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GarySound

Underwater Mics

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How many times in your career have you had a last minute request from production to record underwater sound effects for an underwater shot perspective. Well, it’s happened to me twice in the past three years. Since I don’t carry a hydrophone in my kit (probably should) I’ve had to rig something each time very last minute. My first attempt was an old SM58 wrapped in a trash bag hardwired back to the mixer. It sounded ok but the bag eventually leaked and soaked the mic pretty good. It never quite sounded the same. The second time around was more successful. With a little more time to prepare.. I decided to try and vacuum seal a Sanken COS11 and a SMV transmitter (yes I’m crazy) in a “Food Saver” vacuum bag. I used the 11” wide tube variety at about 4’ Long. I also added a box of 24 AA batteries at bottom end for ballast. It worked like I knew it would and gave us that old school “Twenty Thousand Leagues Under The Sea” sound effect. Needless to say.. production was thrilled.

 

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11 hours ago, GarySound said:

 

How many times in your career have you had a last minute request from production to record underwater sound effects for an underwater shot perspective. Well, it’s happened to me twice in the past three years. Since I don’t carry a hydrophone in my kit (probably should) I’ve had to rig something each time very last minute. My first attempt was an old SM58 wrapped in a trash bag hardwired back to the mixer. It sounded ok but the bag eventually leaked and soaked the mic pretty good. It never quite sounded the same. The second time around was more successful. With a little more time to prepare.. I decided to try and vacuum seal a Sanken COS11 and a SMV transmitter (yes I’m crazy) in a “Food Saver” vacuum bag. I used the 11” wide tube variety at about 4’ Long. I also added a box of 24 AA batteries at bottom end for ballast. It worked like I knew it would and gave us that old school “Twenty Thousand Leagues Under The Sea” sound effect. Needless to say.. production was thrilled.

 

b4e03e1071252dd3f665f89aafec4e0f.jpg

 

6cc24b9312171d4bad45cd75216e574a.jpg

 

d7b0f46bfbf2c19a754237628604daae.jpg

 

 

 

Sent from my iPhone using Tapatalk

 

Was the TX floating? Wondering about signal strength. 

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Tx must have been at least on surface or very near. My experience has been with actors wearing Mm400s, as they go in, you hear a few “ glug glugs” from the mic, then total radio silence.

 

Jim Rillie

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Gary, darn cute solution. Antenna and/or transmitter body would have to be above water line to get any RF radiation. The antenna out of the water would be best. The microphone could be six feet down "listening" to the sounds in the water. That's what the pictures show, antenna out of the water along with some of the transmitter case. Again, darn cute solution.

The vacuum bags have to be pretty well made to hold a long term vacuum seal and if there is a leak, you can tell before putting the rig in the water. If the bag leaks air and loses the vacuum, it isn't water tight either.

Best Regards,

Larry Fisher

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14 hours ago, GarySound said:

vacuum seal a Sanken COS11

I don't know anything about this mic as I'm a software developer / editor, but out of curiosity:

How can a mic receive audio in a vacuum? (I know in space it's not a problem in the movies, but this is earth...)

Or is there enough air left to carry the sound or does this work on another principle?

 

Bouke

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20 minutes ago, Bouke said:

I don't know anything about this mic as I'm a software developer / editor, but out of curiosity:

How can a mic receive audio in a vacuum? (I know in space it's not a problem in the movies, but this is earth...)

Or is there enough air left to carry the sound or does this work on another principle?

 

Bouke

There will be some air left in the bag and even more importantly, there will be mechanical coupling between the bag and the mic. There won't be so much air that it causes to bag to float up out of the water, the major reason for using a vacuum bag. At least this is my best guess. I would also guess that the frequency response would be all over the map but what would a listener use for comparison? Aquaman has better things to do than write articles for Stereophile.

Best Regards,

Larry Fisher

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Mechanical only would work if the membrame is very heavy, and that would make the mic useless in air :-)

Frequency I don't know, but I would think that the speed of sound in thin air is the same as in normal pressure.

(The sonic boom happens at the same speed no matter the altitude of the plane.)

 

Bouke

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Well, whatever the case... on would, should, and could....    it seems Mr. Gossett said it worked just fine... My hat is off to him for a nicely solved solution to a last minute request by production..  Good job Gary!!!

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Actually, the end product did had some residual air left in the bag which allowed the mic to work better than the effects of trying to record in a vacuum. The mic gag was about 3.5’ long and 11” wide. I hung the sealed bag in the water, ballast down, with the transmitter and antenna just above the waterline. I also reduced the power of the SMV to 50mw so I could get the longest battery life possible.

If a mixer finds himself/herself in this situation.. renting a true hydrophone would be my recommendation. My 2nd choice would be to put a PZM microphone in the bag instead of a lav mic. The PZM creates it’s own mechanical coupling so, my guess is that it would be less affected by the physics of it all. In my situation, production laid this on me at the last minute. I didn’t have a PZM in my kit and tracking down a hydrophone rental was overruled by time constraints. On the day.. I had an Olympic Champion in the water with a camera above the surface and a submersible camera below so, I had to improvise and improvise I did.


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I own two of these and used them on Cousteau expeditions
 
http://www.aquarianaudio.com/h2a-xlr-hydrophone.html
 
mike



Thanks Mike. If you want to sell one... I’m your buyer. lol


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Was the TX floating? Wondering about signal strength. 



The tx MUST be kept above the water line to work.


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Although I own and use a Bruel & Kjaer hydrophone I have had great results for many applications from simply submerging the Countryman B6 mic - which is tiny enough to simply trap a protective air bubble over the diaphragm. Unfortunately my B6 died on a shoot last year but I'm certain to replace it at some point since it's such a useful and compact 'hydrophone' to always have in my FX bag.

 

Jez

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I can remember being at NAB and seeing a B6 in a glass of Coke if I remember...  a few years ago...  maybe water, but one or the other...    Just the mic portion with the plug outside the glass.. 

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I recently bought a couple of hydrophones off ebay from a seller who acquired a large batch of ones that had been taken off US navy submarines. 

They seem to need impedance matching, which I'm working on a solution for at the moment. So I think they are high impedance piezo heads. I think the barrel adaptor impedance matching solution is going to cost as much as the mics did, but if it all works out I will be very happy.

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A few added comments:

Have used ex US Navy hydros but when they were sent back for checking was told they were classified so goodbye!!!

 

My first use of a MM400 was on a swimming instructor teaching a disabled child in a pool.

I clipped the transmitter on the top rear hem of her swimming costume so aerial was behind her neck.

Captured her dialogue and also the child blowing bubbles under water!!

 

I use B3's with my four MM400's as they are more robust than the B6's

 

mike

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I used the Aquarian Audio Hydrophones this fall on a shoot and found they sounded pretty good for the price.  The main issue I had with them is that their high frequencies are drastically rolled off, so that although the humpback whales sounded OK, the sound of water lapping on the boat was really midrangy and boxy sounding.  Unfortunately, we all know what water is supposed to sound like, so I wasn't completely happy with the results.

 

The nice thing about having the high end rolled off though... is that the Aquarian audio mics noise floor is pretty good, and, as well,they have good sensitivity for quieter sounds. 

 

 I also used the Ambient ASF2 hydrophone.  This is the more budget of the two that Ambient sells, and costs about twice what the aquarian audio mic sells for.   It has a really distinct hiss, which kind of ruins it's flatter frequency response.   It's also quite quite an insensitive mic and really needed a lot of gain, which didn't really help its noise floor either...  

 

I also had the opportunity to work with some really expensive ($10,000)  hydrophones, which sounded great, but are really just ridiculously priced for casual or occasional use.  So I'm still looking for a decently sensitive, low noise floor, flat response hydrophone that doesn't break the bank...  I like all these stories of using countryman lavs, and they work in a pinch, but they aren't so great for a job where you want to be slinging your mics into 40 feet of salt water at a moments notice, several times a day...

 

Cheers,

Brent Calkin

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1 hour ago, Freeheel said:

I also used the Ambient ASF2 hydrophone.  This is the more budget of the two that Ambient sells, and costs about twice what the aquarian audio mic sells for.   It has a really distinct hiss, which kind of ruins it's flatter frequency response.   It's also quite quite an insensitive mic and really needed a lot of gain, which didn't really help its noise floor either...  

 

 

Did you also try the more expensive Ambient version? Is that also in the 10k$ range? 

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3 hours ago, Freeheel said:

I used the Aquarian Audio Hydrophones this fall on a shoot and found they sounded pretty good for the price.  The main issue I had with them is that their high frequencies are drastically rolled off, so that although the humpback whales sounded OK, the sound of water lapping on the boat was really midrangy and boxy sounding.  Unfortunately, we all know what water is supposed to sound like, so I wasn't completely happy with the results.

 

 

What model Aquarian were you using? 

I know one of their models has a low impedance output which works well with our standard preamps. While most of their model have a high impedance output. Maybe you were hearing the effect of this impedance mismatch? They sell adaptor cables for those mics.

I was recently on a field trip where we had a couple of DPA Hydrophone and some Aquarian Audio Hydrophones. They sounded different but tonally pretty comparable. We ran the Aquarian Hydrophones through some type of impedance matching barrel adaptor. It was not my setup so Im not sure of the specifics.

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I did not have the opportunity to test the more expensive Ambient mic, (the ASF-1 MKII)  and would love to hear some real world opinions on it.  

 

The Aquarian I was using was the "plug and play" H2A-XLR.

I had it plugged straight into a Sound Devices 744T, so it should have been a pretty ideal signal chain.  Their manual notes that high frequency response is reduced by cable length, but I only had a 30ft cable on it, so I doubt if that was the issue.  The manual claims a frequency response of 20hz to 100khz, but my experience would indicate, even if that was true, that the response graph would be anything but flat, and I find it irritating that they would leave that detail out of the specifications.

 

Cheers,

Brent Calkin

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They used to have an EQ hint on their site, but I don’t know if it’s still there. They said back then that it would make the recording sound more like a stereotypical underwater recording, but I cannot remember what it was

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My Aquarian Hydrophones were the P48 version and did not seem to suffer any relevant HF loss

after all we are not recording concert orchestras under water!

The two I have give a a very compelling stereo result.

mike

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On 12/16/2017 at 1:09 PM, GarySound said:

My first attempt was an old SM58 wrapped in a trash bag hardwired back to the mixer. It sounded ok but the bag eventually leaked and soaked the mic pretty good. It never quite sounded the same.


If I ever need to do a last second recording underwater, I'd be giving my Aputure Diety (inside a bag, like you did) a go, as impressed with how it can survive a dunking (skip ahead to 5 minutes in, to see that part of the review. Not good once wet! But bounces back ok once dried out, and it is so cheap I won't be nervous about it):

 

 

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