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Piezo Ceramic Speakers

I'm looking for a topic to do an oral presentation on as part of my course at university (physics)...

I remember hearing about flat panel speakers, which don't use magnets to move volumes of air, they utilize the vibration of piezo crystals...

I'm searching around on google and online journals, but does anyone here have links to an explanation of their working to help out?

Any help would be appreciated as always
Thanks
< w o g o n e . c o m / l o l >

Piezo Ceramic Speakers

Reply #1
So far I've found some very interesting stuff about them, flat panel speakers sound like they'd be good contenders for high end speaker systems?

This link to Home Cinema Choice has an interesting to read, but brief description of how they work and what is available..

I'm after more to do with the complex pattern of vibrations made to produce the sound, it's some hugely complex algorithm I'd guess?  I pretty much understand how the piezo crystals work, converting electric current to movement in various ways (for instance in your LCD watch)

[edit]
http://www.avbusa.com/avb2001/sonix.html
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Piezo Ceramic Speakers

Reply #2
That is the basis of things. When current is applied to crystals such as quartz they change size. The more current applied the more they expand. Similar technology is used in tunneling electron microscopes. The interesting thing is not only do they change size when current is applied. The produce current when their size is changed. They can also produce light. If you take two rough pieces of quartz and bang them together in the dark they will light up. I don't have any technical links for ya. But you might do a search for sonoluminescence. I did some research on it a few years back. Interesting subject. A tank of water with high power transducers at the top and botom has a bubble of air released from the bottom. As the bubble starts to rise the transducers kick in forcing high power soundwaves from the top and bottom of the tank into the water. They cause the bubble to stabilize somewhere about the middle of the tank where the waves meet and cancel. Once the bubble stops it then starts to expand and contract rapidly and emmits weak narrow spectrum light. There is nothing special about the bubble either. Just plain air.

http://www-phys.llnl.gov/N_Div/sonolum/

http://www.lcm3b.u-nancy.fr/lcm3b/Posters/...uillotmodif.pdf
http://www.morganelectroceramics.com/piezoguide4.html
http://www.piezo.com/history.html

Piezo Ceramic Speakers

Reply #3
Thanks  That's a freaky demonstration of physics!  I'll take a look at it more thoroughly once I've got my research done..

It's just how this 'disturbed mode' of vibration is created in the flat panel, and why that creates proper sound waves that spread out in a circular pattern that is eluding me
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Piezo Ceramic Speakers

Reply #5
 Interesting!  I will have to stick with my explanation for a while untill I digest all that.


"It's  M A G I C!"

Piezo Ceramic Speakers

Reply #6
Flat panel speakers don't use piezo crystals !
They are electrostatic speakers (summary here : http://www.howstuffworks.com/speaker5.htm).

Electrodynamic are the most common (99 %)
Piezo are used for cheap tweeters
Electrostatic for high end medium-treble speakers
Ribbon for high end tweeters
Compression chambers ? Horns ? (english word, please...) for high efficiency medium-treble speakers, either very low, or high end.
Plasma for high end tweeters
Cold plasma has better bass but is experimental (low efficiency, produces ozone)
Paper speakers remained a gadget.

Did I forget something ? Oh yes, I heard also of "engine-speakers" for bass in theatres, but I don't know anything about them.

Piezo Ceramic Speakers

Reply #7
Quote
Electrodynamic are the most common (99 %)
Piezo are used for cheap tweeters
Electrostatic for high end medium-treble speakers
Ribbon for high end tweeters
Compression chambers ? Horns ? (english word, please...) for high efficiency medium-treble speakers, either very low, or high end.
Plasma for high end tweeters
Cold plasma has better bass but is experimental (low efficiency, produces ozone)
Paper speakers remained a gadget.

Did I forget something ? Oh yes, I heard also of "engine-speakers" for bass in theatres, but I don't know anything about them.

What about something like these:

http://www.manger-msw.com/

Edit: Seems that some very high end speakers (Audio Physic Medea for example) have used these in the past actually..

Speaking of some of these different technologies, have you (or anyone else) ever actually used or heard some of this stuff?

I'm wondering because I'm thinking about experimenting with building some loudspeakers in a few months, and some of the unique drivers and technology I've been reading about sound pretty interesting.

More specifically, I've been looking at some ribbon tweeters and leaf-ribbon? tweeters such as the SA 8535, Philips RSQ8P, or the Orca  Ravens, as well as some of the ceramic membrane drivers from Accuton (I think the Lumen-Whites and some Avalons use these), in addition to the Mangers I mentioned above.

I'm pretty new to loudspeaker design theory (I have a whole lot to learn), but in researching the various solutions, these seem to present some interesting possibilities.  What I'm wondering though, is that if these products are as good as they are supposed to be, how come these type of technologies are not more widely used?  Is it simply because of cost (traditional drivers cost much less), or is it because most of this stuff is only hype?  Or is it just the natural inertia present in the industry and a general unwillingness to embrace new ideas?

I'd like to hear some comments on this kind of stuff from someone who really knows about it.

Also, do you happen to know of any good, unbiased sources for information (online) on the advantages and disadvantages of all of these different technologies (electrostats vs horns vs dynamic, etc), and also the advantages and disadvantages of the different materials and build types used in dynamic drivers (kevlar, aluminum, paper, different variations, etc)?

I do know that with some of this stuff there are downsides, like with the ribbon tweeters for example, vertical dispersion is supposed to be somewhat poor compared to traditional dome type dynamic drivers.

Oh and BTW, since I know that you have those Dynaudio Gemini's, do you know if Dynaudio is still selling individual drivers?  I can't seem to find anyone selling their stuff anymore.. like they've stopped or something.  I've been looking around for some comparable drivers and I see Scan Speak mentioned quite a bit for their tweeters, as well as Seas.  Focal also seems to be pretty highly regarded.. do you have any experience with any of them Pio2001?

Piezo Ceramic Speakers

Reply #8
Quote
That is the basis of things. When current is applied to crystals such as quartz they change size. The more current applied the more they expand. Similar technology is used in tunneling electron microscopes. The interesting thing is not only do they change size when current is applied. The produce current when their size is changed. They can also produce light. If you take two rough pieces of quartz and bang them together in the dark they will light up. I don't have any technical links for ya. But you might do a search for sonoluminescence. I did some research on it a few years back. Interesting subject. A tank of water with high power transducers at the top and botom has a bubble of air released from the bottom. As the bubble starts to rise the transducers kick in forcing high power soundwaves from the top and bottom of the tank into the water. They cause the bubble to stabilize somewhere about the middle of the tank where the waves meet and cancel. Once the bubble stops it then starts to expand and contract rapidly and emmits weak narrow spectrum light. There is nothing special about the bubble either. Just plain air.

piezo electrics don't work that way at all. i'm going to give you the benefit of the doubt and assume you aren't a physicist, cause that's just negligent dissemination of plain old wrong info.

"piezo" implies that when you create strain within the material, you also change some other eletromechanical property of the material. piezo electrics (can be quartz, but very often they're made out of ceramics) induce a voltage when you strain them. piezo resistors change their resistances. i'm not sure exactly how the resistors work but here's how the piezo ceramics work:

you have this material, with a crystal lattice, right? the lattice points form cells in the material, and in a piezo electric the cell has a dipole moment. if you strain the material, you change the lattice spacings, and therefore the dipole moment. this creates an <I>electric field</I> across the material. also, if you apply an electric field across the material, the opposite happens: the material gets thicker/thinner. NOTE: piezo electrics allow VERY little current to pass through them. that's why their power dissipation is so low.

SEMs (scanning-tunneling electron microscopes) as far as i understand them apply a voltage between the sample and needle point. the needle is held close to, but obviously not touching the surface of the sample, so that in classical theory, you expect nigh zero current in the needle. quantum mechanics, however, predicts that some of the electrons can tunnel through the potential barrier (air) to get to the lower potential (remember the needle is at a lower voltage?), so you do detect a current. the amount of current is very sensitive to the distance between the needle and the sample (decaying exponential), so you get real pretty pictures of "surface structures". like insects and dna and stuff. i think what you meant was that piezo electrics are used in AFM (atomic force microscopes), which they are. the cantilever beams are made out of piezo electrics. atomic forces (not sure what those are exactly, never really studied the mechanism) move the cantilever, induces a voltage which you can measure.

you can search for sonoluminescence, but you won't find anything explaining it. well, maybe you will, but it won't be a generally accepted explanation. the simple reason being that <I>no</I> condensed matter physicist <I>really</I> understands sonoluminescence; the honest ones will say this. also, the bubble doesnt have to form in the center of the tank, it can form anywhere. it's just that if you want to look at just one bubble, then it's easier to set it up so that you contain a single node in the single node in the center of the tank. and the soundwaves don't have to be "high power." that's what makes it so damn interesting. and the light is <i>not</i> a narrow spectrum. it's pretty much the opposite. people at one time thought that it was caused by incredible heat, but that's not the case, since the frequency output is pretty much flat (iirc... it was a long time since i knew this stuff). more info: the frequency of the light flashes is well defined (i.e. it blips with a certain frequency, not the light has a certain frequency) and as far as i know NO ONE has been able to time resolve the flashes. the upper bound for the duration of a flash is something like <10ps, which, at least to me, is amazing. also amazing is the amount of power these things put out. you use low power density sound waves to generate photons that by any right should require temperatures on the order of (or greater than) the surface of the sun. sonoluminescence isn't the only instance of this amazing phenomenon of power focusing, but it's one of the more well known.

god, that was long. but i hate it when people try to explain things when they don't understand what they're talking about at all. thats why i don't try to explain anything to do with audio here

edit: summary--
electric field != current
AFM != SEM
small wavelength == xrays != small bandwidth

edit2: realized that i had a "first:", but no "second:"

Piezo Ceramic Speakers

Reply #9
Forget about electrostats and all that crap. This is obviously the future of hi-fi speaker design

Piezo Ceramic Speakers

Reply #10
Quote
Flat panel speakers don't use piezo crystals !
They are electrostatic speakers (summary here : http://www.howstuffworks.com/speaker5.htm).

I beg to differ.

the flat panel speaker technology being talked about here is the implementation of NXT's "SurfaceSound", -->
http://www.nxtplc.com/nxtsound/technology/...Sound/index.asp
A riddle is a short sword attached to the next 2000 years.

 

Piezo Ceramic Speakers

Reply #11
Quote
.. I'm thinking about experimenting with building some loudspeakers in a few months, and some of the unique drivers and technology I've been reading about sound pretty interesting.

great.
Quote
More specifically, I've been looking at some ribbon tweeters and leaf-ribbon? tweeters such as the SA 8535, Philips RSQ8P, or the Orca Ravens, as well as some of the ceramic membrane drivers from Accuton

ribbon is nice

Quote
What I'm wondering though, is that if these products are as good as they are supposed to be

some are. you can take expensive drivers and make shit out of these and you can take cheap drivers and work wonders. it all depends.
Quote
how come these type of technologies are not more widely used?

is high end mainstream?
Quote
Also, do you happen to know of any good, unbiased sources for information (online) on the advantages and disadvantages of all of these different technologies (electrostats vs horns vs dynamic, etc), and also the advantages and disadvantages of the different materials and build types used in dynamic drivers (kevlar, aluminum, paper, different variations, etc)?

google!
The BEST source for drivers:
here
in summary:
drivers should be.
a: stiff
b: with high damping
c: low weight
warious materials accomplish that pretty well
seas have those magnesium cones. wery rigid. but has a very ugly breakup mode with a 12(18?)dB dual resonance. Only very experienced DIYers can get them right. When they do, this is the most enjoiable driver out there(lowest IM distorsion)
Focal makes W samdwich cones. not as rigid as magnesium but is easy to get it right. considered the most transparent in midrange. Do you know those 20000+ Utopia speakers? Those use focal drivers. funny thing is that those drivers cost 150$ each. Funny heh?
and there is skaaning. custom order and stuff. THE greatest and most expensive.(500$ not SO expensive)
kevlar is allready an aged technology.
aluminium is rigid. not so ugly as magnesium but not so great either.
paper is considered aged but it is a great material (coated)
PP(polypropylene) is considered the most bs material. BUT skaaning uses it.

Quote
I do know that with some of this stuff there are downsides, like with the ribbon tweeters for example, vertical dispersion is supposed to be somewhat poor compared to traditional dome type dynamic drivers.

there are no downsides for ribbon. 


well there is a SEAS 27tffc. The tweeter that rules low end(27$). built like a tank and can be crossed at 1800hz.
then there is the high end. Scan-Speak 9500-9900, SEAS excel, Focal etc. for 80-150$. If you get them right, they sound the same. How they sound? go to your local hifi shop, ask the most expensive speaker with dynamic drivers and you get the picture.
Then there is the Hiquphon. The ultimate high end. more sparkle.
you want more?
there is ribbon.
in the low end the HiVi Research RT1 and in the high the orca. you mentioned some philips ribbons. if you wan't to experiment then go for it. the Ravens are proven to be worth the money.
don't have experiense with plasma drivers 
Quote
do you know if Dynaudio is still selling individual drivers? I can't seem to find anyone selling their stuff anymore.

dynaudio dont sell drivers for diyers no more. :'(

Piezo Ceramic Speakers

Reply #12
please look at line arrays too.(12 seas magnesiums with couple of ravens, dipole ofcourse. aaaarllhhh)

Piezo Ceramic Speakers

Reply #13
Quote
What about something like these:

http://www.manger-msw.com/


They seem to fit in the electrodynamic category.

Quote
Speaking of some of these different technologies, have you (or anyone else) ever actually used or heard some of this stuff?


I've heard speakers with ribbon tweeters. Unfortunately I don't remember the name, but I didn't like their treble.

I've heard some speakers with horn tweeters. The Aeria Compact had the most natural treble in the speakers I listened to when I bought the Dynaudios

? ) reported the hole experiment as representing "a lot of work, time and discouragement" before achieving a product that works.

Quote
I see Scan Speak mentioned quite a bit for their tweeters, as well as Seas.  Focal also seems to be pretty highly regarded.. do you have any experience with any of them Pio2001?


No, sorry. I went in shops to listen to some speaker, and the one I liked most was a kit : the Dynaudio Gemini, so I bought the elements, had the box made by a cabinet maker, and just followed the plan.

Piezo Ceramic Speakers

Reply #14
Quote
Quote
That is the basis of things. When current is applied to crystals such as quartz they change size. The more current applied the more they expand. Similar technology is used in tunneling electron microscopes. The interesting thing is not only do they change size when current is applied. The produce current when their size is changed. They can also produce light. If you take two rough pieces of quartz and bang them together in the dark they will light up. I don't have any technical links for ya. But you might do a search for sonoluminescence. I did some research on it a few years back. Interesting subject. A tank of water with high power transducers at the top and botom has a bubble of air released from the bottom. As the bubble starts to rise the transducers kick in forcing high power soundwaves from the top and bottom of the tank into the water. They cause the bubble to stabilize somewhere about the middle of the tank where the waves meet and cancel. Once the bubble stops it then starts to expand and contract rapidly and emmits weak narrow spectrum light. There is nothing special about the bubble either. Just plain air.


piezo electrics don't work that way at all. i'm going to give you the benefit of the doubt and assume you aren't a physicist, cause that's just negligent dissemination of plain old wrong info.

Actually I am not as wrong as you say. True my terminology was lacking. You got to cut a layperson some slack here. But it is true that when current is applied they distort, expand, or change shape slightly. And when pressure is applied they distort or change shape slightly and generate a small electrical charge or other emission. There was nothing inherantly wrong with what I said. My terminology was just lacking. All you said was basically the same thing I said in a more technical propper manner.

Piezo Ceramic Speakers

Reply #15
Quote
Actually I am not as wrong as you say. True my terminology was lacking. You got to cut a layperson some slack here. But it is true that when current is applied they distort, expand, or change shape slightly. And when pressure is applied they distort or change shape slightly and generate a small electrical charge or other emission. There was nothing inherantly wrong with what I said. My terminology was just lacking. All you said was basically the same thing I said in a more technical propper manner.

yeah, i was pretty harsh, and i am sorry. it's just that physics to me is the way audio is to some people here, and i get all emotional-like when i see something i think is wrong. i shouldn't have phrased the first paragraph that way, since i could pretty much tell where you'd made the mistakes and from reading your sources, i could tell why you made them. and they were all pretty understandable mistakes for someone not too familiar with the terminology. from lay person to lay person, i suppose that terminology is not terribly important, but current and electric field are totally different things. really, you want to apply a voltage. hooking a current source to a piezo element is just asking for trouble.

more on topic, i don't think that piezo electric elements would make very good elements, since the stroke tends to be fairly small. "bender" beams and diaphragms can get deflections up to around a mm (or a little more), which might actually be enough. as i said, i don't design speakers. it has also just occurred to me that the voltages might get a little high. but again, i'm not sure whether it's a problem or not to have a wire on the diaphragm carrying ~100V or not... it just seems like a bad thing to me.

 
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