REVEL F-208 SPEAKERS
So accurate, so musical and so natural-sounding that you’ll be captivated!
Revel is a dedicated high-end brand founded by Harman International in 1996, and the F-208s were designed by Kevin Voeks, who’s been Director of Engineering at Revel since that time. Voeks was previously the head designer at Snell, having taken over from founder Peter Snell after his tragic death from heart attack, aged just 38, in 1984. Prior to working at Snell, Voeks worked for famous Canadian manufacturer Mirage. As a point of interest, Revel was only the second company actually started by Harman (itself now owned by Samsung), because apart from the harman/kardon brand, all the other brands owned by Harman are the result of acquisitions and mergers.
Some measure of the popularity of Revel’s F-208 floor-standing loudspeakers can be gauged by the fact that this model has been a best-seller in Revel’s line-up ever since it was first introduced in 2014. It’s part of Revel’s Performa3 Series, which, being positioned between Revel’s PerformaBe Series and its Concerta2 Series, puts it exactly in the middle of Revel’s five different series (not counting its architectural speakers).
The curvy cabinets in the Performa3 Series are similar to those used for the company’s flagship Ultima2 Series, being formed with contiguous wood layers and finished in highgloss piano black or genuine American walnut using a process Revel says: ‘ is developed and overseen by Italian luxury cabinet-makers and exceeds automotive finish quality.’ (The last words of this comment are no doubt a dig against speaker manufacturers who boast of using ‘high-tech automotive paints’ on their cabinets.)
The Revel F-208s are certainly impressive, as they stand more than one metre tall (1.182 metres, to be precise) and sport no fewer than four drivers on the front baffle— two 200mm-diameter aluminium-coned bass drivers, a 133mm-diameter aluminiumconed midrange driver and a single 25mm aluminium-domed tweeter.
This means, of course, that the Revel F-208 is a true three-way design, which is my favourite implementation because it means that the all-important midrange frequencies are being reproduced by a single driver that’s dedicated to the task, so you not only get the purest tonality but also pointsource sonic delivery.
The bass and midrange drivers have resonance-free cast aluminium chassis and the voice-coils and magnets use a geometry that results in a stable flux field even at high volume levels, which has the effect of reducing distortion. The aluminium cones have ribbing that Voeks says results in more piston-like behaviour which ‘ eliminates a major source of resonances that are clearly audible in most other loudspeakers.’ The surrounds of the bass drivers and midrange driver are made from Santoprene, which is a thermoplastic vulcanizate made from rubber particles encapsulated in polypropylene. Santoprene combines the longevity of rubber with the flexibility of foam without any of the drawbacks of either material and as a result is one of the very best materials available for use in loudspeaker surrounds.
Rather unusually for a high-end loudspeaker, the Revel F-208 uses high-order crossover slopes either side of both crossover frequencies (270Hz and 2.2kHz). Although it’s not stated in the specifications, Voeks estimates the order as approximating that of a 4th-order (24dB/octave) Linkwitz-Riley characteristic. Voeks says that it’s essential to use higher-order crossover slopes in a loudspeaker if you want low distortion characteristics, minimal compression and high dynamic range. This is because if you use low-order crossover slopes the drivers are being fed audio signals that are outside the frequency range they’re designed to handle, so most of the audio signal voltage ends up simply heating up the voice-coils. ‘ The heat makes the voice-coil impedance go up, and as a result of that the filter network is mis-terminated because it’s not seeing the termination impedance it expects to see, then the network doesn’t work
right anymore and you get peaks and dips in the response,’ says Voeks. Also, when a voice-coil gets hot, it introduces dynamic compression, which squashes dynamic range.
The 25mm aluminium-domed tweeter in the Revel F-208 has a integrated acoustic lens waveguide that Voeks says not only ensures that its dispersion characteristics match that of the midrange transducer in the crossover region, but also actually increases the tweeter’s dispersion at higher frequencies. ‘ This gives the loudspeaker very smooth sound far off-axis,’ says Voeks, ‘ providing consistent sound over an exceptionally wide listening area, which is an important contributor to overall sound quality.’
I loved that the tweeters on the F-208 are at seated ear-height, which is ideal acoustically. And of course you don’t have to use any ungainly (and often very costly!) stands to accomplish this—one of the many advantages of a good floor-standing design. I also loved that the tweeter dome is aluminium, because if you’re going to have any chance of making your speakers sound cohesive right across the frequency range, a very good starting point is to make sure that all the driver diaphragms are made of identical material. Designers who try to marry paper-coned bass-drivers with a metal-coned midrange and a fabric dome tweeter are behind the eight-ball before they even start!
A bass-reflex design, the Revel F-208’s port is on the front baffle, which simplifies room positioning, and the circular port is flared at both ends to minimise port-generated noise. You can ‘tune’ the speakers by fitting the ports with soft foam ‘plugs’. Revel says of these: ‘ If your loudspeakers are located less than about 611mm from walls or other large objects, inserting the port plugs into the loudspeaker’s port openings can reduce the overly-aggressive bass output that can be created by the speaker’s proximity to large surfaces that reflect bass energy. In the F-208 you can experiment with the port plugs in conjunction with the loudspeaker’s Low-Frequency Compensation adjustment to finetune the low-frequency performance even further.’
So what is this Low Frequency Compensation adjustment? It’s a feature of the Revel F-208 that I have not yet got around to mentioning, so now seems as a good a time as any to do so. But before I do, however, we’ll first need to take a quick look at some basic physics, which is that the low-frequency output of any loudspeaker will be greater when it is located close to one or more boundaries (walls, floor, ceiling etc) than it is when it’s located away from such a boundary. This is because the boundary essentially acts as a reflector to concentrate the bass energy. Think about a light bulb. If you just put a single bulb in the middle of the room, its light will shine in all directions, lighting up all parts of the room equally.
If, however, you put a reflector behind the bulb, all the light that would normally have been sent behind the bulb will be reflected forwards. The result will be that the room in front of the reflector will be brighter than before, while the area of the room obscured by the reflector will be darker. Yet the bulb itself is producing exactly the same amount of light as previously.
Exactly the same effect occurs with the low frequencies produced by a speaker. If you put a speaker in the middle of a room, the low-frequencies will spread out omnidirectionally from the cabinet, so that the sound will be almost equally as loud behind the speaker as it is at the front of the speaker. If you move the speaker closer to a boundary, that boundary will reflect the sound forward, increasing the level compared to if the speaker had been in the centre of the room. This effect only occurs at low frequencies, because high frequencies are more directional so, for example, very little of the sound from a tweeter goes behind the cabinet: some does, but most of it goes forwards.
All speaker designers know all about this of course, but none of them know where you will place your speakers, so almost all of them design their speakers to deliver the maximum bass output the drivers are capable of delivering and most of them do their measurements with their speakers elevated from the floor and well clear of any boundaries… even, sometimes, in large anechoic chambers, where there are no boundary effects at all.
This means that when you put these speakers in your room, you will get more bass than the designer’s measurements would indicate, because you are putting the speakers on the floor. And if you move the speakers closer to a room boundary such as a wall, you’ll get even more bass. And if you move the speaker close to a side wall as well, yet more bass again!
The tweeter’s acoustic lens waveguide ensures its dispersion characteristics match that of the midrange