How to Find the Right Speaker Cab

Finding the right speaker cabinet to match your amp head can be daunting. Even for experienced buyers, making sure your ohms and wattage numbers all fit right is absolutely essential when building a stack. We recently invited Tim from EarCandy Cabs to share some insight and outline what to keep in mind when searching for the right cab.

Make sure to check out the EarCandy Shop here on Reverb for all your cab needs.

Ohms

When properly matching a cab and amp, the ohm rating of each must be taken into consideration. Mismatching ohms loads can cause complete failure of your amplifier, leading to a costly repair.

First, locate your amp's specific output for different ohm loads, such as 4 ohm, 8 ohm, or 16 ohm speaker outs or a ohm selector switch that will switch your amp’s load. (Many solid state amps and some tube amps will simply state operation between 4 and 16 ohms is suitable and safe, and operation outside this range is not recommended.)

Next, locate the cabinet’s recommended ohm load, usually stated on the input plate on the back. Make sure the amp’s output or ohm selector switch matches the cabinet’s ohm load. If your cab doesn’t have the ohm load stated on the back, check the manufacturer’s instructions or use a multimeter and a speaker cable to check the cabinet’s ohm load. Remember to always use a speaker cable, and turn the amp head off when hooking it up to the cabinet.

Pro Tip: Always turn your amp’s volume all the way down before turning your amp on or off.

Wattage

There are a few different options to consider when striking the right balance between your amp's wattage, your cab's wattage and your tone. It’s always a safe bet to use a speaker cabinet with double the wattage rating of your amps highest wattage output. For example, if you have a 100 watt amp, a 200 watt speaker cabinet will ensure safe, clean clear operation of your guitar rig for years.

A speaker cab rating double the wattage of your amp, however, may not be totally necessary. It's not the wattage alone that determines the volume coming through. For instance, a tube amp rated at 100 watts is a lot louder than a solid-state amp rated at 100 watts. Even when the output transformers on several different amps are running at 100 watts, the way the machinery (transistors or tube) inside translates that into decibel levels can vary. You can safely run a 100 watt cab with a 100 watt amp, although you’d never want to dime your amp (turn it all the way up) with this setup. Especially with tube amps, you wouldn't want to turn the amp up past 6 or 7 if your amp and cab wattages match exactly. Please keep this in mind when running foot pedals that can increase the decibel level of the amp’s output.

Leave Yourself Room to Grow

If you are using a guitar amp head that runs 100 watts at 8 or 16 ohms and you are getting your first cab for it, get a cab that is 16 ohms. The reason I say this is because if you get a cab that is 8 ohms, that’s it—you are done. If the lowest ohm rating the amp runs is 8 ohms and you have an 8 ohm cab, that single cab will be all that you can power with your amp. This same rule applies with an amp that runs 8 and 4 ohm loads or any amp that runs 16, 8 and 4 ohm loads. For example, if you have an amp that runs 8 and 4 ohm loads, you will want to get an 8 ohm cab to leave yourself options. You could run an 8 ohm cab solo (creating 8 ohms of resistance in the amp) or run two 8 ohm cabs (creating 4 ohms in the amp).

This may seem counterintuitive, but it is part of the math of parallel circuits. In parallel wiring, adding a speaker of the same ohm load as an existing speaker will cut your ohm load in half. For example, a pair of 16 ohm speakers will equal 8 ohms, a pair of 8 ohm speakers will equal 4 ohms, and so on. In the case of running two 8 ohm cabs with an 8 ohm amp (or two 16 ohm cabs with a 16 ohm amp), keep in mind you would have to run both cabs at all times to keep the load at the head cut in half.

In series wiring, a set of 16 ohm speakers in series will equal 32 ohms (not good). A set of 8 ohm speakers in series will equal 16 ohms. Parallel wiring is often paired with series wiring in 4x12 cabs. This is simply where one side of the cab is wired in parallel and the opposite side is wired in series. Wiring in parallel and series will yield an ohm load identical to the ohm load of all four speakers. For example, four 16 ohm speakers will be 16 ohms, four 8 ohm speakers will be 8 ohms.

Quick Tip

If you are mixing speaker models in your cab, your highest wattage capability is only as good as your lowest rated speaker multiplied by how many speakers are in the cab. For example, you might have a 2x12 with a 35 watt speaker on the left and a 100 watt speaker on the right, either wired in series or parallel (both wiring models achieve the same thing in a mono speaker cab). You now have a 70 watt speaker cab (35 watts x 2), NOT a 135 watt speaker cab. Though it’s true each each speaker will take on some of the character of the other speaker, especially the decibel rating, the wattage rating is a measurement of how much voltage the speaker can handle and this will not change. In a four speaker cab, the wattage will be four times the lowest rated speaker. If you are using a combo amp and an extension cabinet, this rule still applies.

To recap:

  • Always use a speaker cable to hook up your speaker cab to your amp.
  • Always match the ohm load of the amp’s speaker output to the ohm load of the speaker cab being used.
  • Always be sure to use a speaker cab with at least the same amount of wattage as your amp’s highest output.
  • If you aren’t sure of the ohm load of the speaker cab, check with the manufacturer or test it yourself with a multimeter.
  • Never plug and unplug your speaker cable from your amp or cab while your amp is on. Turn your amp off while hooking or unhooking your speaker cab.
  • Turn your amps volume all the way down to power up or power down your amp. This will prevent the annoying “pop” that some amps create when turning them on or off. The surge of power in that “pop” has been known to blow speakers due to the surge of wattage than can be hidden in that millisecond-long popping sound.
  • With mixed speakers, your speaker cabinet’s wattage capability is only double (for 2x12s) or quadruple (for 4x12s) that of your lowest rated speaker.
  • Leave yourself room to grow. A pair of 16 ohm cabs in parallel will equal 8 ohms, a pair of 8 ohm cabs in parallel will equal 4 ohms.

F.A.Q.

I tested my cab and it is supposed to be an 8 ohm cab but tested out at 10 ohms. Is this ok?

Yes, every speaker has its own footprint and many will blankly state "8 ohms" or "16" ohms” but if you look closely at the speaker specifications from the manufacturer next to the ohm load it will have what is called the "RE rating". Many times this will be different but close to the blank 8 or 16 ohm rating, a small variance in the ohm load like this will not cause any damage. Resistance (measured in ohms) in a live, powered up rig, will relate to frequency somewhat; higher notes present less resistance and lower notes will present more resistance. This natural variance in resistance also does not cause any problems.

I have a 5 watt practice amp but my speaker cab is 100 watts, will running a 5 watt amp into a 100 watt cab damage my speakers or amp?

No, as long as the ohm load between the amp and cab match, everything will be fine. Though you may not reach optimum tone levels from the speaker or speakers, no damage will be sustained to the amp or speakers.

There are two inputs on the back of my cab and both seem to do the same thing, which one should I use?

What you have is either a speaker cab that allows you to run another speaker cable from that existing cab to another speaker cab (something called daisy chaining, usually done with parallel wiring) or you have a stereo cabinet. If the label on the input panel doesn’t specify, you can do the following to safely figure out what you have:

Get a 9 volt battery and touch both the negative and positive tabs of the battery to the tip and sleeve of your speaker cable. If both speakers in your cab move in or out at the same time (known as phase), then the speakers are wired together and it is a mono cab. If only one speaker moves, there is a good chance you have a stereo cab, or possibly one good speaker and one blown speaker.

Simply unplug the speaker cable from the first input on the cab and plug it into the second input and repeat the same test, if the other speaker moves and the first one doesn’t, then it is absolutely a stereo cab. If you can’t see the speakers because the cab has a permanently installed grill cloth, you will need to run a small signal into the speaker cab inputs from something like a phone or mp3 player and see what you get. Sound from both speakers while using only one input means you have a mono cab.

Due to the nature of a parallel output, you can use either as an input and subsequently the other as an output. The left input is usually the “In” and the right is usually the “Out” according to manufacturing convention.

Can I run the output of my speaker cab into a second amp to provide a signal for that amp?

Absolutely not. That speaker output on the back of your cab will carry voltage just like the speaker out on the amp itself. You will want to use a line out on the first amp. If the first amp doesn’t have a line out, you will want to use an A/B switch to split your signal path into another amp.

Note: EarCandyCabs.Com nor Reverb.Com are responsible for any damage sustained to any gear due to experimenting with information in this article. Please always refer to the manufacturer’s instructions for proper set up of your amp and speaker cab.

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