Speaker Frequency Sweep & Resonance Tester Reference

What Is 20 Hz?

20 Hz is the theoretical lower boundary of human hearing, the lowest frequency that most people can perceive as a distinct pitch under ideal conditions. In practice, hearing sensitivity at 20 Hz varies significantly between individuals, and most adults lose the ability to perceive tones at exactly 20 Hz well before old age affects higher frequencies. What you feel at 20 Hz is as important as what you hear: the physical pressure sensation from a powerful subwoofer is the primary perception mechanism for infrasound at the hearing boundary.¹

What is 20 Hz?

Using 20 Hz in a speaker test

Setting the sweep to exactly 20 Hz and holding there for 10–15 seconds reveals several things at once. First, whether your speaker or subwoofer produces any audible output at this frequency: many consumer subwoofers rated to '20 Hz' are already 6–9 dB down at this point relative to their 40 Hz output. Second, whether the driver is operating within its excursion limits: at 20 Hz, a driver works harder per acoustic watt than at any higher frequency, and large cone movement is visible even at moderate volume. Third, whether any room surfaces or objects resonate sympathetically at infrasonic pressure levels.

20 Hz in audio engineering contexts

In audio production, 20 Hz is the canonical lower limit of music and film content, but very little intentional content actually sits at this exact frequency in most recordings. Pipe organ pedal tones can reach 16–20 Hz on the largest instruments, and some electronic music producers intentionally synthesise sub-20 Hz content for its physical effect. In film and game audio, LFE channels are specified to extend to 20 Hz. Subwoofer benchmarks that quote 20 Hz figures are testing at this exact frequency; in most rooms, room gain and placement produce in-room response curves that make the practical 20 Hz level substantially higher than the anechoic measurement.

Evaluating 20 Hz extension in real room conditions

Because room gain below 30 Hz in a typical listening room can add 3–8 dB of output at the listening position relative to anechoic measurements, the 20 Hz sweep result at your seat reflects both subwoofer capability and room acoustic contribution. Set the sweep to exactly 20 Hz and hold the tone for 15 seconds at your normal listening volume. What you perceive is the in-room level, not the subwoofer's free-field output. A subwoofer rated to -6 dB at 20 Hz anechoically can produce usable output at 20 Hz in a small room because room gain supplements the subwoofer's natural rolloff.

Verifying that perception is not a system artifact

A 20 Hz tone at typical listening levels requires your system to produce genuine infrasonic output. For speaker testing, confirm that you are hearing the tone as a physical pressure sensation or indistinct pitch rather than as an artifact from the amplifier or signal processing chain. Disconnect the speakers and play the 20 Hz tone at your listening level through the system with speakers off: if you still hear output, the amplifier or a connected device is producing a harmonic artifact at a higher frequency rather than the 20 Hz tone itself.

This verification step is especially important when testing near the limits of your system's capability. Some amplifiers exhibit increased harmonic distortion at very low frequencies, and a 20 Hz tone played at high level can generate a 40 Hz or 60 Hz harmonic that is far more audible than the fundamental. If the disconnected-speaker test reveals an artifact, reduce the sweep volume and retest, or verify with a known-good source that your signal chain is clean before concluding your subwoofer cannot reach 20 Hz.

Comparing 20 Hz perception to 40 Hz for a practical reference

Run the sweep at both 20 Hz and 40 Hz at the same volume and compare the perceived level. At 40 Hz, most subwoofers produce near-full output and room gain is present; the tone should be clearly audible and felt as a physical pressure. At 20 Hz, the same subwoofer should produce noticeably reduced output, typically 3–9 dB less than at 40 Hz depending on the design and room. If the two tones sound equally loud, room gain is providing exceptional extension at 20 Hz, which is most common in small rooms with sealed subwoofers in corner placement.⁴

Understanding 20 Hz in film and game audio reproduction

LFE channels in Dolby and DTS film mixes carry content that extends to 20 Hz. The frequency sweep at 20 Hz confirms whether your system can reproduce this content before you evaluate bass quality on film soundtracks. Hold the sweep at 20 Hz and note whether output is audible or only felt. For typical film viewing SPL around 85 dB reference level, a subwoofer rated to 20 Hz should produce a clearly perceptible physical sensation at this frequency during the sweep test, even if it does not sound like a distinct musical pitch.

Why most home theatre systems do not deliver 20 Hz meaningfully

Delivering audible 20 Hz content at reference level requires substantial amplifier output applied to an efficient driver in an appropriate enclosure, with room gain providing additional reinforcement. Most satellite and soundbar systems do not produce usable 20 Hz output because their drivers and enclosures are not designed for this range. The 20 Hz sweep quickly reveals this: if you hear no output and feel no physical sensation at 20 Hz at your normal film listening level, the system's practical bass limit is higher than the specification implies, regardless of what the product description states.⁵

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What Is 40 Hz?

Use 40 Hz as a deep-bass reference point. This critical audio frequency sits at the boundary between sub-bass and bass in most acoustic systems. It is the fundamental frequency of the lowest notes on a 5-string bass guitar, the deep pedal tones of a pipe organ, and the heaviest low-end content in bass music production. For speaker testing, 40 Hz represents the upper edge of the range where most subwoofers reach their rated output level and where full-range speakers begin to roll off significantly.¹

What is 40 Hz?

Testing speakers at 40 Hz

Setting the sweep to 40 Hz and holding it reveals how your speaker handles deep bass fundamentals. Full-range bookshelf speakers rated to 50–60 Hz are already past their -3 dB point at 40 Hz and produce noticeably reduced output compared to their output at 80 Hz: this is normal for speakers of their size. Dedicated subwoofers should produce full output at 40 Hz with no distortion. If a subwoofer sounds strained or produces buzzy distortion at 40 Hz at normal listening levels, its amplifier gain staging may be misconfigured or the driver is near its excursion limit for that volume setting.

40 Hz in practical system setup

Many home theatre and hi-fi processors recommend setting the main speaker low-pass filter to 80 Hz, which routes the main speakers' 40 Hz content to the subwoofer instead. In a 2.1 system without a processor, the main speakers receive the full range including 40 Hz, which can push bookshelf or satellite speakers beyond their design parameters at high playback levels. Testing at 40 Hz specifically (held steady for 10 seconds at your normal playback level) reveals how your speakers handle this demand. Audible distortion at moderate volumes here is a clear indication that a subwoofer or a crossover setting is needed to relieve the main speakers of deep bass duty.

Using 40 Hz to evaluate subwoofer and main speaker handoff

The 40 Hz sweep is one of the most direct checks for whether your bass management crossover is set correctly for your main speakers. A correctly configured crossover routes all 40 Hz content to the subwoofer before it reaches the main speaker inputs. Hold the sweep at 40 Hz with both main speakers and the subwoofer active. Output should come from the subwoofer's position, not from the main speakers. Move close to one main speaker's woofer while the 40 Hz tone plays: any clearly audible output from the main speaker cone at close range means the bass management crossover is not filtering the main speaker input at that frequency.

Testing the crossover effect at 40 Hz with main speakers only

Disconnect or mute the subwoofer and play the 40 Hz sweep at your normal listening level through the main speakers alone. The output level and character reveal what the main speakers contribute at 40 Hz without bass management filtering. A full-range bookshelf speaker rated to 50 Hz at -3 dB should produce noticeably reduced but audible output at 40 Hz. A desktop satellite speaker with a small woofer often produces no audible output at 40 Hz at normal listening levels. This tells you exactly how dependent your system is on the subwoofer for reproducing the bass guitar and kick drum fundamentals that sit at and below 40 Hz.

Understanding 40 Hz in the context of room modes

In a room whose length is between 4 and 5 meters, the first axial mode falls between 34 and 43 Hz, directly in the 40 Hz range. When the sweep produces a dramatically louder tone at 40 Hz than at 35 Hz and 45 Hz at your listening position, a room length mode is the likely cause rather than the subwoofer producing elevated output. Confirm by walking to the rear boundary of the room while holding the tone: at the room boundary, the mode pressure maximum produces the loudest output, and at the room centre along the length axis the pressure minimum reduces the apparent 40 Hz level substantially.⁴

If the 40 Hz tone does not match the calculated length mode, check the width and height dimensions for axial modes near 40 Hz. A room 4.3 meters wide has a first width mode at 40 Hz (343 ÷ 8.6), and a ceiling height of 4.3 meters produces a first height mode at the same frequency. These modes can overlap and reinforce each other, creating a broader and more persistent bass buildup than a single axial mode would produce. Mapping the room dimensions against the 40 Hz sweep result helps distinguish between a speaker or subwoofer issue and a room geometry issue that requires placement adjustment or treatment instead.

Verifying 40 Hz reproduction in studio monitoring contexts

Verifying that a studio monitor system reproduces 40 Hz accurately is a prerequisite for reliable mix decisions in the sub-bass range. Hold the sweep at 40 Hz for 10 seconds at your mixing level and note whether the output sounds full and controlled or thin and attenuated. Studio monitors without a subwoofer typically roll off below 50–60 Hz, which means 40 Hz content in a mix is underrepresented on the monitoring system. Mixing bass guitar and kick drum fundamentals at and below 40 Hz on a monitor that rolls off in this range creates mixes that translate with more low-end weight on full-range consumer playback systems than intended.

Comparing 40 Hz perception across different monitoring references

After noting the character at 40 Hz on your primary studio monitors, run the same sweep on a full-range secondary reference or on a consumer playback device. The secondary reference produces either a different level or a different character at 40 Hz compared to the monitors, quantifying the gap in your monitoring system's low-frequency accuracy. A monitor system that produces accurate 40 Hz output gives you reliable information about the bass content you are adding to the mix; a monitor that rolls off above 40 Hz requires you to rely on experience and consumer reference playback to fill in that information gap before finalising bass decisions.⁵

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What Is 80 Hz?

In home theatre bass management, 80 Hz is the practical handoff point between main speakers and subwoofer. It is the THX Reference and Dolby Atmos recommended crossover frequency: the point at which bass content moves from the main speakers to the subwoofer. Below 80 Hz, bass is non-directional for most listeners, meaning the subwoofer can reproduce it from any position in the room without affecting localisation. 80 Hz appears constantly in speaker and subwoofer specifications as a reference measurement point and system calibration anchor.¹

What is 80 Hz?

Using 80 Hz as a system calibration reference

Setting the sweep to exactly 80 Hz and holding it while adjusting your subwoofer crossover control is the most direct way to find the correct crossover point. With your main speakers playing only content above 80 Hz (via your receiver's bass management) and the subwoofer crossover set at 80 Hz, you should hear a seamless transition: the 80 Hz tone should be equally audible whether the main speakers or subwoofer is producing it. Increasing the subwoofer crossover frequency above 80 Hz produces an audible overlap region; decreasing it below 80 Hz can create a bass gap if your main speakers do not extend cleanly to 80 Hz.

80 Hz in mixing and mastering contexts

In audio production, 80 Hz sits in the upper bass range where kick drum body and bass guitar fundamental content live in most popular music. An 80 Hz boost in a mix adds weight and fullness to the low end; a cut reduces mud and improves low-frequency clarity. Studio monitoring requires accurate reproduction at 80 Hz because it is a musically critical range for most genres, and an uneven response at this frequency leads to poor EQ decisions that translate badly to other playback systems. The frequency sweep at 80 Hz is useful for confirming that studio monitor output is consistent between left and right channels at this reference frequency before beginning a critical listening session. A sustained 80 Hz tone held for 10 seconds also reveals any cabinet resonance or port noise that only appears at this specific frequency under sustained load.⁴

Setting the subwoofer crossover using 80 Hz as a reference tone

Setting the subwoofer crossover frequency by ear using a sustained 80 Hz tone produces a more accurate result than relying on a receiver's default setting. With your receiver or processor's bass management set to 80 Hz for all speakers, hold the sweep at exactly 80 Hz and listen to whether the tone sounds seamless. Increase the subwoofer's own crossover knob from its lowest setting upward while the 80 Hz tone plays. The crossover knob should be set high enough that the subwoofer contributes to the 80 Hz output without being so high that it is also contributing at 120 Hz and above.

A correctly aligned crossover at 80 Hz sounds like a single, coherent tone: you cannot hear whether it is the subwoofer, the main speaker, or both contributing. An incorrectly aligned crossover produces either a thin, hollow quality at 80 Hz if the subwoofer is crossed over too low, or a bloated, reinforced quality if both are contributing simultaneously and in phase. The sustained 80 Hz tone reveals both problems immediately because the effect is continuous and easy to evaluate during a single adjustment pass.

Using 80 Hz to set subwoofer volume level relative to the main speakers

With the subwoofer crossover set and phase confirmed, the 80 Hz tone is the correct reference for setting subwoofer output level relative to the main speakers. Route signal only to the main speakers, note the perceived loudness at 80 Hz, then mute the main speakers and route signal only to the subwoofer. Adjust the subwoofer volume control until the 80 Hz tone matches the loudness you heard from the main speakers. This level match ensures the subwoofer neither overwhelms nor underserves the crossover frequency, producing the most seamless integration at the handoff point.

Understanding why 80 Hz bass is non-directional in most rooms

Because 80 Hz has a wavelength of 4.29 meters, the interaural time difference (the delay between the signal reaching the left ear versus the right ear) at 80 Hz is too small for the auditory system to use for directional detection. The interaural time difference for a 40 cm head width at 80 Hz is approximately 1.17 milliseconds: less than half the 12.5 ms period of the wave itself. This means the ear cannot extract directional information from the phase difference between the two ears at 80 Hz, which is why placing a subwoofer anywhere in the room produces a bass tone that appears to come from the main speakers rather than from the subwoofer location.

The upper boundary of subwoofer localisation

Above approximately 100 Hz, interaural time differences become large enough relative to the wavelength that some listeners can detect the approximate direction of the bass source. A subwoofer crossed over at 120 Hz or higher may be audibly localisable by some listeners in the room. Running the sweep at 80, 90, 100, and 120 Hz while the subwoofer plays at those frequencies with the main speakers silent reveals the frequency at which you personally can identify the subwoofer's position in the room. This personal localisation threshold determines the practical maximum crossover frequency for your system.

The transition from non-directional to localisable bass is not a sharp cutoff but a gradual increase in localisation accuracy with frequency. At 90 Hz, most listeners still cannot reliably point to the subwoofer, but at 120 Hz a clear majority can. Room acoustics also shift the boundary: reflective surfaces near the subwoofer create early reflections that provide additional directional cues, effectively lowering the frequency at which localisation becomes possible. If you can localise the subwoofer at 90 or 100 Hz, try moving it away from walls and corners before concluding that a lower crossover is necessary.

Why 80 Hz remains the standard despite individual variation

80 Hz was chosen as the THX crossover reference because it is below the localisation threshold for most listeners in most room conditions. Individual variation in localisation ability is real, and some listeners can localise a subwoofer contributing at 80 Hz in certain room configurations. The sweep test at 80 Hz, run with only the subwoofer active, lets you confirm whether you can personally localise bass at this frequency in your room before committing to it as your crossover setting.⁵

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What Is 1 kHz?

The 1 kHz sine tone is the shared reference point for speaker sensitivity. When manufacturers rate a speaker at 88 dB SPL or 93 dB SPL, that measurement is taken at 1 kHz, 1 watt, at a distance of 1 meter. This makes 1 kHz the acoustic benchmark against which all other frequencies in a speaker's response are compared. In human hearing, 1 kHz sits near the midpoint of the frequency range where our ears are most sensitive; the peak of the equal-loudness contour falls around 2–4 kHz, with 1 kHz just below the most sensitive region.¹

What is 1 kHz?

Testing speakers at 1 kHz

Running a sine tone at exactly 1 kHz reveals midrange driver clarity and cabinet coloration in the upper midrange. A clean 1 kHz sine tone from a quality speaker sounds smooth and pure: any buzzing, ringing, or roughness added to the tone indicates midrange driver resonances or cabinet coloration in this range. Compare both speakers in a stereo system at 1 kHz: the output levels should be matched closely. A noticeable level difference between channels at 1 kHz indicates a driver sensitivity mismatch, a crossover component fault, or a wiring issue. On a two-way speaker, 1 kHz falls within the woofer's operating range, so a clean result confirms the woofer is behaving linearly well below the crossover point where cone breakup modes typically begin.

1 kHz in studio and broadcast applications

The 1 kHz reference tone is used in audio engineering to align gain levels across signal paths. A 1 kHz sine tone at 0 dBFS fed into a signal chain is the standard reference for setting headroom, input sensitivity, and gain staging. In broadcast, a 1 kHz tone at -18 dBFS or -20 dBFS is transmitted before programme material to allow receiving engineers to align incoming levels. For personal speaker testing, running a sustained 1 kHz tone allows you to match output levels between two speakers by ear or with a simple SPL meter before critical listening. Because 1 kHz sits in the range where human hearing is most sensitive, even small level differences between two speakers are immediately obvious at this frequency, making it the fastest single-point check for channel matching.⁴

Using 1 kHz to calibrate monitoring level for mixing sessions

In professional studio environments, monitoring at a consistent calibrated level produces more reliable mix decisions than listening at whatever volume feels comfortable on a given day. 1 kHz is the reference frequency for this calibration because it represents the most sensitive part of the equal-loudness contour, where a given SPL level produces the strongest perceptual loudness. Set the sweep to exactly 1 kHz and adjust your amplifier volume until the tone reaches 83–85 dB SPL at the listening position using a simple sound level meter or phone-based SPL app. Note the exact volume control position and return to it at the start of every session.

Why consistent calibration frequency matters

At 1 kHz, the relationship between input level and perceived loudness is predictable and well-documented. Equal loudness contours show that human sensitivity at 1 kHz is close to its peak: a 1 kHz tone at 80 dB SPL sounds approximately as loud as a 60 Hz tone at 95 dB SPL. Calibrating at 1 kHz anchors your monitoring level at a frequency where loudness perception is stable. Volume calibration at an off-frequency point such as 10 kHz would give inconsistent results because high-frequency sensitivity varies much more with individual hearing than midrange sensitivity does.

Setting relative levels between main monitors and near-field references

Hold the 1 kHz tone at the calibrated level from your main monitors and note the perceived loudness. Then switch to your near-field reference (a second set of monitors on the desk, for example) and adjust its volume control until the 1 kHz tone from the near-field reference matches the perceived loudness. This creates a consistent relationship between the two monitoring systems so that when you switch references, the primary variable is the speaker's frequency response and room contribution, not a volume level difference that would skew your perception of the mix.⁵

Comparing 1 kHz character between different monitoring systems

Comparing the character of a sustained 1 kHz tone between two different monitor systems at the same calibrated level reveals how differently each system reproduces the upper midrange. Hold the sweep at 1 kHz and listen for 5 seconds on your primary monitors. Note the quality: forward and present, slightly recessed, or tonally coloured? Switch to a secondary reference system and listen to the same 1 kHz tone at the same playback level. The difference in perceived tonal character at 1 kHz between the two systems reflects the difference in their respective frequency response curves at this frequency.

A 1 kHz tone that sounds brighter on one system indicates that system has elevated output in the 800 Hz to 2 kHz range relative to its midrange average. A tone that sounds slightly recessed or muffled relative to the other system indicates a dip in the same range. Because 1 kHz is within the most sensitive hearing range, even a 1–2 dB difference between systems produces a clearly audible tonal character difference. Knowing which monitor system sounds brighter at 1 kHz helps you make mixing decisions that account for that system's voicing rather than translating those characteristics unintentionally into the final mix.

Reading the 1 kHz character as a midrange driver health indicator

On a two-way speaker, 1 kHz falls within the woofer's operating range below the crossover. A 1 kHz tone that sounds rough, buzzy, or coloured rather than pure and clean indicates a midrange driver resonance or cone condition problem in the woofer. A pure, smooth 1 kHz sine tone from a speaker confirms the driver is operating cleanly in its intended range. This is a reliable indicator because 1 kHz is well within the woofer's pistonically linear range on most two-way designs, and any coloration at this frequency is the driver's own response rather than a crossover artifact.

If the 1 kHz tone reveals a coloration that persists across different amplifiers and signal sources, the issue is likely mechanical: a voice coil rubbing against the magnet gap, a deformed cone from previous over-excursion, or a surround that has lost its compliance. These problems are not repairable by crossover adjustment and indicate the driver needs replacement. Running the sweep at 1 kHz periodically over the speaker's lifetime provides a baseline for detecting gradual degradation before it becomes audible on programme material.

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What Is 16 kHz?

By the time you reach 16 kHz, the test is no longer only about speaker output. At this frequency, age-related hearing loss becomes a significant variable: many adults over 40 have measurably reduced sensitivity at 16 kHz compared to younger listeners, making it a practical high-frequency hearing test point. For speaker testing, 16 kHz sits near the upper limit of the frequency range where most dome tweeters maintain full output, making it a useful reference for tweeter health and extension.¹

What is 16 kHz?

Testing tweeter health at 16 kHz

A sine tone at exactly 16 kHz is the most direct test of tweeter function at the upper end of its operating range. Run the sweep to 16 kHz on both speakers and compare output levels between channels: they should be well-matched. Any difference above a few dB at 16 kHz between two nominally identical speakers indicates a tweeter performance discrepancy. Ribbon tweeters (such as those used in Adam Audio monitors) typically maintain output more consistently at 16 kHz than soft domes, which can develop voice coil resonances near their upper frequency limit. Horn-loaded tweeters may show narrower dispersion at 16 kHz than at lower frequencies.³

16 kHz as a personal hearing check

Because age-related hearing loss (presbycusis) affects the high-frequency range first, beginning with 16–20 kHz before progressing down, the 16 kHz tone is commonly used as a self-administered high-frequency hearing check. If you cannot hear the 16 kHz tone at a comfortable volume level on a system you know reproduces it correctly, your high-frequency hearing sensitivity may have declined. This is not a clinical hearing test, and the result is affected by the speaker or headphones used, the listening environment, and individual factors including tinnitus. Treat it as a rough indicator, not a clinical finding. Running the same check at 12 kHz and 14 kHz alongside 16 kHz gives you a more complete picture of where your personal high-frequency sensitivity begins to roll off.⁴

Comparing 16 kHz reproduction between tweeter designs

Comparing a soft dome tweeter, a ribbon tweeter, and a horn-loaded tweeter at exactly 16 kHz during back-to-back sweeps reveals how fundamental design differences affect high-frequency extension. Soft domes (used in most studio monitors at typical price points) often show gradual output reduction approaching 16 kHz, resulting from the increasing stiffness of the dome material and voice coil mass near their mechanical limits. Ribbon tweeters (found in Adam Audio monitors) generally maintain more consistent output at 16 kHz because their very low moving mass extends the usable range without the dome resonance effects that limit soft domes.

Setting listening position correctly for 16 kHz comparison

At 16 kHz, tweeter directivity narrows significantly: the wavelength (2.14 cm) is shorter than most tweeter dome diameters, causing output to concentrate in a narrowing cone directly on-axis. To compare 16 kHz output between two tweeters fairly, sit at tweeter height and centred on-axis with each tweeter during the test. Any deviation more than 15 degrees off-axis at 16 kHz produces a measurable drop in output that could make one tweeter appear to be rolling off when the measurement angle, not the driver, is the variable.

If your listening position is fixed (as with a desktop setup), you can still make fair comparisons by rotating the speaker rather than moving your head. Turn each speaker to face your listening position directly, measure or estimate the on-axis angle, and run the sweep at 16 kHz with both speakers individually oriented for on-axis response. This removes the angle variable and isolates the driver's intrinsic 16 kHz output. For floor-standing speakers, use a laser pointer or smartphone level app taped to the tweeter face to confirm on-axis alignment before each sweep pass.

What a 3 dB difference at 16 kHz means in practice

A 3 dB output difference between two tweeters at 16 kHz represents a meaningful difference in perceived high-frequency air and extension. On well-recorded acoustic music at moderate to high volume, the tweeter with 3 dB more output at 16 kHz produces a more extended, airier quality on cymbal shimmer and vocal sibilance. Knowing which tweeter is producing more output at 16 kHz helps you understand why two otherwise similar-priced speakers sound different on high-resolution content.⁵

Using 16 kHz to check for tweeter protection circuit engagement

Some active monitors and powered speakers include a tweeter protection limiter that reduces output above a certain level to prevent damage. A sudden, non-gradual output reduction at 16 kHz during the sweep that begins only above a specific volume level is a protection circuit engaging rather than natural tweeter rolloff. Natural rolloff is gradual across 10–20 kHz; protection limiting typically has a sharper onset that appears abruptly at a volume threshold.

Distinguishing natural rolloff from protection limiting

Hold the sweep at 16 kHz and increase volume in 1 dB steps. Note whether the apparent output at 16 kHz continues rising proportionally with each step or whether it levels off abruptly at a specific volume position. Natural rolloff means the 16 kHz output is consistently reduced relative to 8 kHz at all volume levels, not that it stops increasing at a specific volume threshold. Protection limiting means the 16 kHz output stops increasing at a specific volume even though the 8 kHz output continues to rise with each 1 dB increment, which identifies the protection circuit.

When protection limiting engagement is a normal design feature

Many studio monitors and active speakers include tweeter protection that engages near 0 dBFS input level to prevent overload on transient peaks. This is a feature, not a fault. Protection engagement during normal mixing levels should not occur. If the 16 kHz protection circuit engages at moderate listening levels during a sine sweep at this volume, the protection threshold is set lower than the speaker's intended operating range, and the manufacturer's technical support can confirm whether this indicates an incorrect setting or a unit requiring service.⁶

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