How does an amp "see" the load?

[CadillacMatt 10+ year member]

Okay, newb question here about electrical.

(hypothetically...) Say I have an amp that puts out 1000wRMS @ 1 ohm. I have a 1000wRMS speaker with a 1 ohm DVC (total ohm load = 1). Speaker getting roundabout 1000wRMS, right?

Okay... now say I take the same amp, but have two 1 ohm DVC subs wired down to a one ohm load. Amp still sees one ohm load, what exactly is happening? Would both subs be getting 1000wRMS? Does the amp pull twice as much current? Work twice as hard?

Thanks I'm just trying to get a better understanding about car audio electrical. //content.invisioncic.com/y282845/emoticons/veryhappy.gif.fec4fed33b4a1279cf10bdd45a039dae.gif

Click to read more...

 

[groundpound4200 5,000+ posts]

your amp would see 1/2 ohm

edit- 2 dvc 1 ohm subs can only be wired to .25 ohm, 1 ohm, or 4 ohms //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

are you saying that you have 2 subs with a final impedance of 1 ohm wired to the same amp? Then it would be .5 ohms total to the amp assuming its a monoblock

 

[wu501 10+ year member]

oops..also misread the original post.

 

[n2audio 5,000+ posts]

To rephrase your question.

A dvc 2 for 1 ohm getting 1000w

A pair of dvc 4's for 1 ohm, each getting 500w.

current flows according to the resistance in its path. If there are two loads of equal resistance connected in parallel the current will flow equally between the 2.

 

[CadillacMatt 10+ year member]

Ok I'm sorry, I'll give you an example with what I'm trying to do.

2 Fi Q's, 1 ohm DVC - each sub's voice coils wired in series to 2 ohms. Two of these subs wired to the amp in parallel would yield a 1 ohm total load on the amp, correct?

as opposed to...

say, 1 Fi Q, 2 ohm DVC - sub's coils wired in parallel. Total of one ohm load on the amp.

Now if the amp states that it can deliver 1000wRMS to a one ohm load, either of these setups yield a one ohm load... will both subs get 1000wRMS, or like n2audio said each sub will get half of the power put out by the amp? And if I had three subs of equal resistance, a third of the power, four subs, a quarter of the power so on and so forth? If that's the case it seems like it's having each sub on a seperate "channel" or something.

 

[groundpound4200 5,000+ posts]

Ok I'm sorry, I'll give you an example with what I'm trying to do.
2 Fi Q's, 1 ohm DVC - each sub's voice coils wired in series to 2 ohms. Two of these subs wired to the amp in parallel would yield a 1 ohm total load on the amp, correct?

correct. If its a 1 channel amp

if its a 2 channel and each sub gets a channel, each channel will see its own load, in this case 2 ohms

 

[CarAudioGuru 10+ year member]

2 woofers (4 voice coils). Dual 1 ohm drivers wired in series (to themselves) and then wired in parallel to the amp. So the final load is 1 ohm

Each "half" of the amplifier (positive wave form and negative waveform) will see 1/2 the load or 0.5 ohm. BUT...the total load is still 1 ohm.

So now you have twice the cone area, but half the power to each woofer, and double the inductance /reactance (much more back "EMF") so now the amp will get twice as hot.

Draw the same amount of current , because the load is still 1 ohm as before.

BUT..TWICE AS HOT!!! Should play about the same SPL, within a dB or so.

 

[CadillacMatt 10+ year member]

Ah I apologize I neglected to mention that it would be a one channel amp...

So basically if I have two 1000wRMS woofers @ one ohm total load, I should get an amp that puts out around 2000wRMS @ one ohm, right?

Case in point - 2 Fi Q's , 1000wRMS each wired to a total one ohm load on the amp. (disregarding what people have been able to "push" them to, I'm assuming the base measurement here). In order to push these subs to their full power, I would need an amp that puts out at least 2000wRMS @ one ohm? Amp in mine would be an AQ2200D, 2200wRMS @ one ohm.

Thanks again for bearing with me I'm really trying to learn this stuff

 

[liljojo4711 10+ year member]

correct

 

[n2audio 5,000+ posts]

So now you have twice the cone area, but half the power to each woofer, and double the inductance /reactance (much more back "EMF") so now the amp will get twice as hot.

Do you even know what back emf is?

 

[CarAudioGuru 10+ year member]

Back electromotive force is a voltage that occurs in electric motors where there is relative motion between the armature of the motor and the external magnetic field.

It is a phenomenon that always tends towards the contrary of what happens!!

Let´s suppose: if lines of a magnetic field are cut by a conductor, than a voltage is generated in this conductor, which causes a current of electrons to flow in one direction. At the same time, like trying to avoid this, ANOTHER voltage is created that tends to neutralize this effect, and it forces the electrons to flow in the contrary direction. As you know, the back-emf is directly proportional to the velocity of the magnetic field. It is proportional to the relative motion between them.

A speaker is an electro-magnetic device. As voltage and current flows into the speaker and as the voice coil moves thru the magnetic field - equal OR greater voltage/current comes out of the speaker and back into the output transistors of the amplifier. Think of an amplifier as though it is a voltage “pump”.

You've seen "Back-EMF" in action, probably many times. You've hooked up an amplifier to one woofer, and leasts say it is 1,000 watts. Like all amplifiers (typically) after about 30 minutes of "pounding" the amp get warm.

But now you've changed your speaker system and went to 4 - 4 ohm woofers to get more cone area. The impedance is the same, but after 20 minutes , the amp gets REALLY HOT!!!!. But...it 's the same impedance ???(but higher inductance /reactance because of all the voice coils)

Back-EMF is your culprit. Should NOT be a surprise to anyone that the amplifier is getting hotter, there are more voice coils hooked up! Duh!!!//content.invisioncic.com/y282845/emoticons/veryhappy.gif.fec4fed33b4a1279cf10bdd45a039dae.gif

It is the way things are. Answer this question: what is electrical charge? Why is that we have positive and negative charges?? Answer: nobody knows!!! We must accept this condition!!! It belongs to the laws of the universe, since the Big Bang created it.

And last but least, back-emf corresponds in a way to inertial forces in the movement of a mass through space.

Inertia is a mass and has no intrinsic force. The electron has a mass ( ca. 1/1840 of the mass of a proton). Just to compare, the Newton´s first law states that a mass will maintain its linear direction of movement, unless the resultant of the forces applied on it be different from zero.

When you interrupt a current, the flow of electron tend to continue, like having inertia (no voltage difference, no electrical pressure and the flow should stop). Nevertheless, magnetic fields appear alongside the current which act like forcing electrons keep on their movement.

(See “Lenz’s Law, and Faradays Laws of Induction)

Is this FUN....Or what!!!!!

 

[GearGuy2001 10+ year member]

Back electromotive force is a voltage that occurs in electric motors where there is relative motion between the armature of the motor and the external magnetic field.
It is a phenomenon that always tends towards the contrary of what happens!!

Let´s suppose: if lines of a magnetic field are cut by a conductor, than a voltage is generated in this conductor, which causes a current of electrons to flow in one direction. At the same time, like trying to avoid this, ANOTHER voltage is created that tends to neutralize this effect, and it forces the electrons to flow in the contrary direction. As you know, the back-emf is directly proportional to the velocity of the magnetic field. It is proportional to the relative motion between them.

A speaker is an electro-magnetic device. As voltage and current flows into the speaker and as the voice coil moves thru the magnetic field - equal OR greater voltage/current comes out of the speaker and back into the output transistors of the amplifier. Think of an amplifier as though it is a voltage “pump”.

You've seen "Back-EMF" in action, probably many times. You've hooked up an amplifier to one woofer, and leasts say it is 1,000 watts. Like all amplifiers (typically) after about 30 minutes of "pounding" the amp get warm.

But now you've changed your speaker system and went to 4 - 4 ohm woofers to get more cone area. The impedance is the same, but after 20 minutes , the amp gets REALLY HOT!!!!. But...it 's the same impedance ???(but higher inductance /reactance because of all the voice coils)

Back-EMF is your culprit. Should NOT be a surprise to anyone that the amplifier is getting hotter, there are more voice coils hooked up! Duh!!!//content.invisioncic.com/y282845/emoticons/veryhappy.gif.fec4fed33b4a1279cf10bdd45a039dae.gif

It is the way things are. Answer this question: what is electrical charge? Why is that we have positive and negative charges?? Answer: nobody knows!!! We must accept this condition!!! It belongs to the laws of the universe, since the Big Bang created it.

And last but least, back-emf corresponds in a way to inertial forces in the movement of a mass through space.

Inertia is a mass and has no intrinsic force. The electron has a mass ( ca. 1/1840 of the mass of a proton). Just to compare, the Newton´s first law states that a mass will maintain its linear direction of movement, unless the resultant of the forces applied on it be different from zero.

When you interrupt a current, the flow of electron tend to continue, like having inertia (no voltage difference, no electrical pressure and the flow should stop). Nevertheless, magnetic fields appear alongside the current which act like forcing electrons keep on their movement.

(See “Lenz’s Law, and Faradays Laws of Induction)

Is this FUN....Or what!!!!!

Nice copy and paste

http://www.newton.dep.anl.gov/askasci/phy00/phy00351.htm

fail

 

[CadillacMatt 10+ year member]

So a mono block with two subs connected to it in parallel is basically behaving like a two-channel amp would, with the power equally distributed between them (assuming identical subs with identical resistance)?

 

[n2audio 5,000+ posts]

from what little I have read back emf has little to no effect on the amp as it is shorted at the outputs. It can have some effect from one speaker to the next because it acts as a damping force.

 

[CadillacMatt 10+ year member]

^

^^