The Xaudia Blog

15-05-2011

Mic of the month – Melodium 42b

Our Microphone of the Month for May is the magnificent Melodium 42B ribbon microphone.

Evolving Melodium 42b – serial no. in the 1700s, 4300s and 6600s (L to R)

The Melodium 42B was conceived as a French alternative to the RCA 44 family of microphones, and is in its own way every bit as good as the more celebrated RCA mics. At 32 cm high and 14 cm wide, and weighing 2.65 Kg, the 42b is a huge microphone with a large ribbon (68 mm long by 4.2 mm wide) and big powerful magnets*, to give a strong output with low noise.

We have been lucky enough to have four of these through the workshop, and have had the opportunity to observe some for the finer details that have evolved during the production of these beauties. Over the years the grill of the 42b has been refined, with the holes becoming larger, and a solid unperforated band appearing across the bottom of the microphone. Later microphones have a three pin connector at the rear, whist early models are hard-wired.

The magnet structure has also changed over time – earlier models have U-shaped magnets above and below, whereas the later microphones have four block magnets, arranged in pairs and connected by metal plates to complete the magnetic circuit.
The photo on the left shows the later style of magnets. The transformer and inductor are in the circular metal can below. Some models have a rectangular can, but the transformer and inductor inside are similar, at least in the ones we studied. The transformer has a ratio of 1:14, giving an output impedance of 50 ohms**

There is also a facility to adjust the ribbon tension, which should be mandatory on all ribbon mics!

Here’s a short summary of the changes with serial number:

1500 – Small grill holes, fixed cable (no connector), U-magnets with North marked, rectangular transformer case
1700 – Small grill holes, fixed cable (no connector), U-magnets, circular transformer case
1900 – Small grill holes, fixed cable (no connector)r, U-magnets, square transformer case
3400 – Small grill holes, connector, U-magnets (unmarked), rectangular transformer case
3700 – Big grill holes, connector, U magnets, rectangular transformer case
4300 – Big grill holes, connector, U magnets, rectangular transformer case
5100 – Big grill holes, fixed cable (no connector), U-magnets, rectangular transformer case
5300 – Big grill holes, connector, U magnets, rectangular transformer case
6100 – Big grill holes, connector, U magnets (North is marked), rectangular transformer case
6600 – Big grill holes, connector, block magnets, circular transformer case
8000 – Big grill holes, connector, block magnets, circular transformer case

The latest serial number that I know of is number 9250, on the Coutant website, which has large grill holes and a connector.

The 42b has a three-position switch on the front which is used to select “Speaker”, “Voix”, and “Musique” modes. In the first two positions an inductor is switched in parallel with the output transformer which causes the lower frequencies to be rolled off.

Above is a frequency plot that I recorded in our anechoic mic testing chamber (well, more of a walk-in cupboard really!). This was recorded at 40 cm distance from the sound source, which is a concentric full range speaker, using a swept sine wave technique.

The bottom end boost due to proximity effect is pronounced, even at this distance, and the effect on the sound is very musical when capturing acoustic instruments. Of course sometimes you don’t want or need the proximity boost, and the switch conveniently corrects for this at speaking and singing distances.

If you are lucky enough to come across an old Melodium 42b but are disappointed with the sound, it may well have an oxidised ribbon and will need cleaning. The strong magnets are prone to attracting little shards of iron, which stick to the magnets and interfere with free motion of the ribbon.

* It is worth noting that the magnets on these microphones can fade with time – a healthy 42b should have a magentic field between the pole pieces of around 4000 Gauss. One of our microphones measured at just 1500 gauss and it was necessary to replace the magnets with suitable modern alternatives. If you have a Melodium with a weak output it may be worth having the field measured and the ribbon checked. Xaudia can of course help with all those things.

** For optimum results with modern equipment a matching transformer is recommended.

Here are some Melodium links on the web:

Mattéo and Axel at Infernale Machine studios in Beziers, France are both Melodium enthusiasts and there are some good photos and some information in French about servicing and cleaning these microphones on their website.

George at Kore Studios is also a fan – here is a rather lovely song that was recorded at Kore using a 42b for vocals: East Wind by Ed Laurie.

The original Melodium brochure is available to download from Professor Stan Coutant’s excellent website.

Updated 9/10/14 with additional serial numbers

Meazzi and Framez ribbon mics revisited

April’s MOTM was a nice old Framez ribbon mic, and its chunky Meazzi sister also made an appearance. Here’s the article… and here are the microphones:

I’ve had the opportunity to compare these in the anechoic box – here’s how they look (click to enlarge).

Frequency plots for Meazzi and Framez mics

The Meazzi has an overall flatter frequency response, but in both cases there is a significant peak around 4KHz, which should add attack to recorded percussion and clarity & presence to vocals. The Framez is slightly more sensitive in the mid range, but falls away somewhat below 150 Hz.

Whilst revisiting these mics, it is worth looking at the Meazzi’s perforated backplate resonator, which contributes to the pickup pattern and frequency response.

(Nb. Both microphones were fitted with 1.8 micrometer ribbons and wired for low impedance.)

23-04-2011

Summer is here, and it is Reslo season.

Another typical day at the Xaudia studio & workshop…

Outside the studio …. flowers, blue sky and cows.

And inside, in the basement workshop…. a Reslo production line!
We see a lot of these little British microphones. The original ribbons are quite thick and have an unusual ‘square wave’ corrugation. Very often these have oxidised and become noisy, and after 50 years they usually benefit from a clean and a fresh ribbon.

14-04-2011

Microphone of the Month – Framez ribbon microphone.

April’s microphone of the month (MOTM) is this glamorous shiny blue ribbon microphone by Framez (not to be confused with Framus!)

This has no model or serial number, but is probably from later 1950s or early 60s. Framez were an Italian brand related to Meazzi – according to one source the name is a contraction of Fratelli Meazzi (trans. Meazzi Brothers), which does sound plausible. Framez / Meazzi also made some cool oddball guitars, and were associated with Wandré Pioli. Fetish guitars have much more information about these guitars.

Back to the microphone! This looks very much like a copy of the RCA 74b ‘junior’ microphone, but us physically somewhat smaller. And it is a pretty good microphone in its own right. The magnets have retained their strength over the years, measuring a healthy 4500 gauss between the pole pieces. It has a hefty transformer with taps for both low and high impedance, making it suitable for both recording and PA use.

This one arrived with a thick flat ribbon – probably a DIY ‘kitchen foil’ repair. With a proper 2.5 micrometer ribbon installed, and the mic rewired for balanced, low impedance operation, the sound is clear with a strong output, just lacking a little of the low end proximity boost that you find with many ribbon microphones. The ‘low’ impedance tap is 1:45 ratio, which gives around a 450 ohm output with the 2.5 micron ribbon.

I’m actually very impressed with this little microphone, and it looks great too!

Update 23/4/11

We managed to get hold of a Meazzi ribbon microphone for comparison. It’s a little less glamorous, and has a similar ribbon dimensions, but a very different motor assembly.

Strange things you find inside mics, part 2

A few months ago I wrote this blog post about the strange things that I had seen inside ribbon microphones. In those cases the ‘strange things’ in question were put in there deliberately by previous owners or techs trying to repair or improve the microphone.

Since then I have come across a couple of microphones which contained even weirder things – insects!

Before modern foams, felted wool was widely used in microphones for shock mounts, wind shields and the like. Unfortunately, moths love this stuff too.

Here’s an old STC4033. You can see the moth eggs on the lower block of green felt.

Worse still, one of the moths had become lodged behind the ribbon:

Moths also seem to like the wool lining and felt mounts on AKG D12s – here you can see the eggs and damage to the lining in the inside corner of the grill:

Anyway, I guess the lesson to be learned is that microphones should be stored in dry, clean places and not in the garage, or at the bottom of the wardrobe.

😀

(thanks to Steve Parry )

13-04-2011

DYNAMICKÉ MIKROFONY

I love Czech!

31-03-2011

MOTM: Shaftesbury Velodyne Supreme

As you may know, I study quite a lot of vintage ribbon microphones. In general these are simple devices, with just a ribbon, motor, magnets and output transformer . The details and quality of the parts may vary, but most have the same mode of operation. But just once in a while something surprising comes along. Like this Shaftesbury Velodyne Supreme microphone, which is a ribbon microphone with a twist.

The output of a ribbon mic will scale in proportion to the length of the ribbon, at least up to a point. The idea behind the Velodyne was to give increased output by using a super-long ribbon. Normally that wouldn’t give you as high an output as it should, because of ‘rippling’, or other incoherent vibrational modes. But by fixing the ribbon in multiple places they claim to avoid this problem. The microphone was sufficiently novel at the time for the inventors to apply for protection.

The full patent application is here.

Well that’s the theory. In practice the microphone has one giant ribbon that goes round corners, and each length of ribbon has a ‘node’ in the middle, so in total it has 8 elements, each at 45 mm x 4 mm. So 360 mm of vibrating ribbon!

What is more, the microphone has no transformer! I guess the designer thought it had enough impedance already and did not need one.

I wonder how well it worked? Sadly we may never know. The ribbon is broken in many places, and is glued down, so it will net be an easy thing to replace. I’m still struggling over whether to try and get this working or not. I suspect it really ought to be left in its historic condition, but I am curious about how it would have sounded.

Postscript: History shows that this design was not a success. Whether this was for sonic or economic reasons, we can only speculate, but Shaftesbury appear to have abandoned the concept. Their later ribbon microphones were a much more conventional affair, like this Shaftesbury RT model – ribbon, magnets and transformer.

22-02-2011

Mic of the Month – Zephyr 30RA high impedance ribbon mic

February’s MOTM is a ribbon microphone made by Zephyr, of Australia. It’s nice to see a microphone that begins with the letter Z!

The mic has a very “retro sci-fi” look, with hammerite paint and a punched metal grill. The name plate reads “High fidelity velocity microphone type 30RA, but despite the misleading model number, the mic is actually a high impedance mode, and the output transformer is marked “50K’.

The magnets are still healthy on this one, kicking out around 2500 Gauss between the pole pieces. The ribbon is 2.5 mm wide and 28 mm long, similar in scale to a Reslo RBL or Grampian microphone.

The back of the ribbon element is covered in lots of felt, to stop air blasts and brighten the mic for vocal use. Removing some of this opens the sound up a bit. This beast was probably intended for use with a home tape recorder, and would have worked very nicely in that application.

The ribbon itself is mounted on a removable plastic saddle, which makes servicing very simple. Which is a good thing, because this one is stretched. This idea is also seen on Reslo and other microphones.

With a new ribbon, and a suitable impedance-matching buffer, the microphone sounds rich and full – well worth the time spent to get it up and running again.

21-02-2011

New workshop part 2: Construction Time Again

After a morning with glue and a staple gun, sticking acoustic foam to the soft walls, our new microphone testing chamber is up and running. Here are a couple of photos….

The chamber is hooked up to pink noise and swept-sine equipment, and can collect a frequency plot in a matter of seconds. I’m still working on validation, testing different speakers and mics for best performance, but the facility is already proving its worth.

14-02-2011

New workshop! (part 1)

It’s been a quiet month so far for blogging, but a busy one at Xaudia.

We’ve spend the last week building a new microphone workshop in the basement below the studio, including an ‘anechoic’ isolation booth for mic testing. Ralph & Jane have been helping out with building and painting.

Here’s the empty room, waiting to realise its potential: