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Old 23rd November 2004, 06:27 PM   #1
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Default Yet Another NSB Thread...

One of the (way too many) projects I have going on is to make a batch of eight-foot line arrays using NSB's and the Onkyo buyout tweets. They will be a self-sealing clamshell design using ripped 6" PVC pipe. In case anyone is interested, I peeled open an NSB magnet shield to see what's inside:
Click the image to open in full size.
Click here for full-size image.

Also, I'm experimenting with varnish and ferrofluid. I don't have a speaker measurement system in place yet (lots of research to do first), but here is a pic if NSB's with various combinations of varnish and FF:
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Click here for full-size image.

-Casey Walsh
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Old 23rd November 2004, 06:45 PM   #2
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Where did you find a large bottle of ferrofluid? I'd not mind playing with some myself.
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Old 23rd November 2004, 07:04 PM   #3
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Hi rcavictim:

I got it from an eBayer called emovendo. He couldn't tell me the viscosity, saturation magnetization, or carrier chemistry, but at 1/3 the cost of FerroTec's offerings, I thought I'd get some to experiment with.

After I bough from emovendo, I foud another eBayer (jeffkenp) that had some at a similar price and the specifications are viscosity=6 cp @ 27 C (quite low), saturation magnetization = 400 gauss, carrier base = hydrocarbon.

-Casey Walsh
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Old 23rd November 2004, 09:55 PM   #4
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Default Re: Yet Another NSB Thread...

Interesting stuff.

What's a "self-sealing clamshell"? Is this an Isobarik configuration?

What do you do with the ferrofluid? Do you pull off the dustcap and squirt in the fluid? It would be interesting to see what this does.
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Old 23rd November 2004, 11:25 PM   #5
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Quote:
What's a "self-sealing clamshell"?
Imagine ripping an 8-foot section of 6-inch schedule-40 PVC pipe lengthwise so that you are left with two half-round troughs. Now use a 6 x 8 baffle for the drivers and some 6 diameter half-circle end caps for each trough. Re-connect the halves with a piano hinge and latches, then outline one of the baffles with a sealing rubber strip.

Quote:
Is this an Isobarik configuration?
Nope, just a basic sealed, stuffed box.

Quote:
What do you do with the ferrofluid?
No need to remove the dust cap to inject the ferrofluid, just use a hypodermic syringe and needle. I used about mL. My concern is that the paper voice coil former will either emulsify and fall apart, or will wick the ferrofluid away. I just removed the dust caps so I could see what was going on.

-Casey Walsh
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Old 24th November 2004, 04:23 PM   #6
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I don't follow the purpose of the other half pipe. I assume it's a cover for portability. I'm not sure what the trough would do sonically, but it will detract from the looks. For portability, just build 2, 1 in each half pipe. Make it so they attach together firmly face to face for transport. Then it's only 1 tube for a pair of speakers.

I've thought about something similar and that size only gives you 700-800cc per driver with edge to edge mounting. The resulting Q of the box ends up quite high at around 1.2 . The NSB's 2 liters each just to have a Q of 1, still high. I'm planning to test it with some aperiodic venting (drill a bunch of small holes in the back with polyfill in the tube), so the small box size didn't matter.

Also, a perfect seal become less crutial. One thing I dislike about arrays is cutting the driver holes. 17 3.5" driver holes on a baffle 6" x 8ft seems problematic. I was thinking 2 strips of wood with a groove to slide the edge of the drivers into. Slide the drivers into one groove and seal it with glue, epoxy or whatever. Mount the strip on the other side. Seal any open airspaces between the driver baskets from the back. Attach this baffle to the half pipe.
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Old 24th November 2004, 05:57 PM   #7
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I like the clam shell idea. Is the idea to allow it to open to like +270 degrees to give wider coverage?

Will this get a little heavy? Looks like lots of magnets in the NSB.
I've been searching for reasonably priced lightweight drivers (neodymium) but haven't come up with anything.

I see NSB's jumped from their low of 49 cents back to 69 cents for 32+.

That's a 40% increase in price!
They're too expensive to rip apart just for fun now. :-)
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Old 24th November 2004, 06:12 PM   #8
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I was thinking something like the sketch below. The tweet array fits into the empty cavity of the closed NSB array.

-Casey Walsh
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Old 24th November 2004, 06:14 PM   #9
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Hmmm, image didn't make it... Lemme try again:

Click the image to open in full size.

-Casey
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Old 24th November 2004, 07:40 PM   #10
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Ingenious!

How about a three section clam shell where the tweets fold out too?

You already know, but careful ripping the PVC pipe. Some of it's internally tensioned and wants to close up on itself. This may also lead to problems of it not fitting together after it's ripped.
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