Monday, November 14, 2016

Everything You Ever Needed To Know About Speakers

They're not as sexy as a new guitar or amp, but they do all of the heavy labor and grunt work for them.

They're the most crucial element in converting your guitar tone from electrons to your ears, yet are often the most overlooked.

How many people buy a combo amp without even considering the speaker, let alone the differences from one type to the next? I was guilty of this for years... whatever came with my amp was good enough, I figured. When I first began working at a recording studio almost 20 years ago, I learned that Celestion Vintage 30s were the preferred upgrade for Marshall cabinets at the time, in place of the stock G12T-75s that many deemed to be harsh. So for years after that, I used a 2x12 cabinet loaded with V30s for just about everything, assuming it was the standard. Recently, I began experimenting with other options, and the results have been ear-opening to say the least.

We'll get to the different types of speakers and some fun rock-and-roll history about halfway down, but first, a little background on the technical terms involved: magnets, voice coils, cones, watts, ohms, impedance, dBs, and sensitivity. Oh, and don't forget: NEVER TURN ON ANY AMP WITHOUT A SPEAKER LOAD CONNECTED!!! It's the easiest way to ruin a good amp, as the speaker completes the circuit, and all of that power has no place to go otherwise, except back into the place it came from... NOT good. Also, ALWAYS use a proper speaker cable between amp and cabinet, never a guitar cable. Yes, there is a huge difference, and a powerful amp can melt the shielding of a guitar cable and short out the cabinet, which is actually worse than having no speaker connected... get it? Anyhow, moving right along...

Anatomy of a speaker:

In this cross-section diagram, you can see the elements of a basic speaker, including the magnet and voice coil, which, when hit with power from the amplifier, generates a magnetic field between the two which moves the voice coil in accordance with the electrical signal. The voice coil pushes the cone, or diaphragm, to create sound waves, relative to the amplitude (how far the cone moves) and frequency (how fast it moves) of the signal. It's the exact same principle as a dynamic microphone like a Shure SM58, but in reverse. So, kind of magic, but not really. 

AlNiCo (Aluminum-Nickel-Cobalt) vs Ceramic magnets is a very subjective comparison, with much to do with the rest of the speaker's construction and circuit. In general, ceramic magnets are stronger, lending to a brighter, louder output with more edge, while Alnico provides a more even compression and warmer breakup at lower levels. Of course, there are exceptions to both of these rules, and the best way to determine which is best for you is to try both in the same amp. I've heard Jensen Alnicos sound warmer than ceramics in Fender tweeds, all other things being equal, while a ceramic Greenback might breakup smoother than an Alnico Bulldog in a Vox AC30. Your mileage will certainly vary.

Watts are the most common term thrown around in relation to speakers, and measure the power handling of a speaker. Rule of thumb, don't exceed the power rating of a cabinet or individual speaker with your amplifier output, or else you could blow that voice coil by exceeding what the magnet can handle (Note: most guitar amp output is measured in watts RMS, not peak; A 100w amp is capable of putting out substantially more at peak power, so providing a speaker with adequate power handling is very important. Especially if you turn it up to 11 like Nigel Tufnel). This only gets complicated when using different types of speakers in the same cab or combo... in that case, you multiply the lowest-wattage speaker by the total amount of speakers (i.e., in a 2x12 cab with 60-watt & 30-watt speakers, multiply 2 x 30 = 60 watts power handling max). Easy, right? Just wait...

Ohms, which measure impedance, are a little trickier, and without getting too complicated with Ohm's law and physics, i'll try to keep it guitarist-simple. In general, it's always best to match the output impedance of your amp with a corresponding speaker or cabinet for the most efficient transfer of power possible, although there are some safe mismatches that you can get away with in a pinch if necessary, depending on your amp. 

With tube amps, doubling the number coming out of your amp is a safe rule of thumb, i.e., a 4ohm output into an 8ohm cab, or an 8ohm output into a 16ohm cab is usually fine, especially on Fenders or Mesas (Leo Fender was notorious for running 8ohm speakers on 4ohm taps in his older amps, and vice evrsa), but older Marshall power transformers are much more sensitive to mismatches, so I would try to avoid it unless you know for sure the amp can handle it. When mismatching up, be extra careful of volume, as it will fluctuate accordingly, and is essentially making your amp work harder. NEVER exceed double the amp's output impedance though, as this can put too much strain on the output transformer and possibly damage it beyond repair. Lower impedance is also tolerated in most well-built tube amps, but no more than half, i.e., an 8ohm output into a 4ohm cab. This will also make your tubes run hotter, and can lead to failure depending on how hot or cold they're biased to begin with (I wouldn't do this with any older vintage-style amps, or anything if I could help it). Play it on the safe side. You can always check with your amp manufacturer, or a knowledgeable tech, as well. 

Regarding solid state amps, higher impedance mismatches are safe, resulting in less output volume, but lower impedances can be hazardous for your amp's health. Again, the best bet is the right match, but if not possible, go UP!

In a cabinet with multiple speakers, all should be of the same impedance. The overall impedance of the cabinet will depend on how it's wired internally: series, parallel, or a combination, and I've borrowed some diagrams from the Eminence website to explain these methods...

In series wiring, the speakers run one into the other as a big loop, and impedance is simply added up (i.e., 2 x 8ohm speakers = 16ohm total impedance). You wouldn't want to exceed 16ohms total, so in the case of a 4x12, you'd need to stick with 4ohm individual speakers. I'm not the biggest fan of series wiring, since the speakers create one big circuit; if one blows, the sound goes completely dead, and could damage your amp since the speaker is no longer connected in the circuit. No bueno.

Two 2 ohm speakers = 4 ohm load
Two 4 ohm speakers = 8 ohm load
Two 8 ohm speakers = 16 ohm load
In parallel wiring, each speaker is hooked up to the input jack independently, and impedance is calculated by dividing the common impedance rating by the number of speakers (i.e., 2 x 8ohm = 4ohm total load). I prefer parallel wiring for 2x12 cabs, because if one speaker blows, it won't affect the other, and you can make it through the gig safely with a proper mismatch, since an individual speaker will always be of higher impedance than the cabinet total (power handling may be an issue though, depending on the speaker).

Two 4 ohm speakers = 2 ohm load
Two 8 ohm speakers = 4 ohm load
Two 16 ohm speakers = 8 ohm load
There's also series/parallel wiring, a hybrid style used in 4x12 cabs when needing to reach a specific impedance. In this wiring, which is like having two series 2x12s wired in parallel with each other, the overall impedance matches the common impedance of the four speakers, i.e. 4 x 8ohms = 8ohm total load. I like this wiring for 4x12s, as it allows for 8ohm or 16ohm total impedance much easier than in parallel, plus it's a fun way to mix two different pairs of speakers in the same cab.

Four 4 ohm speakers = 4 ohm load
Four 8 ohm speakers = 8 ohm load
Four 16 ohm speakers = 16 ohm load
When using multiple cabinets on an amp with a pair of parallel outputs, you want to double the selected output impedance, i.e., with a pair of 4ohm outputs, like an old Fender, you should connect cabinets rated at 8ohms each (because those cabs will be in parallel with each other, and total a 4ohm load. Because science!). Most Mesa/Boogie heads feature a single 8ohm output and a pair of 4ohm taps for this very reason. If attempting to use two cabs of different impedance, here's a fun math problem to do first:


R1 is the impedance of cab 1 (let's say 8ohms), and R2 is the impedance of cab 2 (16ohms). That means 8x16 = 128, 8+16 = 24, 128/24 = 5.3ohms total impedance, so use your amp's 4ohm outputs (Or, if you don't like doing math, buy gear that matches). 

There are some rare instances of external speaker jacks wired in series rather than parallel, such as some MusicMan designs of the late 70s... it's always worth double-checking this with a manual or local tech before risking any damage to your amp. 

Much more can be said of impedance, but I'd like to keep things as simple and guitar-centric as possible here.

Now that we've covered all that, it's time to talk sensitivity, measured in decibels (dB). A speaker's sensitivity rating tells you how much of the amp's power gets converted into sound, basically; the higher the sensitivity, the greater perceived volume. Most guitar speakers are rated somewhere between 94 and 103dB; this may not seem like a huge range, but dB is a logarithmic measure of relative loudness, and a 3dB increase is essentially a doubling of power (and vice versa for a -3dB decrease). I learned this the fun way when trying to combine a Celestion G12-65 speaker (16ohm, 65 watts, 96dB sensitivity) with a G12H-30 speaker (16ohm, 30 watts, 100dB sensitivity) in the same cabinet... the H30, although rated at less than half the power handling of its partner, completely dominated the 65 to the point where I could barely hear it. I'd never taken notice of speaker sensitivity before this, but that 4dB difference proved to be a massive disparity. The G12-65 now resides in a 1x12 box by itself, while the H30 has been paired with an equally-sensitive partner, an old Vintage 30, in a 2x12 configuration that now has incredible 3-D depth and articulation, much nicer than the pair of V30s I had used for years. The H30 compliments what the V30 lacks and vice versa.

Speaker sensitivity doesn't necessarily have to match, as a 4x12 with two pairs of speakers of different sensitivities can sound great (generally, with the louder speakers in the bottom, and the lower sensitivity pair on top, angled up). Also, if you're mic'ing up the speakers to feed a PA or recording console, the disparity difference is moot anyway, and the only matter is when standing in front of the cab... do you like what you hear? Maybe a brighter speaker like an H30 will sound great to you with a warm, crunchy G12-65 filling in the mids in the background, whereas I prefer the 65 to be in the forefront. 

A Vintage 30 (left) and Heritage 30 (right), living happily together, in parallel & equal sensitivity, inside an Avatar 2x12

G12-65 mounted inside a Seismic 1x12 open back cab. 
Low-mid crunch for days, with plenty of clarity to boot.

"American-style speaker" is a broad-ranging category, which usually starts with Jensen, the speaker of choice for Fender in the 50s, and also includes Altec, Oxford, JBL, CTS, Eminence, and ElectroVoice in that category. As a huge generalization, the "American" sound can be defined as "hi-fi", with clean, tight, powerful bass, crisp, bell-like, glassy highs, and a bit of a dip in the midrange frequencies. 

You'd typically find a Jensen P12Q in an old tweed Deluxe, or a pair of P- or C12Ns in a tweed Twin (P denoting alnico magnet, C for ceramic). Fender began using Oxford speakers in 1961, during the blonde and brownface era, and Oxfords are also associated with smaller blackface models, such as a 12K5 in a Deluxe Reverb, or a 10L5 in a Princeton Reverb. CTS were a fixture in Ampeg amplifiers throughout the 60s, and although not as popular in Fenders as Jensens, a Super Reverb with four Alnico CTS 10"s is quite an impressive beast. Due to demand for even higher fidelity, particularly in the higher end of the tonal spectrum, Fender also began offering 50-watt JBL speakers as an upgrade in it's higher powered amps, such as D120Fs in a Twin Reverb, and D130Fs in the giant, hellacious, Dick Dale-inspired 2x15" Showman cab (the D130 was in fact created specifically for Dale's huge surf guitar sound). JBLs could also be found in both Duane Allman & Jerry Garcia's 70's cabinets, and as mentioned in our SRV Gear Guide, Stevie Ray Vaughan was a big JBL fan early on, until a more powerful option came along. 

A '59 tweed Twin with Jensen P12Ns

Oxford speaker from a '66 Deluxe Reverb

A silverface Twin Reverb with JBL D120Fs

Dick Dale's strat and a pair of massive JBL-loaded 2x15" cabs

Influenced by these high-power, high-fidelity designs, ElectroVoice came onto the scene in the 1970s, and their huge, heavy, 200-watt EVM-12Ls can be found in many of Mesa/Boogie's Mark I and II combos of the day (Altec 417s were also available as a factory option from Mesa, and preferred by Carlos Santana in his Mark I combos). SRV eventually loaded all of his cabinets & combos with EVs for their unmatched power handling and high sensitivity, as he wanted to hear pure amplifier tone with as little speaker breakup or coloration as possible, and was tired of blowing speakers on the road. Nowadays, the "world's greatest guitar loudspeaker" also comes in a 300-watt model, designed for heavy metal biker/viking guitar god Zakk Wylde.

Rear view of a Boogie Mark II combo with a "Made for Mesa" Black Shadow branded EVM-12L

One of SRV's prized '64 Vibroverbs, loaded up with an ElectroVoice EVM-15L

Although we've been focusing specifically on guitar designs, any article on speakers would not be complete without mentioning Eminence and their impact on the music world through Ampeg's 8x10" SVT bass cabinets. Bob Gault, the founder of Eminence, started his company in 1972 after working for Chicago Telephone Supply (CTS) and providing the original speakers for the colossal 1969 SVT beast. Striking a deal with Ampeg as their exclusive supplier, Eminence grew to become the largest manufacturer of speakers in the world, providing thousands of 10" speakers for Ampeg SVT cabs as well as the rare but equally powerful 9x10" V9 guitar cabs (The V9 was the guitar equivalent of the SVT, both head & cab). Like many, I always wondered why 10" speakers worked so well for bass, when conventional wisdom would think that larger 15"s or even 18"s would be preferred, but aside from situations where pure sub fundamental tone is needed, an 8x10" array covers much more surface area than a 2x15" similar-sized cabinet, thereby pushing more air, plus the 10" speakers are able to react quicker to transient attack due to shorter excursion than larger speaker magnets. This adds to the punch and upper harmonic presence in the signal, especially when coupled with the muscular, thick midrange of an Ampeg SVT head. The traditional 8x10" is wired up as eight individual 32ohm speakers in parallel for a 4ohm total load; the V9 was three parallel sets of three 4ohm speakers in series, also for a total load of 4ohms. Both cabinets were designed to handle 300-watt heads. Eminence continues to make a wide range of both guitar and bass speakers today.

A rare Ampeg V9 guitar cab (left) and vintage SVT cab (right), loaded with CTS/Eminence speakers

To say Celestion falls under the category of "British-style speakers" is an understatement, as they single-handedly invented the category, having been associated with Marshall and Vox amps since the early 60s. Known for a forward midrange presence and smooth, compressed crunch when pushed, the sound of 60's British rock is tied to Celestion, most notably Alnico Blue "Bulldogs" in Vox AC30s famously used by the Beatles and Brian May of Queen, and G12M "Greenbacks" in Marshall 4x12 cabinets and "Bluesbreaker" JTM45 combos (the latter's nickname derived from Eric Clapton's use while in John Mayall's Bluesbreakers). Eventually, the G12H was created to provide a Greenback-like tone with higher power handling, as the original 25 watt Greenbacks were being blown nightly by chaps like Jimi Hendrix, Jimmy Page, and Jeff Beck. Since then, many varieties of Celestion have emerged, all bearing homage to the traditional British sound... G12-65s became the 4x12" speaker of choice in the late 70s & early 80s, then Vintage 30s found their way into many Marshall & Boogie cabs in the late 80s and 90s. Nowadays, the H30s and Creamback models are gaining popularity with many boutique amp builders looking for classic tones with modern specs. John Mayer uses combinations of G12-65, Alnico Gold, and H30 speakers in his cabs, and his tone is second to none, in quality OR cost.

A Marshall 4x12 loaded with Greenbacks

Two Bulldogs in a Vox AC30, wired in series 

John Mayer's cabs, with G12-65s (top of both), Alnico Golds (bottom left), and what appear to be H30s (bottom right). Amp heads are a Two Rock (left) and Dumble Steel String Singer (right).

Another British speaker that deserves mention is Fane, who at one point were responsible for 75% of the speaker market in the UK. Found almost exclusively in Hiwatt cabinets, Fane speakers were also used in early Sound City and Simms-Watts products. Considered similar to the Celestion sound but a a bit more hi-fi, with tighter bass, smoother, clearer highs, and that similar pushed midrange, it's been said that Hiwatt's reputation had as much to do with Fane speakers as the amplifiers themselves. At 50 watts per speaker, they could take a beating that Celestions could not at the time, and became a favorite for use at larger venues with Marshall's 200w Major heads as well as with Hiwatts. Just listen to Pete Townshend's tone on The Who's Live at Leeds, and no further explanation will be necessary. 

A Fane speaker in a Hiwatt cab

As for newer names to the speaker game, we must include Weber and Warehouse Guitar Speakers (WGS) in the list. I've got a Weber 6" upgrade in my Fender Champion 600 combo that's just fantastic, and have used both a WGS G12C and G12Q in my Echopark Vibramatic 13 combo with great success. The G12Q helps make the amp a bit more home-friendly, as the high sensitivity and power handling of the C made it the loudest 13-watt amp I've ever played! Great tones, though. I'm looking forward to trying more models from both companies in the future.

So, what's the moral of this story? Have fun experimenting with speakers! Many cost about the same (or less) than a stompbox, so try a new Eminence or WGS to spice up a boring combo amp, or research what some of your favorite players use. Try a Celestion in a Fender, or a JBL with a Marshall... J.D. Simo's '67 Deluxe Reverb sounds incredible with a beat-up Vintage 30 in it, and Duane Allman played his Marshall heads through JBL D120s to much acclaim. My Princeton Reverb took on a whole new attitude when the stock Jensen was replaced with a Celestion G10. Just keep those general rules of thumb regarding power and impedance in mind to prevent a speaker cone from landing on your lap, or even worse, blowing an output transformer in your amp. Good luck and good tone!

(Disclaimer: i have no affiliation or endorsements with any of the manufacturers mentioned in this blog)

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