The 4th topic
Exhaust sound and breathing sound- noises in "The Silent World"

In the last topic, we explained you should tap when you hear nothing from the speaker. This time, we will explore exhaust sound and breathing sound. Hope you will enjoy it.

It was more than a half century ago that "The Silent World", the documentary movie of captain Cousteau, investor of scuba equipment, got Grand Prix in Cannes International Film Festival. We are not sure why captain Cousteau titled the movie "The Silent World". Probably because we cannot talk underwater. In recreational diving, it is true that divers were in the silent world, neither to be spoken by nor to speak to.

However, actual underwater world is not completely silent. We can hear various sounds, even though they are tiny. We wonder if they are voices of creatures. But comparing to the voices of birds and insects, rustling trees, sound of wind blow, and sound of waves, it seems true that underwater world is "The Silent World."

You can hear two more sounds in the sea. They are theme of this topic, exhaust sound and breathing sound. Exhaust sound is caused when exhaust air bubbles are hit each other or moved together. On the other hand, breathing sound is caused when you breathe air from regulator. These two sounds are necessary sounds for divers to breathe, but they do not exist in "The Silent World" originally.

The exhaust sound and breathing sound are troublesome for Logosease.

First, let us explain exhaust sound.

Exhaust air is collections of bubbles. It has four bad features. Below is the list of them.
  • Sound of bubbles passing close to your ear disturbs hearing the voice from speaker .
  • When a big bubble touches on Logosease, it acts as tapping and may switch to transmitting/receiving mode.
  • The microphone on Logosease picks up the sound of passing bubble when it passes near Logosease.
  • Bubbles in front of Logosease interferes ultrasonic wave for communication of Logosease.

Tip to prevent these troubles are to breathe slowly and not to exhaust too much air. This method is as same as breathing method of diving. Once you learn the proper breathing in diving, you will be able to control the situations when it's hard to hear voices due to the exhaust sound, or in malfunction by tapping with exhaust air.
However, a speaker him/herself does not notice if microphone picks up sound of bubbles, or bubbles interfere transmitting ultrasonic wave. If a speaker does not pay enough attention to these conditions, a receiver on the other end would not get the transmitted voice.

How should we speak for better communication?
It's very simple. Incline your head a bit to right and speak.
Just by that, exhaust bubble will move the opposite direction from Logosease, and as a result, it will give less influence to Logosease.

We will summarize the tips for reducing influence of exhaust sound.

  • Breathe slowly
  • Incline your head to right when you speak

Second, let us explain the breathing sound.
When you breathe air from regulator, you hear sound like "Sh--" (audible sound). At the same time, this sound is released as inaudible sound in the ultrasound range. The microphone receives the ultrasonic wave, and you hear your own breathing sound from the speaker. This is the logic that you hear "Sh--" from Logosease speaker in breathing.

Some regulators release little breathing sound in the ultrasonic wave, and some releases large one. We don't know exactly what type of regulators release little breathing sound. This is because there are regulators which have breathing resistance listed in the spec. but no regulators which have ultrasonic wave range listed in the spec.

We have tested several types of regulators of famous manufacturers and tuned Logosease at the proper level with which you can ignore the breathing sound. Nevertheless if you hear large breathing sound from speaker, there might be some regulators releasing the ultrasonic wave more than we expect. To know whether ultrasonic wave from regulator is the cause of noise or not, cover the second stage of the regulator with both hands. Once breathing sound becomes smaller, the cause of noise is the second stage. Countermeasure for the trouble is to breathe slowly. By this way, you can make breathing sound smaller. If this does not work, we recommend you to overhaul regulator or exchanging current second stage to other one.

Here are tips to make breathing sound small.

  • Breathe slowly
  • When ultrasonic wave from second stage is large, consider overhauling the regulator

Did you enjoy the stories of the two nuisances, exhaust sound and breathing sound? After reading this column, you may think "How about with rebreather?" In fact, we have already tried it. It was amazing, brilliant, and unbelievable. Not only we heard no exhaust and breathing sound, but also we could pronounce clearly because of a space in front of our mouth. Except hard sounds for pronunciation "p", "b", and "m", sound quality might be more than that of full face mask. If the price of rebreather goes down, rebreather is one of the equipment we want to use regularly.

On next topic, we will talk about ultrasonic wave in fishfinder.

In recent years, portable fishfinders for anglers have become popular. Fishfinders detect signs of fish by emitting either two frequencies of ultrasonic wave, 50 KHz or 200 KHz, continuously. The ultrasonic bands are different from that of Logosease, but it's very close. Are there any influences? We will report the result of our experiment.