Supravox 215 EXC Field Coils

Supravox is one of the oldest and most prestigious names in hifi audio, and for decades their full range speaker drivers have been used in high-end home and pro audio applications. The 215 cm size, roughly an 8 inch driver, has been a mainstay for Supravox since the beginning, and I thoroughly enjoyed owning a pair of their classic 215 RTF 64 drivers in the past, a high water mark for me for the 8 inch “wide-band” driver. Here we have one of Supravox’s top end products, the 215 EXC field coil, a superbly refined top quality offering and one of the very few modern field coils in production.

Field coils are odd beasts. Harkening back to the early days of radio when the magnets required to energize a speaker cone were still huge, heavy, and expensive, the field coil, being an electromagnet, got around this problem by using an electric charge to excite the speaker. Most early radios had a field coil speaker powered by a choke in the circuit. Of course, as time went by magnets got smaller and cheap, and before WW2 the field coil was well into obscurity.

Until sometime in the last 20 years or so, when they were suddenly back on the market, but this time being made solely by boutique level makers, and with price tags that make the eyes water. These days brands like Feastrex, Lowther, Voxativ, and of course Supravox all make or have made a high end field coil wide band driver. And of course Oleg Rullit’s field coils in particular are masterfully beautiful works of audio art. Being low inventory, super niche items, field coils don't hit the used market with any frequency. Not quite a white whale but not an every Saturday item either. So most folks have never heard one. That sure makes it irresistible.

One word about the field coil power supply. As I mentioned above, in the old days the choke in the radio circuit was used to supply power to the field coil, but today’s modern versions require a dedicated external power supply. Being high end audio, these run the gamut from a simple car battery to massive custom power modules using archaic mercury vapor rectifier tubes and rivaling a refrigerator in physical size. Simple and basic, to elaborate and way over the top, like a single ended amplifier the power supply is something that really matters for the field coil. In the case of my experience with the 215EXC, I used a modest lab/bench power supply, giving the speakers between 7 and 14 volts. Not the ideal solution from a fidelity standpoint, but within budget.

So how do they sound? Excellent. The Supravox field coils are very smooth and relaxed, open and effortless, and with a good bit of bass energy in an open cabinet. One of the nice things about field coils is that you can tailor the sound profile by varying the voltage applied. In the case of the Supravox 215 EXC, the coils are low voltage and only require between 7 and 14 volts to fully energize. At 7 volts, the sound is softer and more closed in with good image and an easy to listen to profile. Dialed up to 14 volts, the sound becomes more aggressive and forward, more driven, and more strident. At higher voltage, details and spatial cues are more evident. The variations in between bring more or less of these qualities the higher or lower you go in voltage.

In my Telefunken baffles, these drivers have a richness to their sound that is very pleasing while still presenting plenty of detail and separation if it appears in the recording. In direct, back-to-back comparison to the Visaton B200, the Visaton make more bass, and goes higher, but the mid-range is somewhat more “natural” from the Supravox field coils. This matches pretty well to my memory of the 215 RTF 64, which I was also able to directly compare to the Visaton years ago.

Overall, the Supravox 215 EXC are some of the finest sounding 8 inch drivers I have heard to date. I preferred them at 12-13 volts, but these are easy to dial in to your taste. These definitely have the Supravox “house sound” which for me comes across as open, relaxed, and warm. Some will want a tweeter, but I think for my 50 year old ears these can be run full range. If you’ve been curious about field coils, the Supravox are an easy entry into that strange and archaic part of the high end audio world.