Bringing 828 cabs up to snuff...

[alancohen]

So now that I'm going to be home from work for a few weeks I can't resist catching up on a few projects.

Since my 828 cabs are relentlessly in the way in my garage I thought I'd at least put them on wheels. I got some 2" rubber-wheeled casters from HD and now at least they're mobile.

While I was at it I couldn't resist getting off the backs for the first time since I bought them. I expected a nightmare inside, but they're pretty clean. Here's a few shots:













I really don't want to gum them up with spray insulation. I have plenty of Ultra denim (last pic) that I can use to further insulate, but where should I add bracing to stiffen her up a bit?

And I guess the first order of business is to build a port board for the bottoms. 6" round? 4" deep?

Oh yeah, the business end:



And even the backs are not too bad. I think I'll keep the battle scars rather than paint them.

[alancohen]

I just picked up some N801-8A crossovers. I guess they'll fit nicely in that center panel in the back?

Pair Vintage Altec N801 8A 2 Way Crossover's 800Hz | eBay

[bowtie427ss]

I guess they'll fit nicely in that center panel in the back?

Yes, provided they're cut to spec.

but where should I add bracing to stiffen her up a bit?

Everywhere! But, particularly behind the horn flares. The two factory braces are minimal, and i notice those aren't even there? Next place is the wide open panel acreage, especially the side panels behind the vent panels. A side to side brace from approximately the middle of those areas can do wonders to take a lot of the bounce out of them. IMO, the one piece back also wants for a front/back brace just below the woofer.

[fpitas]

What bowtie said. Knocking on the cabinet can give you an idea what needs bracing. Oak dowels, maybe 1" or 1 1/4" diameter, work pretty well, as do 1x2s etc.

[alancohen]

Thanks, guys. There's a part of me that wants to hear them unbraced first. But I'll have to wait for my crossovers.

Maybe I'll cannibalize the N1285s from the A6s. This way I'll be able to see what they sound like at 500, 800 and 1200. I'll have to see how they're hooked up to the two woofers. Anyone know if they're series or parallel?

[bowtie427ss]

I also forgot to mention the "horn mounting board" as Altec called it in the 50's/60's. That's the "L" shaped piece with t-nuts spaced for 811/511 mounting that spans the top of the cabinet across the top panel of the horn, and as such forms a very effective stiffening brace for that panel. You can get the basic dimensions from the 60's enclosure guide, but you'll need to modify the dimensions for 3/4 inch material rather than 5/8.

[Alien_Shore]

So now that I'm going to be home from work for a few weeks I can't resist catching up on a few projects.

Since my 828 cabs are relentlessly in the way in my garage I thought I'd at least put them on wheels. I got some 2" rubber-wheeled casters from HD and now at least they're mobile.

While I was at it I couldn't resist getting off the backs for the first time since I bought them. I expected a nightmare inside, but they're pretty clean.

Those look VERY clean! You scored a nice pair there, Alan.

Here's where I'd start in shoring them up (sorry for the crude drawing):

[mah]

Brace the bottom panel, too.

[GM]

Yeah, with castors, doubling up on the bottom's panel thickness wouldn't be overkill.

GM

[alancohen]

I think pine braces on the sides would act like bracing on a guitar sound board. They would still vibrate. Oak braces might be better, but that's a lot of oak ($$$) and a lot of weight.

Since I also build balsa model planes, I'm used to trying to add stiffness without adding a lot of weight. I was thinking along these lines:



I got some 1-1/4 x 1-1/4 x 36" deck bannister blanks at HD for $.84 each. I think I can trim them for a tight fit and get away with installing with just wood glue. I'd rather not put screws in the sides, but I would if necessary.

I know in order to retard unwanted vibration, which causes feedback on hollowbody guitars, they will tie the soundboard to the back under the bridge with a block of wood. It loses most of its acoustic properties this way, but it stops feedback cold.

And yes, I also broke down and bought some gap-filling spray insulation. Yuck.

BTW, I can also add a couple from the front to the back (lighter red). I can attach struts under the LF mount and then screw them to the back. Two screws through the back will secure them tight.

Yeah, with castors, doubling up on the bottom's panel thickness wouldn't be overkill.

The casters are not only for ease of moving. My house is built on a slab, but the living where these will be going is built on a raised floor. Since I have HW floors and area rugs, I'd rather insulate the boxes from the floor as much as possible to reduce unwanted vibrations. I want to hear the speakers, not my floor

I suppose I could add two more full-length from top to bottom behind the LF mount.