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-   -   Half Chang build (http://www.diyaudio.com/forums/full-range/109576-half-chang-build.html)

bobtrancho 6th October 2007 12:41 AM

Half Chang build
 
2 Attachment(s)
I've started my Half Changs. I'm using 18mm "maple/birch" ply that I found at my local Lowes. It turns out that the ply has a birch veneer side and a maple veneer side . The birch side is very erratically figured so I'm going with the maple side. The drivers will be FE206s - that pile of blankets in the background covers them as they are burning in.

As you can see, the cabinets are all cut and the driver hole has been routed. I'm waiting on the delivery of a 30 chamfer bit I ordered from MLSC to finish the holes before assembly.

That gives me time to start asking questions and soliciting advice. Specifically:

- Damping - right now I'm planning on damping the rear, top, bottom and one side of the chamber to start. I have some polyester batting but was intrigued by the use of cork in the recent PAWO thread. I'd appreciate any advice/opinions about my damping locations and choice of materials.

- Bracing - I'm planning three internal braces. One horizontal offset behind the speaker, another window brace a little more than half way down the chamber, and a vertical brace from the lip of the vent slot angled up to the front (like Marce used in his Curvy Chang). Should this last brace be offset or centered? Again, any comment or advice is welcome.

- FE206 prep - the drivers already have about 36 hours of burn in and should easily have 100 by the time I'm ready to mount them. Dave has told me that he's now working on a 2nd gen of 206 mods (EnAbl, etc) so I am holding of on any intense mods right now but will be adding duct seal to 3 of the 6 arms and a felt pad to the rear of the magnet. It would vastly improve the WAF if I could color the cones flat black or very dark brown, Dave has indicated that his new mods may allow black gloss acrylic in the final stage and though I'd prefer it not to be shiny, I might have to settle. Has anyone out there successfully dyed or stained Fostex cones and dark color? And, if so, how? Scottmoose has suggested ~4 ohm series resistance so I will try that, also.

Work, family and waiting for the router bit will mean I won't get back to these for a few days but I'll post again once they are partially assembled and ready for damping, etc.

Crossblade 6th October 2007 07:21 AM

Isn't this the first Half Chang?

Please post how they sound, when you finish them :smash: :)

planet10 6th October 2007 07:48 AM

Re: Half Chang build
 
2 Attachment(s)
Quote:

Originally posted by bobtrancho
Should this last brace be offset or centered?
Offset.

dsve

Scottmoose 6th October 2007 08:27 AM

Nice material. Good luck weith the build.

3 - 4ohms are a requirement for the 206 to work properly in this box BTW; the response will be all over the shop if you run it without.

bobtrancho 10th October 2007 12:38 AM

The chamfer bit arrived today and I was able to chamfer the speaker opening and get one box almost completely glued up and the other about 1/2 done.

http://www.trancho.net/HC/HC_2.jpg

Tomorrow I'll mount the FE206e and do the final fit for the speaker brace (on the right below). I am unsure as to whether or not to use the additional brace at about 1/2 way down the full length of the cabinet as I'm not sure if it is really needed and don't want to eat into the chamber volume more than I have to.

http://www.trancho.net/HC/HC_3.jpg

I'm saving the final cuts on the piece that goes in the opening for when I'm fresh tomorrow as that Sears combination saw you see in the background is the single worst tool I have ever purchased - it is impossible to cut an accurate 45 angle as the arm has so much play that it twists almost 1/4" over the 9 1/2" crosscut. So I'll have to use my circular saw and just take a lot of time setting up and making test cuts ("measure twice, cut once") and will probably have to cut a tad over sized and file/sand for a nice fit.

Then it's on to duct seal and felt on the drivers; some cork and poly damping; and by Thursday I should be able to clamp on the other side and fire them up for a preliminary test run.

Scottmoose 10th October 2007 09:00 AM

You'll get considerably more benefit from fitting the brace & loosing a touch of volume (I anticipated some loss through bracing etc) than if you didn't. You can't have too stiff a box.

larkinrulez 10th October 2007 10:21 AM

Quote:

Originally posted by Scottmoose
You'll get considerably more benefit from fitting the brace & loosing a touch of volume (I anticipated some loss through bracing etc) than if you didn't. You can't have too stiff a box.
Si...and you get some "virtuell" Volume through stuffing

Godzilla 10th October 2007 03:37 PM

Its amazing how it looks like a traditional back horn when its all sealed up.

Scottmoose 10th October 2007 03:44 PM

:) Just tell them it's a BLH -I bet the majority of people would accept it, no question, unless they looked closely.

bobtrancho 10th October 2007 05:15 PM

Then again, if you told most people it was a BLH they'd say "Bacon, lettuce and ham ???"

Braces are in and glue is drying. Once they are set enough for me to remove the clamps I'll start on the angled pieces at the horn. I hope to get them glued in tonight so I can begin adding the the damping tomorrow.

I jerry-rigged three 10 ohm resistors from Radio Shack in parallel to give me 3.3 ohm series resistance until my Mills resistors from Parts Express arrive. By that time the 206s will have over 80 hours of burn-in and I'll have added the duct seal and felt. Once Dave's phase plugs arrive they'll go back into surgery.

I hope to fire them up tomorrow sometime, though it will be in the basement with concrete floors and walls. If all goes well I'll move them into the living room by Friday and fiddle with damping a bit before sealing them up for good.

Then I have to deal with finishing them...


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