Help with design of this Altec mid bass horn

[atilsley]

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?

[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

[atilsley]

Thanks again GM.

I asked about sq root as I was trying to understand height and width of horn mouth....so I now understand the horn throat is more than just the driver cutout.

My horn's throat, therefore will be smaller, 18cm by 20cm...close to altec standard for driver cut out.

Flare is ' line of best fit' based on 31 inches.

Axial length is 40cm.

Sm is 68cm x 68 cm (26.7 inches 2).

Volume of cabinet 260 liters.

We'll just see how it sounds. Under $80 of materials to experiment with an idea...the cost of having my cake while eating it too...!

I can run some eq and correction for any dips/peaks anyway.

With this type of (115hz) horn, what would your preferred high xover point be, given 511/902 in use?

Kindly

[atilsley]

Testing now....bigger sound presented, but not more punchy...maybe the drivers are just so good on their own? I've not heard an Altec bass horn before...so unsure how to assess.

[atilsley]

OK, I can report that something special has happened...the horns work and sound great!! Back chamber is 60 liters, sealed and damped. Response is much tighter than in the big 620 cabs.


I'm very surprised by the bass depth, especially that these horns are 115Hz cut-off. I suspect I'm getting good bass to 70Hz...I will check this with my test CD.

[Altec Best]

With any DIY cabinets I think measurements are in order ! Otherwise you won't know what you are actually producing with them. Nice Job !

[atilsley]

With any DIY cabinets I think measurements are in order ! Otherwise you won't know what you are actually producing with them. Nice Job !

I concur...a mate and I will be testing on Fri. Stay tuned.

[Alien_Shore]

Great project, Andrew.
So good to see the experimenters diving in and creating something new. Did you model the sealed box that you wound up with, or did you just take a guess at the dims?

[atilsley]

Great project, Andrew.
So good to see the experimenters diving in and creating something new. Did you model the sealed box that you wound up with, or did you just take a guess at the dims?

Thanks...I like trial and error.
I figured the back chamber would be on the large side...so I can always fill up some space inside if necessary. It's well damped also.

[atilsley]

Here's a reading taken from 1m. Bass depth is quite good for the size of the horn...but ragged reading from 400Hz.

The 902/511 is quite flat through to 14,000