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Posts Tagged ‘Hydrophone recording’

IMG_2200

It was at Sunday 19th of September 2021 that I suddenly decided to go on sea to record with the hydrophone. The weather- and tide forecast promise me a few hours of decent circumstances.
But when I arrive at the harbor, people there like to chat about my kayak and equipment. So when I finally went on I was getting late. The wind had increased and the tide was getting too low for the place where I was heading to, so after 4 km paddling I ended up beside a pier in Viðey island which is only 800m NA from Reykjavik Sundahöfn harbor.
I tied my boat to the pier and put the hydrophone about three meters below the boat. It surprised me how quiet this place was. Almost no sign of life, mussels or shrimps, probably because just 700 meter away is a dock for cruise ships which have most likely destroyed the ocean floor in this area with their powerful propellers.
Nevertheless the silence is as interesting in the ocean as the silence on open land, so it is worth listening to.
While I was recording, the ferry to Viðey came and went. So be careful, you need to lower the volume between 11 to 14 min because the propeller noise will be very loud .
You can get an idea how Bethowave 7121 hydrophones perform in this recording. It comes straight from the recorder. No noise reduction, just fade in and out and downgrade from 24/48 wav to 256 kbps mp3

(mp3 256 kbps / 58Mb)

Recorder: Sound devices MixPre6
Mics: Benthowave BII-7121
Pix: LG G6

Location: 64.161135, -21.855538
Weather: Gust 5-8m, cloudy, about 7°C

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IMG_2200

I have used hydrophones for several years, mainly Aquarian H2a XLR and JFR piezo’s. But I have never been happy with the sound quality.
Comparison is hard to find on the internet and most hydrophone recordings there have been fixed in a post process so it doesn’t give me clear  information how it actually sounds. Most hydrophone manufacturers don’t give a standard or important information so buying a quality hydrophone for thousands of dollars can be a risky task. 
Last summer (2020) I spent several hours recording on Jökulsárlón Glacier lagoon. I noticed behind the sound of H2a was something very interesting soundscape which H2a couldn’t clearly capture.
So I decided  to get a better hydrophone before I continue to record in this lagoon.
I contacted both B&K and Teledyne Reson to check the price and options. Both his manufacturers gave me useful information but the price was higher than I was ready to pay for a good car so I continued the search. Ambient has two interesting hydrophones but they do not show important information. When I ask for Frequency and S/N graphs, Ambient just sends me the user manual which is already on their website. Same with Cetacean Research and Dolphin Ears, which either give me strange answers or no answer  So I continue to search through several manufactures.
Suddenly and surprisingly I found Benthowave, a company which was ready to custom made hydrophones for me, hydrophones where I got all necessary information for my needs. It was almost too good to be true, so it takes me several weeks to decide to let Benthowave build my dream hydrophone.
The base was built on BII-7122 but additional with balanced output w. BII-1082 ultra low noise amp and 15meter long cable.
No problem, I would get it after 6 to 8 weeks! But that was too late for me. My recording project actually started that time in late May. Before that project starts it is necessary to build a customized floating platform and power supply for the new hydrophone which can take two to three weeks. 
So I ask Benthowave which low noise hydrophone they have in stock. It was only a single output BII-7121 with internal BII-1081 amp.
Two weeks later they were in my hands.
 My first impression was a huge disappointment. I was almost sure I had thrown money out of the window. But after I build my second power supply, these hydrophones start to rock. It was two key figures that were important to know to let them work without problem.

1. While this hydrophone is so sensitive at low frequency, higher voltage means better performance to avoid internal amplifier overload/dropout.
2. These hydrophones are sensitive for EMF. From the power supply box (made out of metal) must be a wired ground connection to the water which will be recorded if any EMF pollution is around

Other things must be kept in mind because these hydrophones use an external battery power supply, but NOT Phantom power. Use a recorder which has „Combo input“, (XLR and jack input) or 3,5mm jack input. Use only Jack to connect the hydrophone to the recorder so you will never mistakenly get Phantom Power into the hydrophone. It might be possible to use Triton Big Amp for recorders that don’t have Combo input. But I haven’t tested it yet. I will write an update when it has been tested. I use non-standard XLR connectors in and out of the battery box so even blind men can not connect the hydrophones without correct cables.

Conclusion of the comparison
I am not sure if this comparison gives a correct picture of the Aquarian H2a. Mine have a LOM phantom power adapter which has a small amount of gain and probably makes tiny changes in the frequency curve.
Anyway, with this adapter it sounds similar to the original. I put this adapter to avoid extra noise which I got only in the SD744 recorder and with HPF off. This adapter also avoids other strange and unusual noises which I think is caused by the 48Volt phantom power which I think is too high. But with the adapter the H2a  is driven by 5Volt.
This comparison was done in Sundahöfn port of Reykjavik. In a corner which is mainly used for depreciated ships so it was quiet, without loud ship engine noise.
The hydrophones were placed side by side in 1,5m depth with 2,5m separation, from a floating pier with two bonded boats. The gain on the MixPre6 was at 30dB for both hydrophones and HPF was off 
There is pretty much difference between these two hydrophones, both in frequency range and sensitivity. Benthowave BII-7121 frequency range is from 0,5 hz to 60 Khz at +/-3dB V/μPa. On spectrograms I can see it can as well detect sound up to 80Khz  or as high as I can record at 192Khz.
The hydrophone sensitivity is -158,7 +/- 0,2dB plus +26dB BII-1081 amplifier gain (-185dB) and self noise is 25dB μPa/1KHz.
Aquarian H2a frequency range is 20Hz-4.5KHz +/- 4dB and the self noise is  „low noise“ whatever it means. Sensitivity is -180dB re: 1V/µPa. My Aquarian hydrophones are not new, so new model might have increased sensitivity. Compared to BII-7121 it seems be close to -165dB. With the LOM Phantom power adapter the sensitivity is closer to -170dB re: 1V/µPa  and the frequency range seems to be on spectrogram close to 100-7Khz.
It was not easy to normalize the level of these hydrophones while they have so different frequency ranges. To do that I tried to normalize the level by listening to constant pump noise in the background in the recordings and make it as equal as possible in combination with the level meters. 
At the moment I can’t say much about the self noise. It could be difficult to compare these two hydrophones while they are so different in frequency ranges. I somehow expected to hear lower self noise in BII-7121. But it might be as good as it gets.  It is -24dB below sea state zero at 1Khz,  which is very good, even for much more expensive hydrophones. But to know exactly what it means for me I need to test them in quiet lakes.  I will put an update here as soon as I have done that.
I must say, the BII-7121 has very nice sound quality, Just as I expected. It is almost possible to hear the depth of the field, while H2a sounds flat and all high frequency is missing. But keeping in mind these two hydrophones have very different prices so in fact it is unfair to compare these two hydrophones.  One piece of BII-7121 cost about USD 1,244.- (base price), while H2a XLR cost USD 194.  I should rather compare Benthowave to Teledyne Reason like TC-4032 which cost EUR 3,640.- or Bruel & Kær like 8106 which cost DKK 86,470.- I think they will all sound similar.
Benthowave seems to be built on rather cheap plastic materials and glue, it looks very fragile and seems to be not as robust as Teledyne or B&K. But as long as Benthowave can offer me the same or similar sound quality at a lower price I am happy with that.
BII-7121 could have been heavier.  It weighs only 95gr while H2a weighs 125gr which is even too light. The BII-7121 cable is Gepco MP1201 Quad Star.      
In the recordings below you can hear in some headphones an unpleasant „low frequency noise“ due to the wind. This is because there was a lot of wind on the day when this was recorded. The cables to the hydrophones were mostly up on the pier where the wind got an awkward amount of play around them.  
This „wind sound“ will usually disappear once I have built the „floating platform“ for the hydrophone.
I will post pictures when its done, plus other experiments too.

__________________________________________________________________________________

Recording straight from the recorder, only add +12dB in post
Benthowave BII-7121

Recording straight from the recorder, only add +12dB in post
Aquarian H2a 

Normalized recording BII-7121  

Normalized Recording H2a 

Recording with BII-7121 of a Tugboat propeller 250-300 meter away. This recording is straight from the recorder, no extra gain.
Notice at 3:55 the amplify goes up and down. I am not sure what it is. I think it could be a strange behavior of the hydrophone when they are in „strong“ current or water flow, in this case from the tug propeller, which was though not very strong. It could be as well the ground cable which lost contact to sea while waves pass the pier.
H2a normally makes a low frequency noise in water flow or current. But I am sure this current was not strong enough for H2a to make a noise.  
I will write an update as soon as I figure out why BII-7121 acts like this.
All updates will be added here below by date. 

More information about hydrophones & underwater sound:
Construction and testing of low-noise hydrophones (pdf)
Sound in the sea
Hydrophone Review: Ambient ASF-1, ASF-2, Aquarian Audio, JrF by Sach Poff

Quality open headphones are recommended while listening at mid level.
If the media player doesn’t start to play, please reload this individual blog in new tab or frame

Update 9th of May 2021 ——-

Hydrophones with frequency range down to 1Hz are very sensitive for all movement in water or water flow, which seems to cause an overload for the internal amplifier so the audio output turns on and off while it happens.
At the moment I would recommended for everyone who like to order Benthowave hydrophone to ask for custom HPF at 10Hz or 20Hz, otherwise the hydrophone will be only usable during calm days 
If default HPF is in the hydrophone then is it necessary to make some kind of „flow noise reduction“ for the hydrophone, similar protection cages which CRT make for its own hydrophones. 
Rycote BBG 25mm fits perfectly for this BII-7121. But that is not the final solution. Original BBG did not work well so it needs some changes which I am working on.
I will post an update later when I think I have found the final solution.

Update 30th of August 2021 ——-

The BIG-7121 tested with a 25 volt power supply (with six 18650 Li-Ion cells).
It does not completely fix the overload / dropout in the amplifier.
Compared to 16 volt and recording from SOT Kayak the hydrophone can now withstand much higher waves (up&down) and tide current (@8m depth)

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Vatnajökull is the largest ice cap in Europe by volume (3,100 km³). Vatnajökull has around 30 outlet glaciers (icefall) flowing from the ice cap. Svíafellsjökull is one of them.
Glaciers are not a playground for everyone. They have its own weather system and the gravity force will destroy everything that get lost in the ice.
Two British students lost their lives 1953 in a storm which lasted for 10 days on the glacier. It was not until 2003 that some of their equipment was found, carried forward with the movement of the outlet glacier. No human remains were found.
Two German tourist have been missing since 1st of August 2007 when they were on a hiking trip on Svínafellsjökull. Nobody knows what really happened but it is most likely that they fell in a swallow somewhere on the glacier, but their equipment was found in a small valley, high in the nearby mountains.
All glaciers have been shrinking fast last decade. That can be easily seen at the end of Svínafellsjökull witch now has a big glacier lagoon that did not exist few years ago.
As glaciers the glacier lagoons can be also dangerous. Icebergs can suddenly fall off the icefall and make huge waves in the lagoon, also when icebergs turns around or brake down in a parts.
I got in touch of these forces when I was recording the lagoon under Svínafellsjökull, 23rd of May 2014. I hid the equipment from other tourist in a landslide nearby and about two meters above the lagoon surface. Two Aquarian hydrophones where placed in the lagoon and a pair of MKH20 was used to pick up the sounds above the lagoon. The idea was to record in two or three hours.
I was in another place with my second recorder to record a sound close by the glacier.
After one and half hour I suddenly hear a big „bang“ with a long powerful echo from nearby mountains. All the icebergs on the lagoon suddenly moved around as a beans in a boiling pot.
I ran to the recorder´s place on the other side of the lagoon. The bag with the recorder was floating between the Icebergs so it was no problem to locate it in the muddy water. I disconnect the battery and took it inside to dry it as fast as I could. But nevertheless, it had several malfunctions since this drowning.
I am not sure what really happened. The flood line does´t goes all the away to the recorder´s place. I think it is most likely that some icebergs pulled the recorder by the hydrophones into the lagoon.
Thanks to Sound Devices in US and the reseller in Iceland (Pfaff-Borgarljós and Bragi Kort) I got a new recorder for a very nice price. Most of the loss was then covered by the insurances.
Update: In late summer 2020, I took the recorder apart, piece by piece, and cleaned it. It is now in top condition.

Flóðbylgjan við Svínafellsjökul

Jöklar og umhverfi þeirra getur verið hættulegt þeim sem það ekki þekkjir. Jöklarnir eru síbreytilegir og hafa sitt eigið veðrakerfi. Því ber að umgangast þá með varúð. Skemmst er að minnast hvarf tveggja þjóðverja á Svínafellsjökli þann 1. ágúst 2007 .
Mér var það svo sem lika ljóst að jökullón geta verið hættuleg þann 23. maí 2014 þegar ég staðsetti upptökutæki við jökullónið neðan við Svínafellsjökul. Tveir Aquarian vatnahljóðnemar voru staðsettir ofan í lóninu og aðrir tveir MKH20 hljóðnemar ofan við lónið. Sjálfur fór ég með annað upptökutæki til að hljóðrita upp við jökulinn sjálfan.
En líklega er aldrei of varlega farið. Eftir u.þ.b. eina og hálfa klukkustund kvað við mikill hvellur frá jökulsporðinum sem bargmálaði í fjöllunum ofan við jökulinn. Stuttu síðar fór allt jökullónið á hreyfingu eins og iðandi suðupottur. Mér varð því ljóst að upptökutækið við lónið gæti verið í hættu. Hljóp ég því sem fætur toguðu að staðnum, en allt kom fyrir ekki. Tækið var komið út í lónið og flaut þar í tösku milli ísjaka. Eftir að hafa þrifið það og þurrkað kom í ljós að tækið hafði bilað varanlega eftir þessa sundferð.
Allt bendir til þess að ísjaki hafi dregið tækið í lónið á vatnahljóðnemunum því flóðlínan hafði ekki náð upp að staðnum þar sem tækið hafði staðið. En skaðinn var skeður sem leytist þó á endanum þokkalega farsællega þó tjónið hafi verið eitthvert. Með óútskýranlegum hætti vistaði upptökutækið upptökuna áður en það drukknaði. Það sem hér má heyra eru síðustu andartök tækisins.
Síðla sumars 2020 tók ég upptökutækið í sundur, stykki fyrir stykki og hreynsaði það. Það er nú í topp standi.

Recorder: Sound devices 788
Mics: Aquarian H2n-XLR & Sennheiser MKH20 (AB40)
Pics: Canon EOS-M (See more pictures)
Recording location: 64.007509, -16.883081
Weather: Calm, cloudy, around 9°C

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I got a grant to record nature sounds in the Vatnajökull national park from the association “Friends of Vatnajökull”. It was not a trouble free trip, but anyway it was very instructive and I recorded many hours of very interesting and lovely sounds. Most of the recordings are long and unbroken. Some of them are up to 6 to 10 hours long so they contains many things I have never heard until now when I am registering the collection and searching for material to publish.
In 22nd of May I spent most of the day near Jökulsárlón glacier lagoon. I recorded around three hours in the lagoon with hydrophones. I was located close to the ejection because there it was most likely to catch some wild life activity.
When I started following recording the current was flowing out of the lagoon. Three or five seals were diving nearby between the icebergs which slowly were moving towards the ejection.
It was stunning when I put the hydrophones in the lagoon.
What a sound! It was much louder than I thought and was both stunning and frighten.
The several thousand years old ice was melting with cracks, screeches and scratching the bottom of the lake. Sometimes I could detect a deep rumble sound in a distance, probably when icebergs were scratching the bottom of the 200 meters deep lake. Comparing to all those loud sounds, everything was peaceful above the surface.

Hljóðin í Jökulsárlóni. 1. hluti

Ég fékk styrk s.l. vetur til að hljóðrita hljóðvist Vatnajökulsþjóðgarðs frá samtökunum  Vinum Vatnajökuls. Það gekk á ýmsu á meðan á því stóð en á endanum var ég komin með mikið af áhugaverðu og skemmtilegu efni. Mikið af þessum upptökum eru langar og ósltitnar eða 6-10 klst langar svo ég hef ekkert hlustað á fyrr en nú þegar ég stend í því að skrásetja upptökurnar.
Þann 22. maí var ég staddur við útfallið við Jökulsárlón og hljóðritaði undir yfirborði lónsins með vatnahljóðnemum. Bæði hljóð og hljóðstyrkur kom verulega á óvart. Þarna var aldagamall ísinn að bráðna með hvellum og ískri um leið og hann skrapaði botninn á leið sinni að útfallinu. Öðru hverju mátti heyra drunur einhvers staðar utan úr djúpi lónsins og stöku sinnum mátti heyra hljóð sem hugsanlega komu frá 3-5 selum sem syntu ekki langt frá upptökustaðnum.
Það var óneitanlega mun háværara niðri lóninu en á yfirborði þess.

Download MP3 file (192kbps / 34,4Mb)

Recorder: Sound devices 788
Mics: Aquarian H2a XLR
Pics: Canon Eos M (see more pictures)

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