Port length calculator

Every input must be a finite number strictly greater than zero; zero, negative, missing, or non-finite values fail with invalid_input and are not billed. Use the page at no charge, or call the API at $0.002 per successful request.

How Helmholtz port length is computed from diameter, Fb, volume and port count

The returned port_length is therefore Leff minus 0.732 times D, in inches, and it is the length of each of the N ports because they are identical. The endpoint does not model flared ends, slot ports of rectangular section, stuffing, leakage, or driver displacement volume; those are netted out of the box volume by the builder before the call.

Input contract, units, response fields, and validation errors

Errors always name the canonical field so the web form can mark the right control. Magnitudes above the documented ceilings fail so a typo cannot blow the isolate. A familiar check is a three-inch port, forty hertz, two cubic feet, and one port; the same box with two ports shortens each tube because the total area rose. POST a JSON body with four required fields. port_diameter is the inner diameter of each circular port in inches; aliases diameter, d, Dv, and port_d are accepted. tuning_frequency is the desired box tuning Fb in hertz; aliases frequency, fb, Fb, freq, and hz are accepted. box_volume is the net internal enclosure volume in cubic feet after driver displacement is subtracted; aliases volume, vb, Vb, and enclosure_volume are accepted. port_count is the number of identical ports as a positive integer from one to sixteen; aliases n, N, ports, and number_of_ports are accepted. Each numeric field may arrive as a JSON number or as a numeric string; booleans, objects, empty strings, NaN, and Infinity fail with invalid_input. Zero and negative values fail because Helmholtz length is undefined for a vanishing diameter, a zero hertz target, an empty cabinet, or zero ports — that is the contract this capability exists to enforce, and those failures are not billed. port_count must be a whole number: one and a half ports is not a physical layout this identity covers. On success the body echoes the cleaned inputs and returns port_length as the geometric length of each port in inches, port_area as the total circular area in square inches, effective_length as Leff before the mouth correction, end_correction as k times D, a formula string restating the identity, and unit set to in. Missing fields are invalid_input and are not billed. Successful API calls use the published $0.002 base price; the free browser path runs the same solve function without consuming prepaid balance.

Where a speaker port length calculator earns its keep

Home subwoofer builders who have already chosen a net internal volume and a target Fb from a Thiele–Small alignment still need a cut length for the PVC or cardboard tube they will glue through the baffle. A three-inch port in a two-cubic-foot box at forty hertz is a different stick of pipe than the same port in a four-cubic-foot box, and cutting twice because the end correction was forgotten wastes a weekend. Studio-monitor and small PA cabinets that are being rebuilt with a new woofer need the same identity when the original tube is lost and only the box volume and a target Fb remain on a drawing. Car-audio enclosures packed into a trunk are even less forgiving: two identical ports are often used to keep each tube short enough to fit, and this calculator accepts port_count so the pair is sized together instead of guessed. Spreadsheet users who already compute Vb can call the API from a script and pin port_length in tests so a shop ticket never disagrees with the page. Keep every input finite and strictly positive, send volume in cubic feet and diameter in inches, pin port_length in your tests, and you get a reproducible duct length for a subwoofer, a car box, a monitor rebuild, or an edge worker without standing up an enclosure-design suite of your own.