I cannot help much here...
I use what was in my basement...
I only use one bottles or pipes at a times...Adjusting it mechanically for a better timbre instrument perception...
It takes me almost a year after the passive material treatment to increase the Helmholtz grid or the mechanical equalizer like i call it because it is a grid not a couple of bottles......
I did not count them but i have more than 40....Under 50....
I tune them almost one at a times and fine tune the lenght of each one neck with ears like someone fine tuning a piano...
Some are traditional Helmholtz resonators with a neck... Other are a tubes with no neck and work more like a diffuser than a damper...Anyway each resonator absorb and diffuse...The diffuser simply diffuse more...
Dont desesperate about the variables.... You must confide and trust in your ears perception of very well known instrument....( piano choral voices)
Any errors or imperfect tuning you will make will be corrected and fine tuned at the end by another one.... After more than 40 pipes i feel no distortion of the sound at all.... All improvement in a relatively large bandwith sample like a human voice, is a TRADE-OFF, corrected by another pipe...And the process go on...
This grid cannot be implemented in a living room....
And dont do it if you dont enjoy the experimenting process...There is no short cut way.... You cannot compute S.Q. with an A.I. for now...You must use your ears....
I did it because learning was fun.... And incredibly each addition was a relative improvement.... At the end i stop because any addition was a decrease in improvement... Simple...
I cannot help you for the material used or the proportion because i did compute nothing.... It was way more fun to listen and correct it... One at a time...with my basement junk...
Sometimes using an " approximation walk" experimental method tthrough all variables, of plus and minus guessing estimates, with multiple tubes tuning , is way more powerful than 9 identical tubes on the main reflective spot of the room... Like the ready made product "Argent room lenses" that inspire me one evening 2 years ago and which cost more than my audio system....My Helmholtz grid cost me nothing and is more powerful anyway....
A cue: locate them around the first reflective point on the wall beside each speakers, and dont use the same tubes nor the same proportion symmetrically...I place some behind my listening position between the speakers but on the opposite wall.... Anyway experimenting is key.... No room is similar...
And remember that the passive material treatment between diffusive surface, reflective one and absorbing one is complementary with the grid and cannot be spare... Active mechanical control by the grid and passive material treatment are complementary... One cannot replace the other ....
By the way the gas cans millercarbon has seen were there BEFORE i created my grid with plumber pipes and tubes... my virtual page has no image of this grid.... I even use paper toilet empty rolls then i dont want to attract the smile of " idiots" with photos of my " mad scientist" audio room....I am not crafty person at all.... But i can read psycho-acoustic articles or book.... This inspire me...
By the way they are cues about my journey in my thread : "miracles in audio.... "
And dont put any water in the tubes it is not necessary.... 😊
My best to you....
