Buying Advice - Bass Amplification

Bass Amplifiers & Speaker Cabinets

Need-to-know basics about amps

In general, more watts equals more volume, but there is much more to this than meets the eye, or ear for that matter. Firstly, the relationship between watts and volume is not linear, e.g. a 200 watt amp will not sound twice as loud as a 100 watt amp, it will sound about 30% louder. To get double the percieved volume you need 10 times the watts, so the perceivable difference between say 100 watts and 120 watts is very little, assuming the amps and speakers are of the same efficiency. Speaker efficiency plays a key part in the volume formula too. More efficient speakers will will give a higher percieved volume for the same number of watts from your amp. This difference can be quite marked which is why two amps of the same power rating can yield noticably different volumes.

Secondly, using two cabs or adding an extension cab to a combo will have the effect of nearly doubling the watts you get from your amplifier. This is because when two 8 Ohm cabs are run together you get the equivalent to a 4 Ohm load on your amp (we could get into techno-blab here with an in-depth explanation but we'll save that for another time). So, an amp rated at 100 watts into 8 Ohms will give around 180 watts into 4 Ohms. Bass amp output is usually rated into either 4 or 8 Ohms so make sure you are comparing like for like when checking out gear. It is not uncommon to see bass amps rated at 400-800 watts into 4 Ohms, this would equate to around 250-480 watts into 8 Ohms. Most bass amps have two speaker outputs, allowing the use of two 8 Ohm cabs giving you a 4 Ohm load on the amp (always check the manual to see what your amp can handle and the Ohm rating of your cabs before adding cabs). Some combos have an external speaker output for adding an extra cab, take a look on the back panel.

If you need to have enough volume to match a drumkit, you're probably looking at a minimum of 100-120 watts (into a single 8 Ohm cab) assuming you are using good quality gear. If not, i.e. you are just playing with an acoustic guitarist in a restaurant etc., less power may be enough depending on your situation, ideally try some systems out to see what volume you need.

If you are playing in good sized pub/club venues with a drummer and maybe two guitarists, then you want at least a good quality 150 watts (into a single 4 x 10" or 1 x 15" 8 Ohm cab). In an ideal world, to give you more headroom and because you don't want to be running your amp too hot all the time, we'd suggest going for one and a half to two times the figures above. Around 150-200 watts/8 Ohms for a smaller band situation and 200-300 watts/8 Ohms (into a single 4 x 10" or 1 x 15" 8 Ohm cab or a 2 x 10" & 1 x 15" cab together) for bigger bands or larger pub/club type venues. There are many amps on the market with much higher power ratings, these are useful if you are playing in larger venues where the bass won't be in the PA or on large stages where the bass won't be in the monitors and you may end up some distance from you rig, especially outdoors.

Remember, you only need to be loud enough to have a good balance with the drumkit (assuming it isn't miked up in the PA). If any player is so loud you can't hear the drums properly, then you've got a bad mix, and if you're in a smaller venue, you're probably too loud as well!!. If you're in a venue where the drums are being put through the PA, then any extra volume required for the bass in the mix should ideally come through the PA too. That way the sound can be properly mixed, as if too much volume is coming off the stage, there's nowhere to go with volume in the PA.

The choice of speaker size is in part dictated by the type sound you want. These days most players are looking at either 10" or 15" speakers. 10" speakers have lower mass than 15" speakers and so can move quicker giving a punchier sound. 15" speakers move much more air and produce more low frequencies. Nowadays there are many good quality cabs with 2 or 4 10" speakers that can produce plenty of bottom end, but to get the best combination, many players combine a 2 or 4 x 10" cab and a 1 x 15" cab to get a combination of punch and low end warmth.

Many bass cabs also come loaded with a high frequency compression driver or piezo-electric horn that gives presence and definition to the tops, particularly useful for getting the best out of distortion, slap style and the bright sound of new strings. These horns usually have a separate control to mix in the amount of top end you want.

12" speakers should not be dismissed, even though they seem to be less popular these days. Double bassists like the sound of 12" speakers, and similarly they often suit fretless bass styles also. They have a slightly mellower and fuller sound than 10's and are worth taking a look at. A good quality 12" speaker cab will have more bottom end than a budget 15" one. If you're looking for something relatively portable, a small good quality combo with a 12" speaker could be just the answer.

One other factor to consider when choosing your bass cab(s) is the practicalities of size and weight. Bass cabs are usually both big and heavy, although in recent years there has been a lot of development in the direction of reducing both size and weight. Speakers with Neodimium magnets are much lighter than speakers with conventional iron magnets and modern cabinet designs produce much more bottom end from smaller cabs. But they are still quite a size and weight, getting a 4 x 10" cab (let alone an 8 x 10"!) in and out of a small car or up and down a staircase by yourself soon becomes a chore. For this reason it has become popular to use two smaller cabs, a 2 x 10" and a compact 1 x 15" cab together. This gives a system that is easier to transport and is more adaptable to different situations as you can use your amp with both or either of the cabs. Bear in mind a combo will be even heavier, a powerful 4 x 10" combo for example really needs two people to move around if you value your back.