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Orb Clones

post #1 of 22
Thread Starter 
Thinking of making some Orb clones, if not for the sake of the project then for the WAF.

Here's my rough plan, though I'd like to hear any thoughts you guys may have:

Drivers

I'll be using 3" full range drivers. Probably this Tang Band W3-881SJ. The downsides I initially see are the low power handling (15 watts RMS) and the impedance (8 ohm), making it difficult to do a "mod2" knockoff at 8 ohm, though I could add a resister in there if necessary.

If you have any suggestions for a better driver, I'd love to hear them. I'm looking in the $20-50 range.

Enclosure

I'm thinking of using 5" foam balls (here at JoAnn Fabric) as a base. I'll cut one side flat, then use fiberglass fabric and an epoxy resin to provide an exterior shell. (Added bonus: Maybe I'll do a final layer of black fiberglass or carbon fiber for a nice look.) I'll finish it up by hollowing out a majority of the inside , leaving some styrofoam for internal damping, drill two holes in the back for terminals, and add a mounting hole or some other method to attach it to a wall or stand.

I can't figure out how I'm going to secure the speaker to it. I'm thinking of possibly gluing it in, or making some sort of mounting bracket that I can glue on, and have threaded inserts on.

Future
  1. I'm thinking if all goes well, I could do a "two way", and make an independent tweeter. Because of space limitations, I'd probably have to go with first-order crossovers for both speakers, but I could set it fairly high (7k?) since the 3" driver will be full range.
  2. Upgrade to mod 2 or mod 4
  3. 8" Subwoofer? I found 10 and 12" foam balls!

Again, please let me know any thoughts or ideas you might have.
post #2 of 22
From my experience with fiberglassing I'd use packing tape and a spray on release agent to get the foam ball out. Then you could cut up the ball and glue them back on. Using a long set of tweezers would aide in that process.

For mounting them I would fabricate 1/4"-1/2" thick MDF mounting rings and them just fiberglass them in however you want them.

When you get to the point where you want a nice smooth surface that is paint-able take your resin before you mix the catalyst and mix in talcum/chalk powder (baby powder works great) to make a nice paste and then mix in your catalyst. Apply, let it set, and then sand it smooth with a foam high grit sanding pad.

You have some great ideas with your DIY speakers and I hope you post pics and keep us updated on your build.
post #3 of 22
as an alternative to fiberglass, you might try wood.

if you don't have to have exactly round, you might consider getting some furniture feet (aka bun feet) and then drilling a ~3" hole through with a door handle type drill bit/cutter. then mount the driver on the front put a 3" wooden plug in the hole in the back. 3" wooden plugs are something that you can buy, btw. run the wires out the top or bottom.



http://www.thehomefabricstore.com/in...iewCat&catId=6

or you could use spheres, but i'm not sure how you would flatten out the front. i suppose that you could drill the 3" hole through, then just sand down the front lip until enough surface area is exposed to mount the driver.
http://www.save-on-crafts.com/woodball.html

good luck with your project!
LL
post #4 of 22
Thread Starter 
Natedog - Unfortunate name, considering the news, eh? Thanks for the tips. I'd never heard of the baby powder finish coat but I'll definitely give that a try if I go that route.

LTD- I really like your idea of furniture legs. I'll be investigating that further later today. Nice graphics haha.

I could pretty easily route out the inside of the chamber too, then I wouldn't need a plug and I'd have a "unibody" speaker. The only disadvantage I see right now is cost, since the legs are $20 vs $5 + another $5 in materials. But 10 dollars for a lot sturdier cabinet isn't bad at all...who am I to complain?
post #5 of 22
i'm sure the price goes down with scale. i'm not sure if the big box stores stock something like this, but if so, it seems like it could actually be pretty cheap. i just linked to that site so that it would be clear what the concept was. i don't have any idea if that site has good prices or not.
post #6 of 22
Thread Starter 
I was able to find the original manufacturer of the ones you linked to. I can't find anything quite that size from a big box store. The ones you linked have a 6" diameter at the widest point, which seems a bit large for what I want to do. However, I found this one which is a lot closer to what I am looking for. I'll have to flatten it out, maybe with a belt sander.

Having found the original manufacturer, I can specify the wood I want. I'm thinking soft maple; from my guitar days I always liked the sound of maple acoustic guitars, so I figure that's at least a good starting point. Thoughts?
post #7 of 22
Quote:
Originally Posted by tculverhouse View Post

Natedog - Unfortunate name, considering the news, eh? Thanks for the tips. I'd never heard of the baby powder finish coat but I'll definitely give that a try if I go that route.

You are essentially making a type of hairless bondo. It works really well when you want to move fairly quick on a project. We could fabricate a fiberglassed box, have it sanded/smoothed, and put the first coat of paint on it in a day with that process.
post #8 of 22
cool. one other thought...are you sure that those drivers will work in an enclosure that small?
post #9 of 22
Quote:
Originally Posted by LTD02 View Post

cool. one other thought...are you sure that those drivers will work in an enclosure that small?

the Vas of the driver he specified is .08 cubic feet, so it should not be an issue unless he decides to go with a different one.
post #10 of 22
i just got curious and modeled it up.

if the hole is 3" diameter and 3" deep, that is 21.2" cubed. there are 1728 cubic inches in a cubic foot. so that is only 0.012 cubic feet. in a sealed enclosure that small, i am seeing a 6db peak at 350hz and a qtc of 1.645. no good.
post #11 of 22
Quote:
Originally Posted by LTD02 View Post

i just got curious and modeled it up.

if the hole is 3" diameter and 3" deep, that is 21.2" cubed. there are 1728 cubic inches in a cubic foot. so that is only 0.012 cubic feet. in a sealed enclosure that small, i am seeing a 6db peak at 350hz and a qtc of 1.645. no good.

ouch. good point. That wouldn't sound too good.
post #12 of 22
Start with something like a rubber ball or balloon (something hollow in the middle). Do a few layers of fiberglass. cut out a hole for the speaker. Hot glue a MDF ring to it. Then do a few more layers of fiberglass. Done.

That's how car audio guys do it.
post #13 of 22
Thread Starter 
I'm going to be taking a little bit of a different direction. I found a thread over at diyaudio about using Ikea bowls for spherical speakers. I'm going to use some of the 5" bowls. Should be pretty simple this way.

Also, the drivers I originally stated are on back order, and I'd like to get most of this done this weekend. So I ordered these off of Madisound. Due to the high impedance (20 ohm), I'll be using two in parallel.

As far as enclosure size: I am aware that this is a bit small for these drivers. Assuming a thickness of 3/8" (seems reasonable from the picture), I get an internal volume of 0.025 cubic feet, though net volume will be a bit less due to the cutout and volume of the driver, so maybe something more like 0.023 c.f. Using this volume and the values published for that driver, I get a 6dB peak at 216 Hz and a Qtc of about 2.

If I port it, I could do a 3/4" diameter by 1 3/4" length port and reduce the peak to 11 db at 143 Hz, below my crossover frequency. I know the port is a bit small in diameter, but due to enclosure dimensions, I can't really go any larger.

Thoughts? Should I port it?

EDIT: Two in parallel will have separate enclosures (mod 2 style).
post #14 of 22
man, should've gone with these: https://www.madisound.com/store/prod...oducts_id=8801

they have a smaller vas and what seems to be a decent FR.
post #15 of 22
"Thoughts?"

while not really a thought, here is that driver in your enclosure.


LL
post #16 of 22
Thread Starter 
Is that the ported or sealed (I assume sealed)? What software are you using?
post #17 of 22
that is sealed. winisd is the software.
post #18 of 22
Thread Starter 
If I put in a first order high-pass filter at 450 Hz, I can limit the Fsc to 1 dB at 450, and still maintain an F3 of about 130 Hz. I'm not sure if there is software for simulating this (it doesn't appear that WinISD will simulate the filter for me, at least not the free version), however I plugged in all the math in excel and got the following. Setting my crossover at 180 Hz appears to work quite well with this filter. Now, I'm not very experienced in the audio applications of high-pass filters, most my experience is in process control, so I'm not quite sure how accurate my modelling of the filter will be. Anyone have some insight as to how this may actually behave?

EDIT: Detail of my modelling:

Attenuation of frequencies below crossover frequency = 6*log2(450/f)
This equation results in attenuation of 6 dB/octave, as is typical with first order filters
So that
SPL(filtered)=SPL(unfiltered)-Attenuation
LL
post #19 of 22
maybe winisd has changed, but in my version, there is a tab EQ/Filter where you can apply various filters.

i am seeing pretty much the same response that you are. the corner is around 200hz. what will you be doing below 200hz?

i like how you have the skills to model it up from the ground up. i don't have such skills.

the group delay may muddy transient behavior up a bit, but what do you expect?

if i may...anybody as smart as you are shouldn't be screwing around this kind of a build. ;-)


LL
post #20 of 22
How many of these do you need? I found something neat last year for a project like this and might have some left over.
post #21 of 22
Thread Starter 
4 enclosures = 4 drivers + 8 bowls.

What do you have?

LTD- This will be my first build, so I wouldn't say I shouldn't be doing it haha, but thanks. My education (and career) is in chemical engineering, so I have a pretty strong educational and applied background in mathematics.

What version of WinISD do you have? I just downloaded "WinISD Beta" which has a version number 0.44. Below 200 Hz I'll be crossed over to a subwoofer.

Quote:


the group delay may muddy transient behavior up a bit, but what do you expect?

I don't understand what you mean by this.
post #22 of 22
i have winisd 0.50a7. it seems to do everything right, so i never upgraded. maybe that makes me an old geezer.

i never sent them a "postcard", but i figured that posting countless screenshots from their software would keep me in good standing. :-) i'm not sure what their business model is, but i would buy their stuff in a heartbeat if i were a commercial.
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