Internal narrow-band absorption techniques?

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I added a resonant branch.
The position is critical.
It seems to me that it has the maximum effect if placed near the exit.
It has a narrow band: damping is required.
Blue: only the empty port;
Brown: adding a 32cm resonant branch;
Violet: adding acrylic in the branch, empty TL

 

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setup

 

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It seems to me to retrace the history of electroacoustics ...
Some figures moving a cylinder of heavy absorbent 12cm, along the pipe, stuffed box:
green: in the throat
brown: intermediate position
blue: intermediate position
black: to the mouth
yellow: empty pipe

 

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Doubt about dynamics and test (by poor equipment):

 

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... and what about a FRB?

A Helmholtz resonator acts as a bass band. A tube closed at one end resounds at the fundamental frequency and harmonics.
Resonances in boxes often contain fundamental and harmonics.
Why prefer Helmholtz?
How does a fluted resonant branch behave?
Will it have one or two frequencies of action?
If they are multiple, will they be independent or related?
Will it be possible to use a FRB to increase the bandwidth of a resonant pipe adsorber?

 

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The resonance group 0.7-1.5 kHz originates in the box.
I tried to use helmholtzen, branches, different fillings, but I have the best result by covering the free walls with 4cm of polyurethane.
Blue: empty box
green: 4cm polyurethane over 3 walls
Any experience?

 

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I chose to build the speaker.
Today: a single box, only midrange, at listening point.

 

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The pipe facing the floor is harmful.
Parallel to it is better.
Something in topic: is the resonant branch capable of reducing the cone displacement beyond Fc?

 

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What is pipeness?
A pattern nested in the frequency response, masked by the smoothing, which the brain immediately recognizes?

 

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[AUTOQUOTE] It seems to me to retrace the history of electroacoustics ...

I think I should move to managing the back radiation with a correctly aligned bandpass.

However, I will jump to an era where watts and drivers are available cheaply.

I ask forgiveness for the amount of OT interventions.