Review: Beyma 14MC700Nd

"Everything is a hammer. If we don’t have a hammer, we pick the next best thing and use it as one. If we don’t have that, we grab anything and swing away like it’s a hammer anyways."

Can we, really? I am encountering plethora of wild and sensitive dilemmas right at the birth of this review platform. In this case - putting a driver out of its comfort zone deliberately. By design, Beyma 14MC700Nd is a mid-bass driver, certainly not a subwoofer. At Beyma, they are clear about that, specifications point to that as well, and its natural behavior shows the same. But its light and strong cone for the class, strong motor, and promising specs, make it too tempting not to try such driver in a different use case. In my dream sub 20kg subwoofer project maybe. And I have the driver in my paws right now. So let the abuse commence.

We know full well that this isn’t a subwoofer driver. Yet I am putting it through the same evaluation anyways - partly as science and partly because… everything is a hammer. Let’s look at the shared properties of a dynamic driver - what carries over between mid-bass and subwoofer performance, where the limits appear, and whether it is usable as a full-range mid-bass, or worse for the driver, as a subwoofer.

This review is sponsored by MS-Sound (www.ms-sound.cz), who kindly provided the speaker for testing. While sponsorships are very welcome, all technical results and measurements remain completely independent and unbiased.

Looks and build quality:

The 14MC700Nd is a product of the newer 2020 Beyma product line developed with high-end performance in mind. If I ever had doubts about older Beyma products, they are consistently debunked with each model I get my hands on. This driver borrows its design from previously tested units, and even enhances on it a bit. We can see the basket spokes were made lighter here, so the intended "X" design did not make it into this model fully, now looking like "Y" shaped spokes, possibly to save weight too. It is not taking away from the function or beauty of such design in any way. To my eyes maybe otherwise even. Also newly - there are cooling fins on the basket, with openings directly under the spider, so the air can move more freely through the driver motor structure.

Cooling is further aided by a 20 mm wide center pole piece vent, with a thin wire mesh as debris shield, buried 50 mm deep in the motor structure, and 6 direct voice coil venting holes, each 7 mm - 9/32" in diameter. Take that, USA citizens! :-) This issue clearly establishes that we will do basket diameter, spider and dustcap diameters in freedom units, while detailed driver features will have to be expressed by the metric system further on.

Motor diameter is 105 mm at the back, it is 50 mm deep, and it widens by another 10 mm towards the basket. I figured that all these dimensions might be of use for you, so I will measure these on each driver.

Single spider on this unit is a 6" type, and the dustcap fairly deeply recessed in the weatherproofed curved cone, is a 4" type. For this light cone assembly design, the cone feels remarkably strong, certainly in comparison with the competition.

Malt Cross® Technology Cooling System, demodulating ring and 700W/1400W 3” DUO double layer in/out copper voice coil seals the deal for high-end midrange driver class.

Driver specifications:

• Size: 14" type
• Power Handling: 700 W AES
• Impedance: 8 Ohm
• Frequency Range: 55-4000 Hz
• Sensitivity: 99 dB (1W/1m)

Measured T&S parameters are a fair match for a "broken-in" unit and large signal testing after that. Bl strength is matching, while Qes is a bit above specifications, partly due to the extensive stretching of the driver suspension in my test. That carries over to the lowered resonant frequency as well.

The Xmax value includes a plus suffix in my measurement data, as the driver performs admirably under overload conditions, beyond its rated specification.

Here attached, is the manufacturer´s datasheet:

Performance overview and general rating:

The driver performed very well within its specifications. In free air, it sounded round yet kicky - that midrange slap in the chest was very tactile despite no enclosure support. In the test rig, it sounded pleasantly mild and melodic. There will be further listening tests in "MTM V-slotted, coaxial top driver supported design" in development later on. So far, the driver proved itself already. Apart from other modern designs, the sound character puts some nostalgy in me - I would also not hesitate to put such driver in some oldschool design and crossed it over very high, because the behavior allows it (by ear, and graphs also show mild cone breakup behavior). Maybe it will also find its place in the vintage replacement jobs? Despite my fear of issues with deep cone shape and lobing / interference, the sound did not come out overly diffracted or otherwise plagued by directional issues with high frequencies. Good cone shape, strong cone and smaller diameter in comparison to 15" certainly helps with all this.

Noise performance:

For bass duty, greater small signal Fs shift after testing, and some more spider and motor noise indicated that it might not be optimal choice for bass (Excuse me, DOH!). For mid-range and full-range duties without much equalisation though, the noise performance was excellent.

Otherwise it put so much wanted sound out, that testing parasitic noise output with expected program content turned out to be irrelevant. I could not hear any unwanted parasitic noise coming from the driver, just tinnitus creeping in.

• Buy if: You want well behaving, light mid-bass driver with high end output figures.
• Skip if: Full range or outright subwoofer work is what you seek.

The displacement-to-dollar score makes it clear again: This is a driver built for specific applications. I’d not recommend it blindly for general-purpose subwoofer builds, or for scenarios where displacement to price ratio matters. Once we assign the driver to the performance class and designation properly, this issue gets mitigated.

Performance score of 88.6% shows very strong standing of this driver, more so for its core duty - mid-bass.

*The following section is available to Bassometry members only.* (Free sample):

Large Signal Performance Results:

This section presents the driver’s behavior under high excursion and high power conditions. Measurements are conducted using controlled lab procedures to reveal transducer behavior beyond small-signal specs. For a full explanation of the test methodology, please refer to our Bassonomy section.

Measured data look VERY strong. Too strong. And that is why full review is needed, because no scoring system can secure you a good choice and full product understanding. The driver partially "cheated" with its resonance frequency shift, because it shifted permanently prior to data acquisition for these tests. With very soft suspension, it also draws little power, and while it is very efficient, it goes hand in hand with cone control. On that matter later. Despite that glitch, the performance held across the board. In this case, to somehow reflect the situation of substantial resonance frequency shift, 50 percent points were deducted from the dedicated score, and usable excursion was capped at +1dB for suspension safety reasons.

Resonance frequency shift of 8.6% and Impedance shift at Xmax of 34% indicate good excursion range without much nonlinear creep with displacement towards Xmax. This is partly an advantage of high compliance drivers. With the permanent resonance frequency shift, the driver performed in fully stable manner. despite further abuse.

DC cone offset: 6.6% maximum derived from Xmax figure respectively for 15Hz is very good outcome with a driver with such light single spider assembly.

15Hz - 50Hz at Xmax behavior: Frequency sweep up to 50 Hz showed 9,9% offset, which is still a good result, that is not to be encountered in normal use anyways. Brief sweep up to 75 Hz revealed the single thin spider limits though. At 75 Hz at Xmax (mid-bass duty range), it showed 5,6 mm outward bias, meaning 80% cone offset in relation to Xmax. The driver lost control there. While this is inconsequential to the normal range of use, together with Fs drop, it might be dangerous to push the driver into sustained large excursions in subwoofer duty. I believe that it could be fatigued that way into some kind of mechanical failure eventually.

THD figures: With very good distortion figure of 5.0% at 15 Hz, this measurement confirms the driver qualities. At 50 Hz, distortion level reached well down into my measurement error range, marked arbitrarily with lowest value of 0,5% that I decided to write down. Excellent! Full spectrum THD testing would be needed for more exact evaluation.

Excursion behavior: This unit performed impressively under overload conditions. It comfortably handled short-term overload of +3 dB, and even tolerated an undocumented +4 dB bursts without any signs of distress whatsoever. Mechanically, the driver maintained distortion levels below 10% to up to 2.8 dB boost over specified Xmax value. With incredible Xdamage figure of 48 mm, I decided to push it some more. Surprisingly, I found another limit. At 11.2 mm one way the spider was hitting internal motor structure, intensifying that contact sound upon further boosts of the stimulus signal. I got this phenomenon confirmed by Beyma, so this limit is legit. It raises a question - what the Xdamage parameter is really for. Beyma specifies this as a displacement by which the speaker voice coil hits the backplate, but in this case, it basically cannot happen, and with prolonged torture different damage could occur. On the good note though, this happened with circa 6dB subsonic overload above Xmax, and it is nondestructive phenomenon upon short exposure to it. That means you are safe and the driver is no less for this issue, if I can even afford to call it that. In other words, this is not to be experienced in real world, ever. Maybe even better. If you commit very ugly "basstrocities" on the driver, it will let you know loud and clear way before you really mess up big time. Maybe even a red light will light up at Beyma headquarters, and not very friendly men in black will come have a word with you about gentlemanly behavior towards the audio gear.

Mechanical(SPL) compression test:

Note that this test reflects an isolated low-frequency scenario. Once the driver is placed in a specific enclosure, the results can vary significantly. However, as a point of reference, this data set still holds substantial informational value and offers useful insight into the driver's raw performance characteristics./p>

With this driver, suspension self-compression is not an issue. Most of the power will go into the already light mass load losses and radiation.

Final words: Honestly, I was afraid I’d end up with nothing meaningful to say - or worse, a fatal damage. But the Beyma 14MC700Nd delivered more than admirably: excellent results, big output, low parasitic noise and a very pleasant sound. That means, totally approved for mid-bass and mid-range duty. The score without any penalties would shoot it into first position by bassomety measures, despite not even being a bass driver. And that alone my friends, would be a great topic for next article - mid-bass driver specifications have quite interesting relation to bass potential. It is not for nothing that many mid-bass drivers would "apparently" perform extremely well in bass duties, if they made it through mechanically. With the mechanical behavior I have witnessed, I will not try this one for subwoofer duties, the suspension control is fine tuned just right for midband duties and only moderate excursions. But is that a flaw? I would not believe so. It is the incompatibility of the bassheads urge to use the hammer. It’s challenging to give a fair assessment of a product that was designed with a specific purpose in mind when the evaluation metrics emphasize very different qualities. It might be viewed as unfair, but here we are, going all the way, to dig out what’s really going on - what’s what, and what’s even possible. The final score of 88.6% was fought for hardly and admirably. I might be wrong, but this unit seems to be overlooked in the discussions as well. If you don´t abuse its mechanical specifications much, this is very (SPL)sensitive and welcome competition to the mid-bass category.