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winchman
10-14-2006, 09:21 AM
Specifically, what will happen if I connect the output from a plug-in AC to 4.8-volt 50ma DC converter to the terminals of the speaker from a portable radio?

Roger

nheng
10-14-2006, 09:26 AM
At first, the speaker cone will pop toward you or away from you, depending on the polarity of your connection. In time, you may release magic smoke from the power supply as the speaker has very low dc resistance (pretty close to a short circuit).

If the power supply were capable of more current, then the magic smoke would come from the speaker voice coil instead, burning varnish and twisting out of shape.

Den

Todd Tolhurst
10-14-2006, 09:37 AM
You'll hear a 'click' from the speaker, and there's a good chance you'll ruin the DC supply.

Lew Hartswick
10-14-2006, 09:39 AM
Thats a very good description . :-)
...lew...

Evan
10-14-2006, 09:55 AM
Roger,

Why?

winchman
10-14-2006, 10:00 AM
A rapid clicking sound is what I'm after, but I don't want to see any magic smoke.

The converter is normally used for charging a battery pack. So, it seems like it would be OK to run the output from the converter through the speaker coil in series with the battery. Would that damage anything? Maybe adding some resistors in the circuit, and removing them in stages?

I can't think of any way I can accurately measure the voltage that's normally on the speaker coil when it's in use, or I'd just do that.

Roger

Evan
10-14-2006, 10:38 AM
Ohm's law will do. Look on the speaker. It will usually be marked as to dc resistance such a 8 ohms or 3.2 ohms. Many will also be marked for wattage such as 0.1 watts for a small cheap speaker.

With that you can then calculate the current needed to produce no more than 1/10 watt. P (Wattage) = I*E (I is current, R is resistance, E is voltage[Electromotive force]). Assuming 8 ohms, to produce 1/10 watt we calculate I=P/R which equals .0125 amps. If you have a known voltage to start with such as 5 volts (close enough but there is a gotcha to deal with, later on that) then we use Ohm's law to solve for the total resistance required to limit the current to .0125 amps maximum. R=E/I .

This gives 5/.0125 or 400 ohms total resistance. We don't need to be exact here so any resistor at least that large or a bit larger will do.

The gotcha: Small wallwart power supplies are not usually regulated and will often produce considerably higher voltage than the rating when they are lightly loaded. In that case it is necessary to measure the actual output voltage and plug in the actual voltage measured to calculate the required resistance.

CCWKen
10-14-2006, 10:44 AM
You won't get rapid clicking unless the DC converter is doing a poor job of converting.

If you know the orignal max output to the speaker(watts) and you know the speaker resistance(ohms), you can calculate the max volts to the speaker.

Volts = Square Root(watts - ohms)

Evan
10-14-2006, 10:54 AM
Roger,

You won't be able to run the speaker in series with the battery being charged. You can put it in parallel using an appropriate resistor in series with the speaker. It won't make any clicking unless the charger operates by turning the voltage on and off as some do. If you need clicking with a supply around 5 to 6 volts then you could put an ordinary flashing six volt mini christmas light bulb in parallel with the speaker/resistor combination. This would give a flashing light as well as produce a click each time it turned on and off.

smagovic
10-14-2006, 11:30 AM
Ohm's law will do.

P (Wattage) = I*R (I is current, R is resistance). .
Evan, I think you wanted to say that I * R is voltage. Voltage * current is wattage. Take care. Vic

topct
10-14-2006, 12:02 PM
"A rapid clicking sound is what I'm after, but I don't want to see any magic smoke."

What about a little 555 timer curcuit?

They can run at very low voltages and you could adjust it for the rate of click you want.

I don't have one, but I bet there is something out there.

Evan
10-14-2006, 01:24 PM
Evan, I think you wanted to say that I * R is voltage. Voltage * current is wattage. Take care. Vic

That's what I get for posting something before I have had my morning coffee. Thanks Vic.

10-14-2006, 01:57 PM
http://i68.photobucket.com/albums/i17/mscientist/hsmschP.jpg

http://i68.photobucket.com/albums/i17/mscientist/hsmpcbP.jpg

jmm360
10-14-2006, 07:16 PM
I thought speakers were rated for impedence at some frequency like 1khz, not DC resistance. If that's the case an 8 ohm speaker might look almost like a short circuit to a DC supply. Any battery should be able to click your speaker in or out but I wouldn't do more than just click it.

nheng
10-14-2006, 09:29 PM
Jmm360, That's what I thought too ... for the past 40 years until this morning !

The IEC has a standard which defines how LOW the impedance can DROP, all the way down to DC where it is, of course, resistance. The magic number is 80%

Thinking, yeah sure, I bet every Chinese speaker meets this, I took out some 40 ohm equipment speakers from Mouser that I bought a while ago. They measure 32 ohms so I am a believer ... sort of. I'm sure I've worked on larger, higher wattage speakers where the resistance was much lower than the impedance, but won't swear to it anymore ;)

Den

Evan
10-14-2006, 09:37 PM
8 ohm and 3.2 ohm speakers are always very close to that value on DC. Been measuring them for the last 45 years and it hasn't changed yet.

mikem
10-14-2006, 10:28 PM
I use a 9V battery for testing speakers all the time. When wiring a new house for ceiling speakers, the 9V battery is easier than hooking up the stereo to make sure that they work. Only very short touches or smoke will escape from the speakers.

The voltage applied to a speaker is determined by the wattage of the amp. Some of my amps put out 40 volts. I have gotten some stinging shocks from holding a 1/4" phone plug while kneeling on the damp grass running speaker wires for live events. Thanks--Mike.

nheng
10-14-2006, 11:39 PM
Way back, I built a discrete stereo power amp based loosely on an RCA power transistor app note. It was somewhere around 120 watts per channel and had +/- 40 volt power supplies with significant storage capacitance. Due to a minor er-hem, design flaw, it quickly and silently destroyed a set of AR speakers. Can't understand why those ARs couldn't handle 3MHz oscillation at about 40 volts RMS :D :D A \$0.20 mod fixed the feedback problem but the speakers were toast. Learned the value of scopes and dummy loads real fast :eek:

Shaidorsai
10-15-2006, 12:43 AM
You did not say why you wanted "pops" or at what rate. There is a very cheap and simple timer Integrated Circuit called the 555. With a 555 chip and very few additional cheap components it is possible to throw together a circuit that will generate short electrical pulses at any rate from 1 pulse per hour or more, to many thousands of pulses per second, or anywhere in between. You can easily make the pulse repition rate variable over quite a wide range. This circuit can be battery operated or operate off a dc wall-wart. A very neat and useful little circuit device. Google "555 Timer IC" and thousands of circuit applications will pop up. You can drive the speaker through an audio transformer to isolate the circuit and provide a perfect match between the IC and the speaker, thus assuring long life to both the wall wart and the speaker. I'd say you could build a satisfactory circuit for between \$5-10, lots less if you have a friend with an electronics junk box. I have a nice simple little 555 metronome I built over 15 years ago that is still going strong

Later - see the circuit diagram that Mad Scientist posted. That's a 555 Timer circuit. One of many.

Evan
10-15-2006, 01:12 AM
Fellows, Roger is an excellent machinist but the fact that he is asking this question leads me to believe that electronics is not his strong area. I think that the simpler the solution the better.

Roger, it would be helpful if you would describe in greater detail just what you would like the speaker to do.

winchman
10-15-2006, 11:48 AM
Well, I found an old speaker marked 16 ohm. I hooked it up in series with a 330 ohm resistor,and hooked that up to the 4.8 vdc output from the wallwart. I got a soft 60-cycle hum. It got a little louder with a lower value resistor, but even with the wallwart hooked directly to the speakers, it's still not very loud.

What I'm looking for is something that sounds like walking on dried acorns-- sort of a crunching-popping sound. What I'm getting from the wallwart/speaker is nowhere close in volume or pattern.

At least no magic smoke escaped from anything. I think I'll try another approach that's more mechanical, maybe some loose hardware in a revolving can.

Thanks for the suggestions.

Roger

Guido
10-15-2006, 04:46 PM
Reading between the lines, sounds like Roger is rigging up something to be placed in the bushes, so's when the kids, they coma 'a trick-or-treating.

His next thread will include questions regarding quick start/stop of a buzz box stick welder going to ground thru a carbon rod. Lotsa flashes, etc especially in front of a mirror, or two? Saw one one night, laying in a wet flower bed, dancing/bouncing all around---------fire--smoke----

Just musing--------

G

topct
10-15-2006, 04:55 PM
The sound in Windows that you hear when you clear the recycle bin, if made into a loop and sped up a touch?

10-15-2006, 05:22 PM
Something mechanical. Hmmmm. Ok how about a small concrete mixer with a hand full of stones in it? Then toss in some bubble wrap.

RobDee
10-15-2006, 10:19 PM
Ohm's law will do. Look on the speaker. It will usually be marked as to dc resistance such a 8 ohms or 3.2 ohms..

Geeze!

Speakers aren’t measured in resistance. The value marked on the speaker is its NOMINAL IMPEDANCE.

The formula is XL=2pifL for inductive reactance.

nheng
10-15-2006, 10:41 PM
RobDee, you are correct but the dc resistance is still pretty close to nominal impedance, with lower limit of 80% per IEC. At other frequencies, the impedance is a crap shoot. And, that 8 ohm speaker could be 16 ohms, 24 ohms or even higher at some frequencies, lower at others.

If you amp were ac coupled, you wouldn't even care much as to what the dc resistance was. With most modern amps being dc coupled, you still may not care much except when looking at short circuit currents and safety ratings of components in output stages, power supplies, etc.

Looking at figure A in the following link, it's clear that some speakers aren't going to follow IEC recommendations either. The impedance is all the way down to 3 ohms at 20hz and looks like it probably goes even lower. This is for a speaker marked as 8 ohms. Add an enclosure and cross-over network and it all changes.

http://www.churchsoundcheck.com/imp1.html

As I mentioned, a fairly new, 40 ohm speaker measured 32 ohms for dc resistance, so in this case it did meet IEC. For most purposes, though, this is irrelevant.

Although its fun discussing, none of this helps with Winchman's sound effects.

Den

darryl
10-15-2006, 11:51 PM
Speakers generally do measure with an ohmeter pretty much what the rating printed on it says. In use, as Den said, the impedance can and does vary all over the place. It's not unusual for an 8 ohm speaker to show an impedance of 20 or more ohms at certain frequencies. Completely irrelevant to your intended application though.

As far as using the speaker and a power pack to make crushing acorn type sounds, you might try rigging up a pair of nails that stick out horizontally from a block of wood, then wire them up with the power pack and the speaker such that if you shorted the nails, the circuit would complete and the speaker would click. Then sprinkle carbon granules from a carbon filter down onto the nails. As they fall between the nails and make intermittent contact there will be a sound somewhat like what you're looking for. Drop little pinches of granules at a time and it might sound like someone walking across frozen leaves- some experimentation would be required, such as the spacing of the nails, etc. Collect the granules for re-use.

Maybe make up a 'pen' which has the pair of nails sticking out the front, wire it up the same way (in series with the speaker and the power pack) and then intermittently dip it into the container of granules. Maybe use a dip and drag motion.

Maybe forget the nails and just use bare wires, and maybe forget the granules and use a tray full of small steel balls. You'll definitely get a repeating clicking type sound depending on your technique.

Just some ideas.

Evan
10-16-2006, 12:12 AM
Geeze!

Speakers aren’t measured in resistance. The value marked on the speaker is its NOMINAL IMPEDANCE.

The formula is XL=2pifL for inductive reactance.

They are when you use an ohm meter. Works too.

winchman
10-16-2006, 03:17 AM
The suggestion of a concrete mixer got me to thinking about using a geared motor from a rotisserie to drive an old pot with some unevenly spaced paddles inside. I'd put an assortment of loose hardware in the pot. The uneven spacing and bouncing of the hardware would give a random pattern which would probably be loud enough for my purpose.

I'll go by the local second-hand shops to see what kind of big pots they have and what sound I can expect from the hardware falling around inside. I might even find an old rotisserie motor, too. One that runs on low voltage or DC would be good.

Roger

Evan
10-16-2006, 08:53 AM
Clanking chains. That shouldn't be too hard.

RobDee
10-16-2006, 09:38 AM
“Ohm's law will do. Look on the speaker. It will usually be marked as to dc resistance such a 8 ohms or 3.2 ohms..”

No Evan. This is your statement and you’re simply wrong. Speakers are not rated, usually or otherwise, in DC resistance and the value on the speaker is not DC resistance but impedance.

The reason I gave the formula for inductive reactance is because as the freq. goes up the impedance goes up.

So we can have an 8 ohm speaker that measures 6.2 ohms resistance but is labeled 8 ohms.

Secondly the only way to measure low resistance is with the four wire method. So using a non four wire meter, especially one without zeroing capability can vary low resistance readings tremendously. Most hand held meters are not four wire and do not have a zero fuction.

The above example was in fact measured with the four wire method. The impedance measured with a meter, also four wire, that allows varying the frequency gives an 8 ohm impedance reading at about 2 khz.

The difference in the resistance and the impedance is about 22.5% quite a lot and this is with meters designed to make low readings not hand held instruments with less accuracy.

RobDee
10-16-2006, 09:58 AM
RobDee, you are correct but the dc resistance is still pretty close to nominal impedance, with lower limit of 80% per IEC. At other frequencies, the impedance is a crap shoot. And, that 8 ohm speaker could be 16 ohms, 24 ohms or even higher at some frequencies, lower at others.

If you amp were ac coupled, you wouldn't even care much as to what the dc resistance was. With most modern amps being dc coupled, you still may not care much except when looking at short circuit currents and safety ratings of components in output stages, power supplies, etc.

Looking at figure A in the following link, it's clear that some speakers aren't going to follow IEC recommendations either. The impedance is all the way down to 3 ohms at 20hz and looks like it probably goes even lower. This is for a speaker marked as 8 ohms. Add an enclosure and cross-over network and it all changes.

http://www.churchsoundcheck.com/imp1.html

As I mentioned, a fairly new, 40 ohm speaker measured 32 ohms for dc resistance, so in this case it did meet IEC. For most purposes, though, this is irrelevant.

Although its fun discussing, none of this helps with Winchman's sound effects.

Den

Den,
True, however even DC coupled amps aren’t running DC to the drivers. At zero signal the driver sees zero volts or very close to it. Inputs to amps with a DC bias would have that DC blocked and it would never be reflected at the driver.

And I’m not picking on you Evan, I think you’re an interesting person, just please, let’s approach accuracy.

Evan
10-16-2006, 10:04 AM
It works fine for identifying cheap speakers. Are you trying to start an argument? Note also that the original question was about feeding it DC.

RobDee
10-16-2006, 10:32 AM
It works fine for identifying cheap speakers. Are you trying to start an argument? Note also that the original question was about feeding it DC.

No, I'm correcting a wrong statement and that is the value printed on drivers, cheap or otherwise, is not DC resistance as you stated. It has nothing to do with the voltage being applied to the driver as right or wrong as that voltage might be for the device it is being applied to.

Look in any electronics catalog that sells speakers and tell me if you find one that lists the impedance as resistance even on three dollar speakers.

Evan
10-16-2006, 10:40 AM
It makes no difference for Roger's purpose.

RobDee
10-16-2006, 10:55 AM
It makes no difference for Roger's purpose.

Look if I said oranges grow on apple trees would you be argumentative in telling me I'm wrong? Of course not.

Giving erroneous information out doesn't help Roger either, then does it? Maybe in your world resistance and impedance don’t matter but in the world of electronics it’s apples and oranges.

Evan
10-16-2006, 11:05 AM
I didn't say you were wrong and the impedance makes not one whit of difference to what Roger is trying to do. You are trying to start an argument. Try elsewhere.

Todd Tolhurst
10-16-2006, 11:21 AM
We're talking DC resistances of several ohms here, not milliohms. For the purposes of this discussion, a four-wire measurement seems a bit excessive.

And since we are talking DC, inductive reactance doesn't play a role.

RobDee
10-16-2006, 12:08 PM
We're talking DC resistances of several ohms here, not milliohms. For the purposes of this discussion, a four-wire measurement seems a bit excessive.

And since we are talking DC, inductive reactance doesn't play a role.

First, we don’t know how many ohms, the driver’s impedance hasn’t been measured. We can take a simple handheld meter and touch the leads to gether with it set on the resistance scale and get several ohms displayed. My response to the statement about using a true four wire test was in response to the belief that there isn't any real difference in the resistance and impedance. There is.

Secondly, we don’t know about the power supply and if it is current limiting. Which, since it is for charging, may well be. We don’t know about the driver and its power handling capacity either.

Third, we may be talking DC but my response to Evan was about his specific statement as to the driver label. I don’t see the problem here. Let’s be correct in our statements, that’s all I’m saying. We wouldn’t tell someone using a file in the wrong direction is ok, would we?

Roger’s problem has to many variables. We don’t know, without testing, anything about the speaker or the supply. Running a battery in series with the speaker and supply as Roger states is not going to give him the result he wants regardless whether it will burn out the driver, supply or both. The best advice we could give is to find another solution to the problem.

I didn’t respond to Roger’s question because we simply don’t have a good answer that will help him. You can’t get a pulse train out of a DC supply so he won’t get the clicking he desires after the first and maybe, final ‘pop’. I believe this had already been well stated by others.

J Tiers
10-16-2006, 05:01 PM
Nheng.... here I is, ISP has been down........

an 8 ohm speaker is generally anywhere from a bit over 6 ohms to about 7.5 ohms "DC Resistance". You can figure out the approximate current at any given voltage from that. 4 ohm speakers are usually at least 3.4 ohms DCR, probably more.

The remaining impedance is made up of back EMF effect due to the speaker motion at whatever frequency the impedance was measured at. Typically that is something like 400 Hz (old) or possibly 1kHz.

The impedance varies all over. At resonance, an 8 ohm speaker may go over 50 ohms, depending on the enclosure.

At several kHz, the 8 ohm speaker may be as high as 12 to 20 ohms due to the inherent inductance.

As far as DC and speakers, it is generally bad for them if allowed to go on at too high a level.

But, I happily use a 9V battery for checking polarity of motion.... and old-time solid state car radios often pulled DC thru the speaker. So it isn't guaranteed speaker death.

If you want a clicking sound, that is another matter...... lots of ways.... but speakers tend to prodce a lower sort of "thunk" sound unless they are for higher frequencies.

I think I would consider recording the sound and playing it back as needed. We used to get a lot of halloween mileage out of tapes of opera recorded at 7 1/2 ips and played back at 1/2 or 1/4 speed.

if you want a neat squeal/raspy sound, kinda like a cicada, try a circuit thru the speaker (and maybe a resistor to limit current), completing the circuit thru an old coarse file and a nail. Run the nail down the file lightly, and you will get a speed-dependent raspy buzz as it bounces off the file teeth.

I suppose you could do it in time to footsteps if you were good.

Use an old file..... after you finish you will probably see why.

tesswalker
10-16-2006, 05:14 PM
It works fine for identifying cheap speakers. Are you trying to start an argument? Note also that the original question was about feeding it DC.

I don't think RobDee is "trying to start an argument". I think he was just pointing out that there is a difference between impedance and resistance which you clearly didn't understand.

I didn't say you were wrong and the impedance makes not one whit of difference to what Roger is trying to do. You are trying to start an argument. Try elsewhere.

I don't think RobDee is "trying to start an argument". I think he was just pointing out your incorrect statement, and made an attempt to help educate you on the difference between resistance and impedance.

We all know you love to have pointless debates, so I'm puzzled why you don't want to debate your your incorrect statement this time?

Tess

Evan
10-16-2006, 05:35 PM
You could always download a few wav files and string them together in the computer. Then either play them there using looping or make a tape from the audio output.

Evan
10-16-2006, 05:40 PM
I don't think RobDee is "trying to start an argument". I think he was just pointing out your incorrect statement, and made an attempt to help educate you on the difference between resistance and impedance.

I said ohms law will do. And indeed it will.

I used to repair professional hi fi and stereo equipment for Pacific Stereo and Hi Fi in Berkeley. I was paid the amazing amount of \$750 per month in 1967 because pay was determined by the amount of repairs you were able to do instead of a set salary. In those days a good wage was \$100 per week.

Don't presume to lecture me on what impedance means.

tesswalker
10-16-2006, 06:12 PM
I said ohms law will do. And indeed it will.

You're correct. Using the claw side of a hammer to bang in nails will do too. It all depends on how proficient you want to be I guess.

I used to repair professional hi fi and stereo equipment for Pacific Stereo and Hi Fi in Berkeley. I was paid the amazing amount of \$750 per month in 1967 because pay was determined by the amount of repairs you were able to do instead of a set salary. In those days a good wage was \$100 per week.

If they paid you based on the amount of repairs, how come you made the same amount (\$750) per month? Most people learn how to do a better job and become more productive so naturally I would expect my monthly earnings to increase every month as I become more efficient. If a good wage was \$100 per week, and you're making \$173 a week (\$750 per month), have you maintained that level of income? I think a good wage today is \$138k/yr. You must be making \$240k/yr? Congrats!

Don't presume to lecture me on what impedance means.

I didn't lecture you on what impedance means. I was lecturing you on what RobDee was saying because you were confusing it for an "argument". You've already made it clear that you don't understand what impedance means.

Tess

jmm360
10-16-2006, 06:12 PM
Evan,
I wouldn't presume to lecture on impedance or any other subject.
I still have no idea what the original poster hopes to accomplish but a straight DC signal can't be the answer. If speakers are rated for DC resistance so be it but it doesn't seem like a valid measurement for any usefull purpose?

nheng
10-16-2006, 06:18 PM
Winchman, A few other sources of sound effects are cheap kids toys including guns, phasers, etc. You might be able to drive an external speaker to acceptable levels for background noise. For louder sounds, you'd have to drop the levels down before pumping them into any amplifier high level (line) input jacks.

You can also get a .wav or other audio file for just about anything in existence and run your pc audio thru a sound system or amp. Den

Evan
10-16-2006, 06:28 PM
The noise level is getting rather high today. I recommend ignoring it. I shall.

I don't have time for pet trolls.

RobDee
10-16-2006, 07:35 PM
The noise level is getting rather high today. I recommend ignoring it. I shall.

I don't have time for pet trolls.

As Harry Truman once said,"If it's to hot get out of the kitchen."

tesswalker
10-16-2006, 07:49 PM
The noise level is getting rather high today. I recommend ignoring it. I shall.

It only appears that the noise level is high. In reality, the signal level is very low.

I don't have time for pet trolls.

Of course you have time. Tons and tons of it :)

Tess