816 advice please

**kieran casey** · February 16th, 2009, 04:38 PM

Hi all you good people, I'm new to your site and although a lot of the technology and some terminology goes over my head I feel that you put good sound first and foremost.

Now I hope I'm doing this right but I would like some advice.

I got bitten by the altec bug after a visit to the repair man with, what I realise now, a substandard tube amp. He has homemade 816s with big tractic horns and tiny tweeters and it all plays effortlessy and wonderful. So I'm going to make some for myself.

I can get a pair of altec 3156s and my question is, would this be a bad idea? I know that 515 Gs are what most would recommend and with some patience I could find a pair.
But are the 3156s totally ruled out?
For the horns my friend the repairman suggests 288-16G. The crossover talk goes above my head and thats all in his hands. Happily I'm saved from venturing further into the hifi male-cow-excrement swamp and looking forward to real music listening.

Yours
Kieran C

Oh yes, one more question, what is the radius on the curved walls of the 816 opening?

**bowtie427ss** · February 16th, 2009, 04:56 PM

Oh yes, one more question, what is the radius on the curved walls of the 816 opening?

I made mine with the same 30-31/32 inch radius as the 828 and 817 flares. I've never seen a drawing that was fully dimensioned for the 816, so i don't know if this is right or wrong, but it worked for me.

**Old Guy** · February 16th, 2009, 08:37 PM

AN11 is here: CPC Production Services - Altec Lansing

And says yer right....

**Audio_by_Goodwill** · February 16th, 2009, 10:11 PM

Originally Posted by bowtie427ss

I made mine with the same 30-31/32 inch radius as the 828 and 817 flares. I've never seen a drawing that was fully dimensioned for the 816, so i don't know if this is right or wrong, but it worked for me.

I've never seriously considered building any, so I never paid much attention to that aspect of the plans..... from what I've read on horns they're conical, parabolic, hyperbolic, or quadratic. I didn't know Altec used a simple radius, which I assume approximates a section of a parabola. I just looked at the plans for the 825, and sure enough it's 30& 31/32..... seems like kind of an odd measurement to me. The sheet for the 211 doesn't specify at all, and the 815 plans don't give a radius, but rather a width every 4 inches. Unfortunetly, I don't seem to have 816 plans...... lost them during a hard drive mishap about 2 months ago :-(

**bfish** · February 16th, 2009, 10:53 PM

Originally Posted by Audio_by_Goodwill

... from what I've read on horns they're conical, parabolic, hyperbolic, or quadratic...

...or exponential, which is what most pre-MR Altecs were at least an approximation of. Expos exhibit a doubling of cross section area at regular intervals of length, the "speed" of which is determined by the flare rate. Since both 828s and 816s share the same horn flares, but have different CSAs due to differing "flat" sides (parallel vs non), either one or both may not be "true" expos.

Still, it stands to reason that a radius could be exponential, depending on the radius' dimensions and the flare rate.

Disclaimer; consider this explanation comes from a guy that told his algebra teacher no one cared what x equaled...

**Audio_by_Goodwill** · February 17th, 2009, 12:30 AM

Originally Posted by bfish

...or exponential....

THAT's the one I couldn't think of...... I knew there should have been 4 before I threw on the more modern quadratic!

which is what most pre-MR Altecs were at least an approximation of. Expos exhibit a doubling of cross section area at regular intervals of length, the "speed" of which is determined by the flare rate. Since both 828s and 816s share the same horn flares, but have different CSAs due to differing "flat" sides (parallel vs non), either one or both may not be "true" expos.

One of theses days I hope to understand horns well enough to build one...... classical horn theory any way. I always knew the horizontal (when looking at something like an 825) was important, but what about the vertical..... which is of course needed to have an area.

Still, it stands to reason that a radius could be exponential, depending on the radius' dimensions and the flare rate.

My thoughts, having had some higher math, is that a constant radius is probably a good approximation over a limited distance....... for example, if you look at a small enough piece of a curve it can be approximated as a straight line.

Disclaimer; consider this explanation comes from a guy that told his algebra teacher no one cared what x equaled...

That could have been the result of several things...... Firstly, being the way math is taught.... too abstract...... or more recently too application based (called integrated math). There really needs to be a balance. Secondly, not all teachers are created equal. Thirdly, I suspect you felt there were fish to be caught, and time was wasting :-)

**valhallax** · February 17th, 2009, 12:46 AM

forgot to add..my 816's are loaded with 418-8h mi speakers

**bfish** · February 17th, 2009, 08:00 PM

Originally Posted by Audio_by_Goodwill

... Thirdly, I suspect you felt there were fish to be caught, and time was wasting :-)

Bullseye! Only back then they wore skirts.

(Although there was some similarity if you didn't wash your hands...)

GM · February 17th, 2009, 10:36 AM

Originally Posted by bfish

Since both 828s and 816s share the same horn flares, but have different CSAs due to differing "flat" sides (parallel vs non), either one or both may not be "true" expos.

Still, it stands to reason that a radius could be exponential, depending on the radius' dimensions and the flare rate.

Right, over short distances it can be closely approximated with just a constant radius or even a series of straight sections, though working out the optimum bend points requires a bit more horn design knowledge, so the 825/828 are half size ~55 Hz exponential (flare factor ('T', aka 'M') = 1)/~110 Hz actual, IOW it's a section sliced out of a larger, longer expo horn. Since the 816 has the same throat area, axial length and side wall radius terminating into a smaller mouth it will have a T = < 1 or moving towards hyperbolic (T = 0.5), so we tend to call any flare between the two a hypex, then define it by its flare factor T (M).

I've never bothered to work out any of the parallel wall horn's flare factors or seen them published, so all I can say about the lot is that I highly recommend going to the extra effort of cloning an 825/828 horn for HIFI/HT apps due to its much smoother response, especially when wings are used, and adding its slanted bottom plate to the dual driver designs. Note that if wings are used in the home that bass traps are normally required behind them due to the cavity resonances that occur in a typical room.

GM

**valhallax** · February 16th, 2009, 11:18 PM

i just set a sound guy up with some 828's loaded with 3156's... they rock! if you put your hand on the cab, it feels like its going to expload. lots of pressure. but the 816 has less volume and much smaller venting, of course. probably not the best driver but they work. if you look up the 3156 in the search area of this forumn you'll see thats was originally used as a br cabinet woofer. as to the actually why it might work in a mildly horn loaded cabinet, ill leave for someone else to explain