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How to Match a Subwoofer and an Amplifier

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by: Kyle Duffy


As you scavenge deeper into the realm of car audio, you begin to realize that figuring out the proper amplifier/subwoofer setup is a lot harder than just matching power ratings. As you sift through all of the different manufacturers, you might notice that the word "ohms" appears often.  Have you found yourself wondering, “Well the subwoofer is 2 ohms, so I should probably get an amplifier at 2 ohms?” In most cases you would be incorrect, for various reasons. To avoid confusion, we’ll let scientists deal with Ohm’s Law and instead focus on the actual matching process. In this article I will explain to you how to match up your subwoofer with your amplifier so you do not end up blowing any fuses, mentally or physically.


There are a few criteria we have to look at first. For example, the distinction between a monoblock amplifier and a 2-channel amplifier, as well as the difference of a single voice coil subwoofer versus a dual voice coil subwoofer. I will discuss these categorically and explain each one, so when it is all said and done, you just have to match up your equipment in a chart to find the answer! Let’s start with some terminology:


CHANNEL


This does not refer to the channels that you switch between on your TV while trying to find the Lakers game, and it does not refer to a channel that is filled with water. In the audio world, the word “channel” refers to the stream of data on one line, or in the case of amplifiers, one cable of power. A single channel amplifier has one terminal that distributes power to a speaker, while a two channel amplifier has two terminals that distribute power. Likewise with 4 and 5 channels amplifiers, it’s the number of routes available for information or power to flow.


   

If you have ever heard the terms “mono” and “stereo” you most likely link that to a sound system. If music is recorded in “stereo,” it means that it has a left and right side, so the left side might output the sound of the guitar while the right side pumps out the vocals. Stereo is effectively 2-channels, so the recording engineers can choose to have certain music play on one side or the other at any given time.


BRIDGING

When you bridge two channels together, they create one channel. This is used most often in 2 or 4 channel amplifiers. If you have two channels but only want to run one speaker, the channels can be bridged, or wired together, to create one single channel. It’s exactly like a wooden bridge in that it connects two paths together as one (Learn more about amplifier bridging).


MONOBLOCK AND CLASS D AMPLIFIERS

Monoblock and Class D amplifiers have only one channel that is typically used for powering one subwoofer at lower frequencies. I find this type of amp to be the best choice for running one or two subwoofers. How do you run two subwoofers off of an amplifier that has only one channel? This can be a headache for those who do not know the difference between series and parallel wiring. If you have two subwoofers, you can wire the subwoofers together in series or parallel and then wire them to the amplifier.


TWO CHANNEL AMPLIFIERS

A two channel amplifier can be wired in a few different ways because it has two channels which you can bridge together to create one channel. You can run one channel to each subwoofer, which acts as though each sub has its own monoblock amplifier hooked up to it. You can bridge the channels together into one channel and run one subwoofer or more, but this option forces you to run the amplifier at a 4 ohm load. While two-channel amps are a good option, I prefer to run a monoblock amplifier system.


FOUR CHANNEL AMPLIFIERS

A four channel amplifier has, well, four channels. This type of amplifier is mostly used to power speakers, not subwoofers. The average car has four speakers, two in the front and two in the back. Each channel connects to one speaker. Simple enough, right? But we can make this somewhat complicated by using subwoofers instead and bridging the channels together. If you have four channels (1,2,3,4), you can bridge channels 1 and 2 together, and then bridge channel 3 and 4 together. So you end up with two channels total. You cannot bridge those two channels into one channel; it will end up destroying your amplifier. The majority of the time, when a channel has been bridged, it turns into a four ohm channel. So if you have two channels, each at 2 ohms, and then bridge them together, it turns into four ohms (I will address ohms soon, so don’t worry!).


SINGLE/DUAL VOICE COIL SUBWOOFERS

Now I have to introduce the two major types of voice coils, Single Voice Coil (SCV) and the Dual Voice Coil (DVC). You will see this a lot as you look through different subwoofers. A SVC subwoofer has one voice coil and one set of terminals, one positive (+) and one negative (-). A DVC subwoofer has two voice coils, each with its own set of terminals. Because of this, DVC subwoofers offer more wiring options than SVC speakers. You will see that most DVC subwoofers can be wired at two different ohm levels, unlike a SVC which can be wired at only one ohm level. There is little to no difference in sound quality between the two types of subwoofers.


PARALLEL WIRING

If you have two parallel lines, it usually means they run next to each other but never touch. Parallel wiring is similar to it. If you wire in parallel, you would hook all of the positive speaker terminals together on one line, and all of the negative speaker terminals on the other.


SERIES WIRING

Series wiring can become a bit confusing. You take a single current path and arrange it among all of the components. It effectively makes a chain, so everything is hooked together as one. The parallel wiring, you would hook together similar terminals only, instead of wiring everything together.


OHM
   

First let’s check the dictionary’s definition of an ohm. “A unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt across its terminals.” Confusing right? Don’t worry, sometimes I have trouble understanding it too! Basically, it’s the resistance to the flow of energy. The higher the ohm, the more resistance. So, 2 ohms has less resistance than 4 ohms. Amplifiers often give their power ratings at 2 ohms and 4 ohms. You will notice that the power rating at 4 ohms is less than the power rating at 2 ohms, or even 1 ohm on some amplifiers. The goal is to buy an amplifier and subwoofers that will give you the most power when you wire them together.

1 SUB   
OHMSVoice CoilParallelSeries
1 OhmDVC0.5 Ohms2 Ohms
2 OhmDVC1 Ohm4 Ohms
4 OhmDVC2 Ohms8 Ohms
6 OhmDVC3 Ohms12 Ohms
4 OhmSVCN/A4 Ohms
8 OhmSVCN/A8 Ohms
    
    
2 SUBS   
OHMSVoice CoilParallelSeries
1 OhmDVC1 Ohm4 Ohm
2 OhmDVC0.5 Ohm2 Ohm
4 OhmDVC1 Ohm4 Ohm
6 OhmDVC1.5 Ohm6 Ohm
4 OhmSVC2 Ohms8 Ohms
8 OhmSVC4 OhmsN/A

COMBINING SUBS AND AMPS

Hopefully you have a greater understanding after reading the terminology section. This next section is aimed at helping you find the perfect amplifier and subwoofer combination. If you did not understand any of the terminology, the subwoofer wiring chart will help you out. The chart is based on a one channel amplifier wiring setup. If you have two subwoofers, it assumes you are wiring them to a single channel. If you have two subwoofers and two channels, you would look at the “1 Sub” section, because each sub gets its own channel. In the end, the power of the amplifier needs to equal the power of the subwoofers. For example, and amplifier that has 400 watts should be paired with one subwoofer that runs at 400 watts, or two subwoofers that run at 200 watts each. Regardless of the combination, the main goal is to equal out the power while running the products at their respective continuous power ratings.


Alright, so let’s say you buy two Kicker 10CVR124 subwoofers. Each sub has an RMS power rating of 400 watts, and each subwoofer is a 4 ohms, Dual voice coil sub. Scan the chart for 2 subwoofers, then find the matching ohm level and voice coil type. So, we look for the DVC (Dual Voice Coil) and then the 4 Ohms right next to it. From here we see that It lists the ohm levels that wiring these subwoofers together in series or parallel will produce. So looking at the chart it says these two subwoofers can be wired in parallel at 1 ohm or series at 4 ohms. Remember what I said about the ohms? The lower ohm level has less resistance. So let’s choose a 1 ohm stable amplifier to give these subwoofers the most power! Because each subwoofer runs at 400 watts RMS, we need to find an amplifier that runs at around 800 watts RMS.


Let’s look at a Monoblock, or single channel amplifier. The Rockford Fosgate R750-1D monoblock amplifier puts out 750 watts at 1 ohm at one channel. While it is not exactly 800 watts, we do not have to be perfect. Just don’t go too much over or under. As it is, this would be a near perfect match. If you decided to wire the subs at 4 ohms, you would have to find an amplifier that puts out 800 watts of power at 4 ohms, which can be very expensive.


Let’s keep the same subwoofers but choose a two channel amplifier. Assume we will not bridge the channels. This changes things a bit, because you need to act as though you have one subwoofer instead of two given that each subwoofer has its own channel. So in this case, we look at the chart for 1 subwoofer, with a dual voice coil, at 4 ohms. It says in Parallel it wires to 2 ohms, and in series it wires at 8 ohms. Lets choose the 2 ohm stable amp to get the most power. I found an RE Audio CTX-1600.2 amplifier which has 700 watts of power bridged at 4 ohms (each channel has 350 watts of power at 2 ohms). Each subwoofer gets one channel, so each subwoofer gets 350 watts to it. This is just about right since each subwoofer has an RMS power rating of 400 watts.


If you took the same amplifier and bridged the channels together, once bridged they stay at 4 ohms. So while these subwoofers would still work, you would have to look back at the 2 subwoofer chart. It has to be wired in series, because this amplifier is not 1 ohm stable.


I would not recommend a 4-Channel amplifier for subwoofers, but if you have to have one, just know that you will not be able to find an amplifier that puts out 400 watts each channel. However, you could bridge each of the channels together, making it a 2 channel amplifier. In this case you would need to bridge a 4-Channel amp with power levels at 200 watts per channel. Once bridged it turns into 400 watts at 2 channels. Does this work with our subs? According to the chart, a bridged four channel amp is classified as a two channel amp. Since each sub gets a channel, you will also look at the 1 Sub section on the chart. The chart tells us that a 4 ohm dual voice coil wires to 2 ohms or 8 ohms, not 4 ohms. Since the subwoofers we choose can only be wired at 4 ohms, you would need to find a different set of subwoofers that are suitable for 2 or 8 ohm loads.


Now you should be ready to start building your own system. Besides an amplifier and subwoofers, you will need to purchase speaker wire, wiring kits among other install accessories. Call us at 1-877-BUY-SONIC if you have any questions along the way.



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