Playing 2 freq!

[epilot]

Hello guys,

Does anyone know if it is possible to play 2 frequencies say 2kHz and 3kHz synchronously with A loud speaker and get just 2 original frequencies at the output of the loud speaker if you know what I mean?
what about doing similar job with an antenna at say 500kHz and 510kHz?

 

[Nigel Goodwin]

Of course it is, what do you think a chord is?.

 

[audioguru]

If the amplifier or speaker, or RF amplifier have distortion then you will have lots of other frequencies too.

 

[epilot]

Of course it is, what do you think a chord is?.

I think so too, but I am not able to see how it is done?!
suppose you have a loudspeaker and a 2 channels signal generator, one channel is set at 2Hz and the other channel is set at say 3Hz. then you connect those 2 channels to your loudspeaker. now can you let me know how does the speaker move its cone to generate 2 mechanical waves (2Hz and 3Hz) at the same time?! I am not able to understand how does an speaker cone is able to do that job!!? the speaker should be able to generate 2Hz or 3Hz or 5Hz in this case at a definite time not 2 frequencies together?

 

[ericgibbs]

hi epilot,
The easy way to understand it, is to get a piece of graph paper.

Plot the two sinewave frequencies on different X axis, using the same amplitude for both frequencies.

Then plot on a third X axis the 'sum' of the first to plots, to the same time scale.

You will finish up with a waveform that is the 'sum' of the other two waves.

This 'summed' wave is the signal that the speaker reproduces.

Does this explain it enough.?

 

[Nigel Goodwin]

You're over complicating it! - don't worry about it, a speaker can quite happily produce the two notes, and many more as well. As Eric says, the two notes mix together and form a new more complicated waveform.

 

[epilot]

hi epilot,
The easy way to understand it, is to get a piece of graph paper.

Plot the two sinewave frequencies on different X axis, using the same amplitude for both frequencies.

Then plot on a third X axis the 'sum' of the first to plots, to the same time scale.

You will finish up with a waveform that is the 'sum' of the other two waves.

This 'summed' wave is the signal that the speaker reproduces.

Does this explain it enough.?

Yes i know that, it means a summation of 2 primary frequencies (5Hz in my example) would be in the output of the speaker not 2 primarry waves(2Hz and 3Hz), Right?

 

[Nigel Goodwin]

Yes i know that, it means a summation of 2 primary frequencies (5Hz in my example) would be in the output of the speaker not 2 primarry waves(2Hz and 3Hz), Right?

No, it will be a complex wave.

 

[epilot]

You're over complicating it! - don't worry about it, a speaker can quite happily produce the two notes, and many more as well. As Eric says, the two notes mix together and form a new more complicated waveform.

No Nigel I am not able to understand it!
If they will mix togather, then we will have A mixed freq (5Hz in my instance) not 2 primary waves?!

Eric explanation is correct wile we have 2 electrical signals (2Hz and 3Hz for instance) at the out put of the speaker we will have just one mechanical wave (5Hz or any else freq(depending upon the primary waveforms and phase) but just one new freq not 2, right?

 

[Nigel Goodwin]

No Nigel I am not able to understand it!
If they will mix togather, then we will have A mixed freq (5Hz in my instance) not 2 primary waves?!

You're thinking of RF 'mixing', as in a superhet receiver, this is a different kind of mixing, in RF you get the two original frequencies, plus the sum and the difference.

Eric explanation is correct wile we have 2 electrical signals (2Hz and 3Hz for instance) at the out put of the speaker we will have just one mechanical wave (5Hz or any else freq(depending upon the primary waveforms and phase) but just one new freq not 2, right?

Like Eric said, draw them out on a piece of graph paper, bear in mind the output can only be in one place at once - so you can't have more than one point at any instant. Just as a speaker cone can't be in more than one place.

 

[epilot]

No, it will be a complex wave.

what kind of complex wave?

Ok, now let me explain it another kind.

we have a modulator (AM for instance), with a 1000Hz square wave carrier and a 100Hz square wave modulating signal. the output freq of our modulator would be 1000Hz, 1100Hz and 900Hz. we connect the output to a loudspeaker, what do you think about the output freq of the speaker? (ie mechanical wave).

 

[epilot]

You're thinking of RF 'mixing', as in a superhet receiver, this is a different kind of mixing, in RF you get the two original frequencies, plus the sum and the difference.
.

Just want to see how 2 freq will be at the output of a speaker for now, we'll reach to RF too

 

[Nigel Goodwin]

Like we keep saying, it will be a complex waveform - get graph paper and draw it!.

BTW, use pure sinewaves and NOT squarewaves, or it's just got MASSIVELY more complicated!.

 

[evandude]

Yes i know that, it means a summation of 2 primary frequencies (5Hz in my example) would be in the output of the speaker not 2 primarry waves(2Hz and 3Hz), Right?

You're clearly confusing what they mean when they say "sum". They're talking about summing the waves in the time domain, not producing a wave at the sum of the frequencies. This should be quite obvious if you actually took the time to draw it out on graph paper as was already suggested.

You are confusing this with a MIXER, as nigel pointed out, which MULTIPLIES the two signals together. This is what produces the sum and difference frequencies. The different signals at different frequencies that a mixer produces are all present in the output as the SUM of the signals. You obviously need to understand the concept of the sum of the signals, as in the simple 2Hz/3Hz case above.

Edit: well just to really lay this to rest (knock on wood) here's a set of plots to help detail what we're all trying to tell you:
Two sinusoidal signals of different frequency
One plot of the SUM of the two signals (what you'd feed a speaker with to hear both sounds at once, the sort of 'complex' signal Nigel is talking about)
One plot of the PRODUCT of the two signals (what you'd get if you fed both into a mixer - notice there's a higher-frequency sine wave 'riding on' a lower-frequency sine wave - these are the sum and difference frequencies)

 

[epilot]

You're clearly confusing what they mean when they say "sum". They're talking about summing the waves in the time domain, not producing a wave at the sum of the frequencies. This should be quite obvious if you actually took the time to draw it out on graph paper as was already suggested.

You are confusing this with a MIXER, as nigel pointed out, which MULTIPLIES the two signals together. This is what produces the sum and difference frequencies. The different signals at different frequencies that a mixer produces are all present in the output as the SUM of the signals. You obviously need to understand the concept of the sum of the signals, as in the simple 2Hz/3Hz case above.

Edit: well just to really lay this to rest (knock on wood) here's a set of plots to help detail what we're all trying to tell you:
Two sinusoidal signals of different frequency
One plot of the SUM of the two signals (what you'd feed a speaker with to hear both sounds at once, the sort of 'complex' signal Nigel is talking about)
One plot of the PRODUCT of the two signals (what you'd get if you fed both into a mixer - notice there's a higher-frequency sine wave 'riding on' a lower-frequency sine wave - these are the sum and difference frequencies)

Oh yeah, that is the whole problem. I know that those primary waves will be summed in 'time domin' like Eric and you said. But I am talking about FREQ summation not time summation.

Please answer this to go to the next point:
we have a modulator (AM for instance), with a 1000Hz sine wave carrier and a 100Hz sine wave modulating signal. the output freq of our modulator would be 1000Hz, 1100Hz and 900Hz. we connect the output to a loudspeaker, what do you think about the output FREQ of the speaker? (ie mechanical wave).

Well I want to talk about Parametric arrays which use 2 primarry waves to generate a new wave as a byproduct of those original primarry waves by a transducer in the sonar and in the air.
and I'll do it after I'll get the response of the above question

 

[evandude]

the output freq of our modulator would be 1000Hz, 1100Hz and 900Hz. we connect the output to a loudspeaker, what do you think about the output FREQ of the speaker? (ie mechanical wave).

As I just said, it will be the SUM of the 1000Hz, 1100Hz, and 900Hz signals! I showed you an example of the sum of two different frequency waves above, it shouldn't take much imagination to guess what the sum of three waves would look like...

 

[epilot]

As I just said, it will be the SUM of the 1000Hz, 1100Hz, and 900Hz signals! I showed you an example of the sum of two different frequency waves above, it shouldn't take much imagination to guess what the sum of three waves would look like...

Ok, well done,
that's what I expected to hear.
a parametric array uses an ultrasonic transducer and utilizes the AM modulation to generate a new wave in the water.
suppose SSB modulation for instance, which we'll have a 200kHz carrier and a 210kHz sideband in the output of the modulator, now we feed tose 2 freq into the ultrasonic transducer to generate new waves in the water due to nonlinearly property of the water. we HAVE TO have those 2 primarry waves in the water to generate that new waves while we have just a SUMMed wave at the output of the transducer!
That is what confused me and I start this thread.

 

[Sceadwian]

It's an acoustical laser =) They have a free air invention called Hypersonic sound which works on the same principals, allowing audio to be directed into very narrow cones at large distances. The Army even has prototypes (and I think a few deployed units) that are used for crowd control, and can even deafen and disable people in it's area of effect.

 

[epilot]

It's an acoustical laser =) They have a free air invention called Hypersonic sound which works on the same principals, allowing audio to be directed into very narrow cones at large distances. The Army even has prototypes (and I think a few deployed units) that are used for crowd control, and can even deafen and disable people in it's area of effect.

Yes I know the story of it, but if you do too, so I must say that I am not able to understand how is it possible to transmit 2 septate frequencies via one transducer, if you know what I mean?!

 

[audioguru]

2 separate frequencies are nearly nothing for a loudspeaker.
Have you heard a loudspeaker reproducing an entire orchestra playing many different frequencies, and each frequency has many different harmonic frequencies, all at the same time?