Its likely that some of you are wondering what the ohms, impedance, voice coil and amp stability means. Lets clear a few things up!
This article will define, in plain English, some of the technical differences between these terms. This is an article written by our resident car audio expert and moderator Orgasm_Donor (aka Mike) that should help answer some of the questions you may have about car audio.
OHMS: Ohms law deals with the relationship between voltage and an ideal conductor. It states that ‘The potential difference across an ideal conductor is proportional to the current through it’. Ok, thats the technical answer. When referring to car audio your speakers have a certain ohm rating. Full range speakers generally have a 4 ohm rating. Some have less. Home audio speakers are usually rated at 8 ohms. Most class AB amplifiers work at 4 ohms stereo, 2 ohms stereo, and 4 ohms mono. When talking about class D mono amplifiers, they are usually most powerful and efficient at 2 ohms mono. At over 1000 watts, its cheaper to make an amplifier 1 ohm mono stable. Generally speaking, if your amplifier’s output rating is at ‘X’ watts at 2 ohms then at 4 ohms it will be ‘X/2′ watts or half the output of the amplifier is being used. Of course some amplifiers output the same at 2 or 4 ohms because of their complex power supply and power delivery system – Not too many amplifiers can do this!
IMPEDANCE: Professionals can write a thousand word essay explaining the topics of impedance and Ohms and their relationship. Lets keep it simple for the average person trying to get his/her system together! Your speakers impedance rating is the numbers discussed above. ‘My subwoofer has an impedence of 4 ohms’ is something you might hear someone say. Calculating multiple speakers and their impedance ratings when building a system can get a little confusing. If you have a class D mono amplifier that gives me 800 watts of power at 2 ohms then ideally you would need to find a sub or subs that will work with this number. You can get an 800 watt sub with a 2 ohm voice coil and that would be perfect! What if you want to run 2 subs? What if you have two voice coils? Thats where math is involved!
VOICE COILS: When talking about speakers that have more than one voicecoil we are usually reffering to subwoofers. Your average full range speaker has one voice coil. It is a myth that a sub with dual voice coils can handle more power. The addition of voicecoils is really just there to give you amplifier power options and help you build and tailor your system efficiently. Basically it gives you more options. Your local independent car audio retailer SHOULD be selling you sub(s) and amp(s) that will work together if he or she is doing their job. If your audio professional does not know what works with what, please run (don’t walk) the other way! Until then, take a look at this guide to set you in the right direction. When you have a sub that has two voicecoils, you have two options for wiring them: Parallel and Series. Parallel is posive to positive to positive terminal, negative to negative to negative terminal and series is positive(1) to negative (2) and positive(2) to positve terminal and negative(2) to negative terminal. A dual 4 ohm sub when wired in parallel makes a 2 ohms load (you always drop the impedance in half when wiring in parallel). That same sub when wired in series will give you an 8 ohm load (you always double the impedance when wiring in series). With two dual voice coil subs at 4 ohms (DVC), you can run them entirely in parallel (all positives go to the positive terminal of the amp) and that will give you a 1 ohm load on the amplifier (the impedence is cut in half each time you parallel each wire) or in series (like christmas tree lights!) it will give you a 16 ohm load. You also have the option of parallelling each sub on its own, then series at the amp (or series at the sub and parallel at the amp – same consequence) and that will give you a 4 ohm load (cut in half at each sub then doubled at the end. And so on and so forth.
AMP STABILITY: Every amplifier has an advertised stability rating. ‘This amp is rated at 500 watts @2 ohms’ and they will usually have a minimum impedance load. Any lower than this number could do damage to the amplifier OR cause the amp to shut down from thermal overload or some amps have special circuitry that can determine a low load and just not turn on at all. Either way, it is not recommended to run an amplifier below its advertised rating. Bad things may happen!
A FEW THINGS TO NOTE: When talking about mono class D amplifiers, sometimes you will see two positives and two negatives on the terminals. This does not mean left and right or ‘stereo’! These are there to help you wire up multiples subs and/or voicecoils. These connections are parallel inside the amp! Also, some amps can be stable down to 1/4 ohm but the brochure won’t tell you that. These amps are generally badass and require a very stable power systems (multiple batteries and high output alternators). Not all amps are created equal! The information above does not pertain to all amps and/or subs! If you come across a wacky 4 voicecoil sub and a 16 volt amplifier, please contact your local professional for advice!