Getting Started with Enclosure Simulation

This tutorial walks through the basics of speaker enclosure design and shows you how to use the simulator to create your first design.

A speaker driver (the cone, magnet, and voice coil assembly) can't produce good bass on its own. It needs to be mounted in an enclosure. The box size, whether it's sealed or has a port, and the tuning frequency all dramatically affect how the speaker sounds, especially at low frequencies.

Enclosure simulation predicts how a specific driver will perform in a specific box. It uses the driver's Thiele-Small parameters (measurements of its electrical and mechanical properties) to calculate:

• Frequency response: how loud the speaker is at each frequency
• Low-frequency extension: how deep the bass goes (F3 and F10 points)
• Impedance: how the speaker looks to the amplifier
• Excursion: how far the cone moves (to avoid damage)
• Port velocity: air speed in the port (to avoid noise)

This lets you compare designs without building them. You can try different box sizes, tuning frequencies, and drivers to find what works best for your needs.

When is simulation useful?

Simulation is great for:

• Designing subwoofers and low-frequency speakers from scratch
• Comparing different drivers to see which fits your box size
• Understanding why a design isn't working (too small, bad tuning, etc.)
• Learning what different parameters do without building prototypes

When simulation isn't enough

This simulator focuses on low-frequency behavior. It doesn't model:

• Mid and high-frequency behavior (cone breakup, diffraction)
• Cabinet resonances and panel vibration
• Room acoustics and placement effects
• Nonlinear behavior at very high power levels

For full-range speakers, you'd typically design the woofer section here, then handle crossovers and tweeters separately.

What is a driver?

A driver is the speaker component that converts electrical signals into sound. It has a cone (or diaphragm), a voice coil that moves when current flows through it, a magnet, and a suspension that holds everything together.

Every driver has specific mechanical and electrical properties. These are measured and published as Thiele-Small parameters (often shortened to T/S parameters). You need these numbers to simulate how the driver will work in different enclosures.

Enclosure types

There are three main types this simulator supports:

Sealed (closed box)

The simplest design. The driver is mounted in a sealed box. The air inside acts as a spring that controls the driver's movement.

• Pros: Simple to build, predictable response, tight bass, small box possible
• Cons: Less efficient than vented, rolls off earlier
• Good for: Home theater, tight accurate bass, limited space

Vented (ported/bass reflex)

The box has a port (tube) tuned to a specific frequency. Below the tuning frequency, the port and box work together to increase output.

• Pros: More output at low frequencies, higher efficiency, less excursion near tuning
• Cons: Larger box needed, steep roll-off below tuning, port noise possible
• Good for: PA speakers, car audio, maximum output

Passive radiator

Similar to vented, but instead of a port, there's a second cone without a motor (the passive radiator). You tune the system by adding mass to the passive radiator.

• Pros: No port noise, compact designs possible, adjustable tuning
• Cons: More expensive, passive radiator has excursion limits too
• Good for: Small sealed-like boxes that need more output

What are Thiele-Small parameters?

These are measurements that describe how a driver behaves. The most important ones are:

• Fs (resonant frequency): The frequency where the driver naturally resonates. Lower Fs = deeper bass potential.
• Qts (total Q factor): Describes damping. Low Qts (0.3-0.4) works well in vented boxes. High Qts (0.6-0.8) works better sealed.
• Vas (equivalent volume): How much air has the same springiness as the driver's suspension. Bigger Vas usually means bigger box needed.
• Xmax (maximum excursion): How far the cone can move before distortion. More Xmax = more output.
• Sd (effective area): Cone area. Bigger area = more air moved = more output.

You don't need to memorize these. The simulator includes a database of drivers with these parameters already measured. For custom drivers, the manufacturer's datasheet will list them.

Where to find drivers

The simulator includes a built-in database of popular woofers and subwoofers, but you can also find specifications for almost any driver:

Loudspeaker Database (.wdr files):

The most common source is loudspeakerdatabase.com, which has thousands of driver specifications in .wdr (Woofer Data Record) format.

• Search for your driver model on the site
• Download the .wdr file
• In the simulator, click "Add new driver" and look for an import option, or manually enter the T/S parameters from the datasheet

Manufacturer Datasheets:

• Check the driver manufacturer's website for the specifications sheet
• Look for T/S parameters (Fs, Qts, Vas, Xmax, etc.)
• Enter them manually in the simulator's driver editor

Built-in Database:

• The simulator comes with popular drivers from brands like Dayton, B&C, Faital, and others
• Start with the built-in database if you're learning—these drivers are well-tested and documented

Let's walk through creating a simple sealed subwoofer design.

Step 1: Add an enclosure

Open the simulator. In the left sidebar, click "Add Enclosure". You'll see a new enclosure in the list. Click on it to select it.

Step 2: Choose enclosure type and size

In the left sidebar, you'll see controls for the enclosure. Set the type to "Sealed" and the volume to 50 liters (0.05 m³). This is a typical size for a home subwoofer.

Step 3: Pick a driver

In the right sidebar, you'll see driver configuration. Click the driver dropdown and search for "Dayton RSS315HF-4". This is a popular 12-inch subwoofer driver.

Once selected, you'll see the driver's specifications displayed below the selector (Fs, Qts, Vas, etc.).

Step 4: Look at the results

The graphs in the center will update automatically. You'll see:

• SPL graph: Shows how loud the speaker is across frequencies. Look for a smooth response.
• Impedance graph: Shows the electrical load. For sealed boxes, you'll see one peak at Fs.
• Excursion graph: Shows cone movement. Make sure it stays under the Xmax line.

In the right sidebar under "Results", you'll see key numbers:

• F3: The -3dB point (where bass starts rolling off). Lower is deeper.
• Sensitivity: How efficient the speaker is. This one shows about 84 dB at 1W/1m.
• Qtc: System Q for sealed boxes. 0.7 is a good target for flat response.

SPL (Sound Pressure Level)

This shows how loud the speaker is at each frequency, measured at 1 meter with a given input power (default 1 watt).

What to look for:

• A flat or gently sloping line in the passband (the usable range)
• Where it starts rolling off (this determines F3)
• No weird peaks or dips (suggests poor alignment)

For sealed boxes, you'll see a smooth roll-off. For vented boxes, you'll see flatter response down to the tuning frequency, then a steep drop.

Impedance

This shows the speaker's electrical resistance at each frequency. Amplifiers care about this because it affects how much power they can deliver.

What to look for:

• One peak for sealed boxes (at Fs)
• Two peaks for vented boxes (at Fs and the port resonance)
• Minimum impedance shouldn't be too low (most amps are rated for 4 or 8 ohms)

Excursion

This shows how far the cone moves at each frequency. The red line is Xmax, the maximum safe excursion.

What to look for:

• Excursion should stay under the Xmax line at your desired power level
• If it exceeds Xmax, reduce power or increase box size
• Vented boxes have much lower excursion near the tuning frequency

Other graphs

Additional graphs are available in the selector:

• Max SPL: Shows the maximum output before hitting thermal or mechanical limits
• Port Velocity (vented only): Air speed in the port. Keep under 17 m/s to avoid noise
• Group Delay: Phase-related measurement. Lower is generally better

Here's how to tell if your design is working and what to adjust.

Common problems and fixes

Problem: F3 is too high (not enough bass)

Solutions:

• Increase box size (lowers F3)
• Choose a driver with lower Fs
• For sealed, reduce Qtc closer to 0.5-0.7
• For vented, lower the tuning frequency

Problem: Excursion exceeds Xmax

Solutions:

• Add a high-pass filter to protect the driver (most effective at low frequencies)
• Reduce input power level
• Adjust tuning frequency (for vented boxes)
• Increase box size (reduces excursion)

Problem: Response has peaks or dips

Solutions:

• For sealed: adjust box size to get Qtc around 0.7
• For vented: check tuning frequency matches recommended alignment
• Verify you entered driver parameters correctly

Problem: Port velocity too high (vented)

Solutions:

• Use a larger diameter port
• Use multiple ports
• Reduce input power
• Increase box size slightly

Design validation checklist

Once you've built your design, use this checklist to verify it will perform well:

SPL Response:

• You're achieving your desired SPL level across the frequency range
• The response is smooth without major peaks or dips
• Low-frequency extension (F3) meets your requirements

Excursion:

• Cone excursion stays below Xmax at your intended power level
• If exceeding limits, add a high-pass filter (most effective solution)
• For vented boxes, pay special attention near the tuning frequency where excursion peaks

Port Velocity (vented boxes only):

• Keep port velocity below 17 m/s as a conservative target
• With well-designed, flared round ports you might tolerate 25-40 m/s without chuffing
• If velocity is too high, increase port diameter, use multiple ports, or reduce power
• Aim for a port dimension ratio (length to diameter) less than 6:1

The trade-off triangle

Every speaker design involves trade-offs between three things:

• Size: How big the enclosure is
• Extension: How low it plays (F3)
• Output: How loud it gets (sensitivity and max SPL)

You can't optimize all three at once. Want deeper bass? You need a bigger box or accept lower output. Want a small box? Accept higher F3 or lower output. Want high output? You need a bigger box or sacrifice extension.

This is physics, not a limitation of the simulator. Understanding these trade-offs helps you make informed decisions.

Good targets for different applications

Home theater subwoofer:

• F3: 20-30 Hz
• Qtc (sealed): 0.6-0.7
• Box size: 40-80 liters per driver
• Type: Sealed or vented tuned to 20-25 Hz

Car subwoofer:

• F3: 30-40 Hz (cabin gain helps below this)
• Type: Sealed (small box) or vented (more output)
• Box size: 20-40 liters per driver
• Prioritize output over deep extension

PA subwoofer:

• F3: 35-45 Hz
• Type: Vented tuned to 35-40 Hz
• Prioritize maximum output
• Watch excursion and port velocity at high power

You now understand the basics of enclosure simulation. Try:

• Experimenting with different box sizes to see how it affects F3
• Comparing sealed vs vented with the same driver
• Trying different drivers from the database
• Adding EQ filters to shape the response

For more details on specific features, see the User Guide.

For technical definitions and reference material, see the Glossary and T/S Parameters pages.