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-   -   Ribbon or planar headphones (http://www.diyaudio.com/forums/headphone-systems/130061-ribbon-planar-headphones.html)

Spasticteapot 19th September 2008 10:37 PM

Ribbon or planar headphones
 
The majority of headphones have quite simply awful high-frequency performance. However, by using either a single ribbon or a combination of ribbons, it should be possible to build a driver that works very well even to high frequencies with minimal energy storage. Also, according to another DIYaudio thread, the ribbon could reproduce an acceptable amount of bass, too - the short length would apparently keep it from "flapping" at low impedances.

Transmissionaudio.com has a picture of a prototype on their page, too.

http://www.transmissionaudio.com/ourribbons.html

The obvious problems with this setup would be weight (enormous) and impedance (tiny.) However, these would likely never leave my desk, and if I can get some metallized Kapton film, it should be possible to etch fine enough traces to get the impedance to an acceptable (1-ohm?) level.

jzagaja 22nd September 2008 06:50 PM

2 Attachment(s)
One of very first ugly ribbon headphone I've made from capacitor foil. More than enough bass. SPL limited but sufficient. Pleasant sound. Almost cost nothing. Can fit into Skype headphones easily (open air is however better).

Spasticteapot 22nd September 2008 07:16 PM

Quote:

Originally posted by jzagaja
One of very first ugly ribbon headphone I've made from capacitor foil. More than enough bass. SPL limited but sufficient. Pleasant sound. Almost cost nothing. Can fit into Skype headphones easily (open air is however better).

Very interesting. How do you compensate for the incredibly low impedance of such a short piece of foil?

jzagaja 22nd September 2008 09:50 PM

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Well just a small toroidal transformer :-) The beauty is when you use these as a binaural microphone and headphone at once. Never tried. Still keep working.

Spasticteapot 23rd September 2008 03:10 AM

Is that the transformer or the headphone?

Also, the noise - distortion? - increases a lot at low frequencies. Perhaps a pleated ribbon would be better?

jzagaja 23rd September 2008 07:57 AM

This is headphone measurement (6mm electret mike, 5mm above membrane in the middle), room noise. Corrugated ribbon could be better because excursion is rather large (4mm).

Spasticteapot 23rd September 2008 12:26 PM

Quote:

Originally posted by jzagaja
This is headphone measurement (6mm electret mike, 5mm above membrane in the middle), room noise. Corrugated ribbon could be better because excursion is rather large (4mm).
That is an impressive measurment indeed. What cap did you get the film from? And how could I wind an appropriate transformer?

jzagaja 23rd September 2008 01:49 PM

2 Attachment(s)
Necessary parts can be taken from old TV, radio and PC power supply (transformer core) or any other electronic waste.

1) Ribbon source is styroflex cap:
http://www.radiomuseum.org/forumdata.../Styroflex.jpg

Smaller the rated voltage thinner the foil. My LCR meter says 10um.

2) Wire (copper enamelled wire, magnet wire) from larger coils (short length) or typical home EI AC/DC adapter. Disassembly takes at least 30 minutes but you can rewind such a transformer for your ribbon as well.

3) Transformer core. PC PSU has larger cores. Core size and material determines power rate, distortion and inductance on secondary (amplifier side). Better the core less wire is necessary for a target inductance (low freq. -3dB point). Typical ribbon transformers has inductance of a few mH. Ribbon speaker has inductance of L2 coil related to LR4 crossover.

Minimum turns on secondary:

=V*10000/(4,44*freq*core_area_cm2*Bmax)

Ferrite core: 10V, 20Hz, 1cm2, 0.5T gives 2252 turns - that's a lot.

Primary (ribbon) side requires low DC resistance (DCR). Tenth of ribbon resistance - magnet wires connected in parallel. Divide above turns by squared transformer ratio = target impedance/ribbon resistance.

Quick and dirty layout:

50 turns of secondary
foil layer
10 turns of primary
foil layer
50 turns of secondary

Should work however ferrite core will saturate a bit.


Transformer transmittance and impedance can be evaluated with ARTA: www.fesb.hr/~mateljan/arta/

Requires stereo mic or line input in your PC.

Appended picture shows best balanced armature motor (single) in Shure E2 in-ear headphone. Midrange resonance isn't good on many recordings. Dipole ribbon, open construction is much more comfortable. Shure cannot be used for binaural playback.

Spasticteapot 30th September 2008 12:58 AM

I've been working on this idea. Due to my extreme inability to use FEMM, I've even enlisted the help of a fellow at the local university. (Being a student has perks, I suppose.)

However, instead of the massive headaches of transformers, I'm thinking of using metal foil on kapton. If I have my math right, six 4" long traces of 4 micron aluminum foil wired in series will have a DCR of 2.1 ohms - easily driven by a solid-state amplifier.

One thing that surprises me is how well the bass measured. From what I understand, a full waveform is unable to form due to the short distance between ear and transducer, so a good-quality seal is needed. However, a ribbon may actually have greater excursion than many headphone transducers, so this may be a non-issue.b

jzagaja 30th September 2008 02:30 PM

Usually metalic pattern is added to plastic foil via oil print. Check the math - several Ohms @ 4um is possible for longer ribbons - few meters long but if the trace is narrow... Capacitor manufacturers can produce serpentine pattern on paper or any foil but the tooling cost ca. 700 Euro. Typical 50m coils of metalized paper (alu and zinc) costs 50 Euro each. I'll check possible resistivity. Total thickness is quite good: 8-16um.

There's a really deep bass from above orthodynamic headphone - depends on distance from membrane. Escursion can be really large so good mechanical clamping is essential.


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