TA-7331-A here we go...

I did rip all the 1 1/2 's plus some extras with one fence setting
I also have a few jigs to help
I like to be efficient but also like to accurate as possible.
Like this one is for blade height on the half laps
View attachment 35080
And a few.of these to set the fence if needed
View attachment 35081
Nice! I like the scribed line for setting the height in the saw, gives you a nice visual compared to using a square. Making jigs can be really fun, I always like to give them nonsensical nicknames.
 
I made a wee bit of progress yesterday making the frame structures.
I think you could use these to support a car for an oil change when completed, should be plenty strong and non resostant.

View attachment 35238View attachment 35239
Kudos Mr. Ed. I am Johnny come lately on this thread -- just wanted to say that's HiFiTown approved wood! This sort of construction grade "plain pine" with hard flooring grade phenol glue is (relatively) similar to the old ERPI and Lansing builds of lore. Plywood came into use back in the 1930's and WE/ERPI was one of the earliest adopters of it for baffles. The only real change to the product besides age of wood, is the glue, which back in the 30's was hide based. Better for sound but worse for moisture resistance. Also ... on the Rola's -- I have been advising customers to consider these still reasonably priced tone cabinet types allot recently -- they are cheaper to obtain and super cool old world build....I am curious to hear about your results on those -- I wanted to also add, I actually like to run those HV field coils at lower than rated DC volts. They will actually get really loud at only 20 or 30 volts! (I actually test them with a 9V battery sometimes!) The only problem, is that your magnet strength is a little underdamped, and that's not always a bad thing. That's the cool part of of FC -- you can adjust! Cool project, man, keep up the good work.
 

MrEd

Senior Nobody
Thank you for kind words and tips.
I am really excited about this.
Trying to be faithful to the design as much as possible, although I am in self debate right now over how much to vary on the driver mounting and size.
Part of me wants to keep it 12 inch drivers only, but if I do that and later want to try a 15 it's going to be difficult to enlarge the hole and keep it tidy.
If I am lucky these Rola drivers will satisfy.
 
How much resonance does an open baffle like this produce?
I built my U-frames out of 3/4” ply with little bracing. Do I need to rethink that?
 

MrEd

Senior Nobody
How much resonance does an open baffle like this produce?
I built my U-frames out of 3/4” ply with little bracing. Do I need to rethink that?
That's a good question.
I am making assumption here because I don't see any other reason for all the cross bracing frames in the design.
It does have me re thinking my SLOB build. 🤔
 
How much resonance does an open baffle like this produce?
I built my U-frames out of 3/4” ply with little bracing. Do I need to rethink that?
The rigidity in most cabinet designs / builds is a bit over done and overrrated in most of the plans. In our experience, just enough countermeasure to prevent parasitic rattles is good... if not, best. To much bracing and cab's get a little too dead, IMHO. If you look at the classics, like early Altec (the baffles with vertical slats, late 1930s Lansing like the Iconic, etc) -- bracing is minimal, and wood is never thicker than 3/4". Often it's 5/8" in places (I should go check some of the early Altec 6xx / Iconic's to be sure). There *are* exceptions to be sure. If you are building something like a K-Horn or something where the cabinet is tuned.... then yes, make is fairly rigid. Walt liked even thinner plywood for some jobs. like some of his WE 755A cabinets (especially the curved one) -- but that was before we decided OB was consistently the best choice after the 1980s. Always use plywood, MDF sounds kind of nastly at times, and too dead at others (a feature it was touted for, perhaps first embraced by AR or JBL in the 50s).
 
Thank you for kind words and tips.
I am really excited about this.
Trying to be faithful to the design as much as possible, although I am in self debate right now over how much to vary on the driver mounting and size.
Part of me wants to keep it 12 inch drivers only, but if I do that and later want to try a 15 it's going to be difficult to enlarge the hole and keep it tidy.
If I am lucky these Rola drivers will satisfy.
Yes, I hope the Rola's work out. I have one -- at least -- that I was trying to match, then gave up. They came in a couple of different cone types. One version has the odd pointy dust cap, often a feature of early Cinaudigraph. Jensen A12's are pretty good. I am going to one of those, or this Rola a try in a system eventually. 15"'s have a natural advantage, but 18"'s even more so. All of these speakers make very nice lower midrange as well, so it's nice not to choke them down too much. Good luck on this....way cool.
 

MrEd

Senior Nobody
Today I am starting to glue up things..
First I am finishing up the driver mounting boards
It seems to me that these are the reference point for everything else.
I am going to shirk my yardwork for today and see how far down the trail I can get.

20210424_115727.jpg
 

MrEd

Senior Nobody
Creeping along... another day another board.
Our weather forecast is a few days of rain into the weekend , that cuts out any yard work and gives possibility of one box finishing up soon.
20210428_194922.jpg
 
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Interested in how these turn out. I built a pair of MJKing’s H-frames. I didn’t have Alpha 15’s to put in them, so I put my 605b’s in. They make wonderful bass, but I tried them once full range. Sounded like they were in a cave.

The bigger front side will probably make a big difference.
Looking really good!!
 

MrEd

Senior Nobody
I have it playing right now via my phone and a little T amp.
Full range it does have have the cave sound.
From the other room it sound quite natural and pleasant.
I an letting it run for a while and then I will do measurements.
Report to follow...
 

MrEd

Senior Nobody
Below is 1/2 octave smoothing with 85v on the field coil vs 35
The Blue line is 35 volts, brown 85 volts

Screenshot (4).png
 

MrEd

Senior Nobody
Today end result with a first order XO, low pass is two .64 mH which I will call 1.3 mH and a 24uf cap on the top.
The only inductors I have in stash are the .64mH, It sound pretty good running the woofer full range, but I still get the dip around 250 from the room.
At this point 50 volts seems the happy spot for the field coil.
1.3 mh LP 24uf Hp with tweeter.jpg
 
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MrEd

Senior Nobody
Below is a comparison of the TA baffle (red) and the Altec 825 with 416 8a 1/6 octave smoothing
I am not liking the dip in the Rola driver@ 70 hz.
It does have great tone, very crisp, dynamic and easy to listen to. Bass is quite clean and articulate.

825  green  TA 7331 blue.jpg
 
Today end result with a first order XO, low pass is two .64 mH which I will call 1.3 mH and a 24uf cap on the top.
The only inductors I have in stash are the .64mH, It sound pretty good running the woofer full range, but I still get the dip around 250 from the room.
At this point 50 volts seems the happy spot for the field coil.
View attachment 37175
A nice reasonable voltage!
 
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