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Basics of wiring Speakers:
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Speakers, mounted in cabinets or as a part of an assembly are the things that make the sounds within you audio system. Wiring them up to provide the most effective load and making sure that all of them are in phase will help you sound as good as possible. Its not really hard to do, as long as you understand a few things about loading and how to connect your speakers to provide an optimal resistive load.
I'm starting with the assumption that you will probably be building some of your own speaker cabinets and will need to know how to wire up the speakers properly. Luckily, the rules are the same for cabinets that are wired into your system. All speakers and speaker cabinets have some resistive 'load', measured in ohms.
When you bought your PA system, or other Audio amplifier, somewhere in the documentation, or possibly stamped on the back of the gear, is something that indicates the 'load' that the system is designed for. In many cases, the Power Amplifier stage will state that a 'load' of 2, 4, 8 or 16 ohms is what you should be using for the Speaker system. If you don't know what you gear is rated for, most audio systems are designed to safely operate with an 8 ohm load; many can operate at 4 ohms. You are safe running everything at 8 ohms; never run below 4 ohms unless you are absolutely certain that your system will handle it properly.
If you have a Power amplifier that is Solid State (Transistors or FET's), you should never apply a dead short to the Speaker load - it may destroy the output stage almost immediately. If you are using a Tube amplifier with an Output transformer - you should never have an open circuit at the speaker load; this can damage the Output transformer (Very Very Expensive!!). See the documentation that comes with your PA System / Power Amplifier to see if there are any cautions for you to take. Some Stereo Solid State Power amplifiers get very grumpy if you don't provide a load for both channels - if one channel has a load and the other doesn't; you could burn out the entire power amplifier (I have a Phase Linear Power Amp under my desk that would make a great boat anchor as a result of this discovery)
You need to keep in mind that the lower the resistance of the load, the more difficult it is for an amplifier to drive the load without distortion. I have never seen a commercial Audio Power Amplifier that can't handle 8 ohm loads effectively, but very few power amplifiers can effectively drive a speaker load that is less than 2 ohms without damaging them. You can always have slightly higher resistance (16 ohms, for example) without damaging results, but too low of a resistance will likely cause you expensive problems.
Figuring out the load
If you have only a single speaker, this is all quite easy, you just match that single speaker to the amplifier, and you are done. In many cases, you will have a number of speakers, and then you must calculate the 'load' that the amplifier will need to support.
There are 3 ways to wire multiple speakers together. They are:
- Series
When you wire in series, the speakers resistance (as measured in ohms) is additive - ie. putting 2 8 ohm speakers in series results in a 16 ohm load.
- Parallel
When wiring in parallel, the resistance of the speakers decreases. 2 8 ohm resistance speakers in parallel result in a 4 ohm load. Its easy to calculate the effect of resistive load when all he speakers are the same initial resistance before placing them into a parallel configuration. Most pro-audio speakers are rated at 8 ohms, and I'll assume that this is what you are using.
- A combination of Series and Parallel
This is really just 2 sets of series wired speakers connected in parallel. This is how you maintain a consistent load with multiple speakers (or you can substitute speaker cabinets in place of the individual speakers shown here).
Impedance
The 8 ohm rating is not what it appears to be. Its actually an inductive resistance (impedance), and if measured using an ohm-meter, it will appear much lower than it really is. The reason that it is not 8 ohms when you measure it with an ohm-meter is because the electrical circuit within a speaker is made of wound wire around a support bobbin that is suspended into a metallic magnetic structure (otherwise known as the Voice Coil). This structure creates an inductor that happens to move a paper (or other material) cone back and forth as audio signals are applied to the wire on the bobbin. The actual inductive resistance of 8 ohms is an odd measurement. Most speakers have a peak impedance somewhere in the lower frequency range where the speaker is resonant, this may be as high as 60 ohms, and as the frequency increases, the impedance goes up again (on large cone speakers, it may be as high as 50 ohms at 20 kHz). The resonant peak can move, depending on your cabinet enclosure. Some people measure the impedance at a given frequency (400 Hz, 1000 Hz, 2000 Hz, etc) and list it that way - some consider it an average of the measured impedance through a given frequency range. The part to keep in mind is that you have to trust the speaker manufacturers on how the speaker is rated. Many speaker companies can provide you with a graph of the impedance/resistance of their speakers at different frequencies.
This graph shows a speaker not mounted
in a cabinet (free-air) starting at 10 Hz
As you can imagine, this frequency sensitive alteration of load is very difficult to simulate - it is a characteristic of a moving Voice Coil. Many Speaker Emulators (inductive load to simulate a speaker) don't respond very much like a real speaker - their impedance tends to be very flat over a large frequency range
Since you cannot measure impedance with a simple ohm-meter, only direct resistance, a speaker will usually appear to measure 2 ohms or less. When speakers fail, they tend to burn up the Voice Coil, and an open circuit occurs - or a dead short occurs (this is less frequent), Either way, it no longer functions correctly. An ohm-meter can detect either of these 2 conditions if you have a good speaker to compare it against.
Phase
You'll notice that there is usually a colored dot on the speaker, or possibly a marking indicating a '+' near one of the wiring terminals. This marking indicates the polarity of the speaker. If you were to connect a 1 1/2 volt battery across the speaker connections momentarily, the speaker cone will jump in or out, depending on which way you touched the speaker wires. The important thing is to make sure that all of the speakers in a cabinet or complete sound system move the same direction when the 1 1/2 volt battery test is applied to it. This is a Phase test. As long as all the speakers react the same, then the speakers are in phase with each other - you want this. Speaker systems that have some of their speakers wired out of phase will sound very thin and will not reproduce sounds faithfully.
NOTE: I use a 9 volt battery to test phase, and when I touch the speaker to it, I only make a momentary connection - only long enough for me to see which direction that the speaker(s) move. Do not apply more voltage or power to a speaker in this fashion when testing phase. Speakers were not made to operate with a constant voltage applied to them - don't do this any more often than necessary. 9 volts should not hurt anything (many high end systems pump 50 or more volts into the speakers, however, it is alternating, causing the speaker to move in and out, not just one way). Testing for phase in an entire speaker system is important to do, if you care about sound quality. This also requires that all speaker cables be wired correctly, otherwise you'll have phase problems no matter how well you wire your cabinets up.
The Dots (or '+') on the speaker is there to tell you how to wire your audio system up without having to revert to testing with a 1 1/2 volt battery. In my diagrams, there is a RED DOT to indicate the polarity of the speaker. You'll notice that in the Series wiring diagram that we connect a wire starting at one speakers dot terminal, then connect a new wire to the same speakers unmarked terminal and connect that to the next speaker's dot terminal. The last connection comes from the last speakers unmarked terminal and this returns to the power amplifier.
Similarly, when wiring speakers in parallel, the dots go together and the unmarked terminals connect together.
When wiring up connectors for speakers, the wire that goes to the dot (or '+') goes to the center tap on a 1/4 inch phone jack, or the RED banana jack. The wire that comes from the terminal on the speaker without the dot goes to the ground (outside case on a 1/4 inch phone jack) or the BLACK banana jack. If you use other forms of connectors, refer to existing cabinet wiring, or the documentation that came with your system.
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For 1/4 inch (and 1/8 inch) phone jacks, you need to verify which
solder tabs go to the + and - connections,
1/4 (and 1/8) inch phone jacks have no standard for which of the solder tabs goes to what.
Open cased Jacks are easy to verify - just look at it.
In an enclosed Jack, you may need to use a VOM/Digital Multimeter to check which connection
goes to what. The + and - relate to how the speakers are connected. The speaker should have a colored dot on it to indicate + or it will be marked with a +. |
NOTE: Pro Gear needs quality connectors - don't skimp in this area when building your own cabinets - avoid Gold connectors if this system will travel frequently; the gold plating will wear off fairly quickly and you will gain little benefit from it. I don't like banana plugs because they are so easy to accidently wire up wrong - If you have people help you, this is one task that they will likely screw up given the chance. If you don't want to, or can't use standard 1/4 inch phone plugs for your speaker cables, I feel that its far better to use a custom connector than to use banana plugs. Call me paranoid, but you can't hear what the audience hears when you are on stage (unless you have a wireless system that allows you to step out into the audience area and listen - I highly reccomend doing this). Tracking down a miswired cabinet while you are attempting to perform is not easy and it does happen. It's your sound that could be affected; you decide.
The dots (or '+') work in the same sort of way you put batteries into a portable cassette player or other electronic gear - Things won't sound right if the polarity is wrong somewhere within the system.
Big Systems
When you have numerous cabinets to wire together, you will need to know what the Power Amplifier is rated at - for example 8 ohms. From here, you have to figure out how to connect your cabinets so that you don't put a load greater than the system can handle. Typically, if your system is not stereo, you end up plugging your 2 PA cabinets into jacks that wire them in parallel. If your system is designed for 8 ohms, then the 2 cabinets should be wired for 16 ohms - 2 16 ohm cabinets in parallel equals an 8 ohm load.
This gets a bit more tricky if you have 7 or 8 cabinets per side to hook up. You'll have to know what each cabinet is rated at (in ohms) and figure out how to connect them up in series/parallel in order to make things work right.
By the way, when you hook things up in parallel, the power thru the speakers is shared equally. This says that you can't casually put unlike speakers in parallel. For example, a 15 inch woofer and 6 inch midrange speaker should not be wired in parallel - the 6 inch midrange is apt to be destroyed once you crank the volume up. What does work is taking like speakers (ones that are rated for the same power handling capacity) and wiring them in parallel. We won't get into crossover networks (which is one way of powering different function speakers within the same cabinet) at this time.
When you wire in series, the load is split across the speakers based on resistance, but because the total resistance is higher, the actual power that each speaker absorbs is less. If you were to wire 2 40watt speakers in series, you end up with a power handling capability of 80 watts. Typically all of the speakers in a cabinet are the same resistance (8 ohms, for example), however you can mix them. Keep in mind that those with lower resistance will absorb more power - they must be able to handle it or else you can burn out a voice coil.
You can build small parallel or series boxes to keep in your chord case to allow you to reorganize your loads while you are on the road. I tend to make these out of Masonite/plastic/wood, or other non-conductive materials. These, along with some short cables (4 foot or less in length) allow you to calculate speaker loading, pick out a the proper adapter box, and adjust properly. If you have a complex set up, it is to your benefit to diagram the wiring for your crew (or other band members), just to make sure that you are connected up the same way each time.
When you have a cross over network, each individual speaker type is connected up such that it functions at specific frequency ranges. This us why a cabinet with a Woofer, Midrange horn and Tweeter can be rated at 8 ohms - the different speakers all provide load to the power amplifier at different frequencies.
NOTE: We do not work on Home or Car Audio. We work only with Pro-Audio applications. We cannot help you with Home or Car Audio questions.
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