Exploring Sound Design Tools: Hydrophone

Continuing with the unconventional microphones theme, this time I've being fooling around with an hydrophone. As you may know, these are designed to better capture sound in water instead of in the air.

I tried recording water movements and props on all sorts of small containers, the kitchen sink and the bathtub. I quickly learned that is important to manage the cable properly since moving or touching it can be quite noisy, specially when trying to get quiet sounds. I was usually using one hand to keep the microphone and cable still and the other to perform the sound.

I also discovered that very small changes in mic placement usually produce vastly different results. On some occasions, just some centimetres were the difference between a close aggressive sound and a distant atmospheric one. I don't know if this is the case because water is denser than air and sound waves move 4.3 faster but it certainly something to keep in mind.

Finally, I have to say I was surprised by how clean the sounds were, although when processing very quiet stuff I did some RX cleaning here and there.

So, on with the recordings. You can individually download every sound via freesound.org or download the whole package through this link.

Bubbles

I first tried to get some bubble sounds. I used a plastic drinking straw to get the small ones and then tried sinking a bowl or a mug with some air inside to get bigger ones.

I tried some effervescent tablets too and got some nice fizzy sounds. 

Movements

Next, I tried some water movements. I quickly found out that submerging the microphone and trying to create water sounds with hand movements doesn't work really well since not a lot of sound energy reaches the mic.

So I tried to record them with the mic just on the surface of the water and got better results that you can hear in the first example below.

I also wanted to get some underwater movements and discovered that the easiest way was to move the microphone itself through a large mass of turbulent water. I did this in a filled bathtub (second recording below).

Steady Water Streams

For this sounds, I was trying to get long samples of water flowing that could be then used for underwater scenes.

To achieve this, you need some kind of water flow. In my case, since I didn't have access to a swimming pool or a jacuzzi, I just recorded the whole filling and emptying process of a kitchen sink and a bathtub.

While doing this, I experimented with different mic placements and amounts of water flowing in. You can get a vast array of result by just changing these two factors as you can hear in these examples:

Metal Kitchen Sink

Here are some other sounds I got in the kitchen sink.

Again, the draining sounds show how important mic placement is. Those changes in the sound intensity were produced by just getting closer or further away from the vortex.

Others

Here are some other random things I tried.

The first one is just me hitting a floating bowl with my finger. The resonance was captured with the mic underwater and close the bowl but not touching it. As the bowl filled more and more, the pitch changed in an interesting manner.

Lastly, the second recording below is how water directly impacting the hydrophone sounds. 

Conclusions

It was nice doing this recording session. I learned that mic placement is crucial when working with these microphones. Having an hydrophone is perhaps kind of a niche purchase, but it could be very useful if you need underwater sounds or want to record anything that involves too much water for conventional microphone to be safe.