What is the cut off frequency for the Altec A7 and A4 horns?

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#8
The A-7 horn is a 110Hz exponential with a half size mouth according to Brue Edgar and the few FR plots I have shows it unloads at 175Hz. The A800 version with wings unloads around the flare rate based on the simple SPL meter measurements of my DIY variant. Both the 825 and 828 cabs resonate at 55Hz.

WRT the A4, I haven't calculated the flare rate or seen any published specs, but based on the measurements of the mid '50s versions I had and one '80s factory plot I'd say 55Hz with a half size mouth. My cabs resonated at 35Hz which agrees with a much later factory plot, so they appear to have been consistant over the decades.

Since it's > -12dB referenced to the horn, it's a bit of a joke in today's world, though it's quite acceptable if the source is tube driven vinyl. For CDs it's better to either retune them higher and use separate subs or best to seal up the horn's rear chamber and use the cab's excess Vb as a sub with one or more appropriate drivers. The same applies to the A7.

Here's the current forum:
http://www.hostboard.com/cgi-bin/ultimatebb.cgi?ubb=forum&f=3729

Altec Library and a much smaller one: http://www.lansingheritage.org/html/altec/altec.htm

http://hifilit.com./hifilit/Altec/Altec.htm

HTH,

GM
 
#9
Thanks GM, here's a pic

I really appreciate your input there GM.

Here is what I did with the A4 cabinets and some flare horn bass ports [yes flare horn bass ports] on the dual 10 cabinets on top of the A4's. They are the red, green, black and blue items. The flare of the horn on the front is 180 degrees and the horn continues back in the same rdial flare inside the cabinets to act as a catchment area or compression chamber for the port. It goes back to about a 90 degree angle of dispersement and is stopped short of the back of the cabinet by a few inches. I thinks it's a neat idea. Not sure why we don't see it out there commercially. Perhaps not worth the hassle when a straight tube works fine. These ports were no easy build either, day after day of laminating fiberglass


Cal's big speakers

Thanks again for your help
Cal
 
#10
You're welcome!

Can't get them through the front door?! Don't ya'll have building codes that require a decently wide front door to get furnuture through? Mine went through with fractions to spare (after I removed the doors). 😉

So those are the vents, eh? Sharp looking! Did you measure their response? I would think that they would cause excessive peaking around/at Fb, and why it's not done.

Now that you have the construction down pat, time to make some 300Hz radials for the A4s. 😉

GM
 
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