low frequency specific mic placement

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christiannokes
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low frequency specific mic placement

Post by christiannokes » Sun Nov 20, 2005 12:59 pm

I learned that when a mic is dead on to a source that you will get a lot of the lows and highs compared to if you angle the mic to the source. "Proximity effect" I guess? I was wondering if you could angle a mic, on a kick drum for example, so that you were getting more 60 hz and less 100. This is just 1 scenario. I'm sure it is possible, but does anybody have any method or mapped out way of doing this?

thethingwiththestuff
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Post by thethingwiththestuff » Sun Nov 20, 2005 3:39 pm

you've got the idea. first, know that that's applicable to directional pickup patterns. omni does not exhibit the proximity effect. however, proximity effect is about well....proximity, rather than "dead on" or angled.

what you are referring to is being "on axis" or "off axis." again, this is really just for cardioids. have you ever seen a polar pattern chart for a mic? that shows you how a particular mic will reproduce frequencies depending upon where in its pickup pattern they come from. directional mics will pick up high frequencies best directly on axis, or dead on in front of a cardioid mic. as you move to either side and towards the rear, you lose high end. low frequencies are more difficult for a directional mic to reject. look up any mic's polar pattern chart, and it will show you how it responds to 1k at 0 degrees vs 45 degrees or 180, and 60 hz at 0, 45, and 180, etc.......

but to answer your original question, yes, and no. mic position is CRITICAL to getting the right balance of frequencies out of an instrument, but there's no practical method to tell you to use. use headphones when you're placing a mic to hear where you need it to be and at what angle it needs to be at.

AGH! PS - proxomity effect has to do with the increase in low end as you move closer or farther away from the source.

Professor
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Post by Professor » Sun Nov 20, 2005 7:11 pm

That's a pretty good explanation right there. Except that all mics will change their patterns and off-axis response regardless of the specified pattern of the microphone. It should be no surprise that Neumann has really great technical info about their mics online, and if you click here, you'll go the technical data page for the U-89 which is a 5-pattern mic. If you click on the little graph at the right, a Flash window will pop open with an interactive graph page where you can click different patterns and frequencies and see how that particular mic deals with different frequencies. You can also check out similar data for fixed cardioid or fixed omni mics that they build.

What you'll find as a general rule for all microphones is that the mics are more omni-directional at low frequencies and more directional at high-frequencies. The only exception is figure 8 mics, at least in the fact that their 'null point' is always at 90? off-axis, though they will widen and narrow a bit with frequency.

As for your specific hope of boosting 60 while dropping 100, well I just can't imagine that happening. You're talking about two frequencies that are less than an octave apart, and both down in the range where the mic is becoming more and more omni. So I just can't imagine that happening through placement, at least not as a general rule about all microphones though perhaps it could apply to one specific microphone.
As an example, if you look at the frequency response graph for that U-89 in Figure-8, then you'll see that the mic has a slight dip of about -2dB centered around maybe 130Hz, while it is back at 0dB at 60Hz, and rolling off below that. That is for the mic on-axis at 0? and it doesn't show a polar plot for the mic at 62.5, so it's hard to say whether an on or off-axis placement would increase or decrease that effect. But you'll notice that is not only for just that model of microphone, but just that pattern on that microphone - it doesn't happen on any pattern for the U-87, the TLM-127, or the fig-8 capsule KM-120.
But it is possible that one of your specific mics might have some kind of bump or dip in its response that is helpful to you in this way, so you could certainly try to find a position for your mics that will do what you're looking for.

-Jeremy

cgarges
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Post by cgarges » Mon Nov 21, 2005 7:15 am

Good answers!

While a mic is aimed straight-on to a source, you generally get the most accurate representation of that mic's frequency response in relation to the source. It's not necessarily more highs and lows. Angling the mic introduces a phase error across the diaphragm, so certain frequencies are skewed, but I'm not sure that that's predictable in any way.

While I'm not sure that it will specifically boost 60Hz and cut 100, a kick drum's fundamental radiates strongest from the point of contact between the head and the shell, so pointing the mic at the bearing edge (the contact point) should give you a stronger LF representation than anywhere else on the drum. The fundamental will more than likely be below 100, so this might be of some use to you.

So, I guess the answer is "try it and see what you get." If it sounds better to you, rockin.'

Hope this helps.

Chris Garges
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joel hamilton
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Post by joel hamilton » Mon Nov 21, 2005 7:46 am

I always picture the polar pattern like a flashlight.(flawed analogy, but it works for me).


I also try mics and aim them at stuff until I discover one that really rocks for that applicaion.

I take note of that, and repeat. For a lot of years.

christiannokes
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Post by christiannokes » Mon Nov 21, 2005 5:40 pm

Thanks for the posts guys. Another piece of the puzzle!

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