Open Back 412? Why Not...

[iscid]

So i gave the search a try to see if anyone had talked about making a ppc412 open back...i saw nothing but people talking about 212s. My question is, has anyone just modified their 412's to an open back? Ya know just give the back a bit of trimming? It's been on my mind lately...

[steamboat]

Great idea! Best thing you could do is get another piece of wood and start trimming it to shape to decide what you like. This way if you screw anything up you didn't wreck your original back. Then you could either wrap the new back in orange tolex or trim your original one but I don't recommend cutting up your original just incase one day you wish you could go back to stock.

Another great thing to try which I do with one of my vertical 2x12 cab ( I set my 2x12's on there side so there vertical I feel this sounds much better and leaves your amp at a good height to make adjustments) is to remove the bottom speaker or speakers if you have a 4x12. Its called detuning a cab. Sounds crazy but it works well. It allows for alot more sound dispersion, doesn't sound so stuffed up with high gain and maintains great low end that you loose a little of by going open back. And it makes your cab lighter!
I found I like the detuned cab for my high gain rockerverb 50, but I still prefer both speakers in my other 2x12 cab that I use for my ad30's and ad15's.

[Sergeantsnowball]

Some of Marshall's old 412 cabs are designed this way. For some reason Orange takes the whole "Power Projection" label to every extent they can.

[everdrone]

you could buy two 212 open backs and convert one to closed back to get the best of both worlds

[Dave666]

I think the Marshall JTM45/100 full stack had a oversized bottomcab closed back and an angled 4x12" cab with open back on top.
If you're very lucky, maybe you can find one of those

[Randy Bass]

I think the Marshall JTM45/100 full stack had a oversized bottomcab closed back and an angled 4x12" cab with open back on top.
If you're very lucky, maybe you can find one of those

I think the trick with those was that the back panel was 7/8 closed with just a sliver open along one side. They look awesome, but I have no idea how the sound was affected by the rear "slot port".

I would go for the Mesa Halfback design myself. If you pick two speakers that sound great in a closed-back cab like G12M-25s and pick two speakers that have fuller bass response like Vintage 30s for the open section, you would end up with the best of both worlds. You can even wire the cab with each pair separate (or with a stereo plate) to give you the effect of owning two totally different 2x12 cabs in the same box.

[Dave666]

I think the Marshall JTM45/100 full stack had a oversized bottomcab closed back and an angled 4x12" cab with open back on top.
If you're very lucky, maybe you can find one of those

I think the trick with those was that the back panel was 7/8 closed with just a sliver open along one side. They look awesome, but I have no idea how the sound was affected by the rear "slot port".

I would go for the Mesa Halfback design myself. If you pick two speakers that sound great in a closed-back cab like G12M-25s and pick two speakers that have fuller bass response like Vintage 30s for the open section, you would end up with the best of both worlds. You can even wire the cab with each pair separate (or with a stereo plate) to give you the effect of owning two totally different 2x12 cabs in the same box.

I forgot about those Mesa's. I played one of those at a gig 15years ago, sounded really great

[iscid]

Sticking with Orange though...does anybody know anyone that has ever done it? I may pick up a second 412 and give it go.

[everdrone]

they had mesa cabs with one half closed back and the other open back

[steamboat]

Why don't you use your current cab but buy another piece of wood to cut and try on the back before you invest more money? Sounds like a way better idea than to buy another 4x12 cut the back panel just to find out you may not like it? Also try detuning the cab like I said above. This is free to try and you may end up liking it. I thought it sounded crazy when I first read about it. Then I tried it and it was exactly what i was after for a fuller sound dispertion without loosing low end. (think of bass cabs there ported) I now have two 2x12 cabs one's normal and the other is detuned. I was ordering some speakers from avatar speaker company shortly after I detuned my cab and asked the guy what he thought of detuning cabs, He laughed and said that's exactly what he does. A 2x12 cab with one 12" alnico gold in it.

[iscid]

I'm buying another cab regardless so I can have one sit at home and one for playing out. Its not really a big deal buying new things and trying stuff out ya know.

[Randy Bass]

I think it will work well if you want the increased sound dispersion and don't mind losing a bit of tightness/punch. It would make sense to get two new pieces of wood to make a top and bottom back panel (like those on most combos) instead of hacking-up the original back panel. It's no more difficult to put new tolex on a couple of small pieces of wood than it is to avoid destroying the existing tolex when modifying an existing back panel.

[Colinofwales]

I have an open back orange 4x12.

It has two small panels on the back (not tolex'd - just bare ply).

I bought it on ebay like that as I wanted an open back sound.

I can take some pictures if you like?

Cheers

[bclaire]

One of the reasons 4X12's were closed back was the fact that a sealed cab forms a cushion of air that helps to protect the speakers. For example, if you were to take the back off of a Marshall 1960 cab loaded with greenbacks and run a Superlead through it, you'd have blown speakers pretty quickly. The cushion of air helps limit the travel of the speaker and prevents them from blowing. That's how you could have four 25 watt greenbacks with a high powered amp back then.

Make sure you have speakers rated high enough to more than handle the output of the amp.

[a.hun]

Actually though there is more than a little truth in the damping thing Billy mentions, back in the day 100W rated Marshall Superleads would quite regularly blow 100W rated 'G12M' loaded cabs.

This is where (and why) the twin 4x12 full Marshall stack came in...

Also, with carefully designed ported bass cabs the port (opening) is tuned to 'support' the speaker driver at low frequencies, increasing efficiency, power handling and reducing distortion. So it isn't just simply a matter of having a sealed cab.
http://barefacedbass.com/technical-info ... -ports.htm" onclick="window.open(this.href);return false;

Yeah detuned guitar cabs can work a treat. Though cynics like myself might say that this is largely because ordinary guitar cabs aren't particularly critically engineered in the first place. Changing the spec some (eg. cabinet volume per driver, closed vs. ported) isn't usually anywhere near as harmful as it would be with a bass cab, and (obviously) can even improve things in some situations.

412OB? Sure why not? Do like the Mesa idea of 'half open' myself.


Andy.