Ports did not turn out like i expected

[BugMan53 10+ year member]

HI ....I just built a 4.02cubic foot box tuned to 33htz for 2 12inch pioneers. Well it sounds really good but i have a few questions.

1st I have 4 3 inch ports and when i built the box they are 1.5 inches from the bottom of the box. How much its it affecting the sound? Or tuning.

Can i throw in some pvc 90degree elbows in it?

2ed the box has 2 chambers that are 2.01cf and through win isd it said to make the ports 15.5inches long. Does that include sub displacement and port displacement. Is this right? The subs are pioneer TS-w304dvd(cheap i know but they work for my DD) can someone check that for me.

3rd do i need a SS filter. Its getting 375rms per sub. They are rated at 300 but i have never had a problem with that much power in a sealed box. They look kinda stressed at low notes but no distortion.

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[jellyfish420 10+ year member]

first, the end of the port has to be at least the width of the port away from the wall. ie port 3" has to be 3" away, second winisd takes into acount for none of the dispacements you hace to do that youself, then recalculate. third your subs will take less power in a ported box than in a sealed box. you shouldn't need a ssf tuned at 33 unless you go around playing bass cd's in the low 20's.

 

[helotaxi 5,000+ posts]

third your subs will take less power in a ported box than in a sealed box.

That depends. Most subs do about the same in a ported or sealed box power handling wise. Remember that the ported enclosure exerts more control over the cone than a sealed enclosure. This extra control means that you can run more power to the sub above the tuning frequency without the sub reaching its excursion limit and bottoming out or tearing a spider or surround.

 

[jellyfish420 10+ year member]

That depends. Most subs do about the same in a ported or sealed box power handling wise. Remember that the ported enclosure exerts more control over the cone than a sealed enclosure. This extra control means that you can run more power to the sub above the tuning frequency without the sub reaching its excursion limit and bottoming out or tearing a spider or surround.

i didn't know that. that is some helpful information. . . but he said low notes. and i'm just assuming that by low notes he's refering to around or probably lower than his tuning freq. and in that case then they would take less power.

correct me if im wrong helotaxi, but around tuning freq, the subs will take less power to reach xmax than in a sealed box at the same freq.

 

[jujumantb 10+ year member]

correct me if im wrong helotaxi, but around tuning freq, the subs will take less power to reach xmax than in a sealed box at the same freq.

very wrong //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Around tuning a sub takes MASSIVE amounts of power to reach xmax, thats what competitors do, throw 10x rated power to the subs just above tuning.

 

[nweibley 10+ year member]

At tuning freq, lets say the sub is at full throw outward. Right as it starts to move back in, there is a huge positive pressure wave ******* into the port and creating loads of pressure inside the box, so the drive has extra work to move back fully inward. Now, lets say the opposite is true, the cone is now fully pulled in, right about to bottom out. Right as it starts to move back out, all of that high pressure is rushing out of the port and there is low pressure inside the box, so you have positive pressure at the port, positive pressure on the open side of the cone, negative pressure inside the box, and negative pressure on the box side of the cone.

All of this means everything is setup at tuning freq to take loads more power than the driver is rated for in a sealed box. The fact that the box has a hole in it does not necessarily (actually almost never) mean that the drive will flop around like it is in free air.

I think you already got that though //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

EDIT: to answer 3rd... yes, I think it is a good idea to get a SSF, because as you drop below tuning freq, the function for cone movement becomes squared (IIRC...) so hitting 5Hz below tuning freq may bottom out at rated power, but hitting 10Hz below tuning freq is bottoming out possibly twice as hard. Sure, you won't hit below your tuning freq every day, but the more you do the more abuse your driver is getting, so why not add a SSF and get the full potentail out of your subs rather than be gentle on the gain...

(The opposite to my explanation is true well below tuning freq.. that is as the cone moves out, there is high pressure inside the box also forcing the cone outward, so much MUCH less power is needed to get the cone to xmax.

 

[somekook 10+ year member]

the cone isnt moving as much in a ported box. this will deffinitely help it ro krrp from ripping any suspension, which is great for power handling of the sub mechanically. but since there is less excursion, doesnt this prevent heat from dissipating from the voicecoil quickly? which would decrease thermal power handling?

 

[helotaxi 5,000+ posts]

Unless you are only playing tones right at tuning for extended periods of time, in which case air moving in and out of the box is minimal, the sub will move a lot of air through the port and will actually cool the coils better than a sealed box.

 

[nweibley 10+ year member]

Unless you are only playing tones right at tuning for extended periods of time, in which case air moving in and out of the box is minimal, the sub will move a lot of air through the port and will actually cool the coils better than a sealed box.

Yup. Vorticies will form in the port and cool air will swirl in and warm air will swirl out. Even at tuning freq... cool air is moving in... there is just a lack of driver movement to draw the cool air over the voice coil.

 

[jellyfish420 10+ year member]

ok, i think i get it. ported can take more power at tuning than sealed. but the BIGGER you go with the box the less power it takes to reach xmax. sorry about all they questions, i just like to know all aspect of what is happening.

 

[BugMan53 10+ year member]

So i need to fix my ports with PVC elbows and get a SSF and i should be set. Can some one help me calculate the area the ports are taking up...I think its Radius X3.14x length but not sure and my math needs work.