Subwoofer Rolloff Test

Subwoofer Rolloff Test

Your subwoofer's rolloff frequency (the point at which output begins to fall measurably) is one of its most practically useful specifications. Manufacturer figures are measured in anechoic conditions and quote the -3 dB point, but in-room extension at your listening position can differ substantially depending on room size, placement, and whether the subwoofer is sealed or ported. Running a frequency sweep in your actual listening room gives you direct information about how the subwoofer performs where you sit.

Sealed subwoofers roll off at 12 dB per octave below their tuning frequency: a gradual, gentle slope that many listeners find more natural for music reproduction.¹ Ported subwoofers roll off at 24 dB per octave below port tuning, producing more output just above the tuning point but a sharper drop below it.² The difference is audible in a sweep, and understanding it helps you set bass management crossovers more accurately.

Setting up the rolloff test

Set the sweep preset to Subwoofer (20–200 Hz) and switch to Manual mode. Disable any EQ, bass management, or room correction software on your receiver or processor before testing: you want to hear the subwoofer's native response, not a corrected version of it. If your subwoofer has a crossover control knob, set it to its maximum value or bypass it if possible so the sweep signal passes through without additional low-pass filtering that would mask the true rolloff point. The sweep tests the subwoofer in isolation, so the input signal should contain the full low-frequency range without additional filtering from your receiver. Set your subwoofer volume to a moderate listening level before starting: too quiet and you will miss the rolloff entirely, too loud and room modes will dominate the result at specific frequencies.

Identifying the -3 dB point

Start the sweep at 80 Hz and descend manually toward 20 Hz at a slow, steady pace. As you move through 60–50 Hz, the output should remain strong and full. Below 40 Hz on a sealed sub or below port tuning on a ported sub, output begins to decrease noticeably. The -3 dB point (where the tone sounds roughly 70% as loud as it did at 40 Hz) is your practical low-frequency extension limit. Note the frequency displayed in the tool at that point. Continue sweeping downward to find the approximate -6 dB point for a complete picture of the rolloff shape.

Using the result for system setup

Once you know your subwoofer's actual in-room -3 dB extension, you have two practical uses for it. First, you can set your receiver or processor's bass management crossover at or slightly above this point to ensure the subwoofer operates in its most controlled frequency range. Second, you have a reference for evaluating bass content in music and film: content below your subwoofer's -3 dB point will be underrepresented in your room regardless of what the recording contains. Built-in DSP EQ (if your subwoofer has it) can boost this rolloff region, with the trade-off of increased excursion demand at those frequencies.

Comparing sealed and ported rolloff shapes in the same room

Comparing a sealed and a ported subwoofer's rolloff shape during back-to-back sweeps in the same room reveals the practical difference between the two alignments in your specific acoustic environment. Run the sweep on the first unit from 80 Hz downward to 20 Hz and note the frequency at which output becomes difficult to hear at your listening position. Then run the same sweep on the second unit without changing the room or position. The sealed unit's output decreases gradually below its cutoff frequency at 12 dB per octave; the ported unit produces stronger output at its port tuning frequency but drops sharply below it at 24 dB per octave.

Reading room gain contribution at very low frequencies

Room gain adds several dB to subwoofer output at very low frequencies in smaller rooms, inflating in-room extension measurements beyond what a free-field measurement would show.³ For a sealed subwoofer rated to -3 dB at 30 Hz anechoically, room gain in a typical 30-square-metre room often produces usable output at 22–25 Hz in-room. The rolloff sweep reveals this directly: if the output at 25 Hz sounds audible and full rather than attenuated, room gain is providing meaningful extension beyond the anechoic specification.

Calibrating the volume level before comparing rolloff depths

Before comparing -3 dB points between two subwoofers, confirm you are listening at the same amplifier volume setting for both. A subwoofer with 3 dB more sensitivity than another appears to have a lower rolloff point at the same volume control position because it produces more acoustic output per watt.⁴ Set a reference tone at 80 Hz on both subwoofers and adjust the volume until they sound equally loud before starting the rolloff sweep. This calibration removes sensitivity differences from the comparison and isolates the actual rolloff frequency.

Comparing in-room rolloff against the manufacturer specification

Comparing your in-room rolloff measurement against the manufacturer's published -3 dB point reveals whether room acoustics are extending or restricting your subwoofer's bass output. Manufacturer specifications are measured in anechoic conditions at 1 meter with the subwoofer's controls set flat. Your in-room sweep includes the contributions of room boundaries, room gain at very low frequencies, and the effects of any room mode near the rolloff point.

When your in-room rolloff is deeper than the specification

An in-room -3 dB point that falls lower than the specification means room gain is extending the practical bass response. This is beneficial for music and film but can mislead you about the subwoofer's limits: a sealed subwoofer that sounds full at 22 Hz in a small room may produce much less output in a larger space. If you move the system to a different room, re-run the rolloff sweep to establish the new reference.

When your in-room rolloff is shallower than the specification

If the sweep shows audible rolloff beginning higher than the manufacturer's -3 dB point, the most likely explanation is a room mode cancellation null near the rolloff frequency. A room mode at 35 Hz in a room with a 4.9-meter dimension (343 ÷ 9.8 = 35 Hz) can produce a 4–8 dB dip at the listening position at that frequency, making the subwoofer appear to roll off several Hz higher than it actually does.⁵ Move your listening seat by 40 cm and re-run the sweep: if the apparent rolloff point shifts, a room mode is responsible rather than the subwoofer's actual extension.

Treat the shifted measurement as the real reference for your seat, because the anechoic specification describes the driver, not the room you sit in. If moving the seat restores the low end, the problem was the null and not the subwoofer, so a small reposition of the listening chair may be the cheapest fix available. Only after ruling out room modes should you question the subwoofer's own extension, since the sweep at the seat is what you actually hear during playback.

When to use this

Use this test when setting up a subwoofer for the first time, after changing placement, or when troubleshooting a perceived loss of deep bass. See where a sub's rolloff really ends and compare two subwoofers in the same room position or verify that a room correction system has improved your subwoofer's in-room extension.

Examples

Unsure whether the subwoofer was extending as deep as the spec suggested in the current room position

Confirmed -3 dB at 26 Hz in the room. Room gain from corner placement extended the rolloff 8 Hz below the anechoic spec

Deep bass sounded less impactful after furniture rearrangement that moved the subwoofer

Sweep found a room mode cancellation null at 35 Hz at the new position. Moved the sub 60 cm and the rolloff test confirmed recovery of 4 dB at 35 Hz

REL T/9i Subwoofer Test

REL's T/9i pairs a front-firing 10-inch long-throw woofer with a 10-inch down-firing passive radiator, and it is built for two-channel music as well as home theatre systems.¹ Unlike AV-oriented subwoofers built to maximise bass extension and impact, REL's design philosophy prioritises seamless blending with main speakers through its high-level input (a Neutrik Speakon connector that taps the speaker terminals of your power amplifier directly), giving the subwoofer the same amplifier characteristics and timing as your main speakers. REL rates the T/9i down to 28 Hz at -6 dB in a room.

The blending test is the most diagnostic sweep you can run on the T/9i. Set the subwoofer's crossover control to your main speakers' approximate -3 dB point, then sweep slowly from 40 Hz upward through 200 Hz. The goal is to hear a smooth, uninterrupted increase in frequency without any hump or notch at the handoff between the T/9i and your main speakers.² A hump indicates the sub and mains overlap too broadly; a notch means they do not overlap enough, leaving a gap in the response. Fine-adjust the crossover frequency and phase control while sweeping until the transition is as smooth as possible.

Below 40 Hz, the T/9i's down-firing configuration interacts heavily with the floor material and proximity to room boundaries. Sweeping from 40 Hz downward while moving the subwoofer slightly will reveal how much the floor coupling changes the bass level at each frequency. Hardwood and concrete floors produce more coupling than carpet. At 28–30 Hz, the T/9i is near its -6 dB point; audible output is present but begins to roll off noticeably. Keep volume at a comfortable level during deep testing.

Specifications¹

Testing the T/9i crossover blend with your main speakers

Testing the crossover integration between the T/9i and your main speakers requires both active simultaneously during the sweep. Set your receiver or amplifier to output full-range signal to the main speakers with no high-pass filter on the main outputs, engage the T/9i via its high-level Neutrik input, and set the T/9i's crossover control to approximately match your main speaker's rated -3 dB rolloff point. Sweep from 200 Hz downward to 20 Hz in Manual mode. Through the crossover region (typically 60–120 Hz depending on your main speaker size), the transition should produce a smooth, continuous increase in bass presence without a hump or gap.

Adjusting the T/9i crossover control while the sweep plays

Position yourself at your normal listening seat and run the sweep in a repeating loop near the crossover frequency between 60 Hz and 120 Hz. Turn the T/9i's front-panel crossover control slowly while the sweep plays. When the crossover frequency matches the main speakers' rolloff point, the handoff sounds seamless. Too low a crossover setting creates a gap in the response; too high a setting causes both to contribute at the same frequency, producing an audible bass hump.

Switching phase to find the optimal integration point

After matching the crossover frequency, switch the T/9i's rear-panel phase control between 0° and 180° while the sweep plays at 80 Hz. One phase position produces a fuller tone; the other produces a thinner one. The fuller phase position confirms the subwoofer is adding to the main speakers' output rather than partially cancelling it at the crossover frequency. Use this phase test before finalising the crossover position, because the optimal crossover frequency and phase are interdependent.

Measuring floor coupling effects on T/9i bass output

Below 50 Hz, the T/9i's down-firing passive radiator couples directly with the floor material beneath the subwoofer, and this coupling is a significant variable in its actual in-room performance.³ Set the sweep to Manual mode and hold at 30 Hz. Then move the T/9i laterally in 10 cm increments while the tone plays and listen at your seat. The perceived level changes with each position because floor coupling varies with proximity to room boundaries and with the floor material's acoustic impedance.⁴

How floor material changes the measured rolloff curve

Hardwood and tile floors transmit bass energy into the room through the floor structure, producing more coupling than carpet, which absorbs a portion of the energy before it can radiate back into the room. Run the rolloff sweep from 80 Hz down to 25 Hz with the T/9i on its intended surface and note the frequency at which output becomes difficult to hear at your listening seat. If possible, place a thin rigid board under the T/9i temporarily and repeat the sweep: a hard surface under the subwoofer typically raises perceived bass output by 1–3 dB at the deepest frequencies.

Using the coupling comparison to choose the final placement

The comparison between the original floor coupling result and the board-enhanced result reveals how much of the T/9i's low-frequency performance depends on the floor interface. If the improvement with the board is consistent and audible, a permanently placed floor-coupling board improves in-room bass output without repositioning the subwoofer. If the improvement is minimal, the floor surface is already transmitting bass energy effectively and the placement is optimised for its current floor type.

Run the board comparison before committing to a permanent position, because the result predicts whether placement alone will settle the low end. If the board lifts the deepest frequencies and you would rather not add hardware, moving the T/9i toward a boundary instead can achieve a similar gain through natural room coupling.⁵ The aim is a placement where the rolloff reads evenly at your seat without extra aids, so measure floor coupling under a down-firing sub before committing to a fixed spot.

SVS PB-2000 Pro Subwoofer Test

With the SVS PB-2000 Pro, a 12-inch aluminum cone driver and three flared cylindrical ports handle ported bass extension in the low-20s Hz range.¹ Ported subwoofers use port tuning to extend low-frequency output beyond what the driver alone can achieve: near the port tuning frequency, the port and driver combine their output, producing higher SPL than either could generate alone. Below the port tuning frequency, output drops rapidly and driver excursion rises sharply because the port no longer controls cone motion. The PB-2000 Pro is rated to 17 Hz at -3 dB.

Port noise is the critical test for this subwoofer. At high playback levels near port tuning (approximately 20–30 Hz), the air velocity through the three port tubes can produce turbulent noise: a chuffing, whooshing, or coarse texture layered over the clean bass tone.² SVS designs the triple-port arrangement to minimise this, but at maximum SPL it can still occur. To test for it, sweep from 40 Hz downward at your highest normal listening volume and stop to listen at 20–25 Hz with your ear near each port opening individually. Any port producing audible noise while the other two remain clean indicates asymmetric port loading or a partial blockage.

Below the port tuning frequency, driver excursion rises rapidly; this is the most dangerous operating range for a ported subwoofer. The PB-2000 Pro includes a subsonic filter in the DSP to protect the driver from overexcursion. Confirm this filter is enabled via the SVS app or rear panel before sweeping below 20 Hz at any significant volume.

Specifications¹

Comparing port noise across all three port openings

Comparing the airflow noise from each of the three port tubes on the PB-2000 Pro reveals whether the ports are loading symmetrically or whether one tube is producing disproportionate turbulence. Set the sweep to Manual mode, descend to 22 Hz, and hold the tone at your highest normal listening volume. Position your ear within 5 cm of the first port tube opening and listen for 10 seconds. Move to the second tube and repeat, then the third. All three ports should produce the same character of air movement at the current SPL level.

Diagnosing an asymmetric port as an obstruction or manufacturing issue

If one port tube is noisier than the other two at the same playback level, the most likely explanation is a partial obstruction inside that tube. Factory packing material occasionally enters a port tube during shipping, and small objects can partially block one opening over time. Shine a light into the noisier port tube with the subwoofer powered off: if you see material inside the tube beyond the first few centimetres, it requires removal before the next use. SVS technical support can confirm whether the tube can be cleared without opening the enclosure.

Verifying the subsonic filter before deep bass testing

Before running any sweep below 20 Hz at any volume level, confirm the PB-2000 Pro's subsonic filter is active.³ Below port tuning, the port no longer controls cone motion, and driver excursion rises rapidly.⁴ The SVS Sledge amplifier's subsonic filter limits signal below its cutoff frequency, protecting the 12-inch aluminum cone from the range where the cabinet provides no loading at all.⁵ A disabled subsonic filter during deep low-frequency testing is the most common cause of driver damage on ported subwoofers.

Confirming the filter is active through the SVS app

Open the SVS app, navigate to the parametric EQ section, and locate the subsonic filter toggle. The factory default has it enabled, but it can be inadvertently disabled during EQ adjustments. Confirm the filter is active and note the cutoff frequency. SVS typically sets it near 16–18 Hz for the PB-2000 Pro. With the filter confirmed, sweep downward from 40 Hz at a moderate volume and listen for the gradual output reduction that begins as the filter takes effect below 18 Hz.

What correct subsonic filter behavior sounds like on the sweep

With the filter active, sweeping below 18 Hz produces a smooth output reduction with no sudden volume drop or mechanical noise. If you hear mechanical noise below 20 Hz before the tone becomes inaudible, the driver is receiving more excursion than the filter is blocking, indicating the filter frequency may need adjusting upward by 2–3 Hz via the SVS app.

Always arm the subsonic filter before the bass drops and re-enable it before any deep sweep if you disabled it during EQ work, because the ported driver has no other protection below tuning. Treat a 2 to 3 Hz upward adjustment as a tuning step rather than a fix, since the deeper cause is excess excursion the cabinet can no longer control. If raising the cutoff still leaves mechanical noise, the driver may already be near its travel limit and the volume should come down rather than the filter moving further.

SVS SB-3000 Subwoofer Test

The SB-3000's defining diagnostic is its sealed rolloff curve.¹ Inside the sealed enclosure, a 13-inch driver and 800-watt RMS amplifier run on SVS's Sledge DSP platform; sealed subwoofers roll off more gradually than ported designs, typically 12 dB per octave below the cutoff frequency, producing a more natural, articulate bass character but with less maximum output at the lowest frequencies compared to an equivalently sized ported design.² The SB-3000 is rated to 18 Hz at -3 dB, placing it at the infrasound boundary.

The rolloff test is the defining sweep test for the SB-3000. Starting from 80 Hz in Manual mode, sweep slowly downward. At 40 Hz, output is full and clean. From 30 Hz downward, the sealed rolloff begins: the tone grows progressively quieter in a smooth, gradual slope rather than the sharper transition you hear from a ported subwoofer. By 20 Hz, you are near the -3 dB point. Below 16 Hz, audible output drops significantly and the 13-inch driver is moving air you feel more than hear. Keep volume moderate for this entire test; the SB-3000's amplifier will push the driver hard near its extension limit.

The sealed enclosure has no port and therefore no port noise issues. What to listen for instead is any mechanical noise from the driver itself at deep frequencies: a rhythmic ticking or scraping at very low frequencies indicates voice coil rubbing, which means the driver has been overextended at some point. A subtle clicking at 15–20 Hz on a new unit is the spider tensioning, which is normal on first use. Persistent scraping or grinding is not.

Specifications¹

Characterising the SB-3000 sealed rolloff below 30 Hz

Because the SB-3000 uses a sealed enclosure, its rolloff shape below the rated extension frequency differs fundamentally from ported subwoofers. A sealed rolloff at 12 dB per octave sounds gradual during the sweep: as you descend from 40 Hz toward 20 Hz, the tone grows quieter in a smooth, even slope without the sudden sharp drop that characterises ported enclosures below their port tuning frequency. Sweep from 50 Hz downward to 18 Hz in Manual mode at your normal listening volume and observe how the perceived level decreases continuously without a sharp transition point.³

Using rolloff shape to optimise the crossover setting

The gradual sealed rolloff means the SB-3000 can reinforce content slightly below the crossover setting without a cliff edge in the bass response. Room gain from nearby boundaries often extends the usable range a few Hz lower than the anechoic specification, particularly in smaller rooms where room gain below 40 Hz is substantial.⁴ Note the frequency at which the tone becomes difficult to hear clearly at your normal volume. Set your receiver or processor bass management crossover approximately 15 Hz above this point. For the SB-3000, this typically places the crossover between 50 and 80 Hz depending on room size and placement.

Comparing consecutive runs to detect driver instability

Comparing two consecutive sweep runs at the same volume level reveals whether the SB-3000's driver behavior is consistent or whether mechanical changes are occurring during operation.⁵ Run a complete sweep from 80 Hz to 18 Hz, then immediately run the same sweep again without adjusting any setting. The result should be identical between the two passes in terms of the frequency where output becomes difficult to hear and the character of the tone throughout the sweep range.

Identifying normal spider settling versus a persistent problem

A small difference between run one and run two in the deepest bass range (below 25 Hz) is often normal spider settling on a new or recently rested subwoofer. The spider stiffens slightly during extended rest and relaxes with use, shifting the effective resonant frequency by a few Hz. This produces a minor change in the lowest audible frequency between the first and second run. It typically disappears after 5 to 10 minutes of operation.

How voice coil contact produces a distinctly different pattern

Voice coil contact with the magnet assembly produces a consistent rhythmic scraping or grinding sound that is present on both sweep runs and worsens or maintains with continued use rather than fading. A scraping sound that is consistent across all runs and does not decrease after 10 minutes of operation requires service, as it indicates the voice coil former is contacting the magnet assembly at some point in its travel.

Run the comparison sweep whenever you suspect mechanical noise, because a one-off sound during a single pass can be misleading. If the scraping only appears on the first run and then fades, you are almost certainly hearing spider settling rather than a contact fault. Reserve service action for noise that survives repeated runs and several minutes of operation, since that pattern is what distinguishes a healthy driver from one with a voice coil that has left its centred travel path; catch voice-coil rub on a sealed enclosure by comparing two sweeps instead of trusting a single pass.