# How can I make a speaker "kick" air?

Hi

I am new to the world of arduino. I am doing a project were I need to control a speaker unit. I need to make the speaker cone move at a low frequency, so that it makes one “kick” of air.

The speaker I have is a woofer speaker: 50 Watts 4 ohms

Anybody know what I need to do this or know of a similar project with a guide.

Start by determing the real electrical (and mechanical) parameters of the speaker. 4Ohm 50W tell you absolutely nothing of value. Next step would be to measure and graf the relationsship between current and excursion. After that you can model upp a controlled current source that pulls the membrane back to its maximum position, flips the polrity of the current and then releases it.

nilton61: Start by determing the real electrical (and mechanical) parameters of the speaker. 4Ohm 50W tell you absolutely nothing of value.

I'm not sure I know what you mean.

You may have to do a lot of empirical testing.

Are you trying to make a vortex ring device using a speaker? I'm working on that, too. I'm not going to type in loads of stuff until I find out what it is you are trying to do.

Like any speaker system, you have to isolate the front from the back. The out-of-phase "wave"from the back of the speaker comes-around to the front at the speed of sound, and it will tend to cancel the sound (or wave/impulse) from the front. A large sealed box can be used, or maybe you can use a "tuned" ported box, or a long pipe.

A bigger speaker will move more air, as will a speaker with a larger X-max.

Power (Watts) is calculated as Voltage squared/Impedance. 15 VDC will give you slightly more than 50W. But, speaker ratings can be tricky. A 50W speaker should be able to handle the bass from a 50W signal (which is most of the 50W), but a 50W amplifier playing undistorted music at full volume is only putting-out an average of around 5W. You speaker can probably stand short 50W pulses, but it will probably burn-up with 50W constantly applied for several seconds.

A square wave (or DC suddenly applied) has a high-frequency component and a low-frequency component. A woofer can't produce high audio frequencies, but it can produce mid-frequencies. So with DC, you'll get a more of a "click than a "thud". If you wan't a particular sound, you'll need to use an audio amplifer and probably a few cycles of a low frequency sine wave.

polymorph: Are you trying to make a vortex ring device using a speaker? I'm working on that, too. I'm not going to type in loads of stuff until I find out what it is you are trying to do.

Yes it is a sort of vortex cannon. It is a speaker mounted on a tube. I’m trying to make a different way to give tactile feedback.

I’m trying to make a different way to give tactile feedback.

A big speaker into a smaller diameter pipe will act as a nozzle to increase the velocity of air flow. That should make it easier to feel a "puff" of air. But a nozzle also tends to choke-off the flow, so you can over-do it and it might give you less "kick" and more "puff"... I think it's going to take some experimentation.

An 8 inch speaker with an 8 inch pipe and a choke at the end of the pipe down to about 3/4 the size of the pipe should give you a vortex ring that can travel long distances.

Check Youtube for videos. I cannot access it from work.

Thank you for all the feedback. But I'm not having problems with how to construct the device, that is not the problem. The problem is that I don't know how to drive/power the speaker from an Arduino board.

Connect the speaker to a H-bridge controlled by arduino.

Have a PWM signal pull the membrane to its outermost position (the value must be experimented) When the position is reached reverse the voltage and give full voltage long enough to give a decent “kick” but short enough not to damage the speaker,

I agree with nilton61, with the caveat that you'll need a PWM with a frequency much higher than the default, though. High enough that the speaker won't move, except to move from "zero".

As as the speaker is DC connected as shown in the schematic it will. The magnetic for will be proportional to the average DC-component which is not equal to zero. The real caveat is more likely damaging the speaker.. No smoke, no fire

I mean the Arduino default analogWrite frequency is fully in the audio band. In fact, well within the bandwidth of a woofer.

http://arduino.cc/en/Reference/analogWrite

analogWrite()

Description

Writes an analog value (PWM wave) to a pin. Can be used to light a LED at varying brightnesses or drive a motor at various speeds. After a call to analogWrite(), the pin will generate a steady square wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite() on the same pin). The frequency of the PWM signal on most pins is approximately 490 Hz. On the Uno and similar boards, pins 5 and 6 have a frequency of approximately 980 Hz. Pins 3 and 11 on the Leonardo also run at 980 Hz.

So you will hear a short sound just before the kick. You may even use this sound to determine the level. Make a experiment where you increase the duty cycle until the sound distorts. That would be the maximum "pull" befor you reverse and "kick"

What do you think happens when you feed a 490Hz signal into a speaker? For 50% duty cycle, it will respond as if it had a DC bias of 2.5V... with a 2.5Vpeak 490Hz square wave. Kind of defeats the purpose of smoothly pulling it back and letting it go when the speaker is flying back and forth between zero and full excursion (by full I mean the max it will move at 5V).

How will you tell when the "sound distorts"? What does a square wave sound like when it distorts?

You will definetely hear the speaker hitting it limits

Yes, you'll hear it hit the limits as it roars at you at 490Hz. Hardly what you need to create a vortex ring or "kick" of air.