DIY Lightweight Composite Cab Build

[alexclaber]

And btw, port tuning is more predictable with tube type ports - shelf ports tend to have quite a lot more end effect and thus have to be made significantly shorter than WinISD predicts.

Alex

 

[Nook]

shelf ports tend to have quite a lot more end effect and thus have to be made significantly shorter than WinISD predicts.
Alex

Maybe told somewhere before, but I've never found a satisfying answer: Is there any rule (of thumb) regarding this? I have only read that one half of the port height must be subtracted from the lenght compared to the tube port, but not sure at all. Thanks
BTW: how do you (all) solve carpeting around the shelf port? Do you carpet inside the whole port scowl or make an offset in the wall thickness and fold carpet just a bit around the port(s)mouth? Any smart solution appreciated...

 

[51m0n]

If you can make 810s and PA gear light enough that sound as good then people will buy them if only cause haulage will get cheaper.

 

[asad137]

2w/2m, or 100w/10m is a more realistic measurement of real world performance. Both values produce a chart directly comparable with 1w/1m.

Wouldn't it have to be 2W/1.414m to be compared to 1W/1m?

Asad

 

[alexclaber]

Maybe told somewhere before, but I've never found a satisfying answer: Is there any rule (of thumb) regarding this? I have only read that one half of the port height must be subtracted from the lenght compared to the tube port, but not sure at all.

It's about 2/3 the predicted length for a typical shelf port but it isn't terribly reliable. I've found the best way is to start with the calculated length, test the tuning, shorten it a bit, test it again, shorter a little more, etc, until you get where you need to be. It's a right pain for one-off cabs!

Alex

 

[Nook]

It's about 2/3 the predicted length for a typical shelf port but it isn't terribly reliable. I've found the best way is to start with the calculated length, test the tuning, shorten it a bit, test it again, shorter a little more, etc, until you get where you need to be. It's a right pain for one-off cabs!

Alex

O.K., muchos thanks... I'll try it.....or end up making it 3/5

 

[Petebass]

And btw, port tuning is more predictable with tube type ports - shelf ports tend to have quite a lot more end effect and thus have to be made significantly shorter than WinISD predicts.

Alex

Hmm... I didn't have this problem with the shelf port on my DIY 2x12. It predicted a port length and it measured correct to within 0.5Hz.

 

[pflail]

Okay, I just joined to see this thread. Somebody from the BFM forum pointed me to it because a couple of weeks ago I needed to build a couple of subs for my band. I posted a thread about building a sub out of fiberglass foam core and got blasted for it. The only reason I didn't do it was because of a tight time schedule and well, there was a little insecurity involved. I work with fiberglass on a regular basis, I used to work for a homebuilt aircraft company, and I'm about to start (in a couple of months) on a fiberglass foam core airplane. I already have the kit so it's just a matter of getting started.

Your results are exactly what I had in mind. After reading this thread I'm definately gonna go back and rebuild the horns this way. I've got all the material except the foam.

After getting blasted on the other forum it has been wonderful to read your results here. My 13yr. old son was so mad at me for not stepping out and building this way. I should have listened to him!

I was gonna layup the 4x8 sheets, then cut the panels, hot glue it together, do fillets and layups in the corners, then put the top on in sections. Well, I better get started.
Your rig looks good! I wouldn't have gone w/ the carpet, though.
Rick

 

[Stumbo]

Your results are exactly what I had in mind. After reading this thread I'm definately gonna go back and rebuild the horns this way. I've got all the material except the foam.

If you have time, post a thread of your own.

 

[Petebass]

If you have time, post a thread of your own.

Yes please!

 

[jlepre]

I wonder how the test went at rehearsal the other night?

 

[zac2944]

I wonder how the test went at rehearsal the other night?

The testing went well.

I typically use a SVT-450H & SVT-410HLF combo at rehearsals. So for the testing I used the SVT head with my composite 210. I'm no tone description master like some of the folks here (Kjung comes to mind), so all I can do is compare the 210 to the 410.

The two things that I noticed right away about the 210 was that it was more efficient than the 410, and had a more clear and even tone. I went back and forth between the 410 and 210 without changing settings on the amp to compare the two. The 210 was noticeably louder. They are both 4 ohm cabs, so I can only assume there was a difference in efficiency. Tonally the two were pretty different. The low end on the 410 is bigger and can get boomy where the 210 stayed pretty tight. Low end was there with the 210, but the 410 could get really full and fuzzy compared to the 210. I actually liked the tighter low end of the 210 better in the band mix. It made it easier to hear the others in the band, but still had some authority. The mids and highs were a lot more clear and defined on the 210 compared to the 410. The hi mids were more prominent than the low mids. The highs were there, but not glassy of over the top like a SWR cab or that Marcus type of tone. My guess is that the upper midrange character comes from the 2510's. They have a lot going on in the mid to upper midrange.

I didn't try to drive the 210 any harder than I needed too. I'm not trying to find its limits just yet. I'm sure the 410 could have gotten louder than the 210 if I cranked the amp.

One bad thing I noticed is a slight buzz coming from the 210 somewhere. I couldn't hear it while playing with the band, but when I was the only one playing and listening very close to the cab I could hear it. It could be a lot of things, so I'm going to have to trouble shoot it at home when I get a chance.

Just to be clear to those who were concerned. The cab DOES NOT walk around or vibrate around on the floor when played loud. I didn't notice any excessive vibrations coming from the walls of the cab.

I'm pretty happy with what I've heard so far. Tonally, my intent was do design a cab with a more even response to use when I don't want all that in-your-face bass that I get from my Schroeder 1212R. I think I've accomplished that.

 

[zac2944]

I work with fiberglass on a regular basis, I used to work for a homebuilt aircraft company, and I'm about to start (in a couple of months) on a fiberglass foam core airplane. I already have the kit so it's just a matter of getting started.

pflail, welcome to TalkBass. Your project sounds fantactic. Please post some details here if you get it under way.

This project should be a piece of cake for you with your experience. Go for it. Don't listen to those nay sayers!

Your results are exactly what I had in mind. After reading this thread I'm definately gonna go back and rebuild the horns this way. I've got all the material except the foam.

What type of foam will you use? Do you think the high end foams are worth the extra money for a project like this? I went with XPS, 1" and 0.75".

I was gonna layup the 4x8 sheets, then cut the panels, hot glue it together, do fillets and layups in the corners, then put the top on in sections. Well, I better get started.

I thought about a lot this method, but chose to make the core in one piece insted. If you're going to use xps foam, be careful with hot melt. The XPS will get too hot and expand if you expose it to a lot of hotmelt.

Your rig looks good! I wouldn't have gone w/ the carpet, though.
Rick

Finishing is a b!tch. Carpet is just so much easier and is very durable. Maybe on my next build I'll go for a fancy finish. These guys here on TB get rabid though. It would have added a month onto my project if I did a painted finish. I think a few TBers would have gone nuts. For my next build I think I'll hold off on posting until after I'm done.

 

[kraigo]

These guys here on TB get rabid though. It would have added a month onto my project if I did a painted finish. I think a few TBers would have gone nuts. For my next build I think I'll hold off on posting until after I'm done.

Geez, we selflessly provide you with the motivation to finish your project and this is the thanks we get!

KO

 

[zac2944]

Geez, we selflessly provide you with the motivation to finish your project and this is the thanks we get!

KO

Forgot the winking yellow guy for sarcasm. Fixed it for you.

 

[coolrunner989]

Awesome job man, I really envy you.
I think you should try for a (2)12" or 15" next

 

[Stumbo]

I went back and forth between the 410 and 210 without changing settings on the amp to compare the two.

He Zac, when you have a chance, see if the 210 can be e.q.'d to sound like the 410.

 

[pflail]

Zac, thanks for the encouragement.
I'm a drummer but play a little bass (hey, they're the most important instruments aren't they?) and my son is starting to learn bass so it's good that I found out about this site. My brother is deep into bass so I'll have to ask him if he's signed up here. Over the years he's built several basses (one including latheing the neck), several cabs and he also is into upright bass. He's an engineer too and he always seems to be fiddling around with it.

What type of foam will you use? Do you think the high end foams are worth the extra money for a project like this? I went with XPS, 1" and 0.75".

They've got XPS at our local Lowes and that's what I'll use. They have it 1" and 1/2". I'm thinking I'll use 1" for the interior speaker enclosure, 1/2" for the interior horn walls and 1" for the exterior. Is the high end foam worth the extra? Well, if I were at 10,000 ft. I think I would want the best stuff I could get if it increased the safety factor in an airplane. With a cab, what's it gonna do? Fall apart during an awesome slap happy solo? FWIW I have an old Goldwing ultralight kit and the forms were hotwired out of 2 solid blocks of 4'x8'x2' foam. It doesn't look like the high end stuff, but I think I'll trust it anyway. My A&P friend said it's the fiberglass that's the most important.

If you're going to use xps foam, be careful with hot melt. The XPS will get too hot and expand if you expose it to a lot of hotmelt.

That's what I was thinking too. I was gonna try experimenting w/ just spot tacking it w/ a cabosil slurry between the tacks. I may just go with the way you did it.

Finishing is a b!tch.

You're obviously more meticulous than me I don't like to use carpet 'cause I usually mess a seam or two up. Yours looks great!
I had thought about putting some pigment in the final coat(s) or maybe adding some graphite. I've never used it but somebody earlier suggested duratex. That might look good if you could get a good mechanical bond.

The biggest problem I'm trying to get my head around is putting the final side on. There's no way I can get in and tape all the seams if I put the side on in one big piece. It looks that I could have everything at least seamed on one side of each wall. The interior speaker I could seam from the inside through the access panel and I could reach up the horn mouth to put seams on the outsides of the other interior walls. Maybe I could drill some holes and pour epoxy down it, sorta like dowels.

I may try experimenting with a T39 horn for our bass player instead of the bigger T48 to begin with.

As for your cab sounding smoother and louder, I used to own a fiberglass drum set and that was a characteristic of it's sound also. It may just be that the walls flex less than a wood cabinet.
Rick

 

[zac2944]

They've got XPS at our local Lowes and that's what I'll use. They have it 1" and 1/2".

My A&P friend said it's the fiberglass that's the most important.

I'd say it is more the core thickness than the core material that is important. As long as your core has relatively good shear strength you're fine. Glass matters too, but I chose 7781 for its workability. 8 harness satin weave cloth is really easy to work in and around corners and it drapes well. It doesn't wet out as easy, but wetting out was not my concern.

Just don't forget that the stiffness is a function of the square of the core thickness. All other things being the same, the 1" core will produce a panel that is 4 times stiffer than the 1/2" core. I used 1" with 3 layers of 9oz. 7781 glass per side for my baffle, and 3/4" with 2 layers of the same glass per side for every other panel. This was all based on experimentations and what I thought would be appropriate.

I was gonna try experimenting w/ just spot tacking it w/ a cabosil slurry between the tacks. I may just go with the way you did it.

I think there is merit to building using pre-made panels and joining. You can make your panels very strong and light with minimal effort. I'd recommend getting 2 melamine 4x8 sheets. Use one like a table top. Apply some PVA and or wax, then lay down your sandwich directly on the treated melamine board. Melamine, mold release, epoxy/glass, foam, epoxy/glass, then finish up by laying the other melamine board on top. Of course treat the top board with mold release too. Then add as much evenly distributed weight as you can to the top board. This will push out excess epoxy. You'll result in a very light, flat, and aesthetically neat panel.

If you're going to bond glass to glass check out Plexus. A lot of guys in the boat/plane building use this stuff and swear by it. I've never, but you can find a lot of info about it at places like boatdesign.net/forums, etc.

The biggest problem I'm trying to get my head around is putting the final side on..

Yeah, this took me some time to figure out too. I can only imagine how difficult it would be with a horn design. I did the rear panel last. That's the one with the terminal plate on it. I created the joining fillet for that panel and with the aid of some peelply I then removed the rear panel once the fillet had cured. This allowed my to glass right up to the edge of the rear panel. Once I was finished glassing the inside of the baffle and walls, I dropped the core for the back panel into position and laid the interior glass up with access through the speaker holes in the baffle. Not so easy with a horn. Just don't forget that you can bond your last panel in place with something like Plexus. Full glass the edges and bond glass to glass. I would do some testing first, but I imagine this would giver you a nice finished join that is plenty strong.

As for your cab sounding smoother and louder, I used to own a fiberglass drum set and that was a characteristic of it's sound also. It may just be that the walls flex less than a wood cabinet.
Rick

I'm sure the stiffness helps, but I'd like to think it has more to do with good drivers and proper cab volume and porting.

 

[alexclaber]

Just weighed my barefacedBass Compact 15" cab. 32lbs! I bet fibreglass composite would knock a whole load more weight off but I don't even know where to start with that kind of build process. It seems you're now drawing the short straw if you have to help with the guitar amp, not the bass amp!

Alex