Originally Posted by H Stevens
I am noticing that 4000 series and 16 Ultra series owners are stating and recommending the Extended mode (2 ports) vs. the Standard 3 ports open. Is it because of the extension? Is there a difference in the audio quality of the bass? Have you taken measurements and the results are showing significant more output in Extended mode that is just preferable? What about in the 40 to 80Hz range, is there any noticeable differences in those frequencies between the Extended and Standard configuration?
Yes, the additional extension is the reason why the Extended mode is almost universally recommended. The subwoofers in the Ultra series are specifically designed to have the most SPL, that the subwoofers are capable of producing, below 20Hz. Those frequencies require bigger cabinet volumes, more powerful amplifiers, and lower port tunes in order to have high SPL numbers. The Standard mode is available to people who prefer it for various reasons, including a lot of room gain below 20Hz (typically from a very small room). But, this is strictly a YMMV issue which everyone needs to decide for himself.
The review I am linking for you is of the PB16, but you can find one for the PB4000 (the PC4000 would be essentially the same) that would demonstrate similar results. You can look at the shape of the frequency response, for the different port tunes, in the graph shown at the top of the page. That will show you the extra extension of the 16Hz mode. Further down the page, you will see a table that shows the max output for the different modes. As demonstrated in that table, the Standard 20Hz port tune has about a 1.5db advantage from 20Hz to about 40Hz. Above that, the max output is more equal.
A 1.5db advantage in that narrow frequency range may be audible, but it is relatively negligible to most people. The difference at 16Hz, however is ~9db more output, in favor of the Extended mode, and that advantage continues for several Hz below the tuning point of 16Hz. That difference is not negligible at all. With the right low-frequency content, it is a very
substantial difference! And, even with movie content that doesn't reach quite as low, with quite as much SPL, there can be some difference in the "bass weight" between the two modes.
I believe that the Extended mode may also produce relatively more low-bass tactile response (TR) than the Standard mode, due to the additional constriction of the air flow through only two ports, rather than three. I think that constriction would be expected to increase the particle velocity, which creates TR, although I don't know whether anyone has tested that in a specific way. If I am correct, that additional low-bass TR may also be a beneficial attribute for many people.