Glossary of Speaker Terms
This page presents some of the more popular terms used
to describe the performance of a loudspeaker in a musical instrument amplifier.
While some are standard terms used in the design and manufacture of loudspeakers,
the rest are subjective terms traditionally used by musicians to describe
the overall sound of a particular loudspeaker and are generally related to
its frequency response and its inherent anomalies that occur at high volumes.
Have a speaker term you want to add or see explained here? Please write us.
Point and Click the term for a description, example
of use in context, and additional information about the term.
|Cone Cry, Ghost Notes, Edge Yowl
||Damping, Damping Factor
||Flabbing, Farting Out
|Gap, Gap Energy
||Pot Cover, Magnet Cover
||Rare Earth Magnet
||Voice Coil Rub
|Additional General Audio Terms|
Context: This speaker is much more aggressive than the one it replaced.
Description: A speaker is said to be aggressive when it exhibits a sharp, or
snappy response to pick attack, etc. Usually indicative of a lightweight,
low mass cone structure and a large magnet. In the time domain, such a quick
response to pick attack would normally be accompanied by overall brightness in the speaker,
but careful design and selection of the cone, dustcap, etc. may be employed to avoid
an accentuated top end.
Context: I prefer AlNiCo magnet speakers over Ceramic magnet speakers.
Description: AlNiCo is a type of alloy (mixture of several metals) magnet
which was used extensively in loudspeakers between 1930 and 1960. The price of
cobalt (the 'Co' in AlNiCo) began to skyrocket, so the industry was forced
to develop other types of magnets. Powdered ferrite magnets were developed
using the ceramic process and subsequently became the standard magnet for loudspeakers.
Oddly enough, AlNiCo magnets are still the most widely used magnets in the world,
being employed in everything from weapons systems to analog meter movements, to
debris separator grates in manufacturing processes. The unique properties of
AlNiCo magnets which make them desireable for musical instrument speakers are
discussed on our Let's Talk Speakers Q & A page.
Context: This speaker has excellent attack.
Description: Similar to aggressive, attack has to do with how
quickly the speaker reacts to the input signal commanding it to move. Accuracy
is also very important, because if the cone moves too quickly it will
overshoot or move farther than it is supposed to, then retreat, then move back
out. The result is what is called ringing and can cause the note to sound
overdone, or clicky. The challenge to the speaker builder is to design a
system that will respond adequately to these quick attack notes (such as single note
picking leads), while designing in adequate system damping to control the ringing.
Context: The midcone corrugations help quench bell modes.
Description: When the speaker cone is vibrating in response to the input
signal, many minor resonances and new frequencies appear in the resultant
radiated signal in addition to the desired signal. Some of these are called
bell modes. They are minor resonances on the surface around the circumference
of the cone. The frequency is related to the radius (and circumference) of the
cone. To stiffen the cone in an effort to prevent bell modes, ring corrugations are
added at various intervals between the apex and the surround of the cone.
A cone which all but eliminates these is called the curvalinear, or trumpet
cone. Because it is always curving from the apex to the surround, it presents
a high mechanical resistance to the bell modes and prevents them from occurring.
An example of the use of a curvalinear cone for musical instrument speakers is the
Kendrick Black Frame. The curvalinear cone exhibits smoother breakup, especially
at higher power levels.
Context: This speaker developed much more body after it was broken in.
Description: Body has to do with the overall composite projection of
the sound from the speaker. Being a totally subjective term, it's difficult
to describe. My interpretation of it is that at a high average volume, the
desired overall tone is achieved in the upper mids and highs, while retaining good, tight
control on the low end. It's as though you have a feeling the mids and uppers
are being pumped out at you by the strong, well controlled low end.
Context: This speaker is too boomy, I think I'll try it in another cabinet.
Description: All speakers have a fundamental bass resonance. If the
speaker is not well damped by either the amps output circuit or the particular
installation, it will tend to vibrate at its bass resonant frequency. This
is perceived as a 'fake' bass note and can be annoying, particularly since
most of the time it wouldn't necessarily be related to the frequency of the
signal being applied to the speaker.
Context: It doesn't break up quite as smoothly as I like.
Description: Below a certain frequency, say 900hz, the cone vibrates
as one piece, much in the same way a piston goes up and down in an engine.
Above that 'piston band limit' frequency, the cone vibrates in sections.
By the time a wave travels from the apex at the voice coil all the way
out to the edge of the cone, a new wave has started at the
voice coil. Think of a series of ocean waves. One comes in and crashes
against a sea wall, the sea wall generates a new wave that starts back out
into the ocean where it meets a wave coming in, they crash together, and
for a moment it looks like a stationary wave going up and down, but not
travelling. The same thing happens on the surface of the cone. The result
is comb filtering and other anomalies that create the texture of the overall
sound. Interestingly enough, this all takes place between around 1 and 4Khz, where
our hearing is most sensitive. If you look at a speaker plot,
you'll notice the response of the speaker is fairly smooth until it gets in
this region. Although some mathematics can be applied to the design of breakup
characteristics, most information found on the subject uses phrases such as
'years of experience', and 'empirical data.'
Context: It's bright but also has good low end.
Description: As the name implies, bright generally means having
an abundance of high end response as opposed to the mids and lows. A speaker
with a low mass, hard cone and a large magnet will generally yield
accentuated high end. Balance between the lows and highs can sometimes be
achieved by proper dustcap selection.
Context: I'm sure I hear a buzz on the low notes.
Description: There are generally two sources of buzz or rattle
in a speaker. The first is due to a voice coil rub. If the voice coil has
been overstressed due to heat from too much power, it will deform and touch
the plate ring or the center pole. Sometimes it will only come in contact
at peak excursions of the cone, such as during big bass notes. If the
inside of the voice coil comes in contact with the pole, it might not even
be noticeable, since both surfaces are fairly smooth, and the result would
be a minor amount of what might be called white noise. However, if the outside
of the voice coil comes in contact with the plate ring, the individual windings
of the coil rub against an edge of the ring and the result would be similar
to running your fingernail down the teeth of a comb. Some manufacturers actually
hang the voice coil closer to the pole than to the plate ring for this reason.
The second source of buzz or rattle is from a magnet assembly that has worked
loose from the speaker basket. There is a description of this problem and a possible
cure on our Let's Talk Speakers Q & A page.
Context: I don't get the AlNiCo mojo, I get along with ceramic magnet speakers just fine.
Description: Ceramic is a process rather than a particular kind of
magnet. A powdered ferrous material (Strontium, Barium, etc.) is pressed and
pounded into a desireable shape, then fired in a furnace. Ceramic types of
magnets aren't as efficient as far as magnetism per pound as AlNiCo magnets,
but are much cheaper. For instance, a 40oz ceramic ring magnet for loudspeakers
costs about $3 in quantity. A 40oz AlNiCo ring magnet costs about $50.
Ceramics require alot more force to demagnetize than comparable AlNiCo magnets,
and are great for high powered speakers where the magnetism from the voice
coil might partially demagnetize an AlNiCo magnet.
Context: Part of the texture of the tone is due to comb filtering.
Description: For some reason we find it desireable when a composite
signal has some of its frequency components dropped out in either a sweeping
or a random manner. Some of this comb filtering undoubtedly occurs on the surface
of the cone due to the transmission line effect of the cone itself as the
frequencies leave the voice coil, travel out to the surround, bounce back and collide
with new waves coming out. The result is cancellation or reduction in amplitude of some
of the frequencies, but not always the same frequencies. If you've ever seen
a spectrum analyzer used to set up a PA system, you've seen all the vertical
pips or LED displays that represent the different frequencies to be analyzed and
equalized. All of these vertical pips on the screen or the LED indicators
look like the teeth on a comb, hence the term comb filtering. If you could
sweep through all these frequencies and randomly decrease or drop out some
of them, you would have the effect of comb filtering. Another example of
comb filtering is with a Leslie speaker connected to a keyboard. Mr. Leslie
invented his rotating speaker cabinet to emulate the natural comb filtering
that occured with a pipe organ. Since the ranks or sections of pipes were
separated for the necessity and convenience of installation, the sounds from
one section would collide with another and create a natural comb filtering effect.
Context: This new speaker sounds really compressed.
Description: New speakers sometimes sound really tight and compressed. A typical
paper pulp cone is dipped in a mixture of acetone and acrylic as part of
the manufacturing process. The apex of the cone where the voice coil attaches
is usually doped a little heavier than the rest of the cone to give it added rigidity.
The surround out at the periphery of the cone is also dipped in the mixture.
So, the surround is a little tight when new. After several hours of playing
at high volume, the surround begins to loosen up and allows the cone to move
more freely. The result is that the speaker seems to come alive with more
body and overall sound projection.
Cone Cry, Ghost Notes, Edge Yowl
Context: I replaced that speaker because it had too much cone cry.
Description: As the speaker cone is vibrated by the voice coil, it can
generate frequencies of its own that may be strong enough to be audible along
with the intended note or signal from the musical instrument. These notes or tones may or
may not be harmonically related to the intended note, and in some cases
may be either higher or lower in frequency than the intended note. This usually
means that the voice coil is driving the cone so hard that it is overcoming
any damping and is essentially out of control. Sometimes manufacturers use
huge magnets and loose spiders so they can win the 'sensitivity ratings' contest,
but the result is a system that is difficult to control. Edge yowl is the term
used to describe sounds that occur when the surround resonates, imparts energy
back into the cone, and generates tones and notes that may or may not be
harmonically related to the intended note.
Context: Is that a seamed or one piece cone ?
Description: A typical cone for a guitar amp is made of paper pulp.
It starts as a slurry, looking like what toilet paper is reduced to in a
bowl of water. Then, a cone-shaped screen the desired shape of the finished
cone is dipped into the slurry. A vacuum is applied to the backside of the
screen cone, so the slurry is attracted to it. It is then peeled off and dried.
Later, it is trimmed to the final dimensions and is dipped in a mixture of
acetone and acrylic to strengthen it. If you look closely at a vintage one
piece pulp cone, you can see the little dots that look like holes in a door screen.
An alternate method is the seamed cone. It starts out as circular piece of
paper with a section cut out that resembles a piece of pie. Then, the cone
is placed in a mold that causes the pie shaped gap to close and then glue is
applied at that seam joint. Historically, the processes for the pulp mixtures and
other operations were closely guarded company secrets.
Context: Definitely a crunchy speaker.
Description: Crunch is that sound you hear when you have the volume
high enough to hear definite breakup patterns in the speaker, yet they seem
well controlled as well as enhance the overall texture of your tone.
Sometimes a very slight amount of flabbing due to loss of control of
the cone can actually add texture and crunch to the overall tone and
is desireable. Of course, too much flabbing is perceived as a
stuttering in the tone and sounds like the tone has holes
punched in it. Very annoying as well as disruptive to the texture of
Damping, Damping Factor
Context: That amp had a very high Damping Factor.
Description: One of the dictionary definitions of the word
damp is to deaden a shock. In other words, a device or method is used
to stop vibrations or oscillations caused by mechanical shock. In the
case of your automobile, the shock absorbers deaden the oscillations
of the suspension system in order to make the ride more comfortable
and improve handling. Damping is also very important in loudspeakers.
Quite simply, if the speaker system consisting of the voice coil,
the cone, and the spider was allowed to vibrate freely without any kind
of damping, it would be very difficult to achieve any kind of recognizable
or useable acoustic signal from it. We want to be able to blast the speaker
with a big signal, have it respond, then stop vibrating almost
instantly when we remove our signal. Ok, so how do we do it?
Strangely enough, since the voice coil is always immersed in a fixed
magnetic field, it acts as a part time motor, part time generator. When
you drive the loudspeaker with a signal from the amp, it causes the
voice coil to move in the magnet field and then impart its movement
on the cone to produce the acoustic signal. But, as soon as the
signal from the amp goes away, the cone and voice coil start to fall back
to the resting, or no-signal position. As the voice coil is moving
back 'home', the windings of the coil cut across magnetic lines of
force in that fixed magnetic field and the result is that a voltage is
developed in the voice coil. It has now changed operation from a motor
to a generator. The generated voltage is called back EMF, or flyback,
and is fed back up the line into the amp and appears in the output circuit.
This voltage would continue to be generated until the cone stopped vibrating
and finally came to a rest at its home position. One way to stop the
oscillations is to make it difficult for them to occur. The easiest
way is to put a big load on the voice coil when it is in its generating
mode of operation. Ever notice when you turn on the rear defogger in
your car, the engine idle RPM goes down slightly? That's because the
defogger requires quite a bit of current to operate so the load it puts
on the alternator makes it more difficult for the engine to turn the
alternator. You can take any simple permanent magnet motor, such as that
used on a slot car or other toy car, and after temporarily shorting
the terminals together, you'll notice it is more difficult to spin
than with the terminals open circuit. This is electrical damping.
With a typical guitar amp, although you always use the correct speaker
impedance load as suggested by the manufacturer, as an AC signal power
amplifier, or simply, an AC power supply, it has an internal source impedance
that is lower than the impedance rating of the speaker connected to it. The
ratio of this internal source impedance to the suggested speaker load
impedance is called the Damping Factor, and is usually at least
5 or higher. The higher the number, the better, generally, and is a measure
of how well the output circuit will quench or stall the oscillations
in the speaker by providing a big electrical load to them during the time
the voice coil is acting like a generator. Of course, the resulting electrical
power doesn't just disappear, it ends up in the output circuit of the
amp where it is dissipated as heat. It's odd to think of the output
tubes acting as a dummy load for this flyback power, but that's how it works.
Output tube bias, transformer turns ratio, and wire sizes all affect the
damping to some degree. Sometimes those flyback voltages from the
voice coil we spoke of earlier can get quite large. If you ever see a
schematic of a guitar amp and notice the designer has installed solid
state diodes between the plates of the output tubes and ground, it is
to help quench those flyback voltage spikes.
Context: It seems to be a few DB louder than the other one.
Description: First and foremost, the term DB is dimensionless. You can
use the term DB to express the differences between any two quantities, as long as you
know what you are comparing. The term decibel, or DB, was first used by telephone
pioneers to determine losses and gains of power in telephone circuits. It is
simply a method of compressing large numbers into a more manageable, simple form.
It is convenient for us to use the term DB and the math used to define it,
since it is based on a logarithmic scale well suited to human hearing,
which itself is logarithmic rather than linear in its behavior. Basically,
the scale is compressed by representing the square of a number by only a
doubling of the DB number representing it. For instance, a 10db change
would be ten to the first power, or simply ten times. 20db would be ten to
the second power, or ten squared (that's where the '2' in 20 comes from)
or one hundred times. 40db, then, would be ten to the fourth power, or ten
thousand times (10x10x10x10). As you can see, we can now represent any
quantity between 10 and 10,000 with the numbers 10 through 40.
In the case of loudspeakers, we test a speaker by placing a microphone exactly
one meter in front of the speaker. If we had a perfect speaker, we could
drive it with one watt of electrical power and the microphone would
have one watt of acoustical power impressed upon it. This would give us a
reading of 112db. Of course, speakers are very inefficient, most being in
the range of 1% efficient or less. So, you typically see speakers rated at
92db, 96db, 98db, etc.
Let's do an exercise in comparing DB levels and speaker efficiencies.
Let's say you have a speaker that is rated at 102db SPL and I have
one that is rated at 92db SPL. We know that a perfect speaker is 112db. Yours
is 102db. That's a difference of 10db, or 10%,(112-102) so your speaker is 10%
efficient. Mine, on the other hand is 92db, a difference of 20db, or 1%,
(112-92), so my speaker is only 1% efficient.
That means your speaker is 10 times more efficient than mine. If
we put 5 watts into both of our speakers, yours would sound
twice as loud as mine.
The average human ear perceives a doubling in volume when the power has been
increased by 10db. As difficult as it may be to believe, this means that as
you are playing your guitar at a comfortable level of, say, 4 watts from
your amp, you would have to turn your amp up to put out 40 watts for you
to perceive a doubling in volume. This is often confused with 3db, which is a doubling
of power, not a doubling of perceived loudness.
Context: It sounded fine in an open back, but very diffused in a closed back.
Description: Sometimes a particular installation causes a speaker
to lose its focused projection altogether. It loses clarity, attack, becomes
somewhat muddy, and changes character completely. Unfortunately, it seems
very few speakers work equally well in both closed back and open back cabinets.
Context: It has the large aluminum dustcap.
Description: The dustcap covers the voice coil to keep dirt and
debris from fouling the voice coil gap. It can also be used to even out
the peaks and dips in the frequency response of the speaker. For more
information visit our Let's Talk Speakers Q & A page.
Context: It supposedly has very high efficiency.
Description: When converting from one form of energy to another,
there is always some loss, so we express it as a measure of efficiency.
In the case of loudspeakers, we are converting electrical power to acoustic
power. Most loudspeakers are very inefficient, on the order of 1% or less.
The rest of the power is turned into heat. See DB for more
information on speaker efficiencies.
Context: It has noticeable fizz.
Description: Fizz can be caused by high frequency ringing of the
cone or by the inside of the voice coil rubbing against the center pole.
The cone ringing would sound more like a ghost note or single tone, while
the voice coil rub would sound more like weak white noise. Both can be
annoying if they are pronounced even at low volumes.
Flabbing, Farting Out
Context: This speaker is really flabby.
Description: Flabbing, or Farting Out, is when the magnetic circuit
loses control of the voice coil at high volumes on low bass notes. Since,
with a big composite of tones, the mids and uppers are more or less supported
by the low frequencies moving the cone in and out, the farting out can be very
annoying and completely disrupt the structure and texture of your overall tone.
Big magnets with tight gaps usually assure good, tight control of the voice coil
under all conditions. Sometimes the speaker gets the blame for a problem that
is occuring in the output circuit of the amp. Blocking in the output circuit
from overdriving the output tubes, an unstable output circuit, and 120hz ripple
components from the power supply on the signal can cause flabbing that appears
to be a speaker problem.
Context: The energy in the gap is called flux.
Description: The word flux comes from a Greek word which
means 'to flow'. Of course, we know flux does not flow like current,
but is static. It's convenient to think of it as a current, though and
the mathematics used in magnetic circuits is very similar to
volts/amps/resistance we use in electrical circuits. The concentration
of magnet flux in the radial gap around the voice coil is what the
voice coil works against to make it move in and out and impart its movement
on the cone. The more flux, the better, generally. We usually think
of so many lines of flux per square centimeter in the gap. The gap energy
of modern speakers is in the range of 10Kgauss to 18Kgauss. That means
it has 10,000 to 18,000 lines of flux per square centimeter. There's
an interesting relationship between the size of the magnet and the gap energy.
For instance, if a particular magnetic circuit had an 8oz magnet and had
8,000 gauss of flux in the gap, it would take over 60oz of magnet to
double the amount of flux in the gap. It's almost proportional to the
square. That's why you see some speakers with huge magnets. In order to
get high sensitvity in the speaker using wide gaps, they have to employ
a very large magnet.
Fs, Bass Resonance
Context: What's the bass resonance of this speaker?
Description: Fs means 'System Frequency', or 'Frequency of the System'.
Everthing in nature has a natural period or resonant frequency and so
do speakers. When the voice coil moves the speaker cone out, something is needed to
restore the cone to its normal or resting position. This is the job of the
spider attached at the rear of the cone and to the voice coil. So, with the
mass of the cone and the spring action of the spider working together, there
happens to be one single frequency where the two will work together to spring
back and forth until losses in the system cause them to stop. This
single frequency is the system resonant frequency. In loudspeakers, we tend
to call it the bass resonance frequency, since most of the speakers we use
are 8, 10, 12, and 15" in size. These all have system resonant frequencies
down around 100hz, which is a bass frequency.
Gap, Gap Energy
Context: The Gaussmeter measures gap energy.
Description: The amount of gap energy and the size of the voice
coil determine the amount of torque or pulling power one has available to
move the cone in response to an input signal. Ideally, the cone, spider,
and surround would be very stiff so as to exhibit excellent damping, while
the coil and gap energy (called the motor circuit) would be designed to
be very powerful. Getting alot of flux (gap energy) in the gap is limited
by the size of the magnet, the gap spacing (gap length), and the type of
steel used for the magnet circuit steel parts. Modern high production volume
speaker manufacturers tend to use big gaps so they have less chance of voice
coil rubs, and use steel parts with higher carbon content because it is cheaper.
The higher carbon content limits the amount of flux the steel can conduct because
the carbon acts as a resistance to the conduction of the flux. They compensate
by using larger magnets to achieve the flux density they desire.
Context: Way too harsh and brittle.
Description: Speakers are like any other system, including the
output circuit of your amp. When driven too hard, they square wave.
Some manufacturers, in an effort to get the sensitivity of their
speaker high without going to a huge magnet, shorten the voice coil.
Putting more or all of the voice coil within the magnetic field of the
gap ensures all of the coil windings of the voice coil cut across magnetic
field lines of force when energized. The problem occurs when the coil
is energized with a big enough signal that takes it to its excursion limit.
In other words, it runs out of coil windings in the gap and just stops moving.
The result is squarewaving of the mechanical signal or force to the cone, and
it sounds very harsh.
Context: It sounds too HIFI-ish, no character at all.
Description: As the name implies, a speaker that is too HIFI-ish
might have good sensitivity as well as other redeemable qualities, but
for guitar tone it's just too flat and boring sounding. Guitar amp
speakers are all about music sourcing, not music reproduction, so a
good guitar amp speaker is anything but flat and HIFI-ish sounding.
Context: It's got a honking midrange.
Description: Usually nasally sounding, a peaked midrange
in the area of 800 to 1200hz that is up several db from the low end.
It resembles talking through a megaphone. A speaker that lacks low end
and is pretty weak on the highs can also appear to be honking, simply because
the mids are normal but the other ends are lacking. The balance is way off.
Context: What's the impedance of this speaker?
Description: The impedance of the speaker is the mathematical combination
of reactance and resistance at a particular frequency. Most speakers
used in the music business are either 4, 8, or 16 Ohm speakers. A simple
way to check the impedance is to measure the DC resistance of the voice
coil with a Volt-Ohmeter. If it measures more than 4 ohms but less than
8 Ohms, you call it an 8 Ohm speaker. Same for the 8 to 16. For more
information on Impedance or Z, see our Let's Talk
Speakers Q & A page.
Context: What components make up the magnet assembly ?
Description: The magnet assembly is made up of the magnet, the back
plate, the front plate, and the pole. The magnet is sandwiched between
the front plate and the back plate. The diameter of the pole is reduced
at the rear so it can be pressed into a hole in the center of the back plate.
The front plate has a large hole in the center which is about 25 to
30 thousandths of an inch larger in diameter than the outside diameter of the
voice coil. Similarly, the pole, at the point where it sticks through the
large hole in the center of the front plate is about 25 to 30 thousandths
smaller in diameter than the inside diameter of the voice coil. The magnetism
from the faces of the magnet get conducted through the plates and pole, so
that the magnetic energy is focused in the gap between the pole and the big
center hole on the front plate. The foregoing was an explanation for a typical
ceramic or AlNiCo ring magnetic circuit. For an AlNiCo plug type magnetic circuit,
such as what you would find on an old Jensen P10R, a square horseshoe metal
piece called a field case is attached to the back of the magnet plug and to
the front plate. At the other end of the magnet, a small pole piece made of
steel is attached that fits in the large hole in the center of the front
plate. This is necessary because we need the magnetism from that end of the
AlNiCo plug to make a right angle turn to focus the energy in the voice
Context: It gets too muddy at higher power.
Description: As you turn up the power and get into audible cone breakup
with good texture and tone, the lows might not follow along and sound muddy or
supressed compared to the rest of the signal.
Context: Real peaky, very audible.
Description: All speakers have peaks and dips in their frequency
response. However, some areas of the response may be so pronounced they
stand out in the crowd. Sometimes designers will try different sizes and
types of dustcaps in an effort to correct the peakiness.
Context: How do I know if I have the speakers phased properly?
Description: Technically, speakers are AC (alternating current) devices,
just like a vacuum cleaner or a blender. They really don't care which way they
are hooked up or plugged in, they'll work just fine. However, in the case of musical
instrument amplifiers, we often find several speakers connected in parallel to
get more sound from the cabinet. So, it stands to reason that we want all of these
speakers which are connected in parallel to work in unison, or, in other words,
move the air in step with one another. To achieve this, we identify the 'plus'
terminal of all the speakers and make sure they are tied together. Same for the
'minus' (usually unmarked) terminal. For the plus terminal, you might find a red dot,
a '+' mark, or some other form of unique marking. When dealing with speakers
of unknown origin, unmarked speakers, or vintage speakers, it is best to test
the speaker to determine which terminal to label the plus terminal. To do this,
simply touch a 9 Volt battery across the speaker terminals and observe the
motion of the cone. If the cone moves out, then you have connected the plus
terminal of the battery to the plus terminal of the speaker. The point to be
made here is that regardless of the origin of the speaker or speakers you are
testing, you are now characterizing them and marking them, so you'll know
the polarity of them when you decide to use them at a later date in an amp.
So, let's run down some final points to be made about speaker phasing and
1. As far as connecting speakers are concerned, the terms polarity
and phasing are interchangeable.
2. When using several speakers in parallel in the same cabinet, we
connect them in such a way that they are always pushing and pulling
air in step with one another. This concept verifies the notion that
the real reason for phasing or polarizing speakers is to satisfy an
acoustic requirement, not an electrical one.
3. You might find that some vintage speakers, particularly JBL and
Jensens, were reverse-polarized. This means that a plus voltage
on the plus-indicated terminal of the speaker will actually cause
the speaker to move in rather than out.
You will want to make a note of this or relabel it for your convenience.
Another point to be made here is that if a person is accustomed to
thinking a plus on the plus-indicated terminal causes the speaker to
move in rather than out, it should be noted that this thinking is
also correct. Again, the speaker is an AC device. The purpose of
characterizing and marking them is for the convenience of the user to
ensure they will be connected for proper acoustic phasing.
4. In a single speaker installation, polarity means nothing. You may
connect the speaker terminals to the wires from the amp either
way. You may hear people talk about absolute polarity or
some other term used to describe the effort of knowing and
maintaining a specific phase or polarity relationship from the
pickup on the guitar, through the amp, and to the speaker. What
this means is that it is important to them that when they, say,
stroke down on the strings, the speaker moves out initially
rather than in. Some feel this specific phasing is critical to
Pot Cover, Magnet Cover
Context: Many vintage speakers had pot covers.
Description: Historically, pot covers, or magnet covers were for
cosmetic purposes. They were usually quite a bit larger than the magnet structure,
so at first glance, the magnetic system appeared to be huge. Very impressive.
With the advent of ceramic magnet speakers and the competitive nature of the speaker
market, pot covers fell by the wayside. There is currently a resurgence in their
use, however, in the home theatre and entertainment system market. The leakage
flux from the magnet can affect the operation of nearby televisions and other
electronic devices, so manufacturers are installing them for those
applications. Vintage pot covers were either steel, bakelite, plastic, or
aluminum. Modern ones are all steel since their purpose is for magnetic shielding.
Context: What's the power rating of this speaker?
Description: If you were around in the early 70's, you undoubtedly
remember the race to see who could make the biggest HIFI power amp and how much
they stretched the truth about their power output rating. They finally
standardized on an RMS rating at a certain impedance and distortion, etc.
Well, speaker companies didn't standardize on anything and still haven't.
The official, or accepted design technical standards are :
RMS --------- RMS power the driver can safely handle.
Peak Power -- The amount of power the driver can handle for 20% of the time.
System Power - The amount of power required to burn the voice coil.
Excursion Limit Power -- The power required to move the voice coil to its mechanical limit.
P.M.P.O. -- Peak Music Power Output. The most meaningless power rating of all. It
is for marketing only, and indicates the amount of power the amplifier will put out in a very
short amount of time such as on music peaks.
The published power ratings and how they are determined vary
among manufacturers. One thing is for sure, though, they are usually
higher than any of the technical design ratings. For instance,
some speaker manufacturers rate their speakers at twice the RMS value, while
others use up to four or five times the RMS value for their rating. They make the assumption that no
one would put a steady tone (RMS or continuous power) into the speaker for very long, and also
realize that music is transient in nature.
Another big problem with truth in power rating is the fact that copper
has a positive temperature coefficient. The voice coil wire is copper, so
as soon as it starts heating up its resistance goes up. All electromagnetic devices are
current devices, that is to say, they respond to the current through them, not
the voltage across them. For many reasons, speakers have always been driven
by amplifiers that have voltage source outputs rather than current source outputs.
This means that for a given input, the amp will put out a certain voltage
and the assumption is made that the load (the speaker) resistance
won't change much. In reality, as the amp puts out enough voltage to put, say 40 watts
into the speaker, the speaker voice coil begins to heat up, its resistance goes up,
and before you know it, the speaker is only drawing 20 watts from the amp. Speaker
manufacturers are well aware of this fact, and make use of it in determining their
published power ratings. Of course, if you had an amp whose output was a true
current source, it would keep pumping 40 watts, regardless of the resistance
change in the voice coil.The common term used to describe this effect is
Power Compression. An example of this is after you've gigged
for a lengthy period of time and you notice the speakers in your amp
seem to lose attack, the loudness drops, and they get kinda mushy,
you are experiencing the effect of power compression.
Some manufacturers rate their speakers based on a mechanical limit rather than
an electrical one. WeberVST for instance, rates its model P10Q at 20 watts,
because at around 30 to 35 watts the voice coil will bottom out and cause a
cracking sound. The voice coil itself would handle much more than 20 watts of
electrical power, however.
Context: The speaker has a broad presence notch .
Description: The loudspeaker has a major fundamental resonance
which is mainly determined by the spider and the mass of the cone. A second
resonance occurs at the surround. It's not major, but can have an dramatic effect
on the frequency response of the speaker. The surround plays an important part
in the overall sound, because it acts as a terminating impedance for the waves
travelling out from the voice coil to the edge of the cone. If the surround
goes into an oscillation of its own, it will either disconnect from the cone
and refuse to terminate the waves, sending them back towards the voice coil,
or at certain frequencies will completely absorb the waves. This surround
resonance is around 800 to 1000hz. Usually, in a frequency response plot,
it appears as a dip around 800 to 1000hz. This dip can be as much as 6db
deep and can be as broad as 200hz. Since a 10db difference in sound level
is perceived as a doubling or halving of sound, the 6db drop at the presence
notch would certainly be noticeable. There would be a pronounced drop in the mids.
The player would have a tendency to turn up the volume to restore the mids,
with a resultant increase in the lows and highs. Hence the term presence notch.
Context: This speaker is really punchy in the midrange.
Description: When a speaker has good attack, lots of body, and exhibits
good control over the power band, it is said to be punchy. Some speakers
are punchier in certain areas of the response curve, but aren't necessarily
Rare Earth Magnet
Context: The rare earth magnet makes the speaker very lightweight.
Description: Although ceramic magnets have performed well for 35 years or
so for the loudspeaker industry, other industries and users of magnetic materials
have continued to search for lighter, more powerful magnets. One example is
starter motors for automobiles. Many new materials have been used, however
the processes to strengthen the magnets during their creation have vastly
improved. One of the materials used for the rare earth magnets is neodymium.
A neodymium magnet exhibits tremendous strength for a given size. Some speaker
manufacturers are starting to use rare earth magnets. When you consider the number
of large PA bins used at a typical stadium venue, you can certainly appreciate
the weight saving advantage they offer. Also, they are very difficult to demagnetize
once they are magnetized, so they are perfect for high power speakers.
Context: This speaker is very smooth.
Description: Not to be confused with HIFI-ish, a smooth speaker
exhibits a well balanced frequency response while maintaining good
breakup characteristics, sensitivity, and overall desireable operation as
a guitar amp speaker.
Context: What is the function of the spider?
Description: The spider is that yellowish/brown corrugated disk
attached to the cone and voice coil at the base of the cone. It's major
responsibility is to provide a restoring force, or spring, to the cone
so that the cone can return to its normal resting position after being
moved by the voice coil in response to an input signal. The spider is
normally made of a bakelized or phenolicized fabric and has several
corrugations. It's height is usually determined for convenience to
fit the voice coil, spider, and cone into the basket chosen and also to
accomodate the amount of travel by the cone. Technically,
the spider is designed to be at least twice as wide as the corrugations
in the surround of the cone it is used with.
Context: What is the SPL of this speaker?
Description: SPL means sound pressure level. Acoustic pressure
is normally measured in a unit called a Pascal. We tend to convert it to
power so we can think in terms of power gains and losses. When someone
asks "What is that speakers SPL?", they are normally referring to a
manufacturers rated SPL value. This rating, like the manufacturers power
rating, is another one to take with a grain of salt. Since, with SPL,
like power, it's the bigger the better, the SPL ratings get exaggerated
a little. If you look at a response plot, you'll
immediately wonder how one determines the SPL rating. A typical guitar amp
speaker might vary from 92db to over 115db on axis in the test chamber, so
you have to wonder how they come up with a number. Some use an average,
some just pick a level at a midband frequency, while others use one of the
highest readings on the plot. Some manufacturers use a calculated
SPL. It is derived from a formula which includes various known parameters
of the loudspeaker, such as magnet strength, Q, magnetic energy from the
voice coil, weight (or mass) of the system (cone, spider, etc.). Plugging
these numbers into the formula yields a calculated, predicted SPL.
It's kind of like predicting how fast a car will go when you know the
weight of the car, the gearing, and how much horsepower you have.
Context: The surround had that silicon glop on it.
Description: The surround is that area out at the periphery of
the cone and usually has from one to three corrugations. Its main purpose
is to connect the cone to the rigid basket while allowing the cone to vibrate
freely. It also serves to terminate or dissipate the waves or vibrations
that travel up the cone towards its periphery. It has its own resonant
frequency and can have an effect on the overall frequency response by
putting a notch or peak in the response at certain frequencies. The resonating
surround can also impart energy back into the cone, producing an audible signal that
is often referred to as edge yowl. Since the cone is at its thinnest
at the surround, and in the case of a cloth surround, very pourous, it is easy
for low frequencies to leak through the surround
from the rear to the front and cause some cancellations. This is particularly
true in a closed back cabinet where pressure builds up. For this reason, some
cones are doped or sealed at the surround. Some manufacturers dope the
surround to suppress the surround resonances, thereby reducing the effect of
the resonances (or anti-resonances) on the response of the speaker. A third
reason is to strengthen and protect the surround from effects of constant
flexing, temperature, humidity, etc. Since the doping reduces the texture and
complexity of the sound from the speaker, many guitar players prefer undoped
Context: This speaker exhibits very good sustain .
Description: There is a fine line between a speaker being over and
underdamped. If it's underdamped, it can be harsh, ringing, and sound
brittle. If it is overdamped, it can sound thin, choked and compressed.
When it is just right for a particular installation, it has just the
right breakup, texture, and sustain.
Context: I like the overall texture of this speaker.
Description: The texture of the tone is the overall effect of the
comb filtering that occurs during breakup, the control of the breakup itself,
and the control of the low end at high power levels. For instance,
some like the early breakup sound of a straight, simple cone such as that used
on a P12R. This is the typical 50's tweed sound. Others like the smooth, big,
clean low end, late breakup, warm sound of a P12N. It's a matter of taste and
Context: Where can I get the T-S Parameters for this speaker?
Description: Loudspeakers are electromechanical devices, or more
precisely, electroacoustic transducers. The goal is to convert energy
in the form of electrical power to energy in the form of acoustic power.
Since loudspeakers have both electrical and mechanical properties,
it stands to reason that there are specific mathematical quantities
that represent both the electrical and mechanical properties. To
design a set of mathematical formulas to combine these quantities and
then describe the overall characteristics of the loudspeakers was the
goal of two acoustic researchers named Neville Thiele and Richard
Small, hence the term T-S Parameters.
They measured a few of the parameters of the loudspeaker such as electrical
resistance of the voice coil, free air reasonant frequency, inductance of the
voice coil, and the cone size. Then, they would mount the speaker in
a sealed box of a known volume and remeasure the resonant frequency
as well as a few other parameters. Their extensive set of formulas
could then be employed to determine and estimate very accurately the remaining
unknown quantities of the loudspeaker (or driver), such as the system
Q, the volume of air displaced by the cone, voice coil (motor) strength,
overall efficiency, and estimated SPL. The resultant parameters are
invaluable to speaker cabinet designers, enabling them to design the
cabinet, porting, etc. to match and be compatible with the parameters
of the loudspeaker. In very simple terms, if you consider the
loudspeaker as a signal source with a specific characteristic impedance,
by using the T-S Parameters you would be able to design a cabinet that
would match the characteristic impedance of the source. This would allow
the loudspeaker to operate at optimum efficiency over its frequency
and power band. Most manufacturers will provide the T-S Parameters of
their loudspeakers and drivers upon request, and some offer examples
of designs for both sealed and ported enclosures which will be
optimum for their loudspeakers and drivers. By searching the World
Wide Web, you can find many examples of cabinets, formulas, and driver
data. When you read about a particular guitar amp speaker enclosure
and the ad says Thiele cabinet, it means that the designer
has employed the T-S parameters of the loudspeaker(s) he or she is
using in the design of the enclosure or cabinet.
Context: What size is the voice coil?
Description: The voice coil is the real heart of the speaker. It
gets energized by your amps output signal and moves the cone in and out
to produce the audible sound. The voice coil is wound on a round former,
about 1 1/4" long, and is made of either paper, Nomex, Aluminum, or Kapton.
Each has its advantages and disadvantages, the advantages having to do with
power handling ability, the disadvantages having to do with weight. A coil
is usually either two or four layers of copper wire. Some coils are short and are about the
length of the width of the front plate, or gap. These are called even hung,
or under hung voice coils. A coil that is longer than the thickness of the
front plate is called an over hung coil. The underhung coil is more efficient
(louder for given input signal), but reaches it limit sooner than a longer coil.
An over hung coil isn't as efficient as an under hung coil, but can travel farther
before reaching its limit.
Voice Coil Rub
Context: It sure sounds like a voice coil rub.
Description: Probably the most common failure in loudspeakers.
Usually occurs after applying too much power to a speaker for too long a time.
Unfortunately, many vintage and vintage style speakers get their best tone
when taken to the limit. The gap or space between the voice coil and center pole
or between the voice coil and the front plate hole is only about 10 thousandths of
an inch in vintage and vintage style speakers, and about twice that in
modern high production volume speakers. In either case, that's not much room
for the voice coil to expand or deform much. Excessive heat in the voice coil
causes the shellac or other chemical holding the voice coil wires in place to
soften, thereby allowing the wires to shift around. The heat can also cause
the former material to crack, delaminate, or deform. The result is a rub
between the inside of the voice coil and the center pole or between the outside
of the voice coil and the plate hole.
Context: It sounds way too weak, something's wrong.
Description: Thin sounding, no dynamics, reduced lows. In an
AlNiCo magnet speaker, it usually means the magnet has been partially demagnetized.
If the speaker has been reconed, it may not have been recharged, or remagnetized,
since many reconers don't own or have access to a magnetizer.
Context: It has that smooth, woman tone.
Description: This sound is attributed more to the setup than
it is to a particular speaker characteristic. Typically a sweet, smooth
sound that is produced by turning down the treble control on the guitar
and running through a cranked amp. Good control on the low end but not too
bassy, smooth overall tone with rolled off highs. An example is the solo on
Cream's "Sunshine of Your Love"
WeberVST gratefully acknowledges the following individuals for their
contribution to the descriptions and contextual use of the speaker terms
presented on this page:
Joe Pampel, Dale VanZile, Akbar Anwari, Dr. James Bardsley, Don Williams,
Rick Erickson, Paul Croft
Content © 1996 Weber Vintage Sound Technology