AC vs DC speakers [Archive] - Audio & Video Forums


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08-16-2005, 07:57 AM
My kid has a pair of car audio, 12" boomers connected to his home audio amp... naturally they don't bump as they would if they were connected to a 1,000 watt car amp, ( thank God! ), but, my question is can this cause damage or eventual loss of the A/V receiver?
And what is the technical difference and requirements between AC & DC speakers? :confused:

08-16-2005, 09:30 AM
Are the driver 4ohm ,8ohm,can your receiver handle the ohms.The problem is if the receiver as enought power for them .If the speaker at high volume start clipping the receiver cant handle them and might overheat.Pat.P

08-16-2005, 11:05 AM
The power coming out of an amp whether it be car or home is DC. There is not such thingk as ac/dc speakers.

08-16-2005, 06:06 PM
power coming out of an amp is AC not DC..... DC + voice coil = BAD!!!!!!!!

08-16-2005, 07:15 PM
In actuality, the amplifier generates a completely new output signal based on the input signal. You can understand these signals as two separate circuits. The output circuit is generated by the amplifier's power supply, which draws energy from a battery or power outlet. If the amplifier is powered by household alternating current, where the flow of charge changes directions, the power supply will convert it into direct current, where the charge always flows in the same direction. The power supply also smoothes out the current to generate an absolutely even, uninterrupted signal. The output circuit's load (the work it does) is moving the speaker cone.

DC is direct current IE batteries. Get the facts straight before putting out bogus information.

Here's a link that explains how it works.

08-16-2005, 07:50 PM
I find it hard to belive that you are an audio engineer and don't know the basics of how an amp works. I'm amazed every day by something but this takes the cake.

08-16-2005, 09:15 PM
I find it hard to belive that you are an audio engineer and don't know the basics of how an amp works. I'm amazed every day by something but this takes the cake.
he works on the music processing side and hasn't got a clue about the engineering or electronics behind the instruments he's using?

08-17-2005, 05:01 AM
amps put out AC. DC to a speaker will burn out the voice coil.

08-17-2005, 05:08 AM
Actually I do know about how an amplifier works and also how a speaker works, I do repair both for a living. The only DC that should be present in an amplifier is from the outputs of the power supply anything other than that is a problem. Take a minute to put a meter on the outputs of an amp, you should get maybe around 100mV DC anything more means there is an issue. Now switch your meter to AC and there will be voltage present. Take the simplest form of audio, a sine wave, it is a pure AC signal. When the DC offset of the amplifier is too high then you have a square wave. Take a DC signal and apply it to the input of your amp and your speaker will only move one way and probably burn the voice coil of the speaker. That is why amps provide DC circuit protection, to prevent any high amounts of DC offset from leaking out of the amp into your speakers. do a little simple test just put a 9 volt across the terminals on a speaker.

08-17-2005, 06:09 AM
I am wrong and apoligize for it. Apparantly the ac gets converted to dc to back to ac out to the speakers. I also apoligize for being a little sarcastic. I was in a bad mood last night and let my emotions take over which should not have happened.

I posted this over at PE where many EE's hang out and they correctly corrected me. Pelly3s my apology again. Jeeze, maybe I better stay away from trying to build a DIY amp. Well, I learned something in the process.

I feel like a real klutz and rightly so. But, at least I'm man enough to admit my mistake and learn and carry on. Well, enough babbleing. Here is a post on the PE site that explains the situation better than mine.

08-17-2005, 06:28 AM
Hey its not a problem, apology accepted. I may only be 22 years old but I built my first amp when i was 15 and have been working on stuff since then. Thats why I do this for a living :) its fun. No hard feelings here, its just another day in the life of audio. The concept of an amplifier can be confusing actually because it does employ both AC and DC signals inside it at the same time. And you should try to build an amp, hell I still blow stuff up when I build them lol thats the fun part as long as you dont get hurt. Im here for the same purpose as almost everyone else, to teach and to learn.

08-17-2005, 07:30 PM
I'm no techy, so I guess I should keep out of these discussions. I assumed you worked on the mixing side of things. I know a recording fellow or two who are great at their jobs but know squat about electronics. One of these days when I have more time on my hands, I'd like to get a deeper understanding of what goes on in the innards of the stuff I love.

08-18-2005, 04:14 AM
Don't worry about it Poneal, you're a proven good guy around here.
We all have our "days". Personally, I gotta watch that drunken posting thing.
Jim Beam can make you think you're a genius

08-18-2005, 04:31 AM
Just a theoretical example (right?), don't do it.

9 volts DC will fry a speaker now.

I use 1.5 volt batteries to test speakers at yard sales and the like but I only connect them to the speaker terminals for less than a second. If you hear a pop when you connect the battery (for a very short period of time) you know the speaker is not completely fried. Doesn't tell you much about the distortion of the speaker but at least the voice coil isn't burnt out.

08-18-2005, 05:09 AM
exactly what one guy posted over at the PE board. He said he always gets tense when doing as you said with a 1.5vold because he used a bad amp one time on a tweeter and the voice coil shot out. Not a good thing. :-). I took some flack for this post over at the PE board too. So again my apology to all. I think I will do a DIY amp in the near future once I get these 3 ways done. My AR.Coms have all been sold (only one left on ebay) so I now have the funds to buy the drivers and xover parts for it. Have a good one. Paul.

08-18-2005, 05:58 AM
You guys have your ACs and DCs all mixed up. First off, an amplifier is AC (music) in and AC (music) out. Since most amplifier inputs are capacitor coupled and capacitors block DC in its operating range, I doubt you would get the results pelly3s stated by putting DC on the amps input. You would get his results if you put the DC across the speaker, providing there was enough current. I check speaker polarity using a AA battery across the speaker terminals making sure all cones move in the same direction when positive polarity is applied to the plus terminal.

The DC in an amplifier is used for supplying the electronic circuits and biasing the output transistors. There are usually several stages of amplification (transistors/drivers) some provide voltage amplification some current. When one stage has performed its function the signal is then passed onto the next stage until the desired "amplified" signal (voltage and current) is achieved at the outputs. I'm not even going to try explaining different classes of amplification (A, AB, D) single-ended, or push-pull outputs. It would just confuse the issue.

The difference between a car system (battery supplied) and a home system (AC outlet supplied) is the home AC is converted to DC within the device. Most electronics (TVs, stereos, receivers, run on AC converted to DC. Most electrical devices in your home run on AC (motors, oven heating elements, lamps, etc). In a car system there may also be some conversion, but it would be a DC to DC conversion to ensure the correct DC voltage and current is provided to the device.

Yes there is some DC component (DC offset) to AC, but thats in the designing stages of the transistor and tube circuits and doesn't come into play here. I'm not that familiar with the "DC Protection Circuit", but it makes more sense it's a circuit breaker in the power supply providing current for the output transistors. When the output transistors start to draw too much current the breaker opens until its back down to a safe level. The protection circuit may be an actual circuit breaker/fuse (requiring a manual reset, replacement), or a thermal switch attached to the output's heat-sinks. Hope this helps.

08-19-2005, 09:16 PM
Phew ! Lots of interesting info here... Thank you...

Also discovered the reciever has a built in protection circuit & led readout that lets you know when you are over doing it...

4 ohm "Punch" car audio speakers. Huge massive magnets... dual voice coils...

08-20-2005, 02:12 PM
I work at at church took the grill of the old speaker that were in church for at least 30 years there was 6 car speakers in series they only added a tranformer on the speaker box from there to amp.The transformer usaly are 70 volts and you can handle100 watts.No complicated crossover and you could transfer to 4 ohms,8 ohms ect.Pat.P