1/4 scale 828 A7 cabinets

[Cal Weldon]

Hi, new to this forum.

I have heard about a scaled down version of the A7. I have a 4" woofer and a small horn I want to put into a small 828 lookalike box. I am only mildly concerned about the sound. These are just for fun, I have enough speakers, including the real 828 and 210 [A4] cabinets. You can see the 210's in the background of the photo

This is the exiting system I tried with those small aluminum enclosures. I think I can do better.

Thanks for your help in locating the small boxes,

Cal

[Mr. Widget]

Now that sounds like fun.

I'll make you pair of perfectly scaled A-7s including "Voice of the Theater" graphics on the sides if you want. I could even scale the 511B horn if you like. It only takes time and money. If interested send me a PM.

Widget

[Cal Weldon]

Thanks Mr Widget,

Yes I will send you a PM to discuss this further.

First will this woofer fit the box? I'm thinking about the depth of it.
4.5" woofer

I think the tweeter I have will work for now, I haven't seen one that works that well as a lookalike but the sound of the one in the pic is OK.

Cal

[GordonW]

Man, what you need for a tweeter, is one of those little multi-cellular Jensen tweeters, such as the one that went into the SG-222 coaxial Jensen speaker from the 1960s. Yeah, it's only a "6-cell" design... but really, it's the right size AND it's multicellular!

Here's a pic from an old Jensen catalog, that I swiped from a kind soul that posted it up on the AudioKarma board earlier this week. Check out the SG-222 pic!

[GordonW]

Hey, another idea just popped to mind...

A square-front box, with TWO of the 4.5" woofers mounted side-by-side, and one of your existing small bi-radial horns above one of them, per box... miniature JBL 4435????

Man, that's tempting to build. I've got a whole bunch of extra 4" and 5" drivers...

Regards,
Gordon.

[Mr. Widget]

Here is a drawing of a 12" tall Altec A-7 based on Altec drawing number 825 from 1968. I looked at several A-7 drawings and they do vary a bit from one to another.

This drawing is in 1:3.5 scale. It will accommodate a 4.5" woofer if the woofer depth isn't too great. All dimensions are in inches. If anyone is interested, I can post all of the dimensions. I left many out as they can get fairly dense at this scale.

Widget

[sa660]

Originally posted by GordonW
Hey, another idea just popped to mind...

A square-front box, with TWO of the 4.5" woofers mounted side-by-side, and one of your existing small bi-radial horns above one of them, per box... miniature JBL 4435????

Man, that's tempting to build. I've got a whole bunch of extra 4" and 5" drivers...

Regards,
Gordon.

Could it the 4612-OK???

[Cal Weldon]

Originally posted by Mr. Widget
This drawing is in 1:3.5 scale. It will accommodate a 4.5" woofer if the woofer depth isn't too great. Widget

Hi Widget,

The woofer is 2.5" deep
Scale is 1:3.5
That means the 8.75" actual 828 cabinet depth divided by the 3.5 scale = 2.5 inches clearance from the baffle to the back of the cabinet. This would work but it means the little woofer would be touching the back panel. I wonder if we should think about bumping the panel to accomodate?

Gordon, I like your enthusiasm but I'd like to stick to the 828 type cabinet as these are for show as much as anything else and I already have the parts.

Cal

[Cal Weldon]

Oh and Gordon,

Yes the multicell coax horns would be great. I was thinking along the lines of a 604 duplex horn or one like you have shown. Those would be ideal.

[Mr. Widget]

The horn could be shortened a bit to give more breathing room for the woofer. Since we are shrinking a design based on horns and bass reflex and the physics of sound isn't shrinking I imagine these would sound pretty... unusual. I would also be concerned about the wall flexing of the 0.18" plywood cabinet. The original is way under braced but that gives it some of it's... character.

Widget

[Cal Weldon]

Originally posted by Mr. Widget
The horn could be shortened a bit to give more breathing room for the woofer.

The horn will be top mounted

[i]I imagine these would sound pretty... unusual. [/B]

Uh ya, I'm athinkin' these are still just for show. Might hook them up in the garage or something

[i]The original is way under braced but that gives it some of it's... character.
Widget [/B]

Character is a very nice way of putting it.

You should hear what they sound like when you update the drivers to some decent PA stuff. The cabinets combined with the cowbells create a sound of their own. Kinda like the wind howling through the trees on a nasty day. Ah well, keeps the girls dancing.

Cal

[Cal Weldon]

I think I would like the scale apply to the inside dimensions. IMHO these should be made from 3/8" or 7/16" - no?

Cal

[Mr. Widget]

By shortening the "horn", I meant the woofer horn as shown here.

As for material thickness, I would use 3/16" birch plywood available at hobby stores it will have the closest look to the original 5/8" plywood.

Widget

[Cal Weldon]

Originally posted by Mr. Widget
By shortening the "horn", I meant the woofer horn as shown here.
Widget

Ah yes, methinks i got it now.

Cal

[Wardsweb]

Here are some A7 mini from Japan