Scaled down VOTT

[pizzazz]

Hi Gang!

I am going to take an existing 828 (VOTT)
cabinet and scale it down by 1/3. New
dimensions are 20w 16d 28h. The reduced size
seems to call for a 10 inch woofer.

Am I on the right track? I love the VOTT
design, but the wife will not let me have them in the home, so building a scaled-down
pair will make her happy, but I need to verify the woofer size to cabinet size ratio.

Any help is appreciated.

Mike

[bowtie427ss]

Has the Mrs expressed specifically what turns her off about the full size VOTT?

If it's the overall size, there's not much to be done about that. However, there are ways to make the 828 box more visually pleasing. If it's the unique and open front that offends her, flip them over, mount the horns in the vents, and put grills on them. If it's the lack of natural wood grain, then look into building your own A7 Magnificents.

I don't know a lot about horn theory, but i'm pretty sure that as you scale the A7 down, you're going to raise the bottom cut off frequency of the horn. The end result is not going to perform the same as a full size 828. I suspect this is the reason Altec never produced a box with a horn flare smaller than the 825/828/816 boxes.

The rest of the board will correct me if i'm wrong, but i don't think altec ever horn loaded anything but 15 inch bass drivers.

[pizzazz]

Hi

Thanks so much for the info.
I agree the bottom frequency will be
affected.

The Ms. does not like the size and bland
looks, but my friend can make a pair with the
carcass dove-tailed, using hardwood plywood
the end result truly a work of art.

I simply LOVE the design, and always have
since high school, back in 1970!

I will play around, maybe these would sound
just fine.

Mike

[Old Guy]

I gotta back GM's play here. I think a scaled A7 will be nothing but a novelty. I wouldn't bother.

If you need something small look at the Model 14's that are for sale in another thread. they are going to sound a LOT better than what you plan to do.

There is a fellow building 1/4 scale A7's but they are, as I said, a novelty item.

[dhook17322]

Has your wife experienced A7's performance? The option of upgrading A7's to Magnificents is a very desirable option in terms of appearance and sound quality. A plan B would be to find a pair of Model 19's, smaller but still excellent in performance. Good luck in resolving the problem.

[GM]

Greets!

You should scale it around a specific driver's ~effective piston area (Sd) just as Altec did, so with a 8" x 16" = 128"^2 throat area (St)*2/3 = ~85.33"^2, an odd value, with a typical high efficiency (HE) 12"er's ~78"^2 Sd being closest, so to keep the same 2:1 St aspect ratio equates to ~6.25" x 12.5"; and since 30"w/8" St = 3.75, then the external width = 6.25*3.75 = 23.43" and you can either scale the rest or start with a different size driver.

That said, Mike's right, the horn and cab tuning (Fc, Fb) goes up and since it won't be optimized for the driver's frequency response (Fr), it could perform anywhere from 'entertaining' to can't wait to use it for firewood, but the odds of it sounding like an A7, only more compact, is a 'pipe' dream based on my own scaling attempts.

I've never seen an official Altec 12" loaded horn even though the 414 is an excellent horn driver in its own right, but they knew that dual drivers can be optimized for 'close enough' horn-like performance in a more compact package, so for studio/HIFI apps there wasn't any need for a large/complex build cab like RCA's back loaded horn (BLH).

Much better performing overall IMO is to use dual 414Zs in ~5.2 ft^3 (min) net tuned to whatever works best in-room with the basic dims a function of the component size, so assuming an internally mounted 811 to help with SAF, minimum external dims assuming 3/4" material are 20.25" W x 17.50" D x 34.75" H, which also yields a 'close enough' net cab volume (Vb) after the components and bracing Vbs are deducted.

If component cost is too high, a single 414 will work, but you'll lose the extra performance that makes it ~horn-like, so at this point you're better off overall using a 416 series to keep the XO point relatively low.

GM

[Brek]

Or just buy some Model Nineteens.

[dhook17322]

Actually a pair of Model 19's just popped up on ebay. ALTEC MODEL 19 NINETEEN MONSTER SPEAKERS AWESOME