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[Art Welter]

Testing a new HF horn today, occurred to me that I had never actually seen what plastic sheet does to sound when placed over a speaker, though I have heard how bad it can sound.

Having done hundreds of outdoor shows with tarps or plastic sheet over the speakers for extended periods of time, it was obvious that the HF was reduced, but not as obvious how bad the comb filtering was.

A "tarp EQ"of a 6-10 dB HF shelf boost helps correct the general downhill trend, but no way can the comb filtering be corrected, explaining the nasty sound.



The thicker the plastic, the worse the effect.
The depth of the HF horn will also affect the location of the dips.
The white line is with no plastic, the light blue is a 1.1 mil thick garbage bag, the orange is around 5 mil thick.

Yikes.

Art Welter

[Moby (Mike Diack)]

Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness.
M

[TJ (Tom) Cornish]

I sense a market for a new recording plugin:

Outdoor Festival - Transforms your music from the boring pristine-ness of standard recording techniques to the dynamic, warm (dry?) live outdoor concert sound we all crave.

There should also be an app for that, so I can play my ITunes library through this filter.

P.S. - Version 2 forthcoming - will include Gunness De-Focusing

[James Feenstra]

what about the effect of a blow through or scrim?

[Geoff Doane]

Art Welter wrote on Tue, 18 January 2011 02:04

, it was obvious that the HF was reduced, but not as obvious how bad the comb filtering was.

That's what a tester found back in the '80s when he wanted to know what the popular "tissue paper over the tweeters" of studio monitors was really doing to the sound of the speakers.  The tissue paper didn't really reduce the overall level very much, but did create serious comb filtering.

Why it was a desirable technique is anybody's guess.

GTD

[Art Welter]

James Feenstra wrote on Tue, 18 January 2011 08:38

what about the effect of a blow through or scrim?

It would be interesting to test, as would perforated metal screen of various percentage of openness.

If anyone wants to send me some material pieces, I'll give them a shot, a 15 inch by 10 inch piece will fit over the small horn.

I tried the Acoustone grill cloth I normally use, it had almost no effect that could be detected.

Throwing a towel over the horn (as drummers often do with their monitor )  muffled the HF pretty evenly, without a lot of comb filtering.

[Art Welter]

Geoff Doane wrote on Tue, 18 January 2011 09:21

Art Welter wrote on Tue, 18 January 2011 02:04 , it was obvious that the HF was reduced, but not as obvious how bad the comb filtering was. That's what a tester found back in the '80s when he wanted to know what the popular "tissue paper over the tweeters" of studio monitors was really doing to the sound of the speakers.  The tissue paper didn't really reduce the overall level very much, but did create serious comb filtering. Why it was a desirable technique is anybody's guess. GTD

It allowed your mixes on NS 10s to sound like they went through an Aphex Aural Exciter without having to rent one...

A pair of NS 10s sitting on the meter bridge of a console have so many diffraction issues that the addition of some tissue paper makes little comparative difference.

[Tom Reid]

Moby (Mike Diack) wrote on Tue, 18 January 2011 01:04

Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M

Cheesecloth?

Or a wall of fire.

[Greg Cameron]

TJ (Tom) Cornish wrote on Tue, 18 January 2011 05:44

I sense a market for a new recording plugin: P.S. - Version 2 forthcoming - will include Gunness De-Focusing Cameron Pro Audio. "Procrastinators of the world - contemplate uniting!" Art Welter Hero Member Offline Posts: 4874 Re: The Sucking Sound of Tarps over Speakers Moby (Mike Diack) wrote on Tue, 18 January 2011 00:04 Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M Did some more testing after Gian P. Portanova asked me in a PM : “Would the affect be minimized if you add some thin cloth over the speaker first, then the bag?” I replied that a thin organic cloth like cotton would attenuate (absorb) more highs, but the comb filtering would remain. The comb filter effect is primarily from cancellation due to reflection (seen in the even spacing of nulls), but the (plastic) bag also seems to vibrate in "breakup mode" (or kazoo modes), adding an additional random effect. Below are the results of some more tests, done using FPPO (fixed point per octave, 24 points per) which gives a less accurate, but easier to read picture than the 1.5 Hz frequency resolution shown previously. For overall HF attenuation of about 3 dB, a cotton T shirt does the trick. A bath towel lowers the level another 3 dB or so, though with larger peaks. Good for those who have noise induced hearing loss, still lets 4K through   . A high thread count bed sheet (tough to breath through) is obviously reflective, with deep nulls at regular frequency intervals. It does not seem to have the extra random kazoo effect of the plastic membranes. The lower curves show the response of the cotton T shirt with thin and thick plastic sheet over. Putting the cotton on the inside of the plastic slightly lowered the frequency of the nulls due to longer path length. Response still sucked, and lost more HF. Time to do some real work.. Art Welter Tim Brackett Sr. Member Offline Posts: 281 Re: The Sucking Sound of Tarps over Speakers I would be interested in seeing results from high density plastic such as those very thin trash can liners.  In my experience they seem to do less damage than heavier plastic like your typical trash bag.   Art Welter Hero Member Offline Posts: 4874 Re: The Sucking Sound of Tarps over Speakers Tim Brackett wrote on Wed, 19 January 2011 12:14 I would be interested in seeing results from high density plastic such as those very thin trash can liners.  In my experience they seem to do less damage than heavier plastic like your typical trash bag.   At 1.1 mil, the thinner stuff I used is pretty thin, I think anything thinner would not be durable enough to use in bad weather. It was only slightly less bad than the thick stuff   . How thin are the liners you are talking about ? Dave Rickard Hero Member Offline Posts: 2903 Re: The Sucking Sound of Tarps over Speakers Moby (Mike Diack) wrote on Tue, 18 January 2011 00:04 Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Dave Yorkville dealer "The wrong piece of gear, at the right price, is still the wrong piece of gear." "If you don't have good stuff at each end of the signal chain, (mics and speakers) what you use in between is just turd polish."--Dave Dermont frank kayser Sr. Member Offline Posts: 378 Re: The Sucking Sound of Tarps over Speakers I read about those the other day - I did like the idea - it would be interesting to see the effect. Bennett Prescott Hero Member Offline Posts: 8924 Re: The Sucking Sound of Tarps over Speakers Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? -- Bennett Prescott Director of North American Sales ADRaudio d.o.o. Cell: (518) 488-7190 "Give me 6dB and I shall move the world." -Archimedes Art Welter Hero Member Offline Posts: 4874 Re: The Sucking Sound of Tarps over Speakers Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules? The website says very little. Dave Rickard Hero Member Offline Posts: 2903 Re: The Sucking Sound of Tarps over Speakers Art Welter wrote on Sun, 30 January 2011 12:13 Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules? I think the fabric is woven from Elvish thread...   Dave Yorkville dealer "The wrong piece of gear, at the right price, is still the wrong piece of gear." "If you don't have good stuff at each end of the signal chain, (mics and speakers) what you use in between is just turd polish."--Dave Dermont Scott Raymond Hero Member Offline Posts: 1628 Re: The Sucking Sound of Tarps over Speakers Dave Rickard wrote on Sun, 30 January 2011 16:43 Art Welter wrote on Sun, 30 January 2011 12:13 Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules? I think the fabric is woven from Elvish thread...   The first thing I thought of was Gore-Tex that lets water vapor out and keeps the rain off, but I can't see Gore-Tex being very acoustically transparent.   Scott Chris Hindle Hero Member Offline Posts: 1080 Re: The Sucking Sound of Tarps over Speakers Dave Rickard wrote on Sun, 30 January 2011 17:43 Art Welter wrote on Sun, 30 January 2011 12:13 Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules? I think the fabric is woven from Elvish thread...   I'm thinking more along the lines of a very specific material, in a very specific weave using the waters' surface tension to do the blocking. "Ya, whatever. Just stick a '57 on it, and get off the stage" Chris. Too Tall (Curtis H. List) Hero Member Offline Posts: 1591 Re: The Sucking Sound of Tarps over Speakers Tom Reid wrote on Tue, 18 January 2011 12:21 Moby (Mike Diack) wrote on Tue, 18 January 2011 01:04 Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M Cheesecloth? Or a wall of fire. This is why you do not use front loaded cones outdoors. I also have done my fair share of rain dates, but we never put tarps over the front of the PA. Only the top and back where the power amps racks live. The High frequency horn were fairly deep and the 15" cones were build back into the cabinets to physically time align the speaker. Add using expanded metal and foam on the inside water from a hose never touched the 15" cone drivers. The subs were also horn loaded. This is a problem for any company that has only front load drivers. Rationalize as you will, if you put a tarp over the PA the system should be off. The output with tarp is unacceptable. Forgive me for being out of touch, I just remembered that many line array boxes have front loaded low-mid and they are everywhere. OUCH!!! how many drivers are lost to rain? Too Tall         Curtis H. List                  Bridgeport, Mich.            I.A.T.S.E. Local # 274 (Gold Card)         Lansing, Mich Independent Live Sound Engineer (and I'm Tall Too!) Art Welter Hero Member Offline Posts: 4874 Re: The Sucking Sound of Tarps over Speakers Too Tall (Curtis H. List) wrote on Wed, 09 February 2011 09:29 Tom Reid wrote on Tue, 18 January 2011 12:21 Moby (Mike Diack) wrote on Tue, 18 January 2011 01:04 Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M Cheesecloth? Or a wall of fire. how many drivers are lost to rain? Not that many, and if they have been treated with water resistant material, less. Even without treatment, they last a long time.Untreated monitor cones are a problem, water (or whatever liquid) pools and softens the cone. I know the front loaded Willie Nelson rig leased from Showco in the mid 1980's was not covered overnight, it continued to sound like a mid 1880's Showco rig for years . Didn't smell so good when the sun started drying out the rat fur.. Art Welter ProSoundWeb Community Re: The Sucking Sound of Tarps over Speakers Print Pages: 1 2 3 [All]   Go Up « previous next » ProSoundWeb Community > Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > SR Forum Archives > LAB: The Classic Live Audio Board FUD Forum Archive > The Sucking Sound of Tarps over Speakers

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[Art Welter]

Moby (Mike Diack) wrote on Tue, 18 January 2011 00:04

Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M

Did some more testing after Gian P. Portanova asked me in a PM :
“Would the affect be minimized if you add some thin cloth over the speaker first, then the bag?”

I replied that a thin organic cloth like cotton would attenuate (absorb) more highs, but the comb filtering would remain.

The comb filter effect is primarily from cancellation due to reflection (seen in the even spacing of nulls), but the (plastic) bag also seems to vibrate in "breakup mode" (or kazoo modes), adding an additional random effect.

Below are the results of some more tests, done using FPPO (fixed point per octave, 24 points per) which gives a less accurate, but easier to read picture than the 1.5 Hz frequency resolution shown previously.


For overall HF attenuation of about 3 dB, a cotton T shirt does the trick.
A bath towel lowers the level another 3 dB or so, though with larger peaks. Good for those who have noise induced hearing loss, still lets 4K through   .

A high thread count bed sheet (tough to breath through) is obviously reflective, with deep nulls at regular frequency intervals.
It does not seem to have the extra random kazoo effect of the plastic membranes.

The lower curves show the response of the cotton T shirt with thin and thick plastic sheet over.

Putting the cotton on the inside of the plastic slightly lowered the frequency of the nulls due to longer path length.

Response still sucked, and lost more HF.

Time to do some real work..

Art Welter

[Tim Brackett]

I would be interested in seeing results from high density plastic such as those very thin trash can liners.  In my experience they seem to do less damage than heavier plastic like your typical trash bag.  

[Art Welter]

Tim Brackett wrote on Wed, 19 January 2011 12:14

I would be interested in seeing results from high density plastic such as those very thin trash can liners.  In my experience they seem to do less damage than heavier plastic like your typical trash bag.

At 1.1 mil, the thinner stuff I used is pretty thin, I think anything thinner would not be durable enough to use in bad weather.
It was only slightly less bad than the thick stuff   .

How thin are the liners you are talking about ?

[Dave Rickard]

Moby (Mike Diack) wrote on Tue, 18 January 2011 00:04

Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M

Anyone heard these?

http://www.undercovernyc.com/protection_ranges#fs_w

[frank kayser]

I read about those the other day - I did like the idea - it would be interesting to see the effect.

[Bennett Prescott]

Dave Rickard wrote on Sat, 29 January 2011 00:09

Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w

Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB?

[Art Welter]

Bennett Prescott wrote on Sat, 29 January 2011 14:27

Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB?

Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules?

The website says very little.

[Dave Rickard]

Art Welter wrote on Sun, 30 January 2011 12:13

Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules?

I think the fabric is woven from Elvish thread...  

[Scott Raymond]

Dave Rickard wrote on Sun, 30 January 2011 16:43

Art Welter wrote on Sun, 30 January 2011 12:13 Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules? I think the fabric is woven from Elvish thread...

The first thing I thought of was Gore-Tex that lets water vapor out and keeps the rain off, but I can't see Gore-Tex being very acoustically transparent.  

Scott

[Chris Hindle]

Dave Rickard wrote on Sun, 30 January 2011 17:43

Art Welter wrote on Sun, 30 January 2011 12:13 Bennett Prescott wrote on Sat, 29 January 2011 14:27 Dave Rickard wrote on Sat, 29 January 2011 00:09 Anyone heard these? http://www.undercovernyc.com/protection_ranges#fs_w Heh, I've heard them, and in fact that rig in that configuration where that picture was taken. They work very well. If there is a HF reduction I was unable to measure it reliably, so maybe 1dB? Pretty cool trick, wonder how they manage to let sound waves pass unobstructed but stop water molecules? I think the fabric is woven from Elvish thread...

I'm thinking more along the lines of a very specific material, in a very specific weave using the waters' surface tension to do the blocking.

[Too Tall (Curtis H. List)]

Tom Reid wrote on Tue, 18 January 2011 12:21

Moby (Mike Diack) wrote on Tue, 18 January 2011 01:04 Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M Cheesecloth? Or a wall of fire.

This is why you do not use front loaded cones outdoors.
I also have done my fair share of rain dates, but we never put tarps over the front of the PA.
Only the top and back where the power amps racks live.

The High frequency horn were fairly deep and the 15" cones were build back into the cabinets to physically time align the speaker.
Add using expanded metal and foam on the inside water from a hose never touched the 15" cone drivers.
The subs were also horn loaded.

This is a problem for any company that has only front load drivers. Rationalize as you will, if you put a tarp over the PA the system should be off. The output with tarp is unacceptable.

Forgive me for being out of touch, I just remembered that many line array boxes have front loaded low-mid and they are everywhere.

OUCH!!!

how many drivers are lost to rain?

[Art Welter]

Too Tall (Curtis H. List) wrote on Wed, 09 February 2011 09:29

Tom Reid wrote on Tue, 18 January 2011 12:21 Moby (Mike Diack) wrote on Tue, 18 January 2011 01:04 Interesting...apart from the response issue, If you use a tight garbage bag you end up with the worlds biggest kazoo. There must be something that lets noise through but not wetness. M Cheesecloth? Or a wall of fire. how many drivers are lost to rain?

Not that many, and if they have been treated with water resistant material, less.

Even without treatment, they last a long time.Untreated monitor cones are a problem, water (or whatever liquid) pools and softens the cone.

I know the front loaded Willie Nelson rig leased from Showco in the mid 1980's was not covered overnight, it continued to sound like a mid 1880's Showco rig for years .

Didn't smell so good when the sun started drying out the rat fur..

Art Welter

[ProSoundWeb Community]