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Cab vibrations & movement...

#21
Are you playing mostly on a wood floor? I know when I play on anything that isn't wood, my bass cab doesn't vibrate much, but once I go on wood floor, like certain stages, it'll vibrate, I usually just put down a dry wash cloth on top, it'll suck up the vibrations.
As for the movement, idk what to tell you, i've never had a cab vibrate so much it moves itself.
 
#23
Which cab are you running by them?

Maybe if I get motivated tonight, I'll take the back panel off and shoot some pics of the guts of my 4x12. Give everyone an idea of the internal design.



zachoff said:
My practice space is concrete & I've put some foam under the cab to keep it from moving around but it still vibrates stuff off of the top. I'll try the bracing though. 2" dowels, huh?

It has two bracings front to back but nothing side to side or top to bottom.
Click to expand...
 
#24
zachoff said:
I'll try the bracing though. 2" dowels, huh?

.
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3/4" is sufficient. What matters is the distance between them, not their size. Rule of thumb, you should not be able to fit an 8 inch long rule in the space between braces and each other or the cab corners. That's with 3/4" thick panels. With 1/2" call it six inches.
 
#25
billfitzmaurice said:
3/4" is sufficient. What matters is the distance between them, not their size. Rule of thumb, you should not be able to fit an 8 inch long rule in the space between braces and each other or the cab corners. That's with 3/4" thick panels. With 1/2" call it six inches.
Click to expand...

I know on my 412, that the speakers are mounted from the back (rear panel access). Since not front mounted, I know getting good bracing may be a problem so you don't land lock your drivers into place.
 
#27
I'm not Bill... but here's some of what stands to be gained by properly damping/bracing a speaker enclosure:
  • Eliminate (or significantly reduce) standing waves (an acoustical phenomenon which create undesirable peaks and valleys in the frequency response). Cutting the standing waves will result in a more accurate reproduction of the amplifier's output
  • Eliminate audible distortions (not the good kind)
  • Stop the cabinet from shaking like a whore in church so your tube amp won't be subjected to unnecessary trauma
  • Perhaps most importantly, get more head room out of your amplifier!!! When your speaker cabinet is vibrating/resonating, it is essentially operating as a 'sound absorber'. When a speaker enclosure is properly damped & braced, it will optimize the amount of energy that the speakers can turn into sound pressure. As a result, you should be able to achieve the same relative volume without turning the amp up as high. As a bonus this will likely result in longer life for your power tubes :)
 
#28
it should be night and day.

what's the real trick is getting the right amount of batting in there, because you can actually "cheat" the internal volume a bit with batting. to an extent. But yeah, bracing to "kill" the shell, batting to focus the tone and kill standing waves in the box.
 
#29
carbonfold said:
I know on my 412, that the speakers are mounted from the back (rear panel access). Since not front mounted, I know getting good bracing may be a problem so you don't land lock your drivers into place.
Click to expand...
That's one reason why most manufacturers switched to front mounting 30 years ago.

Bill, to re-post my question from another thread, can you generally characterize the tonal changes (improvements?) after adding bracing and batting to an unbraced/unstuffed cab?
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Tighter lows, smoother mids, less boom.
 
#31
carbonfold said:
Which cab are you running by them?
Click to expand...

It's an older/custom 2x15... There's no serial number and I asked them about it. Apparently, I bought it from the guy that started Atlas cabs & this cab was his blueprint for future ripoffs. Ha. Honestly, I don't know that whole story, but that's basically what Emperor told me.

**edit))

It's this one..
emperor06.jpg
 
#32
Pics of the inside would go a lot further in seeing the problem. Put cross bracimg in there per bills diagram. May not look exactly like that due to driver layout but you get the idea. If it's rear panel access, you can use the side to side and top to bottom braces to help anchor the front to back ones. I'd cut the front to back ones just a hair long, maybe 1/16 - 1/8" so you can really torque the back on so it doesn't rattle. Run screws through the back and into the ends of those braces. If it's not lined inside, do that while you're in there too.
 
#34
zachoff said:
Yeah, probably would. Ha.

emperor02.jpg
Click to expand...

looks like you have some work to do.

1. You gotta add some bracing. What's in there ain't doin ****. You can go the dowel route that Bill posted an image of, but you'll have to make measurements as to where the dowels line up because next you're going to add some lining ("batting") to the inside of the cab.

2. get some egg-crate mattress topper or other such batting and line every bare-wooden surface inside that cab. Over the handles too. You can use a staple gun or velcro, whatever suits you.

If you like the sound of the cab before, well, it'll be night and day.
 
#35
From what I see there, there are some pretty big problems...

-No bracing.
-No damping material.
-Completely deficient/incorrect porting.

The damping is something anyone can do, the bracing will be more effort, but is possible. The porting will take some work. Holes in the baffle don't make for proper porting or tuning.

I personally would want to do something about the rear mount speakers too...but that's just me. ;)
 
#36
At the very least I would put non-structural bracing on all side and top panels and on the removable back panel. Some OSB 1" x 3" x whatever length glued and stapled, standing tall. I would also use some weather strip to seal between the cabinet and the back plate, if there isn't already some on the cover. Air leaks cause problems too. And WHAT is with the baffle plate being grille cloth wrapped and THEN installed? No wonder the speakers are rear mounted, the cloth is flush against the baffle board!!! This looks like they went for pretty box over functional box to me. The "port" holes with netting stapled on the back is just plain infuriating to me. You'll be lucky if you don't burn up those 15's anytime soon. In this scenario, without knowing the inner box dimensions, I'd say you either have too much or too little airspring and those voice coils are gonna cook.

Wow. I know who I will not be buying a cabinet from.
 
#38
adbass said:
looks like you have some work to do.
Click to expand...
Big time. That could serve as the poster child of how not to build a speaker. The removable back makes proper bracing very difficult, while the corner cleat construction adds weight for no good reason. The staggered drivers reduces midrange dispersion and causes combing. The ports are half the diameter they should be, while no ducting of the ports means the cab is probably tuned too high, leading to boomy response. I hope it didn't come unlined with damping, but expect it did. From a cosmetic standpoint painting the baffle and TNuts black would look a lot better.
It looks like the designer basically used a 60s vintage Fender cab as a model. For guitar that's OK, but for bass the only way it could be made worse would be to make it open backed.
 
#40
Wow, i guess the shell maybe salvageable. I'd remove the baffle and ditch it. Cut a new one with the drivers aligned vertically and put four 4" ID ports in it. You can use pvc pipe for this. Need internal measurements to get,proper length/tuning. I'd also set the new baffle back an inch and make a grill cloth frame for the front. This will let you front load the speakers and glue the back permanent when you get that far.

And +1 to what everybody else recommended here as well. Use dowel or double thick plywood strips for the bracing, not osb. You can get plenty out of the half sheet you'll be getting for your new baffle. Place one strip perpendicular to another strip, glue them together and consider that one stick of bracing.
 

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