Transcript
Tech Three’s a company
Gaining entrée into the elite hi-fi club takes more than just bright ideas. Often, it takes more even than just money. It helps that the two people who conceived Vivid, Philip Guttentag and Bruce Gessner, are both acoustic engineers. But their expertise and their dream of a local speaker making a noise on the world stage might have ended with predictable doors being slammed in their faces if circumstances hadn’t brought them together with one of the speaker Bruce and Deone world’s gurus. Gessner with Philip Through their interest in Guttentag, the driving sound and music, the two force behind Vivid became involved with the Audio in South Africa. former boss of Britain’s B&W Right: Laurence Dickie, loudspeaker company, Robert a speaker “visionary”. Trunz, who now lives near Pretoria. Trunz proved to be the go-between that connected Guttentag, Gessner and the final piece of the puzzle: Laurence Dickie. Outside of the speaker world, Dickie isn’t widely known. Inside it, he is revered as a visionary whose concepts resulted in such groundbreaking designs as the radical B&W Nautilus speaker. He’d been toying with ideas that entailed not only for the speaker enclosure, but also the speaker drive units themselves. Getting those ideas through the reality stage seemed fruitless – until the trio got to meet in 2001. Since the initial model’s introduction three years later, the range has grown to three. Reaction from the specialist media has been overwhelmingly positive.
Beautiful
NOISE
Striking style and high-end performance – a South African breakthrough in sound
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OT just anybody gets to rattle the teacups in the hi-fi nirvana club, where singlemindedness and a wallet only slightly smaller than an overnight bag are minimum criteria for membership. If you’re expecting to be taken seriously by some of the most discerning (many would say snobbish) and idiosyncratic clientele on the planet, you need to be very, very good. So it’s surprising and refreshing that a South African company has steadily been carving a niche for itself in this demanding arena. 54
KwaZulu-based Vivid Audio makes a range of speakers with arresting looks and, according to audio buffs worldwide, phenomenal sonic abilities. The price tags are correspondingly arresting: the company’s top K1 full-range floorstanding model comes singing in at a breathtaking R100 000. Although there may be others that cost plenty more, the simple fact is that 99 per cent of what passes for loudspeakers costs a tiny fraction of that. Can a product from Kloof truly make it against the
Right: In the B1, the central D50 midrange driver deals with frequencies between 900 Hz and 4 kHz, with the range beyond being handled by a D26 tweeter.
POPULAR MECHANICS • AUGUST 2005
It’s so wide At home in plush classical surroundings or starkly modern elegance, the striking Vivid Audio styling combines form and function – striking appearance, plus rigidity and resistance to phase effects caused by traditional box shapes.
established heavyweights in the extreme upper end of the audio world? In a sense, it’s like building a car that not only blows Ferraris into the weeds, but also impresses your partner with your sense of style and drives your fellow board members insane with envy. Not easy. Particularly when, in the case of Vivid, you’re not simply bolting together a kit of parts chosen from the world’s electronics shopping list: the whole thing is actually being built from scratch, to your own design. POPULAR MECHANICS • AUGUST 2005
Looks aside, a deliberate Vivid characteristic is extremely wide mid-band dispersion, gradually narrowing with ascending frequency. The result is natural sound in most listening rooms, and the controlled off-axis response ensures a wide “sweet spot” where the optimum sound imaging can be enjoyed. In fact, the wide-dispersion characteristic means that the recommended speaker position is toed-in so that their axes cross in front of the listening position, which also avoids exciting sidewall reflections. Smallest floor-standing model is the B1, which incorporates four drivers in a 3 1/2 way system. Its single D50 midrange driver does duty between 900 Hz and 4 kHz, with the range beyond being handled by a D26 tweeter. Below 900 Hz the B1 uses two C125 mid-bass drivers, one mounted on the front baffle and one on the rear baffle of the cabinet. These two drivers are internally coupled via a screw tensioning unit for reaction cancelling. Both drivers receive the same signal at
frequencies below 100 Hz; above this point the drive to the rear is progressively attenuated, leaving only the front driver to operate all the way to 900 Hz to keep the distance between drivers at a minimum around the crossover point. The integral stand is made from the same carbon fibre loaded polyester compound as the enclosure. A total of five custom spikes are mounted around the periphery of the base. Within each of the streamlined arms, separate conduits to guide the Van den Hul interconnecting cable away from the two internally mounted crossovers into the base. Precision machined WBT goldplated terminals at the rear of the base allow unobtrusive connection.
Centre stage As Vivids have been designed from the start with home theatre applications in mind, the C1 Fullrange Centre Channel model was a logical move. This has a similar set-up to the B1, though with two C125 mid-bass drivers (patents pending), 55
Tech The doubly curved form of the cabinet walls results in high intrinsic rigidity further enhanced by moulded lateral bracing, ensuring a favourably high cabinet resonance.
Right: D series tweeter voice coils and formers with D50 foil assembly. Right below: The C125 158 mm radially polarised bass/mid driver. Far right: MLSSA plot of a typical B1 loudspeaker’s frequency response (partial).
For every reaction…
WHAT’S WITH THE CURVES, ANYWAY? It’s hard to understand why a wave radiating from a loudspeaker would be reflected by a sharp cabinet edge. There’s no wall, no baffle – just air. The thing is this: in a conventional box speaker, as the sound moves outwards from the tweeter, it forms hemispherical waves, with one edge running along the flat cabinet front until it reaches the edge. It turns out that the sudden change from being bounded on one side to being completely free is almost as big a shock as running into a hard surface. (Designers of stealth aircraft know all about re-radiation. Their aim is to minimise radar reflection to the point where the plane becomes virtually invisible; one of their aids is a smooth surface.) The secondary sound waves set up by the reflections described above mix with and distort the main sound. Using a single, smooth curve instead means there is no
mounted on either side of the central mid and high domes. The two drivers are identically driven to preserve a symmetrical horizontal polar pattern at all frequencies. There’s an optional matched stand with similar design features to that of the B1. For ultimate performance, the K1 floor-stander offers a similar performance to the B1, but with the potential for
Radial magnet technology permits the mounting of drivers with a minimal separation ensuring the widest vertical beam at crossover while also having an intrinsically low stray magnetic field, which allows placement close to video monitors.
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longer a single point at which the sound space changes from half space to full space. In turn, this means that there is no interference and a smooth off-axis response. A flat boxlike surface also emphasises the differences between types of drive units, possibly negatively. A typical cone mid-range driver concentrates the sound into an ever tighter beam as the frequency approaches the point at which it crosses over to the tweeter (2-3 kHz). However a tweeter’s wide dispersion at the lower end of its range means teeth-grinding quantities of high frequencies reaching the listener, especially after reflecting off room surfaces. At the bass end of the spectrum, Vivid chose a vented design to improve low-frequency distortion performance – but this presupposes smooth movement of the air. So, the bass ports are gently flared to avoid turbulence.
increased level and detail through the use of four low frequency drivers in conjunction with mid and high units. Above 900 Hz it’s much like the B1, and below that it uses four C125 midbass drivers – two mounted on the front baffle and two mounted on the rear baffle. These four drivers are internally coupled in pairs via screw tensioning units for reaction cancelling. All drivers receive the same signal at frequencies below 100 Hz; above this point the drive to the rear is progressively attenuated, leaving only the front upper driver to operate all the way to 900 Hz to ensure good vertical dispersion at crossover.
Sculpting a unique shape An inevitable consequence of the flowing lines was the choice of enclosure material: moulded polymer. Vivid selected a synthetic resin filled with a blend of graded mineral particles and mediumlength carbon fibres. The moulds were cast from patterns cut from solid using multi-axis mills driven directly from the
3D models created in the design process. The doubly curved form of the cabinet walls is intrinsically rigid, and moulded lateral bracing enhances this rigidity. These two factors ensure that the cabinet’s resonant modes are sufficiently high in frequency. Direct mechanical excitation of the enclosure is, in any case, avoided by rigorous use of compliant mounts for every driver, and reaction cancelling between the two low-frequency drivers. Result: no net movement of the chassis below 100 Hz. Reaction cancelling is also applied to the design of the low-frequency venting where a pair of ovoid ports, with streamlined profile to minimise air turbulence, are positioned on the front and back of the cabinet. The result is an extremely stable low frequency performance with a rather novel appearance. Interestingly, it’s far stiffer than an equivalent square box.
When a current flows through the coil of a loudspeaker driver, a force acts both upon it and the magnet surrounding it. The recoil velocity is proportionally smaller than that of the much lighter coil and cone and radiates a correspondingly small acoustic signal, that is, until it’s coupled to an enclosure having many times the area of the cone at which point its contribution can become significant. In addition to this simple area issue, if the cabinet suffers from structural resonances then the coloration may become a real problem. Compliant speaker mounts can decouple the driver from the cabinet, but beware resonance problems. Vivid’s solution to this has been to place identical drivers on opposite faces of the enclosure and couple the magnets rigidly together. As long as the drivers both receive an identical drive then the forces in the magnets will cancel completely and no motion will be transmitted to the enclosure. The two drivers are driven with identical signals below 110Hz. Above this frequency a differential force begins to appear, so the driver pair must still be decoupled from the cabinet. Fortunately they don’t need a mount that is as complaint – in this case, a pair of o-rings under each driver flange does the job. A similar reactioncancelling action had to be taken in respect of the speaker cabinet’s vent system. Air rushing in and out of a port results in a small reaction force on the cabinet. Two opposing ports cancel the cabinet reaction completely. PM
Source: Vivid Audio (Pty) Ltd, P O Box 343, Kloof 3640.
[email protected] ●
POPULAR MECHANICS • AUGUST 2005
POPULAR MECHANICS • AUGUST
2005
Specifications Vivid Audio K1 Configuration ................................................................................. 3 ½ way vented cabinet Cabinet material .......................................... Complex loaded carbon fibre-filled polymer Finish ................................................................................................. High gloss automotive Drive units .........................................................................................26 mm metal dome hf 50 mm metal dome mf 158 mm metal coned lf (four, coupled) Sensitivity ....................................................................................................... 89dB/1w at 1m Nominal Impedance (Ω) ....................................................................................................... 6 Frequency range (Hz).....................................................................- 6dB points 35 – 44 000 Frequency response (Hz).......................................... 39 – 41 000 +/- 2dB on reference axis Harmonic distortion (2nd and 3 rd harmonics) .................. < 0,5% over frequency range Crossover frequencies (Hz) ............................................................................ 100, 900, 4000 Power handling (music program) watts rms .................................................................. 600 Loudspeaker dimensions (H, W, D cabinet, D base) mm....................1 300, 280, 450, 488 Net mass (kg) ...................................................................................................................... 56 Vivid Audio B1 Configuration ................................................................................. 3 ½ way vented cabinet Cabinet material .......................................... Complex loaded carbon fibre-filled polymer Finish ................................................................................................. High gloss automotive Drive units .................................................................................26 mm metal dome hf unit 50 mm metal dome mf unit 158 mm metal coned lf unit (two, coupled) Sensitivity ....................................................................................................... 89dB/1w at 1m Nominal Impedance (Ω) ....................................................................................................... 4 Frequency range (Hz).....................................................................- 6dB points 35 – 44 000 Frequency response (Hz).......................................... 39 – 41 000 +/- 2dB on reference axis Harmonic distortion (2nd and 3 rd harmonics) ................. < 0,5 % over frequency range Cross over frequencies (Hz) ........................................................................... 100, 900, 4000 Power handling (music program) watts rms .................................................................. 300 Loudspeaker dimensions (H, W, D cabinet, D base) mm....................1 095, 265, 375, 420 Net mass (kg) ...................................................................................................................... 38 Vivid Audio C1 Configuration ..................................................................................... 3 way vented cabinet Cabinet material .......................................... Complex loaded carbon fibre-filled polymer Finish ................................................................................................. High gloss automotive Drive units .................................................................................26 mm metal dome hf unit 50 mm metal dome mf unit 158 mm metal coned lf unit (two of) Sensitivity ....................................................................................................... 90dB/1w at 1m Nominal Impedance (Ω) ....................................................................................................... 8 Frequency range (Hz).....................................................................- 6dB points 35 – 44 000 Frequency response (Hz).......................................... 39 – 41 000 +/- 2dB on reference axis Harmonic distortion (2nd and 3 rd harmonics) ................. < 0, 5% over frequency range Cross over frequencies (Hz) ........................................................................... 100, 900, 4000 Power handling (music program) watts rms .................................................................. 300 Loudspeaker dimensions (H, W, D) mm ......................................................... 268, 755, 330 Net mass (kg) ...................................................................................................................... 23
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