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.

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