Can someone explain the science behind ported boxes?

[TeamHT]

A ported box is a HP filter, 12dB/oct. Notice how ported boxes roll-off at around 24 dB/oct instead of the average 12 for sealed boxes. Imagine the cone of the speaker as a weight, imagine the suspension as a spring, and now hang the weight from the spring and you have a resonant system. Compliance, resonance, it's all there. The port is essentially a smaller spring and a smaller weight attached to the first one. The port itself is similar to a helmholtz resonator. At a certain frequency, depending on tuning, the port will resonate. The energy providing this continued resonance is the backwave of the speaker. At port resonance, the speaker motion is resisted and the cone barely moves. At tuning, I think the port is 90 degrees out of phase with the sub, no biggie. As you go down in frequency, the sub unloads and it might as be free-air. Above that, the port and speaker are close enough in phase so that the response adds.

So, a vented enclosure extends the response of a speaker by adding another lower resonance powerred by the speaker.

This is one level of understanding of vented boxes. It can get more complex and does.

[Dezzy FN Baybee]

A ported box is a HP filter, 12dB/oct. Notice how ported boxes roll-off at around 24 dB/oct instead of the average 12 for sealed boxes. Imagine the cone of the speaker as a weight, imagine the suspension as a spring, and now hang the weight from the spring and you have a resonant system. Compliance, resonance, it's all there. The port is essentially a smaller spring and a smaller weight attached to the first one. The port itself is similar to a helmholtz resonator. At a certain frequency, depending on tuning, the port will resonate. The energy providing this continued resonance is the backwave of the speaker. At port resonance, the speaker motion is resisted and the cone barely moves. At tuning, I think the port is 90 degrees out of phase with the sub, no biggie. As you go down in frequency, the sub unloads and it might as be free-air. Above that, the port and speaker are close enough in phase so that the response adds.

So, a vented enclosure extends the response of a speaker by adding another lower resonance powerred by the speaker.

This is one level of understanding of vented boxes. It can get more complex and does.

Ok now it all makes sense to me. My last ported box was tuned to 45Hz and my car peaked at 57Hz. So basically I needed to tune my box to about 55Hz to get the full benefit of using a vented enclosure(in an SPL sense). So if I were to tune to 25Hz with the exact same box I would have the same score as the 45Hz box because of the fact that my car liked 57Hz anyway. Please correct me where I'm wrong.