"Micro-Beaming" (Of Tweeters)
 

In article , Fleetie
wrote:
Put very approximately, you seem to get a half-power beamwidth of the
order of 45-90 deg across when the wavelength is similar to the
diameter.

Hmm! 45-90 is a bit of a range. So diameter~=25mm, c~=344m/s, so
f~=13.7kHz.

I'm surprised. I'd have thought at that kind of frequency, the central
lobe would be considerably narrower, but I can't contradict you at the
moment.

That seems not to explain the extremely noticeable "micro-beaming"
effect, but maybe there are other things coming into play. I mean as I
said, the "sweet spot" is 1 or 2 cm at about 3 or 4 metres from the
tweeter, which is considerably less than ONE degree.

I get similar effects (albiet using ESLs). They show up when listening, and
also when I move a measurement mike around. They seem to be caused by the
interference effects between the direct and reflected soundwaves. This
means that peaks and dips are only the order of a half-wavelength apart
even when the sound source radiates over a wide range of angles.

If you wish to reduce this, then the best bet is probably more in the way
of HF absorber on the room walls. Having directional speakers can reduce
the side-wall effects, but still permits those from the wall behind the
listener. That said, the rear wall effects are more likely to be 'common
mode' for both your ears, and show up when you move fore and back rather
than side to side, so are probably less significant in conventional stereo
imaging.

Slainte,

Jim

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