Hello, I would like to understand better what happens on a speaker with high EBP if it's placed in a sealed box. I know that the lower end of the frequency response is going to extend less and is going to drop with something looking like a 6db/octave filter unlike vented one where the drop if sharper. But given the fact that the lower end is not needed is there any other disadvantage in doing so? I would think that this would be a way to lower low frequency distortion in high output lvls without using a high pass but from some experiments it looks tome like the linear movement of the driver is increased for the same lvl of playback at the same frequency.
closed box has a 2nd order lower roll-off (12 dB/oct); vented 4th order (24 dB/oct).
for effects on specific drivers/box have a look at this useful online calculator (closed vs vented box):
http://www.mh-audio.nl/Calculators/CCB.html
edit - closing a vented box will:
- raise lower cutoff frequency (may be bad if you like/need it)
- increase driver excursion at former helmholtz resonance frequency (may eventually be a problem for low frequencies)
- reduce driver excursion below former helmholtz resonance frequency (good)
- reduce group delay at former helmholtz resonance frequency (good, but anyway there will not be much output here)
- remove previuous duct resonances (good)
- remove eventual chuffing of port (but again, there will not be much output in that frequency range anyway)
- may increase heating up of voice coil and internal air volume
- .... (there will be more that I am not aware of!)
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raise lower extension ? what do you mean by that. i though that the system will loose low frequency extension? or are you speaking only for the woofer output without the reinforcement of the port? the helmholtz resonance frequency is the resonant frequency of the driver or the tuning frequency of the port?
sorry for my poor wording: you are right, the lower cutoff frequency will be raised. the box will lose lower extension.
corrected the post above!
helmholtz resonance is the resonance of box with port; it's result is the output of port.