DIY Lightweight Composite Cab Build

[alexclaber]

Good work, I like the testing! Your ZacLite cab performs very well and the Schroeder makes a very interesting plot which shows why they're perceived as so loud and fat in a unique way.

Alex

 

[zac2944]

Good work, I like the testing! Your ZacLite cab performs very well and the Schroeder makes a very interesting plot which shows why they're perceived as so loud and fat in a unique way.

Alex

Thanks Alex. I've been getting very good results with the ZacLite at gigs and what I'm hearing only seems to confirm what I see in the test results. I used the ZL210 at a 200-300 person club gig last Friday night and at an outdoor private gig on Saturday night. No problem with volume or low end. Cuts through just fine and didn't get any boom. The tweeter array and hi mids from the 2510s are great for slap and really provide definition without being glassy. I'll be using it at [Invalid or Expired Link Removed] evening too. Load in is now a gig bag, and a 23lb 210. That's it! Now, if I only had one of those MarkBass F1 heads....


The 1212R is no joke. There's the "low-mid hump" that everyone uses to describe its tone. You can't deny it, its all there in the plot. About a 10dB hump centered at about 150Hz. Any idea of how you would calculate a SPL on the 1212R plot to determine what the F3 and F10 would be? If you look at full spectrum the SPL wouldn't be that high, but if you look at the hump it is pretty high. I know it doesn't seem to have more output than the other cabs on that plot, but you can really crank that cab and it holds tight. When looking at max SPL, it truly smokes the other two cabs (ZL210 and SOB). I'm guessing the drivers can take the thermal stress and the x-max is limited by the very small Vb. I believe Bill F. once did a nice job of explaining how/why the slanted baffle low Vb set up works. I believe the slanted driver's upper mids are attenuated, resulting in all the low mid output and not much deep bass (below 60-70Hz).

 

[zac2944]

Oh yeah... Any data on your BareFacedBass cabs? I'd love to see a FR plot. They look like killers! Very light, great price, and on paper look like they will crush. What would it cost to ship one to the US? I think my next composite cab will utilize a 3015LF. I've never heard one though. Are they really as good as they look?

 

[alexclaber]

Thanks Alex. I've been getting very good results with the ZacLite at gigs and what I'm hearing only seems to confirm what I see in the test results.

Excellent. They're great drivers the 2510-IIs, especially if you're not looking for massive bottom.

The 1212R is no joke. There's the "low-mid hump" that everyone uses to describe its tone. You can't deny it, its all there in the plot. About a 10dB hump centered at about 150Hz. Any idea of how you would calculate a SPL on the 1212R plot to determine what the F3 and F10 would be? If you look at full spectrum the SPL wouldn't be that high, but if you look at the hump it is pretty high. I know it doesn't seem to have more output than the other cabs on that plot, but you can really crank that cab and it holds tight. When looking at max SPL, it truly smokes the other two cabs (ZL210 and SOB). I'm guessing the drivers can take the thermal stress and the x-max is limited by the very small Vb. I believe Bill F. once did a nice job of explaining how/why the slanted baffle low Vb set up works. I believe the slanted driver's upper mids are attenuated, resulting in all the low mid output and not much deep bass (below 60-70Hz).

I have no idea how you'd specify sensitivity for a cab with such weird response but I think you're spot on about why the max SPL is so high.

Oh yeah... Any data on your BareFacedBass cabs? I'd love to see a FR plot. They look like killers! Very light, great price, and on paper look like they will crush. What would it cost to ship one to the US? I think my next composite cab will utilize a 3015LF. I've never heard one though. Are they really as good as they look?

I'll try to get some good measured plots at some point. I've attached my predicted response based on WinISD Pro simulations for the lows and manufacturer's response for the rest, all run through crossover modelling software. Once you move off-axis the spike in the highs from the 605Nd totally vanishes so the real-world response is flatter than this plot suggests.

Alex

 

[ehque]

Here's the thing about peel strength. It is usually not a function of your epoxy type. When you peel the glass off of the foam, it always takes a layer of foam with it. That tells me that the adhesion strength or "peel strength" is greater than the tensile strength of the foam core. In a sense, you can never get a peel strength greater than the tensile strength of your core.

That sounds about right. There's probably no way to strengthen the joint beyond the weaker of the 2 surfaces. You see the same thing crop up in headstock repairs - the glue is almost always stronger than the wood, so a new crack will actually break along another line instead of the expected old one.

Good question. Is there a market for boutique cabs? If a Sadowsky can cost three times what a Fender costs, why can't a boutique cab cost three times what an average cab costs?

Well there probably is.

Now you are starting to get the strenght differnace divinicell nidacore and such bond all the way through between cores... there is not peel but if a failure happens the core is destroyed not just top layer with mechinacal bond.

Silica is a thickner but is very strong however to much will crack easily... that is somthing this project must also take in concideratin much like a boat hull the strucure will be taking on great forces. the laminate must remain somewhat flexable to keep from cracking.

I am quite sure even the divinicell is also not as strong as resin. If it IS stronger than resin, it's probably a lot heavier! heh. No 2 ways about it unless you use inhomogenous materials like carbon fiber or wood, where most of the strength comes in one direction.

Zac, have you done any stress tests on the panels that you made? Specifically, how much force can you put on the panels before delamination? What is the maximum deflection? If i'm not wrong, resin isn't elastic, so damage can be done with small angles of flex over a long time, like what soundwaves will do. Have you calculated some ballpark values for that?

It would be interesting if your cab "opened up" like a acoustic guitar does as the joints are slowly teased by the vibrations of the soundboard. Of course i dont mean the thing falling apart, but the sound is supposed to change.

 

[alexclaber]

There it is!

Alex

 

[zac2944]

Zac, have you done any stress tests on the panels that you made? Specifically, how much force can you put on the panels before delamination? What is the maximum deflection? If i'm not wrong, resin isn't elastic, so damage can be done with small angles of flex over a long time, like what soundwaves will do. Have you calculated some ballpark values for that?

It would be interesting if your cab "opened up" like a acoustic guitar does as the joints are slowly teased by the vibrations of the soundboard. Of course i dont mean the thing falling apart, but the sound is supposed to change.

I did some qualitative testing to make sure the composite panels were stiff enough by comparing them to plywood samples. Sorry, but no data to present. A few pages back in my calculation comparing core materials you can see data that is a good representation of what I'm using. Look at the flexural stiffness results for 1" XPS core. The numbers are theoretical, but should be pretty close.

The fiberglass/epoxy matrix is elastic to a degree. You can bend it to a certain point without deformation. Think of the pounding a boat hull take on over the years. Sound pressure in my cab is nothing compared to choppy seas! I would be very surprised if any thing moved or got weaker over time.

One thing to worry about with epoxy/fiberglass/foam composite is too much heat. This can weaken the structure and cause failure. This is why you often see fiberglass painted white; so it doesn't get too hot. We're talking pretty hot though, maybe 200F before you'd notice anything. It could get this hot inside a car if your cab was painted black and had the sun beating down on it all day. Even if it did get this hot, I doubt there would be any deformation since there is not normally any load on the cab. Deformation can happen on airplane wings when they get too hot because they are under load, but a cab is a bit different. I'll be careful next time I gig in Hell!

 

[zac2944]

Thanks Alex. I've been getting very good results with the ZacLite at gigs and what I'm hearing only seems to confirm what I see in the test results. I used the ZL210 at a 200-300 person club gig last Friday night and at an outdoor private gig on Saturday night. No problem with volume or low end. Cuts through just fine and didn't get any boom. The tweeter array and hi mids from the 2510s are great for slap and really provide definition without being glassy. I'll be using it at [Invalid or Expired Link Removed] evening too. Load in is now a gig bag, and a 23lb 210. That's it! Now, if I only had one of those MarkBass F1 heads....

I found the limits of the ZL210 this weekend. We were playing our first gig at the new Hard Rock Cafe in Boston. The venue is not that big (300-400ppl), but on stage I had to compete with with 6 EAW wedge monitors. The sound engineer was really working them too. Once everyone got their levels up, the ZL210 was lost. I could see the drivers pounding, but couldn't hear much coming from them. Usually I don't put any bass in the monitors, but this night I had to. Luckily the EAWs sounded great. The drummer and I were sharing a wedge/submix so I just had the engineer add some bass to our wedge and everything was fine.

As nice as this cab is, it is still only a 210. Every cab has its limits. I still remember finding my 1212R's limits playing for 1000+ in a large Boston hotel convention hall. Normally it had crushing sound, but on that stage it was lost. It was the kind of gig you'd bring a stack to.

I'm glad I was able to find the ZL210's limits on a stage with a good monitor setup. I know it wouldn't take much for the GK1001 I use to kill the 2510s. We'll be back there again in a month or so, and I'll give the 1212R a shot. I think it will stand a better chance.

 

[Stumbo]

Once everyone got their levels up, the ZL210 was lost. I could see the drivers pounding, but couldn't hear much coming from them.

How was the ZL210 placed? Would it have helped to have it angled up at you?

We'll be back there again in a month or so, and I'll give the 1212R a shot. I think it will stand a better chance.

How about using both cabs?

 

[zac2944]

How was the ZL210 placed? Would it have helped to have it angled up at you?

I had it pointing at me on the floor, then I tried it on a chair. It was just at it's limit on that stage. I could hear the mid through highs just fine, but the low end got swallowed up.

How about using both cabs?

Easy transport is my thing, so carting two cabs goes against my policy. I also couldn't run two 4ohm cabs with my GK1001. [/QUOTE]

 

[Petebass]

I found the limits of the ZL210 this weekend. We were playing our first gig at the new Hard Rock Cafe in Boston. The venue is not that big (300-400ppl), but on stage I had to compete with with 6 EAW wedge monitors. The sound engineer was really working them too. Once everyone got their levels up, the ZL210 was lost. I could see the drivers pounding, but couldn't hear much coming from them. Usually I don't put any bass in the monitors, but this night I had to. Luckily the EAWs sounded great. The drummer and I were sharing a wedge/submix so I just had the engineer add some bass to our wedge and everything was fine.
.

Thank you, Thank you, Thank you. I've trying to quell the TB myth for years, that the bigger the PA the smaller the rig you need. Not true! I've always found the opposite and now you know why.

As nice as this cab is, it is still only a 210. Every cab has its limits.

Exactly. I've driven some pretty highly regarded 2x10's to their limits, and quite easily too. Can you see now why people are calling for a 410 or 610 version of the Zaclite?

 

[zac2944]

Thank you, Thank you, Thank you. I've trying to quell the TB myth for years, that the bigger the PA the smaller the rig you need. Not true! I've always found the opposite and now you know why.

We're on the same page with that one. If you're on a loud stage and want to hear your rig, it has to be loud too. This just makes sense. If you're going through the monitors then I guess your rig doesn't matter all that much.

Exactly. I've driven some pretty highly regarded 2x10's to their limits, and quite easily too. Can you see now why people are calling for a 410 or 610 version of the Zaclite?

A 410 or 610 would be cool but as I read someone else's post here, if you can fit a 3015LF in your cab it should have a 3015LF. That driver looks like it kicks major a$$, and I can't see a reason to build a 410 or 610, when I can get better results with the 3015LF. Although I would love to do another cab, I can't afford it at the moment. Also, it is rumored that the 3012LF is supposed to be released at this winter's NAMM. I might have to hold out for that one. I'd love to do a composite two 12" like the Schroeder/Tech Soundsystems. It would be a very tough build, but I'd love the challenge.

 

[redstaraudio]

Very cool. We explored some similar paths very early on in our product development. Lots of different options to explore.

Wood is such a fantastic material, especially plywood, that it's very hard to come up with a design/materials/construction process that beats it in enough areas to really warrant a commercially viable product. But it can be done. Just depends whether you want to do one, two, five, fifty or five hundred. Lots of things change when you start thinking fifty or five hundred...

We can definitely appreciate the work and engineering that Zach put into that cab.

Redstar Audio

 

[zac2944]

Wood is such a fantastic material, especially plywood, that it's very hard to come up with a design/materials/construction process that beats it in enough areas to really warrant a commercially viable product.

You hit the nail right on the head. If you are going to sell cabs, it is all about cost. You can use stiffer and lighter materials, but figuring out a way to make it commercially viable is the key.

This sort of technology (sandwich composite) may not be well suited for mass manufacturing, but I think it is a great fit for the DIY and high end custom builders. The materials aren't prohibitively expensive and the techniques are not too difficult to master, but it is the time and labor involved that get you. The DIYer has time and the high end custom builder can charge for the time. This is not too far off from the Bill Fitzmaurice designs. You don't see these types of cabs mass manufactured because of the extra effort they require in the build and design stage, but they are great for the DIY builder.

Maybe I should put together sets of plans and instructional videos for building lightweight sandwich composite cabs? Anyone interested?

 

[fast slapper]

Maybe I should put together sets of plans and instructional videos for building lightweight sandwich composite cabs? Anyone interested?

YES!

 

[spode master]

Hey Zack Just wondering (without getting into all of the physics equations) Is there a rule of simple thumb for scaling the size of the box with relationship to how thick the core material needs to be??

Another question.

How damped are those ports you molded, they look really thin. Do they ring at all?? Or are they prety inert?

 

[zac2944]

Hey Zack Just wondering (without getting into all of the physics equations) Is there a rule of simple thumb for scaling the size of the box with relationship to how thick the core material needs to be??

Determining how stiff the cab panels need to be depends quite a bit on the design of the cab itself. If you've got a large wide baffle it will flex more than a shorter narrower one, assuming all material parameters are the same. Then you need to determine just how stiff is stiff enough? I based my design on being as stiff as plywood samples I tested. Could you get away with less stiff panels? Probably. I've never really done any testing to try and document how panel stiffness effects output. So the short answer is no. I don't have any quick rule of thumb for determining how thick the core material needs to be, or how stiff a panel needs to be, when scaling up to a larger cab.

One rule of thumb with sandwich composite panel construction is that the stiffness of the panel is a function of the square of the core thickness. In short, if you double the thickness of your core, your panel is four times stiffer.

Here's a graph displaying core thickness vs. panel stiffness. It is purely theoretical, but based on proven engineering math. I don't have the equipment to generate accurate values for panel stiffness, but I can confirm that stiffness does increase with the square of the core thickness. Simple qualitative bending tests easily confirm this.

Does that help illustrate what I'm talking about?

Don't forget, the beauty here is that you add virtually no weight when you thicken the core. The XPS foam has a density of approximately 2lbs/ft3​. I used about 1ft3​ for my design. I could have made it about twice as stiff by adding an other 0.75lbs of foam to the core. That just makes me giggle like a little school girl.

How damped are those ports you molded, they look really thin. Do they ring at all?? Or are they prety inert?

I was worried about this too. They are pretty thin, but relatively stiff. I haven't had any issues with them vibrating or making noise, so I'd say they are "inert".

I did have a buzz going on in the cab for a while, but I determined it was an air leak in one of the piezo drivers. They are not air tight and require a sealant around the piezo element housing and screws. I had to remove the array and reseal the leaky driver to make things airtight. It was a pretty easy fix.

 

[Blight]

How did I not see this thread before!?

fcdjkshfvlSAFOP dsf;l';'S

Zac, I don't know you, but...I...I think I...love..you....

*attempts to collect dignity from floor*

Yeah, I second some some in depth instruction (though this whole dang thread has been extremely educational).

 

[Curtybob]

You may have covered this before and I just missed it, but what about a hybrid using something like 1/4" plywood in place of the outside layer of glass? Like, build the shell with light plywood, then a layer of epoxy, a layer of foam, and then layup the inside of the cab.

It would help people like me that aren't scared of making wood look pretty, and shave some weight off a larger cab in the process.

 

[kraigo]

I think he did cover it before: The stiffness goes up with the square of the thickness of the panel. 1/4" of plywood isn't very stiff and since it's thin it wouldn't get that much stiffening from the glass either.

Someone correct me if I'm wrong, but I think this was ruled out earlier in this thread.

KO