DIY Altec 2 Way Build ala JELabs - 802/32/414

[doglv]

It is good advice to put the 32 as close to the woofer as possible, but be careful to make sure that the driver clears the woofer! An 802 on that bent horn makes for rather narrow clearance behind the baffle. You have been warned! Measure!

The thing to remember about an autoformer with a resistor across the primary is that it gives you a nice solid termination for the filter network. You calculate the values according to this nice fixed resistor instead of a nominal impedance value which varies with frequency. This is not a "reflected" load. it is a directly connected frequency insensitive load.

Then, the reflected, i.e. transformed, impedance variations of the driver are stepped up to high values by the transformer and have less effect on the filter since they don't change the value of that resistor so much by appearing in parallel with it.

You can basically size the primary resistor to pick the cap values you want to use! High resistor = smaller value caps.


The difference between this and an L-pad is that only one resistor is needed whereas an L Pad or pot has multiple resistors in a voltage divider configuration. An L pad presents a constant resistance to the input whereas a pot does not.

No attenuator is needed here since the autoformer is an attenuator, operating after the filter has done its job.

Werner's crossover looks pretty good, although not exactly free. I don't see the need for the variable termination except perhaps for voicing experiments, but otherwise nice job.

I'd also try with and without any LF zobel. I almost always like things better without.

Thanks Joe… I’ve seen your various autoformer hacks, but can you point to a “real” auto former whether vintage or new or just comment on what you’ve been using?

JE reminded me and It might be helpful to explain one difference between the 15” woofer variants and the 414’s is that the 414’s are running full out up top.

 

[J-ROB]

I have tried a few Triads, Peerless, and those Werner jobs, plus a few other old stock autoformers and two winding transformers.

An autotrans is a single-winding transformer, basically. Some speaker matching units are actual two-winding transformers.

The advantage of Werner's is that they are purpose designed whereas the taps are like 2-4-8-16-32-125-250-500-2000 on commercial units, not much granularity. Werner's have plenty of resolution on the attenuation settings.

Werner units sound far better than any of the vintage units. The Magnequest TL-404 autotrans (also on C core) is also really good sounding but doesn't have the fine steps of the Werrners.

I was tempted to snag some Slagle nickel jobs once I totally figure out my preferred ratios and such, but really I'm totally happy with the Werners. I can't help experimenting though. I gotta stop.

 

[marantzfan]

And the plot thickens...

I’ve got a decent handle on how I’m going to build and attach the face frames now. So the “how to” on cabinet assembly is coming into focus.

I’m not buying any crossover parts yet. I’m really curious to see where this conversation leads.

 

[Roscoe65]

On your 200hz suckout. look at a table of wavelengths of sound and compare to dimensions of interior of cabinet.

If any dimension is 1/4 wave of 200hz, that means that the refection back to the cone will be 1/2 wave or 180 degrees out of phase and cancel.

I just installed a 1" thick rockwool board in my WE 728B equipped "753 cab" to get rid of a narrow 400hz suckout. I put it in at an angle from front to rear so that it will destroy standing waves along the vertical axis as well as front to back, and screw with side to side reflections also. Suckout is gone and it tightened up the sound quite a bit otherwise.

i glued two wood slats to the rockwool for added structural stability.

A 4x2' 1" rockwood board is $12.99 shipped from Amazon Prime. Enough for two speakers.

Pic is sideways. Bottom of cab is where the wire comes out. Rotate in your mind.

View attachment 5316

I’ve unpacked my late (MDF, fixed panels) 614 cabinets to take see if I could convert them to 9849 cabinets. As luck would have it the 414 is centered more in the 614 than the 9849 so no go. However, I did take a closer look at the factory 614 cabinets and made these observations:

1. They are made of 3/4” MDF, with one cross brace on the front and rear panels.
2. They are 24” X 20.5” X 15.25”. The front port is 2” x 7”. There is an inset grill (which I do not have).
3. They are appear to be lined with yellow fiberglass bat (2”?) on all sides.
4. There is a yellow fiberglass bat installed diagonally from the top front to the back rear.

It seems the factory engineers knew What they were doing.

 

[J-ROB]

Those 614s are probably made out of particle board not MDF.

Some say particle board is actually better than MDF thanks to being variable density, less dense in the center of the board than on the outside edges. I don't have any dog in this hunt, preferring plywood with Altecs.

The basic design goes back to the early 30s Lansing Iconic. About a 50 year career.

 

[Roscoe65]

Those 614s are probably made out of particle board not MDF.

Some say particle board is actually better than MDF thanks to being variable density, less dense in the center of the board than on the outside edges. I don't have any dog in this hunt, preferring plywood with Altecs.

The basic design goes back to the early 30s Lansing Iconic. About a 50 year career.

Philosophically I prefer plywood as well, but since these came that way I have no problem. I was actually pointing out that Altec applied the rigid insulation bat trick in their enclosures dating back at least to the 1970's. I'm finding that a lot of classic manufacturers employed a lot of techniques we are employing today.

Aside from Altec 414's, I also own a pair of Goodmans Triaxiom 212's. I would guess they are similar in spec to the Altec 414A, albeit with a whizzer cone and concentric horn tweeter. Of particular note are the enclosure recommendations for the drivers.

• The standard enclosure is 12,500 cubic inches (7.23 cu ft!) with a pretty large port.
• An alternative enclosure is 7,800 cubic inches (4.5 cu ft - pretty ideal for a 414A), using an ARU Acoustic Resistance Unit (10" x 10" aperiodic vent). The appealing aspect of this is that one could swap out baffles on this enclosure and use it for a Goodmans 212 or an Altec 414/32A. It would also make me wonder if the ARU enclosure would also work well for the Altec.
• In all the recommended enclosures, Goodmans recommends hanging 2 felt curtains behind the driver. This seems to be a popular approach among high-efficiency factory speakers of the era (1960's). I know the Diatone 2S-305 used a variation on the back wall (felt that was folded against the back wall https://www.ebay.com/itm/Early-Mode...m=121560521545&_trksid=p2047675.c100005.m1851). I think with light coned, efficiency drivers it is important to control the back wave coming through the cone.

This has also made me think more about open baffle/aperiodic loading. If we mount our removable baffle in a frame a few inches deep, we now have an open baffle speaker. I've also been thinking along similar lines as Joe - we can line the back of this open baffle "enclosure" with a large aperiodic vent, say a piece of 2" absorptive material. This could potentially knock down the back wave enough to make the speaker more manageable in the smaller room while retaining the openness of the speaker. This is not dissimilar to the approach used on my old ESL-57's. They were open dipoles, but the back wave was tempered by felt/coir on the rear of the speaker. Some people take that out. I didn't.

 

[J-ROB]

Altec applied the rigid insulation bat trick in their enclosures dating back at least to the 1970's.

I had a c.1953 618 with a slab of Owens Corning 703 rigid fiberglas across the inside and only a small rectangle of fiberglas on the back panel. That was a very lively box.

The original Lansing cab had "pillows" stuffed with dense filling that extended about 8" out on several sides, getting the damping material out into the central cab space where velocity is higher. I'll look for a pic.

 

[ICTWoody]

Hey guys. Finally picked up my cabinets yesterday from my buddy after we installed the 414's. Pretty excited to get them up and running. But I have a couple of questions...

I am using 8ohm drivers in these... I had the 414-Z's reconed by Bill at GPA at 8ohm so I'd have both 8 and 16 ohm versions (for another project I'll use the 16's in). Both my pairs of 802D's have 8ohm diaphragms.

My question is regarding the networks. I am planning on trying both JE's network, attached, as well as J-Rob style "single 1.5uf cap." In Joe's schematic, it has the values for the 8ohm drivers, but I wanted to be clear if this was when using both an 8ohm woofer and 8ohm CD, or does it just attenuate the CD to match a 16ohm woof? As for the J-Rob style, I'm assuming I need to go 3uf instead of 1.5uf now?

Next question was regarding damping the cabs. I was planning to use 2" thick OC703 equivalent and just placing batts on the back, top, and side. Basically 3 opposing interior faces. This is how altec had done it in my Flemenco's when I opened them up. Any reason this wouldn't be good in the case of the 614 box?

Thanks!

- Woody

 

[TubeHiFiNut]

Hey guys. Finally picked up my cabinets yesterday from my buddy after we installed the 414's. Pretty excited to get them up and running. But I have a couple of questions...

I am using 8ohm drivers in these... I had the 414-Z's reconed by Bill at GPA at 8ohm so I'd have both 8 and 16 ohm versions (for another project I'll use the 16's in). Both my pairs of 802D's have 8ohm diaphragms.

My question is regarding the networks. I am planning on trying both JE's network, attached, as well as J-Rob style "single 1.5uf cap." In Joe's schematic, it has the values for the 8ohm drivers, but I wanted to be clear if this was when using both an 8ohm woofer and 8ohm CD, or does it just attenuate the CD to match a 16ohm woof? As for the J-Rob style, I'm assuming I need to go 3uf instead of 1.5uf now?

Next question was regarding damping the cabs. I was planning to use 2" thick OC703 equivalent and just placing batts on the back, top, and side. Basically 3 opposing interior faces. This is how altec had done it in my Flemenco's when I opened them up. Any reason this wouldn't be good in the case of the 614 box?

Thanks!

- Woody

View attachment 6533 View attachment 6534 View attachment 6535 View attachment 6536 View attachment 6537

Nice cabinets, Woody!

 

[Redboy]

Aw dang... those cabinets are perfect!! I want a pair.

Real nice, Woody!

 

[marantzfan]

Hey guys. Finally picked up my cabinets yesterday from my buddy after we installed the 414's. Pretty excited to get them up and running. But I have a couple of questions...

I am using 8ohm drivers in these... I had the 414-Z's reconed by Bill at GPA at 8ohm so I'd have both 8 and 16 ohm versions (for another project I'll use the 16's in). Both my pairs of 802D's have 8ohm diaphragms.

My question is regarding the networks. I am planning on trying both JE's network, attached, as well as J-Rob style "single 1.5uf cap." In Joe's schematic, it has the values for the 8ohm drivers, but I wanted to be clear if this was when using both an 8ohm woofer and 8ohm CD, or does it just attenuate the CD to match a 16ohm woof? As for the J-Rob style, I'm assuming I need to go 3uf instead of 1.5uf now?

Next question was regarding damping the cabs. I was planning to use 2" thick OC703 equivalent and just placing batts on the back, top, and side. Basically 3 opposing interior faces. This is how altec had done it in my Flemenco's when I opened them up. Any reason this wouldn't be good in the case of the 614 box?

Thanks!

- Woody

View attachment 6533 View attachment 6534 View attachment 6535 View attachment 6536 View attachment 6537

Those looks great!

Your plan for the insulation is exactly what I’m going to be doing, except that I’ll be using denim instead of OC703.

Man, I’m falling behind here.

 

[ICTWoody]

Those looks great!

Your plan for the insulation is exactly what I’m going to be doing, except that I’ll be using denim instead of OC703.

Man, I’m falling behind here.

I took the fiberglass and cut it all down on the table saw. It cuts so nice. Need to order up some Duelund wire and some binding posts and stuff. And sort out the network options.

I reviewed the box damping thread and just went LEDE on the batting. Should be good.

Here’s some pics.

- Woody

 

[Salectric]

Very nice cabinets! What impresses me most is the perfect cutout for the port. Did you make a jig for a router perhaps? My ports are cut with a handheld jig saw, then sanded to smooth and straighten the cuts, but they still look pretty awful compared to yours.

 

[ICTWoody]

Very nice cabinets! What impresses me most is the perfect cutout for the port. Did you make a jig for a router perhaps? My ports are cut with a handheld jig saw, then sanded to smooth and straighten the cuts, but they still look pretty awful compared to yours.

I'll be honest... I have no clue how he went about cutting the ports. He's a finish carpenter with his own company and is really good at it. As far as I'm concerned it was just some sort of magic.

- Woody

 

[TubeHiFiNut]

As Arthur C Clarke said, "Any sufficiently advanced technology is indistinguishable from magic."

 

[je2a3]

@ICTWoody

Those 614 cabs look great! Cool MCM stuff in the background too. Is that your loft?

Don't worry too much about textbook capacitor values. In my mono system I'm using a 1uf PIO cap (ala J-Rob) + L-pad with the 32A/802 (8 ohm 'fram) sitting on top of a Heath AS10 cabinet (Jensen 10PF woofer, exploring other 10" options at the moment).



The small value PIO cap gives a very gentle slope which exploits the full range capability of the low frequency driver and the horn/driver is there to mainly supplement the upper harmonics. Thus a midrange capable and smooth sounding driver like the alnico 414 is a requirement.

Your damping arrangement looks very nice.

Enjoy!

 

[ICTWoody]

@ICTWoody

Those 614 cabs look great! Cool MCM stuff in the background too. Is that your loft?

Your damping arrangement looks very nice.

@je2a3

It is my loft. Thanks for the compliments. It's a huge luxury to have all the space to play with speakers!

So just to simplify for my simple mind...

If I want to go J-Rob style (planning on building both on boards and then A/B-ing for fun.) With both 8ohm 414's and 8ohm 802D's what cap value should I use? I bought a bunch of GE and NOS Russian PIO caps. I have 1.5's... but I could put them in parallel if I'm needing to have 3uf there.

And I wasn't sure if in your crossover I needed to double the cap values for the 8ohm driver(s) if it was assuming a 16ohm woofer, or if that was for 8ohm drivers both high and low.

Sorry if I'm a little slow on the uptake on the circuit stuff... aesthetics are much more my area than electronics. :-)

- Woody

 

[je2a3]

Not a problem @ICTWoody, very nice loft!

I was encouraging you to experiment and not worry about the complexities of impedances and textbook XO calculator values. Since you already have the proper ingredients - 614, 414, 802 & 32 - you are just seasoning the recipe to taste.

Start with a 1.5uf + an 8 or 16 ohm variable L-Pad (for fine tuning the efficiency of the compression driver/horn to the 414). If you find the sound too smooth or putting you to sleep even with the L-Pad at max, go to a 2uf or 3uf. You might find that as the uf value goes up, the sound will become crisper or even harsher.

OTOH, if you already have the parts for my published XO, build it as-is and get familiar with the sound. Then proceed as above with the simpler J-Rob approach for a different flavor. I spent one whole afternoon with Joe a week ago and see why he prefers the simpler XO to mine (with HF/EQ boost).

BTW, it would be handy to have a smart phone RTA app. I use Octave RTA + the audio generator (for pink noise) from Audio Tools on my iPhone. This will give you a visual clue of what's happening as you experiment with capacitance values and settings on the L-pad.

 

[ICTWoody]

Not a problem @ICTWoody, very nice loft!

I was encouraging you to experiment. Start with a 1.5uf + an 8 or 16 ohm variable L-Pad (for fine tuning the efficiency of the compression driver/horn to the 414). If you find the sound too smooth or putting you to sleep even with the L-Pad at max, go to a 2uf or 3uf. You might find that as the uf value goes up, the sound will become crisper or even harsher. Since you have the proper ingredients - 614, 414, 802 & 32 - just season to taste.

That makes sense to me.

What about the network schematic of yours I reposted above? Do I just go 2uf and 8uf since I'm running the 8ohm 802D?

- Woody

 

[je2a3]

That makes sense to me.

What about the network schematic of yours I reposted above? Do I just go 2uf and 8uf since I'm running the 8ohm 802D?

- Woody

Yup, you got it! But again, the 16 ohm values might also give a smoother sound with your 8 ohm diaphragms.