Review: RCF LN19S400

There’s a quiet curiosity that comes over you when you first notice certain pieces of audio gear. The kind that makes you pause and look a little closer. The RCF LN19S400 is exactly that kind of driver. Its über-sharp look and subtly unconventional design suggest a fresh approach to subwoofers.

Why 19"? We’ve already seen these quirky in-between dimensions in mid-bass drivers. But it does make sense: 18" PA drivers are still displacement volume limited in certain advanced designs that require extra oomph, while 21"s get unbearably large and heavy. The neglected in-between needs have been around for some time, and now they’re finally being addressed. Or are they?

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.

Looks and build quality:

Right out of the box, the LN19S400 looks fresh, advanced, professional, even geeky, sacred-math-involving, and whatnot. Compared to previous RCF products, almost every part of this new design has been overhauled, changed, or improved. There was nothing technically wrong with the older designs, but sometimes they looked like someone had taken an untreated hunk of iron dug from the field, slapped it onto another piece of rough metal or ferrite, and voilà: an exceptionally performing unit was born.

In certain areas, that unsophisticated, rough look made me wonder how they managed to get such impressive performance from what appeared to be such a raw product. While it was certainly a fully competitive product line back then, its cosmetic features were a stark contrast to some competitor´s designs, which looked much more polished. At least on the outside. Not anymore.

This time, RCF is coming in sleek. This is such a reference-quality, polished product that it deserves a moment of appreciation just for that.

A 19" heavy weatherproofed speaker cone, paired with a 21"-ish sized accordion style surround, is slightly curved. While the underlying material properties of the cone initially made me think it might be soft, the overall structural integrity is very strong. Certainly on par with other high-end models. Also this time, the suspension feels a little stiffer than what’s typical for the RCF product family.

The slightly rough, "square-dotted" 6" dustcap is equally robust, complementing the subtly aggressive design while balancing all the softer elements.

Parabolic, eight-double spoked basket houses a new compact neodymium motor with a diameter of approximately 139 mm and depth of 80 mm. A 55 mm pole vent chamfered toward the inner motor structure is protected by a hexagon-shaped metal grille, fitted 70 mm deep. Six additional direct voice coil cooling vents, each 13 mm in diameter, further aid in coil cooling. Between the double spokes, roughly 20 × 20 mm windows lead directly under the spider to the basket platform.

Now I am intrigued! Despite the “hypervented” magnetic structure (dual-forced hypervented by RCF’s own description) design common to most RCF drivers, which usually pushes air very forcefully through the motor and generates some noise, this unit feels noticeably more airy in its cooling approach.

The whole design feels very purpose built and cohesive. For an advertised long stroke with a highly appealing Xmax of 17 mm, this lower model is equipped with a 4" voice coil, 42 mm in length. Slightly oversized 8" spider, now five ridges deep, with tinsel leads woven in, means the LN19S400 should be able to handle this excursion without a hiccup.

With net weight of just 10.9 kg (24.03 lbs), it’s very light - "light-eighteen-inch-light". It could certainly make for an ultra-light, "single person carry" portable box, but at that point, you WILL have a running sub that will need some securing.

Driver specifications:

• Size: 19" type
• Power Handling: 1500 W AES
• Impedance: 8 Ohm
• Frequency Range: 25-1000 Hz
• Sensitivity: 98.5 dB (1W/1m)

Measured Thiele & Small parameters align well with lightly broken-in and burned-in unit. The BL strength appears slightly higher than specified, while Qes and Qts are a little lower - both just above the stated specifications. As is typical with RCF, their woofers consistently hit the mark or exceed expectations.

The Xmax value includes a “plus” suffix in my measurements, reflecting the driver’s impressive performance under certain overload conditions - well beyond its rated specification.

Below attached is the product datasheet:

Performance overview and general rating:

We mounted the unit in a compact 130 L ported enclosure tuned to 30 Hz and enjoyed a summer measurement and listening session. A comparative one, alongside B&C and Beyma 21" peers. The LN19S400 performed squarely between typical 18" and 21" solutions in terms of output. Not quite threatening the 21"s, but for the lower model of the two RCF 19" units, it provides a viable choice while absolutely holding its own. And that is more than good enough.

Displacement volume of this design still competes with many 21" units, making it a worthy option for cinematic or subsonic work.

The unit under test delivered a balanced, strong sound. Personally, I found its signature somewhat "meh-average", but my colleague Martin at MS-Sound, with no less knowledge and authority, was thoroughly impressed. See, subjective evaluation can only go so far. Interestingly, the discontinued LF21N551 model was more to my liking, yet somewhat unappealing to other ears in the room. Go figure!

Regarding raw performance, the results are within expectation.

Performance score hitting 80.2% mark shows solid standing of this driver while the displacement to dollar score of 94.4% exactly reveals how much air can this driver move in its class for its price. RCF scaled that one excitingly well.

This new design also handled itself admirably regarding overall behavior. Very cultivated working noises while retaining some of those "hypervented cooling" qualities.

• Buy if: You want an entry into high-end light subwoofer class while moving a lot of air in the bottom-end bass region with sensible program content.
• Skip if: You suspect size compatibility issues in your current rig plans, or plan running the driver "hot" in direct radiating designs.

*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.

While the LN19S400 showed mostly very favourable results, forward cone offset appeared in my sweep tests. This was not the entirely positive outcome I had hoped for, especially given the stiffer suspension compared to the usual RCF product family approach. Despite the above-average Xmax rating and overall behavior, this driver is better suited to designs that do not rely solely on direct radiation under high-demand conditions in the upper subwoofer frequency range. More details follow below.

Resonance frequency shift and Impedance shift at Xmax figures indicate the new approach - LN19S400 stiffens up noticably, holding the driver within acceptable bounds most of the time, despite top-end excursion capabilities for its class.

DC cone offset: A 0.34 mm forward offset at 15 Hz is exemplary, resulting in 100% offset score derived from the speaker’s Xmax.

15 Hz – 50 Hz at Xmax (Sweep) Behavior:
During frequency sweeps, at 40 Hz, which might represent a second excursion peak in a 30 Hz tuned bass-reflex enclosure, I have observed instability creeping in, with a forward bias reaching up to a concerning 6,3 mm, resulting in a 36% score. The driver maintained this state under sustained stress without any fatigue or further deterioration of its performance.

At 50 Hz, the driver could be (and shortly was) pushed into a failure mode if driven to Xmax. However, with normal program material in a typical acoustical design, reaching Xmax at 50 Hz is unrealistic. I therefore chose to record the former score without subjecting the driver to additional or repeated punishments in my scoring.

Power draw tests show that indeed, the suspension is stiffer, eating from the power capacity of the driver somewhat. But it is absolutely bound to happen due to the various tradeoffs of a high-end design with a large excursion span. There is nothing wrong in this particular design compromise, the numbers are also more than fine.

THD figures: Insanely good outcome at 15 Hz with 2.5%, and no less awesome at 50Hz, but not into full Xmax level. Still basically in the range of reading error at 50Hz. Those newer designs perform exceptionally well.

Excursion behavior:

Here, usable excursion would have risen to +3 dB both mechanically and in terms of distortion. The LN19S400 absorbed a controlled +4 dB boost without any performance issues. While it sounded mildly stressed, its small-signal T&S parameters showed no noticeable change afterward, with nearly identical Fs in final measurement. This driver is one sturdy beast.

At this level of stress, the driver cone moved approximately 32 mm one way. Apart from possible long-term fatigue, there is little to worry about large excursions below box tuning with this speaker. No excessive parasitic noises were detected, and the mechanical noise levels were the lowest I’ve experienced on any PA subwoofer to date (yet again). If you want a driver that behaves nicely with “motor out” configuration, this one is IT.

The usable excursion score was ultimately reduced to +1 dB due to the previously mentioned stability results upon overload. Within the normal operating range, however, the LN19S400 remained fully reliable and stable.

Mechanical(SPL) compression:

...As explained in the previous reviews, we can see almost no suspension compression to speak of, right to the +3dB overload point where it breaks. The driver excursion scales almost perfectly towards Xmax, and 2 dB past that point with superlinear behavior. Very interesting!

Final words: No politics to the reviews, no politics to the reviews. I SAID, no politics to the reviews! Damnit, damnit!

This product was announced well over a year ago. I was there to witness the announcement, and wanted to purchase these drivers from day one. The vaporware LN19S450 model simply disappeared from RCF’s webpage altogether as well as LN16S400. With extremely late product deliveries for certain items and no recourse or communication from RCF to potential customers, this did not stay unnoticed.

Even AI acknowledges the chatter on forums, and it jokingly tried to help me with a review intro on that note:

"Today, we’re reviewing the RCF LN19S5400. A driver so rare, so elusive, even its own engineers aren’t sure it existed. Traits: Can’t be seen in daylight or in stock. Strategy: Build something too powerful for mortal use, leak two images, cancel it, and cause eternal GAS in the forums."

Too much? Perhaps. But it also highlights a pattern: RCF’s innovative drivers can generate hype, demand and curiosity, yet it repeatedly leaves unfulfilled desires and frustrations. I get that. The end user of a single driver unit is not very important for RCF, and that´s completely okay. Though there could be certain decency about that. Of course, rest assured that this commentary has no effect on the driver review or its scores.

As for the Driver Itself:

Would it have passed the overload tests without a hiccup, I’d probably be simping and weeping over the unannounced LN19S450 and LN16S400 models, both of which sound even more exciting than this one. The LN19S450 would secure solutions with SPL densities (box volume per output) unheard of. The LN19S400, however, proves to be a well functioning addition to the market, with very favorable qualities in the displacement department. Its general mechanical strengths make it highly capable in scenarios requiring high excursions.

Looking at the deep cone and motor, long suspension, and long coil, I even tried exerting lateral force on the cone to see if the voice coil would lock up in the motor structure as often happens with car audio speakers. No bueno - the driver remained stable and stiff despite all my efforts to decenter it. On the RCF webpage, the spider is only described as "4." Are they now using four-layer spiders? That would certainly explain this impressive lateral stability.

Overall, the LN19S400 is a very likable speaker that offers its own set of advantages and stands out as a solid, reliable choice in its class.