Building a new OB

Bob in St. Louis · « **Reply #60 on:** 15 Feb 2007, 03:32 pm »

Here's the idea I can't get out of my mind:

A chicken wire frame or skeleton wrapped on both sides with resin coated fiberglass strips.
The drivers would be mounted to 3/4" plywood "rings" that would be predrilled to hold the drivers.
These rings would be incorporated into the fiberglass to provide a nice flat mounting surface.

This way, you could have smooth flowing radii for that "organic look", the 'wrap-arounds' would be a smoothed radius to eliminate diffraction, and your imagination could run free with the design.
I would THINK it'd be a relatively resonance free structure.

Now, I know sanding fiberglass is GREAT for your lungs,

but does anybody know if the resins/epoxy are safe to use in a NON-ventilated basement workshop.
It's in the single digits/teens here, and I don't want to go outside with my project (not that the resin would even "set-up" with those temperatures.)

Any ideas/criticisms regarding a fiberglass baffle?

Bob

hurdy_gurdyman · « **Reply #61 on:** 15 Feb 2007, 03:56 pm »

Bob,

I think your idea is a good idea (finally!

), but I'd wait until spring and take it outside. Epoxy fumes are both toxic and extremely flammable.

Dave

JohninCR · « **Reply #62 on:** 15 Feb 2007, 06:10 pm »

Bob,

I think the wire frame may prove difficult to build up from for a smooth surface at the end. You live where materials variety isn't an issue, so I'd suggest starting with the wood rings as you planned. Then get a sheet of rigid foam or maybe even rigid fiberglass insulation. Add layers of that to get to the thickness you desire and trim it to the shape you want with a serated knife or other shaping tool. This would also give you the ability to listen to them at an in progress phase, before the more involved and time consuming finish work with resins.

BTW, I wouldn't work with any kind of resins or finishing products without a well ventilated work area. Maybe a papermache type process with something stronger like cardboard or posterboard and waterbased finishing materials may be ideal for the cold weather work. Then the kids or wife can help too, making it fun for them too.

If it's really cold and going to stay thay way, do a pair out of ice, for temporary outdoor listening.

Bob in St. Louis · « **Reply #63 on:** 15 Feb 2007, 06:37 pm »

Quote from: JohninCR on 15 Feb 2007, 06:10 pm

If it's really cold and going to stay thay way, do a pair out of ice, for temporary outdoor listening.

Bite me!

You can make yours out of sand castles dude! aa

Just kidding John.

It was in the single digits (F) this morning

This weather sucks.

A forum member emailed me with a link to a resin manufacturer. The usual precautions for a well ventilated area are the only problems listed in the MSDS that concern me.
http://resinresearch.net/index.html

A paper mache "1st" attempt might not be a bad idea until the weather warms up. I could listen to the paper mache baffle until spring time, then coat it in resin. i have my doubts that paper mache would last very long with the vibrations.

I'd like to start this project very soon, but I need to develop a proper magnet mount for a pair of Hawthorne Audio fifteen inchers before I get radical on a baffle.
In the end, I believe I'll end up with a three piece speaker.
One 'piece' holding the Augie close to the floor.
Another 'piece' straddling the Augie holding the Coaxial.
And the final piece being the baffle itself.
This being a SEVERE P.I.T.A. to make simple adjustments (like toe) might just cause me to make a base that everything sits on. But of course vibration isolation is in order if I do that.

Bob

mcgsxr · « **Reply #64 on:** 15 Feb 2007, 06:59 pm »

I have been battling with that PITA 3 piece structure in my head too. Love what JohninCR did with his version, but I lack the skills, tools, and time to generate that level of finish.

I have been wondering though if I could isolate the driver from the baffle, with rubber o-rings or something?

Any truth to the idea that using 3 (rather than eight) bolts or screws would have less vibration connect to the baffle?

Just thinking out loud here, and I KNOW that these resin ideas are beyond me!

Bob in St. Louis · « **Reply #65 on:** 15 Feb 2007, 07:22 pm »

Quote from: mcgsxr on 15 Feb 2007, 06:59 pm

I have been battling with that PITA 3 piece structure in my head too. Love what JohninCR did with his version, but I lack the skills, tools, and time to generate that level of finish.

Yea, John's mount kicks but!! Very sexy lookin' hunk o' wood he made. Building a structure big enough to hold a 15" driver AND having to hover it above another 15 makes me shy away from his design with that forward lean to the "post". Holding a heavy driver at that angle would need some big feet that extended forward quite a bit. John was holding an 8" B200 if I remember correctly. I'm preferring to straddle the lower driver. Straddling it would keep the overall center of gravity in a straight vertical line. This would also keep the overall size from front to rear down to a minimum also.

Quote

Any truth to the idea that using 3 (rather than bolts or screws would have less vibration connect to the baffle?

Can you rephrase that please? I'm not sure I follow....Actually, now that I'm reading the 'quote', it seems the website has turned your "8" into a smiley... weird.
No, I don't think anything short of the maximum would be good. I've had problems before even with using eight quarter inch bolts, nuts, and washers, crushing the particle board on a test baffle. Making strange enough noises that I contacted the driver manufacturer about a replacement driver. Duh, the wood was crushing, causing the washers to rattle.

Bob

mcgsxr · « **Reply #66 on:** 15 Feb 2007, 07:48 pm »

I fixed that by changing it to spelling the word eight.

A good friend of mine believes that by using less bolts, with rubber washers, the vibration effects would be less.

I don't know.

JohninCR · « **Reply #67 on:** 15 Feb 2007, 08:21 pm »

Yes, 3 piece construction is a pain to adjust placement. My mistake the first go round was to recess and front mount the B200, and rear mount the woofer. You want to be able to just take the baffle off easily and then move the other 2 easier. Bob, your coax 15 is deeper than the B200. Note that the real weight of my B200's are over the T shaped base, so the weight is well distributed and stable. Just extend the center part of the T forward close to your baffle plane.

Here's a couple of pics of what we're talking about. Note the base of the support structure is 3 pieces, 2 for the woofer (like pontoons) and the T shape for the upper main driver.

Bob in St. Louis · « **Reply #68 on:** 15 Feb 2007, 10:13 pm »

John, that rig is purely inspirational

But I have some questions:

How is the baffle supported?
How is the Augie supported? I don't see any "mechanism".
Do the bases buzz because of proximity with each other?
And most of all, how does it sound?

Bob

JohninCR · « **Reply #69 on:** 15 Feb 2007, 10:49 pm »

Thanks Bob,

The B200 is flush mounted in front of the baffle, with foam and rubber washers decoupling the frame and bolts from the baffle. The baffle is actually held upright by the driver and is quite dead.

I drilled holes in my Augies (a simple process as it turns out) and bolts run through those vertical supports connect to the thick plate on the driver.

Full reports on sound will come once I have some more things built and everything get measured.

Bob in St. Louis · « **Reply #70 on:** 16 Feb 2007, 03:56 pm »

Good deal John, thanks for the explanation.

Does anybody know if fiberglass can be wet sanded (to keep the dust from getting out of hand)?

Bob

p.s. I'm still too big of a puss to drill holes in my driver.

JohninCR · « **Reply #71 on:** 16 Feb 2007, 06:22 pm »

Quote from: Bob Jackson on 16 Feb 2007, 03:56 pm

p.s. I'm still too big of a puss to drill holes in my driver.

The Augies are cast aluminum, which is softer than I thought and non-magnetic. I just put a piece of masking tape over the vent, and fuzzy cloth between the basket legs and cone to catch any shaving. Just take care not to run the bit through the cone (5-6 turns of tape on the drill bit 1/2" from the tip as a security stop might not be a bad idea). Then just use rubber washers so you don't put too much pressure on the cast aluminum, and you're in business (treat it more like bolts on an oil pan than lug nuts on a tire). Piece of cake for a clean install, so don't be a puss.

Bob in St. Louis · « **Reply #72 on:** 16 Feb 2007, 10:42 pm »

I suppose I deserve that after the "Bite Me" comment.

Understood John. But it's a bit like the first time I install a rear spoiler on a Honda Accord years and years ago. I stood over the trunk with my drill in hand just staring at that pretty paint job I was about to drill into.

Where did everybody go John? Let's ALL talk about some OB's aa

Bob

JohninCR · « **Reply #73 on:** 2 Mar 2007, 04:45 pm »

Just a quick update regarding styrofoam as a construction material. Even the fairly coarse beaded stuff sands surprisingly smooth. Just find the right resins that won't eat it, and baffles that beat the Jamo's in function and form should be easy.

Bob,
It's definitely the way to go for what you have in mind to spruce up your stop sign rig. Just pick up a sheet of 4" thick and go to town. You can even use tape to hold them on to test at intermediate stages with raw sanded styrofoam. Then even with just a very thin layer of epoxy on both sides, it becomes a very rigid material due to what I believe is called the "skin effect" of multi-layer constructions.

Bob in St. Louis · « **Reply #74 on:** 2 Mar 2007, 05:27 pm »

John, my weekend will consist of Sunday and Monday. I'm VERY seriously considering starting the "B.O.B.'s" (Bobs Open Baffles) wire mess/fiberglass structure. Before I start that, I'll need to frame mount the Augie, and yes...I'll be drilling holes in the frame

. As both drivers will be "attached" to the same structure, I need to finalize the magnet mounting for both drivers so I can see what kind of footprint size I'll have.

Spring time is coming, good time to make a dusty stinky mess in the garage.

I'm not sure I like the idea of styrofoam inside fiberglass though John.
"Squeeking" is the word that comes to mind.

Bob

JohninCR · « **Reply #75 on:** 2 Mar 2007, 06:55 pm »

Bob,

I'm just trying to make your life easier. Obviously foam doesn't have the strength for any connection, so it needs to be completely enclosed by a resin. That's necessary anyway to paint it. Once covered there won't be any noise unless there's a void with loose material.

As a little encouragment to get us both rolling, drop me a note when you start. Then I'll start working on a pair of rings that I want try for my SI's AND something new for a pair of B200s. I'll post pics when I have something listenable. Keep in mind that I'll be spending some time working on those days as a further handicap.

Sometimes I post stuff in attempt to solicit input from others with more experience, but much of the time I post in order to show how easy this stuff is. I'm convinced this is the easiest method yet. Just call me Mr. Easy. You'll get to buy the first round of drinks for this one.

Bob in St. Louis · « **Reply #76 on:** 4 Mar 2007, 04:15 am »

Quote from: JohninCR on 2 Mar 2007, 06:55 pm

drop me a note when you start.

Approximately seven hours from now the sawdust will fly. aa

Quote

You'll get to buy the first round of drinks for this one.

What time of day do you start?

Bob

JohninCR · « **Reply #77 on:** 4 Mar 2007, 04:34 am »

Quote from: Bob in St. Louis on 4 Mar 2007, 04:15 am

Quote from: JohninCR on 2 Mar 2007, 06:55 pm
drop me a note when you start.
Approximately seven hours from now the sawdust will fly. aa

I'm not getting up that early.

Quote

Quote
You'll get to buy the first round of drinks for this one.
What time of day do you start?
Bob

Since there's no power tools involved, I guess I'll have to take an alcohol handicap too and have Cornflakes in a Can for breakfast. That means no talking to any customers tomorrow and restrict my work to in front of the computer and clearing my desk. I better jot down some plans tonight. I hope I don't need any supplies.

Bob in St. Louis · « **Reply #78 on:** 4 Mar 2007, 12:37 pm »

I went to Home Depot on the way home from work last night. Picked up a few things I knew I needed: One piece 3/4" plywood, fiberglass resin, fiberglass cloth, "dip tray" ect... In my hast (lack of organization

) I got home and realised I had forgetton the wire mesh!

Home Depot is 18 miles from me. Just far enough to be a pain in the ass when I have to get supplies. Especially the famous "second trip to the hardware store" we've all made for things you forgot........

The selection of fiberglass supplies was very thin. They sell the resin in quart or gallon sizes. They sell fiberglass cloth and fiberglass mat. Not sure the difference between the two, so I bought one of each. They only come in nine square foot packages for $7 each. Seems high to me, but I'm not the fiberglass professional, so what do I know? That's the end of the selection. I don't know what else I was expecting, but it seems like there should be more???.

The seven hour thing is out the window. Just by a little bit.

Quickly sketched a few ideas on paper, think I came up with a cool design. We'll see. When I'm finished, you guys will be the judge.

Bob

Paul W · « **Reply #79 on:** 4 Mar 2007, 02:07 pm »

Here is my source for fiberglass and resins. Good selection, good prices, fast service.
http://www.defender.com/

I haven't read this whole thread, so sorry if this is duplicate or conflicting info:
-Chicken wire may not provide enough support for a good frame...try 1/4" - 1/2" "hardware cloth" from your local Ace, True Value, etc. You can cut it and then crimp it to make turns etc.
-The polyester resins are inexpensive but produce wicked fumes...work outside if possible. Epoxy is more expensive but somewhat less toxic.
-Both resins are very difficult to sand without long setup time...they tend to gum up sandpaper. A coat of the featherlite Bondo is easier to sand and, since you don't need much strength, consider Water Putty as a sandable topcoat.