Is there anyway i can record and playback sound happening between 0-20hz?
I assume most microphones and speakers dont go below 20, but there has to be a way!
You have couple of things to consider. Our ears have essentially no useful response to sound below 20Hz, so you won’t be able to hear what you record. So, we need to consider what your requirements actually are.
What is it you wish to record?
What is the purpose of the reproduction?
Asking for recording down to zero Hertz is meaningless, so you do need to place non-zero bound on the lowest frequency you want to record.
It isn’t hard to make a microphone that will go down to nearly DC, most audio systems will deliberately AC couple the system to avoid problems that come with unwanted low frequency junk. Appropriate coupling of even a cheap microphone capsule will probably get you to very low frequencies.
As to reproducing them. It is all a matter of scale. You need to move ever larger amounts of air to reproduce low frequencies. However if you are indoors, very low frequencies couple into a room well, and it isn’t all that hard (but still reasonably heroic engineering) to create a loudspeaker that can reproduce quite low frequencies. The physics of loudspeakers is such that below the system resonance the cone excursions become much more extreme and a speaker would need special care, and probably active compensation, to ensure that it didn’t self destruct. Eventually you end up with a large piston that simply pressurises the room you are in. Still not clear about why one would do this however.
Alternatively, if you want to somehow hear the very low frequencies, you can frequency shift them into the audible band. The really simple way is to play the sound back at a faster rate, but that is probably not all that satisfactory. There are DSP based mechanisms that can pitch shift. It can be as simple as taking the Fourier Transform of the entire recording, and then shifting the result up and then transforming back.
Who is your audience? Even if you can record it accurately, and play it back accurately, no one can hear it.
Is this some kind of nature project? Are to trying to record, er, worm song*, play it back to other worms, and see if they respond? If this is the case, there may be other complicating factors. Some animals might receive such vibrations via conduction through the earth or through water, for example, and perhaps wouldn’t react to the same frequency propagated through the air.
*I have no idea if worms sing, it’s just a hypothetical.
I would try using a woofer or subwoofer (passive, not active) as the “microphone”. Their frequency response may say it only goes down to 30 Hz or whatever, but it won’t be zero, it’ll just be less efficient.
If you had some way of generating sound waves of a known amplitude down at the frequencies below 20 Hz that you’re interested in, you could determine what equalization to apply to remove the speaker’s frequency response. Failing that, if you can at least generate some kind of sound at those frequencies, you could check that you’re picking up something. Then, as a first cut, you could try an equalization like multiplying the amplitude by f0/f for f < f0, for some cutoff f0 (e.g. f0 = 30 Hz or whatever the speaker’s lowest frequency is said to be).
I presume you have some audio software like Audacity to look at the waveforms you record.
A bass driver is a good suggestion. Indeed there has been recent interest in using them to record bass drums in recording studios. A bass driver of known parameters in a sealed enclosure of known volume could provide equalisation parameters from first principles. ZenBeam’s first order approximation holds a vital truth. Your output from the driver drops with frequency.
There are several manufacturers of microphones that have relatively flat frequency responses to below the sub 1 hz regions. Bruel & Kjaer are probably the best known for general purpose and specialty mics like that. For playback, there are decent amps out there, but really this seams something that you would be watching on a scope or speeding up for playback.
Heading to the cemetary, aren’t ya?
As far as recording it goes, scientists who study elephants have been doing this for years:
There are also some suggestions on specific types of equipment to use. I would expect there’s more to it than they describe there (particularly if you’re using a digital system and have to muck about with the sampling rates), but it’s not a bad place to start.
On the reproduction side, electropneumatic transducers are probably the only way to create serious amounts of very low frequency energy. Basically a modulated source of compressed air. They can create insane power levels and have no intrinsic low frequency limit, apart from the drop in level proportional to frequency. (Most people have seen such a loudspeaker in use - in Apocalypse Now, the scene where they play Ride of the Valkyrie from the helicopter. The speakers are powered by a compressed air bleed from the jet turbine. Very seriously loud.)
Luckily for low frequency work this isn’t an issue. For ultrasonic work it most certainly is.
Worms probably not, whales maybe?
I figured underwater recording would be a whole new set of complexities that the OP would ask about.
Im actually trying to record sounds between 12-17hZ for an underlying track for a black metal band i work with.
Ive researched and found that sounds of around that frequency the brain can still pick up and it creates feelings of dread and nervousness. Would be excellent for an ambient sound!
Then I presume you are talking about this in terms of live performance? People’s home stereos are unlikely to be able to reproduce it, but you could use some specialized gear during a concert.
I thought that might be an issue. I was hoping to get it in peoples homes, but concerts are good too.
MikeS: I’m so glad you mentioned elephants; that’s the first thing I thought of when I saw the thread.
And, thanks for the link, it’s a great one!
I use ELF and ULF in production work all the time.
Usually to add oomph to kick drums and bass, sometimes floor. Also, sub-bass for hip-hop.
It’s possible to record, esp. if you make a subkick
But to get around 17-20 Hz you’ll need an extremely large driver and cone, at least a 12". probably a 15". And your sound source will need to kick out enough energy to drive that mother. Unlikely on a kick drum.
Just use a gated signal generator sidechained to whatever you want to have subbass. Add a harmonic exciter to expand the range. Or just use the Waves RBass plugin…
If you get this to work, be prepared for the venue manager to wonder why their alcohol and food sales mysteriously drop when the band plays. And if the patrons actually get sick, do you really want a nickname as the VBs? (Vomit Band.)
IIRC, that is what they did in theaters for the movie “Irreversible”. They played a very low frequency sound all the way though the movie to reinforce the sense of dread. Haven’t seen it, but from what people tell me, that movie makes you wanna hurl just by itself - this must have been pretty intense.
Also, there is no way that you are going to get 15-20 Hz tones in people’s homes - most Hifi systems fail around 50 Hz or higher, your best bet is indeed the Waves MaxBass plugin which utilises the principle of missing fundamental.
Underwater recordings are actually sort of easy - you just need a hydrophone. You’re very unlikely to find one at your local music store, though…
I heard infrasound might be an explanation for feeling someone’s watching you, and other supernatural phenomena.