This unusual‑looking microphone is designed specifically for Decca Tree arrays.
Braingasm are a specialist microphone repairer based in Rome, Italy. In addition to servicing, restoration and modification of vintage capacitor microphones (including re‑skinning capsules), the company’s lab also undertakes repairs of a wide range of outboard studio equipment, and even offers an audio electronics design service.
These days it seems quite a lot of microphone repair companies branch out into manufacturing their own microphone designs, and Braingasm are no exception, offering a small but very interesting range of studio capacitor microphones. The current portfolio includes the MP1 small‑diaphragm cardioid mic (sold in stereo pairs), along with three large‑diaphragm models: the Ferro (fixed cardioid) and Multideluxe (multi‑pattern) mics both have FET‑based impedance converters, while the Magnitude is a multi‑pattern valve microphone.
These microphones employ a range of different technologies including transformer or transformerless outputs, valve or FET impedance converters, fixed or variable polar patterns, large or small diaphragms — and so offer not only different features but also different tonalities, making each one interesting and characterful in its own unique way. Yet they are all comfortingly familiar to anyone conversant with the typical fare of standard studio microphones.
However, the subject of this review has a far less familiar format — indeed, it’s unique as far as I know! The Ocula is described as a Diffuse Field Recording System, but if that means nothing, perhaps if I say it’s available in both dual‑ and triple‑matched sets, the latter might give a better clue as to its design.
For these are compact, omnidirectional electret microphones with the capsule housed within a custom‑made Acoustic Pressure Equalising sphere (see the ‘APE Concept’ box). This configuration was first introduced in the revered Neumann M50 microphone, which has become virtually synonymous with the Decca Tree stereo technique employed widely in classical orchestral and film soundtrack recordings.
Although Neumann ceased production of the M50 in 1971, it was replaced by the TLM50 in 1990 (now discontinued) and then the M150 Tube model from 2001. The APE concept is not unique to Neumann, though, and several other manufacturers offer APE spheres as accessories for their own small‑diaphragm omnidirectional microphones. Nevertheless, the Braingasm Ocula is unique, as far as I know, in being a compact omni microphone with a permanently attached APE.
Ball Games
Pub quiz afficionados will no doubt be aware that an American pool ball is 57mm in diameter, while a British snooker ball is slightly smaller at 52.5mm. I mention this only to give a familiar reference: the shiny black Ocula microphone is a little smaller than both, having a diameter of 40mm — the same diameter as the Neumann M50 design.
Each Ocula mic weighs around 56g and has an integral 3/8‑inch threaded insert at the bottom for attaching to a mic stand. The model name and serial number are engraved onto the top of the sphere, while the audio output is carried on a fixed, 5m long (3.4mm diameter) Sommer cable exiting from the rear of the sphere. I found this cable prone to tangling, but a Velcro tie is attached to help maintain the coils in some semblance of order when stored. A genuine Neutrik XLR plug is fitted to the cable, but inside is a tiny circuit board carrying four SMD transistors and a handful of resistors and capacitors to convert between the unbalanced capsule signal and the electronically balanced XLR output. Standard 48V phantom power is required, and this is converted by the circuit board to the 3V bias required by the capsule.
Inside the XLR barrel is a circuit board, which converts 48V phantom power into the 3V required to bias the electret capsule, and also balances the output signal.
The capsule is mounted in a rubber grommet, with the grille slightly proud of the ball surface (presumably because the diaphragm is recessed within the electret’s metal housing). Braingasm have used a high‑quality 10mm omnidirectional electret capsule manufactured in Japan by Primo, the EM‑1272‑Z1. Specs‑wise, Braingasm’s published specs align exactly with Primo’s, stating self‑noise to be a very respectable 14dBA, with a high sensitivity of 39mV/Pa, and a maximum SPL of around 119dB. That self‑noise figure is comparable to many small‑diaphragm DC‑biased capacitor microphones, and is truly excellent for a 10mm electret.
Rather than state the complete microphone’s frequency response or provide a response chart, the specs only give the ‘amplifier response’ (10Hz to 35kHz), which isn’t very helpful... but a datasheet on the Primo website shows the full frequency response chart of the raw capsule, which is essentially flat from 60Hz up to 2kHz, above which the response rises gently, reaching +4dB at 10kHz before tailing off to ‑6dB at 20kHz. I suspect the absence of data below 60Hz relates only to the size of the company’s measuring facility — the Ocula delivered a fine and well‑extended LF response during my evaluations.
However, that raw capsule response will be substantially modified by the presence of the APE sphere, resulting in a boosted high‑end response due to the physics of acoustic pressure build‑up. So, I estimate the Ocula’s actual frequency response rises to a peak of around +9dB at 10kHz, before falling back to about +3dB at 20kHz. Hopefully, Braingasm will publish a genuine measured frequency response chart of the complete Ocula mic before too long.
As I mentioned earlier, the Ocula microphone is sold in stereo‑ or triple‑matched pairs, with the matching said to be within ±0.5dB across the whole usable bandwidth. I was supplied with a stereo matched pair for this review, which shipped in a cardboard box, although each microphone is protected in its own velvet bag, with the cable coil secured by a Velcro strip. Also included with the set are a pair of high‑quality and remarkably compact orbital (ball) mounts, made by a company called Artcise. When attached to these ball mounts each Ocula mic can be angled exactly as desired very quickly and easily, and then locked securely in place, and since the Artcise mounts weigh only 52g each, the total weight of a stereo Ocula array is still only around 215g, and a Decca Tree array about 325 grams. Compared to most Decca Tree mic solutions that’s amazingly lightweight, and would therefore allow a much more slender (and thus less visible) support structure than usual, which is a very appealing feature.
In Use
The electret capsule has evolved to the point of truly professional quality over recent decades, with many manufacturers embracing their benefits, including DPA, Earthworks, AKG, Line Audio and others. Indeed, the Line Audio OM1 omnidirectional microphone has become very popular in the semi‑professional classical recording genre in recent years. I’ve used them myself on occasion with good results, so they seem a valid comparator for the Braingasm Ocula, albeit considerably less expensive.
I found the Ocula mics to be very easy to rig and configure on their versatile Artcise mounts, and their sound quality is impressive — crisp, clear and detailed, with a wide bandwidth extending well to the lowest frequencies. The ‘enhanced’ directionality courtesy of the spherical body is subtle — akin to a hypo‑cardioid rather than a full cardioid — but it definitely makes a worthwhile difference to the stereo imaging when the mics are angled outwards in a spaced array configuration.
In a direct comparison with the OM1, the Braingasm Ocula definitely has a lower noise floor, and the increased HF sensitivity, airy presence, and subtle directionality make them far more versatile in distant‑miking applications, in my view, while remaining very discreet with minimal impact on sightlines.
Although clearly not intended for use in close‑miking applications, the Ocula can be employed in those roles too, of course, bearing in mind that the fixed HF lift can be a little intrusive at times, depending on the source and exact positioning. That said, the HF boost is very smooth and natural, and it responds nicely to taming EQ, if necessary. In many cases, though, I found that its brightness added welcome detail and attack in a natural manner, especially to percussive instruments, helping them to really cut through well in a mix. The slight HF directivity usefully allows the mic’s focus to be directed to specific areas of an instrument in a beneficial way, too — not as obviously as aiming a cardioid mic, but without the proximity effect and phasiness associated with most pressure‑gradient designs.
The Braingasm Ocula is a well‑designed and well‑engineered product filling a particular niche in the microphone market very nicely indeed...
The recommended price of the Ocula feels a little on the high side for me, at over twice the cost of the OM1, making it a big stretch for semi‑pros. That said, the Braingasm Ocula is a well‑designed and well‑engineered product filling a particular niche in the microphone market very nicely indeed, and that alone guarantees its popularity. Its technical performance is also very good, outperforming the Line Audio OM1 in my view and competing remarkably well with established small‑diaphragm capacitor mics.
For both of those reasons I’m sure the Braingasm Ocula will become a popular choice for anyone seeking omnidirectional microphones optimised for use in the diffuse field, with minimal size and weight. And for anyone contemplating building a Decca Tree array, the Ocula is a total no‑brainer as it is perfectly optimised for that role and is capable of very good quality results.
The APE Concept
The Acoustic Pressure Equaliser (APE) is a concept developed in the very late 1940s by the NWDR (Nordwestdeutscher Rundfunk) laboratory — the R&D department of the Northwest German broadcast organisation. The NWDR team was led by Herbert Großkopf, carrying out research into how differently shaped microphone capsule housings affected the overall frequency response and directivity.
Großkopf, by the way, is probably better known for patenting the continuously variable polar‑pattern control, the rights to which Neumann acquired and launched on the studio world in 1949 as the M49 multi‑pattern studio microphone. The APE concept was first introduced in a product just two years later, in 1951, when Neumann brought out the M50 omnidirectional microphone.
The M50 actually looks very similar to the M49, as it shares the same outer casing and has similar electronics. Inside, though, the capsule diaphragm is just 12mm in diameter and is embedded flush at the surface of a 40mm Perspex ball.
In terms of the sphere’s acoustic physics, as on‑axis soundwaves reach the diaphragm, the presence of the sphere’s surface leads to an increase in air pressure for wavelengths comparable to, or smaller than, the diameter of the sphere. In the case of a 40mm sphere, that translates into a graceful HF boost above 2.5kHz, rising to about +5dB, and this is very handy as it almost perfectly counteracts the natural loss of HF energy as sound travels through the air into the diffuse field. And that was the aim, of course — to provide a flat overall response for a microphone placed in the diffuse sound field, as it would be for orchestral recording, for example.
Additionally, though, the sphere also causes a high‑frequency shadowing effect for sounds arriving off axis, and this correspondingly reduces the microphone’s sensitivity to off‑axis high‑frequency signals. In other words, it makes the omnidirectional microphone behave more like a directional microphone at high frequencies — not quite as much as a true cardioid, but more than a hypocardioid.
So, for orchestral recording, where the microphone will be working at a distance in the diffuse field, an omnidirectional capsule embedded within a sphere combines the low‑frequency extension of a standard omni with a natural high‑frequency boost compensating for inherent air losses to maintain detail and brilliance. And, when making stereo recordings, the HF directivity allows the microphones to be pointed outwards to increase the inter‑channel level differences between channels, enhancing the stereo imaging in a similar way to traditional pressure‑gradient mics — and all without sacrificing the low‑end performance of pressure‑operated mics. Hurrah! Jägermeisters all round!
Going APE
The Neumann M50 became an extremely popular mainstay of classical recording from 1951, particularly when employed in the Decca Tree array. Neumann ceased production of the M50 in 1971, partly because of the complexity of its manufacture and the difficulty in maintaining consistent results. However, they later revived the same ideas using newer technology, firstly in the TLM50 (released in 1990) and currently in the M150 Tube microphone. Meanwhile, a number of other manufacturers such as Flea and Wunder have been building homage microphones based around the classic M50.
An alternative approach employed by several manufacturers is to offer dedicated APE accessories that can be fitted temporarily over their own small‑diaphragm omnidirectional microphones. DPA and Microtech Gefell have just such accessories, for example, and in most cases these are simple plastic spheres that slip snuggly over the microphone such that the capsule surface lies flush with the sphere.
Often different sizes of APE spheres are available, too, typically spanning 30‑50 mm — the diameter determining the frequency at which the HF boost and narrowed directionality starts to take effect (the larger the sphere, the lower the starting frequency).
The advent of commercial 3D printing has also made third‑party APE designs readily available, both for specific microphone models and as generic designs to fit specified mic diameters. And for DIY enthusiasts, home‑grown solutions can be also constructed. A good few years ago, I made a set of APEs to fit my own Sennheiser MKH20 microphones from beech wood spheres bought online. I drilled the spheres with a 25mm Forstner bit, sprayed them black, and fitted grub screws to secure them to the mics. They have proven to be highly effective in many orchestral and choir recordings since.
Pros
- Intriguing entry into true Decca Tree mic techniques.
- Elegant engineering.
- A very compact microphone housing with low visual impact.
- Supplied with a versatile ball‑mount for easy positioning.
- Low‑noise, high‑output capsule.
Cons
- Not quite as affordable as one might hope.
Summary
A unique and very practical self‑contained diffuse‑field omni mic with integral APE sphere, as popularised in the Decca Tree mic technique.
Information
Stereo pair £720, triple‑matched set £1080. Prices include VAT.
Stereo pair €700 (approx $812), triple‑matched set €1000 ($1160). Prices exclude tax & shipping.