Yet Another Altec 2-Way

Does anyone out there have the T&S parameters for the Altec 412C?

Here's what I have going on: I have a very nice pair of 412Cs, a pair of 806As, some Faital STH100 horns and some old cabinets (maybe Acousti-craft) that are approximately 5 cubic feet in volume. The cabs are bass-reflex with two Ultra-Flex/Onken-like vents on the fronts--one vent on the top and another on the bottom. The baffle was cut for a 15" woofers, but I'm currently using some 15"->12" adapters in order to install the 412s. Probably not ideal, but it will have to do for now. I have lined the inside of the cabinets with some furniture moving blanket material that I had on hand, using the live-end-dead-end technique. 2" foam on the back panel behind the woofer.

I'm looking for the T&S parameters to help with fine tuning the cabs and in determining a good performing crossover. I've tried running the 412s full range with both 1.5uf and 2.2uf caps, with the 2.2uf cap sounding better to my ears. A quick and dirty frequency sweep with the 412s installed in the cabs shows a response from about 40Hz to 10kHz, which means that there is a lot of overlap between the 412 and 806 with the 2.2uf cap bringing in the 806s at 4.5K. I'm clearly liking what I'm hearing with the 806 going down lower, which makes me wonder if I'd be better off with a 2nd order crossover ala JE Labs, treating the 412 more like a 414.

Any advice would be greatly appreciated.
 

je2a3

Senior Member
Back in the late 90s I started my Altec 2-way with the 419A bi-flex which is the later version of your 412C. It had nasty break up modes in the top end which led me to the 414A. A couple of months ago I was testing a single 412 that I have here and it seemed smoother on top than the 419A but still not good enough for full-range operation (in the context of a 2-way) to my ears.

See if this Altec N1600C XO works in the context of your system and taste. No need for fancy parts at the moment, just use what you have in your parts bin. Look into the N1500 XO supplied with the 604-8G 604E also.

 
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Thanks for the tip there, JE! Looks like a great starting point.

EDIT: I believe the 414A is 16 ohm whereas the 412C is 8 ohm. Can this circuit be easily adjusted for an 8 ohm woofer by simply halving the 1mH inductor and doubling the 16uf cap to the LF driver?
 
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je2a3

Senior Member
Thanks for the tip there, JE! Looks like a great starting point.

EDIT: I believe the 414A is 16 ohm whereas the 412C is 8 ohm. Can this circuit be easily adjusted for an 8 ohm woofer by simply halving the 1mH inductor and doubling the 16uf cap to the LF driver?

The low pass section is a series type XO, I'm not sure if the halving/doubling of values in a typical parallel XO apply. Maybe somebody else more knowledgeable with XO design can chime in.
 
The low pass section is a series type XO, I'm not sure if the halving/doubling of values in a typical parallel XO apply. Maybe somebody else more knowledgeable with XO design can chime in.
I think you double L and half C. So 1mh -->2mh and 16uf -->8uf. You might also want to play with the fixed resistors in the tweeter crossover, dropping them in value a bit.
 
Here is the data i have on my 412c. The first is a frequency sweep in my model 15 cabinets with no crossover. The zip file is an rta file for the dats system. The third file is a screen shot of the dats system.Altec412c dats screen shot.jpg
 

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JE/Gary/Katalyst - thank you a ton for all the info you've provided. There is not much out there on the 412C, so I really appreciate it. Lots to think about and some really great starting points as I try to dial in a decent 2-way with the components I have on hand.
 
Oh, and a quick pic for the group of the cabs I’m working with.
 

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Notice on the impedance curve the bi-flex mechanical crossover. Between 800hz and 1200hz. Ideally you would cross the horn at this point. Then take the woofer out at the 800hz point This is what I meant by "Taming the Bi-flex".
 
Now I will speak blasphemy . You have room for a non Altec horn that I used with a Jbl woofer. You could use the Altec compression driver with these horns.
 

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I looked up the horn you have. Should work nice. The closer you space the centers of the drivers the better they integrate .Could you flip the baffle to put the woofer higher? I ask because you were thinking of mounting the horn on top of the cabinet.
 
Thanks for the AK link, Katalyst. A lot of good stuff in there, and I hadn't yet come across that particular thread even after all the Google searches I've performed for "Altec 412C." I don't think flipping the baffle is an option, at least at this point, I'm afraid. Doing so would mean tearing up the vents and probably doing more damage than I can easily fix right this sec. I know what you mean though--in it's current layout the woofer sits quite low and creates a significant distance between it and the 806a mounted on top.
 
I finally got around to throwing together a initial test crossover for this Altec two-way experiment. It's basically a mishmash of Katalyst's LF network to "tame the 412C" and the HF section of the N-800-F network for the 806A. I added the 30923 attenuation network and a 16 ohm L-pad. Sounds pretty good, but perhaps the midrange has been attenuated a little too much for my tastes. I should add that I've set aside the Faital horns for now and am experimenting with some 811B's (i know, i know). I'm new to crossover design and lack any real tools for measuring the performance of speaker drivers other than an RTA on my iPhone. I'm trying to do this by ear for now, but with that said, any of you crossover gurus care to comment on my thinking regarding this crossover (please ignore the individual values in the L-pad...I couldn't figure out how to change them):

Altec_Crossover_Pic.jpg
 
@mdye

What's the dcr value of those 806's ?
- ( I'm wondering if you have the original 20275 diaphragms or the more modern Altec/GPA replacement ( which has a higher impedance > if I remember correctly ) .

re; Crossover Design Observations:

The 4uF cap ( C2 ) functionally does the same thing as the 30923 circuit ( they both attenuate the midrange of the horn ).

One or the other needs to go >> it's easiest to lose the 30923 circuit .

:)
 
@mdye

Simply disconnect the 13R resistor ( R2 ) . Keep the RC bypass ( 3uF over 16R ) for a bit of HF contouring.

Your horn/driver combo's midrange will be restored ( by as much as 8.5 db at 1350hz ) .

:)
 
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