Before our modern era of digital technology, pioneering musicians and inventors had to figure out how to create complex effects like reverb in an all-analog environment. This caused a lot of difficulty, in particular with reverb, as it is a natural acoustic phenomenon that is hard to capture in a compact and easily portable way! In this blog, I’ll go over the basics of how analog reverb works, give some examples of units that were produced, and discuss why non-digital reverb may be worth exploring.
What’s Reverb, Anyway?
Let’s pretend that you clap your hands once in an empty room. That sound will emanate out in all directions before bouncing off the walls. The reflected sound that returns to your ears will first appear as echo, or delay, (in a particularly hard-surfaced room) before quickly washing out into the sum of many reflections. This ambient noise is called reverb. It’s the sound of the room and the resulting responsiveness of the space.
Obviously, you can’t take a huge empty room with you on tour, and different venues have a lot of variance. That’s why audio engineers had to figure out how to recreate the sound of reverb for portable use!
How Does Analog Reverb Work?
When you play an electric guitar, bass guitar, or other amplified instrument, the acoustic signal is transformed into an electrical signal by the instrument’s pickup. This most commonly happens by manipulating a magnetic field. The steel strings vibrate close to magnets that have been wrapped in a conductive coil, and that disturbance creates a tiny electrical signal. An amplifier takes that signal and makes it many, many factors louder in order to move a speaker and knock the walls down at a concert.
Analog reverb uses this same concept but in reverse. If you take that amplified signal, increase it some more, and send it through metal springs, the resulting sound has reverb. But how? At the end of each spring, there is a small component called a transducer. The incoming electrical signal is strong enough to create a mechanical disturbance, or vibration, effectively transforming the electrical signal back into an acoustic wave. This wave is transferred to and through the springs where another transducer converts the bouncy, wiggly acoustic signal back into an electrical signal. This vibration that has occurred through the length of the spring causes the reverb effect that we all know and love. At the output point, the signal is sent through more amplification stages before driving the speaker.
Why So Much Boosting?
Astute readers will notice that we’ve amplified the instrument signal a lot, and many times. This is because all of that signal transfer through springs and conversion is really, really inefficient. Signal loss is problematic with all types of analog reverb, so we have to hit, or drive, the springs really hard. It’s also vital to pick a recovery circuit after the reverb effect that can boost the signal without adding more unwanted noise. It turns out that the audio that comes out of the springs is pretty low-fidelity compared to what went in, so the recovery stage also has to do some heavy lifting with tone shaping and equalization. In many reverb circuits that use tubes, one tube does the input boosting, and another takes care of the output recovery. Solid state reverbs use transistors, but many more than just one are required on each side of the springs.
Some Milestones on the Road to Reverb:
The first successful models of amplifiers didn’t have onboard reverb. It hadn’t been invented yet! Early tweed Fender amps like the 5e3 Deluxe, for example, were built without any effects. When spring reverb exploded onto the music scene, in particular with the craze for surf and Hawaiian-influenced music, manufacturers like Fender rushed to meet the demand by introducing piggy-back units.
The Fender 6g15 was first produced in 1961 and was intended for use with the current Fender line of amps, the brown and cream-colored models (now referred to as the “brownface” era). This unit, and others like it, act like a giant effect pedal that sits between the input instrument and the amplifier. Our custom Chickadee is a product that we built from scratch and is heavily influenced by the 6g15. This model still remains one of the finest examples of standalone spring reverb ever made.
It didn’t take long for Fender and other competing brands to figure out how to insert the spring reverb circuit into an amplifier. This was a much more attractive concept to the average player – who wouldn’t want everything in an easy-to-carry package? Fender introduced the Vibroverb amp in 1963, their first combo amp that included onboard spring reverb. With few exceptions, reverb was forever destined to stay in amps, delighting players and adding extra dimension to their music.
Tube reverb (and tube amp circuitry), would eventually be challenged by the advent of solid-state technology. More affordable and durable transistors could handle the job of amplification, and spring reverb was no exception. In 1966, Fender pioneered the FR1000, a short-lived piggyback solid-state spring reverb. While it didn’t find much success, the FR1000 paved the way for using transistorized circuits in amplifiers going forward. Most amps today use solid-state technology for their onboard reverb, which even includes circuits that use digital reverb emulation.
On this long arc from invention to ubiquitous implementation of spring reverb, the guitar world had some interesting and quirky detours. Also in 1966, Fender produced a reverb unit using licensed technology from the Tel-Ray Morley company. This product was named the Echo-Reverb and produced the reverb effect by passing audio signal across a spinning metal disc. This disc was coated in electrostatic oil (which is why this and similar units are referred to as “oil cans”) and could delay and modulate the sound in addition to creating ambience.
In 1973, Roland started producing the Space Echo, an incredible magnetic tape delay unit that also boasted onboard reverb. Until then, most tape delays focused on the echo, but Roland combined the magic of tape with a miniature onboard spring reverb unit.
More popular in the recording studio versus on the road, a different but related innovation called plate reverb was booming through the 1960s and 1970s. This technology creates the reverb effect by injecting audio signal on one side of a large metal sheet. Much like with spring reverb, this creates an acoustic disturbance which is converted by a transducer. Plate reverb is still used today but has a distinctly different sound than spring reverb. While springs can sound bright, bouncy, and erratic, plate reverb often sounds dense and lush.
Why Choose Analog Reverb Today?
There’s a bit of magic to hearing audio signal pass through real vibrating springs, but most of the secret sauce comes down to two factors: preamplification and spring specifications. Units like the Fender 6g15 piggyback are great because they use real tubes to boost and recover the signal. Even if the spring reverb effect is disengaged, you can use tube circuits like this to further boost, saturate, and enrich the sound of your guitar or instrument before it hits your amplifier. Transistorized circuits do this too, of course, but the ability to use them as a preamp pales in comparison to tubes. Almost all modern reverb pedals use solid-state technology. Spring specifications matter because there are a million differently-sized reverb tanks (springs) that are produced. Extra-long springs can handle long, ambient delays that are darker and richer than modern pedals.
If you’re into vintage and some of the quirky side-quest units that were mentioned above, there really isn’t a substitute. Those effects are ultra-unique, and while modern pedals that emulate them come close, they don’t quite hit the mark. Of course, most of those examples are like a top-shelf aged whiskey: definitely not for everyone, an acquired taste, and best explored in moderation unless that’s really your thing.
Let’s be honest, though: the biggest perk to using a real analog spring reverb today is the ability to manipulate (and abuse) the springs in real time. If you kick, bump, shake, or rattle the spring reverb, you create a thunderstorm of clattering, banging, echoing, reverb-y goodness. The song Decks Dark by the rock band Radiohead uses the unmistakable sound of spring reverb for rhythm and ambience – check it out! A little noise and controlled chaos can go a long way in making your music stand out.
Go Forth and Sproing!
I hope that this post cleared up some of the mystery of spring reverb. I also hope that it has inspired you to experiment with it and hear some examples for yourself! Let us know if you have any questions or requests for future posts!
