My son picked up a Reslo ribbon mic at the local rubbish dump. It's set up like a studio mic — it's upright and receives signals from both sides. It has a good sound, but very low signal. To get a stronger signal should I just use a preamp or an in‑line impedance booster? It's balanced (3‑pin) and is a very handsome piece of equipment — beautifully made and polished (stainless steel?) Even with the low signal I like the sound better than the SM58 which I normally use. However, the fact that it receives signals from both sides would possibly discount it for live gigs — or would that not matter? Any information would be much appreciated.
Steve Evitt
Technical Editor Hugh Robjohns replies: Wow — lucky man finding such a nice mic at the dump! This kind of mic is often sought after by collectors. As you rightly say, the Reslo is a ribbon microphone which uses a thin and very delicate metal foil, suspended between the poles of a magnet, as both the diaphragm and the electrical generator. The nature of most (but not all) ribbon mics bestows them with bi‑polar (figure‑of‑eight) polar responses, which means equal sensitivity to sounds from front and back (albeit in opposite polarity to each other), with very strong rejections to sounds from the sides, above and below — anywhere on the plane of the diaphragm. The other aspect of bi‑polar mics is that they exhibit a great deal of proximity effect — in other words low frequencies are greatly accentuated as you move the mic close to your sound source. This can be used to good effect, but be careful of using the mic too close, as wind could damage the ribbon irreparably.
The output current from any electrodynamic microphone is generated by the relative movement of the conductor in the magnetic field. Whereas a moving‑coil microphone has many sections of conductor moving in the field (each turn of the coil generates its own little bit of current, which all add together), the ribbon has only the one conductor — the ribbon itself. Consequently, the output current is very low. Usually a transformer is used to try to make the signal a practical proposition, but the output will always be low compared to a moving‑coil or condenser microphone.
Without knowing the details of the specific mic I can not tell you its characteristic impedance, but would suspect it to be around 300Ω. It is clearly balanced and should work well with any half‑decent balanced mic preamp with an input impedance of 1KΩ or so. The Reslo doesn't need powering and it would be safest to ensure phantom power doesn't get anywhere near it.
The other thing to be careful of is not to expose the ribbon to strong air currents. I'm amazed it survived its time on the dump. Don't blow onto the diaphragm (beware those plosives when singing or speaking — a pop shield would be a worthwhile investment) or slam the lid of the box you store it in! Equally, I wouldn't recommend using it for kick drums or close‑miked trumpets under any circumstances. However, if you place it sensibly, there is no reason why you shouldn't use it on stage. The thing to do is place it where any spill from other instruments or foldback arrives from the side, as this is where the mic is least sensitive.