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Old 5th April 2013, 06:16 PM   #31
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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

Last edited by anwaypasible; 5th April 2013 at 06:21 PM.
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Old 17th January 2014, 04:04 AM   #32
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I build a sealed sun about 4.6 cu foot is it too large too add a square port too later on??? I might want to port it, eventually.

Sorry was busy haven't posted in a long time!!!!
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Old 17th January 2014, 04:13 AM   #33
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Looks like the (same) STEREO INTEGRITY HT 15...
4.6ft³ = 130.26L
...Port will be very long (BR).
Solution,
Make a 4th order bandpass sub:
STEREO INTEGRITY HT 15,
VC = 62.80 L, FAC = 39.26 Hz, VAC = 48.85 L,
-3 dB 25 - 62 Hz
-6 dB 22 - 71 Hz
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Last edited by Inductor; 17th January 2014 at 04:23 AM.
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Old 17th January 2014, 04:52 AM   #34
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Hi Inductor - re: VC = 62.80 L, FAC = 39.26 Hz, VAC = 48.85 L for SI HT15, what is the sensitivity of this system in its passband? ( thermal and excursion limits too - - if already calculated)
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Old 17th January 2014, 04:54 PM   #35
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Quote:
Originally Posted by anwaypasible View Post
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
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.

Last edited by SS4927; 17th January 2014 at 05:06 PM.
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Old 17th January 2014, 07:01 PM   #36
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Quote:
Originally Posted by freddi View Post
Hi Inductor - re: VC = 62.80 L, FAC = 39.26 Hz, VAC = 48.85 L for SI HT15, what is the sensitivity of this system in its passband? ( thermal and excursion limits too - - if already calculated)
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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Old 18th January 2014, 01:11 AM   #37
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Quote:
Originally Posted by SS4927 View Post
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.
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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File Type: jpg Flare.jpg (96.4 KB, 91 views)
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Old 18th January 2014, 05:26 AM   #38
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Thanks for the explanation Dave, I got it. Venturi stacks are more effective as intakes, exhaust is irrelevant in the application I had in mind. I didn't consider how air would react upon exiting.
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Old 18th January 2014, 07:21 AM   #39
freddi is offline freddi  United States
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Thanks inductor. Do you think the 9.5/20cm vent can handle SI HT15 well with the ~49l 40Hz tuned front chamber? (I'm not sure if I can even build it as have a lot of pain.)
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Old 18th January 2014, 07:47 AM   #40
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freddi,
That's data given by Petoin Dominique (FR) software. It can model (as others) any type of port(s). Doesn't WinISD have some simulations on excursion and thermal? For sometime, not using it.
(Why do you have pain?)
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