You don't want to go with a lower speaker impedance. You want higher impendance.
32Ω or 600Ω would be nice.

Try putting a 33Ω resistor in series with your 8Ω speaker.

Edit: Try putting a 470Ω resistor in series with your 8Ω speaker. Add a 10μF capacitor across the speaker.
The reason the tone in the video sounds acceptable is because you are listening to high frequency tones. The harmonics are pushed out of the range of normal human hearing. At lower frequencies the harshness of the odd harmonics is more pronounced.

 

Look, I'm listening, I'm just replying to everyone while working, when I can. I have like 5 different types of amp chips, so I guess I need to find schematics for those. The point I am trying to make is the dude in the video I posted above is the exact same circuit and his works pretty clear tones. The power supply is a variable switching power supply but I get same results with 9 volt batteries. I will try the suggestions when I get home, just don't understand why I have a different outcome than the video. Also I tried a 4 ohm speaker and it's trivaly the same result

You can edit the audio in a video. Replace the circuit output with a clear tone. Just saying. That’s why it’s important to test.

 

his works pretty clear tones

If the waveform shown in post #16 is actually that of the generated tone then it is not a clear tone, it is a highly distorted one. But if that sounds ok to you, then fine. I think it would sound unpleasant to most people (apart from pop guitarists )

 

Do you have a bipolar 555 which is NE555 or LM555? Its datasheets say its output high with a 200mA load is the supply voltage minus 2.5V. If you have a VERY powerful 9V battery then 9V - 2.5V= 7.5V and across an 8 ohm speaker causes an output current of 940mA that can destroy the 555 and maybe also destroy the speaker. The LED with no current limiting will also cause a very high output current that can also destroy the 555 and maybe also destroy the LED.

Maybe your speaker produces the high frequency harmonics of the squarewave distortion better than the cheap speaker in the video. The squarewave output from a 555 is not the waveform shown in the video, instead it is the sound of a buzzer.

The datasheet says the output of a 555 can go to higher than 500kHz but since the frequency-determining capacitor is very high at 47uF then most of the adjustment range of the frequency pots is much higher than you can hear, down to a POP every 2 seconds.

 

I did not watch the entire video. Everything you need to know about the circuit is there in the first 3 seconds.

The sound in the video is *not* clean. It is a variable duty-cycle rectangular wave, a version of a square wave. The vast majority of the frequency change as he sdjusts the circuit comes from varying the pulse width of 1/2 of the output square wave, while the other half of the wave changes much less. This is a consequence of the standard 555 astable oscillator circuit. So what you actually are hearing is a chord made up of two different fundamentals, one changing a lot and one changing a little, and lotsa harmonics. At low frequencies, the output is close to a true square wave; at high frequencies, it is not.

Compared to a true sine wave, this signal has massive distortion. OTOH, a severely clipped sine wave (which is what a square wave approximates) is the genesis of the "Fuzz Box" and world of guitar effects pedals.

Note that his speaker /microphone / recording system has a limited bahdwidth that is coloring the tonal characteristics of what you are hearing.. In person and with a better speaker, the signal will sound much more gritty and brittle.

And, a true square wave would sound better. The datasheet for the CMOS version of the 555 has a true square wave astable circuit. That circuit also works with the standard, bipolar 555.

There are other problems with the schematic and with the comments in the video, (note: there is no decoupling capacitor across the 555) but this is a start.

ak

 

Do you have a bipolar 555 which is NE555 or LM555? Its datasheets say its output high with a 200mA load is the supply voltage minus 2.5V. If you have a VERY powerful 9V battery then 9V - 2.5V= 7.5V and across an 8 ohm speaker causes an output current of 940mA that can destroy the 555 and maybe also destroy the speaker. The LED with no current limiting will also cause a very high output current that can also destroy the 555 and maybe also destroy the LED.

Maybe your speaker produces the high frequency harmonics of the squarewave distortion better than the cheap speaker in the video. The squarewave output from a 555 is not the waveform shown in the video, instead it is the sound of a buzzer.

The datasheet says the output of a 555 can go to higher than 500kHz but since the frequency-determining capacitor is very high at 47uF then most of the adjustment range of the frequency pots is much higher than you can hear, down to a POP every 2 seconds.

its a NE555. I see what you are saying. So lets start over. what is a good schematic to get 15khz with an 8ohm speaker? All in all that the end goal for this part of the project.

 

what is a good schematic to get 15khz with an 8ohm speaker?

Questions. Can you hear 15Khz? Why 15Khz?

 

Question. Can you hear 15Khz?

yes, im not that old. to be fair, even if I couldn't, it would not matter.

 

So what's the purpose of the circuit?

 

So what's the purpose of the circuit?

its part of a bigger project, and im stepping into learning audio circuits. I am focusing on this current goal.

 

You cannot drive the loudspeaker directly from the 555-timer.
Use a transistor to drive the loudspeaker.

 

The maximum safe output current from an NE555 is 100mA or 200mA. Then the voltage level into an 8 ohm speaker must be limited to 200mA x 8 ohms= only 1.6V peak. The power into the speaker is only 200mA x 1.6V= only 0.32W peak which is not loud and probably not loud enough. A power amplifier is needed if more power (louder from the speaker) is needed.

If a capacitor is not coupling the output from the 555 to the speaker then the pulses from the 555 are DC which unbalances the speaker, its cone does not normally move back and forth, instead the DC pulses cause the cone to move only back or only forward.

Many speakers have a resonance at a low frequency and a peak at a few kHz then the output level drops at higher frequencies. For 15kHz you must use a tweeter but it is fragile and its power must be momentary or limited if it is continuous.

The squarewave from an NE555 sounds like a buzzer. A smooth tone is a sinewave. Many different circuits produce a sinewave.

edit: 15kHz is lower than the highest audio frequency of 20kHz. Old people like me (76 in 3 weeks) cannot hear above 2kHz without my hearing aids.

 

its part of a bigger project,

To get appx 15Khz remove the two pots, install a 47K resistor in their place and change the 4.7uf cap to a 1nf or .001uf.

 

The maximum safe output current from an NE555 is 100mA or 200mA. Then the voltage level into an 8 ohm speaker must be limited to 200mA x 8 ohms= only 1.6V peak. The power into the speaker is only 200mA x 1.6V= only 0.32W peak which is not loud and probably not loud enough. A power amplifier is needed if more power (louder from the speaker) is needed.

If a capacitor is not coupling the output from the 555 to the speaker then the pulses from the 555 are DC which unbalances the speaker, its cone does not normally move back and forth, instead the DC pulses cause the cone to move only back or only forward.

Many speakers have a resonance at a low frequency and a peak at a few kHz then the output level drops at higher frequencies. For 15kHz you must use a tweeter but it is fragile and its power must be momentary or limited if it is continuous.

The squarewave from an NE555 sounds like a buzzer. A smooth tone is a sinewave. Many different circuits produce a sinewave.

edit: 15kHz is lower than the highest audio frequency of 20kHz. Old people like me (76 in 3 weeks) cannot hear above 2kHz without my hearing aids.

ok, can you recommend a diagram thats not over complicated and can run indefinitely. The speaker I am using produces 15khz, no problem

 

Is the speaker just for learning purposes or is it also part of this "bigger project"?

 

 

Is the speaker just for learning purposes or is it also part of this "bigger project"?

Its a full range speaker and even though its a salvaged speaker. its expensive and part of the project.

 

View attachment 244495

thank you for this but what is connected to pin 2 and 7?

 

Connect pins 2, 6, and 7 as you would for 555-timer astable oscillator.
What is not shown in the diagram is the mandatory power supply decoupling capacitor from Vcc to GND.

 

Mr Chips, your circuit with the 555 and transistor is for a DC motor or a lamp, not for a speaker that is made to be driven from AC, not DC.