Re: 2x12 goes BOOOM

fuzzking · Post by **fuzzking** » Wed Feb 25, 2009 7:33 am

shadowplay wrote: I'm pretty sure porting inverts the phase of the back wave so the sound of the back of the cone reinforces rather than cancels the front wave,. More relevant is that a port (basically a hole) tunes the resonant frequency of your cab. I had a similar problem years ago with a custom 2x12 which almost self detonated everytime I used my ebow, which I solved through the scentific process of stuffing a sponge in the port. Not sure if this is the right way to go but it worked for me. The port on your cab is probably in the side handles. or between the speakers.

PS slick looking cab Michael, love the logo, love the logo

oh i get it, we call that "bass reflex" over here. i thought that was only done to bass cabs. hm... i removed a third of the back panel, but i fail to see how that would give me this frequency bump. i'll try a few things out this wekend...

funnystuff:

just called the seller (thomann e-store) to ask them if it's a known issue (cab construction / speaker / what do i know) ... but man, guitar salesmen are not my cup of tea.

so itold the guitar salesman my concerns:

him: "YOU MAY NEED SOME BALLS ON A BIGGER STAGE!!!"

me: "no."

then i tried to tell him that it's like a real resonant peak, occuring only on the low e unfretted, but he just wouldn't get it.

him: "YOU CAN EQ IT OUT"

me: "i don't EQ".

then he tried to tell me about HIS live setup.

and so on.

geez.

øøøøøøø · Post by **øøøøøøø** » Wed Feb 25, 2009 7:34 am

It's probably the cab. Guitar cabinets are almost never designed with anything other than appearance or portability/compactness in mind. They are certainly almost never tuned. Even if they were tuned initially, it all gets thrown out the window if a different speaker is installed. That means you can find all sorts of weird things like what you're describing in guitar amp cabs.

ohm-men · Post by **ohm-men** » Wed Feb 25, 2009 9:22 pm

I'm no expert on the subject, but I had a simelar problem when stuffing 2x12" in a 2x10" Tremolux cab. I also had a "zing/booom" with the low E unfretted, weird.
Since I build the cab myself, I just took a 2" (inch) drill and drilled two "port holes" in the lower outer corners of the baffle board.
It solved the problem, since I knew my baffle board was "floating" perfectly.

Albait the latter can be your problem as well. The fact that the baffle board resonates at a certain frequence (your low E unfretted)
A bass player in a former band I played in had the same (E and A strings, boom-ing like hell) the only thing that helped was to check the speakers and baffle board + the back as this cab has a closed back. Turned out something was a tad loose, so we tighened everything and the problem was gone. Perhaps you should have a peak inside of your cab?

Also I think this is why fender used insulation in his closed back cabs to get rid of unwanted buzzing etc...I did this in a showman cab and it worked there as well.
(Though I had all my cabs ported)

fuzzking · Post by **fuzzking** » Thu Feb 26, 2009 1:07 am

okay, so i'll take a peek inside and try to find anything loose, stuff some extra wool in there ... sigh ...

jerry, what do you mean by "floating" baffle board?

runrunrun · Post by **runrunrun** » Fri Feb 27, 2009 11:39 am

I used to have this cab, used it with a valve jr. and a Vibro Champ... of course those are low wattage amps, but with them i did not have the low E problem. Vintage 30´s on that one. Wayyyy too loud for an apartment with a 5watt amp!

Targ · Post by **Targ** » Sat Feb 28, 2009 8:48 am

Not sure this will apply but.. I know that speaker cabs for stereos are either ported or not and designed that way on purpose. These ports are "tuned" in size to offer just the right amount of back pressure to reinforce the sound. If you removed a back section the FIRST thing I would do is put it back on as you may have thrown this "tune" out of balance.
A closed cab offers back pressure (inverted resonant frequency) to the speaker cone and tames its movement down. This increases its ability to handle power and since your boom is in the low registers it would seem to make perfect sense as this is when the cone is moving the most. It may need to be a closed cab.

By removing a portion of the back, you may have inadvertently caused your own boom. Untamed the beast as it were.

fuzzking · Post by **fuzzking** » Sun Mar 01, 2009 2:02 am

i especially bought the cab because part of the back panel can be easily removed ...

good news is, i moved it around, and the boom is gone. it was standing parallel to a wall, and now everything is fine again. hey hey!!!
it's loud, but it's easer to achieve breakup with it than with the 4x12. with the big cab, the room is literally shaking when the master is above 5.

i patched it with the deluxe reverb so i have a mix of the marshall's low end and the fender's sparkle, and it's very very, very nice.
you should hear it with the brassmaster clone maxed, it's hilarious.

ohm-men · Post by **ohm-men** » Mon Mar 02, 2009 6:26 am

Ah, sorry. Floating baffle board, or at least what I understand under it.
All BF Fender cabs have their baffle boards screwed at 2 inch wood "stripes" so the baffle board doens't actually touch the cabinet directly.
There is a small gap between the baffle board and cabinet. Ofcourse the 2 inch wood touwhes both, but there is no direct contact. (so there the "floating" term comes from, I think) On later SF cabs, the baffles board was glued in a routing (at least on the combo's) thus making the baffle board non floating, this constroction on a closed back cab can easely cause vibration resulting a "Boooom" or simelar.

fuzzking · Post by **fuzzking** » Tue Mar 03, 2009 2:38 am

oh i see. IIRC the board is screwed to extra blocks of wood that sit in the cab, but i'm not sure.