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<blockquote data-quote="Fi Car Audio" data-source="post: 2854134" data-attributes="member: 569083">Before the advent of all the cool programs that calc PRs, I used to approximate a PR design by using the SD of the cone and equating that to a cylindrical port.&nbsp; Given the box size, tuning, and the PR sqin you can calculate the length of the &quot;port&quot; (often obscene given the SD of a 12&quot; PR going into a 1.5 cuft enclosure).&nbsp; From this port length and port area you can calculate the volume of air and therefore the mass of the air in the port.&nbsp; That mass is the theoretical mass your PR will need to tune the box to the frequency you have calculated... I say theoretical as you are assuming that the suspension of the PR is close to that of air (ultra floppy) when in reality it isnt.&nbsp; The floppier the PR, the closer this comes out right.&nbsp; To tweak just add mass.But since we no longer communicate via smoke signals or the pony express, you simply plug in a couple of things into a program to get the same results... along with the graph and excursion levels of the PR at given frequencies and power.Normally you use twice the volumetric displacement for the PR as for the driver itself.&nbsp; (2)12&quot; PRs per 12&quot; sub (with similar excursion levels) or usually you can get away with kicking the PR up to the next size (15&quot; PR for a 12&quot; sub).PRs work great for home... and somewhat well for car applications, although the PRs need to be mounted horizontally (to the axis of movement) as they will sag heavily due to the moving mass and lack of suspension.Thanks...Scott</blockquote>

[QUOTE="Fi Car Audio, post: 2854134, member: 569083"] Before the advent of all the cool programs that calc PRs, I used to approximate a PR design by using the SD of the cone and equating that to a cylindrical port. Given the box size, tuning, and the PR sqin you can calculate the length of the "port" (often obscene given the SD of a 12" PR going into a 1.5 cuft enclosure). From this port length and port area you can calculate the volume of air and therefore the mass of the air in the port. That mass is the theoretical mass your PR will need to tune the box to the frequency you have calculated... I say theoretical as you are assuming that the suspension of the PR is close to that of air (ultra floppy) when in reality it isnt. The floppier the PR, the closer this comes out right. To tweak just add mass. But since we no longer communicate via smoke signals or the pony express, you simply plug in a couple of things into a program to get the same results... along with the graph and excursion levels of the PR at given frequencies and power. Normally you use twice the volumetric displacement for the PR as for the driver itself. (2)12" PRs per 12" sub (with similar excursion levels) or usually you can get away with kicking the PR up to the next size (15" PR for a 12" sub). PRs work great for home... and somewhat well for car applications, although the PRs need to be mounted horizontally (to the axis of movement) as they will sag heavily due to the moving mass and lack of suspension. Thanks... Scott [/QUOTE]

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