[Paul Spencer]
These suggested projects are intended as a starting point for designing your own subwoofer. There are a lot of decisions to be made, and it will take some time to become familiar enough with all the issues to make good decisions. However, the process is simple enough for it to be worthwhile to design your own rather than make a clone.
Why reinvent the wheel? If you can find a good design using parts you can obtain and you think you will get good value, go for it. But in many cases you will want to do something diffent to suit your own tastes. Designing your own can be a big part of the satisfaction.
| | project | recommended uses |
| 1. | 28L compact sealed sub | small rooms, space limits, music only, moderate output |
| 2. | 85L vented sub | home theatre, high output, low extension |
| 3. | 85L passive radiator sub | as for #2 but higher output potential |
| 4. | 250L EBS sub | 15 Hz extension for home theatre |
Project 1: compact sub
Summary: This is for those who want it small! Simple to build, and in small rooms or very solidly built rooms with a lot of
[room gain].
Driver choice: With eq, just about any driver can be made to work in a sealed box, as long as it has sufficient excursion. A 12" driver with an xmax of 12mm and a thermal power handling of 300w at least is recommended.
Box size: If you don't plan to use eq for music-only applications, then choose a volume that gives you the desired Q, which may be 0.707 for reasons of size, or critically damped 0.5. With a Linkwitz transform, you can choose both the box size and bass extension. Output is limited by excursion.
All the other choices are covered elsewhere in the subwoofer wiki pages.
Project 2: vented subwoofer
Summary: This project is larger, plays louder and deeper. 6 dB more output and an extra octave of extension (without eq) is typical. Many feel that vented subs are inferior for music, but this is a moot point. Due to the reduced cone excursion around tuning, distortion is lower.
Driver choice: Most common diy sub drivers are as suitable for vented as for sealed alignments. A 12" driver with an xmax of 12mm and a thermal power handling of 300w at least is recommended.
Box size: 85L net volume is a good starting point with a tuning point around 20 Hz. You should simulate the response and try many different sizes and tuning points before deciding.
Vent issues: The biggest challenge is getting a vent that won't have turbulence at high output. With a box of this size, there is a limit to which drivers can be made to work. If the driver is an ultra high excursion driver, there is no way to design a vent tuned around 20 Hz which will fit in the box without having audible vent chuffing due to air moving at high velocity through the vent.
If tuned to 20 Hz, a 120mm vent must be 0.9m long. This is about the biggest vent you can fit in a box this size. A flare on each end will be required to keep vent velocity to an acceptable level. With 17mm one way excursion, maximum 23m/s vent is likely with this vent. With a flare with a radius of 50mm, you should not have a problem with turbulence. If the xmax is significantly larger, you will need to make some changes: larger box, lower tuning, larger vent diameter and flare radius.
All the other choices are covered elsewhere in the subwoofer wiki pages.
Project 3: passive radiator sub
WARNING! This project will cost more than project 2. A passive radiator box is not superior to a vented box in any area of performance, but it will cost you more!
Summary: This is for those who want it low and loud without being huge! Why chose this over a vented sub? Try designing a modestly sized subwoofer with an ultra high excursion driver and you will understand. You can put a driver like the Tumult with 34mm xmax into an 85L box and achieve probably more output at 20 Hz than any other sub.
Driver choice: If you are going to the expense of getting passive radiators, then choose a driver with some serious excursion ie. 23mm one way xmax or more. If you are using a driver with an xmax of 12mm you might as well spend your money on the best driver you can get and build a vented box. For a 12" driver you should use a pair of 15" passive radiators mounted on opposite sides of the box to each other. For a 15" driver use a pair of 18" passive radiators and for an 18" driver use 3 or more 18" passive radiators. The suspension system of the passive radiators is not linear, hence more of them will have a lesser excursion and better performance.
A passive radiator sub is easily designed with a typical simulation program such as
WinISD. They are tuned by adding weights to the unit.
All the other choices are covered elsewhere in the subwoofer wiki pages.
Project 4: EBS sub
Summary: This is for those who want VERY deep bass. Make the box 50% larger and tune it lower and you can achieve very deep extension. You will sacrifice some midbass output however. As tuning is lower and the box is larger, vent turbulence is much less of a problem. In fact, you may find that a driver you couldn't use in an 85L box due to vent chuffing will actually work without issue in an EBS! This is a great choice for home theatre subs with very high excursion drivers.
Driver choice: Very high excursion is necessary to make the extra extension useful, with sufficient SPL to offset the insensitivity of the ear down low.
Box size: 120 - 140L is typical with a tuning point of around 15 Hz. You will need to experiment with this.
All the other choices are covered elsewhere in the subwoofer wiki pages.
