Calculating Impedance for Speakers and Amp Matching

Calculating Impedance for Subs/Speakers and Amp Matching

This article assumes that you are using Parallel Wiring technique, which is the right way to wire your system.  It does not apply to subs/speakers that are wired using the Series Wiring technique.

There are 2 very important pieces of information you need to match subs/speakers with an amplifier:

  1. RMS wattage rating
  2. Impedance

Matching subs/speakers based on per channel RMS wattage is pretty simple.  Ensuring you have a perfect match based on impedance is a bit more involved.  Here is some info that will help you.

The math behind these calculations is pretty simple if each sub has the same Impedance (i.e. 2 subs each rated at 4 ohm impedance):

Ending Impedance of subs = Impedance of a single sub  / # of coils in all subs

  • Ex. You have 2 single voice coil subs and each has an Impedance of 4 ohms:
    • 4 ohms / 2 coils  = 2 ohms, for these subs you can go with a 2 ohm or 1 ohm stable amp.
  • Ex. You have 2 dual voice coil subs and each has an Impedance of 4 ohms:
    • 4 ohms / 4 coils = 1 ohm, for these subs you can only go with a 1 ohm stable amp, if you add a 2 ohm stable amp via parallel wiring, you burn up the amp!

The Ending Impedance is then used to find either a 1 ohm or 2 ohm stable amp.  Simply put, if the Ending Impedance of the subs is 2 ohms, you need a 2 ohm stable amp.  You could use a 1 ohm stable amp but you will not get all the potential power that amp is capable of producing.  The reason is simple, at 2 ohms the amp is experience greater resistance and hence pushes out less power.  You may be familiar with Amp rating info such as: 500 WATTS X 1 @ 4 OHMS, 1000 WATTS X 1 @ 2 OHMS, 2000 WATTS X 1 @ 1 OHM.  As you can see as the ohms decrease the amount of power pushed by an Amp increases.  So getting back our example where we need a 2 ohm stable amp, we could buy a 1 ohm stable amp but we could get a fraction of the actual power it is cable of.  Essentially, we would be buying a bigger amp than we really need.

In the event the Ending Impedance of the subs is 1 ohms, you can only use a 1 ohm stable amp.  If you try and use a 2 ohm stable amp it will be susceptible to overheating and going into Thermal Protection mode or it could burn out.

The last step, once you do the work to learn the stable impedance rating needed for your subs, you simply match up the total RMS wattage of the subs with the total RMS output of the amp that has the requisite stable impedance rating.

Matching Mid-Range or High-Range Speakers and Amplifiers

If you’re wiring mid-range or high-range speakers (i.e. “mids” and “highs”), you can use the same simple formula but substitute coils for speakers and take into consideration the number of channels on the amp.  Nearly all mid-range and highs amps are 2 ohm stable per channel so to get the maximum amount of safe stable power, without over heating the amp, your goal is to achieve an Ending Impedance of 2 ohms per channel.

Ending Impedance of Speakers = Impedance of a single speaker  / # of speakers

  • Ex. You have 2 mid-range speakers, each has an Impedance of 4 ohms:
    • 4 ohms / 2 speakers = 2 ohms, so on a 2 ohm stable 2 channel amp, you can add 2  4 ohm speakers per channel for a total of 4 speakers.  On a 2 ohm stable 4 channel amp, you can add 2  4 ohm speakers per channel for a total of 8 speakers.
  • Ex. You have 4 mid-range speakers, each has an Impedance of 8 ohms:
    • 8 ohms / 4 speakers = 2 ohms, so on a 2 ohm stable 2 channel amp, you can add 4 8 ohm speakers per channel for a total of 8 speakers.  On a 2 ohm stable 4 channel amp, you can add 4  4 ohm speakers per channel for a total of 16 speakers.

Again, nearly all mid-range and highs amps are 2 ohm stable per channel so when connecting speakers you want to ensure your ohm load does not drop below 2 ohms per channel.

  • Ex. You have 4 mid-range speakers, each has an Impedance of 4 ohms:
    • 4 ohms / 4 speakers = 1 ohms

So if you connect 4 speakers each with an impedance of 4 ohms with a 2 ohm stable amp, you will either overheat and burn out your amp or it will constantly go into Thermal Protect mode.

It is advised that if you don’t know what you’re doing or have questions, ask an expert.  If you ever have any question about what speakers go with which amp, feel free to call us at Five Star Car Audio, 216-475-5868 or come see us at 17170 Broadway Ave Maple Heights OH 44137.

Implications of Series Vs. Parallel Wiring of Subwoofers

When buying subwoofers, be sure to buy an amplifier that has a compatible Impedance rating with those subs. Incidentally, you should also buy a class D mono block amplifier if your running subwoofers. You can get away with buying a class A/B or a two channel amp with a built in crossover but you will sacrifice on quality and strength of sound all else being equal. There is more on this topic in previous posts. Second, you should ensure the subs you buy will enable the amp to operate at its designated safe Impedance rating.

Here are some examples of how to pair subs with specifically rated amplifiers.

  • 1 Single Voice Coil 4 Ohm sub will require a 4 Ohm stable amp ( 2 ohm or 1 ohm stable amps are also stable at 4 Ohms).
  • 1 Dual Voice Coil 4 Ohm sub will require a 2 Ohm stable amp.
  • 2 x Single Voice Coil 4 Ohm subs will require a 2 Ohm stable amp.
  • 2 x Dual Voice Coil 4 Ohm subs will require a 1 Ohm stable amp.
  • 4 x Single Voice Coil 4 Ohm subs will require a 1 Ohm stable amp.

If you’d like to understand the math behind these calculations, it’s pretty simple if you’re connecting speakers with the same impedance:

Ending Impedance = Impedance of a single sub  / # of coils in all subs

  • Ex. You have 2 single voice coil subs each has an Impedance of 4 ohms:
    • 4 ohms / 2 coils  = 2 ohms, for these subs you can go with a 2 ohm or 1 ohm stable amp.
  • Ex. You have 2 dual voice coil subs each has an Impedance of 4 ohms:
    • 4 ohms / 4 coils = 1 ohm, for these subs you can only go with a 1 ohm stable amp, if you add a 2 ohm stable amp via parallel wiring, you burn up the amp!

On a related but side note, if you’re wiring mid-range or high-range speakers (i.e. mids and highs), you can use the same simple formula but substitute coils for speakers.

Ending Impedance = Impedance of a single speaker  / # of speakers

  • Ex. You have 2 mid-range speakers each has an Impedance of 4 ohms:
    • 4 ohms / 2 speakers = 2 ohms
  • Ex. You have 4 mid-range speakers each has an Impedance of 8 ohms:
    • 8 ohms / 4 speakers = 2 ohms

Nearly all mid-range and highs amps are 2 ohm stable so when connecting speakers you want to ensure your ohm load does not drop below 2 ohms.  If it does, you will overheat and burn out your amp.

Ok, now back to matching subs and amps.  Most 1 Ohm Stable sub amps can handle subs that require 4 or 2 Ohm stability.  However, the higher the Ohm load required for the sub(s), the lower the amount of power that a 1 Ohm stable amp will put out, which lowers the acoustical output from your sub(s).  So, as we’ll outline again and again in this post, it is very important to get the right amp for the your sub(s), or vice versa, if you want to maximize the potential and satisfaction from the equipment you buy.

If you buys subs that force the amp to operate at an impedance below its safe/stable designated rating, for instance, if you have 2 dual voice coil subs with a 2 ohm stable amp, you have a few options:

  1. wait until your amp burns up to get the right amp
  2. wire the subs using the Series Wiring Technique and lessening the output of your subs
  3. buy the right amp and wire your system using the Parallel Wiring Technique

We always recommend buying the right amp for specific subs, or vice versa, again to maximize the potential and satisfaction from the equipment you buy.

In the event you have no choice but to go with option 2.  Here is some info for you.

Series Wiring Technique

Wiring your subs and amp using the series technique is very simple.  In a series connection you simply connect the positive terminal of speaker ‘A’ to positive terminal of the amplifier. Then you connect the negative terminal of speaker ‘A’ to the positive terminal of speaker ‘B’.  Then, connect the negative terminal of speaker ‘B’ to the negative terminal of the amplifier.  However, the amp won’t produce full power and the system won’t produce as much SPL as it would with the correct load but it’s also going to allow the amp to operate safely and reliably.  Again, only go this route if you absolutely have to.

Parallel Wiring Technique

Just for comparison’s sake, here is some info about the more common Parallel Wiring Technique, which is also pretty simple.  All of the positive speaker connections are connected to the positive terminal of the amplifier and the negative to the negative.  When speakers are connected in parallel, the impedance (also known as electrical resistance) is reduced which allows the amplifier to put out more power, hence increasing acoustical output of your sub(s).

It is advised that if you don’t know what you’re doing when it comes to wiring, ask an expert or have them do it.  If you ever have any question about what speakers go with which amp, feel free to call us at Five Star Car Audio, 216-475-5868 or come see us at 17170 Broadway Ave Maple Heights OH 44137.

Monoblock Amps

Monoblock amps are the power supplies for subwoofers. Compared to ordinary speakers, subwoofers need more power and do not play high frequencies. Monoblocks are not full range amps, but they do provide optimum power output and efficiency. These car amps have a single channel with no differentiation of right or left. They can power more than one subwoofer.

There are different types of monoblock amps available in the market. Getting a suitable amp that matches your needs can be a challenge. Each type of monoblock amplifier offers distinct features and capabilities. The prices vary depending of features like power output levels, brand, and performance.

If you ever have any question about what speakers go with which amp, feel free to call us at Five Star Car Audio, 216-475-5868 or come see us at 17170 Broadway Ave Maple Heights OH 44137.

Choosing The Right Car Subwoofer

If you are new to car audio, choosing the right component subwoofer can seem like a challenge, with so many subwoofer options out there. How can you decide which one is the best for YOU? The easy route is to choose a loaded and amplified subwoofer package (subs are already matched and mounted with a perfectly matched amplifier already built-in). Just wire and rock! But if you prefer the high performance or custom design of a compnent sub, read on… There are thousands of options in different brands, sizes, power handling, voice coil configurations, etc.

Common Misconceptions

  • A woofer with the highest power handling has to be better than one with a lower rating. Not necessarily.
  • A woofer with dual voice coils has to be better than one with a single voice coil. Not always.
  • 15″ subwoofer has to be better than a 10″ subwoofer. It depends.

Subwoofers are a necessary component of any good sound system. No other speakers can reproduce the low frequencies necessary to experience your music the way the artist intended. Whether you listen to rap, rock, metal, or country… Whether you listen to your music loud or quiet… subwoofers will improve your overall listening experience with the feel of a live concert.

Decision Factors

There are multiple factors to consider when deciding what subwoofer is right for you. Depending on your answers to the following questions, the right subwoofer for you may not be the right subwoofer for your buddy or even your next vehicle.

Your Budget?

How much money are you willing to spend. You must consider the cost of the subwoofer, the cost of an appropriate sized amplifier to power the subwoofer, and any electrical upgrades you may need (high power alternator, extra batteries, etc…) to provide enough power to your amplifier if you choose a high power system.

Your Goal?

What are the goals for your sound system? Do you want to compete in SPL competitions? Do you want to rattle the windows of the vehicles next to you at a stoplight? Do you simply want to improve the sound of your factory sound system? The answer to these questions will help you choose a subwoofer that is right for you.

How Much Room?

How much space do you have available in the vehicle that you intend to have the subwoofer installed? The woofer itself can sometimes be fairly big and heavy and when the woofer is installed in it’s enclosure it gets even bigger. For example, if you only have 5 inches of depth available, you will need a subwoofer that has a depth of around 4.5″ max.

Measure the height, width, and depth of the available space and confirm an enclosure will fit in the space and the sub will fit through the opening to the space.

If you plan to build your own enclosure or have your local car audio shop build one for you, make sure you can fit an enclosure that has the appropriate volume specified for the subwoofer.

If you are limited on space, you may want to consider shallow mount / thin subwoofers that are built specifically for limited space applications or maybe a vehicle specific subwoofer system that has a custom built enclosure designed to fit in a specific space in the vehicle. Another option is to buy an enclosed model that will fit in your trunk without access through the deck. Remember that bass travels through walls in all directions.

Compare Sub Families

In the world of subwoofers, there are many misconceptions. Some people think that the higher the power handling the better the subwoofer. Or the bigger the magnet is, the better the subwoofer will perform. These determinations are not so simple because there are many other factors to consider. This article is not intended to explain ALL of the technical aspects of choosing a subwoofer. But it will help a novice car audio enthusiast with the process.

Once you have decided on a size and budget, there are some key subwoofer specs to consider when researching subwoofers. These specs will help you analyze the performance of the subwoofer and determine which is the better option for YOU.

  • Power — If you want a system that really booms, there’s no substitute for plenty of power. Pay attention to RMS power ratings, not peak or max power ratings. RMS ratings measure continuous power handling or output and are a much more realistic measure of the amplifier’s actual capabilities. Make sure you match the sub’s power handling to your amp’s power output.
  • Sensitivity — Sensitivity goes hand-in-hand with power to achieve high output. A sub that has a higher sensitivity rating requires less power to produce the same volume of sound as a model with a lower sensitivity rating. This is very important to consider because a subwoofer rated at high power handling and rated low in sensitivity is less efficient than a subwoofer with a lower power rating and a higher sensitivity. The best option will be the highest spec of both.
  • Frequency range — Frequency range gives you an idea of how low a note a sub can reproduce accurately. Keep in mind, the actual performance of the sub will depend on a lot of variables including the box type it’s mounted in and whether or not the box has the appropriate volume and/or port tuning.
  • Enclosure type — The type of enclosure a sub is mounted in will have a large effect on the type of sound it produces. In general, sealed boxes give you the deepest, most accurate sound, while ported enclosures produce more volume from the same component subwoofer.
  • Number of voice coils — Dual voice coil subwoofers are a popular choice among car audio enthusiasts who want more flexibility in wiring their sound systems. While typical subwoofers have a single voice coil, dual voice coil (DVC) subwoofers use two separate voice coils, each with its own connections, mounted on one cylinder, connected to a common cone. But dual voice coils do not affect the sound output and they cannot handle double the power of a single voice coil subwoofer.
  • Size of the woofer — Size is a never-ending question — what size subwoofers play loudest and lowest? It’s not an easy question — you need to consider sensitivity, enclosure type, and available power. If your ultimate goal is to have a system that plays loud and low, and space isn’t an issue, go for the biggest subs, but don’t underestimate smaller subs. Properly powered and in the right enclosure, smaller subs can put out plenty of sound.
  • Impedance — Subwoofer power ratings are calculated at a specific impedance. It is EXTREMELY important to ensure that your system configuration is matched appropriately to the power provided by your amplifier at your system impedance. There are a wide variety of amps available, so you shouldn’t have any trouble finding one that will bring out the best in the sub you’ve chosen.
  • Volume Displacement – Volume Displacement is to a subwoofer what horsepower is to an engine.  Volume displacement is the amount of air a subwoofer can move during the standard movement of the cone and is calculated by multiplying surface diameter by xmax. Look for subwoofers that display this information.

Once you have determined what kind of system you want to create, considered how much space you have available, and how much money you want to spend, the only thing left to do is match up your subwoofer or subwoofers with an appropriate amplifier.

Matching The Amplifier

To do this, you need to consider power ratings and impedances. For example, if you are going to purchase a single subwoofer system, you will need to choose a voice coil configuration that will match up the appropriate power from your amplifier.

If an amplifier has an RMS power rating of 500 watts @ 2ohms or 250 watts @ 4ohms and the subwoofer you choose has an RMS power rating of 500 watts, you will want to make sure you can wire your subwoofer at 2ohms.

Subwoofers are available in single or dual voice coil configurations. The number of subwoofers you are wiring together and whether they are dual or single voice coil configurations will determine what your final load or final impedance will be.

For example, if you have 2 subwoofers that are dual 4ohm voice coils, your final impedances can be either 1ohm or 4ohm at the amplifier depending on how you wire them.

If you have 2 subwoofers that are single 4ohm voice coils, your final impedance can either be 1ohm or 8ohms depending on how you wire them.


After considering your space limitations, your budget, and the type of system you are trying to build, you have researched the specifications of the subwoofers that fit into your criteria, and you have chosen a single subwoofer or numerous subwoofers that have the correct voice coil configuration and impedances to match up to a final impedance that will allow your amplifier to provide the proper amount of power, you are all set.

The process of choosing all the necessary components and ensuring they will work properly with each other can be an intimidating process but if you follow our guidelines and compare using the criteria we have outlined, you can have confidence that your money is being well spent.

Subwoofer Power Handling

Most car audio enthusiasts (bass heads) start shopping for their new system once they have decided the quantity and size of subwoofers they want to buy. After all, for bass heads, subwoofers are the main part of the system that creates the window rattling, body-panel-flexing bass they crave!

But a common mistake when choosing subwoofers is the assumption that the higher the rated power handling, the louder it will sound. This is perfectly logical, but not always true.

What Makes A Sub Loud

To understand, you need to know what makes a subwoofer loud (SPL) and some basic physics. Now, don’t expect this post to be a science lesson with a bunch of technical equations and diagrams. This is a basic explanation of SPL and subwoofer power handling.

First, some definitions you need to know:

  • SPL = Sound Pressure Level
  • RMS Power Handling = Continuous amount of power your subwoofer can manage without damage
  • Peak Power Handling = A measure of power that could potentially be managed for short bursts.
  • XMax = The distance a subwoofer voice coil can move in one direction without leaving the magnetic zone a.k.a. how far the woofer can move.

It’s important to also understand that some car audio manufacturers promote ridiculously crazy Peak Power ratings as a marketing tactic to get customers to believe their product will be louder, better, more powerful, etc. However, the crazy math calculations they use to come up with these numbers is not realistic.

Most everyone knows that sound is created by vibration of an object. The vibrating object causes air molecules nearby to move back and forth in sound waves. The more air molecules you move, the louder your sound waves will be. The more air molecules you move within the interior cabin of your vehicle, the more air pressure you will create. This is called sound pressure. The Sound Pressure Level (SPL) is the measurement of this pressure in decibels.

So without going into too much detail, the moral of the story is, the more air you move, the louder it will sound. So buy a bunch of 18″ woofers and you will be loud. Right? Not necessarily.

What Is XMax

There are plenty of other factors to consider. An 18″ woofer has a lot of surface area, but can the woofer move a lot of air? This is where XMax comes in. If the 18″ woofer can only move one 1/16th of an inch, it’s not going to move much air. It is similar to sending a higher frequency tone to a woofer. It’s not going to move much and it won’t be very loud.

So what does it take to get a woofer to have a decent Xmax you might ask? Well… A lot! It takes a good suspension that can handle the movement while maintaining linearity. If a subwoofer does not stay linear in it’s movement, it will create distortion and can even cause a rub or short of the voice coil against the pole piece. Simply put, a good quality suspension is very important.

In order to have good XMax, you also need a strong magnetic field which uses AC current to push the woofer forward (positive) and pull the woofer backward (negative). This magnetic field is created using the magnets on the woofer’s motor structure and the electrical current being transferred through the voice coil.

The Bigger The Better?

So here is where most people make a logical assumption that isn’t necessarily true. Logic would tell you the bigger the magnet, the bigger the magnetic field. The more power through the voice coil, the more XMax you will have. The more XMax you have, the louder you will be. Right? Not necessarily.

I can build you a woofer with HUGE magnets weighing 200lbs and a voice coil that is capable of handling 10,000 watts. That’s easy. But designing a suspension that can keep that power under control is the hard part. If the suspension is so tight and rigid to control the power, it will limit the XMax. If the suspension can’t control the power, the subwoofer could become non-linear causing distortion and even burn the voice coil and now your 10,000 watt subwoofer is a 200lb paper weight.

Additionally, we haven’t talked at all about mass yet. Consider this. Subwoofer A has a power handling rating of 2,000 watts with huge magnets hanging off the back and a cone assembly made of aluminum that has a mass twice that of the cone assembly of Subwoofer B which has a power handling of 500 watts with magnets half the size. Which subwoofer has the potential to be louder?

Subwoofer Efficiency

If you understand this information, this is a trick question. You can’t determine which subwoofer could be louder from this information only. Subwoofer A can take more power but it’s cone assembly is heavier and therefore it takes more power to move it. Xmax could suffer as a result. Subwoofer B can’t take as much power but it’s cone assembly is lighter and therefore, it’s XMax could be as good or better than Subwoofer A thus moving more air. It’s called efficiency. After all, we don’t want to spend the extra money for a HUGE amp or tax our vehicle’s electrical system to power it if we don’t have to. Right?

So the point is… comparing the performance of subwoofers purely based on the power handling rating is not always a fair comparison. There are too many other factors to consider. And once you make your purchase and start the installation, there are even more factors to consider to ensure your subwoofer(s) performs to it’s maximum potential such as enclosure design and port size and length for tuning. Plus if you buy a subwoofer with an RMS power handling rating of 2,000 watts, you are going to want to put 2,000 watts to it. Under powering a subwoofer is often times worse for it than over powering. Then you have to make sure your vehicles electrical system can support a 2,000 watt amplifier. Not to mention a 2,000 watt amplifier (that truly does 2,000 watts RMS) will cost you more than one that does 500 watts assuming they are of comparable quality.

So if you are in the market for a subwoofer, don’t be fooled by peak power ratings created by crazy math. These don’t mean much of anything. RMS Power ratings are what you should be more concerned with. However, this spec doesn’t always reflect performance either, but I will leave this discussion for another article.

Matching Subs With the right Amp

A primary factor in choosing component car subwoofers is choosing the correct amplifier to power the system. If you wire one subwoofer to one amplifier, your matching calculation is straight forward. But if you are wiring multiple subwoofers to a single amplifier, then calculating the total effective impedance of the system is a necessary step for safety and reliability as well as performance.

First, let’s review some terms:

Parallel Wiring

Generally speaking, parallel wiring is where the positive terminals of the source and all loads are wired from one to the next, and the same with the negative terminals forming two loops.

Series Wiring

Generally speaking, series wiring is where the positive terminal of the source is wired to the positive of the first load, the negative of the first load is wired to the positive of the second load, and so on. The negative of the last load is wired back to the negative of the source forming one large loop.

Impedance or Ohm Rating

Ohms are a measure of impedance, or impedance to electrical current flow. A larger Ohm rating equals a greater load impedance. A higher impedance load will result in less amplifier output for that impedance, for example an amplifier will output more power at 2 ohms than at 4 ohms.  Amps can generally be safely wired at 4 or 2 ohms and some even at 1 ohm depending on their design.

If you have an amplifier wired to a single-voice-coil (SVC) subwoofer, there is only one wiring method, so the SVC impedance is what the amplifier must match. But if your sub has a dual voice coil (DVC), or you are wiring multiple subwoofers to one amplifier, then understanding the wiring alternatives offers insight into how best to connect them to maximize performance.

The goal is to deliver as close to rated power to each sub as possible with a given amplifier by wiring the system in a manner that minimizes the effective impedance without exceeding the power rating of the subwoofers.

You may occasionally need to compromise. For instance, some subwoofer/amplifier combinations will not allow full power to be produced safely such as a sub combination that results in a 1 ohm effective load for an amplifier rated at 2 ohms minimum. Instead of burning up your amp, you may be able to wire the combination to result in a total impedance over the 2 ohms so that while the amp will not deliver the full power rating of the subwoofer (and your SPL will be lower), at least the amp will operate safely and reliably.

Since multiple subwoofers wired in combination result in different effective impedance ratings as a group total, we must calculate this total based on our wiring technique. In reverse, we may be able to change our wiring pattern to accomplish needed impedance totals to match the component combinations we desire.

Series Wiring Impedance Calculation

In series wiring, you add the impedances of the voice coils, so wiring two 4 ohm voice coil subs would result in 8 ohms for the system total as presented to the amplifier.

Total Impedance = Sub I1 +Sub I2 + Sub I3 + …

Parallel Wiring Impedance Calculation

While series wiring of multiple subs increases the total effective impedance, parallel wiring of multiple loads lowers the total effective impedance.

With subwoofers rated at equal impedances, the system impedance is equal to the impedance of one sub voice coil divided by the number of subs. So if you have two 4 ohms subs wired in parallel, the system would have an effective impedance of 4 ohms divided by 2 subs for a total impedance of 2 ohms  presented to the amp.

Total Impedance = Sub Imp/# of Subs

Since parallel wiring lowers impedance, always double check to ensure your totals do not run into unsafe levels especially when bridging an amp to increase the rated power available.

Example Impedance Calculations

So let’s look at matching some subwoofer/amplifier systems…

Bob has a great single sub system in his Chevy, but wants to upgrade to two subwoofers. He currently has an 500.1 500W RMS mono block class D amplifier with one  12″ 250W RMS 4 Ohm Subwoofer. Can he add another 12″ subwoofer?

The amplifier is rated at 300 Watts RMS x 1 Channel at 4 Ohms or 500 Watts RMS x 1 Channel at 2 ohms. Since it has been wired to a single 4-ohm sub, the amp can deliver 250 watts with a properly set gain to match the sub power rating perfectly.

Ideally, Bob want’s 2 x 250 watts = 500 watts for the two subs. From the formula above, we see that we can lower the total impedance of the two sub system if we wire in parallel. So we take the 4 ohm impedance and divide by two subs, which results in 2 ohms total impedance. This amplifier can deliver 500 watts at 2 ohms, so each of the 12″ woofers will get their full 250 watts of optimum power. This means we are going to rock big time!

What if Bob wanted to use that same amplifier with a couple new 15″ subs which have a dual voice coil design and can handle 400W RMS. Can he do it with this amp?

The rating on the amp is 300W x 1 channel @ 4 ohms and 500W x 1 channel @ 2 ohms. The 15″ are dual voice coil so the wiring is going to be different than our previous example. If Bob were to use two 15″ subwoofers they could be wired at either 4 ohms or 1 ohm, which would not be enough power at 4 ohms and at 1 ohm would cause damage to the amplifier. If he chose two 15″, they could be wired at either 2 ohms or 0.5 ohm. The 2 ohm wiring would allow them to work with the amplifier and although the system would not get the full power out of the subwoofers, 800 watts, the system would function and deliver excellent SPL performance.

Dual Voice Coil Subwoofers

Dual Voice Coil Subwoofers

Dual voice coil subwoofers are a popular choice among car audio enthusiasts who want more flexibility in wiring their sound systems. While typical subwoofers have a single voice coil, dual voice coil (DVC) subwoofers use two separate voice coils, each with its own connections, mounted on one cylinder, connected to a common cone.

The key difference is the DVC sub offers more wiring options to better match and take advantage of the amplifier. The DVC sub is typically more expensive, but provides multiple impedance connections which may result in more power from the amplifier or to better match the available amp impedance options.

The voice coil differences have no direct effect on the subwoofer performance, frequency response or power rating. A dual voice coil sub does not directly perform better than the same sub with a single voice coil.

  • Parallel: A dual 4-ohm voice coil subwoofer with its coils wired in parallel presents a 2-ohm load to your amplifier. Since an amplifier produces more wattage at a lower impedance, the parallel connection ensures you’ll get the most output from your amp. In the same fashion, if you have a stereo amplifier and two DVC subs, wire both subs for 2-ohm impedance (one per channel) for maximum output.
  • Series: Series wiring lets you configure multiple woofers to one amplifier at an acceptable impedance. Wire both coils in series for an 8-ohm impedance, and then wire two 8-ohm subs together in parallel for 4-ohm total impedance (perfect for most 2-channel amps bridged to mono operation). Another example: if you have a high-powered 2-channel amplifier, wire four 8-ohm subs per channel (each channel sees a 2-ohm load).
  • Independent: You can wire each voice coil to a separate channel of your amplifier, if you prefer not to bridge your amp. Independent wiring is a nice option if you’re wiring two DVC subs to a 4-channel amplifier — one voice coil per channel. Just make sure the signal going to each coil is exactly the same, or the differences will cause distortion.

Some amplifiers are designed with an unregulated power supply — these amps are favored by mobile audio competitors for their superior performance. An unregulated amp’s power increases dramatically when it sees a lower impedance load. For example, an amplifier that produces 75 watts RMS x 2 channels at 4 ohms would double its power to 150 watts x 2 with a 2-ohm load. DVC subwoofers (particularly the dual 2-ohm models) give you the flexibility to wring every bit of power out of this type of amplifier.

Also, if you choose to add an unregulated amp as a power upgrade to your existing DVC subwoofer system, you can simply rewire your subs for optimum impedance. Remember that most car amps are stable down to 2 ohms in normal operation, and to 4 ohms in bridged mode. It’s important to check your amp’s manual for its operating parameters before hooking up a DVC sub that’s wired for low impedance.

A DVC sub offers the same performance whether it’s wired in series or parallel. Its power handling levels, frequency response, and other specifications do not change — the only difference is the impedance presented to the amplifier. As a result, you’ll need to use the enclosure that’s recommended for your sub, no matter how it’s wired.

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