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The other day I played with the effects of a quarter wavelength resonator at the 150 Hz area (pressure minimum).

I tuned the pipet to 150 Hz, 344/150/4=0,57 m and attached the open end at 120 cm from S1, no damping, no paddles inside the horn.

I don’t think this is the right spot to work with a quarter wave resonator but it can be interesting nevertheless.

https://dl.dropbox.com/u/1320184/hififorum/Traadar/15%20tum%20MLTL/periskop.jpg

https://dl.dropbox.com/u/1320184/hififorum/Traadar/15%20tum%20MLTL/SPL-med-och-utan-resontor-150-hz.gif

Green curve: Just the horn
Red curve: Horn with 1/4 wave resonator tuned to 150 Hz

As we can see it didn’t make any change at all.

Just to experiment and see how things work I retuned the pipe to treat the peak at 170 Hz by cutting it a couple of cm shorter and got this result:

https://dl.dropbox.com/u/1320184/hififorum/Traadar/15%20tum%20MLTL/SPL-med-kort-resonator-i-mynningen.gif

It is interesting to how narrow the bandwidth that the tube affects is. So far the tube is without any damping.

Let’s see what happens when we connect the tube as close to S2 as possible. In this case the closest I could get is 25 cm from S2.

https://dl.dropbox.com/u/1320184/hififorum/Traadar/15%20tum%20MLTL/ror%20i%20borjan.jpg

After some trials I found the right amount of stuffing, which turned out to be next to nothing. Just too much and the effect of the resonator was ruined, just too little and I got a sharp notch.

https://dl.dropbox.com/u/1320184/hififorum/Traadar/15%20tum%20MLTL/ganska-liite-dampfluff.jpg

https://dl.dropbox.com/u/1320184/hififorum/Traadar/15%20tum%20MLTL/I%20b%C3%B6rjan%20170%20Hz%20SPL%20fas%203%20dist.png

Green Curve: Original horn
Blue Curve: With ¼ wavelength and damping tuned to 170 Hz

SPL, phase and third tone distortion.

Isn’t this pretty promising? One could take the volume for resonators in account in design rather easy and get a more controlled behavior above the crossover frequency.

/Forsman


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