Bass Amplifiers & Cabs - Buying Advice
Bass Amplification & Speaker Cabinets
(Please note: the following information is for
guidance purposes, and you should always verify that a particular bass amp or cab
is suited to your specific needs.)
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 (two 8 Ohm cabs will give a 4 Ohm load). 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 or combining cabs). Some combos have an
external speaker output for adding an extra cab, take a look on
the back panel.
What power output should your bass amplifier have?
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.
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What size speakers and bass cabs should you use?
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 feature
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 high frequency drivers usually have a separate
control to mix in the amount of brightness 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.
More to come...
Hopefully this is useful, however, there's a lot more to talk about
including valve or solid state pre-amps, EQ types - simple tone, graphic or semi-parametric?
And more... so come back soon for new articles!
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