Closed Back vs Open Back Cabs
Cab design, (shape, baffle, type of sound targeted). Insulation in a cab affects the way the cone of the speaker moves forward and back while producing sound. Insulation reduces the motion, deaden any ambience, and create a very all about the speaker environment. Depending on your tonal goals this can be a help or a hardship.
Think of an open back cabinet. It produces sound from the front and reflected sound coming from the open back and bouncing off the wall behind it. This type of cab results in the speaker cone moving fore and aft in an unrestricted manner. I produces a somewhat 3D room filling surround sound, but, kills the punch and forward focus of the sounds produced. It's excellent for clean rhythms, backing up vocals, and as a vehicle for a solo guitarist, (no band), to really fill up space. The Fender sound.
Now think of a closed back cab. If properly sealed the air behind the speaker is solidly contained. While still allowing the speaker cone to move forward and back it reduces the amount of motion. This results in a tighter sound quality. Also, all sound is focused strictly to the front. The smaller, tighter field of motion X the hard forward punchy focus results in a sound you could describe as strong or powerful or having balls. The Marshall cab and those like it.
There are other variations as well.
The closed back / front ported design is meant to blend the qualities of the first two designs. Porting the front of a cab restores the full motion of the speaker while keeping the full direction of sound strictly coming from the front of the cab. In this case internal sound reproduction is not released through the back of the cab as in the open back and does not result in an airy reverby type of ambience. Rather, the ambience produced is more in the form of a split second delay between the sound coming from the front of the speaker and the sound being released through the ports. These cabs tend to be loud, up front, less punchy or ballsy than closed back designs, but, regaining the 3D quality of an open back in a more forward focused format.
An insulated closed back design is taking the standard closed back one notch further away from the open back. This is a cab all about speaker voicing, deadening any ambience, and striving for a power and punch over everything else. If a closed back is considered ballsy an insulated closed back might be thought of as ballsier. Tightly focused front and center. All echo or ambience minimized and all punch, speaker voice characteristics, and forward focus maximized. Notes are tight and highly defined. Depending on what your going for this design can be a blessing or a hindrance. Depth results in Bass. Freedom of movement results in the production of treble. The closed back / insulated cab results in a subtraction of extreme low and high end. It focuses the tonality on the midrange. Now. This is not necessarily a bad thing. In the case of Hard Rock guitar tones this focus on the midrange, (at the expense of extreme highs and lows), keeps the focus on balls at any cost. For a player focused on a narrow and defined path to hard rock applications the insulated closed back cab might just be absolutely perfect.
So, in the order of 1 being from all about ambience, 3D, surround, airy, spacy sounding, to increasing amounts of midrange and balls, and maximizing the speaker voice's contribution, they would rate as follows:
#2 Closed Back / Ported Front.
#1 Open Back.
#3 Closed Back.
#4 Insulated Closed Back.
While any of these cabs can sound great under the right circumstances, the closed back (4x12) cab is the tradition sound of Dino rock. Of the types discussed here, the #3 would be more classic '70s Dino and #4 would be more '80s Dino.