playing ultrasounds through PC speakers

[jjoensuu]

Hi all,

I ended up double-posting this because I wasn't really sure which
group I should ask the question in.

I am curious about those ultrasound emitting devices that are supposed
to repel insects or other pests. I did not want to spend money on
them, however, since they may not even work. I remember this old "elk
repeller" unit that was sold in Finland back in the early 80's. This
was the type that was to be attached to the front of the car; when you
drove the car, the wind velocity caused the device to generate a sound
that elks supposedly did not like. A technical magazine (Tekniikan
Maailma) ran some tests on the unit back in those days and concluded
that it in fact did not generate much of a sound at all, at least on
the ultrasound level.

In any case, I was still curious on whether ultrasound repels insects.
For this reason I wanted to ask some questions:
A. can generic computer speakers produce ultrasound sound waves?
B. can this sort of tests damage the speakers?
C. does anyone know if sound file containing ultrasound sound waves
are available on the internet? Preferably in .wav or mp3 format.

Apologies if these sound like dorky questions;-) I was just curious
about testing this sort of thing.

Thanks in advance,

JJ

 

[Chuck]

Generally, very small speakers (tweeters) can reproduce ultrasonics at low
levels. the amplifiers may or may not. The conventional sound files and
decoder/players don't do ultrasonics.
You can do them in software and drive an ultrasonic transducer (Haven't done
this since the Apple II days)
As I remember we used to use a digital data line to output a pulse train
that drove the ultrasonic transducer.
The vehicle mounted units you mention do as much attracting as repelling.
They can startle a deer, and it might run in front of you. (Had that happen)

 

[Bob Masta]

Hi all,

I ended up double-posting this because I wasn't really sure which
group I should ask the question in.

I am curious about those ultrasound emitting devices that are supposed
to repel insects or other pests. I did not want to spend money on
them, however, since they may not even work. I remember this old "elk
repeller" unit that was sold in Finland back in the early 80's. This
was the type that was to be attached to the front of the car; when you
drove the car, the wind velocity caused the device to generate a sound
that elks supposedly did not like. A technical magazine (Tekniikan
Maailma) ran some tests on the unit back in those days and concluded
that it in fact did not generate much of a sound at all, at least on
the ultrasound level.

In any case, I was still curious on whether ultrasound repels insects.
For this reason I wanted to ask some questions:
A. can generic computer speakers produce ultrasound sound waves?
B. can this sort of tests damage the speakers?
C. does anyone know if sound file containing ultrasound sound waves
are available on the internet? Preferably in .wav or mp3 format.

Apologies if these sound like dorky questions;-) I was just curious
about testing this sort of thing.

Thanks in advance,

JJ

First of all, everything I have read (aside from marketing stuff)
indicates that ultrasound does not repel insects... or at least,
not mosquitoes, which is how it's usually marketed. And I
seem to recall that the car-mounted whistles may not be
too effective at warding off deer or moose, either. (That
one is a lot harder to test, usually purely anecdotal.)

But on to your specific questions anyway. A lot here
depends on just how loud and how "ultrasonic" you want to get.
Speakers typically have some upper frequency beyond
which output power drops like a rock. So you might get
*some* sound out at 20 kHz, but very soft... and since you
can't hear very well at that frequency anyway, it may be
even softer to you!

If you want to go higher in frequency (and power) you
will need a special high-frequency driver ("tweeter").
I have recently gone through a quest for a client who
needs to deliver very loud 20 kHz (and slightly above)
sound to rats to determine strategies for hearing
protection. The first thing I found was that it is *very*
hard to find frequency response information on
suitable tweeters. That alone narrowed the choices
down to a few units from Parts Express, in the $15-30
range, called "Titanium bullet tweeters". If you don't
need super-high power, then you should look into
piezo horn tweeters... much cheaper, and easier to
wire up as well.

As far as damage goes, speakers are destroyed by
too much power input. (Well, sometimes woofers are
destroyed by over-excursion, but that's not an issue
here.) One problem is that since speakers tend to
be inefficient at these upper frequencies, you may try
to feed them too much power just to get the output
you wanted. Also note that speaker makers use
"market-speak" in their specs. When they say that
a tweeter is good for (say) 100 watts, what they
*really* mean is that "in a full-range system playing
ordinary music that puts out 100 watts *total*, the
small percentage that end up going through the
tweeter will not damage it". If you actually put a
continuous 100 watts at (say) 20 kHz into it, it will be dead
in seconds. So you need a safety factor, or
you need to be prepared to waste a few units
to see what they can really handle.

Note also that tweeters (particularly) can easily
be destroyed if you give them too much *low*
frequencies, which is what you need a crossover.
But that is usually a simple capacitor in series,
often supplied with the tweeter.

As for a file containing ultrasound, you
don't need one. You can download my Daqarta
for Windows package and generate signals
in real-time. (Daqarta is nominally shareware,
but don't let that throw you... the signal generator
and most everythig else keeps working after
the 30-seesion/30-day trial period. You are
welcome to use it forever this way.) I'll be
glad to answer any questions about this.

The real problem, alas, is that most sound cards
won't allow outputs over 20 kHz, if that. They have
output filters that deliberately limit the upper frequencies.
Part of that is to protect your speakers, but mostly
it's because the highest output frequency you can create
(not counting distortion and harmonics) is half the sample rate.
So at 44100 samples/sec you can't expect to get above
22050 Hz... and it's actually more like 20000 in order to
keep the filter costs down. You might do a little better at
48000 (24000 theoretical limit), but beyond that you will
need to get a "premium" or "semi-pro" sound card.
Cards sampling at 96000 Hz would be the
obvious choice here, but make sure they actually
show the higher *output* frequency in their specs.

Best regards,


Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!

 

[Angelo Campanella]

I am curious about those ultrasound emitting devices that are supposed
to repel insects or other pests. I did not want to spend money on
them, however, since they may not even work. I remember this old "elk
repeller" unit that was sold in Finland back in the early 80's. This
was the type that was to be attached to the front of the car; when you
drove the car, the wind velocity caused the device to generate a sound
that elks supposedly did not like. A technical magazine (Tekniikan
Maailma) ran some tests on the unit back in those days and concluded
that it in fact did not generate much of a sound at all, at least on
the ultrasound level.

In Pennsylvania in the 1950's there was a "Deer Repeller" that was
available exactly the same thing... In northern PA, deer often cross the
not-too-active remote 2-lane roads through those forests.. As far as i
can recall, these devices were interesting toys... There was never any
large movement towards their use..., and deer are still sruck by
unfortunate mororists, even here in Ohio...

In any case, I was still curious on whether ultrasound repels insects.
For this reason I wanted to ask some questions:
A. can generic computer speakers produce ultrasound sound waves?
B. can this sort of tests damage the speakers?

It's a good topic for discussion, but don't exect any remarkable
results. It is just as likely that one can attact insects, as is used in
insect killers where said insects are atracted to some sort of death trap.

C. does anyone know if sound file containing ultrasound sound waves
are available on the internet? Preferably in .wav or mp3 format.

For sound cards, the sample rate needs to be fast enough to reconstruct
a sine wave of the requisite frequency. An analog generator would be better.

Apologies if these sound like dorky questions;-) I was just curious
about testing this sort of thing.

Keep us posted.

Angelo Campanella

 

[Father Haskell]

Hi all,

I ended up double-posting this because I wasn't really sure which
group I should ask the question in.

I am curious about those ultrasound emitting devices that are supposed
to repel insects or other pests. I did not want to spend money on
them, however, since they may not even work. I remember this old "elk
repeller" unit that was sold in Finland back in the early 80's. This
was the type that was to be attached to the front of the car; when you
drove the car, the wind velocity caused the device to generate a sound
that elks supposedly did not like. A technical magazine (Tekniikan
Maailma) ran some tests on the unit back in those days and concluded
that it in fact did not generate much of a sound at all, at least on
the ultrasound level.

In any case, I was still curious on whether ultrasound repels insects.

According to Consumer's Union, it doesn't. Roaches placed
in an enclosure with ultrasound "roach ridders" soon found
the devices comfy and moved into them.

For this reason I wanted to ask some questions:
A. can generic computer speakers produce ultrasound sound waves?

Piezo drivers, yes. Paper or plastic dynamic speakers, no.

B. can this sort of tests damage the speakers?

Not enough excursion at high freq. Bass frequencies are
more likely to damage speakers.

C. does anyone know if sound file containing ultrasound sound waves
are available on the internet? Preferably in .wav or mp3 format.

Find some sort of flute or woodwind recording (sine waves) and
raise the speed. One octave higher = 2x the freq.

Apologies if these sound like dorky questions;-) I was just curious
about testing this sort of thing.

Nothing "dorky" about skepticism.