K3 CW Sound Wave Canceling

[John W2XS]

When I first got my K3, I wanted a nice pair of speakers so I bought two Tivoli Audio extension speakers from their outlet store. They look and sound nice, although they have gone way up in price lately.

To get the maximum effect from the stereo AFX performance, I placed the speakers several feet apart on a shelf right above the operating desk. The sound was good.  But every now and then I would have to scramble to more clearly hear a station at a particular CW tone.  Sometimes I would have to plug in the phones to be able to copy the station properly.

Then I realized what might be going on.  Sound waves travel at a speed of 344 meters per second.  Wavelength is speed divided by frequency.  So, the wavelength of a 344 Hz tone is one meter. When two sound waves meet, they can either add together (in-phase, or constructive interference) or cancel each other (out-of-phase, or destructive interference). Since I like to listen to lower frequency tones (like 400 Hz), there seems to be some cancellation going on at certain locations where I normally sit, depending on the particular pitch that I am copying.

I pressed the “pitch” button and walked around the room while listening to various tone frequencies and I “think” that I can find spots where the sound is attenuated. There are other effects going on like reflections, etc. Maybe it is not a good idea to have the speakers too far away from each other.

So, anyway, I will try different locations for the speakers, or drop down to only one speaker and use the AFX with only the headphones.

There is nothing wrong with the K3.  This is basic physics about the sound waves from two sound sources. It has the biggest effects at CW single-tone lower frequencies, and probably is not that much of a factor with the complicated sound waves in normal speech and music. And, I could be filled with hot air, which is also basic physics hi hi.

73,

John W2XS

[Jim Brown-10]

On Thu, 27 Nov 2008 10:09:10 -0800 (PST), John W2XS wrote:

>Maybe it is not a good idea to have the speakers too far away
from
>each other.

Yes, it's a speed of sound issue, and the algebraic addition of
sound waves that are arriving at your ears at different times.
This may help you understand what is going on.

http://audiosystemsgroup.com/AES-StereoASGWeb.pdf

Study the parts about human perception of sound, time issues, and
the directivity of human hearing.

The best way to set up speakers for the K3 if you're listening two
two channels (that is, diversity, or two RXs on two different
frequencies) is with one speaker on your left so that your head
blocks it to your right ear, and the other on your right so that
your head blocks it to your left ear. This minimizes the
destructive cancellations and maximizes your ability to
discriminate which is which.

Note also that the K3 plays some games with delay in DSP, which
can also complicate things. Add to that that the two RXs are NOT
precisely SYCNHRONIZED in diversity mode, which adds a beat of a
Hz or so between the left and the right ears that is MADDENING!  

Wayne -- is there a tweak for this?  

73,

Jim Brown K9YC


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