Ultrasonic speaker or ??

[magnatro]

try a transformer coupler, works best with tweeters!
you can see these in tweeters!

 

[MrDEB]

The addition of a step up transformer is kinda what I was contemplating.
will do some searching.
Lets see I have 50watt tweeters so I need X voltage??

 

[magnatro]

just isolating the tweeter may do the trick.

 

[Nigel Goodwin]

just isolating the tweeter may do the trick.

How would that make the slightest difference to the output power?.

As for transformers feeding tweeters, where have you ever seen or heard of that? - it's a complete non-starter.

Piezo tweeters are effectively capacuitors, BUT still draw power like anything else - as the frequency increases their impedance drops and they draw more power, which is why you use a current limiting resistor on high power amps to stop it damaging both the amp and the tweeter.

 

[audioguru]

The addition of a step up transformer is kinda what I was contemplating.
will do some searching.
Lets see I have 50watt tweeters so I need X voltage??

50W RMS into 8 ohms has an RMS voltage of (the square root of [50 x 8])= 20V.
An ordinary bridged car amp has an output of 8W into 8 ohms so its voltage is 8V RMS.

Therefore you need a transformer with a voltage ratio of (20V/8V)= 2.5. But transformers are rarely used today.

Schools in Canada have a PA system that is distributed at 25V max (to avoid electrocuting any kids that are crawling around in the ceiling). Each speaker has a transformer to set its power. Usually a ceiling speaker is set to 0.5W or 1W.
A 10W PA speaker might be in the school's gym. It has a transformer with a voltage ratio of (25/8.94)= 2.8 which is close to 2.5. The 10W transformer is pretty big and heavy.

Don't get caught stealing the transformer from a school's gym. (smilie)

 

[MrDEB]

Locating a transformer may be difficult. Did a search and found one circuit with a transformer fed by a 555
**broken link removed**
Locating ??
Found several sties that talked about DIY a transformer. A 6-9 to one ratio. THEN they got into formulas and I am lost.
Contemplating the DIY approach as sound quality is not really a concern. Just the frequencies it will carry and amount of output.
I assume by reading, an air core is preferred?
Anyone wind their own transformers here? Just out of the clear blue thinking 100 turns of #22 copper insulated magnet wire with 800 turns of #22 magnet wire on a 1/2" cardboard tube??

 

[MrDEB]

found this circuit
Ultrasonic pest repeller
using a U coil ferrite 150 turns of 20swg and 40 turns of 24swg
now to find out what u coils are?

 

[MrDEB]

here is an interesting schematic

it claims 110db w/ 4a through speaker.
Maybe connect a transformer feeding the piezo and look out deer?!!
**broken link removed**

 

[Nigel Goodwin]

it claims 110db w/ 4a through speaker.
Maybe connect a transformer feeding the piezo and look out deer?!!

No, using a transformer doesn't increase power, it actually reduces power slightly.

But AG's premise is incorrect, a piezo tweeter isn't a particularly high impedance, while it is basically a capacitor it still requires power to drive it. According to the data on them they are about 60 ohms at 20KHz and 30 ohms at 40KHz (based on been about 0.13uF).

 

[MrDEB]

NOW I am lost

Use a transformer to increase the voltage or not?
The schematic here Ultrasonic pest repeller
uses a transformet to drive the piezo tweeter.
Here is an LT SPICE of the second schematic but using a 3 to one ratio.
NOW how to determine db watts etc.
going for a 9 to one ratio?
I want power but the tweeters are only rated for 50 watts.

 

[Nigel Goodwin]

Use a transformer to increase the voltage or not?

It increases the VOLTAGE, but decreases the CURRENT - the actual amount of POWER will be slightly less than you started with due to losses.

The schematic here Ultrasonic pest repeller
uses a transformet to drive the piezo tweeter.
Here is an LT SPICE of the second schematic but using a 3 to one ratio.
NOW how to determine db watts etc.
going for a 9 to one ratio?
I want power but the tweeters are only rated for 50 watts.

As a bridged amplifier off 12V only produces 16W maximum in to 4 ohms, that's not much of a concern. Assuming your amplifier will feed a 2 ohm load (doubtful for a bridged design) then it would theoretically provide 32W in to 2 ohms. Adding a correctly designed and built transformer would provide slightly less than those figures, at one specific frequency.

 

[audioguru]

Wait a minute!
Who says that the cheap no-name-brand piezo tweeter will survive 20V RMS continuously?
It is made to survive 20V RMS for brief bursts of high frequency music where the average is only 4V or less.
Maybe you should turn on the high frequencies to 20V only occasionally like in music.

 

[MrDEB]

BOY I am really getting LOST??
Where did 20volts come from? I missed it I think?
Heres what I have - a PIC that hopefully will output 15-20khz into an amp so the ultrasensitive hearing deer can hear it (deer can hear up to one mile away)
The pic will produce two different frequencies that are random (set one = 2-8khz) second set = 15-20khz)
not wanting automobile going down the road sounding like a bumble bee (2-8khz) the lower frequencies will be connected to a mylar speaker.
The second set of frequencies need amplification. The Piezo tweeters are 50 watt with 94db sensitivity? 3200-27khz frequency range. IF I fed the tweeter both sets of frequencies then thinking maybe run one set of frequencies w/ amp and the lower frequencies w/o amp. This way only one tweeter is needed.
Either way what to drive the tweeter with- push pull amp, 40W chip amp in BTL or amp with transformer to increase voltage??
Sounds like I am getting two different opinions or perhaps in my lack of knowledge of this subject= I am lost.
**broken link removed**

 

[audioguru]

BOY I am really getting LOST??
Where did 20volts come from?

I explained it a few times in this thread.
50W into 8 ohms is produced with a voltage of (the root of [50W x 8 ohms])= 20V RMS.
The cheap piezo tweeter has a sensitivity at a frequency where it peaks of 94dB at a distance of only 1m when its input is the voltage that produces 1W RMS into 8 ohms. 1W RMS into 8 ohms is a voltage of (the root of [1 x 8])= 2.828V RMS.

Nobody knows how many milli-seconds the cheap piezo tweeters will survive 40W or 50W continuously. They are made to play music that has an average power that is 1/10th to 1/20th of the max power that occurs at occasional peaks.

Since the tweeters do not have the manufacturer's name listed then they might not work or might not meet the very brief spec's.

 

[MrDEB]

If I intrepid your explanation correctly
At 50W and 94dB the output is 20v rms?
Then its questionable if the cheap tweeters I purchased will even sustain extended use at 20vrms.
Is there any method I can use to determine what these tweeters are capable of?
Planning on breadboarding the 2 transistor push pull circuit or the 4 transistor circuit and maybe go with it after I try it out on some deer , dogs etc.See what reaction I get
worst that can happen is POOF! or the wildlife run for cover.
contemplating an LED in series so if the tweeter blows then the LED should turn off.

 

[audioguru]

Your tweeters have incomplete spec's. Most speakers have their sensitivity measured at 1W into 8 ohms and at a distance of 1m.
Your tweeters produce 94dB at a distance of 1m maybe when fed 1W into 8 ohms which is 2.828V RMS.
Their sensitivity at 50W into 8 ohms (20V RMS) is 111dB at 1m and is 87dB with 20V RMS and a distance of 16m (52.5 feet). 87dB is not loud.

How far away will the animals be?

 

[Nigel Goodwin]

Heres what I have - a PIC that hopefully will output 15-20khz into an amp so the ultrasensitive hearing deer can hear it (deer can hear up to one mile away)

What makes you think 20KHz will travel any great distance? (because it doesn't), and what makes you think a barely audible tone will scare deer away in any case?.

 

[MrDEB]

As I mentioned, deer have a keen sense of hearing that can detect a noise up to one mile away with a keen sense of direction.
Being such a high frequency, I am aware that the sound will not travel far or at least we can't detect it but perhaps a deer can.
Studies have been done that show that a deer's best hearing range is 2-8khz but can hear ultrasonic tones as well.
My theory is to cycle randomly between 2-8khz but not to loud as humans can hear it (might sound like a bee going down the high way if it was really loud) then include the higher frequencies in random order as well to really confuse the deer and hopefully scare them away from the highway. Being a random sound MAYBE the deer won't become accustomed to the sound hopefully.
The unit for the garden would not include an amp as a PIR senses the deer presence up to 30 feet away but only at night.
At the beginning of this thread I mentioned a product on the market called THE HORNET that uses what I call snake oil to describe their product.
WAVE VARIANCE TUNING. Basically only one low frequency 5khz mixed with one high frequency (20khz) then bounced around in a tube before leaving automobile then bouncing off the road surface. Range stated is 700 feet.
Perhaps have the tweeter inside a tube to bounce around? I would think it would lose energy before it leaves the tube.

 

[MrDEB]

link to the deer avoidance system that uses WAVE VARIANCE TUNING (snake oil term IMO)
**broken link removed**

 

[audioguru]

"Wave variance Tuning" is simply buzz words they made up that don't mean anything. Bouncing sound off the road is simply ridiculous. The discussion about the Hornet has no technical details.

There are whistles that are attached to cars and the air blowing through them cause them to make a very loud ultrasonic sound that scares deer away from the highway.
Your cheap piezo tweeters cannot make such loud sounds.

I asked about what distance you need because when I was designing PA systems for outdoor stadiums the high frequency boost was determined by the air's humidity and wind speed (high frequencies are actually blown away). But the distance from one side of a stadium where the speakers were was pretty far away from the other side of the stadium where the listeners were.