ev are really expensive - very clean - think Stanley Clarke.
They also crunch up quite nicely; think Zakk Wylde: he uses EVM12's in his guitar cabs, and they lack neither bite nor bottom. An old Marshall 4x12 bass cab isn't going to have any appreciable bass fundmental no matter what it's loaded with, but it doesn't matter because what most folks think of as "bass" isn't actual fundamental anyway.
eminence are great.
Eminence makes loads of speakers. Because they are the world's largest musical instrument speaker manufacturer, and they make many other "brands" to spec as OEM models, there is NO "Eminence sound." Saying Eminence speakers sound good is like saying, "I like pie." You need to get specific to the model.
Celestion are guitar speakers IMHO.
Likewise, Celestion also makes a vast array of speakers, even though their 30 watt "greenbacks" are how most musicians know them. All of Trace Elliot's very clean and big-bottomed bass cabinets from the 80's and 90's came loaded with Celestions and I'll put the 15" they used in their 1153 cabinet up against ANY 15", new or vintage.
any cab in the marshal/hiwatt vein will greatly improve with some ports to allow the lowest frequencies to escape thge cab.
...only if you tune the port to the cab volume and speaker parameters, which is highly unlikely as there simply isn't enough air volume in a 4x12 to make a port useful. I have a Marshall 4x15 that is basically a scaled-up 4x12 except that is ported. Even with larger speakers, air mass, and ports, it doesn't have much bottom.
