Aggressive
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.
AlNiCo Magnet
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.
Attack
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.
Bell Modes
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.
Body
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.
Boomy
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.
Breakup
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.'
Bright, Trebly
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.
Buzz, Rattle
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..
Ceramic
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.
Comb Filtering
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.
Compresssed
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
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.
Cone, Diaphram
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.
Crunch
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 the tone.
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.
Decibel
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.
Diffused
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.
Dustcap
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.
Efficiency
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.
Fizz
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.
Flux
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.
Harsh
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.
HIFI-ish
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.
Honky, Honking
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.
Impedance, Z
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.
Magnet Assembly
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 coil gap.
Muddy
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.
Peaky
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.
Phasing, Polarity
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 polarity.
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 their tone.
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.
Power Rating
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.
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 times the RMS value for their rating. They make the
assumption that no one would put a steady tone (RMS 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.
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.
Presence Notch
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.
Punch
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 peaky.
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.
Smooth
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.
Spider
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.
SPL
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
Surround
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. Since the cone is at its thinnest at
the surround, 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 cones.
Sustain
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.
Texture
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 playing style.
T-S Parameters
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.
Voice Coil
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.
Weak
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.
Woman Tone
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"
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Thanx to Weber Vintage Sound Technology for these terms.