Headroom

The tile#

The app’s own Headroom tile on a Dayton Audio DCS205-4 in 25 L tuned to 35 Hz. Change the power, crest factor and distance, add a high-pass, or relax a limit, and watch the bands and lines move.

At 10 W with 12 dB of crest, the peaks go 7.7 dB over the maximum at 10.2 Hz, on driver excursion: below its tuning the box stops holding the cone. With the 30 Hz high-pass the whole band is Clean, 0.5 dB inside the clean limits, and the tightest point moves to 34.7 Hz, where port velocity is now the limit.

• The solid line is the average level, Average SPL: the enclosure’s SPL at its set power, EQ included. The dashed line is Peak SPL, the average plus the crest factor. It turns red where it is over the maximum.
• The coloured bands are what the design can play at each frequency: Clean up to the clean thresholds, Threshold between clean and maximum, Over max above. At each frequency the tightest limit sets them, so the edge can be cone travel at one frequency and port air speed at the next.
• Tgt avg and Tgt peak mark your target level and its peaks.
• The number above the graph is the smallest clean margin anywhere in the band. Once anything is over the maximum, it shows how far over instead, as a negative number.
• Hover for the average and peak readouts at a frequency: power, excursion and port air speed, each against its target and maximum. Click to hold the cursor.
• The tile draws the selected enclosure. Expanded and wide, it lists up to six enclosures under the graph with their margins; click one to show it.
• The EQ button edits the enclosure’s filters on the tile, and a right-click offers Add filter. The lines move with every change.

How to read it#

• Follow the dashed peak line. The gap between it and the top of the Clean band is the clean headroom at that frequency.
• Headroom is in decibels. A 6 dB gap allows about twice the signal amplitude, or four times the power, before the limit.
• Clean means below the clean thresholds, not a promise of clean sound: the thresholds are limits you chose, and a linear model misses distortion and noise near them.
• The limit that runs out first tells you what to change. Cone travel wants a high-pass or more cone area; port air speed wants more port area; heat wants more drivers or less power.

Settings#

Open Settings in the tile header. Pin settings to side keeps them beside the tile when it is wide enough.

• In a new workspace the clean port limit starts at Port velocity under Settings › Simulation…, the warning line the Port Velocity tile draws.
• In a multiple-entry horn the ratios apply to each driver’s own rating and Xmax, and every driver is checked.
• These are the app’s defaults, not the maker’s damage ratings. Your saved workspace may differ.

Music and crest factor#

A sustained bass note and a short kick can reach the same peak with very different average levels. Crest factor is the largest peak over the average (RMS) level, in dB. A sine wave has 3.0 dB; 12 dB means peaks about 4 times the RMS amplitude.

Keep the power fixed and raise the crest factor from 6 to 12 dB: the average line stays put and the peak line rises 6 dB, so the peaks ask for twice the voltage and about twice the cone travel and port air speed. In the explorer that takes the peaks from −1.7 dB to −7.7 dB against the maximum, and the peak voltage from 12.5 V to 24.9 V.

Treat crest factor as an assumption about the signal reaching this speaker. A whole track’s crest factor can differ from the bass after a crossover or high-pass, and the recording, processing and measurement window all change it; a genre name is not enough to choose a value.

What the amplifier must supply#

An amplifier makes a larger copy of its input voltage. The speaker’s impedance sets the current it must supply, and that changes with frequency. When the voltage asked for exceeds what the amplifier can swing, it clips; current limits or protection can also stop it.

The tile’s Amp button opens Amplifier Insights: what one amplifier channel must supply at your target level, EQ and crest factor included, with the frequency of each maximum.

When the target asks for more than the maximum thresholds allow, a Danger note appears; Apply lowers the target until it fits. A multiple-entry horn lists each amplifier channel on its own.

In the explorer at 10 W, the peak current, 6.12 A, comes at 181 Hz, where the impedance is lowest. A rating such as 200 W describes what an amplifier can deliver under test, not what it sends all the time; the signal and the volume set the demand, and brief peaks can need a lot of voltage while the average power stays low.

V rms  = √(25 × 8) = 14.1 V
V peak = V rms × 10^(12 / 20) = 56.3 V
I peak = V peak / 8 = 7.0 A
Crest factor = 20 log10(V peak / V rms)

Listening distance#

Twice the distance is about 6.0 dB less direct sound. In the explorer, Distance moves the listener at a fixed power: the level falls from 96.6 dB to 90.6 dB at its loudest point, and the headroom stays at −7.7 dB, because the driver and port do the same work.

In the app, Distance keeps your Average target at the new distance, so the enclosure’s power changes to reach it: listening at 2 m instead of 1 m takes four times the power and uses about 6 dB of headroom. The correction is for direct sound only; your room’s reflections and modes change the real level.

Choosing an action#

• A high-pass: in a vented box the port does much of the work near its tuning; below it, the cone travel climbs. A high-pass there, like the explorer’s 30 Hz one, cuts that demand, and the low bass with it: check what you gave up as well as what you gained.
• Less drive: a lower target lowers the demand at every frequency.
• More port area: port air speed is a check for noise and compression; flares, area and placement change what you hear. More area usually means a longer port for the same tuning, so check it fits.
• Passive radiators: they have their own Xmax and can run out while the driver is still inside its own.

The thermal check compares the power you set, after EQ, with fractions of the driver’s power rating, Pe. It is not a voice coil temperature or the heat the coil sheds: a rating is a test figure, and sustained level, spectrum and cooling set the real heat. The Max SPL tile’s coil heating rule is the closer estimate.

Limits of the model#

• The tile checks each frequency separately, from 10 Hz to the top of the frequency axis (Upper frequency under Settings › Display…). It does not analyse a recording or add frequencies into a music waveform, and it does not mean every frequency gets the full power at once.
• The target’s reference is the loudest point of the average line in that band. A narrow response peak can set it; it is not an integrated loudness.
• Heating, motor force and suspension changes, and port losses at high level can take a real speaker away from the prediction. The maximum boundary comes from your thresholds, not a measured damage limit.

What to try#

Ask your AI#

Related#