Hi, I'm not really an audiofile, but I do hope that I am in the right place. For a university project I am trying to find (if needed build) a small, handheld 'speaker' that can generate low frequency and even infra-sound (8 - 30 Hz).
Small may not rhyme with low frequency, but I need very little power. The sound waves would travel through a tube with a 1 cm diameter. The tube goes into the mouth of patient and the (infra) sound waves would be superimposed on his tidal breathing in order to dislodge mucus in the lungs. So I only need 1.2 cm H2O (or 120 Pascal) over a surface of less than 1 square cm.
It is important that the device is portable. Any ideas on how this could be achieved would be much appreciated.
Small may not rhyme with low frequency, but I need very little power. The sound waves would travel through a tube with a 1 cm diameter. The tube goes into the mouth of patient and the (infra) sound waves would be superimposed on his tidal breathing in order to dislodge mucus in the lungs. So I only need 1.2 cm H2O (or 120 Pascal) over a surface of less than 1 square cm.
It is important that the device is portable. Any ideas on how this could be achieved would be much appreciated.
How small is small?
Maybe just a small bandpass enclosure with a 6.5" speaker inside attached to a tube?
Since there is no need for audibility just air movement I am not very certain how to calculate this. Maybe just calculate for BR instead and use the pipe as a reflex port?
What are the dimensions of the tube?
Maybe just a small bandpass enclosure with a 6.5" speaker inside attached to a tube?
Since there is no need for audibility just air movement I am not very certain how to calculate this. Maybe just calculate for BR instead and use the pipe as a reflex port?
What are the dimensions of the tube?
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I looked a bit further into your piston proposal, but unfortunately it won't work. Higher frequencies would lead to higher pressure and I would need the same pressure at all frequencies. I also want to be able to regulate pressure which is also not possible with a piston. When I use a speaker, I can easily regulate frequency and amplitude with a signal generator.
So any other proposals would be welcome.
So any other proposals would be welcome.
Thanks Chris, seems like a good idea (even if a bit complex to regulate correctly) but we're talking about a servo motor doing up to 30*60 = 1800 incomplete rotations per minute, speed up/slow down/reversing 3600 times per minute. I don't believe that is possible to be honest. That is just based on intuition though. I don't know anything about servo motors. I've quickly looked up a positional rotation servo and it needs 0.15" for 60° of movement.
So I think I really need a speaker of some sorts. BTW In the mean time I found this Vibralung Acoustical Percussor , which shows that it is possible (and unfortunately also that my idea is not new). Any idea what kind of sound generator they might be using?
So I think I really need a speaker of some sorts. BTW In the mean time I found this Vibralung Acoustical Percussor , which shows that it is possible (and unfortunately also that my idea is not new). Any idea what kind of sound generator they might be using?
likley some sub/woofer will work but you need some numbers
did you calculate the volume displacement required to pressurize the lung + airway volume to your requirement?
then you also have to see if the force from the BL product is enough to get that displacement against suspension and air volume stiffness for a drive current within the speaker rating
did you calculate the volume displacement required to pressurize the lung + airway volume to your requirement?
then you also have to see if the force from the BL product is enough to get that displacement against suspension and air volume stiffness for a drive current within the speaker rating
Bjorno, sorry to impose on you, but as I am new to audio I have a couple of questions for you. Not everything is clear to me.
You work with a tube of 250 cm. Should I use a shorter tube, would I then have to increase the volume of the chamber on the right for the same volume?
I don't think I understand exactly the dB calculations at the bottom of the sheet. First of all, I'd like to clarify that I am looking at 120 Pa to be the RMS of the pressure, not the peak. Was that also your assumption?
Does the length (within reason of course) of the tube matter very much if the material is stiff enough?
You convert 120 Pa to dB, but what is the 421 Pa you mention? I see that value again in the 6 Hz calculation, yet not in the 30 Hz calculation. I don't really understand how to interprete the calcs for these frequencies.
Could you clarify things a bit for me? Many thanks!
You work with a tube of 250 cm. Should I use a shorter tube, would I then have to increase the volume of the chamber on the right for the same volume?
I don't think I understand exactly the dB calculations at the bottom of the sheet. First of all, I'd like to clarify that I am looking at 120 Pa to be the RMS of the pressure, not the peak. Was that also your assumption?
Does the length (within reason of course) of the tube matter very much if the material is stiff enough?
You convert 120 Pa to dB, but what is the 421 Pa you mention? I see that value again in the 6 Hz calculation, yet not in the 30 Hz calculation. I don't really understand how to interprete the calcs for these frequencies.
Could you clarify things a bit for me? Many thanks!
Hi Milachka,
Your Mail:
Of course a possibility but the Design is no more Hand held and Resonance optimized...See the Pictures:
See the Pictures:
No, as the Design is sort of a Helmholtz... See the Pictures
My mistake: 421 Pa is the Throat Pressure, not at the Mouth where it should be ~140 dB...See the Pictures.
b
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This is not a subwoofer project
Why not make something very simple like a very small box with a tube of suitable diameter and length? The speaker mounted in reverse (magnet facing outwards). That way You could make the "box" from 2-3 sheets of wood.You will be using the speaker below resonance but that should not stop You. All you need is an amplifier with enough power to give You the air pressure You need.
As I understand it You're looking for air pressure, not low frequency sound.
Why not make something very simple like a very small box with a tube of suitable diameter and length? The speaker mounted in reverse (magnet facing outwards). That way You could make the "box" from 2-3 sheets of wood.You will be using the speaker below resonance but that should not stop You. All you need is an amplifier with enough power to give You the air pressure You need.
As I understand it You're looking for air pressure, not low frequency sound.
I built a talk box to modulate electrical instrument sounds with my mouth (think Peter Frampton).
Instead of using one compression driver, i used two small woofers. I drilled a hole in a piece of wood (could be a center divider splitting a box in two chambers, or just part of a panel with shared enclosure volume) then i mounted the woofers facing each other so the hole joined the two cones' air mass. Then i drilled a whole down the middle of the piece of wood so the air could escape. Sort of a push-push tube loaded design. The plastic tube that goes in my mouth is plugged into the hole in box.
No pics of design at the moment.
Think of a clamshell isobarik with a solid piece of wood dividing them, with just a hole drilled between them. The panel they are bolted to is inside the box. You drill down the panel to make a final "t" shaped port.
I did a frequency response of it, and the mid-upper response was modulated like crazy as expected. But the bass was not effected. Flat responce to pretty deep. I was not expecting that much bass from the tube.
I am merely mentioning this in case one woofer is not enough.
Instead of using one compression driver, i used two small woofers. I drilled a hole in a piece of wood (could be a center divider splitting a box in two chambers, or just part of a panel with shared enclosure volume) then i mounted the woofers facing each other so the hole joined the two cones' air mass. Then i drilled a whole down the middle of the piece of wood so the air could escape. Sort of a push-push tube loaded design. The plastic tube that goes in my mouth is plugged into the hole in box.
No pics of design at the moment.
Think of a clamshell isobarik with a solid piece of wood dividing them, with just a hole drilled between them. The panel they are bolted to is inside the box. You drill down the panel to make a final "t" shaped port.
I did a frequency response of it, and the mid-upper response was modulated like crazy as expected. But the bass was not effected. Flat responce to pretty deep. I was not expecting that much bass from the tube.
I am merely mentioning this in case one woofer is not enough.
Servomotors are good for VLF, crap for above 100Hz.
The Vibralung Acoustical Percussor probably uses a decent headphone transducer- considering there are nowDr. Dre knockoffs available for $15 that I can easily hear from 30+ feet away powered with 200 milliwatts or less while the users are causing permanent hearing damage, price is not a concern.
I personally have been a big fan of Sony MD7506, and the predecessor, the V6 for the last 30 years or so- the MD7506 is nearly flat to 5 Hz, and connected to a tube you have virtually no inverse distance loss- recall the "speaking tubes" used for communication onnaval vessels prior to any electrical transducers, or the 200 feet of plastic tubing connected to a Sure SM57 as both a transducer and receiver for a 200+ ms delay back in the days of iron men, analog consoles and wooden speaker cabinets.
I have been recently "upgraded", and now have some titanium "gussets" in my cranium after an altercation with a gang-banger neighbor, but I digress- here is the response of a Sony MD7506, no processing, measured with the microphone flush with the ear cup.
Note that as well as the magnitude response being quite flat, the pase response is also quite linear- what goes in is what comes out (other than in the HF regioin, where the differences in individual pinna (as distinctive as fingerprints) insure that no two people hear headphones (or anything else)the same as anyone else.
Cheers,
Art
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I have a really difficult time trying to understand why people motivate themselves to do stuff like that to another person. I have first hand experience in the fact that it really does happen for apparently no reason at all, and if you rise up again run after them and grab them and ask "What is your motivation for doing this? It is completely unneccesery!" then they get the same look a Deer running in front of a fast car gets before sprinting away. Also one other time something similar happened I said: "I'm starting to get tired of this, if you continue I may get irritated." Before approaching my cousin who was also being jumped by the same group. I had no intention of doing anything, just wanted to check up on my cousin, but they ran fast.
To quote my uncle:
"It must be a small man, if he needs to step on others to be big"
Something is lost in the translation, but you get the point.
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