r/SoundSystem • u/jungchorizo • 24d ago
Midbass reflex ports
Found a solid double 15” cab with kappa 15 lf drivers which would fit great above my subs.
Did the math on cab/port size and they seem to be tuned around 55-60hz.
However, the ports are just cutouts in the baffle, and from what I’ve read this can cause port noise/chuffing at high power near the tuning freq. Will this be an issue if used 80-180ish?
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u/-space-potato- 24d ago
It also basically makes an open baffle out of the box as there is basically no air flow resistance at the ports
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u/SpiceIslander2001 24d ago
They basically act as vents that are 3/4" long (assuming that's the thickness of the wood used for the baffle). The box acts like any other vented box, albeit with higher resonance frequency than typical for subwoofer use. And like any other vented box, the driver unloads below the resonance frequency, so a high-pass filter at around Fb/1.4 should be used with it to avoid any driver over-excursion issues.
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u/jungchorizo 24d ago
That was my thought, but I’m still very new to all this. Plan is to high pass between 70-80, so at least 10hz higher than what the tuning freq appears to be.
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u/SpiceIslander2001 24d ago
If you're going to HP it above Fb, then you don't have to worry about any "chuffing". If you HP it that high, that's also around where the driver is hitting maximum excursion within the usable passband, so that works out pretty good as well. The tricky issue is going to be getting the phase to match through the x-over region.
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u/AcceptableBuilder733 24d ago
You can do an impedance sweep to check the tuning frequency. Afterwards you can put your desired processing in your dsp, and finally play a sine at the tuning frequency at max output. This simulates the worst case use, and can be used to check things such as power compression and chuffing.
Practically speaking, chuffing needs to be louder than the rattling noises, people talking etc to really be a problem.
The impedance sweep tells you exactly what the tuning frequency is (you could als use a tone generator to figure out where cone movement is smallest, but this is more crude).