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Author Topic: Acoustic treatment for underside of umbrella?  (Read 1645 times)

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Offline thatjackelliott

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Acoustic treatment for underside of umbrella?
« on: July 10, 2017, 05:45:51 PM »
If this has been asked and answered, please point me to the threads.

I just got one of those Dizzlestick golf cart umbrellas. Sticking my head under the thing, where the mics would sit, it sounds like I'm inside a parabolic reflector. The stretched fabric is very good at reflecting treble energy. Very audible coloration. While most discussions about umbrellas here are related to damping the pitter-patter of raindrops, how might a fellow go about treating the underside of the thing to block reflections? Stuff a sheep into it and hope it stays?

Offline Gutbucket

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Offline thatjackelliott

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Re: Acoustic treatment for underside of umbrella?
« Reply #2 on: July 11, 2017, 10:41:04 AM »
Thanks. I've see that photo and it doesn't address the reflections under the umbrella that make it sound like I've stuck my head into a very large mixing bowl. It's not rain noise I'm inquiring about but how the taut fabric of the umbrella effectively reflects sound down toward the microphones. It least with the Drizzlestick, the coloration is very audible. 

Offline if_then_else

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Re: Acoustic treatment for underside of umbrella?
« Reply #3 on: July 11, 2017, 12:10:46 PM »
Thanks. I've see that photo and it doesn't address the reflections under the umbrella that make it sound like I've stuck my head into a very large mixing bowl. It's not rain noise I'm inquiring about but how the taut fabric of the umbrella effectively reflects sound down toward the microphones. It least with the Drizzlestick, the coloration is very audible.

Why not avoid the umbrella completely and build your own "Rain Hat"?
See my comment in this thread: http://taperssection.com/index.php?topic=174011.45

Offline bombdiggity

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Re: Acoustic treatment for underside of umbrella?
« Reply #4 on: July 11, 2017, 12:14:32 PM »
I think the approach is the same. 

Some soft material like the towel on top will dampen the noise from the rain hitting it.  Thick foam underneath should stop the transmission underneath.  You'd need to fully cover the surface (unlike the pic). 

Depending on conditions getting some distance between umbrella and mics will also help.  I'd not want the umbrella immediately over top the mics unless it has to be due to rain coming from all directions. 

Frankly when windscreens weren't enough to stop heavy wind noise I've covered the entire rig completely with light material without a discernible negative impact.  It sounded way better covered than with the wind blasting them.  Breathable material is probably better but super thin plastic should not significant;ly change the result though you may have an even greater raindrop impact. 

Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline thatjackelliott

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Re: Acoustic treatment for underside of umbrella?
« Reply #5 on: July 11, 2017, 01:37:12 PM »
"Some soft material like the towel on top will dampen the noise from the rain hitting it.  Thick foam underneath should stop the transmission underneath."

Thanks, I'm still not talking about rain noise. I'm not concerned with rain noise. Rain is not the issue. Not rain. The word "rain" is henceforth banished from this thread.

It's the "It sounds like I stuck my microphones into a large mixing bowl" effect I hear when the mics are under an umbrella. A matter of reflection, not transmission.

Hmm, a little more testing: the effect is very pronounced with the Drizzlestick umbrella. That umbrella is small in diameter, but deep, like an oversized basketball cut in half. Because the diameter is small you'd want to push the microphones up close to the "bowl" to shelter them. But that hemispherical/mixing bowl shape causes the reflected sound to be very audible. A more traditionally-shaped umbrella I have here does not sound like that, and the larger diameter means the 'brolly can be raised much farther above the mics and still afford shelter from inclimate weather without audible coloration caused by bowl reflections.

So, I guess that if I want to use the Drizzlestick I could cut a disc of "eggcrate" acoustic foam the diameter of the underside of the 'brolly and paste it up under it to block the reflection. Or I could maybe cut wedges of thick fleece and spray-glue them to the inside of the umbrella.

Or just use a traditionally-shaped umbrella. Not as cute as a Drizzlestick and more of a wind sail, but more neutral in sound.

Offline Moke

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Re: Acoustic treatment for underside of umbrella?
« Reply #6 on: July 11, 2017, 01:56:38 PM »
reign

I haven't seen your posts before. Welcome aboard.
good luck in your journey to umbrella quietness.
« Last Edit: July 11, 2017, 02:08:50 PM by Moke »
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Offline bombdiggity

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Re: Acoustic treatment for underside of umbrella?
« Reply #7 on: July 11, 2017, 02:11:18 PM »
"Some soft material like the towel on top will dampen the noise from the rain hitting it.  Thick foam underneath should stop the transmission underneath."

Thanks, I'm still not talking about rain noise. I'm not concerned with rain noise. Rain is not the issue. Not rain. The word "rain" is henceforth banished from this thread.

It's the "It sounds like I stuck my microphones into a large mixing bowl" effect I hear when the mics are under an umbrella. A matter of reflection, not transmission.

Ah.  Gotcha. 

My suggestion would be foam directly across the underside of the umbrella so you put a "lid" on the bowl.  Then there's nothing getting mixed in the bowl to interfere. 

You didn't say what type of mics you were using.  I'd assume something directional might be less prone to catching reflections from above but it is more thorough to just close the bowl entirely. 
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline Gutbucket

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Re: Acoustic treatment for underside of umbrella?
« Reply #8 on: July 11, 2017, 03:29:10 PM »
If going the umbrella route, use a flatter profile umbrella that isn't overly dish shaped.  I've seen smallish Greek-cross shaped umbrellas the last few years in the section which are quite flat and fit that description, most seemed to be Batman or Spiderman branded.  Also as mentioned, consider using something to damp the high frequency reflection off the taught fabric underside, like foam or dense fabric underneath.  Unfortunately the umbrella needs to be close to the mics to provide rain protection, yet that proximity increases sensitivity to noises from the umbrella.

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Offline Gutbucket

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Re: Acoustic treatment for underside of umbrella?
« Reply #9 on: July 11, 2017, 03:55:47 PM »
Frankly when windscreens weren't enough to stop heavy wind noise I've covered the entire rig completely with light material without a discernible negative impact.  It sounded way better covered than with the wind blasting them.  Breathable material is probably better but super thin plastic should not significant;ly change the result though you may have an even greater raindrop impact. 

Was looking for a photo I thought I had which this brings to mind but I can't find it.   But I'll describe it and post a couple other photos to help paint the picture.  Back in '07 or '08 I built a custom vert bar to do X/Y coincident recording using the ADK TLs in their big super-mount suspension baskets, intended for both on-stage recording and section recording on a tall stand.  The foam screens didn't provide sufficient wind protection outdoors, so I rigged a layer of faux fur rapped around both mics as a  vertically arranged pair with the ends tucked into the baskets.  That worked great.  See the photos below.   Problem was that the arrangement was to tall for sufficient rain protection under a typical mic stand umbrella for unpredictable Florida spring festival weather.  So when weather threatened I carefully wrapped the entire vertical mic arrangement in very thin "dry cleaning jacket cover" thickness plastic and gaff-taped it in place.  The plastic was stretched taught between the two metal rings of the baskets and rested lightly against the fur underneath which nicely damped any tendency toward tympanic resonance.  The plastic was more overlapped and tapped more heavily at the top and bottom to prevent any wind vibration or flappage.  Although done as an emergency foul-weather measure, this worked incredibly well.  We ended up having quite a storm blow through and I noticed no wind or rain noise at all, as well as no sonic issues with the plastic over-wrap.

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Offline Gutbucket

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Re: Acoustic treatment for underside of umbrella?
« Reply #10 on: July 11, 2017, 04:51:39 PM »
Why not avoid the umbrella completely and build your own "Rain Hat"?
See my comment in this thread: http://taperssection.com/index.php?topic=174011.45

^This is where I'm going next, eliminating the umbrellas entirely. 

Thinking of modifying big-ass Sure A81WS windscreens with individual built-in DIY rain hats.  I've already moved to using microphones which don't have problems with moisture.  But still need to protect from wind and prevent rain saturation of the windscreens and mics.

Plan is to affix rain-hat layers on the upper surface of the individual big Sure windscreens using a touch of spray adhesive to fix a top layer of the super-thin dry-cleaning plastic bag material under an over-layer of 10-PPI coarse PUR material.  The thin plastic should be even more sonically transparent, thinner, and even less bulky than the thin layer of polyethylene foam used in the rain-hats in the thread if_then_else linked.  I'll bevel cut the edge of the oval shaped PUR filter material to taper into the shape of the windscreen, essentially making the whole screen a bit thicker on top in profile.  May need to stitch it in place to the finer A81WS outer foam along the edge at a few points. The PUR filter material will break up droplet impact noise and protect the thin water-tight plastic layer beneath.  Water will then run down the plastic and off it's outer edges to the outside of the windscreen.  Remainder of the Sure windscreen foam below the upper-surface hat level will be Never-Wet treated to make it hydrophobic, avoiding water saturation.   The Never-Wet treatment alone has done a good job protecting the BAS foam screens from mist and moisture saturation, but cannot deal with direct droplet pelting saturating the top.   

Sonically, I think this should work nicely- the sonic-veiw along the horizontal plane from each microphone's point of view should be clear without any additional materials interposed in that path.  The PUR material is the same as the inner layer of the A81WS, and I know from previous experience that the thin plastic layer can be sonically transparent.

I'm especially motivated to do this because my oddball arrays require a rather large umbrella to cover the four central supercarioid mics, each inside it's own A81WS sometimes along with a coincident bi-directional.  Even a large enough umbrella which covers the central mics doesn't come close to covering the 2 spaced omnis which are like 5' or 6' apart.   Fortunately the omnis work even submerged, but direct impact rain impact noise and windscreen saturation is still an issue with them, so I may do the same with the smaller windscreens I use on the omnis.     

If this works it will be great to have individual wind and rain protection for each microphone position, in a setup I can use outdoors regardless changes in weather, with the most minimal increased visual impact I can imagine.

« Last Edit: July 11, 2017, 05:46:18 PM by Gutbucket »
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Offline thatjackelliott

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Re: Acoustic treatment for underside of umbrella?
« Reply #11 on: July 11, 2017, 05:17:11 PM »
Right on, gents. NOW we're getting somewheres.

Offline bombdiggity

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Re: Acoustic treatment for underside of umbrella?
« Reply #12 on: July 11, 2017, 05:17:54 PM »
^^ The lighted angel on top the Christmas tree  ;D

I'll bet that worked.   
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline Gutbucket

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Re: Acoustic treatment for underside of umbrella?
« Reply #13 on: July 11, 2017, 05:45:01 PM »
Furry angel.  Was affectionately referred to as "the possum" at a couple fests that year.
« Last Edit: July 11, 2017, 05:46:50 PM by Gutbucket »
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Offline thatjackelliott

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Re: Acoustic treatment for underside of umbrella?
« Reply #14 on: July 11, 2017, 06:20:16 PM »
We routinely stick a $10 plastic hemispherical cup anemometer atop our audience mic stand at festivals. It goes round and round. Just the thing for a radio station. That's all it does. Just goes 'round. So far the bearing (metal on plastic) has not squeaked. Squeak squeak squeak squeak. What's that squeaking sound on the recording?  :yack:

Offline jeenash

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Re: Acoustic treatment for underside of umbrella?
« Reply #15 on: July 12, 2017, 05:38:35 PM »
Not sure but maybe this helps. I made this a long time ago mainly to make a smaller umbrella that wouldn't make my stand too top heavy. I just cut one maybe 2 rib sections (can't remember), cut the excess fabric, and glued the stretched fabric underneath with contact cement. It makes for a fairly flat umbrella. I secure it to the stand with 2 hose clamps.

Offline Gutbucket

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Re: Acoustic treatment for underside of umbrella?
« Reply #16 on: July 12, 2017, 05:48:51 PM »
^Nice umbrella mod!
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Offline thatjackelliott

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Re: Acoustic treatment for underside of umbrella?
« Reply #17 on: July 13, 2017, 12:36:08 AM »
Hose clamps! Brilliant.

Offline John Willett

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Re: Acoustic treatment for underside of umbrella?
« Reply #18 on: July 28, 2017, 11:28:18 AM »
Thanks. I've see that photo and it doesn't address the reflections under the umbrella that make it sound like I've stuck my head into a very large mixing bowl. It's not rain noise I'm inquiring about but how the taut fabric of the umbrella effectively reflects sound down toward the microphones. It least with the Drizzlestick, the coloration is very audible.

Yes it does - there is acoustic foam under the umbrella to do exactly what you asked for.

 

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