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Old 30th March 2013, 04:48 AM   #21
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pics of ghetto porting while awaiting upgraded bracing !
Very loud in this set up
Ghetto Ported output almost feels like double sealed....But bass lacks accuracy
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Last edited by Kingnoob; 30th March 2013 at 05:14 AM.
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Old 2nd April 2013, 03:50 AM   #22
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SHoud I stick to sealed or port this driver?? 4.6cu foot box
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Old 2nd April 2013, 08:54 AM   #23
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Have you measured the T/S parameters?
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Old 3rd April 2013, 01:32 AM   #24
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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.)
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Last edited by Inductor; 3rd April 2013 at 01:41 AM. Reason: int.vol.
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Old 3rd April 2013, 02:25 AM   #25
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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)
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Old 3rd April 2013, 07:50 PM   #26
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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
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Old 5th April 2013, 09:33 AM   #27
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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.
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Old 5th April 2013, 09:35 AM   #28
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well.. pressure buildup especially if the box is sealed, not necessarily if the box is ported .. depends on how tight the space is and how much cone movement you are experiencing.
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Old 5th April 2013, 10:01 AM   #29
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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.

Last edited by anwaypasible; 5th April 2013 at 10:04 AM. Reason: had to correct a word, i fell i guess.
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Old 5th April 2013, 05:30 PM   #30
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Quote:
Originally Posted by anwaypasible View Post
well.. pressure buildup especially if the box is sealed, not necessarily if the box is ported .. depends on how tight the space is and how much cone movement you are experiencing.
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

Last edited by Kingnoob; 5th April 2013 at 05:48 PM.
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