Bolt Hole Spacing - HOW to fit a 515B into a 828 enclosure

[LowOhms]

Howdy folks,

The ALTEC 515B woofer has a 14 and 9/16ths bolt hole spacing.

Unlike the early 825 enclosures, ALTEC's later 828 A7 enclosures have a 15 1/8th inch bolt hole spacing.

What is the "most effective and slickest way" to adapt a 515B to a later cabinet, woofer mounting wise???

Surely, some of you have had to figure this out.

Suggestions please? Thanks - very much.


Low Ohms aka Jeff Medwin

[GM]

Good Q, I don't remember this as the few 828s I messed with all had 421s or similar, but I surely knew about the different frame sizes. Guess I either never had to deal with it or the early 828s had both patterns. Anyway, just off the top of my head, I'd grab a scrap strip of wood, lay out both bolt patterns on each side, use the outer ones to pin it to the baffle, mark/drill the other two, remove strip, use the inner ones to either hold the driver as template or use some scrap hardboard/whatever to make a permanent template. Come to think of it, this was how I remember doing some different horns and seems like I rotated the pattern a little to get more 'meat' between them.

GM

[LowOhms]

Good Q, I don't remember this as the few 828s I messed with all had 421s or similar, but I surely knew about the different frame sizes. Guess I either never had to deal with it or the early 828s had both patterns. Anyway, just off the top of my head, I'd grab a scrap strip of wood, lay out both bolt patterns on each side, use the outer ones to pin it to the baffle, mark/drill the other two, remove strip, use the inner ones to either hold the driver as template or use some scrap hardboard/whatever to make a permanent template. Come to think of it, this was how I remember doing some different horns and seems like I rotated the pattern a little to get more 'meat' between them.

GM

Hi GM and thanks for taking a shot at this.

I posed the question to my good friend and audio buddy, Dennis Fraker of Livingston, Montana ( Serious Stereo. Com ) who runs GPA 604s in MLTLs, after I posted my inquiry here.

Dennis suggested having a 1/4 inch Aluminum ring plasma-cut to fit the stock 15 1/8th inch diameter 828 hole spacing, countersunk for 1/4 by 20 machine screws, and a second set of 4 holes, 45 degrees apart from the 828 holes, tapped 1/4 by 20 at the 515B's 14 9/16th diameter, to attach the 515B frame. So far, that seems the best way I can think of doing it. There will be just enough room in the rear compartment of the 828 enclosure to fit the deeper frame of the 515B driver.

I wonder if anyone else in ALTEC-land can come up with an even better "fresh" new solution ??

Cheers and thanks to all,


LowOhms ...................aka ...............Jeff Medwin

[mah]

"....most effective and slickest way...": Penn Elcom

[GM]

I thought this was for a typical DIYer to do, i.e. "most effective and slickest way" = easiest, cheapest to do. Had I known it was a commercial app I would have suggested jacking up Altec's piece-o crap cabs 4 ft and sliding a properly built one with the right bolt pattern into place, 'killing many birds with one stone'.

GM

[mah]

ROTATE the speaker SOME. Mark and drill new screw holes. OPTIONAL: Tips on using threaded inserts

For a permanent install, GORILLA GLUE would fit the bill.

[LowOhms]

ROTATE the speaker SOME. Mark and drill new screw holes. OPTIONAL: Tips on using threaded inserts

For a permanent install, GORILLA GLUE would fit the bill.

Thanks !! I was aware of threaded inserts, and "passed" on them, as not being a permanent bullet-proof solution. The stock T-Nuts are less likely to be problematical .

No, I personally don't want to do that, but THANKS mah for trying to help .

LowOhms aka Jeff Medwin

[LowOhms]

I thought this was for a typical DIYer to do, i.e. "most effective and slickest way" = easiest, cheapest to do. Had I known it was a commercial app I would have suggested jacking up Altec's piece-o crap cabs 4 ft and sliding a properly built one with the right bolt pattern into place, 'killing many birds with one stone'.

GM

Hello GM,

AMEN, AMEN on doing it right. From scratch !!!

How about this....for EIGHT years now I have been storing SEVEN ( 5 feet by 5 feet ) sheets of one inch thick voidless Baltic Birch in my apartment's second ( unused ) bathroom, waiting for a suitable ALTEC speaker project.

Has anyone ever made a one inch Baltic Birch A7- 828 set of enclosures????

I imagine 3/4s has been done many times. What would one inch sound like?? NOW is the time in my advanced-in-age life to find out !!!

I am not a wood guy, but, I know of a retired industrial arts high school teacher, two towns away, who has a FABULOUS wood shop in his basement. Time to get a quote, with A7 enclosure plans in hand !!!

My initial thought was to make the enclosure as much as possible out of one inch BB, and have the speaker mounting baffle board full-speaker-width out of one inch, and maybe extend the speaker to be 25 inches deep, rather than 24 inches. I was going to have the front bass reflex ports flush with the front of the speaker, as in the 825, not set back 1.5 inches as in the 828. I was going to experiment with final port size by ear.

Speaker will be a A7-8 with 515Bs and 802Ds on a 811 horn. Low powered SE DC amp, 6AQ5 finals. Good wiring.

If you , or anyone else, has suggestions, I AM ALL EARS. My goal is to have NO internal bracing that disturbs the flow of the air, no cross braces, x braces, etc. Sorta like a musical instrument. That's how Dennis built his GPA 604 Serious Stereo MLTL.

Ideas welcomed, the page is open!! Thanks !!!

Low Ohms aka....Jeff Medwin

[Old Guy]

Hello GM,

. My goal is to have NO internal bracing that disturbs the flow of the air, no cross braces, x braces, etc. Sorta like a musical instrument.

http://www.guitarsalon.com/forums/showthread.php?t=5881

I have no idea where you got the idea musical instruments have do not internal bracing...but you should delete the inaccurate info from your memory banks. They certainly do. The rest of your analogy is also completely false. See above link...

An instrument, be it guitar, piano, whatever...uses portions of the body to vibrate sypathetically with, in both those cases, the stings. Those portions of the body, and the amplification and coloration(s) they add are mostly what diffentiate a top shelf instrument from junk.

A cabinet is the opposite....a passive device that should NOT add coloration.

As far as a brace in a corner disturbing airflow more than a simple corner, false too. See Harry Olsen's work on cabinet shapes. His conclusion was the ideal shape was a sphere.

IMHO the project you are talking about sounds more like impress your friends rather than making any signifigant improvements. If your interest is how far an old design can be pushed there are many other places to improve an A7. Sand filling the voids behind the curved panels has been done.

Adding mass the the 511 horn helps. My favorite is modeling clay, can be removed if you don't like it. The crossover...all a thousand times more effective than worrying about the bracing. Don't get lost in the details. Decide what it is you wish to do. Research lots of possibilities, don't fall in love with a few. Above all, experiment. For most of us the search for an elusive goal is more rewarding than a pre conceived plan.