Scan Speak 290001

130 mm flow resistor Scan-Speak Flow Resistor Aperiodic Vent - EACH Cutout size is 4.3 inches. Product picture demonstrate the front and back side of these vents. They are sold each, so order two if you require a pair. Aperiodic vents lower the Q of your driver in a sealed box. They essentially makes your sealed box woofer act as if its in a box that is roughly 20% larger. We recommend using one vent for boxes up to 1.5 cubic feet and two vents for larger speakers. If your box is really undersized or if you are using a large woofer in a small box, you could use two or more, to help reduce pressure in the box. Also known as the "Scanspeak 130mm Flow Resistor #290001".