A port is not only a hole in the box but an area with a (tube) lenght. (WxHxL)
How much do you have at this point (your tube/vent area)?
(You say the internal volume is 4.6cu foot box - 4.6ft³ = 130.26L - and the driver mentioned is the Stereo integrity HT 15" Dual 2 Ohm subwoofer.)
How much do you have at this point (your tube/vent area)?
(You say the internal volume is 4.6cu foot box - 4.6ft³ = 130.26L - and the driver mentioned is the Stereo integrity HT 15" Dual 2 Ohm subwoofer.)
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1. Alignment (BR) 4.6ft³ = ~130L (internal)
Volume Vb : 130 L
Tuning frequency Fb : 19.0 Hz
Port 4" (round) S(area) vents : 78.54 cm2
or 2"x7 1/4" (5cmx18.5cm) (rectangular),
length of the port: 17 3/4" (45.13 cm).
Volume of the port : 0.15ft³ = ~4.2L
Volume of the driver : 0.19ft³ = ~5.4L
Total volume : 0.34ft³ = 9.6277L ~10L
New Vb : 130L (internal) - 10L = 120L (~4.2ft³)
Tuning frequency Fb : 19.0 Hz
New port length : 18.5in (~47cm)
Volume Vb : 130 L
Tuning frequency Fb : 19.0 Hz
Port 4" (round) S(area) vents : 78.54 cm2
or 2"x7 1/4" (5cmx18.5cm) (rectangular),
length of the port: 17 3/4" (45.13 cm).
Volume of the port : 0.15ft³ = ~4.2L
Volume of the driver : 0.19ft³ = ~5.4L
Total volume : 0.34ft³ = 9.6277L ~10L
New Vb : 130L (internal) - 10L = 120L (~4.2ft³)
Tuning frequency Fb : 19.0 Hz
New port length : 18.5in (~47cm)
Another tip. It's important if you use routed or make use of flared ports in your "extreme project", because of air noise at max output or to prevent it to happen. 
Port Flares
Port Flares
look there are some simple rules to think of..
first of all,
if the box isn't cubed, then you will get pressure build up in unequal portions that could really set ajar the movement.. thus increasing distortion because of manipulated soundwaves.
second of all,
consider the speaker..
a question is whether or not the resonant frequency is helpful or hurtful by allowing it.
literally, placing the port at the exact resonant frequency could result in muddy distortion or a bit more freedom to increase slew.
then there is the question of the ports location itself, because sometimes you can get the exact phase as the woofer (and then there would be a time delay somewhat sometimes between soundwave from cone and soundwave from port)
or sometimes you can get the exact opposite phase simply because of where the port picks up the soundwave from inside the box.
then going further towards master quality..
there is the consideration of allowing freedom of movement in the lower bass area below the resonant frequency as helpful for clarity and|or slew , or more muddy distortion.
sometimes a sealed box can decrease the amount of thump from a drum kick if desired.
sometimes a ported box can give extra output where amplifiers roll off at the lower end, or simply allow the amplitude without the equalizer band present.. because once the box loses pressure at the horn frequency the cone has freedom to move more with less power (as long as the impedance hasn't risen in that area of the frequency spectrum).
sometimes simply aiming the tune of the horn (the port tune) at the highest impedance point will be enough to get a flat frequency response.
but maybe you aren't looking for frequency response, yet are interested in the SPL response.
sometimes the difference between the room's resonances and the speaker's impedance peak is far too different, and instead the horn's tune is aimed at something for the room.
sometimes people aim the horn at the lowest frequency the speaker is specified to play.
sometimes people aim the horn at some low frequency that is in coordination with the room's resonance because of intentions to put modulation or phase coherency in practice.
sometimes people aim the horn at a specific frequency to simply dampen the timing of the speaker cone in coordination with the intention to put modulation in practice.
i don't think the choice is really too difficult, because most of the time there isn't an equalizer knob for the lowest notes.. and that means driving the amplifier louder, only to use the equalizer to turn everything else down.
getting louder lower notes with a sealed box breaks the laws of physics, and the only time it does happen is when the soundwaves are split in two so bad that the harmonics are working together (either specifically from the cone, or from interaction of reflections from the room) much like a harmonic bass booster.
obviously, if the harmonics are dubbed.. it doesn't happen by chance.
the specific speaker and box size would need to be matched with a specific room & atmosphere pressure.
otherwise the first frequency would always need to be output from a signal processor, and if you are using the room reflections as the secondary.. there are considerable differences in time to take note, and they might be so bad that you need ____ number of feet between you and the speaker before those soundwaves accumulate to add up to the final effect.
and sometimes, the soundwaves accumulate in one area.. then some distance later the accumulation breaks up .. it may or may not accumulate again.
(quite situation unique)
another thing to note about speakers in a box, regardless of whether they are sealed or ported..
do you put the speaker tucked away into the corner of a rectangle, with one pocket of tight and another of loose?
or
do you try to keep the area behind the speaker more loose?
one way or the other is probably going to sound better or show reason & purpose.
and even then..
do you put the speaker tucked away in a corner, then feed the end of the port down into the tight cavity to release some pressure?
i think it's called isometrics if you did.
first of all,
if the box isn't cubed, then you will get pressure build up in unequal portions that could really set ajar the movement.. thus increasing distortion because of manipulated soundwaves.
second of all,
consider the speaker..
a question is whether or not the resonant frequency is helpful or hurtful by allowing it.
literally, placing the port at the exact resonant frequency could result in muddy distortion or a bit more freedom to increase slew.
then there is the question of the ports location itself, because sometimes you can get the exact phase as the woofer (and then there would be a time delay somewhat sometimes between soundwave from cone and soundwave from port)
or sometimes you can get the exact opposite phase simply because of where the port picks up the soundwave from inside the box.
then going further towards master quality..
there is the consideration of allowing freedom of movement in the lower bass area below the resonant frequency as helpful for clarity and|or slew , or more muddy distortion.
sometimes a sealed box can decrease the amount of thump from a drum kick if desired.
sometimes a ported box can give extra output where amplifiers roll off at the lower end, or simply allow the amplitude without the equalizer band present.. because once the box loses pressure at the horn frequency the cone has freedom to move more with less power (as long as the impedance hasn't risen in that area of the frequency spectrum).
sometimes simply aiming the tune of the horn (the port tune) at the highest impedance point will be enough to get a flat frequency response.
but maybe you aren't looking for frequency response, yet are interested in the SPL response.
sometimes the difference between the room's resonances and the speaker's impedance peak is far too different, and instead the horn's tune is aimed at something for the room.
sometimes people aim the horn at the lowest frequency the speaker is specified to play.
sometimes people aim the horn at some low frequency that is in coordination with the room's resonance because of intentions to put modulation or phase coherency in practice.
sometimes people aim the horn at a specific frequency to simply dampen the timing of the speaker cone in coordination with the intention to put modulation in practice.
i don't think the choice is really too difficult, because most of the time there isn't an equalizer knob for the lowest notes.. and that means driving the amplifier louder, only to use the equalizer to turn everything else down.
getting louder lower notes with a sealed box breaks the laws of physics, and the only time it does happen is when the soundwaves are split in two so bad that the harmonics are working together (either specifically from the cone, or from interaction of reflections from the room) much like a harmonic bass booster.
obviously, if the harmonics are dubbed.. it doesn't happen by chance.
the specific speaker and box size would need to be matched with a specific room & atmosphere pressure.
otherwise the first frequency would always need to be output from a signal processor, and if you are using the room reflections as the secondary.. there are considerable differences in time to take note, and they might be so bad that you need ____ number of feet between you and the speaker before those soundwaves accumulate to add up to the final effect.
and sometimes, the soundwaves accumulate in one area.. then some distance later the accumulation breaks up .. it may or may not accumulate again.
(quite situation unique)
another thing to note about speakers in a box, regardless of whether they are sealed or ported..
do you put the speaker tucked away into the corner of a rectangle, with one pocket of tight and another of loose?
or
do you try to keep the area behind the speaker more loose?
one way or the other is probably going to sound better or show reason & purpose.
and even then..
do you put the speaker tucked away in a corner, then feed the end of the port down into the tight cavity to release some pressure?
i think it's called isometrics if you did.
most people that build boxes for a living simply have a box with a long rectangle behind it that slides back and forth with marks on the inside to tell them the measurement, then they use some cheap glue that peels off to seal the sliding part to note the frequency response.
but that isn't enough, because of what i said about the speaker performing better in the corner of a rectangle or in the middle.
that is when they either set up another box with the speaker in the middle of a rectangle with an adjustable edge piece.
but even that isn't always enough because sometimes loose on each edge and tight on the top and bottom is bad.
or
even loose on all four sides, but tight because the magnet is right up against the wood is another option.
sliding one edge and one back along long pieces of wood is typically the answer to making quick adjustments.
it's three sides + the speaker baffle, then the other 3 sides .. adjustable 2 with pre-cut pieces for the end cap to fit into each adjustment.
it's just a jig, but it can let one adjust the speaker position from middle of the rectangle to corner with one single end cap.. or slide the whole thing backwards with end cap fillers much the same as the other end cap.
but that isn't enough, because of what i said about the speaker performing better in the corner of a rectangle or in the middle.
that is when they either set up another box with the speaker in the middle of a rectangle with an adjustable edge piece.
but even that isn't always enough because sometimes loose on each edge and tight on the top and bottom is bad.
or
even loose on all four sides, but tight because the magnet is right up against the wood is another option.
sliding one edge and one back along long pieces of wood is typically the answer to making quick adjustments.
it's three sides + the speaker baffle, then the other 3 sides .. adjustable 2 with pre-cut pieces for the end cap to fit into each adjustment.
it's just a jig, but it can let one adjust the speaker position from middle of the rectangle to corner with one single end cap.. or slide the whole thing backwards with end cap fillers much the same as the other end cap.
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So I would be better off making my sealed box Vent ported?? Or Flare ported
Box is Apr-ox 4.5-4.7cu feet large enough to port
Ported would be lower distortion??Sub probably Audible about a mile, or half mile away
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i kinda shrug at the whole flared port versus non-flared port equation.. because some situations require the silence, while other situations can benefit from a little bit of chuffing sound to get the decibels at lower frequencies up more than the speaker could provide.
i imagine if the port was completely silent and the speaker rolled off at whatever low notes it rolled off at, using a port tube the right size to get a little bit of port noise .. it could get a perceived boost in decibel in the rolloff area.
but perhaps there is some confusion as to how much noise is helpful compared to annoyance, or louder than necessary.
i think the word 'chuffing' is loosely defined as it is, and it doesn't help much.
see, when i think of port noise.. i think of the old fisher 3-way speakers or some other ported speaker from the 1990's that made lots of air noise because the port was too small.
but i think those were situations with a 15 inch woofer and a port smaller than 3 inches (2.5 or 3 inches i figure is what it was).
then i listen to my ports and they dont make any air noise unless i really crank up the power with a test tone to get the cone moving 4 or 5 times as much as what it does when casually listening.
i dont know if i hear turbulence from the elbow in the port, or if it is turbulence from the air inside the port entirely.
i know most of the speakers from the 1990's with ports, they didn't come with long extended ports inside.. so there wasn't much surface area to compare the ring edge of the tube or the existance of the tube itself.
even when those flared port caps came out, it was late 1990's when car subwoofer boxes were often bandpass and the port was usually less than 12 inches (i'm guessing 4-6-8 inches)
the excursion was a lot higher with those situations too, causing the air to make noise.
i think if a master had anything to say about it, they would simply say consider the physics of the two when compared side by side.
1. the regular pvc tube is simply flat with air, and if there is a swelling of pressure outside of the hole.. then that is telling you there is too much PSI inside the tube and the diameter needs increased.
2. the flared port kinda demands the air swells as it leaves the port because the physical shape of the flare loses shape (well it expands diameter) before the air gets its chance to exit the tube.
that swelling has audible properties because it touches the air and moves the air like a speaker.
to reduce the amount of swelling while using a flared port, you simply increase the diameter of the port until the air can escape without pressure shoving the air all the way to the distant edges of the flare.
see, not only is it a situation of the air swelling as it moves outwards.. it is also a situation of the air slapping the flare on the way back in.
i've got 3 1/2 inch pvc with a 12 inch woofer if you care to compare.
i also filled the box with polyfil to stop the echoes inside the box and try to get the port tune down a little bit lower.
i think putting the polyfil inside will stop the echo inside the box, and that will prevent the echo from going up into the port where it can echo more (or at the very least, the annoyance creeps out of the speaker box and pours out its ugly character).
i can get deep bass that doesn't sound like it is coming from an organ, but if i were to speak completely critical of it .. i really don't know that i can differentiate between the pvc tube or the speakers, or even the room itself for that matter.
i know it is rich bass, and i know there isn't 2dB of difference.
i know these speakers are from the 1990's era and i can put my ear next to the speaker and hear the same pvc echo coming directly from the speaker.. so i don't think it is fair to say the port is to blame for any 0.5dB or lower of existance.
the noise that comes from a port when it is too small sounds kinda like white snow, but i've also heard it sound brown before (back to those fishers and other 1990's speakers).
**edit**
as for the sealed box being transformed into a ported box..
there are calculators on the internet to calculate the box tune by putting in the current size of the box, then type in the port diameter and length to find the tuned frequency.
easiest way to start is to begin with a port diameter and for the length, put in the longest distance you can get with a 90 degree elbow to bend the port.
that way you know the lowest frequency & can raise it up some if needed.
**edit again**
my bad..
my port is 3 inches, not 3 1/2
i imagine if the port was completely silent and the speaker rolled off at whatever low notes it rolled off at, using a port tube the right size to get a little bit of port noise .. it could get a perceived boost in decibel in the rolloff area.
but perhaps there is some confusion as to how much noise is helpful compared to annoyance, or louder than necessary.
i think the word 'chuffing' is loosely defined as it is, and it doesn't help much.
see, when i think of port noise.. i think of the old fisher 3-way speakers or some other ported speaker from the 1990's that made lots of air noise because the port was too small.
but i think those were situations with a 15 inch woofer and a port smaller than 3 inches (2.5 or 3 inches i figure is what it was).
then i listen to my ports and they dont make any air noise unless i really crank up the power with a test tone to get the cone moving 4 or 5 times as much as what it does when casually listening.
i dont know if i hear turbulence from the elbow in the port, or if it is turbulence from the air inside the port entirely.
i know most of the speakers from the 1990's with ports, they didn't come with long extended ports inside.. so there wasn't much surface area to compare the ring edge of the tube or the existance of the tube itself.
even when those flared port caps came out, it was late 1990's when car subwoofer boxes were often bandpass and the port was usually less than 12 inches (i'm guessing 4-6-8 inches)
the excursion was a lot higher with those situations too, causing the air to make noise.
i think if a master had anything to say about it, they would simply say consider the physics of the two when compared side by side.
1. the regular pvc tube is simply flat with air, and if there is a swelling of pressure outside of the hole.. then that is telling you there is too much PSI inside the tube and the diameter needs increased.
2. the flared port kinda demands the air swells as it leaves the port because the physical shape of the flare loses shape (well it expands diameter) before the air gets its chance to exit the tube.
that swelling has audible properties because it touches the air and moves the air like a speaker.
to reduce the amount of swelling while using a flared port, you simply increase the diameter of the port until the air can escape without pressure shoving the air all the way to the distant edges of the flare.
see, not only is it a situation of the air swelling as it moves outwards.. it is also a situation of the air slapping the flare on the way back in.
i've got 3 1/2 inch pvc with a 12 inch woofer if you care to compare.
i also filled the box with polyfil to stop the echoes inside the box and try to get the port tune down a little bit lower.
i think putting the polyfil inside will stop the echo inside the box, and that will prevent the echo from going up into the port where it can echo more (or at the very least, the annoyance creeps out of the speaker box and pours out its ugly character).
i can get deep bass that doesn't sound like it is coming from an organ, but if i were to speak completely critical of it .. i really don't know that i can differentiate between the pvc tube or the speakers, or even the room itself for that matter.
i know it is rich bass, and i know there isn't 2dB of difference.
i know these speakers are from the 1990's era and i can put my ear next to the speaker and hear the same pvc echo coming directly from the speaker.. so i don't think it is fair to say the port is to blame for any 0.5dB or lower of existance.
the noise that comes from a port when it is too small sounds kinda like white snow, but i've also heard it sound brown before (back to those fishers and other 1990's speakers).
**edit**
as for the sealed box being transformed into a ported box..
there are calculators on the internet to calculate the box tune by putting in the current size of the box, then type in the port diameter and length to find the tuned frequency.
easiest way to start is to begin with a port diameter and for the length, put in the longest distance you can get with a 90 degree elbow to bend the port.
that way you know the lowest frequency & can raise it up some if needed.
**edit again**
my bad..
my port is 3 inches, not 3 1/2
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The more efficiently the air can travel in and out of the port system the more efficiently the sub can work. Could this not be true? I can see a wide flare venturi type port letting the sub have somewhat speedier response time. I like the venturi port that came with my sub, because it is quiet and has to move a ton of air.
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Port for 4th BP - 9.4 cm/20.5 cm (port length), this being of practical dimensions.
91.2 dB vs. 90.6 dB/2.83V/m (sealed) at 0 level/passband,
Xmax = 23.5 mm is consider, I don't have any other info,
Thermal is what is given by the manufacturer, I guess here.
Of course 4th BP is optimal @30 and @50Hz with no attenuation/roll off and sealed has 6dB attenuation@30Hz and 2dB attenuation@50Hz making it 84.6dB@30Hz and 88.6dB@50Hz.
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The port and especially the port flare can have a profound effect on the speakers performance.
The typical store bought flared port has a large radius at one or both ends.
This large radius causes flow separation when the port velocity gets higher (you crank the sub up).
A better type of port termination is an angle of about 22.5 degrees per side maximum.
A slot port with a 45 degree angle at the termination approximates 2- 22.5 degree flares and works well.
Well they say a picture is worth E3 words, so this picture of a port with 2 different flares may shed some light on what happens.
Flare.jpg
Although this is just a simple schematic of what may happen it does show the mechanism by which a large radiused port can lose performance at high SPL's.
The turbulence is plainly visible on the left side but the more gentle expansion on the right side can tolerate much higher flows before any type of turbulence starts.
SS4927 mentions "venturi" type ports.
A 22.5 degree angled flare approximates a De Lavel Nozzle which is used as an impedance matching device between a high pressure, high velocity rocket engine combustion chamber and the atmosphere.
Another popular impedance matching device in audio is called a horn as it couples the high velocity particle motion at the transducer to the quiescent atmosphere.
Well, I hope this helps,
Dave
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