TQW-JCA tutorial

First, some preliminary considerations before using the tool.

INTRODUCTION:

In order to build performant DIY speakers, the choose of the drivers (i.e. Audiotechnology,

Scanspeak, SB Accoustics, Dayton Audio, Faital Pro, Seas, Davis Acoustics etc…) and the crossover

components (i.e. Jantzen, Mundorf, SCR, etc…) drives you towards a relatively high budget.

This means that it is important to avoid mistakes before ordering the components.

As a consequence, the simulation must be as accurate as possible.

In order to build a new speaker from scratch, it is necessary to look for:

• Choosing the appropriate driver

• Crossover design

• In addition, because it’s never the case, a tool to optimize some other aspects: not only SPL flat

response), but also Offset plus Phase and Group Delay.

• A tool to calculate the enclosure specially for Transmission Lines; because the knowledge and the

tools for this technology are not common.

• A tool to verify if your enclosure is well designed (before calculation, to confirm, and after

calculation, to valid the choices)

• A tool to draw the box and wood-cut before construction.

That’s the reason why I developed this full integrated EXCEL spreadsheets with:

• The validation of driver’s choice.

• The Crossover calculation (limited to classic 6/12 dB Butterworth and Linkwitz-Riley).

• The Optimization of this filtering according to Jean Michel Le Cleach’ (JMLC)

recommendations.

• The Calculation of a Quarter Wave Tapered Line, according to Martin King’s specifications.

• The design of the complete Drawings and wood-cut of the Enclosure.

CHOOSING A DRIVER FOR A TRANSMISSION LINE:

Four T&S parameters (without Sd) of a Driver are influencing the sizes of a TL:

• Fs (should be low)

• Re (should be low)

• Qts (should be “medium”, but not too low)

• Bl (should be high)

From my point of view, if you want to realize an enclosure with a reasonable size, the main item which has

to be solved is the cross section (more than the length (L)) of the line.

Below, the curves that give the variations of the close end section (SO) of the line, according to these

parameters. It is an example made with a specific enclosure obtained by varying the 4 parameters one by

one, keeping the others at a medium value.

Vertical axis is representing the section of the close end section (SO) in cm2.

• Fs: the variation is linear, by experience, Fs should be as low as possible below 40 Hz.

• Qts: the section decreases rapidly when Qts increases: don’t’ expect small sections with a Qts less

than 0.35.

• Re: the variation is linear, Re should be as low as possible (that’s the reason why it’s interesting

to put two drivers in parallel).

• Bl: the section decreases rapidly when Bl increases, so it is better to have Bl greater than 6 or 7.

In TQW-JCA Excel Sheet, controlled T&S remain green if they satisfy the following conditions:

CROSSOVER CALCULATION and OPTIMIZATION:

No comment for Two Way Crossover Design, using Butterworth or Linkwitz-Riley 6 or 12 dB.

Find here some complements on JMLC Criteria.

On Axis: or SPL, is the

Response on axis.

This is the resulting curve

of all the chosen settings,

for the response at the

listening point (on this

(good) example, it is

hidden by Coincidence)

In Coincidence: it is

important for predicting

the tonal color of indirect

waves, i.e. due to

reflections or

reverberations.

In Opposition: an

indicative and calculated

response with tracks in

phase opposition to all

frequencies.

Phase Delay: must be

small and continuous and

is to be minimized below

4000 Hz.

The problem is that if you look for the minimum propagation time, you degrade the response in the axis.

Group Delay: Phase variation is expressed here in millimeter rather than milliseconds

The response to a square signal 100 Hz is given as an

indication, because it is necessary first, to optimize Axis,

Coincidence, and Group Delay.

DESIGN OF THE TRANSMISSION LIGNE

With Martin King tables or calculation with the following parameters:

• Fs,Qts,Re,Bl and Sd,

• Frequency (close or equal to Fs), for a Qts between 0.3 to 0.6, it is

recommended by Martin King to take Fr equal to Driver’s Fs; for a Qts

below, to take Fr 5 to 10Hz below, for a Qts above 0.6, to take Fr 5 to 10Hz

above.

• Tapering of the line (Open/Close), it is recommended by Martin King to

take this ratio lower or equal to 0.2.

we get Line Length, and cross sections SO & SL of the line.

The design is a little bit more complex, because:

• the line is folded,

• the length of the line is calculated in the center of the cross section.

At this step, it remains to reduce the ripple by adjusting the driver Offset from about 𝐋𝐢𝐧𝐞 𝐋𝐞𝐧𝐠𝐭𝐡(𝐋)

𝟓 of the Close section SO: in this design, the minimum possible Offset is

the radius of the driver.

Finally, the residual ripple is reduced by Damping in the first part (β1) and the

second part (β2),

These two operations can be easily simulated by Hornresp or AjHorn, as it is

shown on the figure below (in black after getting the best position (Offset) for the

drivers(s) and in red after adding Damping).

β1

β2

Martin King Tables recall:

For more information, connect to www.quarter-wave.com.

Using JCA-AjHorn or JCA-Hornresp

Due to the length of the Quarter Wave Line, the Enclosure is, of course, a Floor-Standing Speaker, and the

line is Tapered plus Folded.

The design includes the following items:

• Cross-over design, drawings and wood-cuts for the two floor-standing Speakers.

• All Drivers plus Open Mouth are placed in Front.

• Drivers are proposed close to the top, but you can move them for Ripple optimization.

• Mouth is at the bottom and you cannot move.

• With 1 or 2 Bass/Medium, plus 1 Tweeter, above, below or in between the Bass/Medium.

• Or with 1 or 2 Broadband in Front without Tweeter.

• The Bass/Medium or Full Range Drivers can be connected in Parallel or Series.

• All sheets are protected by a password (except the cells to be filled).

Plan1 Plan2 Plan3 Plan4 Plan5 Plan6

Bass/Medium Full Range

TQW-JCA is an EXCEL file composed of 12 sheets as follows:

Sheet 1 DRIVER For introducing T&S of the drivers and different sizes for the

enclosure

Sheet 2 JMLC Optimization for Two-way filtering according to Jean Michel Le

Cleach’ recommendations.

Sheet 3 CROSSOVER Two-way Crossover design

Sheet 4 ENCLOSURE Tapered Quarter Wave Line calculation according to Martin

King recommendations

Sheet 5 Plan1 Drawing/Woodcuts for 1 Tweeter above one Bass/Med.

Sheet 6 Plan2 Drawing/Woodcuts for 1 Tweeter under one Bass/Med

Sheet 7 Plan3 Drawing/Woodcuts for 1 Tweeter between two Bass/Med

Sheet 8 Plan4 Drawing/Woodcuts for 1 Tweeter above two Bass/Med

Sheet 9 Plan5 Drawing/Woodcuts for one Full Range

Sheet 10 Plan6 Drawing/Woodcuts for two Full Range

Sheet 11 DATA Internal Data

Sheet 12 Changes Change Control (modifications, corrections and Releases)

If you don’t’ have neither AjHorn nor Hornresp, use JCA-AjHorn.

If you have AjHorn, use JCA-AjHorn

If you have Hornresp, use JCA-Hornresp

Start the design with DRIVER sheet:

And fill in all the parameters (in red on a green background).

Enter Project name, Bass/Medium or Full Range and (optional) Tweeter references.

Enter the T&S of Bass/Medium or Full Range Driver(s).

Specify the type of assembly

with the LAYOUT of Drivers with the help of the

drop-down menu

The Isobaric Push Pull offered here will not generate

usable plans, only the sizes of the quarter-

wavelength line and filtering can be used.

If a value of T&S is unknown, put 0.

Attention!! the impedance at Fc/1K/10K is to be determined precisely.

If you don't know Xmax, you can calculate it from V. Coil and Air Gap.

Just below, this sheet controls the suitability of the Driver(s) for the quarter-wavelength line.

If the Driver(s) fits perfectly, all the boxes remain green.

With orange boxes, we can still simulate the box, but we should expect some "discomforts”.

Introduced values are automatically copied to the other pages.

Note: you may want to use a Bass/Medium with a slightly low Qts: you can then add a series resistance to

improve this Qts, the ideal being around 0.45.

If there is a Tweeter, fill its main T&S, otherwise, put 0.

Also provide information for all Dimensions imposed for the enclosure.

If Full Range, 2-way filtering is useless, go directly into ENCLOSURE to determine the quarter-wavelength

line.

Go to JMLC sheet:

In order to choose:

Tweeter cut-off frequency:

At least 4 times Fr for 6 dB, 2.8 times if 12 dB and 2 times if more

If the cut-off rate chosen for the Tweeter is too low, the corresponding box in the JMLC sheet is switched to

red.

Bass cut-off frequency:

Also chosen here, but there is no control.

It is essential to choose this frequency to get rid of the peak splitting in the treble.

The steeper and/or lower this split peak, the lower it will require a low cut with a steep slope

Type of Butterworth, Bessel, Casc. or Linkwitz-Riley Filters

• With passive filter, only Butterworth or Linkwitz-Riley models are taken into account with slopes

of 6 or 12 dB for bass and 12 dB for treble.

• With active filter, HYPEX recommends Linkwitz-Riley 24 dB, but anything is possible above order

2. With active filter, the resistance series of the coil is set to zero.

Tweeter and/or Bass/Medium shift: 0° or 180°

Depending on the filtering model.

Offset the Bass/Medium and tweeter

Don’t’ mix this Offset with the TL offset!

The first thing to evaluate is the relative origin of the sound, coming from the Bass/Medium driver and from

the Tweeter. By construction, they are never on the same plan, but as represented approximatively on the

following figure.

JMLC gives you the possibility to take it into account in the simulation

A first evaluation of this offset can be made by measurement.

Another solution is to evaluate this Delay (time ➔ mm) by measurement, using for instance, REW.

If Hypex digital filtering has been chosen, HFD can measure and apply a delay on the Channel 1 Bass,

versus Channel 2 Treble, so forget this in JMLC.

Of course, chosen Frequency cut-offs are copied to the CROSSOVER SHEET.

Go to CROSSOVER sheet:

In order to finalize the adjusting of the components with the standardized values of the components of the

filter R, L and C.

• For Coils (L), find the closest value.

• The resistance of the coil, in series with the bass driver is

automatically updated (in 14 AWG) in order to correct the Qts.

• For active digital filtering, this value of the resistance is forced to

zero.

• For Resistances (R) and Capacitors (C), in order to get the closest

values, the sheet helps you by calculating both values in Series or

in Parallel.

The values of the filter components are not affected by the Speaker Offset, so you can go into the JMLC

sheet to refine this offset without having to retouch the frequencies.

A number of Back and Forth between CROSSOVER and JMLC are often needed in order to complete

filtering.

Go to ENCLOSURE sheet:

Choose Fs, frequency of the quarter-wavelength line

Fs is influenced by Qts. The general rule is to choose Fs close to the resonance frequency of the Driver with

the recommendations shown opposite in the green cell. The lower Fs, the weaker the sections of the line will

be, but the longer it will be.

Choose Tapering between the Begin (SO) and Exit (SL) sections of the line.

Be aware of probable problems if you are obliged to tune the Ratio SO/SL under 5.

Do CALCULATE .... you're probably going to get a cross section too big

Choose Reducing the Section to adjust the cross section of the line, while remaining compatible with the

maximum dimensions imposed: you can reduce until the corresponding control versus your constraints

becomes green.

You can see that the smaller you get, the more the cell gradually turns red.

A control is done on this cross-section which must not be lower than Sd*1.5, otherwise, the corresponding

cell turns to red.

Reducing, in parallel with Tapering, are actually a way to play with your settings to respect the dimensions

of the Enclosure.

Do CALCULATE

In fact, you have to do CALCULATE every time you change something.

Checking’s:

Length of the Line

Checking should not

remain red.

No box should pass in

red, the orange boxes

are warnings, the ideal

is that everything is

green.

If one of these cells

remains red, that

means that the

calculation is

impossible.

You probably have to

modify your project.

You can also try to correct the Baffle Step, indicated at the bottom of this sheet, of course, only if it is

identified with the measurements.

Nothing in this tool to do that.

In order to finalize the project, it remains to optimize the ripple by possibly repositioning the Driver(s) in the

line and adding Damping.

Go to Plan1, Plan2, Plan3, Plan4, Plan5 or Plan6 sheet:

Depending on the configuration chosen at the beginning: the proper drawing sheet is indicated both in

DRIVER and ENCLOSURE sheets.

1° With AjHorn :

Create the project and fill in:

• T&S of the Driver, and

specify if there are one or

two drivers.

• Values provided by

Plan.X.

• First, put β1, β2 to 0

You can now try to reduce the ripple: by moving the Driver(s) within the permissible limits of the Front face

of the Enclosure (that’s the reason why we have Plan.X. sheet in parallel)

Plan.X sheet controls the position of Driver(s) on the front panel, so that the appropriate boxes on the

drawing must remain green.

After getting the minimized ripple, by moving Driver(s), you can

add Damping.

300g/m3 in the first part and 200 g/m3 in the second part of the

line, of Dacron Holofil, are generally sufficient.

You can now introduce the values that you have got by tuning or

keep those proposed by JCA-Hornresp.

ANYWAY, you have to fill the RED/GREEN cells, as

described beside.

2°Without AjHorn:

Fill in the cells in red characters on green background, with proposed values.

The addition of Damping in the line changes the speed of the sound and therefore, the length of the

line, so you have to return to ENCLOSURE and CALCULATE.

Dont’ forget to

fill choosen values

!!

3° With Hornresp

Create the project and fill in:

• Depending if you have one or

two Drivers, Hornresp is a

Backloaded with 3 or 4

conical (Con) segments

• The blue cells are the values

proposed to be introduced in

Hornresp for the Horn shape,

by PlanX.

• For T&S of the Driver, take

the ones introduced in

DRIVER sheet and specify if

you have one or two drivers.

• First, simulate without Filling

You can now try to reduce the ripple: by moving the Driver(s) within

the permissible limits of the Front face of the Enclosure (that’s the

reason why we have Plan.X. sheet in parallel)

Plan.X sheet controls the position of Driver(s) on the front panel, so

that the appropriate boxes on the drawing must remain green.

After getting the minimized ripple, by moving Driver(s), you can add

Filling.

300g/m3 in the first part and 200 g/m3 in the second part of the line, of

Dacron Holofil, are generally sufficient.

You can now introduce the values that you have got by tuning or keep

those proposed by JCA-Hornresp.

ANYWAY, you have to fill the RED/GREEN cells, as described

beside.

Dont’ forget to

fill choosen values

!!

The values that you have tuned with Hornresp will certainly modify the TL.

Goto ENCLOSURE to simulate it again, but now, it’s different: you have to try to get the same shape as

proposed by Hornresp.

In order to do that, follow this:

1. Adjust Fs in order to get Line Length

2. Adjust Close Section in order to get the same section as Close

3. Adjust Tapering in order to get Mouth and Ratio.

4. CALCULATE

Its time to complete and refine the dimensions of the TL after tuning (either by AjHorn, or Hornresp,

or No tuning).

So, re-control everything in ENCLOSURE and PlanX.

Turning to orange, or even red, of cells that would be out of tolerance facilitates this control.

Since no solution is perfect, you have to repeat several passes to find the best combination.

Last CALCULATE

At the end, the drawings and wood cuts for two speakers are in Plan.X.