Light Weight Cab Rebuild

[mrjim123]

I have two Avatar B210 Neo cabinets that I am very happy with tone-wise. I'm 60 years old, with a bad back. Even at only 44 lbs. each, these cabinets are becoming too much to lift. The external dimensions of each cab are 18" x 24.5" x 16.5".

I'm thinking of putting the existing drivers into lighter weight cabinets that I plan to build myself. Avatar uses 18mm (0.709") birch plywood. I think I can achieve a weight reduction of maybe 8-12 lbs. per cab by using 0.5" Arauco plywood, even more if I use poplar plywood. I plan to keep the internal dimensions exactly the same, with small increases (to keep internal volume the same) if bracing is required.

Question 1: By going to thinner plywood I would probably need to add additional bracing, correct? I'm not sure how much, if any, bracing Avatar uses, but I imagine they use the thicker wood in order to avoid having to use bracing.

Question 2:
Structural integrity aside, what would be the audible effect of not using bracing? I play at what I would call moderately loud volumes (drums, 2 guitars, keys), with PA support.

Question 3: Would anyone care to guess how much the existing Foster horn tweeter and 12 dB mylar crossover weigh? If the combined weight is more than, say, 2 lbs. I may build without these components and install them in a fEARful headcase (6" midrange + possible tweeter) that I plan to build later.

Question 4: Has anyone built a cab with poplar plywood? How durable is it? I have no experience with it but I know how soft pine board is, and if it is as soft as pine I probably won't use it.

Thanks in advance for any advice.

[gregoire1]

I think it's always worth it to rebuild a heavier cab out of lighter (thinner) materials. Then finish it in custom colors! (black is boring)

[rpsands]

Poplar is about as soft as the cheap pine in my experience (limited). It really wants a strong poly outer coat.

Definitely brace. No section should be unbraced for more than 8" or so for 1/2" ply give or take.

Arauco is good stuff. It's basically pine, but not too bad. It's about 20% lighter than BB, and good poplar is about 30-40% lighter than BB.

[blackmail man]

I recently finished a 212 using 9mm hardwood marine ply.
I don't know specifically what hardwood it is, but its tough and light. 7 ply I think
With a pair of deltalites it came in at 17.5kg.
As rp said, you wouldn't want panels with unbraced sections of more than 8".
My tip would be to check fearful plans and get an idea of what they're doing bracing wise. It's clever, easy to understand and very effective

[mrjim123]

Originally Posted by rpsands

Poplar is about as soft as the cheap pine in my experience (limited). It really wants a strong poly outer coat.

I was thinking of using Duratex paint.

[Stanley Pugh]

Can you DI to the pa and skip the amp?

[rpsands]

Originally Posted by mrjim123

I was thinking of using Duratex paint.

If you're gentle that would be fine. I wouldn't use duratex on a poplar cab for my gigging situation. It's just not going to provide enough dent protection. My poplar cab has a thick polyurea coating, which is quite a bit tougher and has held up well.

The downside to the poly stuff is it's heavy! It adds a couple pounds to make the poplar not much of a savings over arauco in weight.

What I would consider doing myself is, if I had enough wood, do a mix. Baltic birch baffle, back and bottom, poplar for everything else. The back and bottom of cabs seem to get the most abuse for me.

That said, there's nothing wrong with just duratex and arauco. Just don't expect it to take a kick or drop like baltic birch.

[Paul K]

I made a bass speaker cab out of a 22 inch kick drum shell and an eminence 15" Basslite. I used a four L brackets to hold the front and rear panels in place, gorilla glued them in. Ported in the back. It's light, it rocks. Front panel is 1/4 inch ply-3/8 inch foam-luan sandwich. (Luan is kind of like paneling but without the ridges) Back panel is luan-foam-luan sandwich. The back panel needed to be braced. It weighs about 22 lbs. It'd be lighter, but I kept the drum legs to tilt it back. I put a top hat upside down into the top of the drum where I mount my Ashdown Superfly amp. It swivels, so I can plug in the ins-n-outs. Round drum shell is stiff and light, and cheap. The foam core sandwich thing is light and rigid.

Or, I often gig with a pair of Carvin LM-12's stacked with the Superfly. No construction needed, and they're 24 lbs each.

I'll be getting new hips in Jan and Feb '12. That'll help also....

[gtvrb]

That sounds very cool on the kick drum cab. Can you post up a couple of pictures?
Thanks

[Paul K]

Kick_Drum_Cabinet pictures by ptkbass - Photobucket

The handle is from a 67 Bassman 50 cabinet. Jack is a locking neutrik 1/4 (That was stupid-regular would have been just fine). The port was a couple two or three bucks from some on-line audio parts place. The speaker cover is an 18" embroidery hoop painted black with landscape fabric held on by velcro. My lovely wife did the logo. The back panel is braced with a couple pieces of hardwood molding I had lying around--perfect, 'cause it's very rigid. The amp is held onto the tray by velcro, and the tray also has another top hat (inverted and shortened a little) so it mounts to the top of the drum.

I dunno if you'd be able to fit two tens into a 22 inch kick drum shell; might have to go for a 24" shell. I personally have no use for tweaters, so they didn't make it into the design. And no crossover subtracts a little weight.

[wcriley]

Hi, Paul.
I remember this from the Lowdown forum.
VERY inventive and creative cab.

[THORRR]

That Kickdrum Speaker Cab is downright ingenious!

Hats off to you Paul K, for creativity.
Well done!

[robthebassplaye]

Hi!,

So, I spent 2 months, every weekend, making a lightweight bass cab. Here is the first time I have told the tale on the internet...

Allmost got me divorced... I'm 53, and this was a way for me to get the really clean, punchy, awesome bass sound I desire, without breaking my back for those occosional casual weekend gigs that I do.

It is a composite structure, made from 1" extruded foam and fiberglass (this is the same construction they use for ultralight aircraft). I used Eminence KappaLiet 3012LF, Alphalite 6A and ASD:1001 drivers, so it's a 3 way system with a custom crossover that I designed with P-Spice and Eminence Designer. I did a lot of research on the technique for building up the composite structure, that I'm happy to share if anyone is interested.

It cost about $800 by the time I was done, but I now have a really killer bottom that I have measured at over 120dB-SPL @ 1m, capable of 600W and LESS THAN 30 POUNDS!!!

I really like the clean sound of this. The walls, because of their construction, have a very high resonant frequency. All of the components are top of the line, so there is virtually no phase distortion. Many folks want an amp or cabinet that has a certain sound, so this build might not be for them, because it is very, very clean. But my theory is that I can always get the sound I want from electronics up front. You might not agree with that approach, and I totally understand.

Anyway, I have an extremely detailed 40 page document on the build, I used accelerometers to design and test the walls, and pretty sophisticated testing facilities which were available to me. I also did a lot of research on composite construction. This is not for the feint of heart, or those that can't commit to spending a lot of time making it. I used Smith and Larson test gear for the final cabinet testing, P-Spice for the electroinics design, and Eminence Designer for the cabinet and port starting points.

Would I do it again? I don't know , I love using it, less than 30 pounds with that output is awesome. But, it was a lot of work (and cash!).

Did I mention that IT IS LESS THAN 30 POUNDS? OVER 120dB-SPL, 600 WATTS??? Ya gotta love that.

Anyway, if there are any interested folks out there, I'd be happy to post more info about the build and testing process. I can't post everything I have here, way too much technical details and documentatin. But if you are interested, I have it all... And, I'm happy to share.

I tested the snot out of it, and measured virtually everything that can be measured. So, if you are into that, let me know and I'll share. I have pages and pages and pages of technical documents, test results and analysis for this design. Tradeoffs for different materials, etc...

Anyway, if you want to build one, I'll be happy to provide you with any help and details to construct the one I finally decided on. I think it's a great cabinet, one that suits me well.

Rob

[Paul K]

Indeed, cwriley, it's me. Thanks for the kind words from you and Thorrr.

The cab works very well. Lots of good complements on it at gigs and whatnot. The downside is that it does take up a bit of premium real estate on stage. The stacked LM-12's take less room and can be put in the corner where they belong.

Keeping in mind the original poster's quest for weight reduction: If I were to do it again, I'd use 3 or 4 L brackets instead of the eight I used on the front and back. And I'd use the smallest L-brackets I could find with the smallest appropriate bolts to hold it together instead of the larger bolts that fit the existing holes. I epoxied the unused holes as it is, so filling and re-drilling smaller holes wouldn't have been an issue. And steel is heavy; a half pound here and a half pound there really adds up. The gorilla glue around the edge inside and out has done a tremendous job holding it together; so as it is, it's a bit over-engineered. Maybe instead of L brackets: hardwood blocks and wood screws? Would that be lighter?

Again, since weight reduction was the O.P's quest: In a separate project, I gutted a Behringer 12" ABS PA cab and filled it with an eminence delta-lite. A champagne cork fills the tweeter hole. It's light, sounds good, and I can still use it as a wedge monitor when there's a full house PA for the bass anyway. I don't use a low B string, so the bottom octave is full enough for me. It's not as interesting of a project, but it does exactly what I wanted it to do.

[Paul K]

Originally Posted by robthebassplaye

Hi!,
It is a composite structure, made from 1" extruded foam and fiberglass (this is the same construction they use for ultralight aircraft).
Rob

OMG. That is cool!

[Mike Arnopol]

I'm also making some composite cabs using similar techniques. My little 12" cab for a 3012ho weighs 5.7# unloaded and should come in at about 15# loaded.

[Bass Unique]

I used 12mm ply for my larger cab but it has a lot of useful bracing in the form of a long convoluted port.

For smaller cabs, 9mm should be enough. I used a softwood ply as it was lighter and then varnished it with a polyeurethane varnish to give it some knock protection and waterproofing (beer spills....)

If you are putting in bracing I would say on 12mm every 200mm max and on 9mm every 150mm max. Also, try to not divide the panel equally but ensure that each remaining unsupported part is different which will ensure the whole cab does not resonate as one frequency.

The thinner materials do let through more midrange. lighter and stiffer materials are more effective at radiating noise than dense thick heavy ones. You have to think more carefully about bracing. use a thin brace edge on. You only have to be around 4 times thicker where the brace is so dont use too much material!

If you carpet the box, this also helps keep the midrange in without too much additional weight.

For robustness, use good corner protectors but also you can use plastic or metal edge protection strips too.

[robthebassplaye]

Originally Posted by Mike Arnopol

I'm also making some composite cabs using similar techniques. My little 12" cab for a 3012ho weighs 5.7# unloaded and should come in at about 15# loaded.

Hi! I'd love to share experiences... I was considering the 3012HO instead of the 3012LF - are you using a mid driver with that? also, what is the volume you decided on? Are you doing a composite build up, ie extruded foam with fiberglass? Hows it going?

There are not enought crazy folks out there to try this, so I am really anzious to talk with you about it.

Rob

[Mike Arnopol]

Hey Rob--I sent an email, but ';ll pm you with my phone---I'm in Wilmette!

[1n3]

Interesting posts here, particularly robthebassplaye's. On a more pedestrian note...

Originally Posted by mrjim123

I have two Avatar B210 Neo cabinets that I am very happy with tone-wise. I'm 60 years old, with a bad back. Even at only 44 lbs. each, these cabinets are becoming too much to lift. The external dimensions of each cab are 18" x 24.5" x 16.5".

I'm thinking of putting the existing drivers into lighter weight cabinets that I plan to build myself...

AFAIK, the Avatar speakers are modified versions of the Deltalite II. Opinions on them appear to be mixed. Apparently they trade broadband sensitivity for some extra excursion. Can you get complete TS specs for them? If not, you won't be able to do accurate modeling. Perhaps you don't intend to.

And, what do you do with the Avatar cabs afterward? There's not a lot of demand for empty cabs.

So I wonder if you would be better off selling that cab, and buying some retail speakers.