Originally Posted by Test123455
Ummm...any way you could explain this to me like I was a little child? This
is the amp, if it makes a difference. I know different Rythmik subs have different amps.
The purpose of rumble filter is to control the excursion (or displacement) of subsonic signal. Here is the excursion plot for FV12 at 14hz/low damping setting. The plot assumes the input is same for all frequencies and it checks if there is any excessive excursion at any frequency point. It is the best plot to explain the rumble filter. No other manufacturer has shown anything even close to this as I explained that there is no easy way for them to plot. This is part of our design check to understand how well our filter has achieved the objective of rumble filtering. Note there is no smoothing in these plots and yet the plot is pretty much noise free.
The above plot shows a lot of things. First the port tuning frequency is about 21hz. The frequency bands above and below 21hz are passband and stop band, respectively. Ideally we would like to have the peak below 21hz to be of the same height the one above as much as possible. Ours is already very close, about 1.3db difference. Of course, if you set the extension filter to be 20hz and low damping, its subsonic excursion will be further trimmed down at price of about 3.5db attenuation at 21hz as shown below.
The next question is about the trade-off between high damping and low damping. As with sealed sub, high damping provides a more gradual roll-off and therefore does not provide as much rumble filtering capability. The plus side is however lower group delay. The excursion is as follows.
To summarize, the extension filter is just a low end contouring control. If the port tuning frequency is 21hz, setting extension filter to 14hz will not give us 14hz extension. However, its 2nd order HPF characteristic can be used for playing a partial role of the subsonic filtering in the big picture. For HT uses, we recommend 14hz/low damping or 20hz/low damping. The latter is for those who likes to play louder in HT. Only in music playback, we recommend something like 14hz high damping to get a better transient response.The case for FV15/FV15HP
The rumble filtering on FV15 is slightly more aggressive, but still not much more. Here is the plot for 2port, 14hz low damping extension.
Compared to FV12, the filter is slightly more aggressive, but not much more. Note the port tuning frequency is 18hz. Changing it to 14hz high damping shows similar characteristic as in FV12, ie, slower roll-off causes larger subsonic excursion.
Next we compare the case for 1 port tuning.
As one can see, this 1 port mode is similar to FV12 with a lot more excursion at the bottom end in 14hz/high damping setting. It is recommended for music playback. In 2port mode, setting it to 14hz/high damping does not improve much in transient response because the additional rumble filter is in place.