You’ve probably seen a speaker enclosure with a port built into it (also called vent). The air trapped inside the port (or vent) in a ported enclosure acts as an air piston that interacts with the speaker and, in general, helps the same speaker play lower and/or louder than it would in a sealed enclosure.
A ported enclosure is not a new concept in speaker design; a dual-ported enclosure is. A dual-ported enclosure may be a good solution if you’re limited in terms of the space you have for your sound system project.
Is Two Better Than One?
Ports are used to tune an enclosure to a particular frequency. That frequency is based on the speaker’s Thiele-Small (T/S) parameters and the volume of the enclosure. Sizing a port correctly requires a good knowledge of audio design (and some math that is too complex to get into here).
Typically, the port cross-sectional area is selected based on the size of the speaker with the goal of preventing the air, moving in the port, from reaching a speed that is faster than 10% of the speed of sound (that is, 35 meters/second). This is the speed at which the air can begin to cause audible port noise or chuffing.
If your speaker system must fit into a compact space, a port requiring a large cross-sectional area may be too long to fit into your initial design. When this happens, a primary port with a small cross-sectional area can be used to set the tuning frequency, with a secondary port added with a larger cross-sectional area to slow down the speed of the air.
Creating Dual-Ported Systems
Because size is almost always one of the limiting factors for an OEM sound system, MISCO has had to prototype and test dual-ported enclosures many times. This is how the process typically goes:
- A customer provides the performance and size specs they need to achieve with their system.
- Multiple simulations are performed using speaker modeling software to find the best enclosure design.
- A prototype of the enclosure is created using either a CNC-routed MDF (manufactured wood) or a 3D printer that puts out carbon fiber–impregnated ABS. The enclosure material selected will impact both durability as well as sound performance.
- Once the speaker and enclosure are assembled, impedance tests are conducted. Most ported speaker systems exhibit two impedance peaks. The center of the trough (or dip) between the two impedance peaks is the tuning frequency.
- The tuning frequency that was measured with the testing is then compared with the software model to ensure that the tuning is correct.
- The frequency response measurements are taken, and the design and sample are shared with the customer.
Unique to MISCO, customers have the option of having their speakers and systems assembled at our factory in Minnesota or in Asia.
DSP Can Protect Your Speakers
When a speaker system is sent too much power below the port tuning frequency, the speaker no longer has an acoustic load (or becomes “unloaded”). When this happens, a speaker may move extraordinarily far, causing damage to its cone, surround, spider, or voice coil former (also called a bobbin). This could permanently damage a speaker.
A good safeguard against this is an amplifier with digital signal processing (DSP). With DSP, you protect the enclosed speaker from playing below the port tuning frequency with a low-frequency, high-pass filter applied.
