Originally Posted by
RythmikAudio
Phase and ring are related. You cannot get a system with high phase shift and yet give you no ringing in time domain. I understand most people treat some of the characteristics as if they have total degree of freedom. For instance, one thing I mentioned about ported sub is it has 4th order roll off. Most will think it is no big deal, I can live with that. But what i have not told you is 4th order has 2 Q values because a 4th order system can be thought of cascade of two 2nd order system with each 2nd order has a corner frequency F and a Q value. In other words, we have F1,F2,Q1,and Q2. Most will think he has complete freedom of picking F1, F2, Q1, and Q2. Unfortunately, it is not the case. So in reality, when some DIY picks a driver A and puts in a ported box B, most often he will get one high Q value and one low Q value. He cannot get low Q values for both both Q1 and Q2. The most commonly Q value combination is something like Q1=1.1 and Q2=0.6, or Q1=1.2 and Q2=0.5. Now you see the trend? If you try to reduce one Q, then the other Q pops up or if you want to make F1=15hz and keep Q1 and Q2 to the values you want, then F2 becomes 25hz. It is a constant game of seesaw.
[EDIT]
Another way to look at this problem is we compare sealed subs with ported subs. What is added to the system when we go from a sealed sub to a ported sub? The only thing we add is the port tuning frequnecy. That is, we add only one extra degree of freedom and yet we have two new variables F2, Q2 introduced in the system. That is why it is so difficult to controll all F1/Q1/F2/Q2 values exactly what we want them.
Now if someone in college say I have access to symbolic math equation solver that I can solve this problem exactly. What he wil find is in order to get both Q values to be at 0.6 or lower, the enclosure may need to be so big or the driver needs to be so compliant that it becomes impractical. When we have one high Q and one low Q in your system, the ringing at the time domain is mainly determined by the high Q characteristics. That is why it is not a fair comparison for sealed and ported subs. Josh and other has tried to EQ a ported sub to a sealed sub in order to do subjective evaluation. Once you understand the big picture, you don't even bother to do that.