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Discussion Starter · #1 ·
Hi fellas,

Got a box design with a first port resonance is 122Hz. I have read several topics on here itself about this issue, but have not come across a definitive "this is the rule of thumb you should go by" or a final value. Those were a few years back, and would rather not resurrect an old thread. I was wondering if any further testing has been done since to verify the uncertainty of such a scenario and the outcome.

The box is 5 cubic feet net, 10 cubic feet gross. 18.5" x 3" x 55" long slot. Tuning is 21Hz-ish. There will be 2 bends in the port, as opposed to one where it reaches the end and turns and just finishes. It is a long port. Just thought I'd mention as apparently more turns/bends can reduce resonances. Could be wrong.

I was planning on using a very steep (8th order, if possible) LPF to roll this off at a considerable rate - at about 60-80 Hz. I have read Steve's view and Collo's view on this, and I am not sure what to expect if a box whose fpr is 120Hz-ish. Steve says use a port no longer than 36", with a resonance no lower than 190Hz. I have seen Mike P. suggesting a 125hz resonance will be fine with a 4th order @ 80Hz.

What are some of your thoughts/opinions on this?
 

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Discussion Starter · #4 ·
Thank you for clearing that up Mike, For now this will be more music than HT.

See here Mike:


Yes, that port is huge. It needs to be as it is going to be housing a custom built Z v.4 15". With 2000w input the port airspeed still tops 26 m/s, and Collo's flare it program indicates I will still hit chuffing. I am of course taking into account a real world situation - I will not be sending a 2000w 20Hz sine wave for any prolonged period of time, so I concluded I will be okay. If I drop the width to 2.75", it almost hits 30 m/s. Slightly OT but what would you do here?

fusseli: Thanks, that figure helps. If I use a 8th order LPF, assuming 70hz, 122Hz is -38dB. This is close...
 
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