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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? 

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. The unique properties of AlNiCo magnets which make them desirable for musical instrument speakers are discussed in this Premier Guitar article written by our own C.J. Sutton  <click here to read>

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 curvilinear, 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 curvilinear cone for musical instrument speakers is the Kendrick Black Frame. The curvilinear 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 4 Khz, 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 (and far less common) source of buzz or rattle is from a magnet assembly that has worked loose from the speaker basket. If you think this might be the case, please email us to discuss it.

COMB FILTERING

CONTEXT

Part of the texture of the tone is due to comb filtering.

DESCRIPTION

For some reason we find it desirable 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.

COMPRESSED

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.

CONE, DIAPHRAGM

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 desirable. 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.

CHIME

CONTEXT

This speaker has a lot of chime on top.

DESCRIPTION

In contrast to ‘sparkle’ – emphasis on treble frequencies that are just a bit lower than the ‘sparkle’ frequencies. Chime is more of a bell-like tone, whereas sparkles is more like the sound you might imagine in your head that falling snow might make.

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 (dB)

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 10 db 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. 40 db, 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 92 db, 96 db, 98 db, etc. Let’s do an exercise in comparing DB levels and speaker efficiencies. Let’s say you have a speaker that is rated at 102 db SPL and I have one that is rated at 92 db SPL. We know that a perfect speaker is 112db. Yours is 102db. That’s a difference of 10 db, or 10%,(112-102) so your speaker is 10% efficient. Mine, on the other hand is 92 db, a difference of 20 db, 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 10 db. 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

Not to be confused with Magnet Cover, the dustcap is the dome in the center of the cone, It 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 info on the H dustcap, )

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 occurring 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 10 Kgauss to 18 Kgauss. 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 sensitivity 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’. Everything 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 100 hz, 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 a lot 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 square waving 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 mid range 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-Ohmmeter. 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 unfocused or suppressed 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.

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.

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 a 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 traveling 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 1000 hz. Usually, in a frequency response plot, it appears as a dip around 800 to 1000 hz. This dip can be as much as 6db deep and can be as broad as 200 hz. Since a 10 db 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 desirable 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 phenolized 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 accommodate 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 plot, you’ll immediately wonder how one determines the SPL rating. A typical guitar amp speaker might vary from 92db to over 115 db 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.

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. 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 porous, 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 (though we recommend light dope in most cases.)

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.

SPARKLE

CONTEXT

This speaker has a lot of sparkle to the top end.

DESCRIPTION

Emphasis on very high treble, the frequency range that generally can be controlled by the presence knob.  Sparkle is best noticed with lack of chime. Chime is more of a bell-like tone, whereas sparkle is more like the sound you might imagine in your head that falling snow might make.

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 resonant 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. We do not, as guitar speakers are not HIFI speakers where this kind of information makes a difference.

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 underhung 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.