Is there a formula for this resistor?

I often see the modified second-order crossover topology, as I call it myself, used in many speakers. Notice the R1; it is usually found on low-pass filters in both 2- and 3-way systems.

The simulation showed that the R1 is used to modify the slope of the low-pass filter, or someone could define it, in other words, as a Q adjuster.

According to observations, its value usually stays in a range of 0.5 to 2 Ohms. I believe the manufacturers don't put it there randomly. Despite my research into many of Loudspeaker's cookbooks, I found little to no mention of them.

Therefore, I'd like to ask directly: Is there a formula or calculation method for R1?
 

Attachments

  • 2023_08_11_13_17_30_Window.png
    2023_08_11_13_17_30_Window.png
    20.8 KB · Views: 107
Last edited:
Dear Prescott,

Recently you posted a number a questions regarding loudspeaker x/o filtering. I would highly recommend to start experimenting with a basic filter simulator, in order to get some feeling for what parameters and which components do what. i.e. have impact on the transfer functions.
You then no longer need to guess or fidddle with primitive calculators. For basic design and experiments with real systems, however, you need in-box measured files of SPL (usually .frd or .txt format) and impedance (.zma format) . Even if you do not have access to measuring gear yet, many here have posted their measurement files, which could be imported into the simulator.

XSim (developed by Bill Waslo, who has a track record second to none) is free and easy to use: there is thread here on diya on XSim.
The value of R1 depends on the required properties of the lowpass leg of the filter+driver combi.
 
  • Like
Reactions: 1 users
For such a single component, I try out different values in a simulation program (in VituixCAD, turning the mouse wheel up and down with the mouse pointer on the field for the value) until it fits. I don't use a formula for such things and I doubt that there is already a ready-made formula.

Many greetings,
Michael
 
Last edited:
  • Like
Reactions: 1 user
R1 could be one of two things: either a resistor to modify the slope of a second order xover, or, combined with C1, part of a Zobel network. Either way, there are explanations for both readily accessibly by google. I suggest the OP put in a bit more effort rather than expecting to be handed easy answers on a plate to his incessant questions.
 
  • Like
Reactions: 1 user
I would highly recommend to start experimenting with a basic filter simulator, in order to get some feeling for what parameters and which components do what. i.e. have impact on the transfer functions.
There isn't a generic formula for it when used in the context you are referring to, because it's inherently a variable & used / adjusted to suit a specific circumstance and object.

These two comments complement each other well.

In my experience, one might proceed from a theoretical approach, inserting filters and contouring based on the assessment of the respective drivers' measured response. This will give you a basic and rough design from which to proceed. Then, with the aid of the software's built-in optimiser, the solution typically reveals redundant components and/or network legs. So the final schematic might end up a much simplified configuration than what was initially envisaged. Trying to reverse-engineer this back to fundamentals then becomes a complicated and almost futile exercise. So, the advice to work forward is well-given IMO.
 
  • Like
Reactions: 1 users
XSim (developed by Bill Waslo, who has a track record second to none) is free and easy to use: there is thread here on diya on XSim.
Ha! Xsim produced exactly nothing on my PC. LibreOffice Spreadsheet couldn't make it do anything. You better have microsoft Office tapped into your bloodstream to Use this. $600 a year in updates or a brick.
Either way, there are explanations for both readily accessibly by google.
As the Assoc, Professor that gave me a D- in quantum mechanics said, "It is obvious that" blah blah blah. I replaced him with another Assist. Professor at another school that spoke English (with a Pakistani accent), but wasted a year.
LC circuits parallel to a driver suck off current at a particular frequency, to damp a nasty peak or resonance in the driver at that frequency. You don't want zero driver response at that frequency, you want response even with all the other frequencies. The resisitor in the LC circuit limits the amount of current at that frequency sucked off.
 
Last edited:
Ha! Xsim produced exactly nothing on my PC. LibreOffice Spreadsheet couldn't make it do anything.
Eh? XSim is a standalone piece of software. It does not require any office suite, or anything other than a reasonably modern version of MS Windows.

You better have microsoft Office tapped into your bloodstream to Use this.
Nope.

$600 a year in updates or a brick.
FWIW, I'm running Office 2019, standalone. I paid £80 for it, and get the usual updates. I'm no 'power user' but I'm still an academic (even though I don't get paid) & it does everything I need. A slightly moot point though, given that XSim doesn't require any office software to run.
 
  • Thank You
Reactions: 1 user
It does not require any office suite, or anything other than a reasonably modern version of MS Windows.
When the update from Win 98 to Win XP obsoleted my Office suite, and required replacement of my PC mainboard, I fired Microsoft. Try to run your PC with the "free" update provided by the computer repair shop. After a few months the PC reboots every 22 minutes. By that time XP updates were no longer for sale, I would have had to buy a new user Win 7 package, plus Office.
I do sims with an office calculator and RLC equations, plus Kirchoff's laws. Math has no planned obsolescence
 
When the update from Win 98 to Win XP obsoleted my Office suite, my favorite game, and required replacement of my PC mainboard, I fired Microsoft. I do sims with an office calculator and RLC equations, plus Kirchoff's laws.
I don't doubt it did, or that you prefer to design that way (fair enough), but that doesn't alter the fact that XSim is a standalone program that doesn't require any kind of office software at all to use.