Moving air in the Home Studio

general questions, comments and ideas about recording, audio, music, etc.
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alanfc
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Moving air in the Home Studio

Post by alanfc » Thu Jan 06, 2005 2:52 pm

hey everyone, question :

regarding electric guitar cab mic'ing, speaker movement, "excursion", "moving air":

a) is the distance from the mic the key- that is, distance for waves to form?

b)Or is the speaker pumpin going to be captured if I remove the grillcloth and get right close.

I mean which of these will capture the sound of the "movin air" ?. My guess is the first, mic further away. Trouble is, is that the further I move the mic away in this iso-cab, the more nasal it sounds, I assume from more sounds bouncing around even though I have it dampened quite alot.

unfortunately I'm limited to homemade iso-box thing..
my iso-box situation is due to my recording studio (apartment bedroom) and neighbors.
I can get the Rivera up to power tube cook in that iso-box (using an extension 1x12 with an Eminence V30 clone in the box)..I have about 4-5 extra inches to pull back from the grill if further back is better.
But outside of that thing the volume would be a major problem. Not good for my neighbor situation. A good attenuator is not in my budget right now...

thanks

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Re: Moving air in the Home Studio

Post by alanfc » Fri Jan 07, 2005 10:25 am

:( :( :cry: :cry:

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Re: Moving air in the Home Studio

Post by object88 » Fri Jan 07, 2005 10:33 am

I don't have a direct answer for you... just a thought. Sound waves are merely high- and low-pressure variations in the air. So I would guess that as long as the cone can move to it's full excursion (i.e., it's not knocking against the mic), the full wave is formed.

That said, I have no idea what the best mic-to-speaker distance is to capture your desired sound.

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Re: Moving air in the Home Studio

Post by Moon Unit » Fri Jan 07, 2005 10:46 am

Actually, if it's even moderately air-tight, then I belive you'd be looking at some pretty high air pressure inside your iso.

That might actually be used to your benefit if you learn how to take advantage of it.

Some geeks were talking about that several months ago on the board. Pretty cool stuff, potentially.
Last edited by Moon Unit on Fri Jan 07, 2005 10:47 am, edited 1 time in total.

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Re: Moving air in the Home Studio

Post by alanfc » Fri Jan 07, 2005 10:47 am

thanks

indeed I've enjoyed the placement testing I've done over the last few months, how I found that every centimeter counts! I had a project in my DAW just for mic placement with about 50+ positions. For my speaker I've found a couple ideal positions,

however,

I keep reading about "moving air" and mic'ing cabs in a =room=. I can't do it in a room. My iso-cab is my only option.

I just feel like I'm missing out, so this is why I ask.

So, larger question for any other tech folks-
In an Iso-cab, is this goal of 'moving' air an impossiblity?. I mean in the classic sense, really =MOVING AIR DUDE YEAH OW= kind of assault on the mic. Perhaps this is just physics and I can look it up there. The behavior air around a sound source?

thanks

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Re: Moving air in the Home Studio

Post by superpenguin79 » Fri Jan 07, 2005 11:23 am

the way the acoustics work with guitar cabs or any live audio like that for example is the closer you get to the source (i.e. guitar cab in this case) the less ambience from the room..etc.. that you are going to get and the less time that the sound waves actually have to develop and mature to their actual tones and what not.

I believe if I recall that there was a study once that said it takes something like 36 ft. for a sound wave to properly mature and expand to its potential before it decays and fades out and resonates from different textures in the room if you mic straight in front of the source.

For example, if you are doing pop, rock, alternative, R&B..etc. with a guitar cab, I would close mic with the exact sound you want out of the cab first of all for starters.. where you would really want to distance mic is if you are putting more than one mic on the cab for texture, ambience, or if you are recording any type of harder rock/metal bands that like that growl tone because the sound waves have more time to develop and put more midrange and low tones into them as they travel.

If you have a iso cab, I am assuming that you do not have access to unlimited space to play with correct? In this case, you can mic it with the iso cab, but you'll want to add your ambience on the daw when you get to the mixing stage. If you mic without the iso cab, you can experiment more and mic in different positions and try different mic combinations and pollarities..etc... til you come up with something that sounds great for your particular room. Every room is different also and not everything that others have tried in different locations doesn't always work exactly the same in a totally different room. :)

what sound are you going for?
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Re: Moving air in the Home Studio

Post by object88 » Fri Jan 07, 2005 11:57 am

superpenguin79 wrote:I believe if I recall that there was a study once that said it takes something like 36 ft. for a sound wave to properly mature and expand to its potential before it decays and fades out and resonates from different textures in the room if you mic straight in front of the source.
What changes in a sound wave from it's initial state to it's maturation?

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Re: Moving air in the Home Studio

Post by sonikbliss » Fri Jan 07, 2005 11:58 am

Somebody correct me if I'm wrong (which I probably am) but I believe the formula to figure out the length of a soundwave is:

velocity = wavelength x frequency

Sound moves at roughly 1130 feet/second, 344 meters/second, or 770 miles per hour at room temperature of 20oC (70oF).

So plug in your numbers

1130 (velocity) = wavelength x 250Hz (frequency)

Divide 1130 by 250 (or what ever frequency you want to find the length for)= 4.52 feet for a 250Hz sound wave to develop fully.

Try to get the low end right in the microphone and the rest should fall in place. You can just EQ the "air" into the recorded track.

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Re: Moving air in the Home Studio

Post by superpenguin79 » Fri Jan 07, 2005 1:07 pm

object88 wrote:
superpenguin79 wrote:I believe if I recall that there was a study once that said it takes something like 36 ft. for a sound wave to properly mature and expand to its potential before it decays and fades out and resonates from different textures in the room if you mic straight in front of the source.
What changes in a sound wave from it's initial state to it's maturation?

think of it as the source of the sound wave being your guitar cab. Well, for starters the development of the wave is determined by the SPL that your amp is cranking out. If it is a very low volume, the sound wave is going to mature and decay a whole lot quicker than if you had one of those massive walls of stacks they used to put on stage in the 80's for example. :D

When sound travels it expands because you will notice that no matter where you stand in your room even if it is behind your guitar cab that you still hear the sound because the sound waves shoot out sort of like the foul lines at a baseball game in a way for the best way I could describe it without drawing you a diagram. When they travel out in that pattern or whichever occilliation that your amp pumps out, they will reflect off of the harder surfaces and cause natural reverb to happen which gives you sound wherever it bounces from there..etc..

like the above post mentioned... there is a formula for figuring it out. I forget the exact thing off the top of my head for it, but if I remember or come across it I will post it for you. :)
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Re: Moving air in the Home Studio

Post by alanfc » Fri Jan 07, 2005 3:29 pm

cool/thanks !

I was hoping we'd draw in some folks to give this type of info. ! Now we got it :D

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Re: Moving air in the Home Studio

Post by alanfc » Fri Jan 07, 2005 3:32 pm

superpenguin79 wrote:

what sound are you going for?
hi,
I'm not looking to nail anyting in particular, just want spanky authoritative overdrive tones. Using humbuckers in particular. I've come pretty close to what I want, but this moving air thing was sort of escaping me.

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Re: Moving air in the Home Studio

Post by object88 » Fri Jan 07, 2005 3:36 pm

superpenguin79 wrote:When they travel out in that pattern or whichever occilliation that your amp pumps out, they will reflect off of the harder surfaces and cause natural reverb to happen which gives you sound wherever it bounces from there..etc..
So maturation in a sound wave is the addition of ambiance (wall reflections, etc.) before decay?

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Re: Moving air in the Home Studio

Post by sonikbliss » Fri Jan 07, 2005 6:14 pm

I don't know exactly what "maturation" of the sound wave is refering to. But it seems logical to think that the first fully developed wave is always going to be the most powerful and each one following would grow weaker than the one before (unless the room is causing some kind of weird filtering, but that's rocket science). Therefore if you want a more aggresive in-your-face tone mic the amp closely, if you want a more ambient sound mic farther back and capture the sound as the soundwave is fading and being enveloped by the room (of course you must have a room that has natural reverb to do this.)

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