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Post by Deleted on Oct 14, 2013 13:44:49 GMT -6
I have always wondered: How close can I put an acoustic screen (to attenuate sound reaching the mic) behind one side of a figure of 8 patterned mic before it starts to interfere with the way the fig 8 pattern works and affects the sound recorded on the open side of the mic ? hope this makes sense, apologies if it is a dumbass question  |
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Post by popmann on Oct 14, 2013 17:41:28 GMT -6
Don't.
The longer answer is that it depends on the construction and type of the screen....but, farther will ALWAYS be better. The issue is that many tend to not reflect highs but, do lows--and in fig8, the sides are out of phase with each other, so you begin to cancel lows/low mids...and get weird boxiness. I mean, I've experimented with it--but, it's usually only useful on a really loud guitar amps--where there's a LOT of DB bouncing around the room.
The truth is that Fig8 is by far the driest pattern for a place with less than stellar acoustics. I know it doesn't seem like it, since it picks up both sides...but, the reflections from the other side of your room are not going to usually cause issues--particularly if you just avoid the back pointing directly at a flat wall. It's the reflections coming from closer that cause the awful issues--and Fig8 nulls more of them than cardioid. Which is why I think Card only LDCs are this side of useless. Now, technically, if you have a "more than three"--hyper cardioid is technically the driest, but not tons of LDCs have that--and it really alters the frequency response (for better or worse is a judgement)...where Fig8 is the most even keel on most--closer to omni, but rather than all inclusive pickup, it's pretty dry AND even keel frequency wise.
Also consider that with Fig8 on say a guitar amp---the sound on the front will be exponentially louder than the room on the back unless you're in a closet. Thus--it's dry with just a touch of ambience that makes it less claustrophobic.
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Post by svart on Oct 15, 2013 10:53:07 GMT -6
It also matters what the object behind is made of. Figure 8 means that the rear portion is completely out of polarity with the front. that means if anything reflects from the surface behind and back to the mic, can lead to phase issues and likely frequency response issues. If the object is closer than probably 6ft, I would want it almost completely absorptive to at least keep the phase issues from happening.
Angling the mic so that it's not parallel with the wall behind is also good to do, it'll help keep some of these issues from happening too.
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Post by Deleted on Oct 15, 2013 12:23:28 GMT -6
great replies guys, many thanks
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Post by tonycamphd on Oct 15, 2013 12:24:33 GMT -6
IMO, a deep doubled up r30 uncompressed insulation(r60), gobo behind the figure 8 will work great, just don't get it too close, as always, use ur ears to check. Some of those acoustic mic shielding foam doohickys, are really horrible like the one below, they focus very early reflections directly back into the mic...?? You can hear the boxy strangeness talking into it with no mic (go to your local guitar center, and save yourself a return hassle.)  |
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Post by svart on Oct 15, 2013 12:34:31 GMT -6
IMO, a deep doubled up r30 uncompressed insulation(r60), gobo behind the figure 8 will work great, just don't get it too close, as always, use ur ears to check. Some of those acoustic mic shielding foam doohickys, are really horrible like the one below, they focus very early reflections directly back into the mic...?? You can hear the boxy strangeness talking into it with no mic (go to your local guitar center, and save yourself a return hassle.) Agreed. The problem with a lot of those is that they have a hard backing behind the foam. The foam only really works above 2khz or so, and the lower frequencies pass right through it and bounce off the backing and right back at the mic. If you use a gobo like that, at least use rockwool or compressed insulation like Tony does but make sure there is NO hard backing. Two things will attenuate sound, mass and distance, so if the sound passed through a dense material, then across a distance and bounces back to travel back through the dense material before reaching the mic, then you'll gain a lot more attenuation than if you doubled the dense material. Also, extremely dense material can become reflective at higher frequencies the more dense it becomes, so there is definitely a happy point. |
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Post by tonycamphd on Oct 15, 2013 12:48:19 GMT -6
^ agreed, the backing is generally the problem on those, My understanding/experience, the doubled up looser(uncompressed) r60(around 14" thick) adds depth and great gas flow characteristics, with unmatched broadband absorption for it's size, rigid 703/705 will indeed reflect frequencies back, it's better uses are deep super chunk bass traps and general absorption. here are my super chunks 24x24x36, done with ultra touch insulation, r30 stacks, better gas flow than 703/705 at its size, works amazingly well.   |
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Post by Deleted on Oct 18, 2013 15:06:00 GMT -6
very nice corner traps, great job!
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