Help with design of this Altec mid bass horn

[GM]

Thanks gm, I don't understand fully the first para. (btw, I'm using 902's.)

On para two, what is Sm?

I have fixed axial length, but no limit on size on mouth. Hence q re what lowest bass hz can I get depending on choice of flare....

Kindly

I don't know how to explain it any simpler other than you looking at the 210's drawing showing its expansion over 'x' increments.

Sm = mouth area.

St = throat.

You're making a hybrid, hence don't know what the expansion rate the sections actually break down to without you working it out, so could only hazard a guess based on Sm, which I don't know that either.

Anyway, I see you've made them, so now moot.

GM

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GM, could you pls clarify how 128 sq inch throat is worked out. The sq root of 128 is 11.3 inches. When looking at A7 and other cabinets, the driver cut-out is around 8 inches by similar....hence my 18cm x 20cm actual.

Do you count the total area at the begining of the horn (including driver cutout) as the throat?

What does SQRT of 128" have to do with anything?

The 'standard' truncated Altec horn has a St = 8" x 16" = 128"^2/driver, which is approximately the driver's Sd. Remember, a truncated horn is nothing more than a section 'sliced' out of a full size one.

The cutout OTOH is the low pass filter that blocks off a portion of the driver's forward radiation, creating a low pass filter chamber, which ideally increases in net Vb, i.e. a smaller opening with increasing XO point as clearly shown in this early A7-8 [825 cab] for an 800 Hz XO point [fig. 5], which was replaced pretty quick with a HF horn baffle as a better overall performing solution: http://www.lansingheritage.org/image...ign/page04.jpg http://www.lansingheritage.org/image...ome/page09.jpg

GM