Altec 828 horn flare without a rear enclosure

[GM]

The original 828 had a little over an inch above and below the driver. With the 414, does it make sense to offset the placement either lower or higher, rather than place at the centre of the mouth, cause now we have ~3" on top and the bottom.

No, not really as it unevenly shifts the higher frequencies relative to the horn's natural HF downward tilt.


Anyway, seems like you'd want to build it 'stock' to fit 15"/16" and make an adapter to mount 12" with standard rear mount cutout.


GM



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Hmm, with a 8x17" box area, the other dimension is much too small even after factoring in the driver's bulk, so what's the game plan? An oversize box filled with scrap/whatever?


GM

[jocelys1]

The mounting baffle is two sheets of 0.5in. The second is removable if I decide to try a 416/515. So the Vol is around 1.5C.ft to accomodate both. Here's a pic. Hope it makes sense ?

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Hmm, with a 8x17" box area, the other dimension is much too small even after factoring in the driver's bulk, so what's the game plan? An oversize box filled with scrap/whatever?[/COLOR]


GM

The box size is 17*17.2*8.5 (internal). You mean, with the drivers bulk the 1.5C.ft would be too small for 416/515, but ok for the 414. Back to the drawing board I guess - if designed for the 416, too big for the 414....aaaaarrrggh !

The front baffle cutout is 100Sq.in - 8in Width | 12.25 (Height) . That size would be too big for the 414. Would 8 x 8in opening be right for the 414 (0.75x of cone area)

What should I do ?

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[jocelys1]

View from the front and side

[GM]

Got a new calculator that's supposed to be my old one's replacement, so wasn't watching the display as I punched in the numbers and tired enough to not question it's answer at the time. Seems I can't input a lot of stuff the same way..........


Anyway, need to add + 0.30 ft^3 net for the 515 and whatever is required for bracing to the 1.5 ft^3 net, then add little sterile sand, rice, etc., bags/whatever that won't vibrate to reduce net Vb by 0.30 - 0.17 = 0.13 ft^3 for the 414. You might even consider making it somewhat larger [~2 ft^3] to be able to fine it if you want to try questionable recones, other brand/models.


??? The horn throat is 8" x 16" = 128"^2, same as the driver's [Sd]; the low pass filter [driver cutout] IIRC is ~99"^2, ergo 128/99 = 1.293:1 compression ratio [CR] and since the 414's [Sd] is only 78.54"^2, it gets a full cutout as I previously noted. It's this discrepancy that theoretically, and in a HR sim, implies a somewhat substandard performance re the 416/515.


GM

[jocelys1]

Anyway, need to add + 0.30 ft^3 net for the 515 and whatever is required for bracing to the 1.5 ft^3 net, then add little sterile sand, rice, etc., bags/whatever that won't vibrate to reduce net Vb by 0.30 - 0.17 = 0.13 ft^3 for the 414. You might even consider making it somewhat larger [~2 ft^3] to be able to fine it if you want to try questionable recones, other brand/models.

Great stuff Greg, thanks. The numbers match what I was working with. Didn't figure the CR though.

??? The horn throat is 8" x 16" = 128"^2, same as the driver's [Sd]; the low pass filter [driver cutout] IIRC is ~99"^2, ergo 128/99 = 1.293:1 compression ratio [CR] and since the 414's [Sd] is only 78.54"^2, it gets a full cutout as I previously noted. It's this discrepancy that theoretically, and in a HR sim, implies a somewhat substandard performance re the 416/515.

Didn't get this bit about the "full cutout". Did you mean ~ same as the 416/515 opening ?

The 414 is a good mid range driver. With an Sd of roughly 78.54 (414 driver) and throat area of 128^2 (original 828), what can we change to improve performance.
Except the low pass filter (cutout), the rest of the design is more or less fixed.

[GM]

You're welcome!

??? A full cutout for the 414 in its baffle adapter; how else do you plan to mount it in the 416/515 opening?

What I posted earlier, a longer horn to a smaller throat, LP filter, compression chamber.

GM

[jocelys1]

A full cutout for the 414 in its baffle adapter; how else do you plan to mount it in the 416/515 opening? [/FONT][/COLOR][/FONT][/COLOR][COLOR=#222222][FONT=arial][COLOR=#111111][FONT=georgia]

GM, I got it now. From what I understand - make the cutout as large as possible to accomodate the 414 on the 828 mouth. I'll draw up something with the 414, showing a 'possible' cutout with the 828 design.

What I posted earlier, a longer horn to a smaller throat, LP filter, compression chamber.

Understood. There's NO FREE LUNCH.

[GM]

Huh?!

Very few in audio, that's for sure! We're almost always 'robbing Peter to pay Paul', i.e. Hoffman's Iron Law as it applies to audio: TA Speaker Topics: Loudspeaker Design Tradeoffs

GM

[jocelys1]

Here's where we're at. The 414 cutout has a radius till a little past the centre of the surround.