Bass micing and wave length.

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blackdiscoball
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Bass micing and wave length.

Post by blackdiscoball » Thu Aug 12, 2010 9:52 am

So I was just reading an eq article were the author states "now remember to move the mic off the bass amp as bass waves take longer to develop then guitar waves" or something like that. I tried searching the tomb and didn't find anything but it would seem to me that the only thing moving the mic back would do would be change the proximity effect if that was an issue or change the ratio of direct to room sound the mic picked up and very little with how "accurate" the wave is picked up? Am I missing something or is the author just mistaken? It seems I've read discussions on this before but can't remember what was concluded?
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Post by The Scum » Thu Aug 12, 2010 10:12 am

I think your general sense of it is reasonable...but there are times that moving a mic an inch or two makes a big difference, probably as much things like proximity effect, and the sound that's eminating from a particular spot in front of the amp (The dust cap straight on, sounds different from the edge of the cone at an angle...multiple drivers may set up interference patterns, etc).

The wavelength of 100 Hz is about 10 feet...50 Hz is 20 Feet. An inch is a tiny fraction of the wavelength at those frequencies. So the author doesn't seem to be referring to a wave-related factor.

If the longest dimension in your room is smaller than 20 feet, then 50 Hz will be experienced as a pressure, rather than a wave. Check your favorite acoustics resource for information about the "pressure zone."
"take longer to develop then guitar waves."
Huh?

Can you post the exact wording? There may be some clues in the language they use. Who is the author?

I still unrepentantly mic bass amps at a distance of 3 inches. I usually time align the DI track to match.

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Post by farview » Thu Aug 12, 2010 10:30 am

There are plenty of good reasons to move the mic farther away from the speaker, but I don't buy into the 'letting the wave develop' thing.

How we percieve a wave has very little to do with how a mic picks one up. The speaker moves the air at a certain frequency which moves the diaphram of the mic at the same frequency. The closer the mic is, the more direct the sound the mic picks up will be.

Like The Scum pointed out, even if you are only dealing with half waves or quarter wavelengths, you are still talking 5-10 feet for the real low end.

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Post by JWL » Thu Aug 12, 2010 11:07 am

farview wrote:There are plenty of good reasons to move the mic farther away from the speaker, but I don't buy into the 'letting the wave develop' thing.
I agree, I think this is a fallacy. This is NOT to say that moving the mic won't change the sound, it will beyond question. The question is, why does the sound change? Proximity effect, room/direct sound ratios are obviously a big part of the equation.

Personally, I think one strong possibility is that the frequency response in the room changes quite a bit as you move throughout the room, this is caused by comb filtering and room acoustics.

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Post by blackdiscoball » Thu Aug 12, 2010 1:15 pm

His exact words were "Remember that bass waveforms need more room to fully develop compared to midrang-y guitar, so place the mic ten to 12 inches from the speaker to let the sound stretch out." Regardless of theory it doesn't take an expert to hear the difference from moving a mic a half an inch but it just doesn't seem to me that it would have any effect on "waveform development".
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Post by MoreSpaceEcho » Thu Aug 12, 2010 2:43 pm

a foot from the speaker is hardly 'letting the sound stretch out' IMO but what do i know...

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Post by farview » Thu Aug 12, 2010 3:21 pm

It might very well sound better when you pull the mic away, but not for the reasons stated.

All of this is so subjective that it's kind of pointless. There are so many variations on what a 'good bass sound' is that once you multiply that times how many different sounds could possibly be coming out of a bass cabinet and what mic(s) you use, there is no way for there to be a rule of thumb about where that mic should go.

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Post by drumsound » Thu Aug 12, 2010 4:15 pm

farview wrote:It might very well sound better when you pull the mic away, but not for the reasons stated.
And that, good sir, is the crux of the biscuit.

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Post by nick_a » Thu Aug 12, 2010 8:16 pm

I LOVE biscuits.

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Post by CraigS63 » Sun Aug 15, 2010 7:08 am

nick_a wrote:I LOVE biscuits.
Not sure I'd like bass on a biscuit. Salmon, possibly.

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Post by niccolo gallio » Sun Aug 15, 2010 10:25 am

"The crux of the biscuit
is the apostrophe"
C'mon, you can't possibly believe what's written on my avatar..

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Post by Fletcher » Mon Aug 16, 2010 7:30 am

The statement lacks clarification and can not be taken as any form or "universal truth". If you have a mic in front of an 8x 10" SVT cabinet you have a different set of issues than a 1x 15" speaker cabinet... and if you're into older cabinets, like an Acoustic 360 system you're dealing with a "folded horn" design where the sound from the cabinet is meant to be a "long throw" [due to the folded horn enclosure] which means that it could indeed be several feet before you experience the "focus" of the output of the cabinet.

At the end of the day, if it sounds good it is good... and if it doesn't sound good you need to find a solution [which generally won't come in a box or off the internet].

FWIW, one thing I have found to be an amazing help for defining the "vowel" of a bass note is to take the bass signal DI off the instrument, and then run that signal through a Littlelabs "IBP" and send a "re-amp" signal to the amplifier with the "phase knob" engaged. What that does is allow you to tweeze the "phase" of the bass signal coming out of the amplifier as it is heard by the microphone which allows you to better "tune" / "define" the "vowel" of the bass sound in relation to the rest of the sounds that comprise the overall tonal balances of the recorded presentation.

The bass player won't actually hear anything different from their amplifier as there is no other signal in relation to what they're hearing [especially if you're doing a "no headphone" session]... or you can fold some of the DI sound into their cans if you so choose.

The bottom line [or "crux of the biscuit"] is that you get a great bass sound that works and plays well with all the other sounds while the player feels comfortable enough to give a stellar performance [and that stellar performance is indeed the true "crux of the biscuit"].

Peace

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Post by Sean Sullivan » Mon Aug 16, 2010 8:49 am

I've always had the best luck putting a microphone 12-15 inches off the grill of an amplifier, pointed directly at the center of speaker, using a condenser microphone. It gets the "full range" of the speaker. If you need to shove something right up on the grill because of bleed or whatever, I've had the most luck with a RE20. It has less (if any) of a proximity boost.

But, a SM57 or a R-121 or a PR30 or (insert your favorite microphone here) right on the grill doesn't sound bad either. As they say, whatever works for you!
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Post by rhythm ranch » Mon Aug 16, 2010 12:53 pm

Fletcher wrote:FWIW, one thing I have found to be an amazing help for defining the "vowel" of a bass note is to take the bass signal DI off the instrument, and then run that signal through a Littlelabs "IBP" and send a "re-amp" signal to the amplifier with the "phase knob" engaged. What that does is allow you to tweeze the "phase" of the bass signal coming out of the amplifier as it is heard by the microphone which allows you to better "tune" / "define" the "vowel" of the bass sound in relation to the rest of the sounds that comprise the overall tonal balances of the recorded presentation.
Nice! :^:

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Post by blackdiscoball » Mon Aug 16, 2010 2:19 pm

All of this is so subjective that it's kind of pointless. There are so many variations on what a 'good bass sound' is that once you multiply that times how many different sounds could possibly be coming out of a bass cabinet and what mic(s) you use, there is no way for there to be a rule of thumb about where that mic should go.
I wasn't really asking subjectively about what would give me a better bass sound, the question was whether the length of a wave is effected at all in the recording of the wave length. So lets say we have a bass amp in an anechoic chamber and using an omnidirectional microphone we record the bass note with the mic 1 inch away, 1 foot away, and 10 feet away. If we adjusted the volume so it was hitting the mic at the same volume level each time would the wave length sound different? Its a purely academic question as I realize that just changing the volume would change the tone and so Im just wondering "in theory" kind of question.
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