1. When shuld you use the passive radiator?
Reply: Use a passive radiator when you would like to have the extra output of a vented system, but are not able to fit an adequate port into the enclosure. The tuning of a PR is determined by the amount of mass on the diaphram, where the tuning of a port is determined by length. Often if you want to get low tuning in a small enclosure, an adequate port will just not fit. You either need to sacrifice output by going with a smaller diameter port, or sacrifice low end extension by going with a higher tuned port. For example, we use a single 15″ woofer in an enclosure tuned to 20Hz with a pair of 18″ PR’s. If you wanted to get the same tuning with an adequate port, it would need to be 6″ diameter and nearly 60″ long and you would STILL have problems with vent noise.
2.What are the benefits of passive radiator than a simple port?
Reply: A passive radiator does not have the pipe resonance, air turbulence, and escaping internal box noises that the simple port has. They are also easier to implement than a port when the tuning frequency is very low, and most importantly will not compress the output until they reach the limits of their suspension travel.
3. Does the size of passive radiator matter?
Reply: Passive radiators are very sensitive to the surface area of their moving assembly. The larger the better usually until either the passive is too large for the cabinet, or the moving mass of the passive is too large to be used reliably. Larger passives will need more mass to tune to the same frequency as smaller passives. Larger PR area is beneficial as it lowers the effect of the PR Vas on the cabinet, increases the Qms of the passive closer to that of a port, lowers the PR “notch” in frequency, and can allow more output before the PR reaches its suspension limits. All of these combine to give more LF output.
4. What happens when I double the amount of passive radiator?
Reply: If you double the surface area of the passive radiator, and keep everything else the same, you must increase the total PR Mms 4 times in order to keep the same tuning frequency. In other words, both passive radiators now need to each have double the Mms of the original single unit. This is similar to a larger diameter port needing more length to tune to the same frequency as a smaller diameter.
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