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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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Snæfellsnes peninsula has long sand and gravel beaches, especially in the south.
These beaches can easily attract everyone who traveled there. So when I was there on the 1st of July 2021 I did a hike along the beach below the Langholt guesthouse (Garðafjara).
Surf is usually not interesting recording material and there are not many „surf recordings“ in my sound blog. But this beach had a special sound that night
I thought something was disturbing my hearing, but soon I noticed it was the gravel in the surf which made this sound. Instead to be almost constant pink noise, then the noise on this beach constantly changes with every wave. From brown noise to white noise.
As usual the recording gear is never far away so I record this interesting soundscape just before midnight. 

(mp3 256Kbps / 52Mb)

Recorder: Sound Devices MixPre6
Mics: Sennheiser MKH8020/8040 Parallel AB
Pix: Canon EOS R

Weather: Calm to 2m/sec, cloudy,  about 15°C
Location: 64.809722, -23.147333

 

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The eruption was in full action on the 17th of July 2021 and the weather forecast was fine, calm and dry when I decided to go and record at the eruption sites.
I decided to stay not near popular sightseeing places, so therefore I went by bike to get further away to another place at the lava field.
But when I arrived, there was a strong wind because both the eruption and the lava itself has its own weather system due to the heat in the area. Pollution was also high, so it was not easy to operate in the area.
Eventually I found a „good place“ where I had to block the microphones between rocks on the ground right by the glowing lava.
As soon as I pressed „Record“ the volcano stopped erupting and it did not erupt in the next few days, which is very typical for me.
It is quite descriptive of this eruption, although it is a small and beautiful „tourist eruption“, I have not been able to record the eruption itself these four times I have dragged equipment to the eruption sites. There have always been strong gusts and sometimes „small“ hurricanes around the volcano which have made sound recording very difficult. Plus, when it erupts it does not make much sound, especially when no water is involved in the eruption or the lava which would have made an explosion. But when the volcano is active the boiling lava sounds like boiling water in a huge pot.
Even though I could not record the eruption that day as was planned, I managed to record the lava itself without too much wind-, tourists chatting-, drones- and helicopter noise.
The lava did not seem to be moving while I was recording, but I could see embers in the cracks.
I have no clue what makes this „pop“ sound in the lava while I could not see it move. The sounds could be coming from the lava that was possibly rising when the liquid lava flowed under a thin shell crust. Or it just sounds like that when the lava cools down.
The gust rumbling sound in this recording sounds pretty similar as the eruption from the volcano so let’s play with with the imagination while listening.

  (mp3 256kbps / 56,3Mb)

Recorder: Sound devices MixPre6
Mics. Sennheiser MKH8020/8040 (Parallel AB40)
Pix:  Canon EOS R

Location:  63.886300, -22.230307
Weather:  Gusty, 15°C and 35°C at the microphone place, cloudy and high gas pollution.

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For several years I have recorded the soundscape at the same spot when I visit a cottage in west Iceland. Every time I record there I get something different and interesting, all year around.  Forestry has changed the birdlife a lot on this spot in the last 20 years.  Birds like Redwings, Common Redpoll, Eurasian Wren and Starlings are now in increased numbers since the beginning in this century.
I recorded this spot overnight both 6th and 7th of July 2021.
Lot of chicks had already left the nests so the grass field around the microphones was full of birds searching for insects which can be heard in this recording.
The following recording is not an example of the „best part“ which I record these two mornings. It is just a part of the first WAV file at the 6th which I choose because of low traffic. So more of these two days’ recordings will be audible in this blog in the future.
The time is between 2:30 am to 3:05. It is calm and quiet in the beginning until the Common Snipe begins to make a noise with its tail. Young Redwings, Common Redshanks and Snipes are all around the microphones. Other birds are not far away such as European Golden Plovers, Whimbrel, White Wagtail, Eurasian Wren, Rock Ptarmigan, and Whooper Swans in the distance.
This was recorded with four channel IRT setup, but sadly one of the cable was broken so I could only use three of the channels which was though easy to mix into INA-3
This was recorded at 48dB gain (HPF@80hz). In post the gain was increased about 30dB plus gentle RX noise reduction.
Quality headphones are recommended while listening at low or mid level or in speaker at low level.
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(mp3 / 256mbps 69,8Mb)

Recorder: Sound devices MixPre6
Mics: Lewitt LCT540  (IRT setup)
Pix: Canon EOS R

Location: 64.673368, -21.628709
Weather: Calm, cloudy, about 12°C
Other recordings from this location in Stafholtstungur:

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The spring of 2021 has either been windy and cold or windy and wet or both.
Even though birds are usually tough lifeforms, it has been clearly audible that they would like to have warmer days, so instead of filling the air with songs they have been quieter than other years.
Iceland is not rich with audible wildlife sounds. Everything sounds distant so if the air is unstable and wind is more than 2m/sec  then it starts to be difficult to record the wildlife   
From end of February until mid June it has been a very poor circumstances to record in an open field, mainly because of unpredictable and windy weather
In the second week of June I saw in the weather forecast a opportunity to get calm weather for a one day in Látrabjag cliffs so I packed my gear and set off.
On the way in Mjóifjörður I drove off the paved road and followed the old gravel main road to relax and make a coffee. I found a good spot. It was under a mountain slope, surrounded by low birch bush and wild flora. Beside me was a small brook and inside the bush was a shelter from the wind. The soundscape was full of life, so I put up the gear and started to record while taking a nap. 

  (mp3 256kbps / 59.7Mb)

Recorder: Sound devices MixPre6
Mics: Lewitt LCT540s (NOS)  
Pix: Canon EOS-R

Location: 65.614159, -22.823796
Weather: Cloudy, dry, 10-15m/sec, 7°C  

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Here is one of my „COVID recordings“ that I managed to record by Glacier lagoon, Jökulsárlón near the lagoon outfall.
This place is close to the ring road around Iceland so it is usually overcrowded by tourists and other traffic all year round, almost 24/7. I have only been able to dream of recording this place without traffic and human interruption.
But thanks to COVID, on the 10th of June 2020 I managed to record there without too much interruption.
The soundscape is different in this place, but the recording here below is typical for summer soundscape. When I first went to this place some decades ago the glacier was much closer, I guess about 2km away, but today it is about 8km away and much thinner. The sounds from the glacier have almost disappeared. But on the lagoon are large icebergs that melt down rapidly near the lagoon’s outfall. They can emit interesting sounds when they break in pieces.
Arctic terns have nested beside the outfall in many years, but probably because of traffic they seem to have moved the biggest colony closer to the glacier.  In the eighties and nineties when I passed this place every year by bike, Great Skua dominated this area with nests in many places.. But today this big bird is hardly seen near the outfall compared to how it was thirty years ago. Arctic Skua is a common bird there as it has been before.
This recording was made a few hundred meters east from the lagoon outfall.
Not far from the microphone are stranded icebergs which are constantly melting with all kinds of sound.
Most common birds in this recording are Arctic tern, Northern Fulmar, Black Headed Gull, and Razorbill. Other species are audible too.
Common Eiders come quietly close to the microphone and Seals have a fight or mating not far away,
The main background noise is a rumble from heavy surf along the Atlantic ocean coastline  several hundreds meters behind the microphones. Traffic from the ring road no1 is also audible.
Quality open headphones are recommended while listening at mid level.
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  (mp3 256kbps / 65.5Mb)

Recorder: Sound Devices MixPre6
Mics: Lewitt LCT540s (NOS)
Pix: Canon EOS-R

Weather: Cloudy, calm, around 8°C
Location: 64.052841, -16.178658

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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.

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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.
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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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Earthquakes have shaken southwestern Iceland for more than two weeks. They have been counted in many thousands since it began so folks like me are going to feel like all earthquakes below 4 in magnitude are a normal state
But not everyone feels the same way. All those who live close to the source of the earthquakes are going to be very tired of this situation, mainly inhabitants of Grindavík town and nearby places.
When I was working on this blog as an example, an earthquake hit my house which was 5.4 magnitude. It is similar in magnitude as those which first heard in the recording below.
The following earthquakes were recorded in my garage in Reykjavik which is 25-30Km from the earthquake’s source.
The first two earthquakes were recorded with parallel Nevaton MC59O & MC59C, on four channels in  AB40 setup. All other earthquakes were recorded using the Nevaton MC50Quad in MS setup. These Nevaton microphones are the only ones I have that can reach below 10Hz and can therefore also record the fluctuations in the aftershocks.
This recording contains sixteen earthquakes, collected from continuous one week long recording. They are mainly earthquakes which happen during the nighttime to avoid traffic noise. Most of them were above 3 magnitude…I guess.  

(mp3 256Kbps / 24,4Mb)

Quality open headphones are recommended while listening at mid level.
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Recorder: Sound devices 788
Mics: Nevaton MC59O & MC59C parallel in AB setup and MC50 Quad
Pix: Screenshot of the first two earthquakes in the recording

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In recent years I have spent several nights in Skeiðarársandur to record the changes in the ecosystem.
Skeiðarársandur is a huge broad sandy wasteland along Iceland’s south-eastern coast, between the Vatnajökull icecap and the sea. It is a wonderful place to record deep natural silence in a huge open flat landscape.
For hundreds of years Skeiðarársandur has been a barren desert. but recently with shrinking glaciers and smaller glacial rivers, Birch, moss and other flora have occupied the northeast part of the sand. That means the soundscape on Skeiðarársandur will change in the future which will be interesting to record regularly in the coming years.
I have usually stayed at the same spot near a traditional sheep pen because structures like that are attractive for birds like Snow bunting, Northern wheatear and Rock ptarmigan.
I was very excited when I went to this spot on the 9th of June 2020. Because of COVID, there were almost no tourists in Iceland and therefore far less traffic.  So I was hoping for a beautifully quiet night there. I was not disappointed either. It was calm so the silence was deep. I could hear the Atlantic ocean surf among the coastline 20-30km away, which sounds slightly like low frequency rumble in the background of this recording. I could not see any bird but bird songs came from every direction, clearly far away. During the night the glacier rumbled several times in Skaftafell national park like a thunder in the distance. Once a ship engine noise was audible out of the coastline which sounds pretty spooky. It sounds more coming from the sky rather than from the coastline in the horizon, which was probably a reflection from different temperature layers in the atmosphere.
Anyway the ship engine is not audible in the following recording, but maybe in another blog.
The microphone rig was on the top of the sheep pen wall, not far away from the place which I think Northern wheatear has had a nest every year since I started to record this place. (Listen to recording since mid May 2016)
Luckily the Northern wheatear was not far away. This time the bird was not as angry about the hairy microphones as when I first brought the microphones in this place. The bird just sang for me for almost one hour and here comes part of it.

  (mp3 256kbps / 67,7Mb)

Quality open headphones are recommended while listening at low to mid level, or in speakers at low level.
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Recorder: Sound devices MixPre6
Mics: Lewitt LCT540s (IRT Cross)
Pix: Canon EOS-R 

Weather:  Calm to 5m/sek, clear sky, 3 to 7°C
Location:  63.969925, -17.160018

 

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Shortly after I set up my gear in a safe spot near the lagoon beneath the Svínafellsjökull ice fall. I heard thunder behind the Hafrafell mountain
Two minutes later and suddenly all icebergs in the lagoon began to move around like corks in a boiling pot. Big waves paralyzed the shores of the lagoon, in some places for many meters.
„Shit“ was my first thought. „I was not in the right place“. I should have been on the other side of the lagoon and closer to the glacier, where I have spent hours and days in recent years trying to record incidents like this without success. I ran to the lagoon to see what was going on.
…Or maybe I was lucky to be where I was. I saw big waves go far up on the shore at the place where I have been recording the past years. I probably would have damage or destroyed the Phantom power adapters inside the hydrophones XLR´s.plugs   
Thanks to COVID I was now in a place which has been impossible to record because of the tourist explosion in recent years.
Two microphones were now placed under a high steep crawl on the lagoon´s west bank, 5 meters above the lagoon surface. Below the microphones, two hydrophones were put in the lagoon between big rocks to prevent them from getting crushed or touched by icebergs. It was a bad placement for a successful underwater recording. But I  remember quite well what happened in this lagoon few years ago. So I was sure I would lose them both and probably something more if I threw them deeper into the lagoon. 
Although the outcome is OK, even though the hydrophones did not pick up the whole soundscape underneath the lagoon’s surface. 
The glacier calving starts in this recording at 3:15 min far away and behind the Hafrafell mountain, so it doesn’t sound very loud. But it makes a big wave in the lagoon which makes a chain reaction of a few other glacier calving.
Just before the first incident you can hear the hydrophone pick up a sound of crushing ice. It would have been much louder if the hydrophones have been deeper in the lagoon. But recording glacier lagoons is not an easy task when the lagoon is full of ice which can flip without warning.  
This recording was made in the late afternoon so traffic noise from rode no:1 is audible in the background. But compared to recent years, it is nothing. Thanks to COVID.   
Quality open headphones are recommended while listening at low to mid level, or in speakers at medium level.

(mp3 256kbps / 48Mb)

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Recorder: Sound devices MixPre6 
Mics: Lewitt LCT540s (NOS) & Aquarian H2n XLR (Spaced AB)
Pix: Canon EOS R

Location: 64.007567, -16.880922
Weather: Cloudy, calm,  +11°C