Plugging Subwoofer Ports

[Early B.]

Can someone briefly explain the concept or value of plugging ports in a subwoofer for me or provide a good link? Does it make the sub go louder, deeper, change the SQ, etc.? Just trying to increase my knowledge.

Thanks.

[gatemplin]

Can someone briefly explain the concept or value of plugging ports in a subwoofer for me or provide a good link? Does it make the sub go louder, deeper, change the SQ, etc.? Just trying to increase my knowledge.

Thanks.

Plugging ports just lowers the tuning frequency. The vented box is a Helmholtz resonator, so you can google that to find some more info. Lowering the tuning frequency by plugging ports changes the FR, and the sub will dig deeper. Play around with the excel file I just sent you and you can see the changes. Change the number of ports, diameter, Fb, volume etc.

[Early B.]

Thanks. I'll do some research.

BTW - I just plugged both of my ports for the helluvit and the sub sounded like I cut one of its balls off.

[BIZILL]

you will lose upper frequencies when you lower the tuning. you probably lost a lot in the 50-80 hz range?

[McLoki]

The sub is tuned flat with no ports plugged. When you add room gain to this, you often get a pretty large hump just in front of the tuning port.

I find with 1 port plugged it goes back to either flat or slightly increasing with the room gain.

With 2 ports plugged the drop in SPL overcomes the room gain and it ends up sounding like it lost one of its balls.....

Just play with it and see what you like best, but for me - 1 port plugged is about perfect.

Michael

[jdhdiggs]

Early, you are talking about an SVS or another sub made for port plugging and not another make, right?

Generally:
Less ports means more work for the driver, but more protection. It can go deeper, but not as loud. It may also sound cleaner (less boomy) if it has a good amp in the plugged configuration

[tryrrthg]

Thanks. I'll do some research.

BTW - I just plugged both of my ports for the helluvit and the sub sounded like I cut one of its balls off.
I'm pretty sure your sub only has two ports so you probably just turned your sub into a sealed design which would drastically cut the lower frequencies, unless you have some nice room gain.

[wingnut4772]

Hey. I have my SVS plugged to 16hz tune. Is that whay I have that dip from 50 ish to 80ish? Would I be better off just leaving it unported to 20? I love the low though.

[tryrrthg]

Hey. I have my SVS plugged to 16hz tune. Is that whay I have that dip from 50 ish to 80ish? Would I be better off just leaving it unported to 20? I love the low though.
You probably have a dip from 50 to 80hz because of a phase issure. try some different phase settings.

I think the 16hz tune is a little low, it doesn't give you enough port area and over-works the driver. The 20hz tune (one port plugged) should give you solid, in-room output to 18hz or so.

[BIZILL]

I'm pretty sure your sub only has two ports so you probably just turned your sub into a sealed design which would drastically cut the lower frequencies, unless you have some nice room gain.
got that backwards. more ports plugged, the lower the frequency it outputs, but at a sacrifice to overall spl at higher frequencies.

[tryrrthg]

got that backwards. more ports plugged, the lower the frequency it outputs, but at a sacrifice to overall spl at higher frequencies.
Nope, EarlyB's sub is a DIY with two four inch ports. If he plugs them both it becomes a sealed sub.

[gatemplin]

got that backwards. more ports plugged, the lower the frequency it outputs, but at a sacrifice to overall spl at higher frequencies.

No he's right. Early has a AV15 based sub with 2 4" ports. So if he plugs both of them he has a sealed sub.

But you are also correct...for SVS subs.

Edit: Great minds think alike, eh Troy. :)

[BIZILL]

i'm not saying it does not become a sealed sub. obviously if there are two ports and both become blocked it in fact becomes sealed. i've always known sealed subs to hit lower than ported ones. that is, same sub in differing enclosures. maybe i screwed up. i know they are more ACCURATE in a sealed enclosure.

[gatemplin]

i'm not saying it does not become a sealed sub. obviously if there are two ports and both become blocked it in fact becomes sealed. i've always known sealed subs to hit lower than ported ones. that is, same sub in differing enclosures. maybe i screwed up. i know they are more ACCURATE in a sealed enclosure.

Sealed subs dont play lower, the point of porting the box is to extend the response.

The resonant frequency, Fb, of a box sub is always higher than the resonant frequency of the driver, Fs. Often an octave higher (depends on Vb). And then the response drops at 12 dB per octave. So at the Fs of the driver output is down 12 dB. In a ported design, you can extend the response below, sometimes well below the Fs of the driver.

Accuracy is up for debate, it depends on what you mean by that. Group delay is certainly higher in vented designs though.

[BIZILL]

fundamentals 101. maybe i need a refresher course. ported boxes are designed for EFFICIENCY. sealed are not efficient at all. but you are telling me that the sub driver which is offset in an enclosure to negate cancellation will not hit lower than the same sub in a ported box, given higher amplification?

[gatemplin]

Ported boxes are only really more efficient down low around the tuning frequency. Sealed subs can be very efficient too.

The ONLY ways sealed subs can dig lower than ported is in a infinite baffle (overdamped), or by using a Linkwitz-transform.

What do you mean by cancellation?

[BIZILL]

i was told by car audio installers at my old job that a sub will sound better in a rectangular box if it is not exactly centered. they say to mount it to either side of the centerline. don't know if it all made sense to me or not. but they say if it is centered, the sub will be 'battling' itself. what say you?

[BIZILL]

i don't know what to make of it. i see benefits and conflicts with it. but cylinder subs have done well in the past and in the present. those drivers are perfectly centered, obviously. maybe it only applies to square or rectangular boxes.

[BIZILL]

by definition is an infinate baffle synonymous with a sealed enclosure? well i suppose so. usually ib uses a car's trunk as the 'sealed' enclosure.

[gatemplin]

No. Makes no difference. The only time you offset drivers is for diffraction purposes. And it is done in a program like Baffle Diffration Simulator.

The only acoustic cancellation that takes place is for ported subs below the tuning frequency, which is why the output drops at 24 dB/octave initially.

To cancel mechanical vibration you mount drivers on each side of the box.

[BIZILL]

hmmm...must do some more learning/research on the subject it would seem...

[gatemplin]

by definition is an infinate baffle synonymous with a sealed enclosure? well i suppose so. usually ib uses a car's trunk as the 'sealed' enclosure.

An IB is a sealed enclosure because the backwave is kept seperate from the frontwave. The definition is that the enclosure has a volume no less than ten times the Vas of the drivers.

[BIZILL]

i've always wondered what a single sub would sound like mounted via ib in an over-sized box. say a single 12" mounted via ib and you're inside a house where the sub is located in the front door. would that make for any type of sound at all?

[tryrrthg]

Edit: Great minds think alike, eh Troy. :)
Is that why my head hurts ;) especially after reading all your replies. I know everything you said, I just wouldn't know how to explain it!

[tryrrthg]

i've always wondered what a single sub would sound like mounted via ib in an over-sized box. say a single 12" mounted via ib and you're inside a house where the sub is located in the front door. would that make for any type of sound at all?
It would sound OK, you just wouldn't get the ouput you're used to. You need several drivers to reach the same output you're used to. People usually go with 2,4,6, heck some guy even has 18 drivers in their IB's. IB's are supposed to be unriveled by their bass quantity and quality. wish I could install one.

Check out the IB forum for more info:

http://ibsubwoofers.proboards51.com/index.cgi

[BIZILL]

thanks for the input, fellas.

[wingnut4772]

I have tried adjusting the phase setting. The difference between 0 and 180 is only 1db .

[tryrrthg]

I have tried adjusting the phase setting. The difference between 0 and 180 is only 1db .
well you're screwed then :D you better send that sub to Ohio, I'll be sure to dispose of it for you. Heck, I'll drive it back to SVS for you, it's only a few hours drive, it's no problem, really. ;)

you could try other settings inbetween also, 45, 90, etc. if that doesn't work then it is a room/placement issue. Isn't setting up a sub a fun process? :eek:

[jrlouie]

I have a two-ported sub. Plugged one port and the freq response extended. Plugged the other one (essentially sealed), and it flattened my response. I have left both plugged since I have a small room, and don't need the extra output. Probably plugging both just eliminated some room-gain I was getting, therefore helping to flatten the hump.
At least that's what my SPL meter seemed to show ;)

Sometimes I mess with things so much I wonder if I'm just confusing myself :D