O.T. Onken W thoughts ?'s

[Altec Best]

Your Welcome !

You might need about 4-5 sheets or so for those W's...

[edharbur]

Be careful of the bamboo plywood. We've built a bunch of cabinetry from the stuff - people like it because it's green - and it's always a battle with warping and splitting, probably because all the plys have thesame grain orientation. We also make rub blocks for race cars out of a product called Jabrock. It's far denser than the baltic birch (aka finn ply or Russian birch) or bamboo, but the cost is about $1,000 for a 25mm x 1 m x 2 m sheet - about 1" x 3' x 6'. I think that is made in France. Check it out at permalideho.com. It works and glues well, but is tough on cutters.

[Panomaniac]

I never had any warp or split problems with 3/4" Plyboo or the stuff from Bamboo Hardwoods in Seattle. But now you have me worried.
$75 a sheet is a great price. I'd use it on the outside walls with maybe something else on the insides. Are you really ready for a double 15 with sand filled walls? It's a huge project and they are very difficult to move. (I've moved them, and would not want to again).

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Ed, that Jabroc and its brothers looks like crazy stuff. It seems to be German - and the skid plate of choice for Formula One racing!
http://www.permalideho.co.uk/

[juniper]

Edharbur thanks for the advice, I will look into it ... that jabrock stuff looks crazy.. who would think theres plywood under an F-1 car????

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Panomaniac not thinking of doing the sand filled walls just to heavy.... Just read some stuff on onkens over at the diy site, you were cited many a time, very cool you worked with Jean Hiraga...

[edharbur]

For some reason, I thought tht the actual facory was in France, and that Permali UK exported it to my supplier in the US. The stuff is cheaper in the UK, but Permali is protecting their US distributor, and won't sell directly to me. Oh well. If you ever watch F1 or Americn LeMans Series races , you will, on occsion, see a puff of yellowish smoke coming off the bottom of a car as it goes over a bump or curb. This is Jabroc. We make planks for the American LeMans Series cars, and vintage F1 cars.

My last plyboo experience was 3 years or so ago. We brought the material in from out west somewhere, and paid something like $300 a sheet for the stuff. It was not a good experience. They may well have improved it in the meantime - all I'm saying is beware.... As I recall, the stuff we used consisted on lots of strips approximately 1/8" x 5/8" glued together to form a full sheet. No grain going across the sheet to lessen warping and splitting. I remember sitting at lunch one day and hearing a loud CRACK. When we went back to work, we found that a 2' piece of the stuff had split itself in half.

Ed

[GM]

Thanks GM is it just that the vents that are too small? There are a few disigns I have found with this cabinet the largest is about 21.18 cubic feet. I read somewhere that you recommended 24.43 cubic feet for 2 416 b's?

You're welcome!

Well, that and if they are driven with higher power, then dividing the cab into two separately tuned vented cabs is a much better solution than relying on a two stage vent system to average out any specs differences between drivers plus a different tuning may be required for best overall performance in your app.

Again, 'recommended' is a variable based on the driver's specs and needs of the app, but as a general rule for those folks willing to gamble on using published specs, best to build the biggest cab practical and tune it to Fs initially and adjust by ear in room, especially if an AlNiCo re-cone/re-mag as Pano [among others] has found out the hard way that some can require an infinite [or even open] baffle due to a much higher Vas and/or Qts than originally.

GM

[juniper]

GM thanks for responding I truly appreciate it! I tried to PM you but couldn't get through. I dont use high power amps or listen very loud, but do use ss and tube amps in my current set ups. I have a host of amps but it seems that Altecs are very very picky about amplification. One of my 416's has been reconed and per GPA they match very well with the other 416 that was sent to be checked. I need another pair of 416's and when a nice pair pops up I will try to acquire them. I have no ability to measure drivers but going with published specs with perhaps room for error and modification, with a 24.43 internal volume where would you recommned the vents be placed and the shape and size in an onken type cabinet shape? Also would you recommend placing the drivers a little higher or would the design be very different, again keeping the woofers on the horizontal, Thanks again for your help and info!

[GM]

You?re welcome!

Yeah, I got an email informing me my inbox was full, so was in the process of cleaning it out a bit when the crash occurred and if I have your email addy it's not under the 'juniper' moniker or remember your real name if I once knew it [sorry].

Regardless, these are the types of Qs I prefer to answer on-line since others may want to comment/whatever.

Hmm, if true, then GPA should have the relevant specs on record!

~24.5 ft^3 net should be large enough to handle a fairly high Vas and/or Qt, though will probably need to be sealed if yours or your next pair have real high values based on some measured re-coned units and/or your room has much gain down low.

Venting therefore would ideally be highly dependent on the speaker?s sealed in room response unless a high output impedance amp is used, in which case it should be tuned to whatever the driver?s Fs is or at least the average of the two if they aren?t isolated in individual chambers.

Or you can build per the W?s plan and accept whatever performance it yields as most folks apparently do.

WRT vent location, it generally doesn?t matter from a strictly simple reflex alignment POV other than the traditional way is to keep it and the woofer close to the mid/HF due to the vent?s harmonic BW being acoustically like a small third, out of phase, phantom driver and I assume why the W?s vents are up near the top of cab.

As more LF BW became available on recordings though, the vent was often moved to near/at the bottom of the cab to get a bit more floor boundary loading [plus wall in some designs]. As cab size shrunk, they could be moved out into the room, so some designs used rear firing to get a bit more vent harmonics damping via reflective loss without having to reduce its tuning efficiency with internal damping.

As for different alignments, folding the cab in half with a divider board will naturally add stiffness plus the longer path-length will add some TL [? WL] pipe action vent damping with the trade-off that the drivers will need to match ?close enough? and the vent will be on one side, same as my dual 515B cabs when laid on its side.

GM

[juniper]

Thanks GM I appreciate your sage advice!!!!! I will find another pair of 416's and see if I can get GPA to provide the pair I have specs. Then I guess it's decision time. Thanks for all your help!!!!!!!