Passive amplification of a specific audio frequency range(microphone)

[Shploop]

Hi, I want to passively amplify a specific audio frequency range of a microphone.
When I say passively I mean by non-electronic means - no op-amps or transistors.
Like a speaker can be designed for specific frequency range - a woofer/tweeter/etc...
I presume this works in the other direction - If a make a large membrane it will respond more to a lower frequency range relative to a small membrane.
If I place a microphone in the other side of the membrane(opposite to audio source) I will accomplish this goal.

I am looking for something not to just filter, as in a band-pass filter, a specific frequency range, but to amplify it so I get maximum power conversion from audio power to electronic signal - maybe some structure that will resonate in that frequency range.

If you know a good book/website on the subject or an advance method you've encountered, as in adding ridges to that membrane or using a loudspeaker as a means of focusing sound onto a microphone instead of radiating sound or other ideas that are clever, I will be glad to hear.

By the way I want to use a piezo transducer as a microphone and it's resonance freq. is 180Hz...

Oh and one more thing - reduced size is an advantage!

 

[berkeman]

Hi, I want to passively amplify a specific audio frequency range of a microphone.
When I say passively I mean by non-electronic means - no op-amps or transistors.
Like a speaker can be designed for specific frequency range - a woofer/tweeter/etc...
I presume this works in the other direction - If a make a large membrane it will respond more to a lower frequency range relative to a small membrane.
If I place a microphone in the other side of the membrane(opposite to audio source) I will accomplish this goal.

I am looking for something not to just filter, as in a band-pass filter, a specific frequency range, but to amplify it so I get maximum power conversion from audio power to electronic signal - maybe some structure that will resonate in that frequency range.

If you know a good book/website on the subject or an advance method you've encountered, as in adding ridges to that membrane or using a loudspeaker as a means of focusing sound onto a microphone instead of radiating sound or other ideas that are clever, I will be glad to hear.

By the way I want to use a piezo transducer as a microphone and it's resonance freq. is 180Hz...

Oh and one more thing - reduced size is an advantage!

One solution is a parabolic microphone:

http://bug-detectors.net/microphones_voice_booster/microphones_voice_booster_high_grade_broadcast_quality_parabolic_dgpm_2.jpg
http://bug-detectors.net/microphone..._grade_broadcast_quality_parabolic_dgpm_2.jpg

 

[sophiecentaur]

Here's an even bigger one.

 

[berkeman]

Here's an even bigger one.

There's a really cool exhibit at the Exploratorium in San Francisco (well, I'm assuming that they moved this exhibit when they changed buildings recently). There are two chairs facing each other about 30 meters apart, and behind/around each chair, there is a parabolic reflector about 3 meters in diameter. The two reflectors face each other across the room.

When you sit in the chair, your head is at the focus of the reflector. When your partner in the other chair 30 meters away talks in a normal voice, you can hear them like they were right in front of you! Very impressive demonstration of the power of a parabolic reflector!

 

[Shploop]

The problem here is that parabolic microphones have bad amplification in low frequencies due to their shape... you need a really big paraboloid to focus large wavelength sounds(low frequency). Any other solutions? all I could find about these parabolic reflectors is basic no 'patent' to reduce their size and keep the same effect.

 

[davenn]

There's a really cool exhibit at the Exploratorium in San Francisco (well, I'm assuming that they moved this exhibit when they changed buildings recently). There are two chairs facing each other about 30 meters apart, and behind/around each chair, there is a parabolic reflector about 3 meters in diameter. The two reflectors face each other across the room.

When you sit in the chair, your head is at the focus of the reflector. When your partner in the other chair 30 meters away talks in a normal voice, you can hear them like they were right in front of you! Very impressive demonstration of the power of a parabolic reflector!

yeah that's cool,
The Parkes Radio Telescope Observatory in NSW state of Australia has a similar setup as part of their interactive visitor display.

Dave

 

[sophiecentaur]

There's a really cool exhibit at the Exploratorium in San Francisco (well, I'm assuming that they moved this exhibit when they changed buildings recently). There are two chairs facing each other about 30 meters apart, and behind/around each chair, there is a parabolic reflector about 3 meters in diameter. The two reflectors face each other across the room.

When you sit in the chair, your head is at the focus of the reflector. When your partner in the other chair 30 meters away talks in a normal voice, you can hear them like they were right in front of you! Very impressive demonstration of the power of a parabolic reflector!

For some years I had two 1.4m parabolic dishes mounted on opposite facing walls in my lab at School. A good demo and it cost nothing to acquire the dishes. Very disturbing if you walked through the focus and some kid on the other side of the room was telling her mate something dodgy!

 

[Bobbywhy]

Since you have a specific frequency of sound you want to amplify passively (180 Hz), why not just make a resonant cavity and place your microphone inside it? For this low frequency, you do not get "reduced size" because the laws of Physics dictate the physical size of the cavity. Consider this an "Engineering Challenge" and discover some new, innovative way to solve this!

 

[sophiecentaur]

Since you have a specific frequency of sound you want to amplify passively (180 Hz), why not just make a resonant cavity and place your microphone inside it? For this low frequency, you do not get "reduced size" because the laws of Physics dictate the physical size of the cavity. Consider this an "Engineering Challenge" and discover some new, innovative way to solve this!

Up to a point but a Helmoltz Resonator can be made much smaller than one wavelength in size. What you really want is not so much 'Amplification' (which I regard as necessarily involving an active device) but effective matching the impedance of the waves to detector.

 

[Shploop]

I found something about Helmholtz resonance but to manufacture a cavity like that is difficult without specialized equipment... I am still googling for a solution...

 

[Shploop]

ha ha we responded with the same idea the same time :)

found some useful info:
http://www.gcdataconcepts.com/helmholtz.html

 

[sophiecentaur]

"Specialist equipment"? A box with a hole in it constitutes a Helmoltz Resonator, in principle. Take the sub-woofer in your Home Cinema setup; that is acting like a Helmholtz resonator (ported cavity). It resonates at, say 20Hz (wavelength about 15m) but has a low Q factor, I think.
I don't think you are likely to come up with a very simple solution; what you are after could be a a bit demanding if taken to the extreme.
Perhaps if you gave us a bit more detail / context? How big does this thing have to be, for instance? Are you trying to detect a continuous tone at low amplitude? You could use a mechanical resonator (reed) attached to the diaphragm to get a magnification of, perhaps 100 times as long as the source is on for a sustained time.

 

[Shploop]

That means tearing apart my sub-woofer...
and some detail about what I plan to do:
Well the piezo speaker is going to "monitor" the presence of a 180Hz audio wave if I place it in a certain location. For example if I place it in near my living room's window for 1 day I can see how much 180Hz sounds came from the street to my living room throughout the day - like a street noise monitor but for 180Hz and not just 'noise'.

When I said "Specialist equipment" I meant that according to the equation in the website I mentioned above,
I need a certain diameter, certain length and volume and all that stuff to make a resonator for my specific frequency - I can't just find a box and hooray I am done - 20Hz with low Q is still not best for 180Hz and sub-woofer are big.
I want this to be as small as possible - something you can put in your pocket and as accurate as possible for someone without the "Specialist equipment" - things 'in principle' will perform worse or not at all...

If I had a 3D printer I could print one :)

And by the way does the shape of the resonator matter(round/square/etc)? the equation requires only volume but I guess shape has some meaning and can improve the performance of the resonator.

 

[sophiecentaur]

That means tearing apart my sub-woofer...
and some detail about what I plan to do:
Well the piezo speaker is going to "monitor" the presence of a 180Hz audio wave if I place it in a certain location. For example if I place it in near my living room's window for 1 day I can see how much 180Hz sounds came from the street to my living room throughout the day - like a street noise monitor but for 180Hz and not just 'noise'.

When I said "Specialist equipment" I meant that according to the equation in the website I mentioned above,
I need a certain diameter, certain length and volume and all that stuff to make a resonator for my specific frequency - I can't just find a box and hooray I am done - 20Hz with low Q is still not best for 180Hz and sub-woofer are big.
I want this to be as small as possible - something you can put in your pocket and as accurate as possible for someone without the "Specialist equipment" - things 'in principle' will perform worse or not at all...

If I had a 3D printer I could print one :)

And by the way does the shape of the resonator matter(round/square/etc)? the equation requires only volume but I guess shape has some meaning and can improve the performance of the resonator.

If you want to achieve this without even as much as making yourself a wooden box then you are bound to be disappointed, I'm afraid. Things like this are not on supermarket shelves and would need some significant practical input from you.
One thing that is important for a low loss resonator is rigid walls and lots of mass. People used to go wild about mounting loudspeaker drive units inside concrete pipes at one time for this reason. I can't imagine your notional 3D Printer would do you any good at all because you would be stuck with the available fabrication material, which would be low density - you are clearly of the recent generation, imagining that a high tech solution would be necessarily less trouble and would work better. It certainly would not be cheaper at this stage in history.
Google around some more and you should get some idea of just how big a resonator would need to be for a good resonance at 180Hz - it gets worse as you go smaller, if I remember right. How 'big' can you go for?
I have one big question for you about all this. If you are planning to monitor the street sounds during the day then why does this need to be a passive device? Will it not be associated with (i.e. connected to) some electronics, which will be very much 'active'? So it could be a powered device.

 

[Shploop]

It needs to be a low power device - portable and possibly battery operated so less active amplifying means less power. The voltage the piezo will output goes into a circuit that converts the voltage to a DC voltage relative to the amplitude of the sound wave and then A/D converter sends this voltage to a microprocessor and then possibly with USB to a PC...
by small I mean something portable that you can hold in the palm of your hand - actually I was looking for something that could fit in a 16mm diameter tube that has a maximum length of 15cm - so it's portable like a pen and easy to handle.

You talked about pipes is it possible to make a pipe - let's say made out of common hardware store material(maybe PVC - rigid like you said) that will act as a resonator without adding the cavity itself?

 

[sophiecentaur]

I have two hearing aids which last for about two weeks between battery changes. Power consumption for a well designed device is hardly relevant. How are you proposing to record the signals that this detector will be gathering?
This is a fairly demanding engineering job (if you really are concerned about power consumption) so you must approach it as such. There is seldom any point in 'bending the project to fit a pet solution'
Starting from now, I can guarantee I could come up with a very low power amplifier before you had even been down to the hardware store for the parts you'd need to do the job passively.
btw, there is no way that a suitable 180Hz resonator could be made with a cavity the size of a pen.
You appear to be confused about the 'resonator'. The pipe would be the resonator - but it would have to be a reasonable size - unsuitable for your brief

 

[Shploop]

Well I plan on using a tiny solar cell(maybe a bunch in parallel to increase current) to power it if this answers your question about the power consumption.
I have experience with A/D converter and made 3 working projects one with A/D, D/A, a microcontroller and FPGA working together in the same project so I can manage this section of the problem. In this project the samples from the A/D will be stores in some memory with a suitable capacity for the application.

I know electronics more than acoustics and I want passive amplification so I will learn something new and I also like low power devices.

For example if I want this to be used as a wireless sensor network to monitor 180Hz in various places for a long period of time then power consumption is an issue(using the solar cell removes the need to replace a battery)...

plus I like things I make to be scalable so simple is better - If I make this simple with passive amplification - then improving it and keeping power consumption and complexity low is an advantage - especially if I plan to make multiple units.

I love innovative ideas and always like to hear ones and like to think of some - for example I looked into mimicking bat ears as bio-inspiration but It seems they are suitable for high frequency(above 10KHz) - they actually look like these reflectors you and other users mentioned...

You said I need some practical input, that's not a problem I have improvised some things before that people told me "that wouldn't work well or at all, it's not a professional solution..." - and in the end they worked and I am still using them...

You are really inquiring on all aspects of the project - this shows your someone who knows what he is doing :) thank you for that.

 

[sophiecentaur]

The "bat ears" stuff will have shown you the difficulty when you scale things down to 180Hz. More like Elephant's Ears lol.

If you are planning a wireless network then why are you concerned with the extra few hundred microAmps drain involved in doing this electronically? This link gives a circuit (of which you would only need the first two transistors, followed by a simple band-pass LC filter) which would do just what is needed. Current drain would be laughably low. There are loads more examples out there.

 

[Shploop]

Do you also remember my small size requirement?
I have an A/D, micro-controller and a serial-to-usb module take space along with the piezo(by the way it is possible to lower it's res freq - by adding mass to it according to its datasheet) itself that needs to be inside too. also the solar cell that I want to use is connected to a circuit which charges a super-cacapitor(it's a small one - 10mm diameter) and has a nice step-up converter with it and they all take space.

I know I blah blah a lot about all these requirements but I have a bigger plans for this so this has to been done small.

And most important - using all these transistors to amplify is not as interesting...
And yes I have looked into elephants too as they communicate with low pitch tones but think of this! humans hear down to 20Hz and whales to 10Hz their ear structure is massively different in size but still a humans ear hears those low frequency sounds - here something about whale ears:
http://scienceblogs.com/retrospectacle/2007/02/07/what-does-a-whales-ear-look-li/

I say no to saying "NO" - we most find the answer!

A thought I had is to attach the piezo directly to a structure wall as buildings vibrate from low frequency vibrations like earthquakes - maybe to my living room's wall or window frame but I don't know their resonance frequency... this article backs this up:
http://www.performing-musician.com/pm/may09/articles/technotes.htm - "By placing a microphone on a reflecting surface it will become twice as sensitive as it would be if it was placed well away from the wall, because the sound pressure level on that boundary is twice as high. The result is more output and/or less self-noise, which can be very useful."

one more - a male humans voice has a fundamental frequency of about 180Hz maybe looking more on how it is produced can lead to something.

 

[sophiecentaur]

What actual specification do you have for this device? It would be an idea if you sorted out exactly the sound pressure levels you plan to deal with because that would give you an idea of how necessary it would be to invent a special, frequency-selective transducer. You talk in terms of using existing structures for gathering the sound energy. That could be fruitful, if you were lucky, but it makes the point that a suitable device for use 'anywhere' would need to be a similar size.

 

[Shploop]

I have another idea that is possible with the piezo - I attached to a simple fan so it only touches it barely and I got some response now if I could build a small fan that the wind spins and that vibrates at 180Hz I can get some response from the piezo. I know I am talking about wind and not sound but my ultimate goal here is to monitor the best source for maximum amplitude out of the piezo - acoustic or wind it's all about waves in the air or vibration.
If I use sound after all I plan on dealing with everyday sound pressure levels - like when you walk through a street or my 6th floor living room window open(which is near a busy road), for reference of noise levels in some city I found in google:
http://www.edmonton.ca/transportation/on_your_streets/traffic-noise.aspx
(I don't live near there - it's pretty noisy all day long where I live and that's what motivated me, I also have strong winds here)

Another thing I can think of is to build a structure that transfers only 180Hz vibration from one object/wall/etc to the piezo.

My device is for a common man to use and the ultimate goal is renewable energy.

 

[Bobbywhy]

Shploop, if you are putting your trust in the acoustical science technical descriptions at this website:
http://www.performing-musician.com/pm/may09/articles/technotes.htm
then your project is doomed. For instance, the phrase “placing a microphone on a reflecting surface it will become twice as sensitive...” is false. The sensitivity of a microphone is not affected at all by its location. There are plenty more technical errors in the paragraphs as well.

Regretfully, you have been sucked into the vortex of “pseudo science” on the internet. Your project concept remains interesting and seems promising, but your chances of successful completion are seriously hampered by misinformation.

The term “passively amplify” is NOT normally used in acoustics. I think you mean “concentrate” sound energy. If yes, then there are at least three ways to concentrate sound waves: A parabolic concentrator, parametric beamforming, and an acoustic lens.

Already in this thread we’ve seen photographs of parabolic concentrators, a straightforward method to concentrate sound, either to gather sound energy from a distance and concentrate it at the acoustic focal point, or the reverse.

Here is an example of one technique: “Acoustic beamforming of a parametric speaker comprising ultrasonic transducers Abstract: A directional audible sound can be generated in air by means of the nonlinear interaction between intense amplitude modulated (AM) ultrasonic waves, which attracts much attention in the audio industry. In the case of sound reproduction by a parametric speaker comprising an array of ultrasonic transducers, a novel algorithm with Chebyshev window has been proposed to control the sidelobe level of the beam pattern by utilizing the acoustic nonlinearity and array signal processing technique.” Just as a note of interest, certain kinds of sonar use the “beamforming effect” to receive acoustic energy underwater and determine the relative bearing of the source.
And here is a good overview:
http://en.wikipedia.org/wiki/Parametric_array

As for an acoustic lens, here is an article with one example: http://blogs.scientificamerican.com...ets-of-sound-that-may-lead-to-sonic-scalpels/

If you would learn basic acoustics, including reflection, refraction, and constructive and destructive interference of sound waves you would become better equipped to attempt to engineer a system that would advance your goals. Here are some suggested sources that may help you realize your project objective:
http://www.acoustics101.com/
http://www.ecophon.com/en/Acoustics/Room-Acoustic-Design/
http://en.wikipedia.org/wiki/Acoustic_resonance
http://en.wikipedia.org/wiki/Interference_(wave_propagation )
https://ccrma.stanford.edu/~jos/pasp/Acoustic_Energy_Density.html
http://en.wikipedia.org/wiki/Sound_energy_density

Here is one of the best sites to study all aspects of acoustics, full of excellent animations to help the student grasp the fundamentals intuitively: “Acoustics and Vibration Animations”, by Dan Russell, Ph.D., Professor of Acoustics & Director of Distance Education
Graduate Program in Acoustics, The Pennsylvania State University
http://www.acs.psu.edu/drussell/demos.html

Audacity® is free, open source, cross-platform software for recording and editing sounds. You will want this in your toolbox:
http://audacity.sourceforge.net/

The Scientist and Engineer's Guide to Digital Signal Processing
By Steven W. Smith, Ph.D.
See Chapter 22, especially where the spectral profile of human voice is considered.
http://www.dspguide.com/ch22/6.htm

Two examples of infrasound in nature used for communication where the transmission medium is air: elephants and peacocks!
http://www.birds.cornell.edu/brp/elephant/sections/dictionary/infrasound.html
http://www.sciencenews.org/view/generic/id/341606/title/Peacocks_ruffle_feathers,_make_a_rumble

See especially the section on “methods of field recording” at Cornell Lab of Ornithology, The Macaulay Library is the world's largest and oldest scientific archive of biodiversity audio and video recordings of Birds, Mammals, Reptiles, Amphibians, Arthropods, and Fishes. At the bottom of the web page see the methods of Field Recording, Audio Equipment, Audio Techniques, Video Techniques, and Workshops
http://macaulaylibrary.org/

“Our goal in Speech Technology Research is twofold: to make speaking to your phones and computers ubiquitous and seamless, and to help make videos on the web accessible and searchable.”
http://research.google.com/pubs/SpeechProcessing.html

Speech synthesis is the artificial production of human speech. A computer system used for this purpose is called a speech synthesizer, and can be implemented in software or hardware. A text-to-speech (TTS) system converts normal language text into speech; other systems render symbolic linguistic representations like phonetic transcriptions into speech.

http://en.wikipedia.org/wiki/Speech_synthesis
Work at the Audio Laboratory, Department of Electronic, University of York, UK in this area includes music performances using formant synthesis in music technology teaching and articulatory synthesis in 2 and 3 dimensions based on MRI images of the vocal tract.
http://www.davidmhoward.com/voiceSynthesis.htm

As for human languages, I suggest you consider the different modern living languages, including those primitive tongues that use “clicks” to transfer meaning to others. For example, see: http://en.wikipedia.org/wiki/Natural_language
And this: http://dir.yahoo.com/Social_Science/Linguistics_and_Human_Languages/

Finally, The Acoustic Society of America’s website is loaded with information, much or it related to your interests.
http://www.acoustics.org/

Edit: You posted three minutes before me and gave a more complete description of your goal(S), finally. It would have facilitated more utilitarian responses from members here if you had given a complete description of your project in the beginning.

 

[Shploop]

Wow nice reply I will need time to go over this and yes I do mean concentrate and not passively amplify - I am not familiar with acoustic engineering lexicon :)

found very practical info here:
http://en.wikipedia.org/wiki/Acoustic_resonance#Resonance_of_a_sphere_of_air_.28Vented.29

 

[sophiecentaur]

If I use sound after all I plan on dealing with everyday sound pressure levels - like when you walk through a street or my 6th floor living room window open(which is near a busy road), for reference of noise levels in some city I found in google:
. . . . .. . . . . . .

My device is for a common man to use and the ultimate goal is renewable energy.

When I was asking about sound pressure level, I was after an actual figure (to allow you to predict the possible signal levels involved). It's numbers that count when you are trying to assess the feasibility of any novel Engineering idea.

Which brings me tor the second part of the quote, above: How much "renewable energy" were you actually planning to obtain in this way? Do you have any idea (and you need to have one, before you even consider proceding with this) of the total density of sound power in a "street"? If it were really worth while going for as an energy source, how is it that our ears need to employ the equivalent of state of the art techniques in order to hear things? A Watt is a Watt and, if it's not there in the first place, you can't harvest one.
You say, earlier, that you have "improvised some things". It is easy to knock together many 'working systems' but I can guarantee that you have never successfully improvised anything as unfeasible as the energy gathering idea.

 

[Shploop]

Thats what I am looking to see if the street is a good source for energy.
Yes I agree that there is no room for improvisation here but I like to try things and get a feeling of them so I learn and remember my mistakes.
I understand the law of energy preservation and I don't expect to create energy out of nothing and all I wanted is something passive to concentrate 180Hz sound/vibration. I have a circuit to do the rest - 5v regulated and able to give up to 1A or current - I only need about 100mA peak current or even less to power a micro-controller with some sensors so that part is figured out(the device will not be active continuously so a very low current is drawn while in sleep mode so the average power is low).

I want to monitor how much energy I can get from certain places - research!

I am not looking to see if I can get X amount of energy I am looking to see if I have this energy harvester HOW MUCH energy I can harvest from certain places and certain methods of operation and with this amount I know what devices I can power and where I can "charge" my device.

If let's say I get 1mW from attaching this device to my noisy neighbor's door I know I can power a certain device that needs up to 1mW... that's the idea...

And one more thing I managed to charge a capacitor with manually moving a piezo and but charging a big capacitor takes much time, so I need a source that is available(like street noise) that will do the job for me.

If my grand concept is flawed let me realize it on my own - I just wanted a way to concentrate sound...

 

[sophiecentaur]

If my grand concept is flawed let me realize it on my own - I just wanted a way to concentrate sound...

Fine, if you just want to increase the sensitivity of a detector / receiver but a total wast of time if you want to "harvest" energy. Places where my comment may not apply could be in road tunnels, noisy factories (when humans wear ear defenders) and jet engine test beds. A
However, are you aware of any successful energy schemes, working even under such circumstances? Bear in mind that yours is not an original idea and such systems have been 'considered' in the past.
Why not take an Engineering approach to this? You have been relying all your life on the fact that every bit of successful technology you have ever used is based on that approach.

 

[Shploop]

I read many articles about many others who have done the same and these applications are on the rise and I want to make my own - this is not doomed from the beginning it has been done and I can't keep track of all the places I just want something on a small scale that is portable and practical for use with low power devices.
I am not inventing the wheel here and on the other hand not trying to reach the speed of light.

the problem comes down to cost - they can do anything at MIT(they made some chip that harvests thermal,solar and vibration energy) they make invisibility cloaks...
I have limited budget so... I am trying to come up with a clever solution with what I have...

 

[sophiecentaur]

I read many articles about many others who have done the same and these applications are on the rise and I want to make my own - this is not doomed from the beginning it has been done and I can't keep track of all the places I just want something on a small scale that is portable and practical for use with low power devices.
I am not inventing the wheel here and on the other hand not trying to reach the speed of light.

the problem comes down to cost - they can do anything at MIT(they made some chip that harvests thermal,solar and vibration energy) they make invisibility cloaks...
I have limited budget so... I am trying to come up with a clever solution with what I have...

Perhaps you should go to MIT then.

 

[Bobbywhy]

Thats what I am looking to see if the street is a good source for energy.
Yes I agree that there is no room for improvisation here but I like to try things and get a feeling of them so I learn and remember my mistakes.
I understand the law of energy preservation and I don't expect to create energy out of nothing and all I wanted is something passive to concentrate 180Hz sound/vibration. I have a circuit to do the rest - 5v regulated and able to give up to 1A or current - I only need about 100mA peak current or even less to power a micro-controller with some sensors so that part is figured out(the device will not be active continuously so a very low current is drawn while in sleep mode so the average power is low).

I want to monitor how much energy I can get from certain places - research!

I am not looking to see if I can get X amount of energy I am looking to see if I have this energy harvester HOW MUCH energy I can harvest from certain places and certain methods of operation and with this amount I know what devices I can power and where I can "charge" my device.

If let's say I get 1mW from attaching this device to my noisy neighbor's door I know I can power a certain device that needs up to 1mW... that's the idea...

And one more thing I managed to charge a capacitor with manually moving a piezo and but charging a big capacitor takes much time, so I need a source that is available(like street noise) that will do the job for me.

If my grand concept is flawed let me realize it on my own - I just wanted a way to concentrate sound...

Shploop, You prevaricated for two days about what your real project goal is. You let members here attempt to help elucidate for you the physics of sound. Now, in post number twenty-five, you finally reveal the truth: your intention is to harvest acoustic energy! You've deceived me, and probably others here along the way. Hopefully you will never again avoid telling the whole truth when soliciting the advice and assistance from others. Bye bye.

 

[AlephZero]

I want to monitor how much energy I can get from certain places - research!

That's not "research". You don't have to waste your time dreaming about how to do experiments to measure it. Just look on the web. For example http://en.wikipedia.org/wiki/Sound_power_level#Sound_power_level

 

[Shploop]

The device I am working on is to find a source for 180Hz not to harvest it - it doesn't include the harvesting circuit it includes the MONITORING CIRCUIT - so NO I did not deceive I am trying to concentrate 180Hz sound or vibration, other parts of the device are irrelevant - microphone, energy harvester or sending a 180Hz sound eating spider to mars.

I asked here how to "passive amplify ..." nothing more the only relevant reply was from bobbywhy - the reply with the list of sites which was very helpful and I am reading, learning and coming to conclusions.

The application of what I ask doesn't matter I asked a question about a single aspect and that's what I expect to find and answer to - only the reply I mentioned above was really helpful.

sophiecentaur, I wish I could get a degree from MIT but I don't live in USA and don't have money to learn/live there and English is not my native language so that adds to the difficulty, in the future I will study for a degree near where I live and have better knowledge for my project.

And finally let's stop the nonsense - The "parametric array" I saw on Wikipedia is interesting, do you know websites that give practical examples? I found this article and I will read it to get more knowledge(it was mentioned in wikipedia): http://mesoscopic.mines.edu/mediawiki/images/9/93/WesterveltPA63.pdf

 

[berkeman]

The device I am working on is to find a source for 180Hz not to harvest it - it doesn't include the harvesting circuit it includes the MONITORING CIRCUIT - so NO I did not deceive I am trying to concentrate 180Hz sound or vibration, other parts of the device are irrelevant - microphone, energy harvester or sending a 180Hz sound eating spider to mars.

I asked here how to "passive amplify ..." nothing more the only relevant reply was from bobbywhy - the reply with the list of sites which was very helpful and I am reading, learning and coming to conclusions.

The application of what I ask doesn't matter I asked a question about a single aspect and that's what I expect to find and answer to - only the reply I mentioned above was really helpful.

sophiecentaur, I wish I could get a degree from MIT but I don't live in USA and don't have money to learn/live there and English is not my native language so that adds to the difficulty, in the future I will study for a degree near where I live and have better knowledge for my project.

And finally let's stop the nonsense - The "parametric array" I saw on Wikipedia is interesting, do you know websites that give practical examples? I found this article and I will read it to get more knowledge(it was mentioned in wikipedia): http://mesoscopic.mines.edu/mediawiki/images/9/93/WesterveltPA63.pdf

The issue is if you are not specific in your original question about what you are trying to do, then a lot of people waste a lot of time trying to guess what you are doing and trying to be helpful to you. Please be much more explicit in your future threads -- people want to help you, but if you keep wasting their time, they will be less inclined to click into your threads.

 

[Shploop]

Well I have not been a 100%, so here is the general question about the device I want to build:

1) How to do I get maximum response from my 180Hz piezo transducer from any source or energy - acoustic or vibrational.

2) keep the size of the structure/object we are designing as small as possible - something hand-held that you can keep in your pocket(optimal size I want is to this structure/object will have the maximum size of - 16mm diameter, 15cm length).

3) a simple structure is preferable.

4) solutions for any of these sources(acoustic/vibrational) is OK.

My conclusions so far:
*Paraboloid reflector for 180Hz is too big.
*Helmholtz will also be too big according to equations given on the internet.
*Maybe relaying on resonance isn't the answer if I want small size.

Possible solution:
If the device I am designing can be attached to a vibrating object that will act as a "source of vibration" in a manner that will transfer the vibration from source to device with high efficiency(that the transfer has minimal loss of vibration energy) so this way we get more energy harvested with the device.

 

[berkeman]

Well I have not been a 100%, so here is the general question:
How to do I get maximum response from my 180Hz piezo transducer from any source or energy - acoustic or vibrational. And keep the size of the structure/object we are designing as small as possible - something hand-held that you can keep in your pocket(optimal size I want is to this structure/object will have the maximum size of - 16mm diameter 15cm).

Our conclusions so far:
*Paraboloid reflector for 180Hz is too big.
*Helmholtz will also be too big according to equations given on the internet.
solutions for any of these sources is OK.

So this is schoolwork?

 

[Shploop]

Ha ha, no this is a project of mine, I am not a student :)
Although I intend to study electrical engineering and specialize in this field(Energy).

 

[sophiecentaur]

So this is schoolwork?

Actually, I think it's nonsense. He doesn't actually say what he needs this thing to do. What sound level does he want to be dealing with (an actual number) and what level of signal does he want from his microphone ((an actual voltage / power level)? Without those figures there is no answerable question and certainly no justification for not just using an amplifier. It's just a 'wouldn't it be nice to have a magic machine?' statement.

 

[Shploop]

Well I can't give you numbers because I don't know them, I don't have a measuring device.
I said that I want ambient sources like street noise, here's a list of sources and their SPL in dB:
http://www.engineeringtoolbox.com/sound-pressure-d_711.html

this is also good:
http://www.engineeringtoolbox.com/outdoor-noise-d_62.html

I need the device to handle sound/vibrations levels that can be as powerful/loud as possible without ruining it. If it can harvest energy from as many sources that include a 180Hz sound/vibration I can harvest energy from many sources.

here's the datasheet of the piezo I am using for more data:
http://eeshop.unl.edu/pdf/LDT_Series.pdf

I can't seem to find like a "maximum ratings table" but basically I can say it's a flexible transducer that can be 'bended' 5mm to either side with no problem. I read somewhere that these type of piezo transducers are not very durable if stretched much.

I want resonance - because in resonance I get maximum voltage for a given sound/vibration power.
If I vibrate the transducer in 180Hz at X power I get more voltage output then at a higher or lower frequency with the same X power(see "Experiment #1 - LDT0 as Vibration Sensor" in the datasheet). It is possible to lower it's resonance frequency by adding mass but then I don't think I will find a common low frequency ambient source for it to harvest energy from.

Again, I want maximum voltage output from this piezo and If I can keep it in resonance I can get high output voltage for longer time(that's AC voltage and I will rectify it and store it in battery/capacitor).

Using an amplifier is not good because the amplifier will eventually be powered by the piezo itself so it's like a system that just uses power but does nothing(a cup with a hole in it, you can put water but it will be wasted). By using passive amplification I can use the voltage from the piezo to power more 'useful' components.

In the end product the piezo is there just to give power so electronic amplification will only do harm, please stop suggesting it.

 

[davenn]

....I need the device to handle sound/vibrations levels that can be as powerful/loud as possible without ruining it. If it can harvest energy from as many sources that include a 180Hz sound/vibration I can harvest energy from many sources.

.....Again, I want maximum voltage output from this piezo and If I can keep it in resonance I can get high output voltage for longer time(that's AC voltage and I will rectify it and store it in battery/capacitor).

Using an amplifier is not good because the amplifier will eventually be powered by the piezo itself so it's like a system that just uses power but does nothing(a cup with a hole in it, you can put water but it will be wasted). By using passive amplification I can use the voltage from the piezo to power more 'useful' components.

hi there

you not the first one and won't be the last one to consider harvesting sound to generate an electric current ... it is a topic that comes up on the forum a few times or so a year.

and you will get told the same thing all the others do ...

you obviously don't realize how little energy there is in all the ambient sound that is around you.
its absolutely miniscule ! just stop and think for a moment how much amplification has to be done to the tiny signal generated by a microphone to make it useable.

even shouting directly into the front of a microphone will generate at best ~ 100-200mV
normal rectifier diodes take ~ 600 - 700mV (0.6-0.7V) to conduct so you can't use them
some Schottky Diodes have a lower conduction voltage. But the point is you are not going to get anything out of them that is useable to charge something or to be stored

You are not going to be charging any capacitors or batteries any time soon.
You cannot amplify it ... as the power required to run the amplifier would be substantially more than what was generated by the microphone ( or other audio pickup device)

there is NO passive amplification of an AC or DC voltage, all voltage/current amplifiers require active components that need power added to the circuit to make them work

Really hate to burst your bubble, but its just not feasable

regards
Dave

 

[Shploop]

thanks you, your reply was one of the best and to the point and supports my claim that electric amplification is useless here(as I already said):

Using an amplifier is not good because the amplifier will eventually be powered by the piezo itself so it's like a system that just uses power but does nothing(a cup with a hole in it, you can put water but it will be wasted). By using passive amplification I can use the voltage from the piezo to power more 'useful' components.

that's why I wanted PASSIVE amplification from the beginning...
again by passive I mean concentrate the sound using a non-powered structure(we talked about helmholtz etc...)

to continue the discussion, I know that in some factories in the industry they harvest the energy from large motor and such that vibrate at a certain frequency, so instead of harvesting acoustic energy how about vibration like I already said?

If there is a source that vibrates constantly at a certain frequency(and some decent amplitude) then a device that will attach to it can tap into that energy and say charge a capacitor in 1 Day and use that energy the next day to send some sensor data or other low power application.

what do you say davenn, enough power out there? maybe a car motor?

EDIT:
found someone patented something like I wanted...
https://www.google.com/patents/EP2348606A2?cl=en&dq=thermo+harvest+energy&hl=en&sa=X&ei=g0CWUZTwG8bnswaUnYCoCQ&ved=0CDMQ6AEwADgU

https://www.google.com/patents/US20050134149?dq=piezo+harvest&hl=en&sa=X&ei=OzyWUZBHhcu0Bt_XgfAD&ved=0CGQQ6AEwBzgU

also from a vehicle(car...):
https://www.google.com/patents/US7936113?dq=piezo+harvest&hl=en&sa=X&ei=9zyWUeCcD4iqtAag0oC4Dw&ved=0CGsQ6AEwCDge

and also a complete circuit for wireless sensor:
https://www.google.com/patents/US7081693?dq=piezo+harvest&hl=en&sa=X&ei=aj2WUYj4JsTZtAb904HIBw&ved=0CEgQ6AEwAzgo

one more:
https://www.google.com/patents/US6407484?dq=piezo+harvest&hl=en&sa=X&ei=OT6WUaGYBYfltQbh-IDoCg&ved=0CDMQ6AEwADg8

guess I need to find a different way, all has been done...

 

[jim hardy]

I know that in some factories in the industry they harvest the energy from large motor and such that vibrate at a certain frequency, so instead of harvesting acoustic energy how about vibration like I already said?

Where I worked we would have laughed at harvesting energy from motor vibrations - if it's shaking that bad you better fix it. We equip them with vibration monitors to tell us when they do begin to vibrate so we can replace the bearing or whatever.

However - your enthisuasm is infectious..

and -
One experiment is worth thousands of daydreams.

A loudspeaker is a decent transducer. Build something and see what you get - try a small speaker at the end of a tube it'll just fit inside, in fact make it a telescoping tube you can tune like a trombone. Connect a flashlight bulb and voltmeter across the voice coil.
At 180 hz, a quarter wave is about 18 inches and a half wave of course twice that.

See if traffic noise will excite it. Try it near noisy things like trains and planes.
I doubt you'll see the lamp glow at all unless you're directly under an old unsilenced pure jet plane like Boeing 707/KC135, or if you get lucky a B-52..

You'll prove there's not a lot of energy in sound. That's why one measly watt out of a stereo is too loud for background listening.

Post some pictures -

It would be quite interesting to tune that thing for sub-audible range. There exists something called "Voice of the Sea" caused by wind blowing across waves that's in the range of 7 hz. That's an unwieldy wavelength but you could get creative with resonating chambers (Helmholtz?)
I saw a Nature show proposing that homing pigeons use the sub-audio sound picture of their environs to navigate home.
Shortly before a hurricane sharks around SW Florida have been observed to head for deep water. The birds in my Key Largo neighborhood went someplace the day before Hurricane Andrew. Low frequency audio used to be hard to explore because we can't hear it. Nowadays it seems hobbyists have such powerful toys available that much basic research can be done by amateurs.
Have you access to a spectrum analyzer ? Might be a fun project for today's little microcomputers..there's a FFT library for Arduino.

Take a low frequency sensor to the zoo and listen to the elephants, they are known to communicate with sub audio.

http://www.birds.cornell.edu/brp/elephant/cyclotis/language/infrasound.html

http://www.theatlantic.com/technolo...se-of-the-disappearing-homing-pigeons/272751/

Have fun !

old jim

 

[Shploop]

That's what I am talking about! good reply!
I do like to try things and I do have some access to a spectrum analyzer and the telescopic tube is a very neat idea. I searched for some low power LEDS(a common one is 20mA ~2Vdc) but can't seem to find one I can buy here.

basically I've tested my little circuit and I do charge a capacitor(10uf) pretty quickly by manually moving the piezo and that's even with high drop-voltage diodes(as rectifiers), I got some low-drop high-speed diodes to try.

by the way, these vibration monitors you used are piezo? MEMS? electromechanic?

I will explore any option I can find(that I can make myself) preferably that I can change for my own use and will enable some decent energy output.

I think bio-mimicry is the way to go, nature has got many questions solved before we even asked. I am searching amazon for some good books on the subject, Do you recommend any?

and speaking of animals, I know whales communicate at low frequencies too, about 15Hz, there is a funny story about a whale that sings at 52Hz, they say he is the loneliest whale in the world:
http://en.wikipedia.org/wiki/52-Hertz_whale

 

[jim hardy]

I searched for some low power LEDS(a common one is 20mA ~2Vdc) but can't seem to find one I can buy here.

I doubt you'll be able to make 2 volts with a voice coil driven by sound. But experiment.

by the way, these vibration monitors you used are piezo? MEMS? electromechanic?

We monitored large heavy rotating equipment. Some monitors were electromechanical velocity sensors(coil and magnet) , some were based on commercial piezo accelerometers, some were induction based proximity sensors that measure displacement.

Since we produced heat at the rate of 2200 joules/microsecond we didn't even think about nanowatt harvesters.

There may be I think an emergent niche market for such gizmos in remote unattended monitoring and data logging applications, but we used battery powered devices. The payoff would be not the energy but the convenience of not having to change batteries. I think I saw mention of that shortly before I retired a decade ago.

Again have fun. This is an amazing age for tinkerers.

 

[Shploop]

Well someone made just what I wanted to make... just proves my idea was good...
they use 120Hz, even lower then my 180Hz piezo:
http://www.extremetech.com/computing/155102-energy-harvester-that-creates-power-from-ambient-vibrations-finally-comes-to-market

 

[Bobbywhy]

Well someone made just what I wanted to make... just proves my idea was good...
they use 120Hz, even lower then my 180Hz piezo:
http://www.extremetech.com/computing/155102-energy-harvester-that-creates-power-from-ambient-vibrations-finally-comes-to-market

Shploop, you have demonstrated that you are not receptive to experienced scientists and engineers who have advised you here on your proposed project: to "harvest energy from ambient acoustic energy to charge a battery" is not viable. It has been explained that your concept of "passive amplification" of sound waves is faulty, and that, over time, several other posters here on PF have proposed similar projects, only to find them impossible. Have you done a search yet here in this forum on this topic to see how they were resolved?

Your most recent statement above where you claim that "The Bolt just proves my idea was good" is mistaken. In fact, the Bolt in the link requires an ambient source vibrating at around 120Hz in order to charge a battery. That is, a MECHANICAL vibration from a motor, pump, etc. and NOT a sound wave vibration.

Please note: sound waves do carry energy and a tiny miniscule amount could be harvested using a scheme such as you propose. But, (pay attention, please) the charging current would be measured in microamperes and the amount of power would be measured in microwatts. Learn to do the mathematics to calculate acoustic power available in the environments you mentioned. Convert those SPLs (Sound Pressure Levels), given in dB, to units of power (watts). Then consider all the ineffiencies in the conversion process, and arrive at the energy available to store in the battery. You will immediately find this amount is so small that it would be a waste of time to even try it.

 

[jim hardy]

Nanopower electronics can run on these things. Don't plan on them reducing your electric bill, though.

Here's an industry article with some interesting links :
http://www.designnews.com/author.asp?section_id=1386&doc_id=263386&dfpPParams=ind_184,industry_alt,aid_263386&dfpLayout=blog

Click the image to open a window with a little slideshow of eight harvesting schemes.

old jim

 

[Bobbywhy]

Nanopower electronics can run on these things. Don't plan on them reducing your electric bill, though.

Here's an industry article with some interesting links :
http://www.designnews.com/author.asp?section_id=1386&doc_id=263386&dfpPParams=ind_184,industry_alt,aid_263386&dfpLayout=blog

Click the image to open a window with a little slideshow of eight harvesting schemes.

old jim

Hi old jim! Thank you for that interesting article. I saw all eight examples of energy "harvesters" each one innovative and useful!

Observation: None of those eight uses acoustic energy as a source as the OP here has been proposing.

 

[dlgoff]

Observation: None of those eight uses acoustic energy as a source as the OP here has been proposing.

Really?

When the brass vibrates, it generates electricity.

http://www.designnews.com/author.asp?section_id=1386&dfpLayout=blog&dfpLayout=blog&dfpPParams=ind_184%2Cindustry_alt%2Caid_263386&dfpPParams=ind_184%2Cindustry_alt%2Caid_263386&doc_id=263386&image_number=3

 

[russ_watters]

that's why I wanted PASSIVE amplification from the beginning...

You know there isn't enough energy in sound waves to make a useful source of energy, so you want to amplify the energy without inputting more energy. That's called a Type 1 Perpetual Motion Machine because it violates the first law of thermodynamics. https://en.wikipedia.org/wiki/Perpetual_motion

Since it is a violation of the laws of physics, it is not something that can be done and therefore isn't something we entertain discussion of here. Thread locked.