The 5th terminal is also called the grounding or earth terminal and is a little bit of kit with a big job to do.

Ever wonder why you’re not getting quite the level of detail you would expect when trying to chill to your favourite tunes? One cause could be radio frequencies or (RF for short) that can get transmitted through the speakers and cause interference within the amp.

If you are lucky enough to own a set of Fyne speakers from the F500SP to the flagship F1 Series, then you may not have noticed this since you may already have set them up using the recommended “5th terminal”, sometimes called the grounding or earth terminal.

To fully appreciate the importance of this discreet little gem that Dr Paul has spent many years researching and perfecting, you first need to understand more about radio frequencies and speaker voice coils and how they affect our listening experience.

Radio Ga Ga

We now live in a world packed with electronic devices and to paraphrase Freddie Mercury, it’s all gone a bit “Radio Gaga”. We are surrounded by radio frequencies in our day to day lives, one of the most common being mobile phones. As well as radio and television broadcasts, microwaves and of course the Wi-Fi that you’re probably connected to reading these very words all emit signal ranges varying from 100kHz to 300GHz.

RF interference visualisation

RF interference

So, what are Radio Frequencies?

Frequencies or waves are how we define the oscillation rate of the electromagnetic radiation spectrum. Part of the spectrum, from 20kHz to 300GHz, are electromagnetic radio frequencies. What does that really mean? Well, simply put a radio wave is a repeating sequence of peaks and troughs, think of a series of waves in a pond. From the formation of the wave to the end of the wave is called the cycle. The wavelength is the distance it takes to complete one cycle while the radio frequency is the number of times this cycle repeats per second.

Got it, so what is a speaker voice coil?

Ok so now we know a bit more about radio frequencies let’s talk about speaker voice coils. A voice coil is a length of copper wire which is wound around a former and is attached to the throat of the speaker cone, it is secured in place by the spider to ensure it doesn’t move laterally, only in a back and forth motion. The voice coil takes the audio signal sent by the amp and generates energy by reacting to the electro-magnetic field of the speaker motor. It Is this motion that pushes and pulls the speaker cone which moves the air to create the sound waves that we all know and love as music.

copper speaker voice coil

Speaker voice coil on the cone

speaker voice coil cut through

F502SP cut through of driver

So what does this have to do with interference?

So, this tiny little bit of copper which is responsible for so much of the good stuff we listen to can unfortunately pick up RF interference. It acts like an antenna picking up the interference, feeding it back to the amplifier, via the speaker cable where it gets into the amplifier circuitry. Earthing the speaker motor system and chassis effectively provides a degree of screening to these radio frequencies.


Although amplifiers have more or less zero output impedance, it only applies to audio frequencies and not Radio Frequencies. This can cause low levels of noise and distortion with the amplifier, especially if it gets into the negative feedback loop and interferes with the audio signal.

Depending on the design of your amplifier, some are more sensitive to this than others with location playing a factor, but ultimately it can mask those fine details we all want to hear from that favourite well mastered record.

Great! So how does the 5th terminal help?

To understand this completely we had to pick Dr Paul’s enormous brain…. Let’s think back to a night of ferocious thunderstorms we have all experienced. We know that lightning, or electricity, wants to find the shortest and easiest path to ground, sometimes to the determent of your TV aerial! Now, we are not for one moment suggesting you go storm chasing clutching an F500SP and a speaker cable! But by the same principle this is what our 5th Terminal, sometimes referred to as Grounding Terminal or Earth Terminal, is doing. It acts like a screen creating a path of least resistance for the RF interference to channel its way from the surrounding basket to ground through the amplifier. Rather like a ring road in town helps to free up the flow of traffic, this nifty little connection will keep your sound transparent and detailed.

5th terminal green cable 1

Sweet, how do I set up my 5th Terminal?

First of all, check your speaker has a 5th terminal on the rear termination or connection panel. Then, as recommended by our very own lab boffins, using preferably a quality screened speaker cable, connect your 5th terminal to the chassis ground on the back of your amplifier (sometimes labelled GND or earth). If your amp doesn’t have this (it is often used for phono stages), don’t worry, you can simply loosen one of the chassis screws on the rear of your amplifier and connect your earthing cable with a small spade connector. Don’t forget to tighten the bolt back up again.

And there it is. Physics lesson over! Now seems as good a time as any to drop the needle on a bit of AC/DC!