TQWP hull design and Vojta pipe drawings

This program is an EXCEL file that contains the Tapered Quarter Wave Pipes (TQWP) body design tool or Voight’s collapsed horn or tube, which described this acoustic solution in the 30s of the XX century.

The file was taken as a basis John Rutter by calculations David B. Weems, an attempt is made to minimize the scatter of the calculation parameters allowed in this file, an adaptation is made to the metric system of measures.

Also, the author added to the TQWP program a block for calculating body parts with the ability to print sketches with dimensions.

The program is adapted for two viewing modes 800×600 and 1024×768; there are buttons to select a mode on the main sheets of the program.

TQWP Calculation sheet

The calculation block contains all the data required to calculate the dimensions of the case. It should be noted that all dimensions are internal, add the thickness of the materials.

Data can be entered only in cells highlighted in white and only in millimeters, the rest of the cells are informational and protected from editing.

In principle, everything is simple, but I will try to explain the data on which questions may arise.

Internal baffle material thickness: it is advisable to take a dense material that is not subject to resonance (chipboard, plywood, preferably bakelite), at least 20 mm thick, since the partition is an element for fastening the side panels.

Speaker basket outer diameter: external dimensions of the speaker.

Diameter of the effective part of the diffuser: It is advisable to take the data provided by the manufacturer, but you can also measure it yourself, you need to measure the distance between the centers of the suspension of the diffuser, which is also close to the truth.

Bore diameter: useful when calculating body parts.

Natural resonant frequency of the speaker: Required to automatically calculate the tuning frequency of the TQWP cabinet.

Depth of the closed part of the horn: depth of the pad of the closed end of the horn (cone). It is strongly not recommended to do more than 25-50 mm. By changing this parameter, you can change the vertical position of the speaker on the front panel within a small range.

Effective diffuser area: Calculated automatically.

Horn open area: equal to the 2.5th effective areas of the diffuser. Calculated automatically.

Closed area of ​​the horn: Calculated automatically.

Speaker position: Distance from the closed end of the speaker to the center of the speaker bore. Calculated automatically.

Body width: By default, the outer diameter of the head basket is taken as the body width. If you want to change the width of the body, you need to substitute a value by which the width will increase on each side.

Hull depth: internal cabinet depth. Calculated automatically.

Body height: internal cabinet height. Calculated automatically.

Horn open depth: Calculated automatically.

Baffle length: Calculated automatically.

Port height: Calculated automatically.

Port area: equal to the effective area of ​​the diffuser.

Internal volume of the case: Calculated automatically.

Folded horn length: equal to 1/4 of the wavelength of the body tuning frequency. Calculated automatically.

HF head outer diameter: If you do not intend to use an RF head, this parameter can be omitted.

HF head bore diameter: If you do not intend to use the HF head, this parameter can be omitted.

Formulas used to calculate TQWP

The TQWP calculation table is deliberately inaccurate compared to the original file. The question is, what is the open end of the horn, the bottom of the case, or the distance from the top of the port to the back?

In my opinion, the port is not part of the resonator. Although this is my personal opinion. I could be wrong. According to David B. Weems’s calculations, the actual horn length can be 20% longer than the calculated one, so even if I’m wrong, the error is still within the acceptable range.

Sheet “TQWP Housing”

Here the author offers the most basic TQWP drawing. The design provides for the possibility of installing a HF head. Since the dimensions of the case are quite impressive, it is advisable to use a material of at least 20–25 mm in thickness.

The front panel consists of two elements: the main panel, on which the full-range speaker is attached, and the decorative panel, which is glued and screwed onto the main panel with self-tapping screws. The full-range speaker is installed in the cabinet from the outside, flush-in and overlapped with the tweeter.

In order to give more rigidity, the bottom panel is also made in the form of a sandwich. To give a respectable look, two grills are offered, an upper one that covers the speakers and a lower one that covers the port opening.

Brief description of the entered data.

Front Panel: material thickness of the main front panel.

Front decorative panel: material thickness of the decorative front panel.

Rear panel: back panel material thickness.

Side panel: material thickness of the side panels.

Partition 1: thickness of the material of the inner baffle 1. To avoid resonance, it is advisable to use the material as thick as possible. The partition is also a fastening element for the side panels and a stiffener.

Partition 2: thickness of the material at the bottom of the closed end of the horn.

Top panel: material thickness of the top panel.

Bottom panel 1: material thickness of the bottom false panel. It is advisable to use the material as thick as possible, since the panel is the fastening element for the side and rear panels.

Bottom panel 2: material thickness of the bottom panel.

Grill top: Material thickness of the speaker trim.

Lower grill: Material thickness of the decorative panel covering the port opening. Equal to the thickness of the decorative front panel.

Terminal height: If a rectangular terminal is to be used. If the terminal is of a different shape or is missing, leave the cell blank.

Terminal width: If a rectangular terminal is to be used. If the terminal is of a different shape or is missing, leave the cell blank.

Terminal diameter: When using a round terminal. If the terminal is of a different shape or is missing, leave the cell blank.

Distance between speaker housings: Distance between speaker boxes. When using a tweeter.

Lower bypass of the upper grill: Distance between the speaker hole and the bottom edge of the grill.

Lower grill attachment area: The area on the main front panel, not covered by the decorative front panel, for the lower grill attachments.

Bevel on the front decorative panel: Parameter is optional.

Grill cloth thickness: Necessary for the correct calculation of the lower grill.

TQWP Drawings Sketches

After all the mandatory parameters of the materials required for building the corpus have been entered, you can print the sketches of the drawings by pressing the button “Print sketches“. 8 …