Steve Anderson wrote:Interesting results Harry.
Hi Steve i was very happy with the results a very simple experiment .
I wanted to test speaker mic or visa versa one or the other could or could not reproduce the sound frequencies of the other .
Research..... Air is a poor transmitter of sound waves !
Tests in Air are dreadful and we are talking Cm from each other to get any result...and you can see a lot of missing bandwidth which both mic and speaker should be able to reproduce better results ..i was thinking may be it's not the devices but the medium between .
i thought lets change the medium to a liquid and see if this helps and we all know its been used in supersonic light valves idea ,just i have not modulated it on a higher carrier for that purpose /
Two things spring to mind here...
1) The speed of sound in water is about 1,470m/s (metres per second), in air it's around 300m/s.
2) The room dimensions are much larger than the container of water.
Do different frequencies travel in a liquid or air at different speeds ?
looking it up !
As a result, sound waves travel faster in solids than in liquids, and faster in liquids than in gasses. While the density of a medium also affects the speed of sound, the elastic properties have a greater influence on the wave speed. The density of a medium is the second factor that affects the speed of sound.
With the air and water tests i would of guessed that low frequencies would do better seems the case for whales chatting to each other sonar and such but why to the higher frequencies work ,there's a bandwidth increase when using liquids and the higher frequencies .
Dolphins have the ability through echolocation to emit sounds with a frequency of 120 kHz ! so that works well in water for them to find fish with ultra sound.
I was just reading that the U S navy can produce sonar with transducers up to 1 ghz !
Sound waves induced in water, with frequencies ranging from 100Hz up to a 1 GHz.
The higher the frequency, the smaller the features that can be detected, but also the smaller the range of detection becomes. Very low frequencies are difficult to induce in water, they would require humongous “loudspeakers”.
So to detect a submarine at a distance of 10 km you’d use rather low frequencies with wavelengths (in water) of shorter than 10 meter / frequencies of 150Hz to a few Khz.Reflections from room walls/windows/etc. will have quite a delay, several milliseconds easily. Our ear/brain machine sorts all this out for us, but not NBTV devices. With hard walls and windows the reflections could be of quite a high amplitude, enough to produce the results you are getting. The reflections could be modified by room resonances as well.
The 'water bath' will produce reflections that will be so close in time to the source that they're probably of no issue.
It might be worth repeating the 'air experiment' outdoors in a big open field with no wind - see what you get...
The problem with Air test for NBTV the devices have to be very close to 1cm or they don't work at all even to the point you would think cheating with induction of the coils in the speaker to mic that close would help but still don't help ! results are dreadful in air .
Factors like volume don't seem to help either
IN the bath liquid test direction and reflection off the walls from the speak to mic they ... don't have to be close , there are sweat spots where direction of the sound in the liquid becomes strongest when i have time i with try it in a bigger bath but distance wise its better than air as well /
So what i think its showing is the speaker and mic can produce transmit and receive at least a bandwidth frequencies enough to produce the NBTV video ..Looking at the air result what you think the bandwidth was for that result ?
I would think 1 khz to 3 at best replacing the Air medium with water the bandwidth transmit to receive is increased guessing 10khz or over ? ...i know to find out i need to do a sweep test up to 20 khz
Steve A.
Afterthought...also the frequency response of the transducers (speakers/microphones) will affect the received waveform. As we all know NBTV requires a response down to frequencies that few transducers are capable of.
My thoughts here are the speaker as a transmitter i used it must be just due to its size giving better results on the higher frequencies what we know to get a range in loud speakers is to use a woofer and tweeter ...trouble here is a speaker say even twice the size are no longer made from plastic but paper not good for the experiments in water !
I wanted to see once i get my hands on enough oil to give that a go ...
In the Scophony system supersonic light valve used paraffin oil in its light valve again a bit off what i am doing here but in that case it was the modulated supersonic sound waves were changing the density on the liquid changing the liquids transparency to light .
But water has a higher density than oil so results should be different in a transmitting test ....my guess now with studying this is the results would be worse .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.