I use quite a bit of vent area and always have a 90 degree turn.
I've never noted any bad sound coming from any sub I've built. My 12 cube sub with 2 15's has a 5x18 slot and 40 or so inches in length with a 90 degree turn.
What would the resonance be for a 5x18x40" vent on a 12 cu' box? The 90 degree turn is at 19"
I've never noted any bad sound coming from any sub I've built. My 12 cube sub with 2 15's has a 5x18 slot and 40 or so inches in length with a 90 degree turn.
What would the resonance be for a 5x18x40" vent on a 12 cu' box? The 90 degree turn is at 19"
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About 168hz
Safely away from the bandwidth subs are used in, unless you want to cross over higher then usual.
It depends on how wide the shelf is, but mainly what you get is a higher tuning than predicted with its associated harmonics since its acoustic length will be somewhere between the long and short leg.
GM
Resonance is a function of the cross sectional area of the port vs its length, no matter the shape. All ports are in actual fact resonators, and a port coupled to a cabinet becomes a helmholtz resonator. Ports by the very nature will always resonate no matter what, what is important is that any audible harmonic resonances are well out of the ports operating frequency range.
Port resonance vs aspect ratio
So, taking an existing slot port and "cutting it in half" by putting a divider in the center of it made from 3/4 ply would do what to the resonance? (disregarding the slight loss of port cross section)
Dave
So, taking an existing slot port and "cutting it in half" by putting a divider in the center of it made from 3/4 ply would do what to the resonance? (disregarding the slight loss of port cross section)
Dave
Sorry, I need to correct my statement there, the resonance is a function of the physical length of the port. Tuning frequency is a function of cross section area vs its length vs internal cabinet volume.
If you cut a square ports width in half, and its length remains the same, the resonance doesnt change, but the tuning frequency of the system does and the air speed does. If the resonance is too low, then you need a dimensionally shorter port to push it further up the frequency range.
If you cut a square ports width in half, and its length remains the same, the resonance doesnt change, but the tuning frequency of the system does and the air speed does. If the resonance is too low, then you need a dimensionally shorter port to push it further up the frequency range.
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Tuning frequency, Fb, will remain the same for a divided port compared to an undivided port, other than the area change of the divider.
If you "cut a square ports width in half" and block off half, Fb does change.
anything special to consider with port resonance? (similar to the "golden ratio" for ported box dimensions).
Like the sound of bigger than recommended ported boxes tuned low (low 20's/high teens). Feel maybe something exists like such? (optimal port resonance) maybe no one has figured it out? Maybe someone has, but keeps it secret?
asking because had a big slot ported box one time, something was special about it. it literally seemed to resonate bass LIKE a church pipe organ
you know how you make sounds with empty glass bottles, lol, blowing across the top? the angle a which the air moves and speed at which it moves has to be right, or no sound. the whole bottle seems to shake also. swear dude, maybe some frequencies played in box did the same thing to the port, producing another audible, "flute like" sound?
maybe not? (have been branded on other forums/websites for the idea above...maybe people who know car audio but can't take a new fact)
A nice pic.... http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/blowing-on-bottles/
However, don't see how it could relate to the slot port opening at the end of the port, nor the start of the port (inside the box)
Like the sound of bigger than recommended ported boxes tuned low (low 20's/high teens). Feel maybe something exists like such? (optimal port resonance) maybe no one has figured it out? Maybe someone has, but keeps it secret?
asking because had a big slot ported box one time, something was special about it. it literally seemed to resonate bass LIKE a church pipe organ
you know how you make sounds with empty glass bottles, lol, blowing across the top? the angle a which the air moves and speed at which it moves has to be right, or no sound. the whole bottle seems to shake also. swear dude, maybe some frequencies played in box did the same thing to the port, producing another audible, "flute like" sound?
maybe not? (have been branded on other forums/websites for the idea above...maybe people who know car audio but can't take a new fact)
A nice pic.... http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/blowing-on-bottles/
However, don't see how it could relate to the slot port opening at the end of the port, nor the start of the port (inside the box)
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alright, for future newbies (who search "adequate port size to reach Xmax")
The formula (in inches^3)............... S(V) >= 0.02032 * f(B) * V(D)
S(V) : volume of the port opening
f(B) : port tuning frequency
V(D) : S(d) times Xmax
S(d) : subwoofer cone area (πr^2) (r= radius) (r = diameter/2)
remember to convert all measurements to inches when calculating the right side....
0.02032 * f(b) * xmax(inches) *Sd (inches^2)
the left side will be (width * height) of the slot port
The formula (in inches^3)............... S(V) >= 0.02032 * f(B) * V(D)
S(V) : volume of the port opening
f(B) : port tuning frequency
V(D) : S(d) times Xmax
S(d) : subwoofer cone area (πr^2) (r= radius) (r = diameter/2)
remember to convert all measurements to inches when calculating the right side....
0.02032 * f(b) * xmax(inches) *Sd (inches^2)
the left side will be (width * height) of the slot port
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Hope we're staying on topic of the thread, maybe feels the info above should go into a new thread?
can you state the "function" in which you are talking about?
is it like the formula?
do you have an opinion on if the port could act like the opening of an empty glass bottle making noise when air moves across it?
can you state the "function" in which you are talking about?
is it like the formula?
do you have an opinion on if the port could act like the opening of an empty glass bottle making noise when air moves across it?
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