quote:

Originally posted by skot_e Don't mean to be picky, perhaps a typo, but speakers are driven by Alternating Current (AC).

Actually no, speakers are not "driven by Alternating Current" they reproduce the sound using varying frequency DC pulses in a magnetic coil at the base of the cone or other material. The amplifier is powered by AC which is then transformed into DC immediately to utilize the internal circuitry by using voltage rectifiers and transformers to make the AC/DC conversion.

And, if anyone cares to indulge, some more info to aid in hijacking this thread:

Not many electronic devices use Alternating Current without this conversion taking place early in the circuitry, and if they do, the purpose is rather crude. Two examples of Alternating Current in a simple circuit "device" being used directly are: traditional lightbulbs (not LED) and old bell and buzzer telephone (landline) ringers. These circuits use the 50/60Hz AC (depending on where in the world you get your power or phone service) to "flicker" or simply switch on and off rapidly at 50 or 60 times per second. Lightbulbs literally shut on and off before your eyes so fast that you can't even detect it! Hearing works much differently though. Thus, if speakers were driven by Alternating Current all we would hear from them would be rising and falling amplitude pulses at 50/60Hz. DC allows the speaker material to rise and fall ABOVE AND BELOW (+ & -) the amplitude line at VARYING FREQUENCIES to reproduce sound.

Incidentally some situations occur when the 60Hz cycle frequency is audible (humming) through speakers. That is usually caused by a ground fault (inadequate ground), poor quality filtering in amplifiers and other electronics (think Gemini), and/or an electrical inbalance in the power sources of audio equipment due to varying power supply sources within a supply system (i.e. plugging the mixer into one wall outlet and the PA into another wall outlet that is on a different bus or breaker). Also, if other electronics are running (like a frige pehaps) on the same circuit or the length of the electrical run differs greatly in the various power supply circuits, an imbalance is likely to occur.

rofl. nice1.

quote:

Originally posted by St. Michael Actually no, speakers are not "driven by Alternating Current" they reproduce the sound using varying frequency DC pulses in a magnetic coil at the base of the cone or other material. The amplifier is powered by AC which is then transformed into DC immediately to utilize the internal circuitry by using voltage rectifiers and transformers to make the AC/DC conversion.

GRRRR, beat me to it, but yes its partly true, you see ive built my own amp and it is a very complex process to simply explain wether the signal driving the speaker is AC or DC.

There is a way to amplify a DC signal by using what they call a Push Pull transistor set up, or a Darlington Transistor. Now were are getting into a fairly complex area, there are two type of transistors, a PNP and NPN the only main difference between the two is the direction of the current flow from the Emitter.

On a transistor there are three pins, a Base, Collector, and Emmiter. Depending on the type of transistor, a PNP or NPN you can pass a signal though it, and it will amplify it a certain ammount depending on the voltage on the signal coming in to it.

the arrow always points to the N, and the line that the arrow is on is the emiter, it allso shows which way the current can flow.

so by using two NPN transistors like so......

you get an amplyfied signal, and that is basicly how an amp works, ther are a ton of other variables that go into the design of an amp.

So, even though the signal powering the speakers is created using DC, it is more like AC becuase the audio signal changes directions, becuase there are two of those transistor setups, one using NPN transistors like the picture above, and one using two PNP transistors for the other half of the signal.

pleas correct me if im wrong

????
Feed DC to your speakers and see what happens (connect a 9V battery - just don't cook the coils).
I accept I should maybe not have used the term 'drive' but the speaker moves with AC.
EG A sine wave pulses in a positive and negative direction. It does not move from Zero to max, then back to zero then max etc.
For a speaker to move back and forward the fluctuating current is AC

My understanding of the transistor is that the Base is used to fluctuate the DC voltage supplied by the Connector to regulate how much passes through the Emitter, thus creating an AC supply feed to the speaker
I guess we're both articulating the same thing in different a way.

quote:

So, even though the signal powering the speakers is created using DC, it is more like AC becuase the audio signal changes directions, becuase there are two of those transistor setups, one using NPN transistors like the picture above, and one using two PNP transistors for the other half of the signal.

Is this an AB class amp?

Its acctually a class B amp, I wanted to make a class D amp, but I didnt have the parts at the time.

quote:

Originally posted by skot_e I just want to clarify, if you record a track off the mixer into the mp3 player, and you listen on the headphones, it is ok, and if you download a track and transmit it across to stereo, that is ok too, but if you transmit the track played via the mixer, it doesn't work clearly. Is that right?

Yep exactly!

It's got me stumped. Maybe try a different transmitter (that doesn't seem like the issue but worth a shot) should be able to do that instore if you bought it over the counter.

Sorry to drag this on. I found out today at work that the mp3 worked over the stereo. So it must just have something to do with my car radio. Thanks for the replies

Really wierd...
So its only your cars stereo??
You need to try it on as many different radios as possible.
You Always need to remember to test all the variables.
So test recorded mp3s and normal ones and wavs on your system and others and do all that kind of testing. It will tell you for sure where the problem is. Then fixing it is another story but atleast you will be closer to doing so.

Thats real odd. Do other mp3's play normally on the car stereo when transmitted or only on your home stereo?
Without hearing what it sounds like, it could be the mid and high range dropping out - like if someone talks to you with their hand over their mouth. If other mp3's work in the car, it can't be the transmitter can it (also the fact they work on work stereo makes me think this)
And the car stereo works fine when tuning into radio/ playing CD(or tape)? Might the the deck that has the problem.

Its just a really crap situation. Its specific to recorded mixes off my turntables (either record onto my computer or straight to my mp3 player) and transmitted to my car stereo! any other combination works perfect. d/l mp3 to car stereo, recorded to other stereo. i only have a crappy car radio thats why i got the transmitter. im gonna try downing the volume and changing the dc offset.