The EQ4M features the same Air Band that put Mäag on the EQ map — plus a whole lot more!
Mäag Audio were founded in 2009 by Cliff Mäag, an established recording engineer with over 35 years’ of experience. He is also the owner of recording studio The Record Lab in Utah, and amongst his many credits are more than a few Donny and Marie Osmond albums. While audio engineering may be his preferred day job, Mäag also has a background in developing and manufacturing audio equipment, and served as the Production Manager at the NTI and Nightpro companies. It was at the latter that he designed the Nightpro PreQ3 and EQ3D equaliser products, which is where the ‘Air Band’ equaliser — widely regarded as a very musical-sounding EQ — was first introduced, in 1993.
His new company currently offer a 500-series mic preamp (PreQ4, with the AirBand EQ), a couple of native EQ plug-ins via Plugin Alliance (EQ4 and EQ2 — there’s also a version of the EQ4 for the UAD platform), and two 500-series EQ versions of the same EQ4 and EQ2 models. In fact, the EQ4 module was reviewed by my colleague Matt Houghton back in SOS July 2013.
The latest addition to the family is a 1U rackmounting, dual-channel version of the EQ4, called the EQ4M — the M suffix signifies some useful enhancements to the original design. The main technical improvement is down to a decision to increase the power rails to ±18V, raising the headroom margin to a whopping +29dBu (about 8dB more than the 500-series EQ4). The EQ4M also adds a relay hard-bypass, an adjustable input attenuator, an extra 15kHz option on the Air Band EQ section, and the use of detented rotary controls to enable more consistent settings.
Unpacking the EQ4M, I was impressed with the smart construction and elegant blue front panel, with its spacious layout and clear markings. This is a six-band, dual-channel equaliser, and each channel has seven detented rotary controls, one rotary switch, and a couple of black buttons (both with status LEDs). A nice touch is that the umlaut in the Mäag name in the middle of the front panel is made up of two orange micro LEDs, and these indicate when the EQ4M is powered on.
Although there are quite a lot of controls, the panel doesn’t look crowded or busy, thanks largely to the slim knobs with different colour-coded caps, which help recognition of the relevant controls. Impressively, the panel markings around each knob even reflect the detented switch positions remarkably well — that’s quite unusual in my experience — making it easy to keep a log of favourite settings for reset purposes.
On a mildly negative note, there is no user manual in the box, just a card instructing the owner to visit the PDF manual on the company web site. Call me old-fashioned, but I still think a decent user manual is a requirement even for such a simple product as this, and especially so when its first page carries 15 “Important Safety Instructions”!
The rear panel has electronically balanced XLRs for the inputs and outputs, and a (Class-1, grounded) IEC mains inlet with integrated power switch, mains fuse, and voltage selector. I don’t like rackmount products that can’t be turned on-off from the front panel, but at least the EQ4M only consumes around 15W of power.
Internal construction is to a high standard, using conventional through-hole components throughout on a single PCB that covers almost the full floor area of the steel case. The line-level inputs are handled by THAT 1203 balanced line-input receivers, with THAT 1646 balanced line drivers for the outputs. Jumper links are provided to float the output XLR pin 1 shields from the chassis ground, which is a useful feature should ground loops become a problem. All the active EQ stages are based around NE5532 op-amps (there are five per channel), and chunky WIMA ‘red-block’ MKP (polypropylene film) capacitors dominate the PCB. The power supply is a straightforward linear design with an encapsulated toroidal mains transformer and LM337 regulators.
Looking at the front-panel controls now, overall relay hard-bypass buttons are provided for each channel (with green status LEDs) in the centre of the front panel, with the two channel section controls arrayed identically to each side. The left-most rotary knob is an input attenuator marked from 0 to -10, but which actually applies up to 11.5dB of attenuation. Across the middle of the control range, each detent click introduces about 1dB of attenuation, but the first few and last few clicks have little effect. A green signal-present LED starts to illuminate around -20dBu and gets progressively brighter, while a red Peak LED starts at +22dBu, a good 6dB below the clipping level.
There are five main EQ bands, the first four of which have bell responses and fixed centre frequencies of 10Hz (labelled Sub), 40Hz, 160Hz, and 650Hz, with relatively wide and generously overlapping bandwidths of roughly three octaves (Q=0.4). The last band is an HF shelf with a corner frequency of 2.5kHz. All of the band gain-control markings suggest a ±5dB range, but the actual boost/cut levels appear to be -5/+12 dB for the bell-response bands, and -8/+15 dB for the HF Shelf (you can find Audio Precision Analyser plots which demonstrate this on the SOS web site). The 10Hz band might seem unusably low, but because of the broad bandwidth it has an audible effect as high as 150Hz at full boost, so is actually quite effective at manipulating the low end.
Interestingly, increasing the gain for any one band raises not only the level around that selected band, but also the level across the entire spectrum, ultimately by as much as 4dB. So everything gets louder, which is why it was felt necessary to add the input attenuator (an unusual feature for an EQ). A comment in the manual states this gain build-up is an inherent side-effect of this specific circuit design, although this effect doesn’t appear when the bands are being cut rather than boosted. It’s also interesting to note that this EQ design introduces relatively modest phase shifts: a fairly typical ‘smile-curve’ setting, for example, ranges between ±30 degrees.
Of course, the ‘special feature’ of the EQ4M is the Air Band section, which has its own bypass button with blue status LED. This section provides a second HF shelving band, but one which only offers boost, controlled by another detented gain control. Again, this is marked 0-10 but actually dials in a maximum boost of +17dB. As with the main EQ sections, it also introduces a +4dB overall level rise across the spectrum at the maximum setting. With gain settings below 5, the overall gain shift at frequencies below the HF shelf boost is less than 1dB.
The Air Band corner frequency is adjustable between 2.5, 5, 10, 15, 20 and 40 kHz. The 15kHz band is, as I remarked earlier, new to the EQ4M and was borrowed from the company’s EQ2 design as a useful intermediate step between the original 10 and 20 kHz options.
Given that there’s already a cut/boost shelf at 2.5kHz you might wonder why this same corner frequency is duplicated on the Air Band section. The answer is that the two sections have slightly different response shapes, and the way they interact can be useful. For example, the main EQ section’s 2.5kHz shelf can be employed in cut mode to reduce harshness, while the Air Band can be used to restore the level at higher frequencies.
The EQ4M is a very straightforward device to use, even without the downloadable manual, and it sounds very clean and transparent even at quite severe settings. The controls feel solid and precise and the simplicity of the design makes it extremely quick to shape the tonal balance of any mix or individual source.
This clearly isn’t an EQ for the surgical removal of unwanted elements — the bands are all far too wide for that — but for tonal shaping and moulding it works remarkably well, without drawing attention to itself. Naturally, with such wide bandwidths all the bands interact with each other to some extent, so a degree of iteration is often necessary between the settings of adjacent bands to achieve exactly the required response — and the input attenuator is often needed to restore the overall level, too, especially when several bands are being boosted.
As you might expect, the star feature here is undoubtedly the Air Band, which introduces a delightful openness, ‘sheen’ or ‘sizzle’ to just about anything and everything. It works superbly on closely recorded vocals to enhance the breathiness and detail, but without adding any hint of harshness or sounding in any way unnatural. As I mentioned earlier, using the Air Band in concert with the standard HF shelf section in cut mode formed a very powerful tool for taming any edge of harshness without losing the high-end sparkle. Also, the ability to move the shelf’s corner frequency up the band in relatively small increments, and to adjust the amount of boost gain with very fine precision, gives a great deal of control to optimise the settings perfectly.
All of the main section’s filter bands work as expected, and the centre frequencies proved to be well chosen in practice. I was initially rather dubious about the 10Hz band because of the inherent dangers of boosting subsonic energy, but in use — assuming the source material was recorded cleanly and without unwelcome LF rumbles — it actually proved to be a useful band for enhancing or controlling the very low end. I often found myself juggling the 10 and 40 Hz band settings to achieve the low-end sound I wanted, but the results were frequently surprisingly effective. In his review of the EQ4 500-series module, Matt suggested it was possible to achieve a transformer-like thickening of the low end using these controls, and having experienced it first-hand I completely concur.
The bottom line is that this EQ4M is a very well thought-out design that is capable of drawing out the very best of a source’s tonal qualities, and doing so without a lot of effort! I didn’t hear the original EQ4, but I’m sure the additional headroom of this model contributes significantly to the completely effortless and very refined sound quality, even when pushed with very high levels from a DAW’s converters on peak-normalised reference material.
I see the EQ4M as being more useful for polishing stereo stems and complete mixes, and particularly for mastering duties, rather than taming individual sources, and to that end I would have preferred true stereo controls rather than separate channels. So while I can see this arrangement offers greater flexibility, perhaps there is room for a true mastering version with proper switched gain controls as well. The elevated levels of mains-hum components in the right channel (see ‘Technicalities’ box) were mildly disappointing, but overall the technical and sonic performance of this interesting EQ unit is very good, and it is a good example of how great analogue designs still have an audible advantage over software in some areas.
There aren’t many stereo hardware EQs available for around the price of the EQ4M, but amongst them are Malcolm Toft’s Ocean Audio Signature Three Inductor EQ, the A‑Designs EM-EQ2, the Dangerous Music Bax EQ, the TK Audio TK-Lizer and the API 5500 Dual Equalizer.
Mäag give the input impedance as a highish 48kΩ, while the output impedance is a low 50Ω, and the unit clips around +29dBu with a typical 10kΩ destination load. The frequency response with all EQ sections flat reaches -1dB at 10Hz and 70kHz, with a signal-to-noise ratio of -88dB in the left channel and -83dB in the right (ref +4dBu). Crosstalk at 10kHz was around -88dB, and I measured overall THD at 0.001 percent.
My test measurements revealed small differences between the channels, with the left channel performing measurably better than the right, as the latter exhibits higher levels of mains-frequency fundamentals and harmonics. My Audio Precision test set measured the 50Hz (UK) mains fundamental at a healthy -110dBu in the left channel, but 30dB worse in the right, at only -80dBu. The second harmonic at 100Hz is similar in both channels (-100dBu), but all the higher harmonics are nearly 20dB greater in the right than the left. That these ‘spikes’ disappear in bypass mode suggests that they’re induced into the circuitry from the internal power supply, which is physically much closer to the right channel’s circuitry. When asked about this, Mäag confirmed that it was a deliberate design decision — they felt that an internal PSU was more user-friendly and, although measurable, the mains-related harmonics are inaudible. I agree; in most practical situations the different hum levels will go unnoticed.
- High headroom and low phase-shift make for an effortless sound character.
- Air Band section restores a natural-sounding openness to any source or mix.
- Beautifully chosen band settings which work perfectly.
- Internal ground-lift links.
- Overall level rise when any band is used with high boost settings.
- Higher mains hum components in the right channel.
- More fiddly to use on stereo stems/mixes than a true stereo EQ.
This two-channel, six-band equaliser boasts some unusual features and a delightfully transparent and musical sound character.
£1899 including VAT.
KMR Audio +44 (0)20 8445 2446