Moving Air - Drop tuning and Cabs

Fran · Post by **Fran** » Thu Dec 03, 2009 5:56 pm

As some of you know i play in A standard tuning with Master Charger, its low and its loud! So i got this big problem with my Carlsbro 4x12, the back panel is rattling like fuck. The other guitarist has problems with his lead shooting out of the jack on his cab as well which is relevant to this.
So, i got the sound engineer to take a look as at first i thought i'd ripped the Celestions in the cab. Turns out its trapped air! He's advised me to cut two ports into the back panel as the air could eventually rip the speaker cones, i've also lined where the back panel fits on with spongey draught excluder tape to help stop the rattling.

Has anyone else come across these problems? I've noticed some Bass Cabs have a port on the back where the air shoots out. Before i cut the ports with a Hole Saw im wondering if the back panel is the bast place, would the front panel save loss of projection?

aen · Post by **aen** » Thu Dec 03, 2009 6:08 pm

Both of the cabs I've used have great big holes in them. But oddly enough, my 15" cab was sort of farting out with a guiitar, but held up better with bass.

Fran · Post by **Fran** » Thu Dec 03, 2009 6:25 pm

Yeah, i was getting that farty noise along with the panel emulating a Jigsaw cutting wood.
I take it the holes are in the back panel?
Was wondering if i drilled the front panel i might get more projection in the right direction and trouser flapping fun.

analogsystem · Post by **analogsystem** » Thu Dec 03, 2009 7:06 pm

I had a Marsahll 1960a with a rattling back panel. The rattle was so loud that it was audible when playing with a cranked Marshall 2203!

I temporarily fixed it by drilling into the center support cross bar (adding one more screw in the center of the panel). Old Marshall Cabs actually had a screw there anyways.

After a few hours it was rattling again. I think on many of the Marshall cabs, everything is plywood except the back panel which is particle board and just has too much flex. Also the plastic handles were rattling.

I ended up going to another cab as the speakers were getting pretty flabby anyways and now my old 1960a is just collecting dust, waiting to have a new plywood panel made for it.

One of these days I'll make a new back panel, secure it with much bigger screws, and replace the handles with metal ones.

------------------------------------------

The Cab I'm using now is tight as shit with no muddyness or farting. I think this is because internally it is like 2 2x12 cabs stacked instead of one giant chamber. This makes it punchier and there is not as much pressure building up in each cab?
Also the speakers are front loading instead of rear.
Maybe its just better construction.

Fran · Post by **Fran** » Thu Dec 03, 2009 8:47 pm

Where these problems just in high gain situations?
I was using a Bass Cab for a while with no problems but i sold it being as i had the other can with better speakers doing nothing, i regretted it with the problems but the tape seems to have solved it. The port holes will get drilled as well, just as a precaution.

SAVEStheDAY · Post by **SAVEStheDAY** » Thu Dec 03, 2009 10:57 pm

Porting helps to "Tune" the cab to the lower frequencies. I have a Genz Benz G-Flex 2x12 which is super heavy duty, ported, and so insanely dark and bassy I have to dramatically change my amp settings when switching between it and other cabs.

Mages · Post by **Mages** » Fri Dec 04, 2009 12:25 am

the port(s) in a bass cab are actually tuned to a certain frequency, it's not just a random hole. there's also a certain kind of port called a "helmholtz resonator" that is tuned to a certain length so it resonate at a certain frequency. it's works by the same principle as how you can blow across the mouth of a bottle and it makes a tone.

Sloan · Post by **Sloan** » Fri Dec 04, 2009 12:44 am

dude, make it a half-back. chop teh back in half and put some door hinges on it, so you can drop it down when you get through unloading it. wow.

aen · Post by **aen** » Fri Dec 04, 2009 2:20 am

I suppose I should clarify. My 1x15" is about a meter tall, it has a closed back but huge ports on the front, below the speaker. I think they're sloped up toward the speaker, too. I was tuned down to B when I had the dropout on the cab.

My other experience woudl be the twinr everb, which has a "mostly open back" A lot less bass power, but more tradiitonal "tighter" guitar tonez.

Fran · Post by **Fran** » Fri Dec 04, 2009 12:40 pm

mage wrote:the port(s) in a bass cab are actually tuned to a certain frequency, it's not just a random hole. there's also a certain kind of port called a "helmholtz resonator" that is tuned to a certain length so it resonate at a certain frequency. it's works by the same principle as how you can blow across the mouth of a bottle and it makes a tone.

Are you saying random holes are pointless? I gotta do something, if I go past 4 pn amp volume it looks like the cab is going to blow up

Fran · Post by **Fran** » Fri Dec 04, 2009 12:46 pm

Sloan wrote:dude, make it a half-back. chop teh back in half and put some door hinges on it, so you can drop it down when you get through unloading it. wow.

Thats actually a good idea in case I change my enviroment, the cab was fine in the Pistolz band. Plus I can transport beerz in the cab, smuggle into venues, etc.

Gavin · Post by **Gavin** » Fri Dec 04, 2009 6:56 pm

Fuck me, Fran plays so loud he almost blows up his cab.

izodiak · Post by **izodiak** » Fri Dec 04, 2009 10:59 pm

mage wrote:the port(s) in a bass cab are actually tuned to a certain frequency, it's not just a random hole. there's also a certain kind of port called a "helmholtz resonator" that is tuned to a certain length so it resonate at a certain frequency. it's works by the same principle as how you can blow across the mouth of a bottle and it makes a tone.

Didnt know they are that important..
Need to do research..every day I learn something new here. hah.
thanks.

(now I am afraid of Fran, how Your ears can hold it, wow)

Mages · Post by **Mages** » Fri Dec 04, 2009 11:24 pm

I'm just saying that there is a science to it. I don't think there is anything necessarily detrimental you could do, but you would be making modifications without being completely clear on the ramifications. I think making it open back or half back like sloan said would be the simplest way to go about things.

this is what I know about open back cabs; the way fender does their open back cabs with the baffle on top and bottom, creating an opening about 1/3 the height of the cab on the back, actually works out so if you set it close to a wall it works like a bass port.

Fran · Post by **Fran** » Fri Dec 04, 2009 11:42 pm

Thanks Ng.