4 inch SubWoofer 4ohms 20Watts

Key Features

• Moonvoice 4-inch subwoofer / woofer driver

• Approx. 100mm speaker size

• 4Ω nominal impedance

• 20W RMS published power rating

• Ferrite magnet

• Passive speaker design

• Published approximate frequency range of 60Hz–5kHz

• Suitable for compact bass applications

• Suitable for DIY 2.1 speaker systems

• Compatible with suitable 4Ω amplifier boards

Technical Specifications

Understanding the 20W Rating

The speaker is published as:

20W RMS

This does not mean the speaker continuously consumes 20W.

Actual power delivered to the speaker depends on:

• Amplifier output

• Volume

• Audio signal

• Speaker impedance

• Amplifier supply conditions

4Ω Impedance

This speaker presents a nominal:

4Ω load

to the amplifier.

Before connecting it, verify that the amplifier is designed to operate safely with a 4Ω speaker.

Passive Speaker

This speaker does not contain:

• Built-in amplifier

• Bluetooth

• USB player

• Power supply

An external audio amplifier is required.

Frequency Range

The current product specification publishes approximately:

60Hz–5kHz

For dedicated bass applications, the driver should preferably receive a low-pass-filtered audio signal rather than the complete stereo frequency range.

Amplifier Compatibility

The most important electrical requirement is:

Speaker Impedance: 4Ω

Use an amplifier that is designed to operate safely with a 4Ω speaker load.

Recommended System Type

This speaker is particularly suitable for:

2.1 Channel Audio Systems

Typical configuration:

Audio Source

↓

2.1 Amplifier

↓

Left Speaker + Right Speaker + Moonvoice Subwoofer

TPA3116D2 Amplifier Compatibility

The speaker can be used with a suitable TPA3116D2-based subwoofer or 2.1-channel amplifier.

However, many TPA3116D2 boards are capable of substantially more than 20W.

Therefore:

• Start at low volume

• Limit output appropriately

• Avoid excessive cone movement

• Reduce volume if distortion occurs

CA-3316A Compatibility

A mono subwoofer amplifier such as a TPA3116D2-based CA-3316A can be used with this 4Ω speaker when the amplifier output is kept within an appropriate operating level.

The amplifier's maximum rating does not mean that full output should be applied continuously to this 20W speaker.

ZK-TB21 / 2.1 Amplifier Compatibility

A 2.1 amplifier with a dedicated subwoofer output can also be used.

Typical architecture:

Phone / Bluetooth / AUX

↓

2.1 Amplifier

↓

L + R Speakers

4 Inch Moonvoice Subwoofer

Again, control the subwoofer output appropriately because many modern Class-D amplifiers can exceed this speaker's 20W rating.

Low-Pass Filter

For dedicated subwoofer operation, use:

• A 2.1 amplifier with dedicated subwoofer output, or

• A suitable low-pass filter / crossover

This helps keep vocals and higher frequencies out of the dedicated bass channel.

DIY Bluetooth Speaker

Typical system:

Phone

↓

Bluetooth 2.1 Amplifier

↓

Full-Range Left + Right Speakers

Moonvoice 4Ω Subwoofer

Applications

• DIY Bluetooth speakers

• 2.1 desktop speakers

• Multimedia speaker systems

• Compact home-audio projects

• Small bass enclosures

• Electronics projects

• Speaker replacement

• Custom audio prototypes

📦 What's Included

❌ What's Not Included

Unless separately specified, the package does not include:

• Audio Amplifier

• Bluetooth Module

• Power Supply

• Speaker Enclosure

• Crossover / Low-Pass Filter

• Speaker Wire

• Mounting Screws

• Speaker Grill

• Left / Right Full-Range Speakers

• Battery

Important Purchase Note

This product is a:

Passive Subwoofer / Woofer Driver

It requires an external amplifier.

For a basic dedicated bass system:

Audio Source

Amplifier with Subwoofer / LPF Output

Moonvoice 4Ω Subwoofer

For a Complete 2.1 System

A typical 2.1 system requires:

• 1 × Left Speaker

• 1 × Right Speaker

• 1 × Moonvoice Subwoofer

• 1 × Compatible 2.1 Amplifier

• Suitable Power Supply

• Speaker Enclosure(s)

This listing includes:

1 × Moonvoice 4 Inch Subwoofer Speaker only.

📚 Resources

A manufacturer datasheet containing complete electro-acoustic parameters for this exact Moonvoice driver has not been verified.

Therefore, use the published product specifications:

• Brand: Moonvoice

• Size: 4 Inch / approximately 100mm

• Impedance: 4Ω

• Power Rating: 20W RMS

• Magnet: Ferrite

• Published Frequency Range: approximately 60Hz–5kHz

Parameters such as:

• Fs

• Qts

• Qes

• Qms

• Vas

• Xmax

• Sensitivity

should not be assumed without a verified datasheet or measurement.

Getting Started

Step 1 — Select a Compatible Amplifier

Use an amplifier capable of safely driving:

4Ω

Do not select an amplifier solely by its advertised maximum wattage.

Step 2 — Use a Subwoofer Output

For dedicated bass operation, connect the speaker to:

Subwoofer / Mono Bass Output

of a suitable amplifier.

Do not connect it across Left and Right outputs unless the amplifier specifically supports that configuration.

Step 3 — Connect the Speaker

Follow the speaker's polarity markings where provided:

Amplifier + → Speaker +

Amplifier − → Speaker −

Step 4 — Start at Low Volume

Begin with the amplifier volume and bass level low.

Increase gradually while listening for:

• Distortion

• Mechanical rattling

• Excessive cone movement

Step 5 — Use an Enclosure

Install the speaker in a suitable enclosure for finished audio projects.

Enclosure design strongly influences bass performance.

Step 6 — Do Not Guess the Enclosure Volume

Proper enclosure design depends on driver parameters such as:

• Fs

• Vas

• Qts

These parameters have not been verified for this exact Moonvoice driver.

Therefore, an exact “ideal” enclosure volume should not be claimed without measurement or manufacturer data.

Step 7 — Secure the Driver

Mount the speaker firmly to the enclosure.

A suitable gasket can help reduce unwanted air leakage around the mounting surface.

Step 8 — Protect the Cone

Consider using a suitable speaker grill when the driver will be exposed to accidental contact.

🔧 Prototyping and Engineering Tips from RoboGears

1. Match the Amplifier to 4Ω

The speaker's nominal impedance is:

4Ω

The amplifier must support a 4Ω load.

2. Don't Automatically Recommend a 30W–50W Amplifier

The speaker is published as:

20W RMS

A higher-powered amplifier can be used only when its actual output is appropriately controlled.

For beginners, recommending a 30W–50W amplifier without explaining output control can increase the risk of damaging the speaker.

3. Amplifier Wattage Is Not Continuously Forced Into the Speaker

A 50W amplifier does not continuously deliver 50W simply because a 20W speaker is connected.

Actual output depends on:

• Signal

• Volume

• Supply voltage

• Load impedance

However, excessive volume can allow a higher-powered amplifier to exceed the speaker's safe power handling.

4. Use a Low-Pass Filter for Subwoofer Applications

For a dedicated subwoofer channel, use:

LPF / Subwoofer Output

A crossover frequency somewhere in the low-frequency region may be appropriate depending on the satellite speakers and enclosure.

Do not claim that exactly 150Hz is universally optimal.

5. A 4-Inch Driver Has Physical Bass Limitations

A compact 4-inch driver can provide useful bass reinforcement, but it should not be marketed as equivalent to a large 8-inch, 10-inch or 12-inch subwoofer.

Driver size, excursion and enclosure all influence low-frequency output.

6. Enclosure Design Matters

A properly designed enclosure can significantly improve:

• Bass response

• Mechanical control

• Efficiency

• Overall sound quality

7. Don't Calculate an Enclosure Using Speaker Size Alone

Proper enclosure calculations normally require driver parameters such as:

Fs + Vas + Qts

Those values have not been verified for this exact Moonvoice driver.

Therefore, do not give customers a supposedly exact enclosure volume based only on “4 inch.”

8. Sealed vs Ported

Both enclosure approaches can be used experimentally.

Sealed: simpler to construct and tune experimentally.

Ported: can increase output around its tuned region but requires proper enclosure and port tuning.

Do not choose port dimensions arbitrarily.

9. Seal the Mounting Surface

Unwanted air leakage around the speaker mounting flange can reduce predictable enclosure performance and introduce noise.

A suitable gasket can be useful.

10. Avoid Severe Amplifier Clipping

If the amplifier sounds harsh or heavily distorted, reduce volume.

Clipping can increase thermal stress on the speaker.

11. Don't Assume Clipping Is the #1 Cause of Burnt Voice Coils

The current listing says clipping is the “#1 cause.”

Remove that statement.

Speaker damage can result from:

• Excessive continuous power

• Clipping

• Excessive low-frequency excursion

• Incorrect crossover

• Mechanical damage

• Thermal overload

12. Don't Over-Specify Speaker Wire

The current page specifically recommends:

16–18 AWG

For a compact 20W speaker with short internal enclosure wiring, that is unnecessarily prescriptive.

Use appropriately sized speaker wire according to:

• Power

• Cable length

• Installation

13. Never Connect the Speaker Directly to DC

Do not connect the speaker directly to:

• 5V

• 12V

• 24V

• Battery terminals

It requires an audio-amplifier output.

14. TPA3116D2 Requires Output Control

Many TPA3116D2 boards can deliver considerably more power than this 20W speaker can safely handle.

When pairing them:

• Start with low gain/volume

• Avoid excessive bass boost

• Monitor distortion

• Monitor cone movement

15. Test Before Final Assembly

Before closing the enclosure:

• Check speaker polarity

• Check for rattling

• Check amplifier operation

• Test the LPF

• Check mounting clearance

• Check the enclosure for unwanted air leaks

Common Troubleshooting

Weak Bass

Check the enclosure, crossover settings and amplifier output.

Vocals Coming From Subwoofer

Lower the LPF crossover frequency or check the amplifier's subwoofer filter.

Distortion at High Volume

Reduce amplifier output and check for clipping or excessive cone movement.

Rattling

Check mounting screws, enclosure panels and speaker clearance.

Speaker Gets Hot / Smells

Stop playback immediately and reduce amplifier output.

No Sound

Check speaker continuity, amplifier output, wiring and audio source.

Engineering Principle

For a compact woofer:

Correct 4Ω Amplifier + Controlled Power + Suitable LPF + Proper Enclosure

matter more than simply choosing the largest amplifier wattage.

FAQ

1. What is this speaker?

It is a compact Moonvoice 4-inch passive subwoofer / woofer speaker driver.

2. What is the speaker size?

4 Inch

Approximately:

100mm

according to the current specification.

3. What is the impedance?

4Ω

4. What is the power rating?

The current product specification states:

20W RMS

5. Is it a passive speaker?

Yes.

An external audio amplifier is required.

6. Does it have Bluetooth?

No.

Bluetooth functionality must be provided by an external receiver or Bluetooth amplifier.

7. Can I connect it directly to a battery?

No.

The speaker should be connected to an audio amplifier output.

8. Can I connect it directly to 12V?

No.

Do not connect DC power directly across the speaker terminals.

9. Can I connect it directly to 24V?

No.

10. Can I use it with a TPA3116D2 amplifier?

Yes, provided the amplifier supports 4Ω and its output is controlled appropriately.

Many TPA3116D2 boards can produce more power than this speaker's 20W rating.

11. Can I use it with a 20W amplifier?

Yes, provided the amplifier supports a 4Ω load and is operated correctly.

12. Can I use it with a 30W amplifier?

Potentially yes, but the output must be controlled to avoid exceeding the speaker's safe operating capability.

13. Can I use it with a 50W amplifier?

Potentially, but considerable care is required because the amplifier may be capable of exceeding the speaker's published 20W power handling.

14. Does a 50W amplifier automatically send 50W to the speaker?

No.

Actual delivered power depends on the signal, volume, supply and speaker load.

15. Can I use it as a subwoofer in a 2.1 system?

Yes.

That is one of its intended applications.

16. Do I need a low-pass filter?

A low-pass-filtered subwoofer output is recommended for dedicated bass use.

17. What crossover frequency should I use?

There is no single universally correct value.

The appropriate crossover depends on the main speakers, enclosure and desired system response.

18. Is 150Hz mandatory?

No.

It may be useful in some compact systems, but it is not universally optimal.

19. What is the published frequency range?

Approximately:

60Hz–5kHz

according to the current product specification.

20. Does that mean it should play up to 5kHz in a subwoofer system?

Not necessarily.

For dedicated subwoofer operation, an LPF should normally limit higher-frequency content.

21. What magnet does it use?

The current specification states:

Ferrite Magnet

22. What is its resonant frequency (Fs)?

An exact verified Fs is not currently available.

23. Is Fs 65Hz?

The existing page lists approximately 65Hz, but this value has not been verified from a manufacturer datasheet for the exact supplied driver.

24. What is the sensitivity?

A verified sensitivity specification is not currently available.

25. Is the sensitivity 86dB?

The existing page lists approximately 86dB, but this should not be treated as verified without measurement conditions or manufacturer documentation.

26. What is the mounting depth?

An exact verified mounting depth should be measured from the current stock before being published.

27. Does it require an enclosure?

An enclosure is strongly recommended for normal finished bass applications.

28. Should I use sealed or ported?

Either may be used depending on the desired result.

Proper ported-enclosure design requires additional driver parameters.

29. What enclosure volume should I use?

An exact optimized volume cannot be specified without verified Thiele/Small parameters for the driver.

30. Can I use it in a Bluetooth speaker?

Yes.

Use a compatible Bluetooth amplifier with suitable subwoofer output.

31. Can I use two of these?

Yes, provided the amplifier configuration supports the resulting speaker load.

Do not wire multiple speakers in parallel or series without checking the resulting impedance.

32. Can I use it for car audio?

It can be used in suitable custom low-power audio projects, but it should not be treated as a replacement for a high-power automotive subwoofer.

33. Can I use it as a normal full-range speaker?

It is sold as a subwoofer / woofer driver.

For normal music reproduction, use suitable full-range speakers for mid and high frequencies.

34. Is it waterproof?

No waterproof or IP rating has been verified.

35. What is included?

1 × Moonvoice 4 Inch 4Ω 20W Subwoofer Speaker

36. Is the amplifier included?

No.

37. Is the enclosure included?

No.

38. Are speaker wires included?

Not specified as included.

Disclaimer

Minor appearance, cone, frame, magnet and construction details may vary between manufacturing batches.

Where revision-specific dimensions or acoustic parameters are critical, verify the supplied unit before designing the final enclosure.