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DIY Lightweight Composite Cab Build

#441
zac2944 said:
I'm pretty impressed with the piezo array to be honest with you. I think it sounds great. Certainly not harsh or shrill as some piezos can be. I've heard similar arrays before on BFM Omni cabs before and they sounded great as well. That said, I'm not the most picky when it comes to high end so I may not be the best judge. To get an output level that I was happy with I wired them in series/parallel. When they were all parallel, the output was a little higher than I like it. The cab is very bright sounding in general. The 2510s have a rising top end and with the piezo array in there you get a lot of detail in the hi-mid to hi range.
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Gotta tell ya, I found I like the piezo's also. I have to say that Bill F. is right on, on the use of them, at least, also for my ears. I like their high crispyness, and they don't over power therest of the spectrum. And not harsh on the ears. I used them in this single ten cab with the BassliteS2010, for a 19 lb single ten cab, That I have for sale on here, and love the piezo's. I will be using then in future now too.
 
#443
zac2944 said:
I'm pretty impressed with the piezo array to be honest with you. I think it sounds great. Certainly not harsh or shrill as some piezos can be. I've heard similar arrays before on BFM Omni cabs before and they sounded great as well. That said, I'm not the most picky when it comes to high end so I may not be the best judge. To get an output level that I was happy with I wired them in series/parallel. When they were all parallel, the output was a little higher than I like it. The cab is very bright sounding in general. The 2510s have a rising top end and with the piezo array in there you get a lot of detail in the hi-mid to hi range.
Click to expand...

What make / model of piezo's did you use?
 
#444
joegeezer said:
Gotta tell ya, I found I like the piezo's also. I have to say that Bill F. is right on, on the use of them, at least, also for my ears. I like their high crispyness, and they don't over power therest of the spectrum. And not harsh on the ears. I used them in this single ten cab with the BassliteS2010, for a 19 lb single ten cab, That I have for sale on here, and love the piezo's. I will be using then in future now too.
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Glad to hear the piezo tweeter works for your cab.

From what I could gather, the whole deal with Bill's piezo tweeter designs is that they perform much better because they are used in a vertical array. Using multiple drivers allows you to get the output you need without driving them too hard. I'm guessing the driving them full out results in the harshness that they are sometimes known for. Also, I don't think they are good for anything below 2kHz.
 
#447
So, as you can see, your 1/4" thick PVC core panel is much less stiff than my 1" XPS panel.
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There is one factor that you have not calculated... H80 Divinycell has tiny holes that the resin impregnates to create a mechanical bond this makes it much stronger and stiffer... polystyrene will not allow for this because it is closed cell.

As far as polyester goes I hate the stuff and love it at the same time... it is a necessary evil when molding... set time is nice also... you do lose some strength but that should not be enough to matter.

H80 Divinycell is 60$ a sheet with out bulk pricing discounts. not too bad...

Get a laminated sample and make a sample of your set up and test... or call diab and talk to them...

How cool would it be to have a carbon fiber speaker face mold!!!
 
#448
rlwilson89415 said:
There is one factor that you have not calculated... H80 Divinycell has tiny holes that the resin impregnates to create a mechanical bond this makes it much stronger and stiffer... polystyrene will not allow for this because it is closed cell.
Click to expand...

The resin doesn't really add any strength OR rigidity to the panel, from my back-of-the-envelope calculations. Imagine a sheet of dried resin, that's paper-thin. Its not strong nor stiff. The resin just prevents the panels from shearing apart. If Zac's cab stays together, the closed-cellness of XPS isn't affecting the panel strength at all.

In fact, all you need for the resin to stick properly is to rough up the surface with sandpaper, which is what Zac did already.
 
#449
ehque said:
The resin doesn't really add any strength OR rigidity to the panel, from my back-of-the-envelope calculations. Imagine a sheet of dried resin, that's paper-thin. Its not strong nor stiff. The resin just prevents the panels from shearing apart. If Zac's cab stays together, the closed-cellness of XPS isn't affecting the panel strength at all.

In fact, all you need for the resin to stick properly is to rough up the surface with sandpaper, which is what Zac did already.
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You're right. The XPS is closed cell, but when you sand it you open up the cells for better adhesion. This characteristic of the laminate sticking to the core is called peel strength.

I still appreciate rlwilson's input though. I'm always learning new things about composites. It is great to get some input from folks that have real world experience.
 
#450
zac2944 said:
I'm going to try to redo the testing this weekend if I get time. Hopefully I can get some more feedback on procedure and obtain beter data. I'd like to try to get a plot for the SWR 15" Son of Bertha I have too.
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Not looking good. I'm all set up to do more testing today, but the background noise outside today is just too much. I've got 10-20mph winds blowing through the maple trees, a nieghbor rocking out with his leaf blower, and BOS Logan decided to route flights over my house today. Every 180 seconds a 747 flys over at about 300ft. Nope, doesn't look good today.

Damn it!
 
#451
zac2944 said:
You're right. The XPS is closed cell, but when you sand it you open up the cells for better adhesion. This characteristic of the laminate sticking to the core is called peel strength. .
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Zac I have a question. Can you please talk me through the role of the silica? My understanding is that strengthens the adhesive properties of the resin. And from memory, you also used that to bond the glass to the foam didn't you? I'm not sure if the people who are worried about peel strength are taking this into account.
 
#453
Petebass said:
Zac I have a question. Can you please talk me through the role of the silica? My understanding is that strengthens the adhesive properties of the resin. And from memory, you also used that to bond the glass to the foam didn't you? I'm not sure if the people who are worried about peel strength are taking this into account.
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I used two fillers with the epoxy. I used Microspheres (micro glass bubbles) to make a bondo-like lightweight filler referred to as "micro", and I also used Silica. The silica is use to make the epoxy less runny. This is useful if you need top layup on a vertical surface or on the underside of something. You don't get drips or runs as easily.

Before I put the glass on the foam core I put down a layer of micro. Since the sanded foam is rough, it sucks up quite a bit of epoxy. By adding microspheres to the epoxy I reduce the weight.

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.

This might be where high end core materials have an advantage. I haven't checked into this though.
 
#455
zac2944 said:
Not looking good. I'm all set up to do more testing today, but the background noise outside today is just too much. I've got 10-20mph winds blowing through the maple trees, a nieghbor rocking out with his leaf blower, and BOS Logan decided to route flights over my house today. Every 180 seconds a 747 flys over at about 300ft. Nope, doesn't look good today.

Damn it!
Click to expand...

FWIW, I was able to get some more data tonight. I'll post it up when I get some time.
 
#456
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.
Click to expand...

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.
 
#458
Did some more testing yesterday. Things in the neighborhood quieted down in the evening so I gave it a go. I used the same procedure as last time, except I pointed the cab up and took measurements from above.

Here's a look at my ghetto testing set up:

testrig.gif


Here are the results I got:

cabtesting9-1.gif


Just like with my last testing, there is no benchmark here. These results can't be compared with any other testing.

I added a SWR Son Of Berth 15" to the mix this time around. The plot shows a lot of midrange and a noticeable hump from the tweeter. the cab is an 8ohm where the others are 4ohm. I expected to see lower output from the SOB, but its output was just as high or higher than the other cabs. Go figure?

The plots of the ZacLite and 1212R data from test 2 do have similar profiles to the results from test 1, so that's a good sign. Both cabs seem to have measured higher SPL values in the mid and upper frequencies this time around.

It is worth noting that the tweeter attenuators on the SOB and 1212R were both set at the level I normally use them at (50%-75%). If I had more time it would have been nice to see a plot for the high and low end of the attenuation.
 
#459
I have been watching this thread for a bit. I am interested, but also a novice. I have 2areas of questions.

1. Would it pe possible to laminate with the epoxy and glass an entire sheet of foam and then cut panels and glass/epoxy them together? Would this be quicker than cutting the foam first? Doing the lamination first makes it more like traditional construction with plywood.

2. Would a http://www.billfitzmaurice.com/ design work with this type of construction? I have not seen his plans other than the pics people have posted, but it could be a cool merging of design and application?!?!?!
 
#460
King David said:
I have been watching this thread for a bit. I am interested, but also a novice. I have 2areas of questions.

1. Would it pe possible to laminate with the epoxy and glass an entire sheet of foam and then cut panels and glass/epoxy them together? Would this be quicker than cutting the foam first? Doing the lamination first makes it more like traditional construction with plywood.

2. Would a http://www.billfitzmaurice.com/ design work with this type of construction? I have not seen his plans other than the pics people have posted, but it could be a cool merging of design and application?!?!?!
Click to expand...

KD,

Great questions.

1. Yes it would be possible, and it may make the process much easier. Here's why I chose not to do it that way.

When you join the panels you'll need to round off the outer edges. You could do this with a sanding block or file of some sort, but it is not easy to sand both fiberglass/epoxy and foam at the same time. The foam is removed much easier than the glass, so you always end up with uneven surfaces. You could minimize this by using smaller radii when rounding. Then when you lay glass over the rounded exterior corners you'll have a lip where the glass ends. This can be minimized and smoothed, but it will take a lot of work to do this. One trick to minimize this effect is to lay plastic wrap (colored saran wrap is best) over the final wet layer of panel joining glass and smooth it out with a squeegee. This will keep any loose ends from creating bumps. It makes filling and sanding much easier. If you don't care about the outer surfaces being very smooth then you could just leave it be and put on your covering material. I was pretty concerned about aesthetics and decided my method would create a cleaner look. On the inside you'll need to put down a bead of filler and create a fillet before you glass those seams. You'll also need to glass over the exposed foam at the baffle hole cutouts.

There could also be strength issues. A lap joint is probably not going to be as strong as one continuous piece of glass. You'll want to overlap with 2-3 pieces of glass on both sides for bonding the panels.

A huge advantage to doing things this way is that you can do all your layup work flat. This is a big time saver and allows you to create a very nice, smooth, and light layup. There are entire sailboat and catamaran hulls made using a similar method.

If you want to hunt around for some more info on similar techniques, check out this forum: http://www.boatdesign.net/forums/ I've found some good info on that site.

2. BF's designs look like they may be a challenge, but nothing is impossible. I've seen the cabs but never purchased plans, so i can't say for sure how tough it would be. I got my idea for the tweeter array from BF cabs.
 

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