Reading a response

The curve#

• Frequency runs left to right on a log scale, so every octave is the same width: 20 to 40 Hz takes as much room as 200 to 400 Hz.
• Level is sound pressure in dB at the listening distance. The vented example at 1 W is flat at about 88 dB and rolls off below 32 Hz, its tuning.
• Level follows power: ten times the power adds 10 dB and twice the power about 3 dB. The shape does not change, because the model is linear.
• Hover the tile to read the level at a frequency. Each visible enclosure draws its own curve in its colour.

F3 and F10#

F3 and F10 are where the curve has fallen 3 dB and 10 dB below its reference level. 00 Simulator takes the reference from the loudest one-octave stretch of the curve, averaged: for the vented example that is 88.1 dB between 249 and 499 Hz. With the default Auto reference, it uses the outer crossings across the simulated range. An internal dip does not set an edge, but a separate lobe above the threshold can move one.

• Turn on F3 in the SPL tile’s header to mark F3 and F10 on every visible enclosure. The F-point settings cog beside it adds F6 or a custom level.
• Bandpass boxes and horns pass a band, so they get two marks for each level: a low edge (F3L) and a high edge (F3H).
• Under Advanced in the same settings, Auto · loudest octave average is the default reference. Selected band average averages a band you choose, and Response peak measures down from the highest point. Summary tiles always use Auto.
• The Metrics tile compares visible designs by one measure at a time; choose F3 or F10 to compare their extension.

Radiation space and distance#

The Radiation space setting represents how much space the speaker radiates into. For boxes it applies the level offsets below; for horns it also changes the mouth loading, so the response can change shape. It is in the Environment section of the Driver panel and applies to every enclosure in the workspace; the default is half space.

Listening distance in the same section sets where the level is read, from 0.1 to 50 m. Level falls 6 dB each time the distance doubles, so 2 m reads 6 dB below 1 m. Distance moves the SPL and Max SPL curves up and down without changing how hard the driver or the port works.

Bumps and dips#

• A hump above the roll-off means the box is underdamped: a vented box tuned high, or a sealed box that is too small for its driver. Tuned to 45 Hz, the vented example gains a 4.2 dB hump at 48.7 Hz and loses its deepest bass: F3 rises from 30.3 Hz to 40.3 Hz.
• Ripple and dips inside a band come from resonances along a horn’s path, or from two tunings set too far apart in a sixth-order bandpass box. Small ripple is normal; a deep dip is a hole in the band.
• A dashed line marked PR on a vented box is the port’s first pipe resonance, where a real port can add a narrow peak of its own. For the vented example it sits at 482 Hz, well above the band a subwoofer uses.
• Peaks on the Impedance tile mark the tunings. The vented example has peaks at 19.1 Hz and 49.9 Hz with a dip at 31.6 Hz, close to its 32 Hz tuning. The sealed example has one peak, at 53.6 Hz: its resonance in the box, not the driver’s Fs.

A room adds peaks and dips of its own, often larger than any here. The simulation shows the speaker, not the room: From simulation to a build covers what it leaves out and how to compare with a measurement.

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