mikin guitar amp w/close and far mics. phase issues? and more...

[punkin]

I donno...I'm having a tough time keeping up with who's sayin what here but, I will tell you based on my experiences that phasing (mic placement relationship to each other) WILL make a difference when using multiple mics on a single sound source.

Take two mics put them up close...located similarly on two of the speakers...then take another ("the third") mic...put it out about a foot away...listen to the mix...move that third mic out and things will start to come into "focus".

I've done this so many times I can't remember. Press the phase switch on the that third mic or, cut-it out compeletly during playback and it gets louder or cleaner or what have you but it does make a difference...move the mic out to the sweet spot (supposedly in phase with the other mics) then hit the phase switch or cut the mic out during playback and the difference is hardly noticable except...except for the added voicing that this third mic brings to the party.

I realize it's all a matter of taste, setup and other stuff but spatial relationships is a simple fact...it takes time for audio to get from one place to another and if we accept that audio travels in a wave like manner, time/distance renders phase differences.

Oh gaaawwwd...what have I done...the zippos are lit,the flame throwers are charged and ready to go. Sorry...just my rantings about my own experiences...I'm probably wrong. Oh...one more thing...Happy New Year!

 

[mixsit]

On a git cab, one might have a mic on the voice coil and another on the outer rim of the cone. These are miced seperately because, sonically speaking, they are two different sources. Looked at that way, on a 12" speaker, the two mics are going to be at least 4"-5" away from eah other while being only about 1" from each of their sources. Well within the the 3:1 rule.

But my contention is that you can pull both mics back -still equal distance, toss 3-1 and still have the bulk of the source in phase. As a trade off you're simply getting more cross feed and all the other differences in reflections, diffraction, tone that mix with different distances. To the degree you want 'focus' or 'intimate' you work back towards close, or mono.
I think that the primary reason this gets foggy in these applications is when we forget that 3-1 has always been about attenuating phase problems. I still don't see where a ratio says anything at all about which things will be in or out of phase, but there's surely going to be a bunch of combinations that aren't going to fit.
Yes?
Wayne

 

[mixsit]

Oh gaaawwwd...what have I done...the zippos are lit,the flame throwers are charged and ready to go. Sorry...just my rantings about my own experiences...I'm probably wrong. Oh...one more thing...Happy New Year!

I don' know, it's all good.

 

[punkin]

But my contention is that you can pull both mics back -still equal distance, toss 3-1 and still have the bulk of the source in phase. As a trade off you're simply getting more cross feed and all the other differences in reflections, diffraction, tone that mix with different distances. To the degree you want 'focus' or 'intimate' you work back towards close, or mono.
I think that the primary reason this gets foggy in these applications is when we forget that 3-1 has always been about attenuating phase problems. I still don't see where a ratio says anything at all about which things will be in or out of phase.
Yes?
Wayne

Yea babe...I'm with ya...I think things become a problem when you got one closer and another further back...you're right...keep two together move them forward and back together, you simply get more or less in your face with the speakers or more of the stage/live sound.

I'm with ya.

 

[SouthSIDE Glen]

But my contention is that you can pull both mics back -still equal distance, toss 3-1 and still have the bulk of the source in phase. As a trade off you're simply getting more cross feed and all the other differences in reflections, diffraction, tone that mix with different distances. To the degree you want 'focus' or 'intimate' you work back towards close, or mono.
I think that the primary reason this gets foggy in these applications is when we forget that 3-1 has always been about attenuating phase problems. I still don't see where a ratio says anything at all about which things will be in or out of phase, but there's surely going to be a bunch of combinations that aren't going to fit.
Yes?
Wayne

Yes.

I agree with that all the way around. The trick with the pulling away from the cab and remaining "in phase" is the same trick as the moving the mics closer togther laterally. The "trick" (wrong word, I know) is that the "sources" - in this case the voice coil and the cone rim - are so close to each other to begin with, that they quickly blend into a single "source" at a short distance. It's rather like considering the "nearfield" of the speaker. For a 12" speaker (witha 6" max radius) that nearfeild only extends about 6" out from the speaker. Move the two mics only a foot out from the cab, and you're twice the distace of the nearfield boundary and the phase problems are academic.

I'll bet you there aren't a whole lot of us who multi-mic a cab at a distance between 2" and 6" from the cab. It's typically close-miked inside of 2" or pulled back to 6" to a foot or more. This is the area where the nearfield gets mushy. Add in the complication of multi-speakers in a 2x12 or 4x12 and it gets all hashed up between the nearfield of the individual speakers and the nearfield of the cabinet as a whole.

Your point about the 3:1 referring to minimizing phase via volume and not necessarily about the wavelength and distance vs. phase is an excellent point.

As far as distance between the two mics causing phasing problems, by the strict math, the upper end of the frequency rangs has a wavelength of about an inch, give or take. Let's say we're talking exacty 1" wavelength, which is about 13.5kHz. Technically that would mean that a difference of distance between the source and each mic that was anything other than a whole number in inches would be out of phase at that frequency. In fact if one mic were, say 1" away and the other were 12.5" away, they would technically be out of phase by 180 degrees. A wavelength of 1' (~1kHz), OTOH, should mean that any difference in distance that ends in 6 inches (1'6", 8'6", etc.) would throw the 1kHz stuff into phase cancellation.

But we all know it doesn't really work that way. There is so much other stuff to consider in the form of early reflections and reverberation and which frequencies you like and don't like, that it's not possible to give a good answer in the raw as to the "right distances" for near/far miking ratios.

G.

 

[thecugga]

wow ... thanks for all the tips and advice ... this shit is gold!!
ive only had a chance to skim over it all but i'll definitely go over it all in alot depth soon.

im usually recording my metal style band and the heavy tight metal guitar sound has been the hardest part for me to get ... and in my eyes is the most important instrument (along with a good kick and snare sound i guess).

this gives me a ton to go over and experiment with when i go back in and try to put together another crappy sounding tune

thanks again tho ... some awesome help!

 

[LeeRosario]

Well perhaps the approach youre taking might be a little misguided or confusing?

There's no way anyone can give you an instant and correct answer. You have to experiment.

I found that in miking guitar cabs, I like the combination of 3 different mics. It's pretty logical and has never failed me:

This technique is based on high, mid and low and with at least two different guitar amps daisy-chained together.

1) One good tube large diaphram condensor for your highs.
2) One SM57 for your mids
3) One ribbon mic or low frequency dynamic mic for your lows.

Working on a marshall half stack:

On track 1- I'd place the tube LDC just left of center (to the top left cone). A high pass filter was applied at the preamp stage (70hz cut off).
On track 2- I'd place the SM57 just left of center on the Fender vintage tube amp.
On track 3- I'd place a beta 52 just right of center (to the top left cone of the marshall) with a pop filter in front of it.

All three mics where about 1 inch away from the cone. Practically the same distance. This helps prevent phasing. Also by having 3 different mics, it helps prevent comb filtering.

I made sure I eq'd the amps to my liking.

I then had the guitar player play for a while as I mixed and match the levels of all 3 mics. After a while, I realized the Beta 52 actually gave an added saw edge boost at around 4 k that I really liked.

After double tracking (3 left and 3 right), I played around with the phase reverse and EQ for a while until I got the sound I was looking for. Then after that, add effects and print to a single left and right track.

The real answer is actually located on your head: your ears.

1) I don't know who you heard that from, but you might want check again. Just use common sense. Don't blow out your amps and keep them at a reasonable level. Mid volume would be as far as I go on a guitar amp, since I like to keep some of the pressure off the cones for better vibration.

2) In miking, introducing different distances will always give you some kind of issue. No just phasing. The only judgment good enough is your ears. If you hear a choruslike effect while tracking multiple channels, you have phasing problems.

Thats my two cents...good luck man!

 

[cello_pudding]

dynamic mics pick up different freq's at different distances, so taking both back can eliminate phase and suck tone. closer the mic =hotter signal, better s/n ratio, there's more bass (better representation of tone), and the whole point is to capture different frequencies and s/n's to mix them for the more natural tone of room noise/reflections (far condenser), and the initial wave (close dynamic).

but i guess it all comes down to what sounds best and what you're going for, so i'll just shut up now