What is an FRFR Speaker Cabinet and why would you want one?

The HeadRush FRFR 112 Mark II has a 2500 watt (peak) Class D amplifier, 1 × 12 inch full range speaker and a 1 inch high frequency compression driver

When a regular reader asked me a specific question about FRFRs it generated a podcast script but after preparing it, I realized that the episode answers the question but leaves out the what and why of FRFRs. So here we go.

FRFR is an acronym for Full Range Flat Response. What this means is commonly a frequency range of 20 Hz to 20,000 Hz where the frequency response curve is a flat line, meaning no peaks or valleys in any particular frequency ranges. It’s what serious Hi Fi afficiandos have always wanted. A speaker that does not add any colour or flavour to the sound that enters the speaker. Doing this is very hard work involving cabinet and baffle design as well as speakers built for wide and flat frequency response. We can pay a lot of money for a guitar or bass speaker system but none of them are FRFR systems in that definition. HiFi speakers typically used dedicated drivers (speakers) to achieve their response.

No system is perfectly flat. However by using bass drivers, midrange drivers and tweeters, Hi Fi speakers can achieve this goal. The reason that they must do so, is that they are not designed in advance for what they might receive. A well recorded and well produced recording really taxes the speaker system to deliver and it matters because it is the predominant thing that you hear. There are myriad Hi Fi speaker system designs, and they can get really expensive and in the end you do tend to get what you pay for. The physics of acoustic representation are resolute and while HiFi systems originated what we call computational audio, albeit in a very analog way, there is still a difference in the sound of an engineered speaker system that uses drivers of all the same size compared to those that use a variety of drivers. However, we are talking about speakers for guitar and bass music not what might be covered in a High Fidelity publication.

Guitars and basses produce their core sounds in a very limited frequency range. If we allow for second and third and even fourth harmonics, they still do not require the response capability of a great vocalist or string section.

So for us FRFR systems fill a very specific niche.

In what we would call an all analog system, there is no computational audio of any kind, whether analog or digital being used. We have a fairly simple preamplifier and amplifier section, often designed to do a small selection of things really well and to be ok at others. That is why there are so many amps and speaker systems that sound and respond differently. I can get a really nice clean tone out of a Mesa Boogie Triple Rectifier but that was not one of Randall Smith’s primary design goals for the system. When we got to the first black face Fender Twin Reverbs, the design goal was immense volume but without distortion. They deliver on that goal.

However, when we enter the world of digital amplification be that an amp system like the BOSS Katana, a modeller like a TONEX Pedal or a profiler like a Neural Quad Cortex, one of the first things that happens to the analog signal from our instrument is that it is converted to a digital signal through an analog to digital converter. There is a difference between good A/D converters and great ones, but for the frequency range our instruments produce, it’s pretty hard for us to hear a difference. As the signal moves through our analog devices, the sequence of ones and zeros that represent the original analog signal are manipulated by the design until the final stage where a digital to analog converter prepares the signal to be heard through an analog speaker that moves air.

Whether you like that sound or not is up to you and has nothing to do with this article.

The speaker system that receives this signal has to be able to handle a much wider frequency range and add no colouration to the highly processed signal that it receives. This is why plugging any of the digital devices directly into a regular instrument cabinet doesn’t sound right. If a maker says that their regular amp cabinet is suitable for digital converted playback, they are playing a game of jiggery pokery where you are the victim. It just doesn’t work.

While tools like the smaller Katanas use open back designs, the majority of true FRFRs are closed back devices. There are a couple of reasons for this.

In a BOSS Katana combo, there is a digital preamp and power amp. To keep costs down, BOSS uses a very decent full range speaker that sounds pretty darn good but gets colouration from its placement.

In a pure FRFR system, the power amp is in the FRFR system itself, There is no power amp in the Helix, the TONEX, the Kemper or the Quad Cortex, although you can get a version of the Kemper with a built in power amp that then needs a particular speaker system that is neither a traditional cabinet nor an FRFR. In that case the speaker requirement is passive and more like the speaker section of a Katana.

The FRFR takes the converted output signal from your device which is very low output (think preamp) and then runs that through its own power amplifier, typically a Class D design that uses a lot of power to drive the speakers in the cabinet where they are housed. Thus one of the things that we think about in an FRFR is the power output of the amplifier. We call this an active speaker system, and while watts are always watts, a Class D amplifier needs a lot more wattage to provide volume equivalence to what we get from a Class A or Class AB amplifier and its typically more efficient speaker system. Speaker efficiency is the measure of decibels produced at one watt input. FRFR systems are very inefficient. I am not an acoustic engineer but there is a school of thought that less speaker efficiency that requires more power produces better sound. I cannot provide evidentiary support for this, but in sound rooms, it sounds that way to me.

So when we consider an FRFR system, it’s important that we audition for needed volume, not for marketed wattage.

We must also remember that most FRFR systems use a single speaker to produce all the sound. This is in direct contradiction to a true HiFi system, where a speaker could have a 12 inch woofer, one or more 5 or 6 inch midrange speakers and a very small such as 1 inch tweeter. The smaller the speaker cone, the better it does high frequencies. This is why some people prefer bit speakers in bass cabinets, because they deliver more low end and want smaller speakers in cabinets designed for higher frequency instruments. Our traditional amplifiers are the same in this regard as FRFRs. They are not HiFi in the high fidelity sense. However to reproduce the core tones and the harmonics of a guitar or bass, they don’t need to be.

We also know that our digital devices are representing a complete amplifier system modelling the amplifier, the speaker system and the microphone(s) used to capture the sound. Thus the FRFR should never provide any colouration to the signal. Sadly, there are FRFR makers who put addtional volume pots (think Master volume and not that big a deal) as well as tone pots (a very big and uniformly bad idea) in their FRFR systems. The mcmarketing BS says these pots allow the user to quickly tune the sound to the environment. This is true at a macroscopic level but more akin to using a 12 pound sledgehammer for a picture hanger than useful. The best FRFR has NO tone stack because as soon as you run a signal through any tone stack, something is getting stripped off. Remember that Edward Van Halen ordered guitars without any tone stack so as not to take anything away and controlled tone in only one place, on the amp, as close to the speaker as possible and with only one tone stack in the chain. Every time we add another tone stack, we lose something. You may actually find that you do not hear any difference and thus could very reasonably care not at all. Freedom of choice. Human hearing is incredibly inconsistent and loses frequency response and volume acuity over time. This is particularly true for those of us who played in front of massively loud amplifiers or had the headphone volume so loud we suffered tinnitus afterwards. Hearing damage is permanent and will get worse over time. It doesn’t get better.

Next we must look at the space and weight required by an FRFR system. I have bought a number of different ones. Remember that the tiny speakers in a Spark Mini are basically FRFR speakers, albeit in a dedicated use scenario. They rely on computational audio. So do the biggest FRFR cabinets. A bigger speaker system may sound like it delivers more bass, and it may do so, because the larger speaker delivers more subharmonics that you feel more than you hear. Again, your choice. I can say that my FRFR systems with 12 inch speakers take up more room and weigh quite a bit more than my FRFR systems with 8 inch speakers. Until recently small independent FRFR systems did not exist. Headrush now makes one called the Headrush GO rated at 30 watts. It is indeed small and portable and suited to a modeller, being designed as a small option for Headrush’s own modellers. I have yet to see or try one but 30 watts of Class D power is not going get loud enough for playing with a band and will get drowned out quickly in a jam session. However for low volume, good sounding bedroom work, it would likely be ideal.

Newer FRFR systems are starting to add High Frequency Compression drivers, sort of like tweeters, to improve high end response and retain upper harmonics. The example used in the photo has a frequency response of 53 Hz to 20000 Hz which is fine for six string guitar, but is going to let down the really low frequency tones from a five string bass, or seven or eight string guitar. It’s not even appropriate for the low E on a four string bass which is about 40 Hz. Comparatively the low E on a guitar is about 82 Hz. The low F# on my 8 string is about 43 Hz so this FRFR won’t do anything for that. This is why matching the FRFR to your use cases is critical. Now if you downtune your six string to low C, you need about 65 Hz so this FRFR would work for you. The top end of 20000 Hz is just higher than D# in the 10th octave and beyond the reach of human hearing. Most humans in their youth can hear to about 15000Hz but this diminishes with age and of course hearing damage. My point is that the high frequencies are less important to guitar and bass players. However it is important to watch the +- dB ratings. 53 Hz to 20000 Hz in this example has a caveat of -10 dB. That is a massive falloff. So not flat response at all. Check the specs and see that they suit your requirements. A variance rating of +-3dB is the most acceptable and yes the loss or gain is still perceptible.

Modellers and profilers are not meant to be used with regular guitar or bass amps. If you are planning on adding a device like this to your gear closet and you do not want to listen solely with headphones, plan and budget for the FRFR system that sounds right to you. Most guitar and bass amps are monophonic so you only need one, but if your device has stereo effects and thus stereo outs, plan and budget for two FRFR units, the same as you would for a stereo amplifier setup.

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