Breaking in speakers/Eminence Swamp Thang and CV-75s

[BasalGanglia]

I currently own a Marshall DSL 40C, which I plug in to a Marshal JVM C212 2x12 Cab and a Peavey Valveking 4x12 Cab. I prefer the distortion through my boss Me50 using the DS-1 and reverb on. I love the combination of the two. The thundering bass for the Peavey and the cleaner sound from the Marshall Combined. I play stuff like Metallica, Joe Satriani and also songs from Mozart, Beethoven, Bach but played through distortion on most.

Anyway after the Marshal DSL40c creating a buzzing noise wanted to try something different. People on forums where saying the Peavey stock Sheffield speakers could be better. Although sounds good to me. After researching eminence speakers and watching a very good metal video showing lots of different eminence speakers with the same riff repeated for each type. Loved the thundery bass of the Swamp Thangs. 

So found a site where you buy the cab and pick your speakers and they will install them for you. Went with another 4x12 with two Swamp Thangs and two CV-75s installed in an x fashion.

Also went to different guitar shops and tried some amp heads that where available. Ended up getting the Paul Reed Smith MT15 head. But when I tried my new 4x12 cab it sounded muffled like it had blanket over it. At first thought it was the new amp but then swapped with the Peavey and sounded excellent again. 

My question is this. After reading about speakers needing to be broken in to sound better, is this the problem or will it not make much of a difference?  So should I give it a chance and keep playing to hope it will sound better or will it probably not get much better?

I don't know if to contact the company and try to return the cab or ask if they will just swap the speakers with some different ones. Maybe I should of just bought a cab with Vintage V30s or greenbacks that most cabs seem to have in them.

Edited September 25, 2019 by BasalGanglia

[Kiwi]

Could be a wiring problem.  Maybe the speakers are wired out of phase?

[Skinnyman]

It could be phasing and worth checking (how would you check this?)

I’d certainly make the company aware but there’s a good chance that the speakers need to be broken in. 

It’s a while since @BasalGangliaposted this - I wonder how he got on?

[Kiwi]

Phasing is normally due to polarity.  Can be checked with a magnet or can be checked by disconnecting and reconnecting speakers until the phase effect is created.  Could well be that each brand of speaker has a different polarity.