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Old 23rd July 2012, 08:31 PM   #51
Hentai is offline Hentai  Japan
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Yes, that's a really good looking basket. I like that there is alot of air around cone.
I'm working on my own concept but it's using the same idea with the straight bars. I will post some plans soon as i promised
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Old 3rd August 2012, 06:09 PM   #52
Hentai is offline Hentai  Japan
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Hello,

Took a day off from work today to try and push things forward with this project.
A few days ago, i fitted a factory made curved cone. A bit heavy for my taste (17g just the cone). I also run out of cloth suspensions so i used rubber foam single roll type this time.
The cone is shallower so another basket was used. I used the first type voice coil with the high inductance.
Today i did some more measurements to determine where am i standing on the mechanical and acoustical side. Below is a sketch of measurement setup i am using.
Click the image to open in full size.

Impedance Measurements:

First measurements showed something going on in the 1Khz area. This made measuring Le with precision very difficult and the results were doubtful. But as i showed in some post above the FEM calculations pretty much confirms it.
Different spider, surround and cone shows similar behavior in that region, but i observed that lighter cones tend to amplify this effect.
I have done a few calculations, as i even suspected the chamber inside the motor structure would form a resonant circuit somehow but it doesn't check out.
At this point i have a couple of suspects. One is the construction of the voicecoil itself. The inside/outside dual coils in parallel might not have been the best idea. It sure doesn't help at all with inductance, just keeps the Re at good value for a good BL. The other is the suspension system. I used soft spiders as i like the GOTO principle (High magnetic force and as little mechanical resistance as possible) however it might be too soft to handle all the vibrational modes of such light cone.
Here are some curves taken in chronological order:

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Trying a number of spiders, surrounds and cones smoothed it up a bit but i will wait and see how things will change with the new voice coil.
Also to my tastes, i like better the cloth triple roll surround, but of course its a component and its usage is key factor. The reason i like it is that from my results it has the least contribution to the overall moving mass.

Acoustic Measurements:

First pictures i am proud of Sine wave 1kHz.

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Measurements done outside 1m high from ground, 2m closest wall, 1 m mic distance, driver free air.
This weekend i will mount it on a baffle, i think 1.5mx1.5m.

Click the image to open in full size.
Attached Images
File Type: jpg Meas_setup.jpg (44.1 KB, 66 views)
File Type: jpg Imp_Ryu0A1.jpg (149.6 KB, 30 views)
File Type: jpg Imp_Ryu0B1.jpg (167.9 KB, 27 views)
File Type: jpg Imp_Ryu0B2.jpg (191.1 KB, 25 views)
File Type: png Imp_Ryu0C1.png (122.4 KB, 23 views)
File Type: jpg Imp_Ryu0F1.jpg (168.6 KB, 20 views)
File Type: jpg DSC02994.jpg (492.3 KB, 17 views)
File Type: jpg DSC02995.JPG (485.6 KB, 17 views)
File Type: jpg DSC03003.JPG (559.1 KB, 34 views)
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Old 3rd August 2012, 06:29 PM   #53
Hentai is offline Hentai  Japan
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Now the on-axis results:

For reference 1kHz level is around 100dB.

Click the image to open in full size.

2nd Harmonic:

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3rd Harmonic:

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Definately something's going on at 1550Hz.

Click the image to open in full size.
Attached Images
File Type: jpg Ryu0F_fr.jpg (357.2 KB, 27 views)
File Type: jpg Ryu0F_H2.jpg (368.8 KB, 21 views)
File Type: jpg Ryu0F_H3.jpg (368.5 KB, 20 views)
File Type: jpg Ryu0F12CSD.jpg (287.4 KB, 23 views)
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Old 3rd August 2012, 06:37 PM   #54
Hentai is offline Hentai  Japan
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I had no baffle ready but i did had some mid horns for testing, from left to right i will number them 1,2,3,.. The pink trace is the driver in free air with 1khz at around 100dB.

Click the image to open in full size.

Horn 1:

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Horn 2:

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Horn 3:

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Horn 4:

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I also tested a 50Hz TH:

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The way i will use the driver would be a BLH + FLH kinda in this config (dont mind the slopes ):

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Next i will measure off axis and then the new voice coil will enter the scene.
Attached Images
File Type: jpg DSC03013.JPG (445.2 KB, 42 views)
File Type: jpg DSC03007.jpg (205.9 KB, 44 views)
File Type: jpg Ryu0GX-C1.jpg (365.7 KB, 26 views)
File Type: jpg Ryu0GX-Q1.jpg (363.2 KB, 15 views)
File Type: jpg Ryu0GX-Q2.jpg (361.5 KB, 18 views)
File Type: jpg Ryu0GX-Q3.jpg (358.8 KB, 16 views)
File Type: jpg Ryu0GX-TH.jpg (381.9 KB, 19 views)
File Type: jpg Ryu_blh+flh.jpg (370.1 KB, 24 views)

Last edited by Hentai; 3rd August 2012 at 06:39 PM.
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Old 20th August 2012, 10:17 PM   #55
Hentai is offline Hentai  Japan
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Weekends are just too short...

Here is this last 2 weeks update:

New voice coils were tested. Similar with the ones from Beyma 12G50. 9mm heigh 8ohms, 6mm heigh 6ohms 4mm heigh 4ohms . Shorting rings were imployed. One at the base of the magnetic gap and the other right in the gap along the voicecoil. Didnt take pics of voice coils before i installed them but below you can see the 6 ohms in the left and the older 16 ohms to the right

Click the image to open in full size.

Inductance droped as expected and high frequency extension was easily noticeable. One thing sure checked out during experimentation and that is the most important aspect regarding the shorting ring is the copper quality. The location where the ring is positioned is important but not as much as the electrical resistance... at least in my implementation of underhung motors.

Le droped to 1mH with the 9mm VC and to 0.4mH with the 4mm VC

Testing showed the most contribution in inductance reduction came from the thick ring placed near the low end of the magnetic gap as in the picture below:

Click the image to open in full size.
Click the image to open in full size.

Whizzer cone was also added. It is clear now that at such high diameters curved cones have a clear advantage over straight ones but i guess this is just verifying the known facts. Trouble is the curved cones i have available and the ones that i made from layers of washi paper are pretty heavy with a mean value of 18g. Adding all up turns to a Mms between 30-35g.

Working with a factory made whizzer cone model and testing it with about 5 different cones both straight and curved and weighting between 9 and 18g i could see that the interaction between the whizzer and the main cone was constistent in each case.


Click the image to open in full size.

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Click the image to open in full size.

The pictures are not very artistic and some elements are not very esthetic but keep in mind its just a prototype.
As a first conclusion the gap width will be reduced in the final motor design as the space for shorting ring is no longer required. The thicker ring placed under the gap will be used alone.
Attached Images
File Type: jpg DSC03015.JPG (83.0 KB, 25 views)
File Type: jpg DSC03016.JPG (47.2 KB, 24 views)
File Type: jpg DSC03022.JPG (37.6 KB, 37 views)
File Type: jpg DSC03034.JPG (54.1 KB, 42 views)
File Type: jpg DSC03049.JPG (57.1 KB, 35 views)
File Type: jpg DSC03085.JPG (70.2 KB, 33 views)
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Old 20th August 2012, 10:27 PM   #56
Hentai is offline Hentai  Japan
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I have done alot of measuring and testing, time is the enemy and i wont post all of them but i will give a couple of

examples to highlight a few of the problems.

There was also a small loss of data during a power crash and after system rebooted i found that holm hasnt saved any

of the measurements from that session (whole 49 fields!). However i always run one more app in parallel to save data

in txt format for archiving. Holm has the easy way of gating but after a few hourse i could do that manually.

The measurements presented below are for a curved cone, foam half roll surround and linear spider. System resonance

roughly 50Hz.

Impulse response is shown in a time delta of 10ms and frequency response gated at 5ms. Resolution 1/96 octave.

As picture will show, field coil was fed in 0.3A steps starting from 0.6A.


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As you can notice the field coil drive current doesn't affect much the shape of the curves, just very small

differences. It does affect magnitude on all curves tho. I also had 30,45,60 degrees measurements for this example

but these were lost. There is also an increase in distorsion level with decreasing current, i will repeat

measurements with the next test cone/setup.

Ofcourse a deep hole in response can be observed and i will get back to that soon.


Click the image to open in full size.

I also prepared a cone for a mid-bass unit, a 41g Mms. I measured as well from 0.6A to 3A drive current but i will

just post the overlay image and impulse for 2.1A with a 5ms time frame.

Click the image to open in full size.
Click the image to open in full size.

You can find the files in higher resolution in the attached zip.
Attached Images
File Type: jpg 0k2-fr.jpg (185.2 KB, 15 views)
File Type: jpg 0L2_FR_overlay.jpg (180.4 KB, 15 views)
Attached Files
File Type: zip Ryu 0kx 1.zip (695.2 KB, 211 views)
File Type: zip Ryu 0kx 2.zip (681.6 KB, 172 views)
File Type: zip Ryu 0kx 3.zip (571.4 KB, 163 views)
File Type: zip Ryu 0lx 1.zip (637.1 KB, 145 views)
File Type: zip Ryu 0lx 3.zip (754.1 KB, 126 views)
File Type: zip Ryu 0lx 2.zip (642.1 KB, 111 views)
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Old 20th August 2012, 10:29 PM   #57
Hentai is offline Hentai  Japan
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The drop in response around 4kHz was present with both the 1mH and 0.4mH Le voicecoils.

Looking at the graphs and comparing with measurements done without whizzer it seemed to me

that the maine cone fails to meet the whizzer at a high enough frequency or the whizzer

fails to meet the cone at a low enough frequency. Kinda like a 2 way xover with too far

apart xover points. I figured that the added mass of the whizzer lower the highest

frequency the cone would respond to.

So i made another cone, straight this time with a mass of 8g (just the cone) in the hope

that it will reach a higher frequency when the whizzer is added.
As you can see below the drop is not so pronounced anymore.

Click the image to open in full size.

This pretty much sums it up for the past two weeks. 10Khz were reached, the push for the

last octave is on going. I'm still working on the best voice coil version and meanwhile

working on smoothing frequency response.
The previous 1.5kHz dip in FR i believe it was caused by a foam surround i used having a

wider roll and being a little thiner in material. Probably didnt provide a good cone

termination.

Thats about it for tonight. If you have any questions, ideas, thoughts i would be happy to

hear them.
Below are just some shots i took with the driver:

Click the image to open in full size.

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Attached Images
File Type: png Ryu 0M2 - FR -2.4A.png (156.5 KB, 46 views)
File Type: jpg DSC03019.JPG (84.5 KB, 55 views)
File Type: jpg DSC03020.JPG (82.9 KB, 26 views)
File Type: jpg DSC03058.JPG (92.8 KB, 39 views)
File Type: jpg DSC03059.JPG (90.3 KB, 40 views)
File Type: jpg DSC03060.JPG (82.1 KB, 26 views)
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Old 20th August 2012, 10:46 PM   #58
Magura is offline Magura  Denmark
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Your results fits in well with what I have experienced so far.

You need to make a lighter cone, preferably some 4-5g.
This can be achieved with carbon fiber.

If you need pointers for the carbon stuff, let me know.


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Old 20th August 2012, 10:54 PM   #59
Hentai is offline Hentai  Japan
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Quote:
Originally Posted by Magura View Post
If you need pointers for the carbon stuff, let me know.


Magura
That would be great.
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Old 20th August 2012, 11:19 PM   #60
Magura is offline Magura  Denmark
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Quote:
Originally Posted by Hentai View Post
That would be great.
Drop me a mail then, and I'll see if I can sort you out.


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