Circlotron said:
what is a 'hertz' anyway. it's cycles per second, isn't it? if you have 0Hz, you're not producing anything, are you?
unless there's some wierd vortex of sound...maybe there's a negative Hz, that works like a sonic black hole...sucks up the sound around it. then 0Hz would be the mind-boggling threshold between positive and negative frequency.
[quote:
Originally posted by Circlotron
Is there really such a thing as 0Hz or is it an oxymoron? Sort of like a zero ohm resistor.
what is a 'hertz' anyway. it's cycles per second, isn't it? if you have 0Hz, you're not producing anything, are you?
unless there's some wierd vortex of sound...maybe there's a negative Hz, that works like a sonic black hole...sucks up the sound around it. then 0Hz would be the mind-boggling threshold between positive and negative frequency. ]
I would venture to guess that you simply increase your divisor to something larger, like cycles per minute, but vibrations in this range probably don't modulate the air to produce sound...
Someone with more physics than I could explain.
I would have loved to get ahold of one of Danley's cyclone subs when they were in production. Dipole bass to 15hz!
Jason
Originally posted by Circlotron
Is there really such a thing as 0Hz or is it an oxymoron? Sort of like a zero ohm resistor.
what is a 'hertz' anyway. it's cycles per second, isn't it? if you have 0Hz, you're not producing anything, are you?
unless there's some wierd vortex of sound...maybe there's a negative Hz, that works like a sonic black hole...sucks up the sound around it. then 0Hz would be the mind-boggling threshold between positive and negative frequency. ]
I would venture to guess that you simply increase your divisor to something larger, like cycles per minute, but vibrations in this range probably don't modulate the air to produce sound...
Someone with more physics than I could explain.
I would have loved to get ahold of one of Danley's cyclone subs when they were in production. Dipole bass to 15hz!
Jason
Regarding the audibility of sub-20Hz frequencies: according to a psychoacoustics textbook by Brian Moore, sine waves down to 3.5Hz or something are audible when the sound pressure level is sufficiently high (or should I say ridiculously high?), and there is no reason to assume it stops at 3.5Hz. However, below about 16Hz, one cannot accurately hear the pitch anymore, which makes these signals rather useless for music.
0 Hz would be nothing more and nothing less than an increase or decrease of constant air pressure (that's why you need an airtight listening room and speakers to reproduce 0 Hz), i.e. it would be called DC if it was elecrical.
It would of course be possible to measure it with the apropriate means. Or does anyone assume it would be impossible to measure the FR of an amp going down to 0 Hz ?
Regards
Charles
About the confusion over "0 Hz":
True "0 Hz" operation is, of course, impossible (as is a true DC signal), in a philosophical sense: to be truly "0 Hz" in frequency, a signal would have to be infinitely long in duration; it would have to have started infinitely long ago or to stop infinitely long from now. When people talk about a DC or 0 Hz signal/current, it is just a convenient shorthand for describing a signal/current that does not vanish for a long, but finite, time. When someone says that an amplifier/speaker can produce a 0 Hz signal, what is meant is that it can produce a 1 Hz signal, or a .1 Hz signal, or a .000000000001 Hz signal... to an arbitrarily low frequency.
Back on the topic of the down-to-0-Hz transducer:
As pointed out by someone earlier in the thread, an air compressor would be the wrong device for this application; they provide very high pressure but not continuous, large volumes of air movement. A much better, and easier to obtain, source would be the typical floor-standing portable fan; these can move impressive amounts of air around a room. Air ducts or dryer-hose might be good for routing the airflow from the source to the listening room.
While a perfectly sealed room would be necessary for ultra-low-frequency by means of a traditional speaker, it is by no means a requirement for this system. A speaker increases the pressure by compressing the air already in the room; this device adds air from an outside source to the room.
Some ideas for a more linear airflow regulation device:
Take two circular disks, with evenly spaced radial slots in them. The two disks can be aligned with each other so that air passes through the slots of both. By rotating one of the disks, the opening for airlfow is closed off, until the slots on one disk are aligned with the solid areas of the other and no airflow is possible. Use a motor to rotate one of the discs according to the signal.
This same method could be done translationally, with two rectangular plates with parrallel openings. By sliding one plate back and forth in front of the other on a pair of rails, the opening for airflow could be easily linearly varied. An old, damaged, high-excursion speaker motor could be used for translational drive of the plate.
I am not claiming that a 0 Hz capable speaker such as I am describe here is useful, audible, linear, HiFi, or well-designed; I just think it could be a fun DIY engineering project to explore.
True "0 Hz" operation is, of course, impossible (as is a true DC signal), in a philosophical sense: to be truly "0 Hz" in frequency, a signal would have to be infinitely long in duration; it would have to have started infinitely long ago or to stop infinitely long from now. When people talk about a DC or 0 Hz signal/current, it is just a convenient shorthand for describing a signal/current that does not vanish for a long, but finite, time. When someone says that an amplifier/speaker can produce a 0 Hz signal, what is meant is that it can produce a 1 Hz signal, or a .1 Hz signal, or a .000000000001 Hz signal... to an arbitrarily low frequency.
Back on the topic of the down-to-0-Hz transducer:
As pointed out by someone earlier in the thread, an air compressor would be the wrong device for this application; they provide very high pressure but not continuous, large volumes of air movement. A much better, and easier to obtain, source would be the typical floor-standing portable fan; these can move impressive amounts of air around a room. Air ducts or dryer-hose might be good for routing the airflow from the source to the listening room.
While a perfectly sealed room would be necessary for ultra-low-frequency by means of a traditional speaker, it is by no means a requirement for this system. A speaker increases the pressure by compressing the air already in the room; this device adds air from an outside source to the room.
Some ideas for a more linear airflow regulation device:
Take two circular disks, with evenly spaced radial slots in them. The two disks can be aligned with each other so that air passes through the slots of both. By rotating one of the disks, the opening for airlfow is closed off, until the slots on one disk are aligned with the solid areas of the other and no airflow is possible. Use a motor to rotate one of the discs according to the signal.
This same method could be done translationally, with two rectangular plates with parrallel openings. By sliding one plate back and forth in front of the other on a pair of rails, the opening for airflow could be easily linearly varied. An old, damaged, high-excursion speaker motor could be used for translational drive of the plate.
I am not claiming that a 0 Hz capable speaker such as I am describe here is useful, audible, linear, HiFi, or well-designed; I just think it could be a fun DIY engineering project to explore.
Great! My physics course is getting into the stuff that we're discussing on this forum!
I believe that a driver, any driver is whollly incapable of producing a frequency of 0Hz. Hz=c/s, c being cycles. s being seconds for period. Either the driver produces no cycles...impossible it wouldn't exist or, the driver can produce x (being any real number), amount of cycles in zero seconds...again, it wouldn't exist if time was zero. I would be able to accept 0+ but not 0=. Also, loudspeakers create longitudonal waves by moving forward, backward and reaching rest...completing a cycle. Even if the driver only moved outward then stopped at the rest position it would have effectively created a pulse which is wave/2. What I'm trying to say is that in order to move air, the driver must also move and through any movement time and cycles must be greater than zero.
I'd hate to take a negative outreach on this one, but we must all say what we believe otherwise this forum wouldn't be what it is...I guess I'm being the idealist for this thread.
I believe that a driver, any driver is whollly incapable of producing a frequency of 0Hz. Hz=c/s, c being cycles. s being seconds for period. Either the driver produces no cycles...impossible it wouldn't exist or, the driver can produce x (being any real number), amount of cycles in zero seconds...again, it wouldn't exist if time was zero. I would be able to accept 0+ but not 0=. Also, loudspeakers create longitudonal waves by moving forward, backward and reaching rest...completing a cycle. Even if the driver only moved outward then stopped at the rest position it would have effectively created a pulse which is wave/2. What I'm trying to say is that in order to move air, the driver must also move and through any movement time and cycles must be greater than zero.
I'd hate to take a negative outreach on this one, but we must all say what we believe otherwise this forum wouldn't be what it is...I guess I'm being the idealist for this thread.
Various thoughts:
I believe loudspeakers using modulated air from a compressor were used at the D-day landings. No reports of their fidelity (probably busy elsewhere).
0Hz is indeed DC. It might not be directly audible, but changes in air pressure are definitely sensed - I reliably get a migraine before rain.
There's no substitute for real bass.
I believe loudspeakers using modulated air from a compressor were used at the D-day landings. No reports of their fidelity (probably busy elsewhere).
0Hz is indeed DC. It might not be directly audible, but changes in air pressure are definitely sensed - I reliably get a migraine before rain.
There's no substitute for real bass.
This US Army pdf contains everything you would need to know about compressor-based low frequency generators. Take a look at these pictures!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Serow
I have already seen this document. Unfortunately they don't show the rest of the associated horn (you only see the throat in the background) which looks quite ipressive !
The physical properties mentioned by Bose(o) are valid as long as you have acoustic WAVES emerging from your source (i.e. "open space"). But it isn't necessary to have sound waves for our ears, in order to perceive sound.
We basically hear sound PRESSURE (it is a little more complicated of course).
As soon as the frequencies involved are lower than the lowest room mode then you have only sound pressure generated by your driver. As long as everything is airtight (I am aware that this is not very practical but generally feasible) it is therefore possible to have "DC" in a listening room. The pressure change achieved is then defined by the ratio of volume-displacement/room-volume.
Regards
Charles
I have already seen this document. Unfortunately they don't show the rest of the associated horn (you only see the throat in the background) which looks quite ipressive !
The physical properties mentioned by Bose(o) are valid as long as you have acoustic WAVES emerging from your source (i.e. "open space"). But it isn't necessary to have sound waves for our ears, in order to perceive sound.
We basically hear sound PRESSURE (it is a little more complicated of course).
As soon as the frequencies involved are lower than the lowest room mode then you have only sound pressure generated by your driver. As long as everything is airtight (I am aware that this is not very practical but generally feasible) it is therefore possible to have "DC" in a listening room. The pressure change achieved is then defined by the ratio of volume-displacement/room-volume.
Regards
Charles
just blowing air?
From a listener's perspective, sound waves are just air being "pushed" towards them at varying rates. Whether this air is pushed/compressed by a speaker cone, or by a column of air, the result in the end is the same.
Modulated "blowing air" and soundwaves are exactly the same thing!
Quick rough calculation:
An 18" speaker, moving back and forth 1 cm twenty times a second, moves approx. 7 liters of air per second. A 2 ft. square frame floorstanding fan, putting out a 5 mph breeze on its lowest setting, moves approx. 700 liters of air per second. If you can effectively modulate this airflow, then you get soundwaves exactly as if from a speaker. If you wanted to "focus" this into a narrow spot for greater effect, you could still use horns just like with speakers; however, since you can acheive much greater (2 orders of magnitude or more) initial air movement with a fan, horn reinforcement is probably not necessary.
Bose(o) said:
From a listener's perspective, sound waves are just air being "pushed" towards them at varying rates. Whether this air is pushed/compressed by a speaker cone, or by a column of air, the result in the end is the same.
Modulated "blowing air" and soundwaves are exactly the same thing!
Quick rough calculation:
An 18" speaker, moving back and forth 1 cm twenty times a second, moves approx. 7 liters of air per second. A 2 ft. square frame floorstanding fan, putting out a 5 mph breeze on its lowest setting, moves approx. 700 liters of air per second. If you can effectively modulate this airflow, then you get soundwaves exactly as if from a speaker. If you wanted to "focus" this into a narrow spot for greater effect, you could still use horns just like with speakers; however, since you can acheive much greater (2 orders of magnitude or more) initial air movement with a fan, horn reinforcement is probably not necessary.
I just can't resist it...
Bose(o),
I'm curious as to why you've chosen your moniker. Anyway...
Paul Klipsch is walking along the street when he spots Amar Bose on the other side. Cupping his hands about his mouth, he shouts, "Hey, Bose, are you still making those terrible loudspeakers?" Upon which, Bose turns to the wall and mumbles, "Yes."
Bose(o),
I'm curious as to why you've chosen your moniker. Anyway...
Paul Klipsch is walking along the street when he spots Amar Bose on the other side. Cupping his hands about his mouth, he shouts, "Hey, Bose, are you still making those terrible loudspeakers?" Upon which, Bose turns to the wall and mumbles, "Yes."
5 Volts RMS at 0 Hz, wouldn't that be 5 Volts DC?
I would think anything could "reproduce" that.
An old news paper, a rock, your desk, that dead bloated whale washed up on the shore.
Of course if you tried do to some calculations, at some point you would have to get a divide by zero error.
So maybe maybe a rock (if it were big enough) and the whale could do it, but forget about the desk - unless it was made of oxygen free copper.
I would think anything could "reproduce" that.
An old news paper, a rock, your desk, that dead bloated whale washed up on the shore.
Of course if you tried do to some calculations, at some point you would have to get a divide by zero error.
So maybe maybe a rock (if it were big enough) and the whale could do it, but forget about the desk - unless it was made of oxygen free copper.
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