T shirt material for fiberglassing?

Basically trying to save myself a drive to a JoAnne 3 days after they re-introduced a mask mandate.

I'm making pillars to hold a 2" Dynaudio/Volvo dome, a Bohlender Graebner Neo3 PDR planar, and a Focal TN52 tweeter per side.

I have the structural work done using ABS and a plastic welder. Needs a few alterations and more shaping but basically it's far enough to see the next steps:
https://uploads.tapatalk-cdn.com/202...7a26e59475.jpg
From hereI think I can most quickly and easily tackle the cosmetic layer by starting with a fabric stretch as the base for the bodywork, vs more ABS patching and forming.

Normally I'd use spandex and brush resin in for light stuff like this but I don't think I have any -
But I do have a bunch of old T shirts I don't mind sacrificing. I've just never used jersey for this purpose.

I imagine it'll be a little less stretchy, and soak up a little more resin, but otherwise work OK...

Anyone able to confirm or caution against?

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I don't see where it would be a problem, I've used old socks and grill cloth for backer material before. It just gives you the basic shape, then reinforce it afterward.

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Originally Posted by BigAl205

I don't see where it would be a problem, I've used old socks and grill cloth for backer material before. It just gives you the basic shape, then reinforce it afterward.

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Yep, exactly that.

I am not a fiberglass hero but I've certainly done this before!

I’ve used old T-shirts in multiple pillar builds before. No issues so far.

I've always had it in my head to keep pillars as light as possible, because of their role covering the airbags. Putting mids up here is relatively new to me, personally.

The more I think of it here, though - it might be better than a spandex - a little thicker should make it a little stiffer.

I say that because notice a little flexing happens each time I need to remove or install them, mainly because of the two locking tabs at the base.

So I do want this area rigid so my body work and finish doesn't crack, even if it makes them a little more of a pain to install.

The only thing that matters in a material for wrapping to fiberglass is the materials stretchiness and its absorption. You want something that wet outs extremely easily and conforms to many different angles.

Somehow fleece got introduced as a great way to make fiberglass stuff. Fleece is fucking horrid. It takes soooo much resin to get fully soaked. It sags from the weight of not pulled super tight. All around it's just terrible.

Aim for something stretchy and thin. T-shirt material is perfect.

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Originally Posted by geolemon

I've always had it in my head to keep pillars as light as possible, because of their role covering the airbags. Putting mids up here is relatively new to me, personally.

The more I think of it here, though - it might be better than a spandex - a little thicker should make it a little stiffer.

I say that because notice a little flexing happens each time I need to remove or install them, mainly because of the two locking tabs at the base.

So I do want this area rigid so my body work and finish doesn't crack, even if it makes them a little more of a pain to install.

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keeping pillars light is not good! Focus all the weight where the drivers are and it will sound better, and if youve ever seen an airbag go off you really shouldn’t worry about it staying put in any way, even if deadened, it’s the clips that need to remain factory, don’t go adding screws unless factory, but reinforcing the pillars won’t do anything to stop an airbag deployment

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Originally Posted by dumdum

keeping pillars light is not good! Focus all the weight where the drivers are and it will sound better, and if youve ever seen an airbag go off you really shouldn’t worry about it staying put in any way, even if deadened, it’s the clips that need to remain factory, don’t go adding screws unless factory, but reinforcing the pillars won’t do anything to stop an airbag deployment

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That's true - I'm lucky with my selection, this is an odd collection of drivers.

Down low, I already have wooden rings with braces of 1/8" ABS welded to hold the Volvo/Dynaudio domes. Those themselves are already in their own sealed, steel cups, which means I don't need to make these A-pillars acoustic environments, and that's nice. That portion is definitely rigid already. I'm lucky with these, that way.
Attachment 16566

The more interesting part is up higher on the pillars - those really are pair of drivers teaming up to be "tweeters", and that's it:
I have two Bohlender Graebner planar speakers that really essentially have no moving parts - less motion than a dome tweeter. I do want to see how low I can get them to play, but still we're only talking 2000hz and up, probably. Maybe I'll get lucky, 1500hz?

I mocked them up in the basement rig (photo shows it in the process of teardown, but that's the main structure - my fiancee can't wait to see that gone) with the windshield, dashboard, and you can see all the passive Xovers - the tweeter output of the JL XR comp set Xover feeds into the white 10khz Xover on the front of the 'dash'. So in the test rig, the BG Neo3 panels were playing from probably 2500hz (I'm just pulling that from memory, which shouldn't be trusted since I bought those JL XR's in the late 90's) up to 10khz, then my Focal TN52's playing the role of supertweeters, from 10khz up. I just loved the BG's but they only go up to about 15khz. This also avoids beaming, and I think 10Khz is high enough to not be an issue - but I have room to push that Xover point up as well.

I definitely still do need a good baffle surrounding those though. I wouldn't leave it with just a layer of impregnated T-shirt, I do agree with you.

But fortunately, really it minimizes my needs, structurally and acoustically even.
Attachment 16564

There's still the chance that I have to do something a little more than an open-back pillar panel with some stuffing and CCF behind it, I'll probably start with a patch of MLV sealing it in, but I don't think I need to do much - I even tried to make a "worst case scenario" for these BG Neo3's when playing with them -
Originally, they were in an evaluation box with an angled back and stuffing, and they sounded great. Then I moved them into the shallow, flat enclosure below... it's a tiny chamber with a scrap of whiteboard as the back panel, exactly parallel to the driver, even. Still sounded the same, I ran some sweeps and didn't notice much variance in the curves either. Seem very forgiving.
Attachment 16565

So I think some CCF with some MLV making it so it isn't a pure open baffle will be better than the half-assed kludge that it sounds like. :lol:
Easier than needing to make some sort of a cabinet out of the pillars, since the domes and the TN52's have their own enclosures. :cool:

I can't wait to get them installed in the car, on a DSP, and see where my Xover points will ultimately end up.

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Originally Posted by dumdum

keeping pillars light is not good! Focus all the weight where the drivers are and it will sound better, and if youve ever seen an airbag go off you really shouldn’t worry about it staying put in any way, even if deadened, it’s the clips that need to remain factory, don’t go adding screws unless factory, but reinforcing the pillars won’t do anything to stop an airbag deployment

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You also got me thinking today during a slow day of work, having looked at Parts Express junk mail today -
I only own the Bohlender Graebner Neo3's, but GRS appears to have borrowed/stolen/rented the architecture identically. I own both the 8" Bohlender Graebner and GRS flat panels, and did listening, and to my ear they sounded identical. I even measured the two, and they seemed identical as well. So I presume the GRS 3.5" and the BG Neo3's are as close to identical as matters.

I say that because I'm looking at the specs and plots for the GRS ones - just had them up as I was thinking and eating my lunch. Both BG and GRS sell the 3.5" version open (as I own) and with a back cup (which is tiny), so I'm just checking that out-

Predictably, the response with the cup just impacts the low end-
Attachment 16599
vs with the cup:
Attachment 16600
For reference, here's how tiny the cup is (highlighted yellow) - Oh, and check out that impedance plot!:
Attachment 16598
So I'm theoretically liking the idea of a non-rigid wrap around the backside of these, but the structure supporting the driver will be rigid.

That cabin mockup rig is hard core :worship:

Things will sound very different in a vehicle, but still, kudos!

Interested to see where this goes.

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Originally Posted by DubScientist

That cabin mockup rig is hard core :worship:

Things will sound very different in a vehicle, but still, kudos!

Interested to see where this goes.

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As always, for sure. Cars are each also different. But-
1) this was only to experiment to compare the feasibility of experiments and how that shifts image placement. A to B to C comparisons of fundamentals - plus-
2) when it was all really set up, there were other analogs, floor carpet, center console, door and roof panels, played with some panels behind as well.

All these experiments were above dash.
The DSP will handle tuning out the rest.

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Did you solve your fabric wrapping dilemma? Aside from the sagging that can happen another problem is unnatural or poor contoured shapes. In some cases a 2 part foam can yield fantastic results, then lay up your chop mat over the foam after shaping.

I could have foam molded it but I'd have had adhesion concerns. Also - I've only bought that in 5 gallon quantity, i don't think they sell it in small single-project quantity.

I did it with cloth, I thought the epoxy resin I used would have bonded best - but this plastic is really tough to bond to, even roughed up with 40 grit. Even this way, I had some adhesion that I had to follow up in.

But the process wasn't much different than your foam thought-

I did the cloth stretch, and ended up with a bit of a cross-wrap around the front point tray caused the usual wrinkles and deviations from a pure stretch, but that was OK because that was just the basis for the shape.

The next step after the epoxy cured was to rough it up again, then use some tiger hair to build the shape out a little more - sculpting it like you'd do with foam. Then more detail with body filler - I bought some "high adhesion" filler because Bondo over epoxy and even over tiger hair can be an issue - so I also tried to do all my sculpting with the lower layers so the body filler layer is just for smoothing...

...but like every time you create a shape from scratch and have ANY sculpting, once you get your first coat of filler primer down, you see you are in for an endless round of perfecting the shape! The second pic has lighting to show the flaws.

With Xmas and my dad-less nephew buying his first house, I'm not too much further along, in fact I'm 3 months behind schedule -
As usual for projects for myself instead of a customer! [emoji38]https://uploads.tapatalk-cdn.com/202...98c9e81915.jpghttps://uploads.tapatalk-cdn.com/202...66fdf07c03.jpg

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I hate that lol. spend hours getting the shape just right. put the primer down and see all kinds of lines you didn't see before. I am glad this doesn't only happen to me hahaha