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The Stax Thread III - Page 133

post #1981 of 4043

It would be very cool if some of the DIYers would experiment with graphene for their 'stats. Don't know if it is viable to do so in the first place.

 

EDIT: I suppose the thread above answers that.. Maybe in the future.

post #1982 of 4043
Quote:
Originally Posted by jgazal View Post
 

 

Would you please point me thermo acoustic speakers available for purchase?

 

I see the electrostatically graphene you mentioned: http://www.physics.berkeley.edu/research/zettl/projects/graphene_loudspeaker/speaker.html. Which is the thickness of that graphene diaphragm? Is it a single layer graphene or it has a substrate? If it is not a single layer graphene, how graphene in a substrate would differ in quality from mylar?

 

Would you point me where to buy similar single layer graphene or a graphene in a substrate sheets to made larger diameter diaphragms (i.e. a diaphragm for the SR-003 or SR-009)?

 

I think consumers were not concerned about teflon or lithium until they realized their utility.


Thermoacoustic speakers are inefficient at audible frequencies and exhibit a response slope that is unsuitable.

 

The thickness of the diaphragm demonstrated in that paper was determined to be about 30 nm via measured light transmittance. The graphene film would represent a perfect diaphragm transducer.


Edited by dripf - 4/6/14 at 2:21pm
post #1983 of 4043
Quote:
Originally Posted by dripf View Post
 


Thermoacoustic speakers are inefficient at audible frequencies and exhibit a response slope that is unsuitable.

 

The thickness of the diaphragm demonstrated in that paper was determined to be about 30 nm via measured light transmittance. The graphene film would represent a perfect diaphragm transducer.

 

Assuming one could purchase graphene that thin, which it appears one cannot, wouldn't it still be nearly as conductive as metal? An electrostatic diaphragm should not be anywhere close to that conductive.

post #1984 of 4043

The diaphragms are insulated.

post #1985 of 4043
Quote:
Originally Posted by dripf View Post
 


Thermoacoustic speakers are inefficient at audible frequencies and exhibit a response slope that is unsuitable.

 

Can carbon nanotubes film transducers also be classified as inefficient at audible frequencies? I think that article also covers such slope:

 

Quote:
(...)
 
Despite the excellent acoustic performance of the CNT loudspeaker, it has a drawback. As shown in Figure 2d, the output frequency doubles that of the input. The human voice and music sound strange when a commercial bipolar audio amplifier is used to drive the CNT thin film loudspeaker. A simple solution is to add a direct current bias Io to the alternating current for driving such CNT loudspeakers. To achieve this, we use a very simple single transistor amplifier to drive our CNT loudspeaker, which can reproduce the input sound wave signals faithfully. The schematic circuit is shown in Figure S2 of the Supporting Information. Note that the impedance of the CNT loudspeaker is pure resistance (see Supporting Information, Figure S1), and the design of the amplification circuit is much simpler than that for inductive voice-coil loudspeakers. (...)
 

 

Indeed an interesting topic.

post #1986 of 4043
Quote:
Originally Posted by dripf View Post
 

The diaphragms are insulated.

So what's the total thickness (really weight) of the moving diaphragm?

 

I've always thought that graphene should eventually be used for the stators, not the diaphragm.

 

Traits important for the diaphragm:

- lightweight

- high resistance (low conductance)

- very pliable

- long term dimensional stability

- able to flex continuously without break/fracture

 

Traits important to stators:

- high conductivity

- as rigid as possible

- related, high rigidity allows for thinner stators which allows for smaller and more numerous holes which allows for more evenly distributed charge on the surface (no "hotspots")

 

Graphene has conductivity and rigidity that are off the charts.  I'm hoping that one day it will be possible to consistently make the graphene sheets thick enough so that they can be used as ultra strong stators.  There will also need to be a way to shape the graphene sheets (to insert the stator holes, etc). 

post #1987 of 4043
Quote:
Originally Posted by n3rdling View Post
 

So what's the total thickness (really weight) of the moving diaphragm?

 

I've always thought that graphene should eventually be used for the stators, not the diaphragm.

 

Traits important for the diaphragm:

- lightweight

- high resistance (low conductance)

- very pliable

- long term dimensional stability

- able to flex continuously without break/fracture

 

Traits important to stators:

- high conductivity

- as rigid as possible

- related, high rigidity allows for thinner stators which allows for smaller and more numerous holes which allows for more evenly distributed charge on the surface (no "hotspots")

 

Graphene has conductivity and rigidity that are off the charts.  I'm hoping that one day it will be possible to consistently make the graphene sheets thick enough so that they can be used as ultra strong stators.  There will also need to be a way to shape the graphene sheets (to insert the stator holes, etc). 

 

I had this doubt also. I think stiffness can also refer to an elastic material. As I see it, it can take a lot of force without tearing apart, but it does not mean it won't bend. I have found this article particularly interesting: http://physicsworld.com/cws/article/news/2008/jul/17/graphene-has-record-breaking-strength.

 

Quote:
Originally Posted by dripf View Post
 

Thermoacoustic speakers are inefficient at audible frequencies and exhibit a response slope that is unsuitable.

 

The thickness of the diaphragm demonstrated in that paper was determined to be about 30 nm via measured light transmittance. The graphene film would represent a perfect diaphragm transducer.

 

Thank you for mentioning this paper (http://arxiv.org/ftp/arxiv/papers/1303/1303.2391.pdf)! They give the recipe to cook the graphene! Nice.

 

Quote:
Graphene was previously used to construct a thermoacoustic loudspeaker12-14. In the thermoacoustic configuration graphene serves as a stationary heater to alternately heat the surrounding air thereby producing , via thermal expansion, a time-dependent pressure variation, i.e. sound wave. The method is especially effective in the ultrasonic region because of graphene’s small heat capacity (for this reason, carbon nanotube films can also be utilized15-17). However, for thermoacoustic speakers operating at audio frequencies, most input energy is dissipated by heat conduction through the air and does not generate sound12. For example, the power efficiency for a graphene thermoacoustic speaker is exceedingly small, decreasing from ~10-6 at 20 kHz to ~10-8 at 3 kHz12,13. The thermoacoustic approach also suffers from sound distortion because the heating power is proportional to the square of the input signal and the transduction is therefore intrinsically non-linear15.
 

 

So I think thermoacoustic CNT film is ruled out...


Edited by jgazal - 4/6/14 at 4:35pm
post #1988 of 4043
Quote:
Originally Posted by jgazal View Post
 

Thank you for mentioning this paper (http://arxiv.org/ftp/arxiv/papers/1303/1303.2391.pdf)! They give the recipe to cook the graphene! Nice.

 

Awesome! Sounds easy enough. I'll work on getting setup to do this for my DIY drivers.

post #1989 of 4043
Quote:
Originally Posted by dude_500 View Post
 
Quote:
Originally Posted by jgazal View Post
 

Thank you for mentioning this paper (http://arxiv.org/ftp/arxiv/papers/1303/1303.2391.pdf)! They give the recipe to cook the graphene! Nice.

 

Awesome! Sounds easy enough. I'll work on getting setup to do this for my DIY drivers.

Great :D 

But you still can't get thin enough graphene sheets?

post #1990 of 4043
Quote:
Originally Posted by davidsh View Post
 

Great :D 

But you still can't get thin enough graphene sheets?

 

It seems as though I can make them. Also, I actually did find a number of sources online for extremely thin graphene sheets that come backed on foil (the trick is to search 'foil backed graphene sheets'. Then I would acid etch the foil away after gluing it to a diaphragm holder. The problem is they are in the range of $50/square inch, so I'll have to make my own.

post #1991 of 4043
Quote:
Originally Posted by Crashem View Post

Just got noticed my sr009 shipped from japan. A lot faster than I originally thought would happen. Bhse on order. Need to get an amp ASAP. Don't want these sr009 sitting around too long without use. Might have to get woo wee and hook them up to this spare parasound a51 lying around.

 

Wow postman just dropped off my new SR-009s!  That was fast through EML.  Went out on 4/4 from Japan.

post #1992 of 4043
Quote:
Originally Posted by Crashem View Post
 

 

Wow postman just dropped off my new SR-009s!  That was fast through EML.  Went out on 4/4 from Japan.

Congratulations! Yes, that is fast.

 

But more importantly did you find/buy/borrow an amp? That would be the worst torture to have pair of 009's with no amp!

post #1993 of 4043
Quote:
Originally Posted by darinf View Post

Congratulations! Yes, that is fast.

But more importantly did you find/buy/borrow an amp? That would be the worst torture to have pair of 009's with no amp!

The torture has already begun. Waiting on kgsshv from spritzer which should hopefully hit me in 2 weeks. Who knows how long for the bhse I have on order. I started to open the sr009 then stopped when I remembered I could use them. Funny thing is I got my eml 2a3 tubes today and no amp to play them in. More waiting. More torture.
post #1994 of 4043
Quote:
Originally Posted by dude_500 View Post

 

Assuming one could purchase graphene that thin, which it appears one cannot, wouldn't it still be nearly as conductive as metal? An electrostatic diaphragm should not be anywhere close to that conductive.

 

Forgive my ignorance, but I thought in the given structure they can't short circuit the stators. I would think that arcs can't form either, since it's exceptionally smooth. Besides, I expect conductivity is *very* directional with graphene. 

As dripf says, they are insulated, but is that really needed? 

Practice will tell.

They are indeed pretty much perfect materials for headphones, unfortunately not (yet) so much for loudspeakers.

post #1995 of 4043

It's not just about arcing though.  A high resistance on the diaphragm will prevent charge migration and allow the transducers to operate in "constant charge" mode.  Are there any distortion measurements of that graphene project?

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