Vrc is the volume of any rear chamber/space the driver is attached to. Lrc is the length of the rear of the chamber from the driver, or the depth of the chamber.
Fr is the airflow resistance measurement for the lining material. It is in rayls/cm, and can be found on material data sheets online, for a variety of materials. Tal is simply the thickness of the lining you are adding. Vtc and Atc define a throat chamber. You can also think of it as a front chamber area. It is not sealed, but you can do a lot of things with it, with more than just horns.
Fr & Tal are now Ap & Lpt
Ap is the cross-sectional area of the port, and Lpt is the length of the port.
Now we have Ap1 & Lpt. This a chamber/section in front of the throat chamber. If you have seen horns where the opening between the driver and the horn is smaller than the cones diameter that is what this is. Ap1 is the area of the opening, and Lpt is the thickness of the wood most of the time.
The Impulse option is broken down into two more options. Response
This is the Impulse response of the enclosure. Note that it isn't band limited in any way. This means if you are doing a sub, there is no way to limit it to the subs bandwidth. Artifacts above the subs bandwidth will alter the IR from what the true in use IR would be. Spectrogram
This is a different way to look at the IR. Frequency is listed from bottom to top, and time is from left to right. This view is more helpful to newbies as you can see the frequency spread, and can focus on the bandwidth area you need while ignoring the rest.
It will open up a new window.
Go to Tools>Chamber and select the Throat Adapter. Ap1 will be the same as S1, and Lpt will the the thickness of the wood. Let's use 1.8cm here.
The Throat Chamber is a little more tricky, but we can guesstimate. Use the drivers Sd as the Atc, and then try to figure out the distance between the drivers cone base, and the top of it's flange/gasket, then divide it by 3. Using the PDF for this driver I get ~2.72. Remember this is only a fast guess, it would be better to measure the actual dish cc. Take the guessed 2.71 x Atc, and that is Vtc. Vtc=1330.61 This is just a starting point, as the size of the Throat Chamber affects the high frequency loading of the horn.