Flat speaker element for mechanical vibration - Page 1
Forum section: electronics / projects

author: rossmoffett
author_rank: Regular Contributor
timestamp: January 27, 2015, 03:07:16 pm
content: I'm working on a project that characterizes mechanical vibrations that it picks up with an accelerometer. We have some recordings of real data that I'm trying to develop interpretive algorithms for. I'd like to reproduce the real working environment as much as possible, but we can't do that in the lab and the place where we test it is very far from home.What I want to do is be able to attach a flat plate piezo element (or anything similar) to the outside of the sensor enclosure and play the recordings through it to approximate the working environment. This way I know that the microprocessor can handle the taxing real-time calculations it needs to do while it is also working to process accelerometer input. Problem is that piezos aren't very good at reproducing a range of frequencies. I found one that claims to in the mouser data spec, but can't pull the data sheet from the manufacturer because it's being end-of-lifed. More reason I need to snag some up now if I want to build this test kit.Can anyone think of an alternative? Or a reason why this part may not work out as well as I hope? Frequencies of interest are from 1500 Hz to 5000 Hz.http://www.mouser.com/ProductDetail/Murata-Electronics/VSLBG1914E1400-T0/?qs=sGAEpiMZZMuTkJYgZlQcSe0MK9yKnSN8gRDLiheo23o%3d

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 27, 2015, 03:47:49 pm
content: We don't know anything about the signals, the conditions, the sensor, the design amplitude, etc. etc.That piezo speaker would probably work for SOME accelerometers, but it may not have the power or the amplitude, etc for YOUR situation.You told us a lot about the motivation, but not really anything about the gadget itself.For example: if it were a geophone like device, you would need lower frequency and higher amplitude than you could get out of any piezo transducer.PS: Your "subtitle" is way too long. It overlaps the body of the message and renders both unreadable.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: January 27, 2015, 03:49:55 pm
content: how much mass do you have to move - frequency and amplitude with mass give a better idea of motor size/strengthvoice coil motors are used in shaker tables, dynamic loudspeaker drivers have voice coil motors but with too light a suspension to carry much mass but might be a start for a hackby 5kHz mechanical resonances from lack of stiffness makes for poor and unpredictable results without lots of engineering

author: dannyf
author_rank: Super Contributor
timestamp: January 27, 2015, 04:16:42 pm
content: QuoteGet a smart phone that uses its front glass panel as speakers and put your accelerameter on the glass panel. Load up your music into the smart phone and play it back while reading the accelerometer.However, unless you have some super-duper accelerometer, it is not going to react that fast.

author: eneuro
author_rank: Super Contributor
timestamp: January 27, 2015, 04:26:41 pm
content: Maybe customized something like this magnetic transducer BESTAR BMT1212H09:http://www.tme.eu/en/Document/a24c693b666444d8c29fafd0aa0666ff/bmt1212h09_010406.pdfcould work?Also looking for good vibration source and for the moment H bridge with electromagnet (eg. from 230VAC microwave fans ) controlled by MPU like motor is the only thing which seams to have much bigger power than those tiny magnetic transducers since I need in my project vibrate mass 0.1kg with a few milimeter (mm) amplitude displacements and make this without any physical contact with vibration source

author: rossmoffett
author_rank: Regular Contributor
timestamp: January 27, 2015, 04:52:52 pm
content: Quote from: dannyf on January 27, 2015, 04:16:42 pmThis is what I've been doing so far. It is a super-duper accelerometer, the ADXL001 70G model. The phone I have doesn't play through front glass though, I'm just relying on the mechanical vibrations from the case of the phone to the case of the accelerometer, which dampens quite a bit. I'd also like to have something a bit more technical and controlled/reproducible. Up to now it's worked fine to get bugs out of the data logger and such.Quote from: f5r5e5d on January 27, 2015, 03:49:55 pmI don't really have to move the mass, just transmit sound into it. Although it is an accelerometer, we're less interested in physical displacement and more interested in the frequency of the mechanical noise source. The accelerometer is extremely sensitive, so amplitude is not as important as frequency response of the transmission element.Quote from: Richard Crowley on January 27, 2015, 03:47:49 pmI'll change the subtitle, the last time I was active on the forum I was hacking my Rigol scope about five years ago. I know that you don't have enough information to design my project for me, but that's not really the point. My goal is to know if there is a piezo with a reasonably flat response curve through the frequencies that I mentioned, or a good alternative that can mechanically transmit to the outside of a metal enclosure.Quote from: eneuro on January 27, 2015, 04:26:41 pmSounds cool - do you have any documentation on how you did that, or a photo? Are you ordering that part direct from China, or have a supplier in a western nation?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 27, 2015, 05:03:34 pm
content: Quote from: rossmoffett on January 27, 2015, 04:52:52 pmSo should we assume that you already know that the output amplitude of that transducer is sufficient for your requirements?Unless you know that, the frequency response seems like a moot point.

author: LaserSteve
author_rank: Super Contributor
timestamp: January 27, 2015, 05:33:47 pm
content: For a Piezo, the best in the world is probably PIEZOSYSTEM JENA when it comes to Piezo with feedback. However the amplitudes would be miniscule.Getting a Ribbon Speaker to do this would be tricky at best.An open loop Piezo Bender Bimorph might do some of what you ask with Sine waveforms. But you will spend more time calibrating the Bi-Morph or Piezo Disk then calibrating your system.If your target inertia is non existent, this is doable. But if your target has any substantial inertia, 5 KHz electromagnetic linear motion that can follow a waveform is unheard outside of loud speakers or MEMS devices. Follow a sine, yes, follow a pulse at resonance yes, follow a discrete waveform, difficult.Having worked with high speed rotary actuators for years, I can get DC to ~2.5 KHz at 8-10' mechanical on a .6 mm shaft, with an analog PID servo loop and optical position feedback. To get that, my load inertia is limited to ~ 0.3 gm cm^2. But I'm moving tiny mirrors, not a arm with a load on it. As I increase the angle, my frequency response falls off like mad. If I increase the inertia, its even worse then increasing the angle.A coil driven Ribbon Speaker might get you close, but again, your load must have almost no inertia.Can you apply a Fourier Transform to your waveform, break it down into components and attempt to characterize your transducer with one sine wave at a time?I think this is coming down to a speaker element. If that can't do it, your in between a rock and a hard place.If not, you could tape a coil of a few turns to you load. place it in the field of a neodymium magnet and drive the coil with an amplifier.We need to know the magnitude of motion you need.Steve

author: eneuro
author_rank: Super Contributor
timestamp: January 27, 2015, 05:52:15 pm
content: Quote from: rossmoffett on January 27, 2015, 04:52:52 pmDo you mean this magnetic transducer BESTAR BMT1212H09 available athttp://TME.eufor example?For the moment since this quite big vibrating (moving element) is to make noisy sounds by hitting in steel bottom plate, testing something much cheaper and already available based on mentioned magnetic transducer (BESTAR BMT1212H09) which will be driven by MPU in 3 phase configuration- I mean three such magnetic transducer in star configuration and its three windings driven like... 3 phase brushless motorWaiting for parts to test this, but probably it will be better to make this small PCB more powerfull and be able to connect more power full electromagnets if needed.I'm not sure if those magnetic transducer BESTAR BMT1212H09 can work at 5V, while I have already soldered such simply 3 phase ATTiny85 based 0.8Amax PNP/NPN transistors based 3 phase driver, but its specs tells about 7V-12V power supply-this is new thing and didn't tested them yet, but they are cheap no no worry if they will bejust want to see how do they compare to piezo buzzer and if they really vibrate than custom tube could be used (I have one 1m longand adjust resonance frequency to make those vibrations capable to propagate into... not air but ground in my projectAdding somekind of accelerometer to MPU could help fine tune sound frequency to match tube size and compensate for temperature and air pressure changes (speed of sound changes ) so yep probably I need feedback too and accelerometer might be quite cool addon thereUpdate: Probably accelerometer not needed in my project while I have 2 ADC free so one with photodiode is used for light sensing and configuration and another magnetic transducer can be used as feed back on ADC with small adapter, I think

author: ajb
author_rank: Super Contributor
timestamp: January 27, 2015, 06:43:25 pm
content: Taking a step back for a sec. . . for the purposes of your testing, do you really need the accelerometer, or could you simply play back the recorded data directly into the ADC? Presumably the test data was recorded from some sort of accelerometer, right?

author: Puffie40
author_rank: Regular Contributor
timestamp: January 27, 2015, 07:02:07 pm
content: Why a speaker? Strain guages can be used to detect vibrations, and the guage in a bridge circuit can then be used to determine the magnitude of the vibration.

author: Yago
author_rank: Frequent Contributor
timestamp: January 27, 2015, 07:21:27 pm
content: Quote from: Richard Crowley on January 27, 2015, 05:03:34 pmRichard, what about the guys who male plate reverbs (over on GS?), wonder if the same transducer they use be applicable?

author: eneuro
author_rank: Super Contributor
timestamp: January 27, 2015, 07:36:03 pm
content: Quote from: Puffie40 on January 27, 2015, 07:02:07 pmAnother story might be how durable they are?Depending on vibrations type probably even Hall efect sensor could be used if some kind of magnetic field is present and probably radiometric SS495A (<$2 cost) will be better in my type of vibrations with bigger 0.1kg mass at amplitude a few milimeters.So, it will depend on specific project requirementsThere are some possibilities

author: rossmoffett
author_rank: Regular Contributor
timestamp: January 27, 2015, 07:49:44 pm
content: Quote from: ajb on January 27, 2015, 06:43:25 pmThat will work fine too, yes. I kind of want to hear the signal while the data is being interpreted because the events are pretty simple for a human ear to distinguish, but I suppose I could just amplify a line-out from my PC and inject to the ADC directly. Definitely the most elegant/simple solution to my problem.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 27, 2015, 08:47:56 pm
content: Quote from: Yago on January 27, 2015, 07:21:27 pmhttp://www.parts-express.com/cat/tactile-transducers-exciters-bass-shakers/18

author: eneuro
author_rank: Super Contributor
timestamp: January 27, 2015, 09:10:50 pm
content: @Richard CrowleyThis thing in size to an ice hockey puck is really coolhttp://www.parts-express.com/dayton-audio-tt25-8-puck-tactile-transducer-mini-bass-shaker-8-ohm--300-386http://www.parts-express.com/dayton-audio-hdn-8-weatherproof-sound-exciter-transducer--300-387Another weatherproof also looks nity.Yep, RMS 50W power / 100 watts maximum and Frequency response: 40–15,000 (typical)

author: eneuro
author_rank: Super Contributor
timestamp: January 28, 2015, 11:02:29 am
content: Anyway, idea od those exiters (after reading its technical notes) not far away from classic electromagnet + neodymium magnet on moving part and... for prototype should be fineSmall quite powerfull H bridge controlled by MPU should create quite interesting "underground music" and probably no external amplifiers needed

author: rossmoffett
author_rank: Regular Contributor
timestamp: January 28, 2015, 04:38:19 pm
content: I like this bone conducting element a lot.http://www.parts-express.com/dayton-audio-bct-2-bone-conducting-transducer-exciter-45mm-dia-x-25mm-h--240-612I think I'll buy one and see how it works out. While direct-playing recordings to the ADC is definitely the most accurate way to test my interpretive algorithm effects on the microprocessor performance, I think that this bone conductor could be a good tool to make relative measurements of transmittance to the accelerometer as we make design decisions on packaging. Thanks a lot for remembering that site!

author: eneuro
author_rank: Super Contributor
timestamp: January 28, 2015, 06:29:55 pm
content: Yep, this bone exiter also better fits my needs in final productQuoteIt looks like it is capable of a few mm movements at lower frequency (I mean below 1Khz), but ok there is live help so probably email to support should help, but if someone already figured it out and has some real experience with this exiter driving could be nice discuss different methods to drive this thingThere is one thing which confuses me-why its wires are marked black/red - does it need some kind of special amplifier or can be driven by AC current within its power specs?

author: rossmoffett
author_rank: Regular Contributor
timestamp: January 28, 2015, 06:51:44 pm
content: It's designed for speaker replacement. Use any 4 ohm output impedance amplifier. The red/black color scheme is common on speakers to help wire series/parallel speaker arrangements in the correct phase. I'm probably going to find a crummy boombox or car amplifier to drive mine.

author: eneuro
author_rank: Super Contributor
timestamp: January 28, 2015, 07:04:23 pm
content: I'm not audiophile so, it will be hard to find amplifier which will fit my project needs, while this sound will be created on MPU (no playback needed) and want put everything on custom PCB 2inch x 2inch (5cmx5cm) maxIt is time make low cost custom amplifier and outperform those audiophile used for extraordinary sound quality

author: rossmoffett
author_rank: Regular Contributor
timestamp: January 29, 2015, 02:36:52 pm
content: Use a class D amplifier chip from Maxim or similar. Super small and powerful.

author: eneuro
author_rank: Super Contributor
timestamp: January 29, 2015, 03:50:56 pm
content: ThisMAX9709 stereo/mono Class D audio power amplifier delivers up to 2 x 25W into an 8? stereo mode and 1 x 50W into a 4? load in mono modeis quite interesting and have decent power

author: rossmoffett
author_rank: Regular Contributor
timestamp: February 06, 2015, 11:30:23 pm
content: I just thought I'd drop a note here to say that the bone conducting transducer has been a super, super good stimulator for my accelerometer apparatus. It will give me good insight into the final mounting fixture we use in the enclosure by giving some real transmittance numbers and show potential dampening problems.It's also really fun to play with.. I can turn it up such that I hear it faintly, then place it against a desk or wall surface and the whole room fills with sound. Disappointing frequency response, depending on the surface, but still really neat.

author: nali
author_rank: Frequent Contributor
timestamp: February 07, 2015, 09:20:03 am
content: Quote from: rossmoffett on February 06, 2015, 11:30:23 pmThere are a few of this type around now... we use them for our public information displays where vandalism may be an issue:http://www.visaton.com/en/chassis_zubehoer/koerperschall/index.htmlhttp://www.woweeone.com/#!gelaudioshop/c16rb