Help identifying Altec cabinet/model/plans - diyAudio
Originally Posted by zdw11
Plans begin on pg. 96:
How To Build Speaker Enclosures By Alexix Badmaieff & Don Davis : Free Download, Borrow, and Streaming : Internet Archive
This speaker project is best served on the Altec User's Board [AUB] where there are owners, so see you there!
https://www.hostboard.com/forums/f70...ers-board.html
Correct re drivers, though the original used the superior performing, and fairly rare Lansing 800 Hz 808 multi-cell.
FWIW, yes, a little bit familiar with Altec in general and the 820 in that it was part of my DIY speaker, horn design education, DIYing an [improved] stereo pair of A7-500.
In a 'nutshell', these were designed for 16 ohm high output impedance systems, so unless Great Plains Audio [GPA] can make some ~replicas performance wise, best to use GPA's $ AlNiCo $ 416B series for closest performance, though its ferrite 416-8C can be EQ'd to get the desired response, just not the AlNiCo's 'sweetness'.
The 811 horn is still around used at reasonable prices and recommend the GPA 802-8G drivers that are superior to the originals.
Might can find the original XOs used, though can only recommend the early ones [assuming 16 ohm] as the later ones are just basic 8 ohm 2nd order Butterworth IIRC.
Older 515s make less bass, even 'sweeter' mids/HF, so owning 515Bs, it's what I'd use [or GPA's ~equivalent 515C] and EQ to suit.
It has reflex porting out the back/bottom, venting out the bottom/front.
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Thanks GM!!!
Lots of questions now...
- Any ideas/thoughts/tips on converting those plans to a rectangular prism?
- Would it be smart to calculate the internal volume of the cornerhorn plans and recreate that using the appropriate depth?
- Thoughts on frequency response?
- Would it be a bad idea to swap out the 811 horns for 805 multicells and 288 drivers?
- Any advantage/disadvantage to closing off the HF section from the LF?
Really excited on this!!
You're welcome!
It's a bass reflex, so just maintain the net volume [Vb] for same tuning, though depending on drivers used, may ideally need a different alignment [Vb, Fb].
Cab response wise, it will be rolled off below the LF horn's ~110 Hz/F6 down to Fb, so it depends on tuning as to how much. How flat the horn's BW will depend on the woofer's mids/HF response. Bottom line is that it was typically driven with a low power, high to matching, impedance tube system with variable DF tone controls, so the primary goal was highest practical acoustic efficiency in 'X' box size and make it sound good with EQ whereas nowadays it's all about highest practical power handling in smallest box size, EQ'd to 'taste' and no doubt what the pioneers would have done given today's amp/driver power handling with the downside of never knowing what we missed WRT live recorded music playback.
Bad idea? No, some would consider it a major upgrade, though ideally will need a ~500 Hz XO due to driver/horn spacing unless going to listen from far enough away.
Depends on whether the extra volume is required for the woofers to get the desired tuning.
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Thanks GM.
I've found a few old/dead threads on the 821 corner cab and found this unanswered question. Maybe you could share some wisdom...
"The horn cutoff is said to be 80 Hz. Boundary reinforcement and room gain would contribute at some point. One poster commented on the lack of BR as used in the VOT cabinets. But one photo of an 820 system shows a distributed port exiting into the toe space. Anybody know any science about this? Looks like it might have been meant to be some kind of SOTP resistive loading. That space could be made a ducted port to tune the woofer cavity. What effect would the closeness of the floor have?"
Now, I don't even know what SOTP stands for, but I find the question intriguing. I'm also hesitantly curious/inspired by combining the 820 and 817 cabinet designs in an effort to get closer to 40-50hz; feels like I'm opening a can of worms...
You're welcome!
A correction; I'm so used to rattling off A7 design details........ the 110 Hz/F6 is for a single A7 horn, but the 820 has a ~95 Hz/F6, so for two = ~67 Hz if sealed, so assume the 80 Hz is where they tuned the vent, at least originally.
Another is that it's not a bass reflex [BR], but a ~aperiodic vent designed to blend well in a corner; IOW more like a low Qt sealed than BR, which nowadays is done by using stuffing to resistively damp the vent to 'taste'.
Right, floor loaded ducted port; setting on the floor creates a mirror image, doubling effective vent area [Av], lowering tuning ~0.707x [half octave].
Hmm, since SOTA is 'state of the art', can only assume SOTP is 'state of the past or pioneers'.
Recommend ideally using ~20 Hz woofers for HIFI/HT apps and blend in subs up to ~80 Hz if need be.
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Sorry, I've got a few more questions...
- How are you determining this is an Aperiodic vent vs Bass Reflex?
- Would sealing that port in effect drive the resonance of the box lower, or lead to limitations in the drivers upper frequencies?
- In effect, does adding a port to a speaker cabinet only enable you to tune the cabinet to a higher frequency?
Also, sorry for all these questions, I'm really just trying to get a hold on these different variables. Is there a wiki/sticky that I'm missing which describes these types of interactions?
1. All the holes in the floor panel covered by a dense/thick fiberglass insulation pad Vs a slot of ~equivalent area.
2. Higher, so less [mid] bass.
3. It can tune it higher or lower, but normally only used for the latter.
Most likely, but I came to the forums as an advanced amatuer, so ATM can only think of a few I've referred folks to over the decades:
0Thiele Small parameters equations - How each one affects the others
Read Research - Articles
Basic Car Audio Electronics
Elliott Sound Products - The Audio Pages (Main Index)
Quarter Wavelength Loudspeaker Design - Yahoo Groups
http://www.mfr-eng.com/articles/rpp/
0Resonances of open air columns
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Amazing stuff!!
I was able to get ahold of "bowtie" on AK and he had this to say:
"Early and uncommon theater version of the 821 cabinet, they should be gray.
Asian collectors like to call it 822, i know of no documentation to support that being an actual production model however.
It is more likely that the 820 system/821 cabinet was revised into the corner version we're most familiar with when it was abandoned as a theater model. 820 designates a loaded speaker system. 821 is the empty cabinet.
This is early stuff, and very little documentation existed to begin with, and today genuine documentation is more scarce than the gear itself."
Hmm, just now looked at the other pics; didn't know they had a rectangular theater version, only the corner horn one and even then only seen a chainsawed one, though definitely early as it has the 808 HF horn inserts to extend it.
Since the 821A is the finished corner cab only, it seems reasonable for the rectangular one to be an 822, though never aware of it. Scroll down for the early 820 doc: Altec
As for Altec actually marketing this I can't imagine why since the basic horn was introduced circa '49 as the 800 Vott: 800 VOTT
Then in the mid '50s it was updated a bit with a tapered horn as the A7 for the introduction of the new 811 sectoral horn [1954]: Altec
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
wow, that marketing ad for the 820c claims a guaranteed frequency response of 30-22k...
"..two 15" speakers mounted in Altec direct radiating exponential horn. A modified bass reflex principle combined with the advantages of a corner enclosure add additional depth and beauty to the sound"
Is it possible that the "tuned to 80hz" cabinet from the plans would go that much lower when in a corner placement?
Trying to piece this puzzle together lol maybe I should just build it and find out!
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