Yet another Planar Magnetic Line Source, the SMAPPP

[WrineX]

Technology Connections just released a video about battery testers on Duracell. but it displays nicely , what i meant with wider foil traces in the strong magnetic field and thinner ones in the weaker field on top of the magnet if you want it to move equal, i know you know this works like this but i though its fun to see it 🙂 now this is about heat, but in our case the wider part is fed by the small part resulting in less magetic field compares to its size/surface area.

 

[solhaga]

Yes, it is the Lorentz' force vector product that has to be the same.
I did this with my ribbon speakers back in the days.

And for the tweeter membrane for SMAPPP a month ago:

The darker blue area is the conductive aluminium foil, the white areas in the middle are the non-conductive aluminium foils.

So perhaps I should revisit this configuration then?

 

[WrineX]

The darker blue area is the conductive aluminium foil, the white areas in the middle are the non-conductive aluminium foils.

i dont know the magnet motor of these. but i guess magnets are like a planar magnetic ? not like a ribbon (magnets only on the sides) since then it would be reversed (field would be stronger near magnets on the side, hence wider foil to tame them) i always had trouble thinking about it since the first thing i would think is thinner traces is less output (since they can handle less power). but the wider traces are fed by the thinner ones. so they can never exceed the thin traces.. it feels counter intuitive 🙂 but the wider ones have the same power as the thinnest traces in the circuit. but spread over a wider area. hence lower output.

we might had the same thoughts in your drawing but t depends on the magnet motor used 🙂

 

[solhaga]

Here's a top view of the motor and other stuff:

Dark blue squares are the magnets. The conductive traces are 3 mm wide in between each magnet column.
As you can see, it is a push-pull configuration.

When it comes to the counter intuitive, you must remember that it is the current and magnetic field densities whose vectors' cross products that make the Lorentz' force. Even if the current is the same throughout the aluminium strips, the current density depends on the traces' widths.
So if a thinner strip, that then has a higher current density, is in a lower magnetic field density, the Lorentz' force on that strip can be the same as for a wider strip, with then a lower current density, in a stronger magnetic field density.

 

[WrineX]

`yes so we talk about the same outcome 🙂 and i would say small traces in the middle of the gap (smaller then the actual gap) is nice for output like B&G, i think less for even freq response or distortion. looks to be a trade off. by the way nice drawing , makes it really clear !

by counter intuitive i mean it does for me 🙂 it makes sense after all. but at first glans you or at least i though what ?

 

[solhaga]

I thought so, but just to be crystal clear.
The drawing is actually one view of the SMAPPP in Fusion.

To me, low distortion levels are paramount; at the least -60dBr.
SMAPPP now has to be at par or better than:

This is SOB, Solhaga's Open Baffles (Swedish site, but you can always look at the pictures.). They have SB17CAC35 as mids and SB26CDC as tweeters with one tweeter firing back.
I've printed the waveguides from Soma Sonus.

They have distortion level sub -60dB; they are now my references.

Yes, I also always have to think twice about the widths.

 

[solhaga]

Some measurements on a 12µm PET membrane. The aluminium foil is the same; 7µm

I have now seperated the mid and tweeter membrane and reinstated the conductors outside the magnet column.
They are not return leads.

The mid membrane now has five traces and the tweeter three:

The traces have no direct coupling to any hole in the panel, but helps move the membrane as a whole.
For the tweeter, they also increase the compliance as they are in the foam surround.

I've simulated the placement of these traces and concluded that the best positions that gives the least variation of the force on the traces are where they would have been if there were more magnet columns.

External cables closes the circuits.

To keep the corrugations I've added narrow 60µm aluminium tape on the outer edges of the membranes.
I also added 60µm aluminium tape to the mid membrane's middle part. A somewhat rude measure, I must come up with something better.

I have earlier concluded that the mid membrane measure a lot better with as much non driven aluminium as possible, see non driven alu legend above,
but I have yet to compare it for the tweeter membrane.


Mid SPL 1W 1m:

Distortion 1W 0,2m:

The relative high distortion between 300 and 400 Hz is probably because of the hefty middle 60µm aluminium.

Tweeter SPL 1W 1m, without non driven alu in red:

Distortion 1W 0,3m, without non driven alu in red:

Same conclusion as for the mid membrane.
Something to improve is to have 0.5mm between the aluminium parts instead of 1mm.

2HD and 3HD or the tweeter with non driven aluminium:

 

[solhaga]

So here's BOPP (20µm) with 0.5mm spacings.

I've also tried to spray paint the mid membrane.
Not much difference in SPL but lower distortion from 300Hz.
Here are more HD distortion for that one:

For the tweeter it looked a lot worse, so I tried 3mm aluminium tape on the edges to get better corrugation:

And that helped, at least from 3kHz (with tape is purple):

More HDs for the tweeter with tape:

I will now test the 12µm PEN with 0.5mm spacings.

 

[WrineX]

Hmm seems 0.5mm and 1mm is a rather huge difference when talking non driven mylar or other type of backing !

 

[solhaga]

Yes, for BOPP it's -60dB from 400Hz (red) compared to -65dB from 300Hz for 0.5mm painted black (teal):

For the spray painted membrane I took a run of the mill spray paint, the same I've used to paint the speaker's front.
I only sprayed one layer.

But perhaps I can use a more suitable kind of for example spray able varnish or coating to stiffen the membrane.

Any suggestions?

 

[solhaga]

12µm PEN with 0.5mm spacing, the same membrane designs as above.

Mid:
Plain corrugated membrane (red),
Spray painted membrane (blue),
2 mm copper on the edges (green) and
Multiple layers of spray paint (brown).

SPL:

Distortion:

Also with PEN, the spray painted membrane (blue) is the winner with usable SPL and low distortion from 300Hz; -65dB (0.06%) is okay don't you think?
I noticed that for that membrane, the SPL is down at 4kHz and the distortion is up.
It is worth investigating further even if the mid's range from 300Hz to 3000Hz.
I also reckon that multiple sprayed membrane just got to much paint in the pleats or it partially dissolved the PEN.

Tweeter:
Plain corrugated membrane (green),
Spray painted membrane (orange),
2 mm copper on the edges (blue) and
Plain corrugated membrane again (teal).

SPL:

Distortion:

For the PEN tweeter membrane it's the plain corrugated that is the best; around -65dB from 2kHz and up with as low as -70dB around 10kHz.
I did two sets of measurements of that membrane, the last one after having removed the copper tape.

To summarize this:
For the mid it's spray painted BOPP and for the tweeter it's plain PEN.

Mid best BOPP vs PEN:

Distortion:

Tweeter best BOPP vs PEN:

Distortion:

So with that settled (please tell me if I'm wrong!), I can finally get out of this rabbit hole.

But it comes with a huge downside; the resistance for full lenght membranes will be too high.
I'll have to have two tweeter membranes in parallel and three mid membranes in parallel.
I then have to design retainers where the intermediate membrane ends can be connected.

 

[solhaga]

I'd be damned if I do and I'd be damned if I don't.
Let's look at possible combinations of the five and tree traces of the mid and tweeter membrane aluminium traces instead of having multiple membranes in parallel.

For the mid membrane I can then let the inner traces be in series and the outer in another series.
That will give 13.2Ω and 8.8Ω respectively. Those two circuits are then coupled in parallel, that gives 5.3Ω.
The current for the outer traces will then be 50% higher than for the inner traces.
But the magnetic field density is lower there, so it should all even up.

Comparison between ordinary mid (red) and as described above (blue), both are sprayed black paint:

Not much differences, so the new configuration will be the final membrane.

I did almost the same for the tweeter. The outer traces are in parallel (2.2Ω) and in series with the inner (4Ω).
That gives 6.6Ω for a full length membrane. So this time the current in the outer traces are lower than the in the inner.
Normal tweeter in blue, 6.6Ω in green.

So the overall distortion went up and especially the 3HD.
It resembles the results when I had the heavier copper tape on the edges.
I then reckon the current in the outer traces now are too low.
I will make a new tweeter membrane where the inner trace in series with an external resistor (4Ω?) will be in parallel with the two outer traces in series.
So the total resistance will be 4Ω and the inner and outer current will be of the same magnitude.
I can then even experiment with various resistor values.

 

[solhaga]

Even with different external resistor values, the distortion is still too high compared to a normal series tweeter (yellow):

Distortion is almost 15dB higher for some frequencies.

So I reckon there are other things going on here:

• traces not centered,
• tweeter touching the sides or the mid membrane,
• membrane is re-used too many times resulting in weak corrugations,
• wrong kind of surround or weakened surround.

Any suggestions on how to go forward?

 

[solhaga]

I cleaned up a bit and inserted new surround foam.
Then I mounted the tweeter membrane alone:

Blue is the standard tweeter membrane configuration that would be 13.2ohm in full length. All traces gets the same current.

Purple is a membrane with the inner trace in series with the two outer traces that are in parallel. That's 6.6ohm full length.
The outer traces only gets half the current each.

Teal is the same as purple but with a resistor in series with the inner trace. Full length resistance is then 4ohm.
The outer traces gets a little more current.

Red is the same as teal but with a higher resistor value in series with the inner trace. Full length resistance is then 4.6ohm.

As the blue and purple traces are almost the same, I can use the purple configuration without having to have several membranes in series/parallel.

So now it is time to build the full length SMAPPP motors...

 

[solhaga]

This is the intended frame:

I've made mounting jigs for gluing the magnets:

One for each panel; I don't know yet if I can reuse them:

The left front panel has the same pattern as the back right panel and so has the back left the same as the front right.

The eleven front left panels glued in less than an hour, sadly the glue has to cure for 24 hours.

 

[solhaga]

All 528 magnets have been glued to the 44 panels.

So let's mount the panels and the baffles to the frames:

The front will be spray painted black once all the screws are mounted..

Panels and baffles are glued with the same glue I used for the magnets; UHU Max Repair Power that Supermagnete.de recommends:

Back side:

Perhaps I should spray paint it as well; the baffles comes in all sorts of colors.

I've made small plugs to lock the panel assembly to the frames. Glue is of course applied.

Like this.

 

[solhaga]

Just completed the first SMAPPP speaker but the membrane.

 

[OllBoll]

Beautiful!

 

[solhaga]

I don't want to clutter, OllBoll, regarding Båndsei's suggestion of a automated corrugation tool.

Here's what ChatGPT has to say about the temperatures:

For how long do I need to heat the membrane?

The heating time required to corrugate a membrane of PEN, PET, or BOPP with an aluminum layer depends on several factors:

1. Material Thickness: Thicker membranes require more time for the heat to penetrate evenly.
2. Heating Method: Infrared, convection, or contact heating affects how quickly the membrane reaches the desired temperature.
3. Temperature: Higher temperatures reduce heating time but increase the risk of overheating or damaging the materials.

General Guidelines for Heating Time​

Here are approximate durations for each material when heated slightly above its glass transition temperature (Tg):

1.​

• Heating Time: 10–30 seconds
  PET heats relatively quickly due to its moderate thermal conductivity and Tg. Uniform heat distribution is key to avoiding uneven softening.

2.​

• Heating Time: 20–40 seconds
  PEN requires more time to reach its higher Tg and soften uniformly, especially if thicker or if the aluminum layer acts as a heat sink.

3.​

• Heating Time: 5–20 seconds
  BOPP is thinner and softens quickly, but care must be taken not to exceed temperatures that might cause it to shrink or lose biaxial orientation.

Additional Considerations​

1. Preheating the Aluminum Layer: The aluminum layer can act as a heat sink, slowing the softening of the polymer. Ensure uniform heating across the composite material.
2. Uniformity Check: Test the membrane's flexibility after heating. It should be soft enough to form into the corrugated mold without tearing or delaminating.
3. Pressure Application: Pair heating with immediate application of pressure to maintain the desired shape while the material cools and sets.
4. Cooling Time: Allow the material to cool while in the mold to lock the corrugation in place.

Suggested Approach:​

Start with short heating durations (e.g., 10–20 seconds) and adjust based on observed pliability and formability. Conduct trial runs with small samples to optimize both temperature and time for your specific composite membrane.

How can I automate this corrugation process?

Automating the corrugation process for a membrane of PEN, PET, or BOPP with an aluminum layer requires an integration of heating, forming, and cooling systems into a continuous or semi-continuous workflow. Here's how you can set it up:

---

1.​

You can choose between two primary approaches:

• Batch Process: Individual sheets are heated, formed, and cooled in a mold.
• Continuous Process: The membrane moves continuously through a heating and forming system (ideal for high-volume production).

---

2.​

a. Feeding System​

• Use a roll-to-roll system for continuous membranes. The membrane is unwound from a roll and fed into the machine.
• Include a tension control mechanism to prevent wrinkles or slack during feeding.

b. Heating System​

• Equip with a precise temperature control system to heat the membrane to the desired range (slightly above Tg).
• Options for Heating:
  • Infrared (IR) Heaters: Provide focused heating and are energy-efficient.
  • Convection Ovens: Ensure uniform heating, especially for thicker membranes.
  • Contact Heaters: Use heated plates or rollers to directly transfer heat to the membrane.
• Integrate sensors (e.g., thermocouples or infrared cameras) to monitor real-time temperature and prevent overheating.

c. Forming Station​

• Use a corrugation moldor forming roller:
  • Static Mold Press: For batch processes, place the heated membrane into a mold and press it.
  • Roller System: For continuous processes, use synchronized corrugation rollers with grooves matching the desired corrugation pattern.
• Apply controlled pressure to form the material without damaging the aluminum layer.
• Ensure proper alignment to avoid distortion.

d. Cooling System​

• Integrate a cooling mechanismto set the corrugation:
  • Air Cooling: Blow cold air across the formed material.
  • Water Cooling: Pass the membrane through a chilled roller.
  • Heat Sink Plates: Conduct heat away from the membrane using cold metal plates.
• Allow sufficient dwell time for the material to retain its shape.

e. Take-Up System​

• After cooling, the corrugated membrane is collected on a take-up roller or stacked for further processing.
• Include inspection systems to detect defects.

---

3.​

• Use a Programmable Logic Controller (PLC)to manage:
  • Temperature settings.
  • Line speed for continuous processes.
  • Timing and pressure for batch molding.
  • Real-time feedback from sensors.
• Implement HMI (Human-Machine Interface) to allow operators to adjust parameters easily.

---

4.​

• Add a vision systemor sensors to check for:
  • Uniformity of corrugations.
  • Surface defects like delamination or tearing.
  • Dimensions and tolerances.
• Use automated reject mechanisms for defective pieces.

---

5.​

• Start with a pilot line to test the automation process and fine-tune parameters.
• Scale to a larger system with multiple heating and forming stations for higher throughput.

---

Example Workflow for Continuous Automation:​

1. Unwinding: Roll-fed membrane enters the system.
2. Heating: Membrane is preheated via infrared or convection heaters.
3. Corrugation: Heated membrane passes through synchronized forming rollers.
4. Cooling: Corrugated membrane is air or water-cooled.
5. Inspection & Rewinding: Finished membrane is inspected and rolled for collection.

---

Automating this process requires upfront investment but offers consistent quality, faster production, and reduced labor costs in the long run.

I have a IR-heater that I use to remove paint, so perhaps that's a start.

 

[solhaga]

To use thermo forming seems to be a rather complicated way of making a corrugated membrane.
But with 14µm aluminium foil and 12µm PEN, the corrugation should stay intact.

With 14µm I also can get rid of any return wires that are otherwise needed to get a suitable resistance.
I will then have 2.2µm per trace instead of 4.4Ω with the previous 6µm aluminium.

So a tweeter membrane will be three times 2.2 = 6.6Ω and a midrange membrane three times 2.2 + two 2.2 in parallel = 7.3Ω.

The 6µm aluminium foil has been very easy to cut due to the paper backing, the 14µm aluminiumfoil is not as it lacks said backing.

Tests with an applied paper backing have failed; the knife still rips the foil. I've made many experiments but with the same result.

Then I saw a recent youtube video by Joppe/Wrinex where he cuts with the aluminium foil facing down, that is through the paper:

Like the Egg of Columbus, it's simple (well) and it works!

For the reckord, here's how I do it:

1. Spray 3M reMount on the cutting mat. In my case I use 0.15m times 2.5m milk carton as cutting mat.
2. Apply sandwich paper. I find that the strength and structure of sandwich paper works well.
3. Spray 3M reMount.
4. Apply aluminium foil. Any thickness should work.
5. Spray 3M reMount.
6. Apply sandwich paper.
7. Cut with the force according to thickness of the aluminium foil.
8. Remove the sandwich paper in 6.
9. Spray 3M 77 adhesive.
10. Weed. If you weed before applying the 3M 77 adhesive, you'll have a lot of sandwich paper to remove after 14.
11. Apply PEN (or BOPP or Kapton or PET).
12. Rub it in thoroughly. I use an old Letraset rub stick.
13. Pull off the membrane from the cutting mat. The sandwich paper in 2 should remain on the cutting mat.
14. Cut out the finished membrane.
15. Apply talc powder to mitigate the adhesive rests on the back of the 3M reMount layer from 3.
16. Corrugate.

Capisce?