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 Multi-Way Conventional loudspeakers with crossovers

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Hentai
diyAudio Member

Join Date: Nov 2006
Compression Driver

On another note, i mentioned i will be starting to play with compression driver. While it takes longer than expect, i am making some progress in this regard.

Guided by Henricksen's paper "Phase Plug Modelling and Analysis: Radial versus Circumferential Types" I made a spreadsheet to calculate the phase plug parameters. You can see it attached even tho its not really arranged but keep in mind only the blue cells are user inputs.
The excel shows data to draw the piece and also baffle input for AxiDriver. It shows only Reflector side so you will need to draw the baffle according to your compression driver's profile.

You will find attached o picture showing figure 3 from the paper. That is basically a section through the phase plug representing the acoustic path. The air trapped between the diaphragm and the phase plug has a volume and mass defined by length Ld and width (delta). Considering a 2 slit circumferential phase plug you can see how delta will vary for the 2nd slit as circumference will be higher.

For the first phase plug i decided to keep this mass of air constant by keeping the diaphragm surface area acting on each slit constant. This is what the spread sheet will do . knowing that the surface area of a spherical segment is 2*pi*R*h with R being the radius and h the height between the upper and lower segment planes, we can see that we will satisfy the initial condition by splitting h in equal parts.

As you can see in the picture with the 2 circles, h was divided into 4 egual parts corresponding to the 4 acoustic paths in a 2 slit phase plug. The arc length between the dotted lines correspond to Ld. Keeping surface constant will cause Ld to vary, you see. According to Henricksen you can determine a cutoff frequency based on Ld and it states that f0=c/(3.63*Ld). How much will this apply to a varying Ld design will have to check experimentally.

At low frequency we know all the air will be pushed through the slits and at high frequency some it will just compress. Because of this the air has mass and compliance which can be modeled as inductance and capacitance. In the paper we have f0=1/(2*pi*sqrt(LC)) a known formula. When compared to the Ld based f0 something goes wrong as i dont think i interpret it correctly.

Anyways based on this i had my phase plug design parameters for a first try ready. There is one more thing that was on my mind. To me most of the circumferential slit phase plugs dont terminate smoothly. The slit throat grows to the point where it meets the other slits and then boom right into the large exit of compression driver. I thought i should have unite in pairs to make a smoother transition.

In this first try i didnt look for equal path lengths it is something i will try next.
You can see from the pictures tho how the middle section extends to provide a smoother transition. How good it will be, if any? i will test it soon.

You can see some already made PPs, Need to smooth them out and put them in a driver.
Attached Images
 DSC04186.JPG (96.9 KB, 766 views) DSC_0116.jpg (628.0 KB, 782 views) Ryu Phase Plug CS.jpg (35.8 KB, 685 views) RYUPPCD02.jpg (12.3 KB, 679 views) DSC04183.JPG (187.9 KB, 681 views) DSC04155.JPG (152.3 KB, 205 views) DSC04160.JPG (183.2 KB, 206 views)
Attached Files
 Project Ryu Compression Driver.zip (12.3 KB, 19 views)

tinitus
diyAudio Moderator R.I.P.

Join Date: Nov 2005
Quote:
 Originally Posted by Jef Nuyts How do you insert tumbnails? Take care,
when reply to thread, scroll down, and click on 'manage attachment', and find the picture in your file, click on it, and ...

sometimes you may need to scale down or reformat, etc ... which I did
and I also often choose to reframe, to remove what is not needed
it will then need less down scaling, and results in better upload
Attached Images
 field coil 1 40.jpg (333.9 KB, 259 views) field coil 2 50.jpg (375.8 KB, 255 views)
__________________
sometimes we know very little, and sometimes we know too much

RobFreak
diyAudio Member

Join Date: Dec 2009
Quote:
 Originally Posted by Hentai Awesome speaker Jef. Congrats. Pretty good bass i get from the video. Nice. T/S i use WT3 and/or LIMP. With the later you can use a power amp for higher current but you need to make a little test rig. WT3 is very fast to get a impedance curve tho. I assembled the cone for OB. Im waiting for glue to set in and will get it running pretty soon.
Cant wait to read/see the results..

Jef Nuyts
diyAudio Member

Join Date: Jan 2013
Thanks for the replies.

A little test for the tumbnails. I get it, you don't have to insert it thx.

BTW just ordered WT2 from smit & larson audio hopefully a good decision. We'll see...

Cheers,
Attached Images
 IMG_9651 (Kopie).jpg (118.3 KB, 280 views)

Last edited by Jef Nuyts; 3rd March 2014 at 10:02 AM.

_Wim_
diyAudio Member

Join Date: Nov 2001
Location: Belgium
Quote:
 Originally Posted by Hentai On another note, i mentioned i will be starting to play with compression driver. While it takes longer than expect, i am making some progress in this regard. Guided by Henricksen's paper "Phase Plug Modelling and Analysis: Radial versus Circumferential Types" I made a spreadsheet to calculate the phase plug parameters. You can see it attached even tho its not really arranged but keep in mind only the blue cells are user inputs. The excel shows data to draw the piece and also baffle input for AxiDriver. It shows only Reflector side so you will need to draw the baffle according to your compression driver's profile. You will find attached o picture showing figure 3 from the paper. That is basically a section through the phase plug representing the acoustic path. The air trapped between the diaphragm and the phase plug has a volume and mass defined by length Ld and width (delta). Considering a 2 slit circumferential phase plug you can see how delta will vary for the 2nd slit as circumference will be higher. For the first phase plug i decided to keep this mass of air constant by keeping the diaphragm surface area acting on each slit constant. This is what the spread sheet will do . knowing that the surface area of a spherical segment is 2*pi*R*h with R being the radius and h the height between the upper and lower segment planes, we can see that we will satisfy the initial condition by splitting h in equal parts. As you can see in the picture with the 2 circles, h was divided into 4 egual parts corresponding to the 4 acoustic paths in a 2 slit phase plug. The arc length between the dotted lines correspond to Ld. Keeping surface constant will cause Ld to vary, you see. According to Henricksen you can determine a cutoff frequency based on Ld and it states that f0=c/(3.63*Ld). How much will this apply to a varying Ld design will have to check experimentally. At low frequency we know all the air will be pushed through the slits and at high frequency some it will just compress. Because of this the air has mass and compliance which can be modeled as inductance and capacitance. In the paper we have f0=1/(2*pi*sqrt(LC)) a known formula. When compared to the Ld based f0 something goes wrong as i dont think i interpret it correctly. Anyways based on this i had my phase plug design parameters for a first try ready. There is one more thing that was on my mind. To me most of the circumferential slit phase plugs dont terminate smoothly. The slit throat grows to the point where it meets the other slits and then boom right into the large exit of compression driver. I thought i should have unite in pairs to make a smoother transition. In this first try i didnt look for equal path lengths it is something i will try next. You can see from the pictures tho how the middle section extends to provide a smoother transition. How good it will be, if any? i will test it soon. You can see some already made PPs, Need to smooth them out and put them in a driver.
This might also contain some usefll information for you:
Patent US20040156519 - Phase plug with optimum aperture shapes - Google Patents

 8th March 2014, 08:30 PM #506 Hentai   diyAudio Member   Join Date: Nov 2006 Good link Wim, I approached phase plugs more from thoughts i had in mind for a long time rather than complete calculation. For example in my personal experience the concave type of pp like in EV DH3 sound better. and i thought it might be because the transition between slit openings is smoother. One slit doesnt just end in the large diameter of the driver's exit but it will meet the other slit and the section still expands gradually to the exit. This might mean nothing, because if you look at a line array arrangement then most phaseplugs are like that at their exits. Anyways i got to play the high Qes cone. I put it on you tube cuz i listened Hugh Masekela - Stimela from Hope. Just the speaker not tweeter or drivers. On top is the midbass cone i removed. Voice coil is a single layer 0.15mm ECW, 52mm diameter 6mm height. Rdc= 5.9 ohms. Qes = 0.9. Havent measured the cone's weight but its heavier about 30-35g to lower fs as well which is 37Hz Some of my equipment is rented out so i had to come into sound card with balanced signal. Not sure what caused it but it picked up some noise. In that room i got not earth connection on mains so could be it. Even so, i think you can get a vast idea on its timbre. Its not mounted on OB its in the reflex enclosure with the port stuffed shut. https://www.youtube.com/watch?v=dWe4owHDIPM Last edited by Hentai; 8th March 2014 at 08:32 PM.
Frank40
diyAudio Member

Join Date: May 2004
Location: My workshop :-)
Hey,

Hentai, Nice video... it sounds like it has a nice top respond as well.

I am starting to get a good grip on making voice coils, just want to show you that it can be done without being a major company.

This one is made from six layers of fibre glass, winded on both the inside and on the outside of the voice coil former. The wire is 0.15mm.

By the way, I just order some speaker tools to measure TS parameters, will poste them as soon as I can.
Attached Images
 Capture_547.jpg (630.9 KB, 298 views)

Last edited by Frank40; 9th March 2014 at 12:52 PM.

 9th March 2014, 11:31 PM #508 Magnasanti   diyAudio Member     Join Date: May 2012 Location: Georgia that former is just so long
 10th March 2014, 05:59 AM #509 Frank40   diyAudio Member     Join Date: May 2004 Location: My workshop :-) @Magnasanti, Don't worry it will be cut to fitt, it will end at about 35mm.
Jef Nuyts
diyAudio Member

Join Date: Jan 2013
Hi,

Have made a light cone (6 gr) suitable for full range. I wonna copie the cone of B&W mid-ranges. Light and rigid but not the sound of epoxy.
Going to test the cone soon.

This is the procedure:
Take a kevlar sheet and put it on a mold. Spray it with varnish (i used motip heat resistant varnish) on both sides. Press it with foam to the mold till it is a little dry. This will fixate the kevlar textile and keep it in shape. After this put the cone back on the mold after full cure of the varnish and put a layer of thin glass fibre on the back. For minimal use of epoxy put the glass fibre on cardboard and apply, with a little paintroller, the epoxy on it. The cardboard will absorb the epoxy so you have just enough. Put the glass fibre on the back of your cone and wait for full cure.

Cheers,
Attached Images
 P1080152 (Medium).JPG (198.6 KB, 299 views)

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