How to adapt 515B to a later A7 828 cabinet.. Best Way?

**LowOhms** · April 27th, 2015, 01:23 AM

I have some nice 515Bs and GPA rebuilt 802-Ds, and a pair of SHOWCO 9000 ( Emilar 500 copies) horns. All of this is waiting to be mounted into two A-7 enclosures, which I have not yet sourced. Was unable to find A7 Model 825 enclosures, but have a "line" on multiple A7 Model 828 enclosures.

What do I do to adapt the 515Bs to the later model A7-828 enclosures, which, I believe use the wider bolt pattern for the later woofer drivers ?

Do I modify the mounting holes on the 515Bs, slot them a bit, which I am hesitant to do, or is there a "best way" to modify the later enclosures to fit the 515Bs without hacking up the 515B frames?

The 515Bs sound amazingly good to me, into the midrange, driven all alone, on the living room floor, with a SE 6AH4GT 1.2 Watt triode amp !!!

But its now the TIME to get an answer from those experienced, on adapting 515Bs to the later A7 model 828 enclosures.

Thoughts and ideas, advice, most welcomed. Thank you all.

Jeff

**bowtie427ss** · April 27th, 2015, 05:08 PM

Make a pair of access doors on the motorboard behind the horn flares to the left and right of the woofer, large enough to comfortably get your hand in there to place new T-nuts in newly drilled holes on the proper bolt circle for your 515B's.

You can go whole hog and even t-nut and gasket covers for the access holes.

The modifications will be fully out of sight, and your 515 frames left fully original.

The modifications will also allow you to experiment with "other" woofers using that more common bolt circle.

**Audio_by_Goodwill** · April 27th, 2015, 07:32 PM

The bolt circle is different? I thought it was just a matter of the 16" frames being too big for early cabinets?

**endeeinn** · April 27th, 2015, 11:45 PM

Originally Posted by Audio_by_Goodwill

The bolt circle is different? I thought it was just a matter of the 16" frames being too big for early cabinets?

The Altec spec sheet for a 515B states the bolt circle diameter is "4 holes equally spaced on 14 9/16" centers" and the plans for an Altec 828 cab shows 4 equally spaced holes on a 7 9/16" radius which is a 15 1/8" bolt circle diameter.

**LowOhms** · April 29th, 2015, 10:25 AM

Originally Posted by endeeinn

The Altec spec sheet for a 515B states the bolt circle diameter is "4 holes equally spaced on 14 9/16" centers" and the plans for an Altec 828 cab shows 4 equally spaced holes on a 7 9/16" radius which is a 15 1/8" bolt circle diameter.

Yes, you have hit the nail on the head.

14 9/16ths ( 515B centers ) is smaller than the 828's 15 1/8th inch centers.

ANYBODY out there ever fit a 515B woofer into a 828 A-7 enclosure?? Not theorize it, but DO it ?? HOW is the best way??

THANKS,

Jeff

GM · April 29th, 2015, 12:14 PM

Yes, but I had a comprehensive sheet metal manufacturing facility at my disposal to make 12 ga CRS metal adapter rings with threaded weld studs, though ~1/4" thick BB ply, Lexan or similar could be used with countersunk carriage bolts or similar. We heard no audible difference due to the extra filter chamber volume in the few prosound apps I did for others, but never had the ability to make high resolution frequency response plots, so can't say it made zero difference.

Regardless, if I did it today, my router and drill press would make quick work of a plywood adapter and not a whole lot longer if I still just had a hand drill and saber saw and free handed it following a paper template, though whether it's 'best' or not, I can't say.

Of course, don't forget to gasket it with neoprene or other non porous, high density material.

GM

**bowtie427ss** · April 28th, 2015, 07:09 AM

Originally Posted by Audio_by_Goodwill

The bolt circle is different? I thought it was just a matter of the 16" frames being too big for early cabinets?

the frame diameter is only a factor with 210/211 cabinets made for the 15 inch diameter frames. Those cabinets are 32 inches wide overall, not big enough to accept two 16 inch frames.