Build a speaker cabinet in a 19" rack case?

[Rosie C]

I'm thinking how I could use a cabinet like this 6U one to make a bass speaker cabinet. It would suit the rest of our band's gear, and we lug an empty box around anyway to stand the PA on.

 

Not for playing bass guitar, just to boost the low end of the PA for guitar/vocals. I'm thinking of 2 x 8" drivers, and wondering what the best approach is. Making a conventional box out of plywood and just fitting it in seems safest, but I'm wondering if I can do something that just uses the plastic shell?

 

Edit: though it occurs to me that buying a second hand combo amp that fits the space would be cheaper and quicker - if a bit heavier.

 

 

 

Edited March 14 by Rosie C

[Maude]

I am by no means any kind of authority on speaker cab building but my concerns would be strength and rattles.

Would the fibreglass body be rigid enough to not flex with the pressure waves? My limited knowledge says the lower frequency the cab is designed to handle the more rigid the structure must be for the sides not flex and kind of act like a damper to the pressure of the sound waves. An inner ply box could solve this but would the volume left be too small to be effective? If an inner ply box would work then you could wedge packers between the case and ply box to act as braces to remove the (possible) need for internal bracing. 

You would also have to make sure the  clasps cannot rattle if the front cover is removed, same with the handle. 

[Rosie C]

I did think the plywood could be a tight fit to the inside of the case, then I could use expanding builder's foam between fibreglass and plywood. But rattling of catches and handles is a good point and not something I'd thought of!

 

You're right, it may be too small. I can get a larger case and while that would give me other problems stacking, they do come with wheels! 

[Phil Starr]

Funnily enough, I'm helping someone else out with a disguised built in cab. and i was also thinking of advising your to damp the rack cab with expanding foam.

 

A lot depend supon what you mean by:

4 hours ago, Rosie C said:

Not for playing bass guitar, just to boost the low end of the PA for guitar/vocals

 

There isn't really any significant 'low end' in guitar/vocals so perhps you could explain a little more about how you picture using this.

[Rosie C]

Just a perception really that the PA is a bit lacking at lower frequencies and that there's a fuller sound when I plug in a bass amp. I might need to make some with and without recordings to make sure!

 

[Phil Starr]

I can see the attraction of building a cab inside this case, it's a convenient size for a cab and you wouldn'tneed to worry about the finish as it already looks like a bit of pro gear. A 2x8 would work and so would a 10 maybe even a 12. youc ould easily build a bass cab or a guitar cab based on this. If you decide to go ahead PM me and I can help with dimensions and tuning. The only problem I have that is if the vocals /guitar are sounding a bit thin it's the low mids not the bass that needs addressing.

[3below]

I use a 3u rackcase for Sansamp RB-1 and Crown power amp on top of a BF Dubster, with foam backed carpet between cab and case.   As per @Maude's post, two problems have emerged during recent gigs: rattling catches and a resonating top panel. The former to be fixed by swapping the parts around so that  the vibrating butterfly catches will be on the lids. The latter problem requires some heavy duty neoprene foam stuffed between the panels.  This thread has reminded me I must get on the case before next Saturday.

[Rosie C]

I just checked our other case, the catches are on the lid, but they're on the case on the larger models. Strange. 
 

 

Edited November 12 by Rosie C

[Rosie C]

16 hours ago, Phil Starr said:

I can see the attraction of building a cab inside this case, it's a convenient size for a cab and you wouldn'tneed to worry about the finish as it already looks like a bit of pro gear. A 2x8 would work and so would a 10 maybe even a 12. youc ould easily build a bass cab or a guitar cab based on this. If you decide to go ahead PM me and I can help with dimensions and tuning. The only problem I have that is if the vocals /guitar are sounding a bit thin it's the low mids not the bass that needs addressing.

 

Thank you! I expect it will become a summer project, and yes I think you're right it's the "low mids" rather than the bass I need to look at. I'm not sure what frequency range the "sub out" jack on the PA pushes out, I'll try to find out.

[3below]

7 hours ago, Rosie C said:

I just checked our other case, the catches are on the lid, but they're on the case on the larger models. Strange. 
 

 

Same on some of mine, seems illogical given the rattling.