From: whale@leland.Stanford.EDU (Stephen Schmidt)
Subject: FAQ, PART 2
Organization: DSG, Stanford University, CA 94305, USA
Date: Wed, 18 Nov 92 17:52:54 GMT


                                ALT.GUITAR.BASS
			      REC.MUSIC.MAKERS.BASS
                         Frequently Asked Questions (FAQ)

			Part 2: Answers to Questions 10-18

10. How are 5 and 6 string basses tuned? What are the advantages and
disadvantages of them? How are 8 and 12 string basses tuned and what
are their advantages and disadvantages?

  5 and 6 string basses have extra strings either above or below the normal
4 strings. On 5 string basses, the extra string is either tuned to B below
the low E or to C above the high G. Rock and pop players tend to find the
low B more useful, while jazz players and chord players tend to find the
high C more useful. 6 string basses usually add both a low B and a high
C although a few players add a high C and a high F above that. In the 60's
a few makers (notably Danelectro and Fender) made basses that had 6 strings
and were meant to be tuned E-A-D-G-B-E, same as a guitar but one octave
lower. This idea never really caught on, and almost no one tunes a bass
this way anymore.

The advantage to the extra strings are that you can reach more notes in
a given position, and can get some notes you could not otherwise play.
The disadvantages are that the neck must be wider to accomodate the extra
strings and that string sets are more expensive for 5-and-6 string basses.

8 and 12 string basses are constructed similarly to 12 string guitars;
the strings come in pairs, each pair containing a string tuned normally
and another string tuned one octave higher. Both strings are plucked or
picked simultaneously. A 10 string bass could be constructed but no one
has ever marketed one. There have even been a few 18 string basses constructed
which had strings in triplets but these were built more to demonstrate the
strength of graphite necks than for actual use. Also, some 12-string basses
have four triplets of strings instead of six pairs.

The advantage of 8 and 12 string basses is that because two strings are
played simultaneously they have a richer, fuller sound that a regular bass.
The disadvantages are that playing becomes much more difficult because both
strings have to be fingered and plucked. In addition, strings for 8 and 12
string basses can be somewhat difficult to buy as very few companies make them 
and not many people buy them. Many manufacturers of such basses either sell
strings directly or can tell you who supplies strings for their basses. If
you are willing to order strings by mail this will usually get you what you
need.


11. What is the difference between a preamplifier and a power amplifier?

   Bass amplifiers, whether they are combo amps or stage rigs, contain three
components: the preamplifer, power amplifier, and the speakers. The signal
from your bass passes to the speakers in three stages, with an amplifier
between each of the stages. The signal from your bass is carried at instrument
level; floor pedals, which your bass plugs into directly, operate on the
signal at this level. The instrument level signal is amplified to line
level by the preamp. The line level signal is passed to rackmounted effects.
Because the line level signal is more powerful than the instrument level
one, rackmounts effects add less noise relative to the level of the signal
than floor effects do, which is why professionals prefer them. Most preamps
sold commercially also include a number of line level effects, though not
all do. After the line level signal is processed it is passed to one or
more power amplifiers. Most rigs use only one power amp but if you are
biamping you would use two. The line level signal can also be sent to the
PA system if your band uses one. The power amp amplifies the signal to the
the much higher levels that are used to drive the speakers. The power
power rating of a guitar or bass amp refers to the total wattage that is
sent to the speakers by the power amplifier stage of the amp.

You can buy a combination ample that contains a preamp, a power amp, and
a speaker all in one box, or you can buy a separate preamp, power amp, and
speaker cabinet. Professionals do the latter -- it's more expensive, and
usually sounds better. It also gives you more flexibility to mix and match
your components to a particular need. Many combination amps have a preamp-out
jack, which allows you want to send the preamp stage's output somewhere other
than the power amp. There are several reasons for doing that:

(a) You could send the preamp out into a mixing board in addition to
your power amp for sound reinforcement.
(b) You could send the preamp out into a tape recorder and record it.
(c) You could send the preamp out into a bunch of effects, and then
connect the effects' output back into "power amp in," thus putting the
effects in between the preamp and the power amp stages.

Some combination amps, though not all, also have a power amplifier in jack
which allows you to send a signal from a separate preamp to the power
amplifier directly. Most combination amps also have a power-amp out jack
which allows you to send the power signal to an external speaker, either
in tandem with the internal speaker or instead of it. Combination amps
that have all three features are almost as flexible as separate stage
rigs.

12. What is biamping, and how is it done?

Biamping refers to using separate power amplifiers to amplify different 
frequency ranges. (See question 10 for a discussion of power amplifiers.)
In particular, it allows you to use one power amplifier to amplify your high
freqencies and another to amplify your low frequencies. In most bass
amplifier rigs, the preamp signal is sent to one power amp and the output
from that amplifier is sent to the speaker cabinets, where it may be
divided among the various speakers by a crossover in the cabinet; high
signals to small speakers and horns, low signals to larger speakers.
(A crossover is a filter which separates a signal into high-frequency
and low-frequency components: it may have a knob which allows the bassist
to control the dividing point.)
With biamping, instead of splitting the power amplifier's signal, you split
the preamplifier's signal and send each half to different power amplifiers.
Then, each power amplifier drives its own speaker load; again, usually small
speakers or horns for the high frequencies and large speakers for the lows.
Also, the crossover used in biamping is usually active (ie it requires a power
supply) whereas those found in speaker cabinets are usually passive.

Biamping has several advantages:
    (a) active crossovers don't have inductors, so they exhibit less
        intermodulation distortion; 
    (b) active crossovers don't drain the power of the signal to operate ;
    (c) the full power range of each amp is available regardless of the,
        power requirements of other ranges.

For more information on the engineering side of biamping, an excellent
book is Martin Colloms, "High Performance Loudspeakers", 3rd. edition,
pages 188-191 on biamping.

   (c) is important because it takes more power to reproduce low-frequency
sounds than high ones. A typical biamp setup might be to send to highs to
a 4x10 cabinet and the lows to a 1x15, 1x18, or other large subwoofer. If
you send your high end through the subwoofer, your tone will probably
suffer and become muddy, whereas if you send your lows through the 10s they
will not provide as much thump as the subwoofer will. By biamping, you can
send the lows through the subwoofer and still get clarity and tone from the
10s without forcing the 10s to spend most of their energy driving very low
frequencies.
   To get a good sound from biamping requires some fairly close matching
between the crossover, the amplifiers, and the cabinets used. Done poorly,
biamping can sound worse than using a single amplifier and cabinet. If you
biamp, it is better to get a system designed explicitly for biamping than
to assemble components one by one.


13. How do I adjust the setup on my bass (action, intonation, etc?)

   There is an excellent article in issue #153 of the Bottom Line. It
is long but very good. It can be obtained from the Bottom Line archives
by anonymous FTP; the address is kappa.rice.edu (128.42.4.7) and the
back Bottom Line issues are in the /pub/bass directory.

14. What is the difference between the various types of strings?

   There are basically three factors that affect string sound and playability.
The first is whether the strings are flatwound or roundwound, the second is
the gauge of the strings, and the third is the metal the strings are made
from.
   Almost all bass strings are made of a central string which is wrapped
in a second layer to make the string thicker. The central string is called
the core of the string. These are usually round, although some hexagonal
core strings exist. The wrapping comes in two kinds; some strings are
wrapped with flat ribbon and some are wrapped with a round piece of wire.
The first kind, called flatwounds, have a dark sound and are fairly smooth,
which makes them easy on the fingers and the fretboard. The second kind,
called roundwounds, have a much brighter sound, but tend to wear down your
frets or fretboard and chew up your fingers.
  Most people prefer roundwound strings for their brighter sound. Flatwounds
are mostly used for fretless basses, for which the damage caused by round-
wounds is especially problematic. There are also two kinds of compromise
strings, called groundrounds and half-flatwounds. Groundrounds are roundwound
strings which have been ground flat on one side. Half-flatwounds are wound
flat on one side and round on the other. In both cases, the flat side is
put against the neck. These strings provide some of the brightness of
roundwounds without causing neck damage. They are somewhat rare but some
players do use them.
   The second question is the gauge of the string. The gauge is measured by
the thickness of the string in inches. A typical set of light gauge strings
might have thicknesses of about 0.040, 0.060, 0.075, 0.090 for the G, D,
A, and E strings. A medium gauge might be about 0.050, 0.070, 0.085, 0.105.
Heavy gauge strings are extremely difficult to find now, for some obscure
reason. Most companies make three gauges of strings: light, medium-light,
and medium. Some companies will sell you individual strings, which lets
you mix and match your strings to get a unique combination of gauges, but
not too many people do this.
   Lighter gauge strings tend to have a brighter but thinner sound. Heavier
strings have a more solid sound to them. A major advantage to light gauge
strings is that they require less tension to produce a given pitch, so that
they require less force to fret, pluck, and bend, whereas heavier gauge
strings call for a little more finger strength.
   The third factor is the metal used to make the strings. Almost all
strings are made of either stainless steel or nickel. Stainless steel has
a brighter sound at the expense of being a little harder on the fingers. The
difference is not very great, however. You can also get strings which are
plated with chrome or gold, or various black metals. These are more for
effect than because the plating does anything to the tone.
   Acoustic strings can also be made of nylon or gut as well as metal.
Gut strings are quite expensive but sound very nice. You can also get
strings made of silicon and other exotic materials for unusual basses,
but non-metal strings will not work with magentic pickups so most people
don't use them.
   There are a few other factors to consider when buying strings. Many
strings come with a silk wrap around the end of the string which helps to
keep the wrapping on the string from coming unwound. Cheaper strings don't
have this winding. Another important thing to remember is that the strings
have to go on your bass! Most basses require single-ball strings, with the
ball end going at the bridge and the non-ball end being wrapped around the
tuning peg. However, Steinburgers and most other headless basses require
double-ball strings, one ball going behind the nut and the other behind the
bridge. And, to keep things confusing, some headless basses, notably
Kubickis, use single-ball strings by putting the ball end at the end of the
next andtaking the non-ball end onto a post on the body of the bass. You cannot
use single-ball strings on a double-ball bass and vice-versa, so  make sure you
know what you need before you buy.
  You also need to buy strings of the appropriate scale. The scale length
of a bass is the distance from the bridge to the nut, ie the length over
which the string vibrates. Most basses are "long scale" or 34-inch scale
length. A few basses, notably old Gibsons, are "short-scale" or 30-inch
scale length. Modulus Graphite basses are all built to a 35-inch scale
length, as are a few other basses. There is also a "medium-scale" or 32-inch
scale length, and some acoustic bass guitars are built to this scale. When
you buy strings, they need to be the same length as the bass they're going
on, so make sure you know the scale of your bass, and buy the appropriate
strings for it. 

15. How does a bass pickup work?

   A normal magentic bass pickup contains a series of magnets wrapped in
wire. Running a current through the wire wraps create a magnetic field
around the strings. When the strings vibrate, they disturb the magnetic
field (because they're made of metal) and the resulting disturbance creates
an electrical signal in the current going through the pickup. You can make
the pickup stronger or "hotter" by doing any of three things: using a stronger
magnet, wrapping it in more windings of wire, or raising it closer to the
strings. The first two increase the overall strength of the magnetic field;
the third moves the strings to a stronger portion of the field. This lets
the pickup send a stronger signal. The cost is that by forcing the strings
to vibrate in a stronger magnetic field, you increase the drag on their
vibration (because energy is conserved: the signal strength has to come from
the string vibration) and so you lose sustain. There is no optimal height
for the pickups: you can put them anywhere you like as long as you are
getting sufficient signal strength and you're not losing too much sustain.
You can also balance your pickups by {etting them at different distances
from the different strings.
   Pickups come in two kinds: single-coil and double coil. Double-coil
pickups pass the signal through two sets of magnets and wire coils (hence
the name) whereas single-coil pickups use a single set of magnets. The
advantage of double-coil pickups is that the pickups are wired so that
the signal is passed through the second magnet out-of-phase from the
first magnet. As a result, any hum or noise in the signal is cancelled out;
these pickups are sometimes known as "humbuckers" for this reason. They do
sound a little different, though, so many players continue to use single-coil
pickups despite their being a little noisier than humbuckers.
   Some expensive basses also have non-magnetic pickups call piezo pickups
or piezoelectric pickups. These do not contain magnets: instead, they work
by having a small crystal in the bridge of the bass. When the string vibrates
against the crystal, this vibration produces an electric signal through the
crystal, which is sent out to the amplifier. Basses that use non-metal strings
are built with piezo pickups, and some basses use piezo pickups in addition
to magnetic pickups in order to get more variation in tone.

16. How do I record my bass to tape?

This is a fairly difficult thing to do because most recording equipment
is designed to work best with frequencies higher than those delivered by
bass. However, with the right equipment it is not hard to achieve a
nearly professional quality recording of your playing.

The simplest thing to do is to get a tape recorder with a microphone
input and plug your bass into it directly, or send it your preamp signal.
This will only allow you to record on one track, but it's very easy to do
and most people have the necessary equipment at hand. You can also record
using a microphone placed in front of your amplifier, but you will tend
to introduce extraneous noise and unless you are in a recording studio you
are better off using a direct input.

If you want to record multiple instruments, or multiple tracks of a
single instrument, you will need to obtain access to a multi-track
recorder. You can buy four-track recorders at most large music stores,
and professional studios have 16, 24, or 32 track recorders.

Once you have access to a recorder, the main decision you have to make
is whether to send your bass signal to the recorder directly, to pass
the signal through a preamp, or to send the signal to speakers and use
a microphone to record the sounds from the speakers.

If you go direct, you will need to raise your signal from instrument
level to line level. This can be done using a tool called a direct box,
which most studios have, which will amplify the signal but leave it
otherwise unaffected. Or, you can use your own preamp to raise the signal
to line level plus doing whatever effects processing you like. However,
if you are in a studio the engineer may have access to line-level effects
like equalization and reverb which are better than those found in floor
effects or preamps. If you can get the engineer's attention for 15 or 20
minutes consider using the studio's equipment instead as you can get better
performance from studio equipment in many cases. The drawback to so doing
is that it takes time, plus you have to explain to the engineer how you
want the sound to be whereas your preamp is under your own control.

Another common problem is providing a constant signal from the bass. In
particular, if you do a lot of slapping and popping, or you like to play
chords on your bass, you might have a hard time recording a clean track
without a compressor. A compressor will quiet down the louder notes you
play and boost the quiet ones to produce a constant volume in the 
recording. If you don't have access to a compressor, you can try to
simulate this by adjusting the recording volume as you play the track
(or having a friend do it) You can also increase the volume of a bass
solo the same way: turn the recording volume up for the solo, then turn
it back down when the solo is over.

You might also want to use noise reduction to eliminate signal noise, either
from your bass and amplifier, or from a compressor if you use one. If your
recorder has dbx then you don't have to be so critical of the signal
level because dbx noise reduction gives you about 90db of dynamic headroom and
almost no tape hiss.

You will find that some of the notes you play on the instrument are louder than
others. This is called the "sweet spot". Most instruments have them, though
graphite necks can reduce or eliminate them. Your recorder should have
a VU needle or other indicator that will tell you how much volume is being
recorded. Adjust your level so that the VU needle does not spend too much
time in the red zone of the indicator: this is an indication that you are
playing loudly enough to damage the recorder.

17. What are some popular effects for bass and what do they do? Is there
a difference between guitar effects and bass effects? In what order
should I plug them together?

There are five main effects for bass, plus some others that aren't as
widely used. They are: compression, distortion, delay, reverb, and
chorus/flange. Most of these effects come in both analog versions and
digital versions. Analog effects act upon the incoming signal directly,
modifying it to produce the output. Digital effects convert the incoming
signal to a pattern of zeroes and ones (hence the name digital). The
resulting code is processed and the new code is converted back to a
signal. Digital effects are typically cleaner and have fewer side effects
than analog ones do. They are also considerably more flexible as patterns
of numbers are easier to manipulate than electric signals are. However,
analog effects are usually cheaper, and to exactly replicate the sound
of players from the 70's and earlier who used analog electronics, you
have to use analog effects yourself. (Digital effects weren't in common
use until the late 70's, and weren't commercially available until the
early 80's.) However, either one is fine for use with bass. They will
sound a little different, so try both kinds and choose the one you
prefer.

Effects come in two kinds, those designed to work with instrument level
signals and those designed to work with line level signals. Floor boxes
are almost always designed for instrument level, and rackmount effects
for line level. However, check and make sure you know which you have.
It is possible to damage your effects, especially floor effects, by
running the wrong level signal through them.

There isn't all that much difference between guitar effects and bass
effects and you won't damage anything by running a guitar through a
bass effect or vice versa. However, bass effects are designed to work
better on lower frequencies than guitar effects are, so you will usually
get a better sound by using an effect designed specifically for bass.

Most effects devices have several names. Where there aren't too many
the following paragraphs try to give them all, along with the reasons
for using one rather than another. However, if you are in doubt, ask
the salesman what an effect does and you should usually be able to
recognize it as one of those described below.

Compression is an effect that keeps the signal strength of your
instrument constant. It can work in one of two ways: it can reduce
loud signals, or it can amplify quiet ones. Compressors usually have
both functions; effects that only quiet loud signals are called limiters
and effects that only amplify quiet ones are called sustainers.
Compression has two purposes. First, it keeps your volume level constant.
This is used in recordings where constant volume is desirable, and it
protects amplifiers and speakers from having an excessively high signal
sent to them that could burn them out. (Most amplifiers have limiters
built in, which is why they don't get louder beyond a certain point when
you increase the volume control.) Second, they increase the sustain of
your instrument; as the string vibration begins to die down, making
the signal quieter, the compressor raises the quiet signal, making it
sound as it the string is continuing to vibrate. The drawback to compressors
is that they eliminate sharp changes in the level of your sounds. This tends
to destroy slapping, popping, and other percussive sounds, and it also
alters the individuality of your sound by changing the attack and the
muting of your fingers.
Most compressors have three knobs: one which controls how quickly the
compressor will react to changes in the incoming signal (usually
labeled attack), one controlling how much the compressor will boost
the signal (sustain or compression) and one controlling the level the
compressor will try to attain (level). Manufacturers tend to adopt their
own methods of labeling knobs on effects boxes; your mileage may vary.

Distortion adds noise to your signal, causing it to sounds "crunchy" or
"grungy". In the old days, distortion came from driving an amplifier
close to its limit, and you can still obtain distortion this way. You
can drive either the pre-amp or the power-amp to its limit with most
amps: you will usually get better distortion by overloading the power
amplifier, but try it both ways and see what you get. Be careful not
to blow out your amplifier this way, however; turn it up high enough
to get distortion but no higher. If your amp has a limiter, you may
not be able to do this at all. (Players also used to get distortion
by playing with speakers which had rips in the cones. It is not recommended
that you try this.)
Distortion pedals usually have three knobs, one which controlls the mix
between noise and instrument signal, one which controls the tone of
the distorted signal, and one which controls the output level. (Names
of knobs varies too widely to permit suggestions.)

Delay effects take the incoming signal and send it out repeatedly,
with intervals ranging from microseconds to 30 seconds or more. They
can be used to add fullness to your sound, to produce doubled parts
without having to hit each note twice, or, with long delays, enable
you to accompany yourself by playing a 30-second part through a 30-second
delay and then playing a second part over it! Delay boxes usually have
three knobs: one controls the time between repeats (delay), one controlling
the falloff in volume between repeats (level), and one controlling the
number of repeats given (repeats).

Reverb effects are similar to delay effects, but mix in a very large number
of very quick, quiet repeats. They simulate the effect of playing in a
small room, where the sounds from the instrument reflects off the walls,
creating a large number of rapid echoes. They usually have the same
three controls as a delay box, which work about the same way in principle
but will have quite different effects on the sounds.

Chorus and flange effects both simulate the sound of having multiple
instruments playing at once. Consider two basses playing the same part.
They will not be perfectly together; they will be very slightly out of
tune and the players will hit the notes at slightly different times.
A chorus pedal simulates this effect by taking an input signal and
duplicating it, with the duplicate signal slightly delayed and slightly
out of phase with the original. In addition, the amount of delay and
phase shift varies over time. This is designed to simulate the second
player being slightly off from the first one.
The difference betwwen chorus and flange is one of degree only; chorus
pedals use small delays and phase shifts to produce a very subtle
effect. Flangers use even smaller delays but vary the length of the
delay and the phase changes to produce a more noticeable effect. If
you turn on a flanger and don't play anything, you will hear a characteristic
"whoosh" sound which is the result of certain frequencies being cancelled
in the two signals before being sent to the amplifier.
Choruses and flangers usually have three knobs; one to control the extent
of shift produced by the effect (depth), one to control the rate at which
the shift changes (speed) and one to control how much of the second signal
is mixed together with the first (level or intensity). Cheap choruses
will omit the latter knob. Some choruses will have a fourth knob which
controls the overall signal from the effect as well.

Many effects boxes, most commonly choruses and delays, contain a stero
split which allows you to send the original or "dry" signal to one
amplifier and the affected or "wet" signal to another. This is commonly
used to send the dry signal to the PA and the wet signal to the stage
amplifier, or vice-versa. Or it can be used to power two different
stage amplifiers to get a stereo sound, though this involves lugging
twice as much equipment around.

Most players use the following sequence for their effects: compression
first, then distortion, then chorus/flange, then delay, and last reverb.
However, there is nothing magical about this ordering, and you should
feel free to experiment with alternate orderings to get different sounds.

For more information on effects, consult the excellent book "Getting
Great Guitar Sounds" by Michael Ross, which discusses the acoustic
properties of electric instruments and the workings of amplifiers
as well as effects.

18. What do the ratings of amplifiers and speakers mean? What is a watt, or
an ohm? What factors must I consider in connecting amplifiers to speakers?

Any electronic circuit has 3 properties of importance: voltage, current,
and resistance. (Plus some more based on these three). As you may know,
electric current consists of electrons moving along the wires. Voltage
is the amount of energy carried by each electron. Current is the number
moving passed in each second. The total power of the circuit is given by:

Power = voltage * current

thus, increasing either the voltage or the current will increase the power
of your amplifier.
Resistance is the tendency of a circuit to resist the flow of electrons
(hence the name). The formula for resistance is:

Resistance = voltage/current, or,  current = voltage/resistance

Thus, for a given voltage, a circuit of high resistance gives low current,
and a circuit with low resistance gives high current. 

Voltage is measured in volts: you get 110 volts out of the wall (220 if
you're in Europe). This is usually transformed by the amplifier to some
other voltage, and there's not much you can do to change it. However, you
can alter the resistance of the circuit by changing the resistance of the
speakers. Changing the resistance will change the current flow, and therefore
the power of the circuit. Resistance is measured in ohms: typical speakers
and cabinets have 16, 8, or 4 ohms resistance. The current of a circuit can
be deduced from these. Power is measured in watts: most amplifiers have
the maximum amount of power they can deliver in the name somewhere (ie a
Crate B-20 can deliver 20 watts of power). How loud you are depends on
how many watts of power your are delivering.

Substituting the second equation above into the first one yields:

Power = (voltage^2) / resistance

which gives the relationship between resistance and power delivered,
assuming the amplifier's voltage is held constant. In fact, the delivered
power of an amplifier may be less than this if the amplifier is not properly
matched to the load it is driving. Most amplifiers are designed to drive
a 4 ohm load of speakers. If you use speakers of more or less resistance
than the designed load, you will not get as much power as you would get
driving the designed load, and if you supply your amplifier with too little
resistance, you may blow it up. It is always best to supply your amp with
speakers of exactly the resistance it was designed to drive.

Say you have a 55-watt amplifier driving a 4 ohm speaker (which might
be typical). If you replaced the 4 ohm speaker with an 8 ohm speaker,
you would double the resistance of the circuit, which would halve the
current flow. Since power=voltage*current, this would cut the power
in half; thus, your 55 watt amp would only be delivering 27.5 watts.
This is not so efficient (nor so loud), which is why you would have the
4 ohm speaker in the first place... Conversely, if you put in a 2 ohm
speaker you would double the current, and double the power to 110 watts,
if the amp was designed to handle a 2 ohm load. Most amps aren't, meaning
that in practice you would probably get much less that 110 watts.

Why wouldn't you want to have as low a resistance as possible? The answer
is that this would increase the power of the circuit (by increasing the
current) and electric components can take only so much power before they
blow up. Amplifiers and speakers are both rated by the maximum amount of
power they can take without going crispy. Thus, if you have an amp which
delivers 100 watts into 4 ohms, and you attach a 2 ohm speaker to it which
is rated for 120 watts, you will now have a circuit carrying 200 watts of
power whose components can only handle 100 (amp) and 120 (speaker). Something
will fry in short order. Thus, you want to make sure the resistance of your
speaker load is high enough that your amp can take the total power of the
circuit, and each speaker can handle its share of the load.

If you have only one speaker, that speaker is carrying the entire power
of the circuit. However, if you have more than one speaker (and they are
wired in parallel, which they should be) the load is divided between them.
If both speakers have the same resistance (ie, it is equally hard to push
power through them) then each will take half the power, and the total
resistance will be half the resistance of either speaker. (If you have
N identical speakers with R ohms, the total resistance is R/N.) So,
if you have an amplifier which delivers 50 watts through 8 ohms (meaning
that it delivers 100 watts through 4 ohms, or 25 through 16 ohms) and
you hooked it up to two 8 ohm drivers, the total resistance would now
be half of 8 ohms, or 4 ohms, and the amp would put out 100 watts, with
50 going to each speaker.

If the speakers do not have the same resistance, then more of the power
will be pushed through the low-resistance speaker. The formula for the
total resistance of two speakers with resistance R1 and R2 (again, assuming
they are wired in parallel) is:

R = 1 / [ (1/R1) + (1/R2) ]

So, if you are hooking a 4 ohm speaker and an 8 ohm speaker together in
a cabinet, the total resistance will be 1 / [ 1/4 + 1/8 ] = 1 / [3/8]
= 8/3 ~= 2.67 ohms. Thus, an amp rated for 100 watts through 4 ohms would
put out 150 watts under this speaker load. The power is divided among
the speakers in proportion to the resistance: in this circuit the 4 ohm
speaker would get 100 watts and the 8 ohm speaker would get 50 watts.
If you hook together two 8 ohm speakers the resistance is 1 / (1/8+1/8)
= 4, as said above.


-- 
Steve Schmidt			<><		   whale@leland.stanford.edu
I can no longer sit back and allow Communist infiltration, Communist
indoctrination, Communist subversion, and the international Communist
conspiracy to sap and impurify all of our precious bodily fluids!