Guide to WinISD Pro and Hornresp

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   Thanks, updated and the final part:
Export:

Export allows you to view the data showed in Hornresp with programs other than Hornresp.

Window 1: Export the input parameters as an AkAbak-script. Ang must be 2,0 Pi.
Window 2: Exports the schematic diagram as an text-file. The text opened in a program such as notepad shows the horn parameters (such as horn area, height, depth, angle) for every cm horn path from the throat to the mouth. In the input pad opened, you can input the height at S1, S2,... by dividing the corresponding area by the internal width of the cabinet. An increment of 1 will show the values per 1 cm horn path length.
Window 3 t/m 7: Exports as a text-file, showing the specific parameter of that window against frequency. 
How high can you model before the results become inaccurate?

Hornresp models the power response of the horn. This is different than the on-axis response which you might measure with a microphone. The power response is what you would measure at a point if sound radiated evenly in all directions away from the horn, within the solid angle specified in the ANG input. So the modelled results should be fairly accurate up to the frequency where the horn starts to have directivity - where the polar pattern starts to narrow. This is typically at the frequency where the wavelength falls below the diameter of the horn mouth. Above this frequency, Hornresp will predict lower SPL levels than what you would measure on-axis. Hornresp now includes tools to investigate this effect. 
Once you calculate the model, go to the SPL Response chart. Under Tools, select Directivity. If you enter a blank input, you will see the power response. If you enter 0, you will see a prediction of the on-axis response. You can also enter other angles. Also under tools, you can look at the Pattern tool. This will predict the polar pattern at the frequency you input and show you the directivity index (DI) at that frequency. The DI is a number in dB giving the gain over what the level of the power response is.

Tapped Horns:

Hornresp 16.xx and higher are suitable for tapped horn
simulation. This very old, yet recently rediscovered technique allows you to
design a (sort of) back loaded horn with a relatively small mouth area but
still decent efficiency at low frequencies in comparison to normal horns. In
return the frequency/ phase response higher up is ruined, as it's a form of 6th
order BP but up to 3 octaves. It's primarily use today is as a sub/bass horn,
with lots of information spread around the World Wide Web, for instance here and these projects. The
text below will just focus on inputting the tapped horn parameters into
Hornresp.

TH/ TH1:
A standardised simplified tapped horn model consists of three horn segments and
no front or rear chamber, as shown by the lower model in the example.
Characteristic for the tapped horn is that one side of the driver is loaded
near the beginning of the horn while the other side is loaded near the horn
mouth. So both sides are loaded by the horn as opposed to a normal back loaded
horn, where only one side of the driver is loaded by the horn.

The blue lines represent the cross-sectional surface area at that line, the red lines represent the average length (usually down the middle).
Usually the 1st and 3rd segment are relatively short, while
the 2nd segment is by far the longest. By changing the length of the 1st and
3rd segment the design can be fine tuned for a specific driver. The 1st and 3rd
segment in the example have a length of at least half the diameter of the
driver, which is practical if the design is to be kept simple,
construction-wise.

If 4 segments are used in the TH arrangement, Hornresp
switches the model automatically to the upper model in the example. Hornresp
has a “Tapped horn wizard” which can be used to change the driver location
without altering the overall horn length, the horns expansion rate must be
constant. In the example the horn doesn’t expand nor is it tapered (it doesn't
constrict), making it technically a tapped pipe or tapped tube (S1 = S2 = S3 =
S4). If the horn gradually expands it’s called a tapped horn (S1 < S4), if
it's tapered, its called a tapped-TQWT (S1 > S4). 

Note that in contrast to a normal horn where Sd/S1 sets the compression ratio,
for a tapped horn Sd/S2 sets the compression ratio. A compression ratio of 2:1
is considered safe for larger drivers (15” plus), smaller drivers might take a
higher ratio. As a rule of thumb keep the particle velocity at the horn mouth and
horn throat below 30 m/sec for PA use, below 15 m/sec in the living room
(Acoustical Power --> Particle Velocity --> Tapped Throat/ Horn mouth).
Hybrids:

For most tapped horns, the total horn length (S1 - S4) is
quite long compared to normal rear and front loaded BPH. Unless it's a so
called "hybrid" (between a reflex and a tapped horn), in that case there's also a
fairly large chamber, reducing the needed horn length for a certain lower cut
off. The chamber might also be ported (Ap, Lpt and Vtc). The port enters the
tapped horn at S2, whereas the chamber is located between the driver and the
port. The example below shows how a hybrid can be modelled. The enclosed volume before S1 is Vtc, Atc in this case is fairly close to the surface area of the baffle but if resonances are masked it's influences are small anyway.

The blue lines represent the cross-sectional surface area at that line, 
the red lines represent the average length (usually down the middle).
The Fs of the driver used might actually be higher (1.414x) than the
cut-off you're aiming for. Also an actual
measurement will show a (much) flatter frequency response and sometimes a lower cut off. 
Port Assisted Horns: 
Port assisted horns contain a Helmholtz resonator (port) inside the rear chamber. The port is generally tuned at or below the cut off of the horn for three main reasons:

Tuning within the pass band of the horn usually leads to nasty interference; A peaky response or partially less gain than without port. 
At the tuning frequency the cone excursion is (theoretically) reduced to zero, so it can be used for keeping cone excursion under control as this is the highest right below /at the horns cut-off point. Below the tuning frequency however the driver becomes unloaded and the cone excursion (again) quickly rises. For this reason use a high pass filter at or around the tuning frequency. 
For horns that are used as singles or small stacks, the port can be used to extend the low frequency response in the same way a bass reflex can extend the low frequency response over a closed box. In a non-ported horn the driver is only loaded by the (small) closed box below the horn cut-off, which is quite inefficient (especially with low Qts drivers) at lower frequencies. Below the tuning frequency, the roll-off will be steeper in comparison with a closed chamber (~24 dB/octave for ported, ~12 dB/octave for closed chamber). 
Because horns generally have relatively small rear chambers the vent needs to be quite long in order to tune it low enough. Too long and the port will develop a ¼ wave resonance in the intended frequency range. Too short and the port area may become too small, which leads to chuffing aka port-noise, especially at high power inputs.
For this reason you might want to check the “port velocity” in programs such as WinISD Pro  or Bass Box Pro 6, to ensure that it stays below 34 m/sec. Simulate the rear chamber/ port as a normal reflex enclosure and apply the maximum power input in the signal tab. A high pass slope can than be added in the “filter tab” as this will result in a significant decrease in port velocity.

Acknowledgements

In random order: Paul Spencer, Johan Rademakers en John Sheerin

Edited by mobiele eenheid - 30 April 2018 at 7:47pm