Adire Audio Brahma Mk2.5 Rev. A 12"

Overall summary

In this sample and under these test conditions, the 1 volt baseline shows moderate broadband distortion above about 40 Hz, with a pretty notable rise in distortion toward the lowest frequencies. Around 20 Hz THD is ≈6 percent with H2 and H3 distortion contributing, and there is a small broad feature that grows as a wide peak at 200 Hz where even order distortion becomes more noticeable. Above roughly 40 to 80 Hz the baseline remains comparatively controlled.

Distortion in the usable range is high, averaging about 12% from 20 to 100Hz. At the near limit 40 volt sweep, distortion drastically increases as a broad rise rather than as narrow spikes in the entire frequency range. H2 distortion is the dominant contributor through much of 25 to 120 Hz, while H3 distortion becomes more apparent below roughly 25 Hz. Two prominent peaks appear in the mid bass region, with one at 200 Hz dominated by H3 distortion, and one at 300 Hz dominated by H2 distortion, each climbing toward the 25 percent range. We normally wouldn’t focus on these frequency ranges when evaluating a subwoofer, but they are rather drastic and not quiet something you see often.

The large signal data show a BL 70 percent one way limit of 17.46 mm, a CMS 50 percent point at 21.50 mm one way with good flatness and symmetry, and an inductance variance limit of 17 percent at 11.08 mm one way. The BL shelf is narrow, consistent with the note about coil height relative to the split gap geometry. Le at rest is 2.17 mH, with a noticeable position dependence; Le(i) shows only a modest rise with current. This combination aligns with the measured pattern of an increasing H3 distortion component at the very bottom with drive and even order content in parts of the band.
For sealed use, the manufacturers largest sealed recommendation of 1.25 ft³ computes on this sample to about 0.667 Qtc; approximately 1.00 ft³ is needed for a 0.707 target per the project’s standard method, which happens to be their smallest recommended sealed enclosure. The inductance based limit occurs before BL or CMS on this sample, so clean headroom in the very lowest octave is set by Le rather than by motor force or suspension stiffness; multiple drivers will raise clean headroom if very low frequency output at higher levels is desired.

Overall, this subwoofer, in this test shows to be an extremely high distortion driver with poor LSI readings to go with it, and won’t be a great choice if accurate reproduction is your goal. Rarely would we flat out say that, but the distortion performance here is very poor across the entire desired frequency range. Though, it is mechanically capable of high output in a small enclosure.

Manufacturer's suggested use case

Adire Audio positions the Brahma Mk 2.5 Rev A 12" as a high excursion, sound quality oriented subwoofer using patented XBL^2 linear motor technology, a high temperature 3 inch flat wound copper voice coil, non pressed paper cone with carbon fiber dust cap, interwoven lead wires, and a Y35 ferrite motor with a vented pole. The driver is rated 1000 W RMS with a published 28 mm one way xmax and is available in dual 2 or dual 4 ohm coils. The sheet lists sealed guidance of 1.0 to 1.25 ft³ with daily and SQ tuning notes; sensitivity is listed at 84.6 dB (D2) at 1 W/1 m.

Our suggested use case

Based on this sample and these measurements, sealed alignments are appropriate. The largest manufacturer recommended sealed size of 1.25 ft³ lands near 0.667 Qtc on this unit and the 1.00 ft³ size aligns to about 0.707 Qtc using the large signal cold parameters. Distortion rises as frequency approaches 20 to 30 Hz and the 17 percent Le variance at 11.08 mm is the earliest limit, so very low frequency playback at high levels will accumulate odd order content first. For listeners targeting higher clean output in the lowest octave, using multiples is the straightforward way to raise headroom while staying inside the practical clean one way limit set by Le on this sample. Though, due to the very high distortion levels, it is hard for us to actually recommend it for any application where accuracy is a goal.

Testing and linearity limits vs. what is advertised

What it took to reach our high-level sweep limit, and how that compares to the published specs.

High-level sweep rule: Set just under the BL 70 percent point from LSI

High-level sweep limit for this sample: 40 volts

Approximate electrical power at that limit at 20Hz: 400 watts. Real power varies with frequency and impedance. volts

Rated power (published): 1000 watts

Power used to hit the standardized limits in free air, relative to their xmax rating free air: ~29 percent. Hits the 17.5 mm 70 percent BL xmax limit in free air with 290 watts of power.

Claimed Xmax vs. measured at BL 70%: 17.46 mm, only 62.4 percent of the manufacturers claim of 28 mm.

Xmax @ 50% Cms: 21.50 mm, only 76.8 percent of the manufacturers claim of 28 mm.

Xmax @ 17% Le: 11.08 mm, only 39.6 percent of the manufacturers claim of 28 mm.

Manufacturer suggested sealed enclosure size (and its resulting QTC): Claimed 1.0–1.25 ft³. Since we have a specific rule for this test to always use the largest recommended if there is a range quoted, we are using the 1.25 ft³ as our reference for their suggestion, which nets a QTC 0.667.

Required sealed enclosure for 0.707 QTC: 1.0 ft³ nets a 0.707 QTC. This also happens to be exactly their smallest enclosure recommendation.

Xmax @ 50% Cms: 21.50 mm, only 76.8 percent of the manufacturers claim of 28 mm.

Overall performance snapshot

This is our subjective interpretation of the objective data. How we derive these scores can be found on the home page of the testing section.

Distortion & frequency response - TRF measurements

Method recap: Nearfield mic positioned at 1/10th the cone diameter plus 2 inches, on-axis. Response measured to 1 kHz and THD to 500 Hz. 1/6‑oct smoothing. Two drive levels, 1 V baseline and a high level set at 40 V per the under‑BL‑70 rule derived from LSI for this unit. Distortion reported both as percent and by harmonic.

At 1 volt - baseline

Distortion trends upward as frequency falls into the lowest octave, reaching about 6 percent near 20 Hz with H3 distortion visible at the very bottom. From 40 to 80 Hz, distortion is comparatively lower and steadier, but still not what would be considered low. Around the 200 Hz region, distortion shows an elevated, broad peak dominated by H2 distortion. Again, we normally wouldn’t focus on these frequency ranges when evaluating a subwoofer, but they are rather drastic and not quiet something you see often. No other level invariant spikes are evident in the sub bass on this run.

At high level voltage (40 volts)

Distortion increases drastically and broadly with drive, presenting as a steady rise toward the very low frequencies rather than as isolated spikes. H2 distortion dominates much of 30 to 80 Hz, while H3 distortion becomes most apparent below about 25 Hz. Two pronounced peaks appear in the mid bass near 200 Hz (H3 distortion) and 300 Hz (H2 distortion), each reaching roughly 25 percent range. Overall, the distortion performance below advertised drive levels is extremely elevated and concerning across the entire frequency range.

Delta - 1 volt distortion vs. high level distortion

The 40 volt sweep turns the already elevated 1 volt baseline into a much more extreme distortion profile, with THD climbing drastically across almost the entire 20 to 500 Hz band, averaging out around 12 percent between 20 and 100Hz. The single ≈200 Hz feature at 1 volt becomes two distinct peaks near ≈200 Hz and ≈300 Hz, both in roughly the mid 20 percent range. The global rise in THD and the stronger H3 distortion at the very bottom are consistent with this sample reaching its 17 percent Le limit at 11.08 mm one way before the BL and CMS limits, while the narrow BL shelf and small low excursion asymmetry line up with the persistent H2 distortion seen through much of the passband. The 200 Hz peak growth and the added 300 Hz peak at high level could stem from a higher level mechanical or motor related mode, such as a suspension or rocking behavior that is only excited at this stroke, but the exact mechanism cannot be confirmed from these measurements alone.

What this means in practice

In this sample and under these test conditions, the high level sweep shows very elevated distortion, averaging around 12 percent THD from 20 to 100 Hz with dominant H2 distortion through most of 30 to 80 Hz and stronger H3 distortion toward the very bottom. With the 17 percent Le limit at 11.08 mm one way occurring before the BL and CMS limits, inductance behavior is seemingly what effectively caps clean low frequency output on this unit for LSI parameters. The same high level run also produces strong distortion peaks around 200 Hz and 300 Hz. Those midbass artifacts are likely tied to some higher level mechanical or motor related mode that only shows at this stroke, but the exact mechanism cannot be confirmed from these measurements alone. Overall, this seems to be a very high distortion subwoofer in this test.

Motor & suspension linearity - LSI measurements

Method recap: Klippel LSI large-signal identification for this unit, cold and used for enclosure computations. Standard thresholds in this project are BL 70 percent, CMS 50 percent, and a 17 percent inductance variance criterion. Commentary below ties the large-signal behavior to the acoustic results.

Bl(x)

Bl(x) shows how much motor force a speaker produces as the voice coil moves, B is magnetic field strength and L is the wire length in that field. A high, wide, symmetrical BL curve means linear control and low distortion, a steep or uneven drop means earlier output limits and rising distortion, which is why BL(x) is often the most telling single Klippel LSI indicator of real performance.

Bl(x) window and shape

BL 70 percent one‑way limit is 17.46 mm. The BL curve exhibits a narrow peak shelf, consistent with the test engineer’s note that the coil height is not ideally sized to the split‑gap XBL2 motor topology. A narrow shelf concentrates motor force and, when asymmetry is present, can elevate even‑order content.

Bl(x) symmetry

Near‑limit symmetry is close to centered; the symmetry point at xprot limit is ≈0.49 mm. Small low‑excursion asymmetry is present and is about 2mm, which can contribute to H2 distortion, and may be a contributing factor to some of the even‑order distortion observed in the TRF results.

Cms(x)

Cms(x) is suspension compliance versus displacement, the inverse of stiffness. When the curve is broad and symmetrical, motion is linear and distortion stays low. Early roll off or offset indicates progressive stiffening or mis-centering, which adds mechanical distortion and caps clean excursion.

Cms(x) window and shape

CMS 50 percent occurs at 21.50 mm one way. The compliance curve is broad with gentle roll‑off and good flatness through the mid‑stroke, which aligns with the comment of “good CMS flatness and symmetry.”

Cms(x) symmetry

Centering is good over the main operating region, with the asymmetry indicator showing a modest trend only at low amplitude (Akms ≈ −18.46%). This aligns with the relatively controlled mechanical contribution to even‑order distortion at higher stroke. Note: Asymmetry on suspension was unable to be resolved at lower stroke levels on this sample. As you see, the red line is only from 9mm and up.

Inductance - Le(x) and Le(i)

Le(x) and Le(i) measure how a subwoofer’s voice coil inductance changes with position and current. These curves show how stable the motor’s magnetic field is under real movement and drive conditions. When inductance varies heavily, it causes distortion, uneven response, and a loss of upper-band clarity, which is why Le(x) and Le(i) are critical for evaluating how clean and consistent a motor’s behavior really is.

Level and shape

Le at rest is pretty high, at 2.17 mH. The 17 percent Le variance criterion is crossed at 11.08 mm one way, occurring before BL or CMS and thus setting the practical clean one‑way limit on this sample. Le(x) shows a noticeable position dependence, which aligns with the rise in H3 distortion at the very bottom as drive increases.

Current dependence

Le(i) shows a modest upward drift with current, indicating low to moderate additional modulation under drive.

Qts(x)

Qts(x) is the driver’s total damping versus excursion, combining electrical and mechanical losses. Stable, symmetrical Qts(x) means consistent control, while large variation or asymmetry signals uneven damping that can shift response, raise distortion, and cause compression.

Qts stability

Qts near center is about 0.45 cold and about 0.52 warm. As expected, it rises with stroke, especially at larger excursions telling us that diminishing damping as excursion increases, which is consistent with higher distortion toward the lowest frequencies at high drive. Coin in vs coil out QTS is relatively symmetrical.

LSI takeaway

The earliest limiting mechanism on this sample is inductance, with the 17 percent variance threshold at 11.08 mm one way. The BL shelf is narrow with a small near‑limit offset of about 0.49 mm; low‑excursion asymmetry contributes to H2 distortion where present. The CMS window is broad with the 50 percent point at 21.50 mm and good symmetry, so suspension headroom is favorable. Inductance is pretty high and its swing is significant relative to stroke and Le(i) has a modest current dependence, which tracks with the increase in H3 distortion at the very bottom. Qts rises with excursion, indicating reduced control and some compression tendency at higher drive.

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 1.25 ft³ sealed (largest in the range) nets a QTC of 0.667 on this sample.

Sealed volume required for 0.707 QTC on this sample: 1.00 ft³.

Applicable for infinite baffle? Not recommended; Qts is ≈0.45 cold (≈0.52 warm) and the earliest limit is inductance at 11.08 mm one way, which together are not ideal for IB use.

T/S parameters