project, 2 pair 412s with 931-12A horns.

[Phil-G]

So thats it in a nutshell. Dual 412 biflexes with a 931-12 horn. By itself a 412 doesn't have a great deal of bass, but a nice midrange. Maybe in tandem they might deepen the lower end. and with the little mantas and light diapragms, i might have a fairly extended top end. the cabinets will be the make or break. well see

[Phil-G]

i guess what i'll end up with, will be something like a 9844.
i'll probably have to adjust the volume a bit for the 412/419s

[GM]

Measured specs of all of the 412s?

TIA,

GM

[gearfreak]

I did the 604s side by side once, but switched back to stacking them. The centers weren't all that far off one way from the other. So the choice of side-by-side is intriguing. Is that a preference?

Whatever the case, I do think I would like the 110? x 60? of the 931.

GM - I was just searching for specs and found someone's measurements:
Altec 412C full range 12" driver Lansing cinema driver


edit:

* Well, maybe not. Looks like the only is mention of all 4 being fs=37hz. However, the writing on the report in the shot says 30hz.

Not much info in any case.

[GM]

Yeah, I got nothing in a search and frankly, can't recall even knowing they existed other than maybe seeing them in a catalog.

Re orientation, the higher the height to width ratio or vice versa sets its primary polar response, so for up close monitoring, horizontally wide to control/minimize its horizontal response and minimize c-t-c spacing of multi-ways and vice versa for further away.

How 'further' depends a lot on [acoustic] XO point/slope Vs distance to the 'sweet spot' Vs how well time/phase aligned they are.

GM

[Phil-G]

Measured specs of all of the 412s?

TIA,

GM

i can't find any specs for a 412/419. Same basket and magnet as the 414 8a. the only thing i can find is, the 414 is about 5 DB louder @ 1 watt than the biflex.

- - - Updated - - -

Yeah, I got nothing in a search and frankly, can't recall even knowing they existed other than maybe seeing them in a catalog.

Re orientation, the higher the height to width ratio or vice versa sets its primary polar response, so for up close monitoring, horizontally wide to control/minimize its horizontal response and minimize c-t-c spacing of multi-ways and vice versa for further away.

How 'further' depends a lot on [acoustic] XO point/slope Vs distance to the 'sweet spot' Vs how well time/phase aligned they are.

GM

in lieu of TS specs and going by my instincts, i think the 9844 cab needs to be about 10% larger and the port

smaller

.
for what it's worth XO wise i just planed to run the 412s full range and bring the horns in somewhat attenuated and somewhere around 4-6000hz

[GM]

OK, that falls in line with the 420's ~2x higher Qts than the 416s. Per this, Fs is quite a bit higher than the 414 and based on its 30 Hz low corner ~confirms the increased Qts: http://greatplainsaudio.com/wp-conte...-8B.420A.1.pdf


Ignoring the 9844's cab alignment and assuming Qts is 2x the 414's 0.21, Vas is ~the same and [Rs] is typical default 0.5 ohm..........


The basic default vented alignment formula I use is Margolis-Small's HP 67/97 & 41C calculator program: AES E-Library ? Personal Calculator Programs for Approximate Vented-Box and Closed-Box Loudspeaker System Design


Vb = 20*Vas*Qts'^3.3


Fb = 0.42*Fs*Qts'^-0.96


Qts' = Qts + any added series resistance [Rs]: HiFi Loudspeaker Design


414 = [20*230.22 L*.22^3.3] = ~31.13 L, Fb = 0.42*30.2*Qts'^-0.96 = ~54.27 Hz


412 = [20*230.22 L*.43^3.3] = ~284.2 L, Fb = 0.42*39*Qts'^-0.96 = ~36.83 Hz


A ~9.13x net Vb increase for just one driver, so now we know why Bi-flex speakers were sealed alignments.


Using basic 'acoustic suspension' math and max flat 0.707 Qtc': HiFi Loudspeaker Design


414 = 24.68 L / 97.05 Hz Fc


412 = 135.16 L / 64.12 Hz Fc


~5.47x larger, so even sealed it may be necessary to either use a lossy [~aperiodic] vent to bleed off excessive Qt or DSP its 'full range' frequency response.


GM

[Earl K]

Here's the original 412a response ( from 1955 ).




oOOps ( the software won't let me link the pic in > big-bro keeps removing it ).

One ( can't see now ) that it was designed as a full-ranger ( the dotted line represents the response when used in a 606 cabinet and placed in a corner ) .


There's also a Japanese response graph to see ( dug up by Katalyst over at AK, and posted within this thread about using a 412 in his M15 project )



Katalysts phone-app measurements also show the 412's true full-range capabilities.




FWIW, I'd be building all of them in separate boxes to be used as a possible MTM stack ( or quasi MTM in a 2.5 sort of configuration ).
- all placed close to room corners to enhance the low-end .

[GM]

http://www.audioheritage.org/photopo...a_fr_1952_.PNG

[Phil-G]

ok
I'm still trying to decipher the help. GM is there at way you could rephrase things in a simpler form. Also a uniform set of abbreviations would be helpful. when i look for a list, i find a random mix of abbreviation styles.