Cone
Audio, speakers, and home theater calculators
Size a subwoofer box from the driver, tune a round or slot port, pick crossover parts, add sound levels, list the modes of a rectangular room, place a projector from the throw ratio, or pick a TV size and a seat from the viewing angle.
Subwoofer Box Calculator
Subwoofer box calculator for net volume, a sealed or ported alignment, and port length. Dimensions, Thiele-Small parameters, and a round or slot port.
Projector Throw Distance Calculator
Projector calculator for throw distance, the screen size that distance makes, and the brightness on that screen. A throw ratio or a zoom range, and the aspect.
TV Viewing Distance Calculator
A TV distance calculator for the seat, a TV size calculator for the room, and a TV height calculator for the mount. One page, from the screen diagonal and the viewing angle.
Speaker Crossover Calculator
A crossover calculator for 2-way and 3-way passive speaker crossovers. Linkwitz-Riley, Butterworth, and Bessel inductor and capacitor values, plus a high-pass or low-pass section.
Port Length Calculator
A port length calculator for subwoofer and speaker ports. Round or slot, tuning from the length, port area and velocity, and a Helmholtz resonator.
Decibel Calculator
Decibel calculator to add sound levels, drop SPL with distance, and combine speakers at a listening point. Acoustics only: not a noise dose and not hearing protection.
Room Mode Calculator
Room mode calculator for axial, tangential, and oblique modes of a rectangular room, plus a Bonello density check. An acoustic design aid, not a structural calculation.
How these calculators work
The subwoofer box calculator is three jobs on one page. The outside width, height, and depth, minus the wall thickness, are the gross internal volume. The driver, the port, and a bracing allowance come off that to leave the net volume. A ¾ inch wall is the usual MDF default, about 19 mm.
Thiele-Small parameters size the air, not the wood. A sealed box uses Richard Small’s closed-box relations: pick a Qtc and the page returns the net volume, or pick a volume and it returns Qtc, Fc, and F3. A ported box starts from D. B. Keele’s QB3 alignment. That is a starting point, not a finished design, and it is a poor start when Qts is above about 0.5. Bandpass boxes are not on this page.
Port length is the Helmholtz resonator with an end correction: 0.732 diameters when one end is flanged and one is free, 0.85 diameters when both are flanged, and 0.614 when both are free. The air in the port is subtracted from the net volume. The port length calculator is the longer version of that sum: tuning from a length you already cut, pipe resonance, and port velocity. The box page and the port page share the same math. Check the result in a modelling program such as WinISD before cutting.
The projector throw calculator starts from the image width. Throw distance is the throw ratio times that width, and a zoom lens gives a nearest and a farthest spot. The reverse gives the screen a room can hold. Brightness is lumens times screen gain, divided by the area in square feet. The model’s spec sheet is the final word, including where the distance is measured.
The TV viewing distance calculator turns a diagonal and an aspect ratio into screen width and height. A 40° horizontal angle is the immersive THX recommendation, 36° is the THX back row, and 30° is the SMPTE minimum. The range between 40° and 30° is the recommended seat. A 20/20 acuity check, one arcminute per pixel, says how close you have to sit before a 4K or 1080p screen shows all of its detail. Mounting height puts the centre of the screen at seated eye level. These are guidelines, and the same angles apply to a projector screen.
The speaker crossover calculator gives the inductors and capacitors for a passive ladder. It assumes zero source impedance and a resistive load equal to the driver’s nominal impedance. Linkwitz-Riley 2nd order is the default: a flat sum when the tweeter is reversed. A 3-way split adds a midrange band. The values are a starting point to check by measurement or simulation.
The decibel calculator adds sound-pressure levels. The default is an incoherent energy sum, 10 log10 of the sum of 10^(Li/10). A collapsed coherent sum is there for phase-locked sources. Distance is free-field spherical spreading, 20 log10 of the distance ratio, about −6.02 dB per doubling. It does not compute a noise dose, a time-weighted average, or a hearing-protection rating.
The room mode calculator lists axial, tangential, and oblique modes of a rectangular room with rigid walls. Frequency is (c/2) times the root of the squared index over each dimension, with the same 343 m/s at 20 °C as the port page. A Bonello count checks that 1/3-octave bands do not thin out as frequency rises. That check is a planning heuristic, not a building code, and the page is not a structural calculation.