I have answered previously to Skylinestar that if he wants to use FV15HP (same thing applies to FV15) he needs to set the extension filter to 14hz low damping. This is all because the excursion plot.
Here I will show an excursion plot for 2port mode when the extension filter is set to 14hz/ low damping.
This plot shows if one applies the signal of same voltage from 2.5hz to 125hz, how much excursion the woofer gets. The goal is to have a well balanced excursion plot. This is particularly important for vented subs because without any rumble filter, the woofer will get very very high excursion below the port tuning frequency.
Now for 1 port mode, if we put them in 14hz low damping, it will also have similar excursion plot except the port tuning frequency moved down to 12hz.
What is why I have answered to Sky to use 14hz low damping even though there is no rumble filter in 1 port mode. Let us next show the plot for 14hz mid damping in 1 port mode.
Now you can see low end exursion begins to creep up. Next the 14hz high damping in 1 port mode.
Now it creeps up even more. So why we offer this 14hz high damping in 1 port mode? It is becasue even though the excursion plot looks bad, it has much smaller group delay.
Can we predict the excursion plot based on just frequency response? The answer is no. Next I plot all three response curves in one plot.
There is absolutely nothing you can tell here even when you place all 3 together, let alone just look at one curve by itself. That is why I have emphasized over and over agan that one should not EQ below 20hz (as most ported sub should have a port tuning frequency of 20hz or so). Otherwise it will have catastrophic results. One can overload the sub without hearing much improvement in output. This is because all the excursion resourced are wasted in the subsonic band. It is the job of subwoofer manufacturers make sure the excursion plot is tuned just right and after that no one should touch it.
In our two port mode, we do have a 3rd order HPF, so even at 14hz/ high damping, the excursion plot still looks balanced.
But we should not push our luck by boosting below 20hz.Edited by Rythmik - 9/8/12 at 2:33pm