Difference in late 70ies / early 80ies Marshall 4x12

[BesaMoogie]

Ok guys, I have two Marshall 4x12 cabs that were originally loaded with g12-65 speakers. One has the later, big recessed input terminal, the other the earlier small one.
The early one has a really nice response and feel in the bass and low mids register and it pushes a lot of air with my JCM800 head, the late one not. I bought the later cab it with only one original g12-65.
So far, I tried different speaker combos in the later cab, but none of them gave me the response and air push I get from the other one:

- four g12-65; one is the original g12-65 that came with the cab, one g12-65 Heritage and two g12-65 from 82
- two g12-65 and two g12t-75 (vented magnets, 16 ohm)
- another quad of g12t-75 (vented magnets) but rated at 8 ohm.

So, anything I throw at that cab is not giving me the same push as with the other cab. I did tighten all the screws inside the cab. Both cabs are standing on their feets, the casters were removed. Both have the MDF/particle back panel. The last test would be to take out the g12-65 from the good sounding cab and put it in the other one, to see if it is a variance in the speakers. But, the speakers in this cab are baked to the front panel and I don`t dare to remove them to loose the sound.

This makes me think, do cabs have a self resonating frequency causing the difference in response? Did someone experience similar things with 4x12 cabs? Or do I miss something else here?

 

[7704A]

If the materials are the same, the dimensions are the same, and the construction is the same, I'd guess it's the speakers. Cabs can definitely resonate, but my understanding is that cab resonance is largely based on mechanics and geometry, so two identical cabs would resonate the same.

You said the speakers are baked to the panel. Is it possible to non-destructively swap the entire panel at once? I'm guessing no...

 

[Speeddemon]

I assume both are rear-loaded as well?

I can only speak for my experiences with the smaller Marshall 1966A and B cabs (diagonal 2x12), which originally came with the (in my case non-vented) '86 G12T-75's.
I've done a bunch of speaker swaps with the same speakers as you did (minus the vented-ness) and the mix of G12-65 (both vintage and Heritage version) + one T75 wasn't as great as I wanted it to be.
But mostly, the A (slanted) cab sounded thinner and more middy than the B (bottom) cab.
Now, this B cab I settled on one T75 combined with one Mesa V30, including a beam blocker. This is a friggin' awesome sounding cab; beef and character combined.
One thing that helped, was some acoustic polyester wool, that a buddy gave me. I put this inside the B cab (see attached image, when I was still testing the G12-65 Heritage + the original T75).

To improve the sound of the 1966A cab, I had to do the same, but I also put a slab of it on the inside of the back panel.
This did help a lot and basically tricks the speakers into thinking they're in a bigger cab, so to speak. Less standing waves and ugly notches, more beef. You may wanna try that to that cab?

https://www.polyesteracousticpanels.com/product-showcase/acoustic-wool/

Later on, I found this empty, custom built diagonal 2x12 cab (most likely built in Poland, but not by Hesu), which has similar dimensions to the Marshall 1966 cabs, just an inch wider (so about 25" x 25").
I had two pre-Rola G12H30-55Hz Greenbacks lying around...waiting for the right cab.
Initially, after putting those in this custom built cab, I wasn't to happy with the sound. Loaded it up really well with 3" thickm high density acoustic wool (40kg/m3... lemme do a guns per hamburger translation... , 2.5lb/ft3 ) and it finally sounded more like I wanted it to.
In the end I settled on one G12H30-55Hz + the 2nd vintage T75. Really beefy and 'metal' sounding cab now with still plenty character.

 

[MadAsAHatter]

There's a couple of thigs I can speculate at.

The first obvious one is speakers. The only way you can test is to swap those original G12-65's from one cab to the other. You can also try the speakers you used in the later cab in the earlier one to compare.

The next would be cab dimensions. The only difference you mentioned between the two is the input terminal. In theory, that wouldn't make any difference since the change in cubic volume is negligible.

Last thing would be construction and materials. I can only assume the construction and bracing is the same since it's the same model cab. That leaves the materials. The type and quality of materials can affect cab resonance. My understanding is the baffle & back have a larger affect than the side walls. Wood density can be different from tree to tree even in the same species from the same area. Growth rate; for example, is one factor that impact this. Plywood is more consistent than hardwood related to resonance. But depending on the source and grade of plywood, that has some affect on how the sound waves bounce around in the cab.

 

[BesaMoogie]

If the materials are the same, the dimensions are the same, and the construction is the same, I'd guess it's the speakers. Cabs can definitely resonate, but my understanding is that cab resonance is largely based on mechanics and geometry, so two identical cabs would resonate the same.

You said the speakers are baked to the panel. Is it possible to non-destructively swap the entire panel at once? I'm guessing no...

I did not think of swapping the whole panel. Will look into this. But than again, I`m kind of hesitant to mess with that cab as I really like the sound.

 

[thegame]

Knock on the top of each cab, square in the middle on both. You will likely hear a different pitch on each one, indicating different resonant frequencies.

 

[BesaMoogie]

There's a couple of thigs I can speculate at.

The first obvious one is speakers. The only way you can test is to swap those original G12-65's from one cab to the other. You can also try the speakers you used in the later cab in the earlier one to compare.

The next would be cab dimensions. The only difference you mentioned between the two is the input terminal. In theory, that wouldn't make any difference since the change in cubic volume is negligible.

Last thing would be construction and materials. I can only assume the construction and bracing is the same since it's the same model cab. That leaves the materials. The type and quality of materials can affect cab resonance. My understanding is the baffle & back have a larger affect than the side walls. Wood density can be different from tree to tree even in the same species from the same area. Growth rate; for example, is one factor that impact this. Plywood is more consistent than hardwood related to resonance. But depending on the source and grade of plywood, that has some affect on how the sound waves bounce around in the cab.

I will have a look again at the cabs. Maybe there are small differences in the dimensions??? Will have a look as well on the back panel material (is it really the same) and maybe if the bracing if I can find some differences.
So far, a whole speaker swap is not an option because of the above mentioned reasons

 

[BesaMoogie]

Knock on the top of each cab, square in the middle on both. You will likely hear a different pitch on each one, indicating different resonant frequencies.

Yes, I actually did this and the cab that pushes more in the lower department sounded darker when knocking on it. I did not mention this in the OT as it seemed kind of esoteric

 

[Racerxrated]

Not all cabs are created equal. Some cabs, like amps, just have IT. No matter what speakers you re load with, they all sound killer. Others, even though they are the same brand, even year, sound very different even with the SAME speakers from the great sounding cab.
It's hard to quantify, why that is. I guess it's similar to guitars and amps, identical models a few serial # off yet they are noticeably different sounding.
Things like humidity, over the years that may affect one cab, and how that wood ages vs a cab that was stored or spent most of its life in very dry air....I'd venture to guess that might be an important factor.
Maybe grab one of those packets/containers of material that is used to pull moisture out of an environment, car detailers use to restore an interior if it's been flooded in the past, or similar to those 'silica gel' packs we all see in items we buy?
Just a suggestion; maybe the worse sounding cab has been exposed to a humid environment?

I remember buying a mid 70s cab, being super excited and then when I played it, it sounded like shit. I noticed it smelled a bit musty....returned it fast.

 

[BesaMoogie]

Not all cabs are created equal. Some cabs, like amps, just have IT. No matter what speakers you re load with, they all sound killer. Others, even though they are the same brand, even year, sound very different even with the SAME speakers from the great sounding cab.
It's hard to quantify, why that is. I guess it's similar to guitars and amps, identical models a few serial # off yet they are noticeably different sounding.
Things like humidity, over the years that may affect one cab, and how that wood ages vs a cab that was stored or spent most of its life in very dry air....I'd venture to guess that might be an important factor.
Maybe grab one of those packets/containers of material that is used to pull moisture out of an environment, car detailers use to restore an interior if it's been flooded in the past, or similar to those 'silica gel' packs we all see in items we buy?
Just a suggestion; maybe the worse sounding cab has been exposed to a humid environment?

I remember buying a mid 70s cab, being super excited and then when I played it, it sounded like shit. I noticed it smelled a bit musty....returned it fast.

Both of the cabs look beat up and worn down. I had a 30th anniversary cab from the early 90ies loaded with g12t-75 that had the same push, but I stupidly sold it.
I just recently played a JCM900 4x12 from 94 and it did not blow me away. Never thought this is going to be another rabbit hole