I thought you'd seen the boxes?

I have

🙂
I'll just summarize how I calculated the quarter length, because while I trust my (albeit simple) math, I also know that you know some things I don't, and maybe I overlooked some things

😀
1. I found out the wavelength on here:

https://www.omnicalculator.com/physics/wavelength
Then /4, of course. At 70Hz it should be 4.9m. 4.9/4 = 1.225m So in my head, a line through from the first chamber to the last one towards the exit should be ~1.225m long, right?

2. I drew something up on my own and calculated the "line length" accordingly (I will use a Lance-model in the PDF as an example):

I will go from right chamber towards the end: Internal height (24.7cm) - the gap (5cm) + half the circumference of a circle with 5cm of radius. Then again: 24.7cm - the 5cm gap at the bottom and -2.5cm gap at the top, + half the circumference of a circle with a radius of 2.5cm until the end.

I quickly did the maths on a piece of paper and typed it into the PC:

25-5+15,7 = 35,7 for the first part.

25-5-2,5+8 = 25,5 for the second part

25-2,5-2,5+2 (not a half, but a quarter circumference) =22 for the last part

So we end up with a line of ~83cm which is a wavelength of 332cm or 3.32m

The FF85wk has a Fs of 115Hz.

oh wait. I see it now. Your calculation was and is correct!

__The "error" was that I had a speaker with a Fs of 75Hz and wanted to accomodate a quarter wavelength between 70 and 75Hz. That's where i ran "out of line length", so to speak 😀__
That's why I wanted to add a third panel to eek out an additional ~20-25cm to get down to 70Hz.

However I have clarify: I have no knowledge what role the gap-size and width of each section play. I wanted to ask you that anyhow: Why do some of the Lab-models get more narrow towards the end in gap-size

**and** width between the panels?

*How does the length of the panels and the width between panels correspond to the line-length?*

Basic physics tell me if the panel gaps and the width between panels open up towards the end, we should get a "horn like" behaviour, no? Why do we the opposite in a MLTL? 😀
After some iterations I have a rough sketch with dimensions that would end up with the correct line length. (Please keep in mind, the numbers and the sketch don't correlate in any matter. I just like to visualize things, even if it doesn't represent the proportions)

However I don't know the system behind the width between panels and the gap-size, so I don't know how far apart the panels and how big the gaps need to be.

(I calculated the total internal depth that is available minus the panels, and then divided them so that each panel is located half the length after another. If the first "room" is 12cm deep, the second one will be 6cm, the third 3cm and the last one + the vent will be 1.5cm.)

In other words: The total depth of the speaker cabinet with 3 internal walls is 187.5%. The first section/room where the speaker is located is 100%, the one after that is 50%, then 25% and then 12.5% of the internal depth. That's what I learned from your plans, I think. But what's the rule behind that? And how do the gaps correlate?