Help me understand this simple question


Bronze Member
Username: Langless28

Post Number: 92
Registered: Dec-04
so a port is tuned to a certain fq and does that mean that at that fq the bass would be lounder? if so if a song had a nice steady fq phase change(meaning like 100 down to whatever) the bass at port tuning would be louder at that one point, making the steady downfall of notes kinda broken up? plz expalin i want to know everything ha. also
_Chamber 1
Vb = 1.50 cu.ft. (42.48 liters)
Fb = 40.96 Hz.
QL = 7
F3 = 36.43 Hz.
Fill = Minimal Polyfill

No. of Vents = 1
Vent Shape = Round
DV = 4.00 in. (10.16cm)
LV = 10.00 in. (25.40cm)_
what is that port tuned to the 36 or the 40?

Bronze Member
Username: Langless28

Post Number: 95
Registered: Dec-04
also, can i just change the port size to get the desired fq cus my old sub has a port with a fq that i enjoyed, (new and old box are 1.5 cubic feet) or will it mess up the new sub.

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 7792
Registered: Dec-03
the port's tuned frequency is the center point of the peak efficiency of the enclosure. going an octave in either direction from that point will show a decrease in output.
Generally the roll off will be gradual going upward in frequency, and the drop off below the tuned frequency will be very steep.
It's very hard to control a speaker below the tuned frequency of it's ported enclosure, which is why we use subsonic filters below the tuned port frequency to prevent the speaker from trying to produce frequencies below that point.
This loss of control equates to a loss of suspension damping, so the speaker can easily over-excurse and become damaged.
The point of using a ported enclosure, aside from the power handling effects, is for it's improved efficiency at or near it's tuned frequency. This is one reason we tune boxes made for SQ or daily use very low, usually around 35Hz (but still above the speaker's Fs.) This allows a harder hitting response at ultra low frequencies.. The ones you tend to feel, below the point where things start to sound more boomy (above about 40Hz.)
If a system is built for SPL, you want the port(s) tuned closer to the sympathetic frequency of the car's cabin to get the most gain from the enclosure and thus the most output. This is usually around 60Hz though which is very displeasing to most people for musicality.

If you want to alter the port's tuned frequency, you need to change it's cross-sectional area.
The easiest way to do this with a round port is to trim it.
The longer the port with a given diameter, the lower the tuned frequency will be.
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