Booming Cabinet

I have a Groove Tube 2x10 cabinet that I picked up used and unloaded. It looks like it was originally a closed back, low wattage cabinet. I do not have the back panel which is fine because I prefer open back cabinets. Roughly 50% of the cabinet back is “open.” The cabinet is made of thin plywood. It is not well braced and the baffle board is held on by only four screws. I bought the cabinet because it looks cool with my Acoustic G60T head. The head is 60 watts. I loaded the cab with a pair of my favorite cheap speakers. The set up sounds great when playing through my bridge pickup but when I switch over to my neck pick up it booms on the low notes, spiking when I play the “C” at the third fret on the A string. I’ve played the cab with just one speaker loaded, the second hole left empty, and I did not have this problem. I’m surprised that an open back cabinet would act this way. The only thing that I can think to do is to stiffen up the cabinet by adding internal bracing and adding more screws to secure the baffle board. Another idea is pad the inside of the cab with stiff insulation board.
Any one else have experience with this problem? I’ve never had much luck mixing cabinets and speakers or even building my own cabinet. It seems like something is always not quite right whenever I try this.

Thanks

Tom

Doesn't sound like a "real" GT cab, to me. Most of their stuff I've seen over the years has been very well built.

I'm not one to "build" my own cab. I'm really happy with my Mesa cabs--i think Mesa does some of the best cabinetry in the biz. Marshall cabs can be beat to death and still sound good; and I like the old small, mid-60s Fender Bassman/Band Master/Tremolux cabs.

You might try Avatar, I hear good things about them on the net, but never tried one.

Bill

I thought I post an update for anyone interested.

Bill and Tim, thanks for the reply.

Bill:

The cab is a real GT and I didn't mean to imply that it is cheap, although I can see why you read it that way. I think GT intentionally made it light weight to be used for low wattage duty.

Tim:

I completely believe in proper, scientific, based design for speaker enclosures. There is a school of thought amongst some guitar players that "magic" or "mojo" comes into play when it comes to speaker cabs, they believe that the wood, and joints, etc. color their tone. I personally don't think it is practical to count on it. It can color tone, which is the problem that I currently have, but it is impossible to control as it will vary based on frequency and volume.

Now for the update:

I added four more bolts to secure the baffle board to the cabinet. It originally only had four. I played a gig Friday night and now the "booming" happens on the low E. It appears that stiffening the baffle board has dropped the resonate frequency from the low C to the low E. This is definitely a step in the right direction. If I can drop the resonate frequency lower I should be able to eliminate the booming (within the guitar frequency range). My next step is to add some bracing inside the cabinet in order to stiffen the side panels. It will be interesting to see if this solves my problem.

Thanks,

Tom

Interesting, Just treat that thing like a plate girder and brace er up! haha.

Well, I'm with Tim on this one. Granted, a stiff cabinet will certainly help, but the nature of an open-back cab can indeed cause boominess or, conversely, thinness, especially if the size of the rear opening doesn't coincide with the size of the enclosure. If you like the sound of an open-back cab, you're probably better off opening it up even more than it already is. The nature of any given speaker within the cab will change the tone, too. However, if you're really serious about taming the beast, at least to the point where you feel comfortable using just about any speaker, you can use the Thiele guidlines to get pretty close. I had a pair of boomy 1x12 cabs that were also half-open in the back, so I eventually figured out what size of a port and PVC tubing I needed to accomplish my task. I ended up with a rear board with two 2 1/2" diameter ports with 6" length tubing in each cabinet, and voila!.....no more boominess. The cabs are essentially tuned to the speakers I'm currently using. Plus, the ports themselves coming off the back will still give you the sound of an open-back cab, at least to some degree. It's really a win-win situation without having to do a tremendous amount of work.