Passive Radiators Explained: Parameters, Tuning and Speaker Design

Sep 25, 2026 | 0 comments posted by Vincent Zhang

PUBLISHED BY IWISTAO · Loudspeaker Design

How moving mass, suspension and displacement shape bass—and how to choose a radiator for the whole enclosure.

A passive radiator can make low bass practical when a suitable port would be too long for the cabinet. Its success depends on the complete woofer–enclosure system: diaphragm mass, suspension, displacement capacity and box volume all matter. This guide explains the specifications and a workable design process.^{[1], [2]}

1. What a passive radiator does

A passive radiator (PR), sometimes called a drone cone, is an unpowered diaphragm driven by pressure inside the enclosure. A conventional PR has no driven voice coil or magnetic motor. Its mass and suspension interact with the enclosed air to create a resonant bass system related to bass reflex.^{[1], [2]}

It adds no electrical power. It offers a different way to use the active woofer’s rear radiation, especially in compact speakers and subwoofers. An airtight PR enclosure remains a resonant system; it is not acoustically equivalent to a conventional sealed box.^{[1], [3]}

Near tuning, the PR typically supplies much of the bass output while the active cone’s excursion falls. This balance changes with frequency, so the two diaphragms should not be assumed to move in phase throughout the bass range.^[9]

This is useful in portable speakers, soundbars and shallow cabinets where a sufficiently large, low-tuned port is difficult to accommodate. The benefit is packaging flexibility: the PR still needs a suitable enclosure volume and room for its full movement.^{[8], [13]}

Figure 1. Pressure couples the active driver to the passive radiator. Original schematic based on the lumped-parameter description in Reference 2.

2. The four core parameters

Fs: free-air resonance

Fs describes the radiator outside the enclosure, under stated measurement conditions. It is different from the installed system’s tuning frequency, Fb. A fixed rule such as “PR Fs must be 0.7–0.9 times woofer Fs” cannot establish compatibility. Model the radiator, driver and enclosure together.^{[2], [6]}

Mms: effective moving mass

Mms includes the effective moving assembly and air loading, rather than the cone alone. Check whether the published value includes removable weights. Increasing mass generally lowers resonance; it does not guarantee a lower useful cutoff or greater output. Dayton explicitly notes that adding mass also changes Qms.^{[7], [8]}

A port uses oscillating air as its moving mass; a PR uses its diaphragm assembly. On adjustable models, a rear threaded post accepts tuning weights. Adding weight increases total moving mass, while removing optional weights raises resonance if compliance is unchanged. Mass is a convenient adjustment after construction, but it is not the only design variable.^{[4], [10], [14]}

Cms: suspension compliance

Higher Cms means a softer suspension. For an ideal linear mass–spring model:

Fs = 1 / [2π √(Mms × Cms)]

Use kilograms and metres per newton. At a fixed Fs, a higher mass requires a proportionally lower compliance. In the cabinet, air stiffness also contributes; the free-air equation alone cannot give Fb.^{[2], [6]}

Cms describes the complete effective suspension, including the surround and any spider, not just how soft the surround feels. Stiffness can change with excursion, so the small-signal value does not describe the entire operating range.^[11]

Xmax: usable linear travel

Xmax normally describes one-way linear excursion. Xmech describes a mechanical travel limit, which is not a promise of linear operation. For example, SB Acoustics specifies ±17 mm Xmech for the SB29NRX2-00; do not silently use that number as Xmax.^[5]

Insufficient travel can make the PR the output bottleneck. Suspension nonlinearity can produce distortion before a mechanical limit is reached; audible slapping or contact requires reducing level and inspecting clearance. Check the PR and active driver separately across the intended frequency range.^{[9], [11]}

3. Size, displacement and construction

Sd and displacement capacity

Sd is the effective radiating area, not the outer frame area. Nominal sizes such as 6.5 or 8 inches describe a product category, not a complete acoustic specification. Use the published Sd rather than calculating area from the mounting flange diameter.^{[4], [5]}

Compare volume displacement, not nominal diameter or Xmax separately. With compatible one-way linear-travel definitions:

Vd = Sd × Xmax
Total PR Vd = Σ(Sd × Xmax)

Dayton recommends total PR displacement of at least twice the active driver displacement as a general starting guideline. This is a screening tool, not a guaranteed design margin at every frequency or input level.^[4]

Figure 2. The larger single radiator misses the illustrative 2× displacement target; the pair clears it. These are invented calculation inputs, not product specifications or measured output. Guideline: Reference 4.

In the example, a woofer with Sd = 130 cm² and Xmax = 5 mm displaces 65 cm³. A PR with Sd = 200 cm² and Xmax = 6 mm provides 120 cm³—below the 130 cm³ screening target despite exceeding both individual woofer specifications. Two 130 cm² PRs with 6 mm travel provide 156 cm³. Their mass and tuning still need calculation.

From Vd = Sd × X, a smaller area requires more travel for the same displaced volume. The issue is displacement headroom, not that cabinet pressure simply “cannot move” a small diaphragm. One larger PR or several smaller PRs can be viable; an “8-inch PR for a 6.5-inch woofer” pairing remains a candidate to evaluate, not an automatic match.

Diaphragm materials

Paper, polypropylene, aluminum and carbon-fiber designs are available. SB Acoustics lists paper, polypropylene and aluminum PRs; Dayton lists a carbon-fiber model. Material names identify construction, but do not establish a universal ranking of warmth, clarity or bass quality.^{[12], [13]}

Selection checks: compare the finished diaphragm’s mass, stiffness, measured resonances and suitability for the intended environment. Paper coating, polymer formulation, metal thickness and composite construction should be evaluated for the specific part. Do not infer that polypropylene cannot resonate, or that a metal cone guarantees lower distortion.

Surrounds and suspension

The surround supports diaphragm movement; together with any spider it contributes to suspension behavior. Rubber surrounds appear in both the SB29NRX2-00 and Dayton DSA175-PR examples. Geometry and material behavior affect compliance and its variation with movement, so “rubber” alone does not prove linearity.^{[5], [7], [11]}

What to check: for foam, rubber or coated-fabric suspension parts, request compliance, excursion and durability information for that exact design. Inspect used parts for cracks, hardening, permanent sag and loose bonds. A material label is not a lifetime, fatigue or power-handling specification.

Dimensions and installation

Before cutting the baffle, check the outer frame, cutout diameter, screw pattern, mounting depth and gasket surface. Allow clearance for both directions of travel, including added weights behind the cone and a grille in front. Use the actual dimensional drawing: nominal diameter cannot confirm a physical fit.^{[5], [8]}

Check airtight sealing and account for internal hardware when calculating net volume. A shallow enclosure saves depth only if the radiator, weight stack and required travel still fit.

4. What Qms does—and does not—tell you

Qms describes mechanical damping relative to stored energy. A higher value indicates lower relative mechanical loss; it is not a direct rating of bass quality. A conventional unpowered radiator has no motor-related electrical Qes. The woofer’s electrical damping and enclosure losses still influence the complete system.^[6]

There is no universal “quality range” of Qms = 2–5. SB Acoustics lists Qms = 7.3 for its SB29NRX2-00, measured on broken-in units in the Rev. 0 datasheet dated January 21, 2020. This is a counterexample to that proposed limit, not a guarantee of a good match in any cabinet.^[5]

Too little or too much damping?

In an isolated linear resonator, lower relative damping gives a sharper resonance, while greater damping reduces its peak. In a loudspeaker, this does not translate directly into “high Qms means boomy” or “low Qms means no bass.” The driver, enclosure, filtering and listening environment also matter.^[6]

Update the model when changing weights: under the constant-compliance and constant-loss assumptions of SB Acoustics’ technical note, added mass lowers free-air resonance and raises mechanical Q. Treat mass and Qms as related parameters rather than independent tuning knobs.^[14]

5. Troubleshooting bass problems

The checks below are diagnostic suggestions, not one-to-one fault rules. Compare the measured system response and displacement with the model before assigning a cause.^{[6], [9]}

Symptom	Parameters or causes to investigate	First checks
Boom or lingering bass	System tuning, losses, EQ and room resonances; not PR Qms alone	Check response and tuning, then move the speaker or microphone and repeat.
Slapping or distortion at high level	PR or woofer excursion, suspension nonlinearity, contact or loose hardware	Reduce level. Compare both excursion curves with their limits and inspect weights, fasteners and clearance.
Weak or shallow bass	Mass and net volume giving unsuitable Fb, insufficient displacement, leaks, filtering or room cancellation	Verify mass, seals, volume and settings before adding more weight.
Buzzing or unwanted midrange	Loose parts, panels, diaphragm modes or internal acoustic leakage	Locate the source at low level and measure; do not diagnose cone rigidity from listening alone.

6. Passive radiator versus bass-reflex port

Both approaches use resonance to shape bass output. A PR avoids airflow through a port, but it can still produce mechanical noise and distortion. Neither arrangement is inherently superior in every enclosure.^{[1], [3], [9]}

Design issue	Passive radiator	Port
Tuning adjustment	Moving mass; also area, suspension and box volume	Effective length, area and box volume
Output limitation	Excursion and suspension nonlinearity	Air velocity, turbulence and compression
Cabinet demands	Baffle area and moving-part clearance	Space for a suitable duct
Practical tradeoff	Additional diaphragm, suspension and tuning hardware	Simple construction when a suitable port fits

A port is adjustable during development; it is not inherently “fixed.” With PRs, heavy moving assemblies can shake a light cabinet. Matched radiators on opposing faces can reduce reaction forces. Follow the manufacturer’s mounting guidance, particularly for upward- or downward-facing installations.^[3]

7. A practical selection and tuning process

Set the target. Define bass extension, required level, cabinet size and available amplifier voltage.
Collect parameters. Obtain the woofer’s T/S data and the PR’s mass, compliance, losses, area and documented excursion limits.
Calculate net volume. Subtract the space occupied by drivers, bracing and other internal hardware.
Screen displacement. Compare total PR Vd with total active-driver Vd, then model the actual demand.
Simulate and tune. Include each PR, enclosure losses, EQ and protective high-pass filtering; inspect both active and passive excursion over frequency.
Build and verify. Measure impedance and acoustic response, adjust securely mounted mass, and test progressively at the intended operating level.

This is a recommended workflow based on the parameter and system-simulation methods in References 2, 6 and 9. Fb alone is insufficient: the response, displacement and electrical load must all be acceptable.

A simplified mass-tuning example

For one PR, a lossless linear estimate combines its suspension compliance with box air stiffness:

Ceff = Cms / (1 + Vas / Vb)
Fb ≈ 1 / [2π √(Mtotal × Ceff)]

Here Vas belongs to the PR, Vb is net enclosure volume, and Mtotal includes added mass. Vas and Vb must use the same volume units. Use SI units for mass and compliance.^[10]

For illustrative inputs of Cms = 1.0 mm/N, Vas = 20 L, Vb = 10 L and Mtotal = 100 g, Ceff is 0.333 mm/N and estimated Fb is 27.6 Hz. Increasing total mass to 150 g lowers this estimate to 22.5 Hz. These are calculated resonances, not measured −3 dB cutoff frequencies or an optimized speaker design.

The estimate omits losses, suspension nonlinearity and the complete driver response. Adding a second PR changes the calculation; do not reuse the single-radiator weight unchanged. Accuton’s identical-pair method uses half the shared box volume in each radiator’s calculation.^[10]

Adjusting weights in practice

For a PR with manufacturer-provided mass adjustment, use this practical sequence:

Record the starting weight arrangement and identify which removable hardware is included in the quoted moving mass.
Calculate a candidate added mass; use the designated attachment point and stay within the manufacturer’s hardware and loading limits.
Measure at low level, change mass in measured increments, then recheck tuning and acoustic response after each change.
For identical paired PRs, keep the intended mass configuration consistent and verify their behavior.
Secure the final weights and verify clearance, excursion and noise at the intended operating level.

This procedure combines the adjustable-weight construction in Reference 4 with the mass changes in Reference 14. Box volume remains a design input: good parameter matching cannot make enclosure size irrelevant.

8. Worked example: two 3-inch drivers and one PR

Example outcome: for the drivers and assumptions below, one Dayton DSA135-PR 5-inch radiator is a sensible candidate for modeling and prototyping. The smaller DSA115-PR narrowly passes the displacement screen, but the 5-inch model gives more displacement capacity. This is a selection example, not a tested construction plan or a universal recommendation for every pair of 3-inch drivers.

Define the drivers and enclosure

Use two Dayton DMA80-4 3-inch full-range drivers. The manufacturer’s PDF lists these values per driver: Sd = 31.2 cm², Xmax = 2.5 mm, Fs = 93.5 Hz, Qts = 0.41 and Vas = 1.31 L. Keep the complete T/S dataset from that same PDF for subsequent simulation.^[15]

Design assumptions: one shared airtight chamber with 2.0 L net air volume, after subtracting drivers, PR, battery, electronics and bracing; an initial Fb target of 65 Hz; both front drivers moving with the same bass polarity. The volume and target are chosen for this calculation, not supplied or optimized by the manufacturer.

Figure 3. Two views of the same proposed cabinet. Both active drivers and the single PR share one air volume. The 2.0 L volume is an example assumption, not an external cabinet dimension.

For this exercise, feed both drivers a common bass signal through suitable signal processing. If independent stereo channels share the chamber, their pressures combine: opposite-polarity bass components can reduce PR excitation. Two isolated chambers cannot both use one ordinary PR mounted into only one chamber. These points follow from the shared-pressure model in Reference 2. Sum bass at the signal/DSP stage; do not connect amplifier outputs together.

Calculate the combined displacement

Convert 2.5 mm to 0.25 cm, then include both active drivers:

Vd, one driver = 31.2 × 0.25 = 7.8 cm³
Vd, two drivers = 2 × 7.8 = 15.6 cm³
Initial PR target = 2 × 15.6 = 31.2 cm³

The last line applies Dayton’s general 2× screening guideline to the combined active displacement. It is not an excursion simulation or a maximum-output prediction.^{[4], [15]}

Compare single-PR candidates

Candidate	Published Sd / Xmax	Calculated Vd	Screening result
DSA115-PR, 4-inch	54.1 cm² / 6 mm	32.46 cm³	Just above 31.2 cm³; about 2.08× the active pair
DSA135-PR, 5-inch	75.4 cm² / 8 mm	60.32 cm³	More displacement capacity; about 3.87× the active pair

Inputs are from the manufacturer’s no-added-mass specification sheets; Vd and ratios are calculated here. These are specifications and a screening comparison, not measured system performance.^{[16], [17]}

I would carry the 5-inch DSA135-PR into the next design stage if it fits. Its additional displacement capacity is useful with one PR serving two active drivers. The 4-inch part is not automatically unsuitable; it needs closer checking at the required level. A higher ratio also does not establish lower distortion or permit unlimited bass boost.

Selected PR: effective area and materials

The selected candidate is the Dayton Audio DSA135-PR, nominally 5 inches. Its published effective radiating area, Sd, is 75.4 cm². The equivalent circular effective diameter is about 98 mm; the nominal 5-inch size is not the effective piston diameter or the cabinet cutout diameter.^[17]

Equivalent effective diameter = √(4 × Sd / π)
= √(4 × 75.4 / π) = 9.80 cm ≈ 98 mm

Combined active area = 2 × 31.2 = 62.4 cm²
PR-to-active area ratio = 75.4 / 62.4 ≈ 1.21

The PR therefore has only about 1.21× the active pair’s area, yet about 3.87× its one-way volume displacement because its specified travel is 8 mm versus 2.5 mm for each active driver. This illustrates why area alone cannot replace an Sd × Xmax check.^{[15], [17]}

Construction: a black anodized aluminum cone, rubber surround and steel frame. A rear M5 threaded hole accepts the screw used to attach additional tuning mass. These are the manufacturer’s construction details for this finished PR; choosing the same materials for a custom radiator would not reproduce its parameters automatically.^[18]

Published specifications without added mass

Use the following baseline from the DSA135-PR specification sheet. “Without added mass” refers to its published starting configuration, not a cone stripped of factory components. Mms is the effective moving mass including air loading.^[17]

Parameter	Baseline value	Meaning in this example
Sd	75.4 cm²	Effective radiating area
Fs	27.9 Hz	Free-air resonance before adding tuning mass
Mms	21.5 g	Effective moving mass, including air loading
Cms	1.51 mm/N	Small-signal suspension compliance
Qms	3.7	Mechanical quality factor
Rms	1.0 kg/s	Mechanical resistance
Vas	12.2 L	Equivalent compliance volume; not a recommended enclosure volume
Xmax	8 mm, one way	Published linear excursion, not 8 mm peak-to-peak
Vd	60.3 cm³	Published rounded displacement; 75.4 × 0.8 = 60.32 cm³

These published parameters are rounded. Keep their source and mass condition together when entering them into simulation software; a slightly different result from recomputing one rounded parameter does not establish a different part specification.

Estimate the tuning mass

For the DSA135-PR, use Mms = 21.5 g, Cms = 1.51 mm/N and Vas = 12.2 L from Reference 17. With the assumed 2.0 L net volume, the one-PR estimate from Section 7 gives:

Ceff = 1.51 / (1 + 12.2 / 2.0)
= 0.2127 mm/N = 0.0002127 m/N

Mtotal = 1 / [(2π × 65)² × Ceff]
≈ 0.02819 kg = 28.19 g

Added mass ≈ 28.19 − 21.5 = 6.69 g

Prototype starting point: approximately 6.7 g of added moving mass, including any extra fastener or washer mass beyond the datasheet baseline. With the same assumptions, no extra mass gives an estimated tuning of 74.4 Hz. Both results use the simplified lossless model; measure actual tuning before finalizing the weight.

Use the full shared 2.0 L in this calculation because there is one PR. Do not halve the box volume merely because there are two active drivers. The active pair must still be represented together in the complete system model.

Parameters after adding mass

Adding approximately 6.7 g changes more than Mms. In the ideal small-signal model, with suspension compliance and mechanical resistance held constant, free-air resonance falls and mechanical Q rises. Apply the mass-scaling equations to the published baseline Fs and Qms:^[14]

Mass factor r = √(Mtotal / Mms, baseline)
= √(28.19 / 21.5) ≈ 1.145

Fs, new = 27.9 / r ≈ 24.4 Hz
Qms, new = 3.7 × r ≈ 4.24

Quantity	Example result	Status
Additional moving mass	≈ 6.7 g	Calculated prototype starting point
Total effective moving mass	≈ 28.2 g	Baseline plus additional moving mass
Free-air Fs after mass adjustment	≈ 24.4 Hz	Calculated with unchanged Cms
Qms after mass adjustment	≈ 4.24	Calculated with unchanged Cms and Rms
Installed tuning Fb	65 Hz target	Simplified estimate for the assumed 2.0 L net chamber

Do not confuse the 24.4 Hz free-air estimate with the 65 Hz installed tuning target. Enclosed air adds stiffness. These adjusted numbers are calculations, not new manufacturer specifications or measurements of a completed speaker. The calculation holds Cms and Rms constant and does not establish a higher Xmax or output rating. Confirm the final weight, clearance and response on the prototype.

Check fit, drive level and protection

Check the enclosure drawing. Confirm the 5-inch candidate’s frame, cutout and depth against its current drawing and the actual part. Reserve full front/rear travel and weight-stack clearance; avoid interference with the battery and electronics.
Model both drivers and the PR. For a two-channel amplifier, use the intended voltage at each driver and their coherent bass drive. Do not substitute one driver, or double Xmax to represent two drivers.
Set protection from excursion. Sweep the intended bass band and frequencies below tuning, including any EQ. Check each active driver against its 2.5 mm Xmax and the candidate PR against its 8 mm Xmax. Derive the high-pass filter and limiter from those results.
Measure the prototype. Confirm tuning, combined acoustic response, distortion and mechanical noise at increasing levels. Verify the final response in normal placement, with the rear PR unobstructed.

Selection summary: two DMA80-4 drivers → 15.6 cm³ combined displacement → at least 31.2 cm³ for the initial PR screen → one DSA135-PR as the larger-margin candidate → approximately 6.7 g added mass for the assumed 2.0 L / 65 Hz case. Final suitability still depends on available drive voltage, required output and prototype verification. A 65 Hz tuning target is not a verified 65 Hz −3 dB cutoff or a claim of usable output at that frequency.

Frequently Asked Questions

Does adding weight always improve bass?

No. It lowers resonance under otherwise unchanged conditions, but a useful response and acceptable excursion depend on the complete system. Check the simulated and measured result.^{[7], [6]}

Can I add a PR to an existing sealed speaker?

Treat it as a new enclosure design. Check the woofer, net volume, radiator and filters together before cutting the cabinet. A PR system is not a conventional sealed alignment.^[3]

Does a PR need a separate amplifier?

No. Internal pressure excites its diaphragm; the amplifier powers the active driver.^[2]

Can a high Qms radiator sound well controlled?

Yes, a value above five does not by itself disqualify a radiator. Mechanical Q is only one system parameter; judge the completed response and operating limits.^{[5], [6]}

Do I still need a high-pass filter?

Check the modeled excursion below the intended passband. A high-pass filter can limit excessive low-frequency drive; select its cutoff and slope for the actual system rather than applying one fixed value.^[6]

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References

Sources checked September 26, 2026. Manufacturer guidance is distinguished from general design rules. Numerical examples and diagrams are illustrative.

Accuton — Passive Radiator. Overview of the resonant enclosure principle.
https://accuton.com/home-audio/drivers/passive-radiator
KLIPPEL — Parameter Measurement of Passive Radiators, AN 57. Revision 1.0, October 29, 2024; parameter model and measurement method.
https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_57_Passive_Radiator.pdf
Acoustic Elegance — Passive Radiator FAQ. Port comparison, displacement and mounting considerations; manufacturer guidance.
https://aespeakers.com/PRFAQ.php
Dayton Audio — RSS390-PR product information. Manufacturer’s general displacement screening guideline.
https://www.daytonaudio.com/product/1427/rss390-pr-15-aluminum-cone-passive-radiator
SB Acoustics — SB29NRX2-00 datasheet. Rev. 0, January 21, 2020; broken-in parameters, Qms and Xmech definitions.
https://sbacoustics.com/wp-content/uploads/2020/10/10in-SB29NRX2-00.pdf
KLIPPEL — LSIM Linear Simulation manual. Separate free-air, enclosure and loss parameters; displacement and filter simulation.
https://docs.klippel.de/db-lab/simulation-auralisation/lsim/lsim.html
Dayton Audio — DSA175-PR product information. Effect of added mass on resonance and mechanical Q.
https://www.daytonaudio.com/product/1590/dsa175-pr-6-1-2-designer-series-aluminum-cone-passive-radiator
Dayton Audio — DMA45-PR specification sheet. Moving mass including air load and the no-added-mass condition.
https://www.daytonaudio.com/images/resources/295-592--dayton-audio-dma45-pr-specification-sheet.pdf
KLIPPEL — SIM Simulation manual. Nonlinear suspension, enclosure and displacement modeling.
https://docs.klippel.de/db-lab/simulation-auralisation/sim2/sim2.html
Accuton — Passive Radiator Technology. Compliance, box volume and added-mass tuning equations.
https://accuton.com/home-audio/drivers/passive-radiator/passive-radiator-technology
KLIPPEL — SPM Suspension Part Measurement manual. Compliance, nonlinear stiffness, suspension materials and displacement.
https://docs.klippel.de/db-lab/scanningvibrometer-partmeasurement/spm/spm.html
SB Acoustics — Passive Radiators. Examples of paper, polypropylene and aluminum diaphragms; category listings, not performance comparisons.
https://sbacoustics.com/product-category/drivers/passive-radiators/
Dayton Audio — Passive Radiators. Compact-enclosure application and carbon-fiber diaphragm example.
https://www.daytonaudio.com/category/125/passive-radiators
SB Acoustics — Adding Mass to a Passive Radiator. Technical note on moving mass, free-air resonance and mechanical Q.
https://sbacoustics.com/wp-content/uploads/2018/05/Adding-mass-to-passive-radiator.pdf
Dayton Audio — DMA80-4 specification sheet. 3-inch full-range driver parameters used in the worked example; undated PDF, retrieved September 26, 2026. Values are from this PDF rather than mixed with rounded product-page values.
https://www.daytonaudio.com/images/resources/295-586--dayton-audio-dma80-4-specification-sheet.pdf
Dayton Audio — DSA115-PR specification sheet. 4-inch candidate Sd and Xmax; parameters without added mass. Undated PDF, retrieved September 26, 2026.
https://www.daytonaudio.com/images/resources/295-544--dayton-audio-dsa115-pr-spec-sheet.pdf
Dayton Audio — DSA135-PR specification sheet. 5-inch candidate displacement and mass/compliance inputs; parameters without added mass. Undated PDF, retrieved September 26, 2026.
https://www.daytonaudio.com/images/resources/295-546--dayton-audio-dsa135-pr-spec-sheet.pdf
Dayton Audio — DSA135-PR product information. Manufacturer description of the aluminum cone, rubber surround, steel frame and M5 threaded mass-attachment hole; checked September 26, 2026.
https://www.daytonaudio.com/product/1589/dsa135-pr-5-designer-series-aluminum-cone-passive-radiator