Originally Posted by Cabledog
So if I change to a ported box (2.75cu ft if it will fit) I will get more bass at the same volume without adding power? I thought you got more pop and crisp response out of a sealed box and more doom-doom-doom radiating bass I guess you could call it out of a ported box. I also thought you could hear the sealed box around the boat better and the ported would have better sound at a further distance away. I'm not an expert so a bass box for dummies explanation would help educate me the best. Sorry Todd I'm kind of hijacking your thread.
A woofer is simply a piston that moves air. Hopefully it does so accurately. An enclosure is a baffle that isolates the front and rear radiation but also is a resonant chamber. You have some freedom in making it do what you want.
Here are the typical characteristics of each enclosure type.
Starts rolling off the deep bass at a higher frequency but also has a softer or more gradual deep bass roll-off.
Too large of a sealed enclosure is under-damped. It will generate deeper bass with a robust quality that is less obvious in some or most program material. A little dead sounding with less 'liveness' in the upper bass.
Too small of a sealed enclosure is over-damped. It may have a hump in the upper bass and may produce more peak output over a narrower bandwidth, or a bandwidth that is shifted higher. It sounds far more live but can also sound more singular in its tonal construction.
The key is to get the right balance. My preference is a final system (woofer loaded in enclosure) 'Qtc' of between 0.8 and 0.9.
This can be manifest in a variety of ways to achieve several different purposes. You can have an SQ version or a SPL version.
In one version, more of an SQ model, a bass-reflex enclosure is intended to extend the deep bass response. A conservatively designed well-damped ported box will give you another one-third octave of bass extension before reaching its half power point. It will give you a 3dB boost in the lower bass. That's equivalent to doubling your amplifier power or doubling the woofer excursion. Not too shabby for adding a little space, wood and a port. This version can sound similar to sealed with a tight impulse response and good, defined, smooth tonal construction.
In another version, more of a SPL model, the bandwidth is narrowed and creates a far more pronounced boost in bass output. This is the version that gets the reputation as a bommy one-note special. It also leaves the deep bass less protected and you may see a great deal of wasted movement.
A bass-reflex enclosure will give you more deep bass extension and more deep bass output as compared to sealed, but, below the tuned bandwidth it rolls off much steeper. At a frequency that is low enough the system is essentially unloaded. In a good design this area is below most program material. It's a good idea to use a subsonic filter for this reason.
A bass-reflex enclosure has very little cone movement in the resonant area. The port does most of the work. Distortion is very low. At higher midbass frequencies the port contributes little and the cone generates most of the output. The combination of enclosure and port creates a phase shift so that the woofer output and port output are brought back into phase. However, in the process, the bass signal is slightly prolonged in the time domain. But remember, at any given frequency, it is either the port or woofer that is generating a majority of the output. Don't make too much of the group delay because you are mostly immune to it in a well designed ported subwoofer. When you look in the $100 class of high end home free standing speakers, a majority of these are bass-reflex, and these patrons will absolutley not accept bass that isn't extremely accurate. So much of this is in the design and execution.
Sealed is pretty easy to get right. Ported requires a bit more expertise.
The other attributes that you discribed for one or the other really are not accurate and caused by other factors besides 'sealed' or 'ported'. I doubt you would find those to be consistent from one system to the next. Tuning, loading differences in boat to boat, and many other individual execution factors are responsible. You can't over-learn a few limited exposures.