From Heikki:<br /><br />"GROUNDLOOP measuring method by Hss pro.<br /><br />"Resonating the measurement system with a known electronic interferences, like switched-mode power supply or "earth-link" hum. This means that system is responding harmonically/acoustically different with various mediums ie soil compositions.<br /><br />"How its done:<br /><br />"EM sensors we use have an average impedance of 300Ω. This is most common impedance for audio microphones. That impedance was chosen to designed EM sensors because in our measuring system they are connected to digital audio interface´s mic preamps normally used with only microphones.<br /><br />"However, microphone´s membrane is detecting only air pressure changes (mechanical sound). EM sensors instead detect electromagnetic radiation variations, oscillations which are moving average speed of light with 10-100km wavelengths.<br /><br />"EM sensor is basically a copperwire coil with certain length, thickness and size that delineates its sensitivity and usable frequency response. These Demiurg sensors we use are designed to work reliable on 5kHz-100Khz range, so called VLF (very low freq.) range. That range is mostly used only by military (nuclear submarines etc.) because its nonsensitivity for external interference and adequate ability to penetrate water molecules.<br /><br />"Ground loop in audio field is considered as a fault in a system. It means that systems electronic grounding is in contact to galvanic grounding and this produces a ground signal loop. This can be heard also by base 50Hz "hum" sound in a current system (in United States 60Hz).<br /><br />"In my tests in Finland and several surveys in Balkan area I found out that this "hum" is changing its features depending the ground surface location of the current EM sensor. 3D sensor produces 3 simultaneous data feed which gives ability to define directions of the possible oscillation sources.<br /><br />"Further I discovered that like this it is possible to measure different values/EM spectrums from different earth locations excluding environmental interferences caused by lamps, electric wires, power supplys etc. This baseline research knowledge is obtained over 4 years of digital data recording, testing and developing the research equipments during surveys around Europe.<br /><br />"Water soil has an characteristic frequency spectrum/values different to dry soil.<br /><br />"Solid soil produces different spectrum/values than hollow soil. That causes the ability to presume is the ground solid rock or is there empty areas, cavities in the ground. Conductivity in the ground can be observed too.<br /><br />"These results can be made hearable using "data sonification" ie varispeeding the data downward from its original status.<br /><br />"This gives an opportunity to determine ground composition with quite accurate results. Environmental EM status compared to mechanical w<br />...<br /><a href="https://www.youtube.com/watch?v=n6BUbStHYgE" target="_blank" rel="nofollow">https://www.youtube.com/watch?v=n6BUbStHYgE</a>