Review: Beyma 21LEX1600Nd

Modern large-format subwoofer drivers represent the pinnacle of transducer engineering, where every gram of material and every turn of the voice coil is optimized for maximum performance. In professional audio, 21-inch designs have become the benchmark for systems that demand the deepest, most powerful low end, setting the standard for what high-output reinforcement should deliver.

Yes, there are 24-inch models and even a few niche sub-sonic and effect drivers larger than that, but 21-inch has proven to be the sweet spot, capable of being optimized for deepest low-frequency extension while still maintaining enough speed and control to cross over into the mid-bass range, eliminating the need for a dedicated kick-bin in most cases.

I believe this approach traces back to the birth of B&C Speakers IPAL project, and more importantly, to what I call the rise of the "Eurodriver" class of subwoofers. At its core lies an extensively and utterly optimized 4.5-inch multilayer voice coil paired with a sophisticated, lightweight, high energy neodymium motor structure. Since then, manufacturers like B&C Speakers, RCF, Eighteensound, LaVoce and Precision Devices have all contributed their interpretations of that afffordable yet high-end design and class, now with FaitalPro even pushing the limits further with a new 6.5" large coil 21-inch model - though at the cost of added weight and price. This formula just works.

...And here we are, with Beyma 21LEX1600Nd, refining on that formula yet again.

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:

At first, the Beyma 21LEX1600Nd looks unimposing. Continuing on the brand platform X-shape spoked basket in sleek black design and seemingly ordinary specs (for the Eurodriver class anyways), I would completely miss this one if I did not have it lent to me.

Listing through the mechanical design features, the 21LEX1600Nd has a slighlty curved, "non-wetted" weatherproofed ribbed cone that again looks uncompetitive, but upon some force testing, it is surprisingly thick and stiff. At least comparable to the competition, if not stronger. The neck-joint between the cone and spider is further reinforced with thick layer of black epoxy. The cone assembly is suspended on an 8" type spider that is fully soaked in silicone, with tinsel leads woven into it. Smooth 7" dust cap further helps with the cone rigidity.

When it comes to motor dimensions, things get very interesting. The Beyma 21-inch basket platform can probably host a massive 10-inch motor assembly (not counting for wider ferrite magnet solution above the motor neck joint and top motor top plate), and there’s mechanical provision for what might be a monstrous 12-inch spider. Inner basket structure seems to be limiting such solution in excursion though, due to the stepping in the basket construction, serving as a spider mount pad. My educated guess is that any beastlier solution will not be able to do over 26mm one way, which is still very sufficient.

In contrast to the big platform, the 21LEX1600Nd carries a neodymium motor that measures 144 mm across and is 70 mm deep - extremely compact, yet presented without hesitation. The motor base flares an additional 10 mm toward the basket. A 45 mm central vent is covered by a fine wire mesh recessed 70 mm inside. For added thermal management, eight 7 mm circular vents surround the coil movement axis, providing direct cooling. There are further holes and entrances in the basket base, so apart from possible engineered forced air exchange, the design is very airy.

Featuring obligatory Beyma Malt Cross® cooling system, it is exceptional to see 1600 W continuous power input specification on a not overly long 4"!!! voice coil. The competition boasted that this was possible due to switching for CCAW windings on a 4.5" voice coil and still more substantial motor, and here we see that this is now sustainable on the smaller one copper wound too. Big thumbs up! The consequences of that are... On that further on.

Driver specifications:

• Size: 21" type
• Power Handling: 1600 W AES
• Impedance: 8 Ohm
• Frequency Range: 30-1000 Hz
• Sensitivity: 98 dB (1W/1m)

Measured T&S parameters are a fair match for a lightly "broken-in" unit and large signal testing before small signal measurements. Bl strength appears to be larger than specified, while Qes and Qts are little lower - again a bit above specifications. I tried to select the lower qualification results, during measurements, but I got few qualified results of Bl above 39 too. That is a notable upwardly difference compared to the manufacturer´s specification.

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

You´ll find the product datasheet attached below:

Performance evaluation and general rating:

The driver performed very well within its specifications. In free air, it sounded strong and naturally musical. In the test enclosure (my previous project of very compact 130l net, 29Hz tuned ported box), it sounded thick and round. And loud! I do not say it lightly, and, uh, oh, I need to check my manhood, but the 21XL1600Nd generally kept up with heavier and more expensive competition, despite its looks and expectations. Yes, I sincerely wanted to not like it very much. With all the performance results in my hands, tough luck with that.

Beyma markets the 21LEX as "Ultra low noise", low distortion model. That confirmed to be fair claim inside the test box, and outside mostly too. With the performance score of 82.9%, it certainly qualifies to the efficient Eurodriver class.

• Buy if: You want a light and strong entry into the high-end subwoofer, or "motor-out" mounted unit.
• Skip if: You are waiting for the utter high end. I mean, there is no reason to skip this one. That´s the curse of this driver, while noone sees it. The company must cry their eyes out for that.

Displacement to dollar ratio: In this case, the displacement ratio to price gets interesting. The ratio is set somewhat harshly, accounting for very cheap, barely functional units, just giving the output. Breaching 50% means that the value turns on the good side, and that is in bulk volume (over two litres one way) so to speak AND on a high-end speaker. At that point, it is heading into the no-brainer price class for those who want a lot of bass from fewer driver units.

*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.

Most of the results would point toward a driver worthy of the hall of fame class yet again. In the harsh overload tests deliberately designed to push the driver beyond typical use, a few limitations emerged to shoot it down. While the test conditions are extreme and beyond typical use, some of the results touched normal range of use as well.

In contrast to some points deduction, the subsonic overload and THD behavior tell a different story - and an excellent one. On that later in proper section below.

Resonance frequency shift and Impedance shift at Xmax hanging in the thirties means excellent balance steered to the efficiency. Above 80%, there is no room for critique really.

DC cone offset: A 0.38 mm forward offset at 15 Hz is excellent, resulting in 2.7% offset derived from the speaker’s Xmax. That means 100% performance score.

15Hz - 50Hz at Xmax (sweep) behavior: During frequency sweeps, at 40Hz, which might be a second excursion peak in 30Hz tuned bass-reflex enclosure, I could witness instability creeping in, to up to threatening 5mm forward bias, resulting in 39% score. The driver held this way under sustained abuse without any fatigue or worsening. At 50Hz, I would be able to run the driver into failure if run to Xmax, but with normal program content in normal acoustical design, Xmax at 50Hz is unreachable level. So I decided to sustain the score without punishing the driver further into extremely cruel rating. This is a difficult problematics, because small diameter drivers would be able to reach Xmax with normal signal at 50Hz, so I have to question what are the fair performance markers for the score itself. Possibly a reality of the particular speaker cone movement. How about that...

THD figures: Insanely good outcome at 15 Hz with 2.5%, and no less awesome at 50Hz, but not into full Xmax level. This unit does not "speak" any garbage.

Excursion behavior: Here, usable excursion would have risen to +3.2 dB both mechanically and by distortion. Undocumented push to +4 dB beyond Xmax did not harm the speaker at all. At that point, the driver cone was clocked to move at 22 mm one way with no change in T&S parameters to speak of. Apart from long-term fatigue, there is little to worry about large excursions below box tuning with this speaker. No excessive parasitic noises were detected, aside from a slowly healing spider tick and manageable wind noises. The driver noise levels coming from the mechanical parts were basically lowest experienced to date on any PA subwoofer. While the driver sounded somewhat stressed during such large overload, overall motor structure and soft parts behavior was exemplary. The usable excursion score was then unfortunately shot down to +1 dB by other already mentioned overload results. Within the normal operating range, 21LEX1600Nd remained fully reliable and stable. This design needs to stiffen up a bit, to move forward into the subwoofer excellence.

Mechanical(SPL) compression test:

Well, well, well! This does not add up. What is going on?
I’m sure Beyma engineers are now grinning and cackling somewhere in the corner. While it wasn’t Beyma directly who lent me the driver, they still threw me a curveball with this model.

It appears, that this unit uses a "super-linear" suspension design. I measured what I measured - and at the moment, I have no good recourse for it. The driver scaled its excursion with level perfectly, so this is not just a glitch or full measurement error either. This innovative brave approach, giving low noise and lowest THD levels might sadly also be the cause of the reduced overload performance score.

If there is no mechanical compression, the compression must have gone somewhere else then. Upon further diagnostics, with some devices in the measurement chain exacerbating the measurement error, along with a very rough phase-change estimation across power levels, here is the power compression table on the electrical side. Power compression figures are in the most right column, derived from Xmax base level:

Adding the static ~0.3 dB mechanical loss to this actual power compression table, now that scales expectedly! Here is a fully revised table:

It seems that there is a case study article imminent then. Also, it somewhat makes sense with the listening tests, where 21LEX sounded very loud in comparison to competition, full and unusually strong. Until THERMAL compression gets some word in, the more compliant linear suspension will cause this speaker to sound louder. Though we did not exactly withess the performance to weaken noticably in time. Such decay is hard to spot in the long test session.

Final words: Multiple innovative features, keeping copper voice coil material on a strong compact motor, falling into ultra light driver category, safe sub-sonic overload excursion margins, low THD test results, you name it. There is a lot of innovation going on, as well as performance given the price and weight.

With an admirable performance score 80.2% shot down by our torturous stress tests, The 21LEX1600d holds its own. THIS is exactly what scales the tip towards compact 21" one-manned subwoofer designs being possible. With enough care, we might be talking 40 kg weight range for such box without rigging gear on it.

Given the basket platform, it is obvious that something higher in the product line could and should come up one day. I contemplated on that way waaaay before any NDA could touch me: A man can dream - 4.5" to 5.3" copper voice coil on a motor with Malt Cross® cooling system, approaching Bl²Re ratio of 300, at least 40/42 mm (21"/18") long voice coil, to uptick it above the competition into the 2000 W realm and Xmax levels respectable enough for port-assisted design choice possibility instead of port-reliant one, that would be something. RCF was almost there with LN19S450 driver offer, but their "vaporware" business ways kicked in yet again, and after more than one year (!!!) witout delivery, the driver just disappeared from their own pages. So we are dead in the water, waiting.

"Italians! Are you calling us boys? We are coming for you!" Signed - Beyma.