This week, I had an email from a subscriber asking about bass speakers and cabinets. Which ones to use? Which were the best? Power ratings, sizes, impedance, it’s a minefield of technical jargon! So here goes….

First off, let’s deal with size… Modern day bass speakers come in a few different sizes. The smallest is 10″, then 12″ and finally 15″. I have seen speaker cabinets using 8″ and even 5″ but these are unusual unless found in multiple array cabs such as the Phil Jones Bass range. I have also seen bassists using 18″ cabs but modern technology has rendered these obsolete as modern 15″ and 12″ speakers can have the same low-end response as the big 18s!

ampegSound is essentially a movement of air and bass frequency wavelengths are loooong and require a large movement of air to reproduce those low notes. When I was a teenager in the 80s, most of the pro players would use a combination of cabs to get their sound. Usually, they could be seen with a stacked pair of cabs, a 1x 15″ speaker on the bottom with a 4 x 10″ on top. The school of thought at the time was that the 15″ would fill in the low frequencies that the 10″ speakers struggled with and the 10s would look after the mid and high range frequencies, perhaps with the help of a built-in horn for the high stuff.

The large 15″ speakers have a wide cone and reproduce the low frequencies whilst the small 10s are faster acting and more punchy. The 12″ speakers have grown  rapidly in popularity as they are a great compromise between punch and low-end.

These sizes of speakers can be found in many combinations of number such as 1 x 15, 2 x 15, 2 x 12, 4 x 10 etc and there are even some designs which have a mixture such as 1 x 15 and 2 x 10 in the same ‘box’ but this is getting more unusual now. 20783_1583576791901978_1205283224830965585_n

Modern speaker cabinet manufacturers have, in recent years, turned their attention to weight and practicality. With the invention of light-weight speaker magnets and new innovative cabinet design, speaker cabs can now be designed to be small, light and portable but still have fantastic response across the whole bass frequency range.

Now briefly turning our attention to the technical side, I will keep this simple and short. This topic is huge and complex so I will just go through some basics.

Speaker cabinets are rated both in power handling (Watts) and impedance (Ohms) and these figures are vital to the performance of your rig. First off, let’s deal with power handling.

Passive speaker cabs (cabs with no built-in amplifier) are rated in Watts according to the power they can safely cope with. This does not mean they will explode if you exceed the rated power but you MAY risk damaging he speakers themselves if you continuously supply them with too much power.

Let’s say you have a 500W amplifier, if you use a cab rated at 100W and you have boosted EQ settings and the volume on medium, the chances are you will destroy the speaker’s voice-coil, melt the glue on the cone and possibly shake the cabinet to pieces. At the very least, the speaker(s) will probably exceed their limits of physical movement and you will get a distorted sound.

If you go too far the other way and you have a 500W amp into a 2000W cabinet, the speakers won’t be driven efficiently and your amp will have to work harder, causing extra heat and possible failure of your amplifier.

A general rule of thumb is for your amp to be rated at 60% of your cabinet rating so a 500W amp would need an 800W speaker cab.

Finally, we come to the other rating on your cab (and indeed your amp) impedance. Impedance can be thought of as similar to resistance and this is the load that your amplifier ‘sees’. Think about a water pump pumping water through a pipe… The narrower the pipe, the more ‘oomph’ the pump needs to get the water through. A huge pipe would take the load off the pump and allow it to work efficiently but make the pipe too big and the pump would run away and eventually fail. If you spit water through a straw, you can probably build up a fair bit of pressure but try and spit through a hose and you’ll be lucky to get any pressure at all!

Impedance works like the pipe but in reverse. The lower the impedance, the bigger the pipe and the easier the amp has to work to drive the load. Amplifiers and speakers can be rated in any number of Ohms but the common ones are 2, 4, 8 and sometimes 16. Somewhere on your amplifier, you’ll have a rating that says something like “Output 250W into 8 ohms, 500W into 4 ohms”. As you can see, the impedance rating of your cabinet affects the output power available from your amp! Many amplifiers have a minimum impedance rating, usually 2 Ohms and if you exceed that, you risk damaging your amp! If you want to get the full power from your amp, you need to match the impedance by using a cab or cabs of that specific impedance rating. Using more than one cab is pretty straightforward but the reverse of what you might think….

There are 2 ways to join 2 cabinets together, series and parallel. Series means you go from your amp to the 1st cab and then join the 2nd cab to the first. This means that the individual impedances of both cabs are added together. So two 8 Ohm cabs in series would equate to a 16 Ohm load, NOT what we are after. This is an unusual way to connect cabs and requires some specific cables wired in a specific way. Without going into too much detail, this is an unusual way to connect cabs and not standard procedure.

Joining the cabs in parallel, connecting each cab directly to the amp, halves the individual impedance, so two 8ohm cabs in parallel equals a 4 ohm load. Using 2 cabs of differing impedances is NOT recommended!!!

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As you can see, the world of cabs, speakers and impedance is a huge area and is fraught with dangers and issues. To summarise…

Always use a speaker cabinet with a power handling of around 40% higher than your amp.

Never mix cabs of different impedances.

Never use a combination of cabs where the total load is outside of your amplifier’s rating. You could do permanent damage to your amp.

Choose speakers with a wide frequency range, enough to suit your style. Ensure the cabinet has a horn if you’re a fan of sparkling high-end tones or slap.

The bigger the speaker, the more prominent the low-end but smaller speakers respond faster and are more punchy.

 

Have fun!!