On 10/15/2015 03:59 PM, Jörn Nettingsmeier wrote:
On 10/15/2015 03:41 PM, Augustine Leudar wrote:
What can I say Jorn - we have some and they work - not as well as
adverstised obviously but strip away the hype they have something thta
mor
eor less does as described - you'll have to wait a while for those
measurements ;)
For now, the low cutoff frequency would be enough.
Mind you, I'm not saying that these things cannot be great creative
tools. But I'm a sound engineer. I need to deal with the artistic output
of other people, in such a way that they are not going to ram the
speakers down my throat because half of the spectrum is missing. I need
general-purpose speakers, which on a bad day means ten octaves and 110dB
peak SPL.
We've seen all those outlandish claims of magical waveguides that are
just fractions of the wavelength in diameter and yet shape the sound so
wonderfully that a 20Hz beam will travel all the way to the moon (using
the revolutionary VacuProof™ technology that will finally bring
cinema-friendly space battles). The problem is, this waveshaping is not
physically possible. You can make a plane wave, but unless it's a huge
plane wave with respect to frequency, the edge dispersion will make it
fall apart. In the end, it's just a point source with a little dent in
it. I don't even need to wait for measurements.
Even if you consider ultrasonic systems: at some point, the ultrasound
has to be demodulated (it is actually demodulated _everywhere_ in the
beam), and then you again have a frequency-dependent radiation pattern.
So yes, some years in the future maybe we have an ultrasonic projector
that is actually capable of putting a kick drum right in the middle of
the room without frying anything in its path. But as soon as the
baseband sound materializes, it will be (almost) omnidirectional again.
Here's an interesting datapoint:
http://www.ultrasonic-audio.com/images/Acouspade_vs_Audio_Spotlight.png
Consider the Acouspade, to the right. The polar pattern is truly nice,
unless you look at the fact that we are not told what happens below 500
Hz (because very likely, nothing much is happening there), and we take
note of the tiny, tiny dotted line that denotes 4 kHz, which is down by
around 18 dB on-axis, indicating that in the treble range, not much is
happening either.
This is a wonderful tool if you want to whisper textual information at
your visitor. But what you are actually perceiving is your amazing
ability to suspend disbelief in the presence of a friendly voice from
your own species.
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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