS LOCK!!!