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Simple, speaker question. Answered


All I want to do is create a very low, and reasonably audible hum or drone from this speaker ; about as loud as a person humming as hard as they can before their throat hurts and they start coughing.

Is it possible to avoid an amplifier and just run a voltage into it so that it just makes a single tone as described ?

If so:

I found this big broken speaker in the road.
As you can see, the Cone is missing a section, but the surround and spider are intact.
The cone is credit card thickness plastic.

Is it feasible to just patch it up with some similar plastic and contact adhesive; it does not have to be a good sound, just a drone.

I realise that my grasp of electronics is child like and readily accept the impending abusive comments and links to the Google homepage.

Thank you 



Can't resist... just can't resist it... http://www.lmgtfy.com/?q=how+to+fix+a+speaker+cone

OK, now that it is out of my system, yes, you should be able to run the speaker without an amp, just be sure that you don't push whatever device you are playing the sound through too hard, as it could damage the device (without an amp, the sound will not be too loud).

HaHaHa awesome dude
can't stop laughing atm
Keep up with the good work(teaching them how to google) ;) :)

lmgtfy is what you use when you have just put in your 2-weeks notice and your boss asks you a stupid question. (Or when the OP makes a big deal about something that is actually a good question.) ;)

Dear Thegeeke,

Thank you resisting as long as you could before posting the inevitable LMGTFY link. . . I understand.

But I don't think that I explained myself well;

I am not asking if I can feed a device directly in ( I know that would be quiet and possibly damage the device) . . I am asking if I could forget the device, forget the amp and could I pass a certain voltage, current  through it and directly create a very low rumble of reasonable volume.( it is not music that I am after, just a low hum); I read that DC would not work.

As regards to the LMGTFY
. . most sites show how to repair a split or a small hole but the hole in mine is 4" by 5" and the cone is made of plastic;.

I want to spend no money or time and just wondered if stick on a lump of plastic from an old lid, ( which would I understand would be no good for most peoples needs but I only need a hum), would it work assuming that the whole direct feed thing was possible in the first place.

Steveastrouk has answered that part..

Thanks for the advice.

Kind Regards


Gotchya now. :) I believe that if you put DC in, it will work, but you need a way of changing the voltages. In reality, audio signal is DC, but the voltage is constantly changing. If you found a way of causing that voltage to have a slight variance, it would (in theory) result in a noise of some sort (probably a hum if there is only a small variance). At least that's what I am theorising... I'm not an EE, but I do audio work, so that's my guess. :)

I understand exactly what you are looking to do, that is, to make some sort of "noise" without going through the hassle of an actual audio amp or some sort of signal generator. It is actually quite easy to do. But first, a bit of background:

Speaker "drivers" (that is what you have, speaker actually refers to the whole system including - minimally - the driver and enclosure) work by moving back and forth to create pressure waves in the air that we hear. Usually, this is accomplished by the application of an AC voltage and current to make the magnetic motor (voicecoil) move in first one direction, then in the opposite direction. DC voltage and current will only move the motor in one direction until it hits it's physical limit and then it will hold it there until power is removed or the voicecoil burns out.

AC can be described as 2 DC "sources", but of opposite values. Think about it this way; if you place one DC source back to back to a second, but opposite polarity DC source, you have a reasonable facsimile of AC. Also, AC can be simulated by pulsing a single polarity DC source, in a fashion called Chopping. This is important , and you'll see why next.

You can create a mechanical Chopper by placing a pair of contacts on a board, to which you connect the battery positive (+) to one contact and the speaker positive (+) to the other contact. Now connect the speaker negative (-) to the battery negative (-) and that part of the circuit is finished. Next cut a circle out of some sort of nonconductive material, such as plastic or wood, mount a length of bare wire, long enough to more than cover the total length of the contacts on the board,  to one side of the circle. Mount the circle to a small motor (pager or cell phone motors are great for this) and then mount the motor to the board so that when the circle spins, the wire drags across the contacts once every revolution. You now have a mechanical chopper. Varying the voltage and current will vary the speed of the motor, which will change the frequency (pitch) of the sound coming from the speaker.

To vary the loudness of the speaker, change the voltage and current capabilities of the speaker battery. More of each (voltage and current) will change the loudness. Try not to go overboard, though, as you could cook the voicecoil if too much is applied.

Lastly, never let the wire on the circle stop on the contacts. This will allow DC to flow through the speaker uninterrupted. Minimally, it will drain your battery, at worst, it could burn out the voicecoil and then you will need another driver.

I hope you can enjoy this really old device that was in widespread use before the advent of the Vacuum Tube.

The knowledge of history strikes again!


Dear Quercus austrina,

This is why I love Instructables; a perfect answer, thank you.

I now have looked up Chopper circuits and will give this a go.
I'm a fan of clunky, mechanical solutions like this.

Kind Regards


By the way, to "fix" the cone enough to be useable for your particular purpose, all you would need to do is mend the broken part with some glue and some reinforcing bits of plastic to keep the torn edges together. Then find some stiff plastic, like a large plastic lid from a throw away conatiner, that you can cut to cover the top of the cone, all the way, at the inside edge of the black foam surround. That will stiffen everything up and give you a contiguous surface to push the air around.

Show us what you've come up with when you finish the project.

Have fun!

Dear Quercus austrina,

Thanks for the extra info.
I will mend it tonight.

I couldn't help but try the circuit immediately after reading your original answer.
I used a 9v battery and just flicked the wire as fast as I could on and off the circuit.
It worked; obviously slow compared to how it will be with a motor driven circuit and relatively quiet but  not a particularly low sound.

It will, of course improve, when I have followed your cone fixing  instructions.

I didn't dare look up the word ' vibrator"., for the  same reasons.

I will gladly show the finished project  (if I achieve a low, loud hum).

. .. and I may pester you again.

Kind Regards


Yessireebob, you've got it! Goes by lots of names, but the 2 we gave are the most common. And this is probably the easiest one to understand by someone with little to no electronics experience. Real easy to envision how to build and how it works. (Although, if he put "vibrator" in a search box it could potentially be a real eye opener - hehe. I'd put in "electronic multivibrator circuit" to exclude those, ahem, risque results)


You could connect the centre of the cone to ANYTHING and make it shake - a door, a wall, a piece of wood. There's nothing magical about speakers, only that they are compact and optimised for what they do.

Since you have admitted to having limited understanding of electronics, I will try to make this simple.

You can get a 60 HZ hum on the speaker by using a step down transformer. 12v 5 amp should get some sound, but I don't know how loud.

Another thing you might want to try experimenting is wiring the speaker in SERIES with  a 75W or  100W  light bulb.

Also. if you have an automobile alternator  you could take the diode
assembly out and attach the speaker to one of the 3-phase legs
and drive the alternator with an electric motor and make
all kinds of various tones depending on how fast the alternator
is spun
What I have stated is for informational purposes only.
If you choose to try anything I have suggested above, it is at your
own risk.

12V5A would make a potentially deafening roar, fifty watts of bass is quite a lot before getting into audio-amp stuff.

I think you are right. I was only thinking about
how much power the speaker could handle
and not about how loud it would actually be.

Thanks for the warning . I hope F.O.H.
reads this.

Any one who tries this should probably be wearing ear plugs
and give fair warning to other occupants of the building
that they are in.

It might make a winning instructable though:
"The McGyver Audio Bomb"

Dear RavensCraft,

Thanks for the explanation.
The warning has been noted.

"The McGyver Audio Bomb" sounds interesting.


The broken part is nothing to do with making a sound - it's decorative.

I think there is something I am missing here.  I am wondering what is the source of your "a voltage" which you want to "just run into" this speaker?

Perhaps you were thinking of just plugging it into the AC mains power? Or through a transformer connected to mains power?  Doing this would give a 50 or 60 hertz tone, depending on what the frequency of the mains power is where you live.

If that is what you were thinking, I am going to ask you to consider this formula:
P = V*I  =  V*V/R = V2/Z
(See http://en.wikipedia.org/wiki/Ohm%27s_law)
Where V is RMS voltage across the speaker, Z is impedance, and P is RMS power.  Supposing V = 25 volts RMS and Z = 4 ohms.  That gives P = 25*25/4 = 156.25 watts RMS, which is little less than 160 watts, which is the maximum this speaker can withstand, according to the little number printed on it.

Sort of the story here is that if you want to drive this speaker with mains power, you do not want to connect it directly to the mains, which is, I think, something like 220 volts RMS, at 50 hertz, in your country. 

However if you can find a transformer
intended to step the 220 VAC down to something like 6 or 12 VAC (both less than 25 volts), then I think you could connect the secondary from that transformer directly to your speaker, and it wouldn't damage the speaker, although it might damage the transformer since 4 ohms is kind of a big load.  Again you'll have to use ohms law to answer the question of how much current is flowing, how much power, etc.

BTW, even if this works, I think the sound ( a 50 Hz tone) is going to be annoying to listen to, but I dunno, maybe that's the whole point.

The usual trick for driving a speaker with a loud pure tone, is to use a function generator and an amplifier.  That way you have controls, essentially "knobs you can turn",  for both frequency and amplitude.