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Multi-Way Conventional loudspeakers with crossovers

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Old 15th July 2012, 02:30 PM   #41
Allar88 is offline Allar88  Estonia
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Acctualy looking at the picture of the field coil, it looks like the ends of the layers are not perfect layout? With what are you winding the coils, it looks a lot like "made by hand".
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Old 15th July 2012, 03:00 PM   #42
Boscoe is offline Boscoe  United Kingdom
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This looks awesome! What does Vas measure? What's xmax like?
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Old 15th July 2012, 05:09 PM   #43
Hentai is offline Hentai  Romania
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Thank you for your comments.

Boscoe with that particular cone and suspension system Vas is 194.4L. Xmax (caculated) is +/- 3mm or 6mm peak to peak.
Allar that's manufacturer's secret (...joking...)
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Old 16th July 2012, 12:31 AM   #44
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Beautiful work! I have made a few field coil drivers by re-purposing existing motors. I envy your machining capabilities. Those will sound incredible when you are done.
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Old 16th July 2012, 06:44 AM   #45
Boscoe is offline Boscoe  United Kingdom
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Have you done anything more with your other cones yet? What Fs, Vas etc is your target? Forgive me if you have already mentioned this!
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Old 16th July 2012, 06:33 PM   #46
Hentai is offline Hentai  Romania
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Hi Paul, thank you. Would be nice to share some of your thoughts on field coil, specially if you've done some compression drivers.

Boscoe, Vas will most certainly be of high value 150-250l because of low Fs and Mms. As a target i have set 50Hz for Fs. I don't really want to go above this value.

I will use this driver in horn so Vas, Fs don't really mean much on their own but rather the elements that give these values like Mms, Cms, SD make the story.
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Old 16th July 2012, 07:17 PM   #47
Hentai is offline Hentai  Romania
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Other cones waiting their turn. A nice low mass straight cone will be next. Its a DIY cone a friend made for me, looks very good.

Click the image to open in full size.
Attached Images
File Type: jpg DSC02975.jpg (124.6 KB, 1249 views)
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Old 16th July 2012, 07:56 PM   #48
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Mr Hentai you have a personal message!
Great project!
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Old 22nd July 2012, 08:37 PM   #49
Hentai is offline Hentai  Romania
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Hi,

I was able to do some more testing and measurements this weekend and i could plot some important functions.

First plot shows flux density B against field coil current. It also shows Qes, measured for a specific cone assembly ofc but i thought it can be useful to see it.
You will notice the gap saturates around 1.55T and going beyond 2.4-2.5 drive current is not really necesary, altho i measured difference of 0.5-0.7db in SPL at 4 Amps before compression kicks in.

Click the image to open in full size.

At 2.2 Amps the temperature stayed at room level of 28deg C, at 2.5 Amps within 1 hour went to 29deg C. Below you can see the temp plot with the field coil at 4 Amps within 1 hour frame. Previously it ran at 2.5 Amps so it was pretty warmed up.

Click the image to open in full size.

After the hour in the next 15 min it stayed at around 62deg C and after that i stopped it.
At 4 Amps once B won't go higher, beta=(BL)^2/Rdc will start to drop because of Rdc.

Click the image to open in full size.

I'm not ready yet to post some of the impedance or Fr graphs (unless you want to see some really messy ones haha) but with the white cone pictured a post above with a Mms reaching 20.4g i got to 7.38% calculated efficiency and 100.8dB/w/m average sensitivity. The bad news is that i was way off regarding inductance.
Yea, i got the correct value when air cored but once placed in that gap its not the same.
A whooping 3.2mH measured 1kHz (average) took down all response beyond 3-3.5Khz. There was a small resonance around 1kHz so at first i blamed it for the high Le. Surely enough with lower current within fieldcoil and not so much energy to excite resonance Le value drops to 2mH. Curious thing.

So i went back to solving the AC problem. Le= (N*phi)/i, where Le is inductance, N is number of turns, phi is rate of change of AC flux and i is current through voicecoil.
N*phi is the quantity known as flux linkage and FEMM when solving AC problems calculates it. In fact it actually calculates Le as Flux/Current.

Here is result with current voice coil no shorting ring:

3.9mH pretty close to the real world.

Click the image to open in full size.

While we are at it, current density in plates at 1kHz:

Click the image to open in full size.

10Khz:

Click the image to open in full size.

Adding 0.25mm thick copper faraday ring results in:

0.83mH

Click the image to open in full size.

1kHz:

Click the image to open in full size.

10khz:

Click the image to open in full size.

I will redesign the voice coil as i want Le under 0.5mH. I will need to use thicker wire. The journey continues...
Attached Images
File Type: jpg BvsI_measured.jpg (122.3 KB, 21 views)
File Type: jpg Current density plates 1khz FRing.jpg (92.9 KB, 20 views)
File Type: jpg Current density plates 1khz.jpg (93.2 KB, 21 views)
File Type: jpg Current density plates 10khz FRing.jpg (96.3 KB, 16 views)
File Type: jpg Current density plates 10khz.jpg (95.6 KB, 16 views)
File Type: jpg RevsT_measured.jpg (122.2 KB, 18 views)
File Type: jpg TvsI_measured.jpg (122.3 KB, 17 views)
File Type: jpg VoiceCoil v1 Ind 1khz.jpg (35.1 KB, 14 views)
File Type: jpg VoiceCoil v2_ring Ind 1khz.jpg (33.8 KB, 18 views)
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Old 23rd July 2012, 02:27 PM   #50
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Very nice project!

The basket can be made easy and universal as Audio Technology Flex-Unit:
Click the image to open in full size.

http://audiotechnology.dk/files/Dimensions_Drivers.pdf
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