Speaker Cabinets: The World of Ohms
|By Kevin ManieriGeorges Music|
So youre thinking about getting a bigger, louder amplifier.In fact, youre thinking about getting what some people call a half-stack that is, an amplifier head and a separate speaker cabinet. You might even go with a full stack a head and two speaker cabinets.Exciting! And loud!But before you get started, there are a few things you should know about how to hook these things up.
It's all about options
First of all, why do some guitarists and bassists use a head-and-cab setup rather than a combo amp that has it all in one box? There are several reasons. The first is power. Most high-powered amps, especially for bass, come only in a head format. The second is flexibility. The player can choose from a large variety of speaker cabinets that vary in number of speakers, size of speakers, and type of sound. You can also mix-and-match your equipment. Your amp will have a certain tone through a classic 4x12 guitar cabinet; for some gigs, you may use a simple 1x12 for a different tone. Or, you may have a favorite cabinet with special speakers, and use different heads depending on the desired sound.
Making it all work
Always remember that your head-and-cab setup must be connected properly in order to function well. The most important thing to consider is the electrical resistance, or impedance, of each component. This is measured in ohms, and represented with a funny little Greek symbol (?). You want the resistance of your head to match the resistance of your cabinet. For instance, your guitar amp says 4 ohms next to the speaker jack on the back. Simply make sure that your speaker cabinet is also 4 ohms.Some amps can operate at 16 ohms, 8 ohms, 4 ohms, or even 2 ohms. You may see a selector switch for resistance, while some can just be hooked up and turned on. Remember, the lower resistance, the more power comes out of the amp. Most high-powered amps will say right on the box how many watts are available at each resistance level.
Bigger is better?
OK, that was the easy part. Now, what if I want to use multiple speaker cabinets? Maybe two 4x12s for guitar, or a 2x10 and 1x15 for bass. This is the fun part. Get out your calculators, because when you use two speaker cabinets at once, the resistance is halved
(divided by 2). For instance, if I use two bass cabinets that operate at 8 ohms, the total resistance of my setup will be 4 ohms. Two 16 ohm cabinets will bring me down to 8 ohms. Two 4 ohm cabinets will bring me to 2 ohms. I do not recommend mixing impedances, such as a 4 ohm with an 8 ohm, but consult your amplifiers manual to see if this is safe.It is important to check if your amplifier has a minimum load. Many amplifiers are not meant to operate below a certain point, often 8 ohms for guitar amps and 4 ohms for bass amps. In other words, if youre going down to 2 ohms, make sure your amplifier can handle it. Again, consult the back of the amp and the owners manual. Also, connect all of the speakers before turning on the amplifier, even if youre just letting it warm up. Some amps, especially tube amps, dont like to be turned on without having somewhere for their power to go.
A word on cables...
Now, another extremely important word of caution. Always use speaker cable to connect speaker cabinets
. Of[caption id="" align="alignright" width="223" caption="Speakon Connector"]
[/caption]course, right? You would be surprised how many people use instrument cables in a pinch, and end up with smoke coming out of their amp. Label your cables with tape or colored cable ties. Most of the cables at Georges Music actually say instrument or speaker right on them in fine print, just look very closely. For bassists, I recommend cables with those big blue Speakon connectors on the end [see image]. They make a more secure connection and youll never mix them up with your instrument cables.
The rest is up to you! Now that you know how to safely use speaker cabinets, you can tailor your sound with a custom setup. Guitarists, try a little 5-watt tube amp through a 4x12 and be amazed at the volume. Or play your 100-watt big gun through a smaller cabinet for a focused tone with great breakup. Bassists, use 15 speakers for that classic thump, or a wall of 10 speakers for more punch and clarity. Try a 2x12 as well, or mix and match. The combinations are endless. Remember these simple rules and when it comes time to play out, youll have your stack up and running in no time.
Kevin Manieri spends his time in the Finance department at George's Music and when he's not crunching numbers, can be heard blasting out killer bass riffs throughout southeastern Pennsylvania.