recording of ambient low frequencies

[finrot]

Hiya,

I'm trying to record extremely low frequencies (1 hz - 20 hz) in and of a domestic situation (living room and house vibration), directly into a computer.

I've been discussing the use of a speaker as a microphone with friends.

i.e. speaker - pre-amp - sound card

They think that this should work especially in the corners of the room where the pressure changes are greatest.

I'm a newbie at this, any ideas/corrections/suggestions??

Cheers,

Ben

 

[Tapehead]

How about Just doing it and letting us know how it worked.

 

[dobro]

The speaker thing might be the only way to do it - I checked out Earthworks mics, for example (really sensitive, accurate mics) and the lowest they go down to is 9Hz. Not low enough. The speaker thing will work, the question is will it be sensitive enough to pick that stuff up. Only one way to find out, as Tapehead says. Use a large speaker.

 

[James HE]

hmmm... just taking a guess here. But maybe you could you should mount the speaker to a surface, to pick up the low vibrations. Maybe on the floor, doub't you want to drill in to the floor though, so maybe a thin rubbery, foamy substance, like a rubber strip around where the speaker meets the floor (I think some decoupling is in order, or it may get too muddy) and put something VERY heavy on top of the speaker, possibly something that carries a bit of vibrations itself, perhaps the "weight" being attached or making solid contact to another part of the house, like the the adjacent wall, or in a corner to channel even more vibrations. Basically making a huge contact mic. Man I'm getting a neat idea. YOU NEED LIQUID! HA! So you have your speaker sitting on the floor, and a water proof box (got an aquarium?) Filled with water sitting on top of it (fish or no ) I heard of people floating mics in water, do'nt know how, but maybe you could find a way and multitrack it. Having a water mic, and a handfull of speakers making contact around the rooms. To do it true you will need a very clean pre-amp I think, something with pristine analog circutry. Avalon? and top notch Analog to Digital conversion. man that's some money! BUt keep it simple at first. NO gear really has specs that can meet those frequencies efficently. Who knows though, they really don't test for that (or if they do, publish results) You may stumble onto something that works.

If you pull it off, you'll need one hell of a playback system.

one question though, and I'm very intrested, WHY?

-jhe

 

[Sabith]

I'm curious to know what U are actually recording thats making these really low freq's........

Sabith

 

[finrot]

re: why?

Errrm....'cos it's there...no hang on that was a mountain.

Seriously though. I'm a sculptor/installation artist (Previous work and reviews can be seen at http://www.woodeson.co.uk) I'm on a research program at Glasgow School of Art and working on a new body of work. I became interested in the possibilities of making visual/sound art that would be inaudible. If I can make the amplitude big enough (without hurting people) then I think the viewers will experience the vibration but with virtually no sound...

In terms of what I'm trying to record, I live in an apartmant block built circa 1900, in a highly built up area (Glasgow's west end) I have no idea if what I record will be interesting, thus it is literally research. I'm also trying to obtain visual or electronic records of earthquakes As you do...

 

[regebro]

Cool!

If all else fails, you can generate the sound electronically...

 

[James HE]

HA! I knew it. I knew you were doing some instalation! I guess I can smell a sculptor a mile away. I graduated 6 months ago from Virginia Commonwealth University with a BFA in Sculpture. And frankly I haven't made a piece since I left. Sad Sad Sad. I'm too obsessed with audio and building my project recording studio, to get back into it. A matter of time I suppose before a flash of insparation strikes. You ever meet anyone from VCU in Glasgow? Ah well, I'd love to ask you some more questions, but it's 8 am and complete thoughts get interrupted...

BTW. hi slink should be...
http:/www.woodeson.co.uk

(no ) at the end)

-jhe

 

[JC Lives]

Hey finrot from across the big pond. The large speaker concept is a potential thought but my only concern would be if a speaker frequency range is only limited to 20 hz for instance, the speaker is not capable of producing frequencies below that. If it can not produce frequencies below 20 hz, will it be able to pick them up.

I am not an electronic guru or anything, I am just trying to think logically.

Good luck in your endevors.
Joe.

 

[dobro]

James - no regrets, graduate. You're sculpting sound now. A more subtle medium, to be sure.

JC - it entertains me to see us here on the board struggling with this one - we spend all our time getting *rid* of those frequencies. Shockmounts, bass cuts, roll-offs, filters. Sometimes I just stick my fingers in my ears. And along comes someone who wants to *hear* that stuff. We're buggered.

Finrot - if you're gonna generate those frequencies, take some care about the size of the signal you put out. I think it's reliably true that you can harm people with certain frequencies down in that range.

 

[JC Lives]

Another consideration

If in fact these low freq's can be recorded, how on earth are they going to be reproduced????

Along those lines, our hearing can not go that low. I know that the idea here is to feel it and not so much hear it. In order to produce a sound wave so low that it can only be felt kind of goes beyond my comprehension. I would venture to guess that the only way to reproduce anything like this would be to use to orginal source of the sound.

I am not quite sure what produces this low stuff especially in a room.

There is only one thing I can think of that may produce some very low frequencies (a nuke). Please don't try to record this. It would very detrimental to your health. TE HE TE HE.

dobro, do you actually fight with those types of frequencies. I might have that problem but know it because I can't hear them.

 

[finrot]

written in haste

Hey,

Thanks for all the comments, keep them coming.

Quick replies as I'm short on time, fuller versions to follow later.

Yes, I know that low freqs can harm people, 6 hz for example is (allegdly [spell me?]) the resenent frequency of the human bowel...ICK!

Are the frequencies there, I believe so, but I will have to increase the amplitude so that they're perceivable.

Can you feel them, wear a pair of ear defenders and put your hairy hands (or whatever) near a bass bin...imagine removing the audible sound etc.

If anyone wants me to keep them posted about progress send me an e-mail to finrothome@yahoo.co.uk just say microphone list or something. I promise that I wont abuse it

Fuller info to follow asap..

Cheers, Ben

 

[dobro]

On occasion, I've picked up my foot tapping that comes across as a kind of rumble, yeah.

As for not being able to hear certain frequencies: in the first place, you can conceive of ultraviolet, infrared, and gamma rays, right? But you can't see 'em. So why not frequencies you can't hear? But dogs can hear frequencies you can't - they're there, alright. (I bet an elephant or whale could hear those lows.) Second thing: I find it super interesting that the audible sound is better when recorded on gear that can handle frequencies *way* beyond the 20 kHz range of human hearing. In other words, you're recording stuff you can't hear, but it has a positive effect on the bits you *can* hear. Come to think of it, you could apply this principle to your life, too.

 

[regebro]

Reproducing: No sweat, one big-ass muddafucking subwoofer should do it! And if it doesn't the US military has some interesting technology to make subsonic sounds in LARGE volumes. Exploding gas inside a cylinder at 6 Hz for example. Do it right and the sound is directional too!

 

[finrot]

big-ass sub woofer!!!!

Interesting the comment about audio gear sounding better when it includes the in-audible. I've been told that CD players etc don't carry much below 20 hz. So i'm planning on keeping everything as data files on my Mac. This includes poss exhibiting etc.

Re: big ass sub woofer. Celestion a British speaker manufacturer have sponsored the project with an 18" bass driver. They also used their software to design a ported cab specifically to emphasise the low freqs. It's virtually 2m x 1.2m x 0.6m and 18mm mdf...HEAVY. In fact I realsied recently that I'm now doing post-grad research into making my teenage fantasies reality. Well, some of them!

Concerning the large speaker and also the recording. I'm having to design and make my own high pass filter and also my own microphone amp. Does anyone have any good schematics for the electronics? No way can I afford top end pro gear, but I'm a dab hand with a soldering iron. I have plans for the pre-amp but I'm having to enloist Glasgow Uni for the filter as it's WAY complicated.

See ya all.

 

[finrot]

Hey Regebro,

I've come accross a lot of stuff about less than lethal weapons etc. But never anything about exploding gas at 6hz. Surely that's impossible. The fire will burn at it's natural rate, mind you if you could control that..woof woof

 

[finrot]

Oh yes sorry web site is at:

http://www.woodeson.co.uk

e-mail is:

finrothome@yahoo.co.uk

Web site is old documentation reviews etc not new work...

 

[regebro]

Maybe this can explain:
If you have a one cylinder engine that runs at 600 rpm, you will have explosions inside the cylinder at a rate of 10Hz.

 

[finrot]

ahh ha!

So in other words, each "bang" or pulse is one cycle?

So the number of explosions per sec=the fequency in hz.

Fiendish.

 

[regebro]

Eggsactly! Thats some whopping subwoofer!

Hey, I bet that with some ingenious computer control of the amount and timing of the gas youput in, you could actually use it as one big-ass muddafucking subwoofer!

Imagine that Drum'nBass "Baooouuuumm" sound on that one!
Fiendish indeed!