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Speaking Up About Speakers

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Here at MayosMusic, in addition to offering great guitar, bass, ukulele, banjo and autoharp lessons, plus complete luthier services that include guitar, string instrument and amplifier repair/restorations, we are also a great resource service. Consider: the two most important links in your sound chain are the first and last, Pick-Ups and Speakers.  So let's talk about speakers...

The speakers in your amp are the transducers that translate the electrical signals of your equipment into the sounds we all hear as the music you play.  Players like to change tubes, strings, instruments, picks, even internal components like capacitors and such in an attempt to find the magic mix that is "their" perfect tone.  Well, speakers can often be the easiest and quickest (though not usually the cheapest) way to change tone subtly, or even drastically.


Ratings
- Speakers are rated in several parameters and tonal characteristic descriptions by manufacturers and/or users. Let's start with the measured parameters:

Power - Speakers are rated for power handling in units called Watts, with most showing the maximum or peak power they handle.  Some will show their RMS (Root Mean Square) which is the equivalent power if the signal was DC.  Some manufacturers will state their "music" power rating, which is their rating for how much power of random signal (since music is not exactly a perfect sinusoidal waveform) they can handle.

Impedance -   Impedance is the vector magnitude of the combined DC resistance (Ohms - Ω), and the frequency dependant inductance (mH).  It is usually posted as "Nominal Impedance" which is the average impedance over the signal range.  Some manufacturers will display their speaker's minimal impedance, which is helpful for safe and proper connection to power amplifiers.

Frequency Response - The measured minimum and maximum frequencies the speaker can reproduce is the frequency range. Hopefully it is displayed at a given +/- dB range, but is not always (I'll go over that rating in a second).  Frequency range is measured in units called Hertz (Hz), which represents what used to be called CPS, or Cycles Per Second.

Efficiency - The final common speaker parameter (at least for the music industry, those in other industries might concern themselves with more measurements) is its efficiency, also referred to as Sound Pressure Level (SPL).  The efficiency of a speaker means how loud it gets.  They typically measure this in a given cabinet connected to a 1 Watt signal and measured at 1 meter with a control microphone.  Then they sweep the signal or just rate it at 1kHz, or 800Hz, or some other standard.  The measured sound pressure is the efficiency, and rated in deci-Bells (1/10th of a Bell) noted as dB.  Now every +3dB is twice the power, and -3dB is half the power (very important).  And the average human discerns twice the volume to their ears as being around +7dB to +9dB.

Descriptions - The other way speakers are described is in terms of their tonal characteristics.  With words like cool, warm, hot, bright, edgy, smooth, even, brittle, boom-y, bass-y, treble-y, midrange-y, focused, loose, tight, controlled, gritty, bite, etc. etc.  Manufacturers, resellers, and reviewers will describe instrument speakers with these and more descriptive words.  Often describing the speaker at various power levels (low, medium and high), and with a clean and distorted signal.  Stating both how it sounds with a normal signal, and then how it sounds when "pushed" hard and starts to distort, since that is the name of the game for a guitar amp's speaker.

Types - Most speakers in instrument amps are going to be highly efficient paper cone "dynamic element" or "dynamic driver" speakers, referring to the familiar round cone that moves in and out.  Now in Hi-fi, there are many more types/designs of speakers, such as electrostatic, electrets, compression horn, ring radiator, planar, ribbon, piezo-electric, and a few others.  Compression horn drivers are common for highs and sometimes mids in PA speakers, and in some bass amps.  And piezo horns are common in cheaper bass amps for the highs too.  Some Acoustic guitar amps are now using ribbon or even electrostatic (though usually mislabeled and are actually electret) drivers for the highs.  Acoustic amps with ribbons and such will sound very nice and often described as airy, effortless, and with great subtleties.

Tone - Just as pedals and amps can add distortion into your tone, via transistors, op-amps, chips, FETs, and tubes (both pre-amp and power amp distortion), speakers can impart their own distortion to the mix.  Sometimes that distortion is subtle and referred to as "Timbre" or tone, which is the amount of altered sound across the frequency spectrum from electrical signal input to the sound output.  However, most people simply refer to this as the tone, character or timbre of the speaker.  The more noticeable and obvious distortion types are the clipping/overdriving/compression/breakup distortion that is usually collectively referred to as the "distortion" character of the speaker.  This type of distortion is made when a speaker is driven close to or at its maximum power handling.

Magnets - All speakers use magnets to create an opposing force against the induced magnetic field created by the current through the voice coil wire.  In the world of speakers, there are three general magnet materials: AlNiCo (Aluminum, Nickel and Cobalt), Ceramic (Strontium Ferrite), and the new kid on the block Neodymium.  For the most part Neodymium is mostly used for light weight bass amp and PA speakers.

AlNiCo - Alnico is one of the earliest magnets used for speakers.  It is light weight and fairly strong.  Ceramic magnets came along a little later, and while not quite as strong per weight, they are far cheaper to manufacture.  All other speaker factors being equal such as magnet size or strength, voice coil diameter and gap, number of windings, wire type and gauge, cone material and weight, etc. the two will inherently sound different.  This is because AlNiCo magnets are an alloy magnet, verses ceramic magnets, and they are easier to demagnetize.  When a voice coil moves from a signal, the current through the wire coil is generating a magnetic field in opposition to the permanent magnet (thus movement and sound production), and when this happens, the resistance from the spider, the surround, the momentum of the weight of the speaker, and the air resistance against the cone all act to prevent movement, which means the voice coils magnetism is trying to cancel or squish the opposing force of the permanent magnet.  When this happens, AlNiCo speakers react to it, and their permanent magnet is magnetically bent and compressed and this causes the speaker to become less efficient, at its extremes, which means that it exudes an amount of natural compression to the signal being translated into sound.  This does not exist in the same way with ceramic magnet speakers.

Ceramic - Ceramic magnets don't compress, so the voice coil instead moves all the way to the ends of its mechanical limits, which can sound harsh or edgy when pushed hard.  Thus the general rule is that AlNiCo speakers sound warmer, and smooth, which ceramic sounds bright and harsh, when listened to at loud levels.  You can to a certain extent liken the ceramic speaker to a solid state amp, and an AlNiCo to a tube amp, in that their perceived power/headroom and natural compression/distortion are comparable.  However, when it comes to choosing which type to use, it all comes down to finding the right balance of all components, to achieve the end result you desired.

Neodymium - For the most part, Neodymium speakers sound and act like AlNiCo speakers, usually with higher power handling and higher prices, more or less.  While they handle more power, they unfortunately have a less forgiving damage limit when it comes to over heating.  Neodymium is a highly sensitive magnet, which is what makes them sound closer to AlNiCo, however, once they overheat, they are permanently damaged.  This is why most "Neo" speakers have a lot of heat sink fins on the magnet structure.  So while "Neo" speakers are somewhat delicate, if played within their parameters, they can offer a tremendous savings of weight, especially in multi-driver bass cabs like 4 x 10" or 8 x 10".

Combining - Knowing the speakers ratings can help to achieve your tone just like the descriptive ratings.  For example, if you have a 50watt amp, and the speaker is rated at 100watts and 101dB, and you want your amp to "break up" sooner, and get to that sweet power tube distortion range in it's power band, then switching to a speaker that is 80watts will bring you closer to the breakup point in the speaker with the same amp input, and if the speaker is say 98dB, then that is 3dB less (-) efficient, so now your 50watt amp will sound like a 25watt amp (with your old speaker).  Conversely, if you have a 22watt amp that is great for practice, but not loud enough at gigs, then try swapping your speaker for one that is +3dB more (to make your amp feel like a nearly 50watt amp), or to a +6dB speaker (to make your amp sound like it is now 100watts compared to the original speaker).  Playing the numbers game with instrument speakers can help you achieve the tone you are looking for just as much as the tonal characteristics of the speaker itself.

Cabinets
- The cabinet a speaker is in is also very important to its tone, volume, efficiency, and power rating.  A closed back cabinet will impart tighter control on a speaker.  The sealed air inside will hold the woofer like a damped spring.  This can help to control bass.  The trade off is usually a slight drop in efficiency.  An open backed cabinet will sound livelier and usually louder.  It will have a slightly sloppier bass, but the trade off is a more ambient and natural mid and high range, as the back side of the speaker is projecting sound too, and bouncing it off whatever is behind your amp, and creating more sound reflections which can sound more full and natural with sound coming from all over the room much more so than with a closed back cabinet.

Bass amps will want a sealed or ported cabinet, and not an open backed cabinet, as they are looking for bass control and focus, and with more bass control, you can increase the power rating as compared to a looser speaker movement in an open backed cabinet.  You might find your speakers and amp are both great but that the cabinet design is not.  Maybe opening up, partly opening up or sealing off a speaker cab is the change in tone you are looking for.  Some aftermarket speaker cab companies offer convertible cabs that can be configured as open or closed back.


Placement
- Where you place your speaker can impart a change in over all tone and volume just like the cabinet type and speaker model.  Every surface a speaker cab is near, the bass volume will be acoustically amplified.  So if a speaker is on the floor, it will sound bassier than if it is up in a chair, or on an amp stand.  If it is up against a wall, it will sound even bassier, and if in a corner, bassier still.  Conversely, if your amp sounds too boomy and bassy, or if you want to have it cut through better in the mids and treble at a gig, then putting it up on an amp stand will both keep it off the floor, and get the direct line of sight, ear level, cutting sound you might need to be heard in the mix better.

Safety - Wiring up speakers, and more importantly two or more speakers can be a great way to change tone, add volume, drop volume, or if done improperly, damage an amp.  Instrument speakers are rated in 4ohms, 8ohms, 16ohms, and the occasional 32ohms.  Two 8ohm speakers in parallel make a 4ohms load.  And two 8ohm speakers in series will make a 16ohm load.  Usually the 32ohms are for bass cabinets where you have 8 x 10" speakers, all wired in parallel, so you end up with an 8ohms cab.  So the impedance of a speaker and amp should be matched.  Sometimes amps can handle a slight mismatch of one rating up or down, without doing permanent damage to the amp, but do not rely on this.  Transistor amps can handle a speaker with higher impedance than its rated minimum, but are not safe with speakers or a combined speaker load lower than their specified rating.  Now, tube amps are different.  You can usually go up or down the next rating and the amp should be ok, more so if you don't crank the volume.  However, tube amps, due to their output-transformer-coupled design, are not good with a load significantly more or less than their specified ratings.  That is why tube amps will often have multiple output connections, with specified ohm ratings on each.  These are each connected to a different winding tap on the output transformer.  Also, never turn on a tube amp when there is no speaker plugged into it.  With no speaker load to allow the voltage in the output transformer to become a current (and thus move the speaker voice coil creating sound),  the voltage in the transformer will send a Back EMF (Electro-Magnetic Field) wave through the transformer and amp and damage it internally.  This is also known as "flyback voltage" damage in a tube amp.  They NEED a load at all times.

Brands - Are you not sure what speaker you have?  Here is a list of the manufacturing numbers of common instrument amp speakers.  Names in bold are common on Fender and other common amp brands.
67 - Eminence
73 - JBL
137 - CTS
185 - Motorola
188 - GE
220 - Jensen
232 - Magnavox
254 - Packard bell
260 - Philco
262 - Philmore
270 - Quam Nichols
274 - RCA
277 - Emerson
285 - Rola
308 - Stromberg-Carlson
328 - Utah
336 - Western Electric
337 - Westinghouse
343 - Zenith
345 - Astatic
391 - Altec Lansing
409 - BIC
416 - Heath
423 - Philips-Norelco
433 - Cleveland
446 - Good-All
465 - Oxford
590 - Shure
649 - Electro Voice (EV)
706 - Pioneer
794 - Harmon Kardon
843 - Klipsch
847 - University
918 - Oaktron
1056 - Fisher
1098 - Pyle
1279 - Weber
Celestion and Peavey have their own codes...


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