Originally Posted by basshead81
To be fair the SVS PB13Ultra is the cleanest ID sub on the market according to data-bass...atleast it has the lowest THD levels and the most linear response. However I dont use that data as a end all for determining sound quality. I think anybody that has came from a budget sub and upgraded to any of the popular ID sub companies will need to give a bit of time to let thier ears adjust from a boomy one not wonder sub, to a sub that has a good clean response down below 20hz.
I know we all look at the same set of charts and we can walk away with different impression and opinion. Your view of Lowest THD == Cleanest sound, or most linear response == Cleanest sound can be easily challenged in a lot of fronts. If you check out the waterfall plot of PB13U 15hz mode, Josh only plot to -30db below the 0-time response. There is a reason for it. PB13U does have quite a bit of ringing at the lower end and you can see that from impulse response. You do notice the ringing at below 20hz does not drop below -30db even after 300ms (whereas FV15HP 1 port mode drops to below -35db after 250ms). Now waterfall was originally designed to check the enclosure resonance. If we have a bad roll-off filter design resulting in excessive ringing, that is almost same as having a poor enclosure design with an enclosure resonance. But you may ask that it looks like PB13U has the "flattest" frequency response. But in reality is all filters need to have a roll-off contouring curve. The filtering incurs the least amount of ringing is the one with most gradual roll-off and therefore giving the curve that is less flat. But that is just pure mathematics. I know it is counter-intuitive. So is having a longer ringing time equal to the cleanest sound?
Second the linearity of response. FV15HP has very little long term thermal compression. So if we look at the "compression" plot, it is almost flat except the bottom end where the port linearity is the limiting factor. So In that regard, we think FV15HP has more linear response (less compression) and scales better from lowest output plot to the highest output plot.
Third, there is a difference between CEA-2010 measurement and long term response measurement. CEA-2010 is a "pulse" type of max output measurement. On the other hand, the "long term" frequency response in Josh's plot is from steady state. The latter has been used for over 50 years now. But a lot of music and special effects are transient in nature. So CEA-2010 uses "pulses" to measure the burst max output. It serves to complement the conventional "long term" frequency response. I do not know how you interpret the difference between FV15HP and PB13U with respect to those two different max readings with the same subwoofer. But mine is that FV15HP explores the headroom whereas PB13U has no headroom per se. So we should also put that in perspective when we look at the distortion plots between FV15HP and PB13U. If you look at FV15HP one port mode, you will see at the max output (110db plot), the distortion content above 26hz is mostly 2nd order. The 3rd order and 4th order are very low. I remember we had this discussion just a few pages back that Bill and others made comments that high order distortion is more audible and therefore should be kept as low as possible. It is time to put that concept into practice !!! If you look at how distortion content has changed as we move pass below 26hz, it is the 3rd order shoot up and 2nd order goes low and 4th order remains almost under radar. The sudden increase of 3rd order distortion below 26hz is because the amplifier is already into clipping. But the CEA-2010 number indicates that FV15HP should have more output. As I explain, this is because CEA-2010 uses a pulse. Now you can look at the 2 port mode and Josh plot 115db instead of 110db. As you can see there is a slight increase of 3rd order at around 60hz, indicating the amp is into mild clipping while the 4th order remains low. In the hindsight, it is fortunate that Josh plots 1 port and 2 port mode with 5db difference between them. It allows us to observe the distortion characteristic when we can clearly see wheather amp clipping is a factor in distortion number. To summarize, 1) if we can stay within the amp clipping, distortion from FV15HP is mostly 2nd order (which is the least offensive type of HD) and comparing distortion is not as simple as comparing total HD (or THD); 2) the burst output of FV15HP exploits amplifier headroom whereas PB13U does not.
-Edited by Rythmik - 9/3/13 at 11:20am