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repurposing HK20 cabs for fostex 167en--help!

rogerfederer

rogerfederer

determined amateur
Subscriber
i bought some fostex 167en drivers on BT thinking i might use them on my open baffles. but after much research it sounds like they work best in a bass reflex. i thought about the BR boxes for sale on the auction site (ships from moldova) but hope for a cheaper alt. instead, i thought about repurposing a nice vintage speaker cabinet (love that old wood!).

this leads me to the HK20 (thanks to jameswei!). stock image:
http://img.canuckaudiomart.com/uplo...ver__harman_kardon_hk20_speakers_wmanuals.jpg

here are actual pictures: http://albums.phanfare.com/isolated/572zNwTU/1/6412842

the fostex recommended enclosure has a 2" port (2" deep) and a driver aperture of 5.74 inches:

http://www.fostexinternational.com/docs/speaker_components/pdf/recom_enclose/167e_enclrev.pdf

the aperture in the HK20 boxes is approx 7" and the hole left by the tweeter is 3" in diameter.

fostex recommends an internal volume of 15 liters and i calculate the HK box (with no driver in it) has a volume of 15.69 liters -- so pretty close.

so my questions:

1. is there some clever way to fit the fostex driver into that hole without some fancy woodwork with a jasper jig?

2. what should i do about the port? i'm thinking i look for some packing tube with a 2" diameter (cut to 2" depth) and try to fit that into the tweeter aperture.

3. should i go with some more transparent speaker cloth or stay vintage? i think the orig cloth looks kinda cool!

thanks for any ideas! i'm putting this in speakers but i suppose it could go in DIY as well...
 
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cut a new front baffle to fit your new drivers and glue it on top of the original baffle. then, so the grills will still work, install 3/4 x 3/4 square mold around the front edges of the cabinet, thereby extending the width of the top, bottom, and sides. refinish, as viola!
 
Good thought but I'm trying to do this on the cheap
Would those spacers work? Anyone done something like that?
Is this cabinet close enough to the fostex design so it will sound good?
 
Sorry. Missed the photo's on the link. GEES. :scratch2:

Maybe the spacers would work, maybe not. They would require cutting the baffle, so they sit flush at the surface. Post #7 tells me you may not like doing this, but some woodworking will be needed. This should keep it to a minimum.

My idea: Get (2) 3/8" mdf (or ply) "handy panels" from HomeDepot. I would suggest Lowes, but they don't cut. They come in a 2'x2' panel. HD will cut them for you (throw the guy a couple of bucks). Have him (her?) cut the width first on both panels. Then, cut the height.This will leave you with (2) 14x24 and (2) 8x10 scrap pieces.

Out of the scraps, let him rip 1" strips. You want all the rips done lengthwise. You can cut those to fit later. I'll get back to this part.

You now have 2 new "overlay" baffles. These will fit over the originals, and cover all the holes. Mark out where the driver goes, and cut the holes. A jig saw will work just fine here. Also, cut the hole for your port. Personally, I would put the port on the back. This would eliminate the timing issues and the midrange "bleed thru" from it. Choice is yours. Just a suggestion.

After you fit the new baffles, glue it on with liquid nails adhesive (wood glue will work here too). Weight them down with whatever you have, and let it dry overnight.

OK. Back to the strips. They are used to raise the grill off the new baffle and driver frame. Cut 4 for the height, and set them in place next to the cabinet lip(s). Now measure inside them for the top and bottom pieces. Once you have everything fitting good, glue them in place. This will make a shelf for the grill to sit on. A couple of velcro pads, and the grills are removable.

I know this seems like a lot of work, but it really isn't. The only tool you need is a jig saw. Hopefully, you have one. This should not take more than 3-4 hours. Really.

The extra baffle should help stiffen things up. That's a plus, especially with a ported cabinet.

Hope this helps. Any other questions, please feel free to ask.

Phil
 
phil,

thanks for thinking this through. i'll ponder this. trying for the least wordworking option. i do have a jasper jig and a friend has a plunge router. i've seen a jasper jig in action but have not done it myself...

it is so tempting to try the spacers 1st and see if i can make them work.

the fostex design has the port in the front. what are the merits of front vs. back ports? should i stick with their 2" diameter and 2" depth?

appreciate your ideas!

doug
 
I have no idea why they suggest a front port. For sure, they have tested this design and feel confident with it. The only reason I suggested rear porting is also to minimize port noise (chuffing) and what I stated in my post.

Port size, yes. This is what they recommend, so stick with that. If you decide to front port, use something like the "bonanza" one. With the front flair, port noise should not be a problem. In one of my speaker building books (Weems, I think) states "a port can be placed anywhere on the box, but needs to be 3" (or more) away from the rear of the (LF) driver. This will prevent the back waves from entering the port". I've seen designs where the port is side-firing. I don't think it really matters where, but some rules apply.


As far as the rings go, it'll be a bitch to fit them. ANY router jig needs some wood to attach the "pivot point" of the jig to. You have a hole, with nothing to put the pivot on. It can be done, but is it worth the time, the measuring and math, and the trouble? Your call.
 
Doug. No problem. It's what this place is all about.

From what I've read about them, they take time to open up. Some say 50+ hrs. Be patient, those drivers have good reviews. Let me know if anything else pops up.

Waiting for pics and a progress report. :D

Later. Phil
 
OK. Now I'm TOTALLY confused. :scratch2:

Is it your intent to insert the disk into the existing woofer hole, and then glue it into place? Or is this to sit inside the routed recess where the old woofer frame sat.

Those disks are only 1/8" thick. If you intend to use those, you'll need 2 for each box, glued together. 1/4" would be the minimum thickness I'd use. Also, you might have a problem with the driver screws having enough holding strength.

Set me straight on your thought process. :D
 
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