I am trying to figure out what I want to do, stereo-wise, but this still confuses me. If someone can explain Ohms to me, using everyday terms, I would greatly appreciate it.

Speakers and amps always refer to this and I have just nodded when someone else has brought it up. Now I really want to know.

Thanks

 

Ohms (Greek letter omega) are a measurement of resistance. If you will recall from physics class, V=IR, or voltage (measured in volts) is the product of resistance (measured in ohms) and current (measured in amps). Also, P=IV, or power is the product of current and voltage. In everyday terms, voltage is the pushing force that causes things (in this case electrons) to move, current is the amount of movement (or flow), and resistance is the resistance to the flow (aka load: one usually refers to load when speaking of alternating current and resistance when referring to direct current, but I have seen both used interchangably. I have also seen load referring to the sum of resistances in a circuit).

Speakers (aka drivers) have a certain amount of resistance depending on their design (it depends on the length and diameter of wires/voice coils, etc in the speaker). Car speakers frequently have a 4ohm load, or resistance. Home audio speakers frequently have an 8 ohm or higher resistance.

OK, so you may have noticed, or heard, that a certain car amplifier puts out x number of watts at a given resistance, or load (say, 4ohms). That same amp may put out twice the number of watts, or more, at a lower resistance, say 2ohms. This should make perfect sence when one looks at those equations up above. The voltage is constant (say 12-14 volts from a car battery), so when you halve the resistance, you double the current, and when you double the current, you double the power, at a given voltage.

Now, you might be saying, OK so design all these speakers with a really low resistance, like 1 ohm or less. Well, that would create quite a bit of current, and concomittant heat, and would likely melt the circuitry and wires within an amplifier, unless it were designed to handle these exceedingly high currents.

May since? Confused yet?

 

With that being said, does anyone know the minimum resistance that the factory, non-Bose, amp can handle with out burning up? I am less than thrilled with the factory, non-Bose stereo. It sounds Ok at lower volumes but, above a certain point, I get a headache...

Rob

 

...make the same speaker change between and 4 and a 2 ohm?

...make an amp push at 4 or 2 ohms?

Is it how you wire things? If so, what is the difference. I have it in my head it has something to do with wiring, but I could be wrong.

 

alpine website has a nice owners manual for the 10 inch sub with pictures of how different ohms (2 or 4) speakers and different wiring combinations can produce different ohms.

I've heard the stock speakers are 4 ohm in front and 32 ohm in back. But I've pulled the rear speakers and saw no indication of the ohm rating.

http://ecominet2.alpine-usa.com/html...r-1221d_om.pdf

 

You cannot easily make a speaker change its designed resistance. You purchase it at what you want it to be. This is why designing an audio system mean simultaneously taking into account many different variables. You cannot simply buy a speaker, and then automatically make it work with another component. In other words, it makes no since to buy cheap, Crutchfield, $49.99 Blaupunct speakers and then power them with a $1000.00 Zapco amp. Holy ****, you'll probably fry those damn speakers. Likewise it makes no since to buy expensive Dynaudio 3-way components, $800.00, and try to hear anything with some cheap *** amp.

Further you cannot make an amp push at any resistance. It either does or it doesn't. And if it does, it may only do so for a short amount of time before it fries, if it isn't designed to handle that low of a resistance. In the real world, practically all car audio amps are designed to be stable and run for hours with a 4 ohm resistance per channel. Many good (expensive) amps are stable at a 2 ohm load per channel. Few really good (really expensive) amps are stable at a 1 ohm load per channel (and most of these are only 1 or 2 channel amps).

As for your last question: Yes it matters how you are wiring things. Especially if you're talking about wiring multiple subwoofers together to be powered by a fewer number of amplifier channels. This conversation becomes further complicated once we start talking about dual-voice coil subs. There is a tutorial on JL audio's web site that explains this perfectly. Here is the link:
http://<a href="http://www.jlaudio.c...index.html</a>

 

Oops, I hosed the link. Let me try again.

http://www.jlaudio.com/tutorials/wiring/index.html

 

MSGarrett1...

Great explanation, and its nice to see others here with EE knowledge....

Not to add a new level of confusion to the mix, but please remember that speakers are not composed of this purely resistive component. They do have the resistive DC component (series resistance) you mention above, but as frequency changes, so does the impedance (Z in ohms) of a speaker. In other words, the impedance, which is composed of resistive and reactive components (resistors, capacitors, and inductors), is not linear. In fact, the impedance may be very low at certain portions of the frequency band that a speaker may be driven at.

In its simplest terms a speaker is composed of an RLC circuit, which reacts to voltage fluctuations, these voltage fluctuations show up on the voice coil windings, when this change in current/voltage occurs on the windings, the speaker moves and creates sound due to the simple fact that a changing current induces a magnetic field. Because this magnetic field exists, it reacts to the magnet structure at the base of the speaker, and either moves forward or backward depending on the signal. A positive signal drives the speaker forward (pushes air), and the negative signal draws it back (pulls air).

Here is a more comprehensive, very explanatory link worth reading if you care how things work:
http://electronics.howstuffworks.com/speaker2.htm

Thanks to MSgarrett1 for a straightforward initial explanation, and its good to see things like this in these forums, b/c everyone should know how things like a speaker work.

 

Thanks, I will check out the sites you guys listed above during any free time I have today. I just want to understand as much as I can before I start, that way I might be able to avoid a mistake or two.

Thanks Again

 

Good responses from MSGarrett1 & onecoolee. Nice to see.

However, you don't need to worry to much about the details as long as you follow two simple rules:

1) Don't use a speaker with a lower impedance rating than your amplifier is rated to handle. Most automotive speakers and amps are 4 ohms so you don't have to worry too much until you get to the exotic stuff. It is perfectly OK to use 4 or 8 ohm speakers with an amp that has a lower rating, say 2 ohms, no problem here. The only problem is when you have a cheap amp that is only designed to drive a high impedance speaker but you hook it up to a low impedance speaker. You will blow the output transistors or it will shut down if it has thermal protection.

2) Don't want to use an amplifier with a higher power rating than the speakers. It is perfectly OK to use speakers that can handle more power than your amp can put out.

You can break both of these rules if you never turn the volume too high up but you probably would not be asking questions if you weren't planing to crank it up. Also, you never know where too high is until something burns up. The only other concern is you must also replace the wiring between the speakers and the amp and the wires supplying power to the amp if you are putting in some serious power.

This will keep you from having major electrical incompatabilities. Getting that perfect sound is much more complicated.

 

dr_gallup ... I could not have said it better myself ! Thanks for the follow up.

 

Exactly!! Nice. It seems someone has had some formal education in speaker design/fabrication. Also, to be symantically correct, onecoolee is right. One should refer to solely resistive elements in a circuit with direct current as resistance and one should refer to the resistance in circuits with alternating current as impedance . And although one's car battery is supplying a direct current, the current traveling along the wires to a speaker/driver alternates (so as to push and pull the voice coil through the magnetic field of the speaker's magnet) to produce sound.