speaker tone center

How understanding why speakers distort can make all the difference in crafting your tone.

Let’s jump right in and continue with Part II of our discussion that began with “Your Signature Distortion” (September 2009). Part I covered the DNA of a speaker and how the materials used factor into your tone. This month we’re diving in deeper to breakdown how a speaker distorts. We’ll also answer the question, “Is the speaker producing what the amp can deliver?”

There are a number of ways to achieve the distorted tone you’re looking for. If you have a tube amplifier, you can get distortion from clipping your preamp and power amp tubes, not to mention the fact that you can clip your input stage, thus adding a bit of gain and compression right from the input of your amplifier. Of course, you also have a plethora of distortion pedals on the market to give you an infinite variety of distortion. But the funny thing is that all of these distortion makers fall to the mercy of the speakers. Why? Because it’s the way the speakers interpret this signal that will determine your ultimate tone.

How does a speaker distort?
When a speaker distorts, it produces two types of frequencies. The first type is harmonic distortion: this is heard as additional tones which are multiples of the original note played. For example, if the original sound produces 100Hz, you would also get 200Hz, 400Hz and so on, even though these tones are not part of the original sound. The second type is non-harmonic distortion, also known as odd harmonic distortion, and often referred to as a buzz or a rattle in the sound. For example, if the original sound produces 100Hz, the odd harmonic distortion would produce frequencies of 300Hz, 500 Hz, and 700Hz, etc.

When setting your tone, there are a series of specs you need to consider, starting with your guitar and amplifier. The signal from a guitar pickup is mostly all midrange and is not rich in harmonics, with practically nothing coming through above 4000Hz. The sixth string “E” tuned to pitch comes through at about 80Hz, two full octaves above the 20Hz low frequency our ears can pick-up. The standard 4-string bass has a range one octave below the guitar, with the low E at about 40Hz.

The way typical guitar amplifier circuits, such as Marshalls and Fenders, are designed also affects how the speakers will respond. The most obvious difference is that the Marshall circuits let more signal pass through, and the tone controls offer less frequency range. The higher signal means that the preamp tube stage can overdrive the output tube stage more. Additionally, the Marshall circuits have a slight dip in the midrange section, almost an octave higher than Fender amps, metering in around 700Hz. A Fender’s midrange dip is around 400Hz, while the bass response on both amplifiers meter in around 10Hz. Fender’s tone controls allow for a higher midrange frequency to pass with the treble response, meaning more dynamic range for that sparkling, tight sound they’re famous for.

To save time, I’ll spec out the three most popular speakers associated with Fenders and Marshalls, starting with a 25-watt, 12" speaker with a sensitivity rating of 98dB, 1.75" copper voice coil, ceramic magnet and a resonance frequency of 75Hz. Another popular choice is a 30-watt, 12" speaker with a sensitivity rating of 100dB, 1.75" copper voice coil, ceramic magnet and a resonance frequency of 85Hz. The speakers in Fenders are designed to stay clean, so they spec out at 100 watts with a sensitivity rating of 99dB, a voice coil inductance of 1 kHz, ceramic magnet and a resonance frequency of 104Hz.

How does this translate to your guitar tone?
It’s these specs that are directly responsible for your tone, and it’s here where the “disconnect” usually happens for most musicians. We’re not trained to translate these features into the sounds we hear, but it’s this knowledge that can serve as a guideline for you to build your own “tone formula.” Here is an example of a classic one: 50-watt tube Marshall running through two 25-watt speakers (100 watts with four 25-watt speakers will produce similar results). The Marshall circuit allows more signal to pass through, meaning that the guitar input section, the preamp and power section are going to distort. The lower wattage speakers with the smaller magnet and voice coil are going to break up faster at a lower volume. The voice coil will clip and compress, giving you that “sizzle” in the upper frequency range.

This is the classic Marshall tone, but here’s the rub: the lower-wattage speaker distorts so fast that the speaker will not be able to produce the lower frequencies (bass response) that the amp can put out, thus giving you the illusion that the amp has no bottom end. By adding a 30-watt speaker, you can increase the bass response but cut the level of distortion. Now, if you went to the other end of the spectrum and had a Fender amp that was too clean and brittle sounding, you could add a lower wattage speaker with a smaller magnet and voice coil and achieve some nice, mild distorted tones. Changing the magnet to alnico would also add a bump to the midrange section.

Next up in Part III: the “secret weapon” in your tone formula. Stay tuned!

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