Altec 828 horn flare without a rear enclosure

[jocelys1]

A 1.5 C.ft cabinet is doable. The enclosure size is 18x18x11 (External Dimensions)

Couple of questions - the top and bottom panels are parallel and I'm now thinking of using a pair of NOS 414-16b instead of the 515 /416, just cause they are original and the others are GPA kits.

I've read somewhere that keeping the panels parallel causes reflections that can affect sound quality.

What do you think ? Are either of these likely to cause problems ?

[GM]

The 825/828 horn has NO parallel panels, just the compromised original 810 and much later 816, 817.

Yes, I've periodically posted about my trials n' tribulations with trying to negate the 210/211's parallel sides with only so-so success in a HIFI app, but for prosound it's not much of an issue due to venue size, ambient noise 'floor' and acoustically long listening distances; so if a HIFI/HT app, definitely build the 825/828 horn and preferably both flat panels at an angle to make the horn symmetrical unless you plan to set them on the floor or above ear level in which case the original flare is a better choice, with floor mounting in the inverted position same as the Magnificent.

Folks so often ignore that these horns normally have a tilted down acoustic center in the XO BW designed for stage mounting, so the HF horn should be tilted down in most HIFI/HT apps since they are typically ~near field.

GM

- - - Updated - - -

now thinking of using a pair of NOS 414-16b instead of the 515 /416

The horn throat is much too big for the 414, so what little BW the horn actually loads will be cut a full octave according to HR, ergo the rear chamber needs to be reduced by a factor of 4 = 0.375 ft^3.

GM

[jocelys1]

Oh boy.....The Torture never stops - FZ

Thanks GM.

[GM]

Yep, horn design is like a race car's fully articulated, adjustable, independent suspension, so lots of ways to screw it up, but get it right for the track/app it's intended for and the performance blows you away.

GM

[jocelys1]

The cone area of a 414 is ~ 83 Sq.in and the 416 is ~ 128 Sq.in.

Which of these would need to change for a 414 design ?

[GM]

These driver's effective piston area [Sd] are but a small fraction of your numbers, so curious how you calculated them?

Both, 99" is the low pass filter [Lpf] and the 128" is the throat [St].

Regardless, this won't make the otherwise same length and mouth area [Sm] play down to the same tuning; this will require it to be either much longer [~48"] or have different driver specs, i.e. keep the same 1.5 ft^3 compression chamber and trade 6 dB of efficiency [SPL] for bandwidth [BW] by adding 8 ohms of series resistance to flatten the response.

GM

[jocelys1]

Thanks again GM.

The SD was calculated from the drivers I have, mid-surround-edge to the same on the other side, taken as the effective Dia. Is this incorrect ?

Regardless, this won't make the otherwise same length and mouth area [Sm] play down to the same tuning; this will require it to be either much longer [~48"] or have different driver specs, i.e. keep the same 1.5 ft^3 compression chamber and trade 6 dB of efficiency [SPL] for bandwidth [BW] by adding 8 ohms of series resistance to flatten the response.

GM

Could you explain this please. Didn't quite get it.

[GM]

You're welcome!

As a general rule, yes, though accordian surrounds are a little further out, but your numbers are still way off and doesn't appear to be a metric/imperial conversion error, so to make sure we're 'on the same page':

Sd = pi*radius^2

Sd = pi*diameter^2/4

Regardless, Altec acoustically measured their drivers and listed them embedded in the [Vd] volume displacement spec in inches^3, so divide this by the [Xmax] one way linear excursion to find [Sd] in inches^2, then if you want the effective diameter = 2*[Sd/pi]^0.5 to see where it lines up on the surround.

GM


- - - Updated - - -

Could you explain this please. Didn't quite get it.

Hmm, not sure what you're wanting; I mean either the horn must be longer or some form of EQ will need to be applied and this historically has been by driving it with a matching impedance.

GM

[jocelys1]

You're welcome!

As a general rule, yes, though accordian surrounds are a little further out, but your numbers are still way off and doesn't appear to be a metric/imperial conversion error, so to make sure we're 'on the same page':


Sd = pi*radius^2

Sd = pi*diameter^2/4

Regardless, Altec acoustically measured their drivers and listed them embedded in the [Vd] volume displacement spec in inches^3, so divide this by the [Xmax] one way linear excursion to find [Sd] in inches^2, then if you want the effective diameter = 2*[Sd/pi]^0.5 to see where it lines up on the surround.

GM

Yes, I didn't consider Xmax. Was a straight Sd = pi*diameter^2/4.

For the [email protected]

pi*10.25^2/4 = 83 Sq.in

(The mistake was considering 10.75" as the Dia and GOD knows how I got the earlier numbers)

Hmm, not sure what you're wanting; I mean either the horn must be longer or some form of EQ will need to be applied and this historically has been by driving it with a matching impedance.

GM

Understood. Now I know where the 48" and 8ohm resistor came from. Thanks.

Don't want to reinvent anything. I can trade a little SPL | BW keeping the enclosure to 1.5 C.ft.

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.

The original 828 opening has a radius of 13.25". Any changes to the driver opening for the 414 - width /height ?

[jocelys1]

Here's a prelim look at the design. Any changes that you'd suggest ?

- the 8" deep gives a volume of 1.5 C.ft
- the 414 cone area is taken a little past centre of pleated surround (without Xmax)
- the dist above and below the driver can be changed