Project "Groove Scribe"- A DYI stereo 45/45 head.

[Fela Borbone]

Your arguments are valid.!
...but I mean something else (and book too).Phase shifs are created the way you stated and in more ways.
I'm talking about time lags, they affect differently the wave depending of its freq.
Whithin the piece that usually contents drive and feedback coils happens deformations.
They are tiny but for high freqs is like big amplitudes folded and can really build up if boundaries help. They form nodes., like a guitar string... well way more tiny.
You can simulate with the java aopplet"membrane" is freeware...
In the other hand, souri (and i belibe is atalented designer) places the fb device over the stylus.That freak me out...how can it work?

[opcode66]

In my opinion, the phase shifting in most system is a result of drive bleed and the processing electronics. As long as you've created a proper coil and have it as close the the proper field, there should be minimal lag. I understand that the window decreases dramatically when speaking about high frequencies. But, the eq'ing that happens in a negative feedback causes many times more lag then anything physical about producing the feedback. Drive bleed is a huge factor. I see many systems where that is quite obviously happening. Shielding.... All the way.... Drive bleed will have the same effect as lag overall with respect to causing the negative feedback to do the opposite of what you want and even more especially at high frequencies where the peak to peak time is so small. I think people confuse the two (lag and bleed) because of this.

[Fela Borbone]

Yes

[Bahndahn]

What Markrob is not considering is the fact that it is not wave propagation at that point but Newtonian physics that is inducing the feedback current so the calculation is irrelevant here. Regardless of if there has been prior discussion on a topic, that doesn't mean that there isn't yet undiscovered country. No one who posts here was a Neumann engineer or the like. So, yeah, let's keep it in perspective, ok? By the way, no one in their right mind would use steel to couple feedback to drive due to the iron content and the relative permeability of steel for em flux. Want to talk about phase shift, oh boy, that would do it.

I'd like to hear what a Physician has to say about this -- it doesnt take a Neumann engineer, it just takes a Physician or trained engineer. You speek confidently but I'm not convinced yet!

The drive coil itself produces no physical motive force directly. It produces a shifting Magnetic field electrically. That shifting magnetic field (flux) interacts with the flux from a fixed pole magnet that is held rigidly in place. The flip flopping of the EM flux in the presence of the M flux is what is causing the movement in the transducer system.

We aren't talking about wave propagation here. We are talking about objects in motion under forces which are directly coupled.

Here's why:

There is space between all of the particles, mannn. Space is omnipresent. I thought there was no such thing as direct coupling! As far as I am understanding this: of course we are dealing with wave propagation; the coil provides the force [via magnetic interaction, yes] and that force travels through the glue, into the bobbin, up the push rod etc. Freakin fast as ever, yes, but its still a propagation in this way.

This would happen in the car too, force from the motor would travel down the drive shaft at the rate of energy transfer of the drive shaft-material, into the transmission, axel, tires coupled with the road, etc. Each material twisting and binding on the micro MICROscopic level producing 'lag'. The fact that we are burning down the street together is the LOWEST frequency measurement in the motion system, almost unrelated to the level we are discussing.

Please, engineers or physicians out there, clear this up for me. Do I have this right?

[opcode66]

Please, engineers or physicians out there, clear this up for me. Do I have this right?

Physicians are Doctors.

Physicists would be the group to ask.

You can rest assured that Physicists would agree with me. Not sure about Physicians... The coil provides zero force. The magnetic fields supply the forces. Ok?

Please believe anything you want. Free thought my friend.

[sakuszi]

let Gentlemen, that thrown in my two cents, I have a similar problem, speakers, head of sending into space a magnetic field over a distance of 150 mm up to go back to the transducer pickups, the magnetic field of the coil drive speakers also passes through the wires symmetrical, how to solve this problem so as not was an echo during recording and playback at the same time?

[Fela Borbone]

Ooooops!
The applet "membrane" simulate amplitudes in aflat surface, not the lengthwise deformations involved in the fb-drive mismatch depending to space between.
BTW "why you hear what you hear" is amust read for sound and vibration understanding. Dig!

[Bahndahn]

Please, engineers or physicians out there, clear this up for me. Do I have this right?

Physicians are Doctors.

Physicists would be the group to ask.

You can rest assured that Physicists would agree with me. Not sure about Physicians... The coil provides zero force. The magnetic fields supply the forces. Ok?

Please believe anything you want. Free thought my friend.

LOL shucks on the physicians. My bad.

I'm not looking to 'believe', I'm looking to know. This is science, not religion

Anyway, I'm very willing to take your statements as truth, Todd, but up to this point you are saying stuff as truth where my understanding would benefit from evidence/disambiguation. For example, how is it that the magnetic force is omnipresent within the bobbin and through to the pushrod/feedback bobbin? How is possible that the situation is "directly coupled"? Is not that the force of the magnetic field [from the drive coil interacting with the fixed magnet] is localized to the area of the drive coil and 'later' transferred through the medium?

These are my main questions...

[EpicenterBryan]

I'm plodding through all the awesome new discussion here, which will take some time. But this is exactly how I hoped this thread would go. Thanks everyone for inputs!

Although Todd is usually right, I need to think about this a bit. But I'll be the first to say something one way or the other when I process it all and check my facts...

By the time I put together a response you guys usually have already covered it and in this case you guys may have already done that. But let me elaborate on the whole "slot" former thing and eddy currents:

Todd and Fela both made mention to this, and I'll show you what they are talking about:

I'm adding a feature to diminish the eddy-current effects on the bobbin side of the part.

you mean that it shuold have not ring closed shape, and have an cutted off strip like happens in metallic speaker coil fotmers?

Here is a speaker coil former, propped up for a microscope to look inside.

IMG_4305.JPG

Here is the mystery "slit". The slit is there so the strong magnetic fields generated by the coil to oppose the field in the magnet structure do not get decreased as a result of what would be a one turn shorted transformer effect with the non magnetic aluminum form. If this were a closed loop of aluminum in close proximity with the coil, much of the coil magnetic energy would be lost due to eddy currents induced into the coil former.

Still0013.jpg

So the feature Todd would add to his aluminum bobbin would be to cut a thin slit lengthwise to break the "one turn coil" that is created by the bobbin being made of aluminum. I think this is mainly needed for the drive coil since it has to create such large fields for movement within the magnet structure. My gut says it's not needed for the core where the feedback winding are since they move inside their own magnetic source and Generate voltage as they move in the field. Yes, the core will move within fields and generate eddy currents but most of it is in the center core field and not in the ideal zone right at the end where the magnetic fields are oriented for maximum voltage generation by the few copper winding's in the "zone".

Comments?

[EpicenterBryan]

In my opinion all this stuff are more about resonances in the part linkin the drive and feedback, that go really fast and reflects inverted inverted or in phase at the edges of the part, depending of the mechanical impedance of the edge( can be open attached th something heavy or elasstic)
Drive and fb can be in node or antinode of this vibrations and have consecuences in their phases

And this is a totally valid point!
We all have seen short segments of larger different material in push rods - link braces they call them. Vibration dampers?
There are smarter people than me who solved this a long time ago.

Bryan

[Snug Music]

woww ... I've always wondered what this little gap in the aluminum body of the coil. I can really learn a lot from you ... thank you...

[Snug Music]

I once wound a coil of aluminum, but there did not make slot, this quickly became hot coil. it may be that this was caused by the occurring eddy currents?

Greetings Scotty

[EpicenterBryan]

I once wound a coil of aluminum, but there did not make slot, this quickly became hot coil. it may be that this was caused by the occurring eddy currents?

Yes. Here is a section from Wikipedia on the subject:
https://en.wikipedia.org/wiki/Voice_coil


"Aluminium was widely used in the speaker industry due to its low cost, ease of bonding, and structural strength. When higher power amplifiers emerged, especially in professional sound, the limitations of aluminium were exposed. It rather efficiently but inconveniently transfers heat from the voice coil into the adhesive bonds of the loudspeaker, thermally degrading or even burning them. Motion of the aluminium bobbin in the magnetic gap creates eddy currents within the material, which further increase the temperature, hindering long-term survival. In 1955 DuPont developed Kapton, a polyimide plastic film which did not suffer from aluminium's deficiencies, so Kapton, and later Kaneka Apical were widely adopted for voice coils. As successful as these dark brown plastic films were for most hi-fi voice coils, they also had some less attractive properties, principally their cost, and an unfortunate tendency to soften when hot. Hisco P450, developed in 1992 to address the softening issue in professional speakers, is a thermoset composite of thin glassfibre cloth, impregnated with polyimide resin, combining the best characteristics of polyimide with the temperature resistance and stiffness of glassfibre. It withstands brutal physical stresses and operating temperatures up to 300°C, while its stiffness helps maintain the speaker's 'cold' frequency response."

Bryan

[Snug Music]

Thanks Bryan...

Greetings Scotty

[EpicenterBryan]

I still haven't gone through all the discussion but will do so. Only some many hours.

But here is an update on the next step - how to make sure I glue the push rod and coil at a 90 degree angle to the driver disc since clearance with the magnet is going to be an important issue.

I printed a jig. It looks like this. It goes over the driver and has a hole to support the push rod right in the center. It has access on each side so glue can be applied at the union of the carbon fiber disc on the outside and the push rod.

push rod glue jig.jpg

IMG_4309.JPG

IMG_4308.JPG

The 12" rod shown is there just to make sure it was doable, and the angle was dead nuts on. The actual alignment jig is being printed as I post since this one was short by about 3mm. My bad.

But the concept works, and this is what I'll use to glue the push rod / coil combo to the surface of the drive disc. Then I'll hit the union from the underside with glue as well.

Bryan

[Snug Music]

I still haven't gone through all the discussion but will do so. Only some many hours.

But here is an update on the next step - how to make sure I glue the push rod and coil at a 90 degree angle to the driver disc since clearance with the magnet is going to be an important issue.

I printed a jig. It looks like this. It goes over the driver and has a hole to support the push rod right in the center. It has access on each side so glue can be applied at the union of the carbon fiber disc on the outside and the push rod

The 12" rod shown is there just to make sure it was doable, and the angle was dead nuts on. The actual alignment jig is being printed as I post since this one was short by about 3mm. My bad.

But the concept works, and this is what I'll use to glue the push rod / coil combo to the surface of the drive disc. Then I'll hit the union from the underside with glue as well.

Bryan

Hi Bryan, ..smile

'm just amused where I have seen thy tool for centering the Rod ... smile ... here I've tinkered a week ago ... hihii ..

Scotty

[EpicenterBryan]

I'm just amused where I have seen thy tool for centering the Rod

Great minds think alike, Scotty !



Here is a super quick update for tonight:

I've decided to go a super minimalist route for V springs to keep the feedback coils centered when vertical load is applied. These don't need to deal with twisting motions, only vertical loads. The V-spring at the back will have it's usual appearance which eliminates twisting motions.

This is just a mock-up to show you all what I'm thinking. In this photo is a random guitar string and it is magnetic - and much larger diameter that what I'm going to get tomorrow. What I'm going to get is the smallest diameter of Phosphor Bronze wire they have at the hobby shop. It's got spring and is non magnetic. Then when my non magnetic spacers arrive, I'll cut slots in them much like the screw heads shown in this mock-up. Once the drivers and such are installed, something like this spring shown will be glued in place. I will also place some kind of heat shrink material over the Phosphor Bronze V-spring like thing to make sure I apply dampening ahead of time.

I realize that with no load, this will cause a slight "swing" or angular error but when a load is applied as in cutting, this will make sure the feedback coil stays much more centered and does not rub in the magnet.

IMG_4314.JPG

Comments?

Bryan

[Snug Music]

I'm just amused where I have seen thy tool for centering the Rod

Great minds think alike, Scotty !



Here is a super quick update for tonight:

I've decided to go a super minimalist route for V springs to keep the feedback coils centered when vertical load is applied. These don't need to deal with twisting motions, only vertical loads. The V-spring at the back will have it's usual appearance which eliminates twisting motions.

This is just a mock-up to show you all what I'm thinking. In this photo is a random guitar string and it is magnetic - and much larger diameter that what I'm going to get tomorrow. What I'm going to get is the smallest diameter of Phosphor Bronze wire they have at the hobby shop. It's got spring and is non magnetic. Then when my non magnetic spacers arrive, I'll cut slots in them much like the screw heads shown in this mock-up. Once the drivers and such are installed, something like this spring shown will be glued in place. I will also place some kind of heat shrink material over the Phosphor Bronze V-spring like thing to make sure I apply dampening ahead of time.

I realize that with no load, this will cause a slight "swing" or angular error but when a load is applied as in cutting, this will make sure the feedback coil stays much more centered and does not rub in the magnet.

IMG_4314.JPG

Comments?

Bryan

Bryan,..
as it would be if you use for centering the push, thin carbone rods. heating and bending degrees at 90, then at the push spend with Loctite?

Regards Scotty.

[EpicenterBryan]

Here is the update:

Another glorious Saturday full of working out little details. There is nothing like having an entire day to work on one project, and being able to address a bunch of stuff that has to be done before assembling stuff. This is where it gets fun.

The first topic is the new V-spring. In previous attempts, I used stainless shim stock strips and spot welded them into a V. Then I drilled the holes. It was hard to drill the holes in this material as it tended to grab when it punched though and caused some attempts to warp badly and be scrapped. It also caused some holes to drift so they were not where I needed them. In the background in this shot you see a spare welded one I was going to use until I tried something new.

What I did this time was to print a plastic one as a template for where the holes needed to be, and then I used a spring loaded center punch to put indentations in the material where I wanted the holes and put 2 springs worth of holes on one piece of shim stock.

Making a V-spring.jpg

Then I pulled out my 30+ year old hole punch like this one (mine has more dies). I didn't use this last time because it has always been difficult to punch the hole exactly where I wanted. Until tonight. The punches have center nubs in each die, so after I punched locating indentations in the shim stock the tool actually did what I wanted! The holes are right where I wanted.

61T6pw9JdrL._SX450_.jpg

I fine tuned the shape of the V-sring with a pair of scissors after the above photo and then used a grinder to clean it up even more. Imagine that. I could actually make a nice one-piece spring with a pair of scissors and a hole punch.

The next topic is the Torque Tube:

Torque tube setup.jpg

The torque tube consists of an aluminum cap screw which I was able to drill a 0.4mm hole through 1/2 of the head for a 0.25mm piano wire to hook through. That threads into a stylus / link connector you saw on another head version a long time ago and a set screw for a Presto style stylus. Although that part had 1mm carbon fiber rods glued into it as well as a 4-40 threaded nylon rod, I heated it up with a mini torch and was able to melt / remove that stuff and salvage it for this version of Groove Scribe!

I'm thrilled since that part took a bunch of time to make and was very light, even with the set screw. Yes, that's 0.37 grams including the nylon set screw. I'll use Aluminum this time and will shorten it as much as possible.

Other stuff.jpg

I also made some circuit boards that will be glued to the top of the magnets. That is where the coil wires will be soldered as well as the twisted pair wires for feedback connection.

So that's for tonight.
Hopefully I will have more time tomorrow.

Bryan

[Snug Music]

hey .. bryan ... wanted to ask, what have you achieved resonant frequency of the driver with this configuration! diafragm with carbon membrane? Have you ever taken a test? how thick is diafragm?

Greetings Scotty