How Do Sound Frequencies Interact Within a Room?

And how is this related to Electrical Engineering?

I suppose that depends how narrowly you want to define electrical engineering. I have electrical engineering textbooks that cover this sort of topic. In any case, the whole concept of multiple frequencies being carried on a single medium applies to current in electrical cables as well as sound waves in air, mechanical vibrations of a loudspeaker etc. and if you can grasp one of these concepts the rest make more sense.

Now as far as explaining it goes - I don't think I can really. Pressure waves at different frequencies will add together to produce complex waveforms in the time domain. In the frequency domain everything stays separate. The incredible bit is how the ear makes sense of the apparent mess.

The short answer is superposition. Go find a piano tuner and listen as he gets very near the right pitch and you'll hear the "beats". When frequencies are farther off, we don't really hear those "beats". Remember that your ear is connected to your brain which is used to making sense of complex waveforms. An oscilloscope would show all that stuff added.

The cochlea (that snail-shaped thing in the inner ear) acts as a mechanical spectrum analyzer that splits the composite waveform into its constituent frequencies, each with its own amplitude, and sends the aggregate on to the brain in parallel for further processing. How the brain processes this information is anyone's guess.

Thank you very much Mr. Blink.

The link which you have given me has clarified everything.

Vinayak K. S.

About the spectral audiogram curve of babies and adults:

Babies below some 8 months old have a strong attenuation of many dB in the low frequency side of their spectral audiogram, and this attenuation is so strong that it is difficult for them to hear the low frequency voice of their father, and this is apparent in the fact that it is difficult to get their attention speaking to them with normal voice.

So one instinctive way to speak to our babies is to double the frequency of our voice one or even two octaves above normal frequency to facilitate the detection of our voice, and this method has proved to be effective for hundred thousands years since prehistoric ages.

But another problem with the audiogram spectral curve of babies is that their perception of sound runs well above 20 KHz, so some ultrasonic sounds produced by some electronic devices fall well inside the audible spectral band of babies, and this is the case of old TV sets with damaged fly backs generating 15750 Hz, or some powerful DC/DC converters of computer UPS using fast fly back coils that make resonate their own cores or nearby iron parts at ultrasonic frequencies not detectable by adults, and this may be a serious problem when babies need to sleep.

Due to the small geometry of the ear anatomy of babies, their audiogram spectral curve is shifted well above an octave over that of the adults, and this must be taken into account on installing electronic devices around.

Jaime Soto Figueroa

http://www.matharts.cl/

If you look at an oscilliscope view of music, you will see that the seperate frequencies have combined, and are "one" wave-form. But with electronic filtering, a high degree of re-seperation can be achieved. (as in speaker crossover circuits!)

Loudspeaker design articles may be a good resoarce for further questions.

Bryan

It could be useful think to an audio system where electrical low frequency signals are mixed in the time domain creating an arbitrary waveform (that characterizes the related sound). In the system, the next block in the chain will translate the amplified resulting wave into an acustic wave. This last will be a function of the source wave in the time domain. i.e. if the source wave voltage is a function v(t) then the air pressure will be f[v(t)], so time after time the pressure of the air will change in function of the amplitude of the electrical wave v(t). But v(t) is the overlapping of a lot of signal (see Fourier theory), but if we look at it whit a scope in the time domain, we will see only an arbitrary continuos wave! So our ear will transduce the changes in the air pressure into an electrical stymulus leading it to our brain. This will create a sensation: the hearing! I hope to be clear.

You would do well to research 'room modes', as this an important part of how sound propagates within an enclosed space.

A simple, yet very good example is; why people sing in a shower. The harmonics (read wave interaction) produced by the early relection in the closely enclosed space cause a fullness of sound that people without great talent can sound like a harmonized quartet all by themselves. Even if off key, the reflections are all mirrors of the tone so it sounds more harmonious to the ear, at least in the ear of the singer.

The people in the room next door may have a different opinion.

Are you trying to treat a room or just solve a math problem?

Check out these two websites, for information regarding room acoustics:

johnlsayers.com

homerecording.com

Well, this phenomenon is the basis for one of two multiplexing techniques, that is, frequency multiplexing, which makes it possible to transmit many different signals over a single communications channel. Just like a lot of TV and Radio broadcasts can go over the air. The other technique is time multiplexing, where all the signals share the channel, each one occupying part of the time

For further review and enlightenment, great animations of wave interactions at http://www.kettering.edu/%7Edrussell/demos.html ... especially superposition at:

http://www.kettering.edu/~drussell/Demos/superposition/superposition.html

Mr. NDT TOM and all other friends thank you once again for your help...

You correct me if i am wrong...

I think sound wave is a power transmited in air by speaker drivers. And power (wave) of two frequency will travel through air making impact on each others accourding to their types and positions of peaks n vally...

AM I RIGHT.... one song is played with amplifire where there r five instruments and one man singing in song... when amplifire converts all data in song to drive speaker driver ... what happens is all type of waves are combined ( wave from drums, wave from guitar, wave from voice of a man) and final outcome frequency is generated by adding all frequecies and amplitude by amplifire and on that frequency speaker drivers are driven and voice is produced ????

Pls explain me above question...

Thanks n regards

Sound waves (as well as infrasonic & ultrasonic waves) certainly qualify as "a power".

( just ask "Mr. Decibel". ) And, those acoustic waves are generated (and thus transmitted-to-air) by many things in addition to spkr drvrs , as related by our fellow shower-singer. Anything that vibrates at sufficient amplitude at a frequency within our hearing range (that ol' 20Hz-20kHz plus-or-minus ... as high as 40kHz for some asthmatics) will generate acoustic waves in air, liquids, and solids.

Your original post (Q2:) "If i have only one speaker driver then how this driver will move air at 20 hz for beats and 1000 khz for mans voice at same time?" is asking the hand-in-glove type question : "How does a single microphone hear all 70+ instruments in an orchestra and squeeze all of that sonic data onto a single recording track?" That's where Blink & captbryan's posts really kick-in.

Back to "air, liquids, and solids"... sound travels at different velocities through different mediums, BUT, the velocity is independent of frequency. Thus, when a conductor commands a "Forté!" attack with piccolos, bassoons and kettle drums all striking their respective notes at once, each member in the theater hears those notes at essentially the same time (dependent on exact distances to those musicians). A good, high-quality/Hi-fidelity recording simulates what you EARS (each individually) would have heard, at that live performance, by using stereoscopic recording mic's.

It is truly a remarkable thing, what today's advanced audiophile systems can do: e.g., reproducing that "inner timbre" of a live musical performance. Your final paragraph sounds as though you have a pretty good grip on the concept. Google Bob Carver and his latest "Sunfire" creations ... you'll find an interesting page about how he tunes (or, "voices" as he calls it) his audio designs. Also, as I've posted elsewhere, visit www.klipsch.com and if you can still get ahold of the "Klipsch Audio Papers", it will astound you how far the science was already developed back in '41

happy melodies!