Quote Originally Posted by RythmikAudio View Post
F25 has absolutely the least amount of phase shift or group delay (even though group delay is meaningful only for low pass filter). But it is large because it is a sealed design.

FV15HP has all the characteristic of ported subs. It is more efficient and hence output more. Normal nonservo ported subs give us this boomy bass sound. Our servo ported subs greatly reduces that signature and gives us a bit of more "fully body" sound. The instructment may sound slight larger compared to the sound from F25. For anyone with HT application, we recommend FV15HP. For anyone with music as a higher priority, F25 is a better candidate. That does not mean F25 will be bad for movies. It is just that it has less coloration associated with other nonservo subs and can really "disappear" a bit better.
Brian,

I have a couple more questions:

According to your measurements the FV15HP has a 1.5 dB advantage at 20 Hz over the F25, in terms of maximum output. Would you say that this is about the same from 15 Hz to 80 Hz, generally speaking, or does the FV15HP have a larger advantage over other frequency ranges?

We can see the detailed measurements of the FV15HP on data-bass. It appears that the THD stayed well under control (basically under 10% from 30 to 35 Hz and up depending on one port or two port mode), even while it is pushed close to its output limit. We also see that the dominant component of the THD is the second harmonic from 80 Hz until about 28 Hz in both modes. Going lower in frequency, the 3rd order harmonic becomes the dominant component and rises rapidly. This is when the sub is pushed close to its output limits. It seems that this was likely by design, because when we get below 30 Hz we are less hearing the sound and more feeling it and the 3rd order harmonic in that range shouldn't stand out to us like it would at higher frequencies. People find the 2nd order harmonic distortion, less objectionable and some even find it pleasing. Was the F25 designed with a similar approach to the distortion curves, keeping THD under 10% until close to the output limits and the second order distortion being the dominant component from 28 to 30 Hz and up, except distortion being larger than the FV15HP from 40 Hz and below when the F25 is pushed close to its limits (due to the fact that it is a sealed design)?