Sealed, Ported and Distortion

[azzfox]

I origionally brought up this topic in a convo with Garfa about Sealed Enclosures being more prone to distortion than Ported Enclosures. Google "Sealed vs Ported" and in every site it will tell you that Sealed is more prone to it.
Why is this? We have had rough stabs at it but cant seem to make any sense of it. Now we are just confused and curious...

Anybody?

[azzfox]

I am thinking its got to do with sumthing like this: At large volume levels (big excursion) and a quick beat the signal with not match up to the driver due to the push-pull system. eg. if the driver is being pulled back hard and the signal tries to push it forward it will not happen (or not efficiently) and therefore creates distortion.

[253@7k]

Hey there mate, just a question. (I'm a bit clueless in this department) Does porting mean cutting a hole in the box? When would you need to port a box? Finally how big should the hole be? (assuming I am correct).

Cheers, and sorry bout all the Q's
Steve.

[azzfox]

hey, ports arent holes, they are kinda like tubes. to know the right diameter and length you need enclousure designing software like WinISD or Bass Box Pro. you either have a ported enclosure or not. eg. you cannot port a sealed enclousure because ported enclosures are approx twice the size/volume.

[hakhawk]

porting requires cutting a hle and designing a specific tuned length port, its not just a matter of cutting a hole and stickin a tube in there. i dont know how to setup a ported system, so i just went sealed. too much hassle for something that just gets flogged at cruises and parties.

but one of the more experienced stereo gurus on here should be able to explain it quite well. or just google it.

[253@7k]

Ah cheers guys, that sort of explains it, I found some more info that explains the correlation between the volume of the enclosure, the excursion of the sub and the port or tube that is fitted. All together I think you guys pretty much explained the basics for me, cheers.

Steve.

[garfa]

ok pretty much the box size and the actual volume the port is effects how the frequency curve the sub produces sounds.
the sub will need a box of Xlitres. now this volume is important becausse it will effect how the air internally reacts to the sub moving, but more important in the ration of port size to box size.
this will determine where the frequency curve drops off and also how much the frequency just before the roll off is boosted.
the roll off can be extended but it starts at a higher frequency and also hence removes the boost before the roll off.

[Matty081]

my theory as to ported vs sealed is that sealed boxes obviously have internal pressure when the sub is vibrating. Consequently the sub cannot "come back" as quick as it should or to quick on the other side of the scale(pressure pushing it out)and doesn't have as much freedom to move. I think it will wear the sub out quicker as well for this exact reason.
I'm always open for correction of course...

[garfa]

my theory as to ported vs sealed is that sealed boxes obviously have internal pressure when the sub is vibrating. Consequently the sub cannot "come back" as quick as it should or to quick on the other side of the scale(pressure pushing it out)and doesn't have as much freedom to move. I think it will wear the sub out quicker as well for this exact reason.
I'm always open for correction of course...

well think about this, with a ported box its easier for the cone to move therefoer the suspension is getting a harder work out. sort of horses for courses really, i dont think there will be a huge difference in the woofers life span depending on the type of box used as long as it is equally suited to both.

[Matty081]

good point, 6 of one, 1/2 a dozen of the other i guess.

[davey g-force]

Just a theory:

In a sealed enclosure, there is more pressure or resistance from the air. Maybe this air moving/vibrating affects the cone when it's trying to do something else? i.e. when the signal changes with a ported sub, the cone is more free to move with the signal rather than having to fight with the air which is trying to do something else?

[garfa]

Just a theory:

In a sealed enclosure, there is more pressure or resistance from the air. Maybe this air moving/vibrating affects the cone when it's trying to do something else? i.e. when the signal changes with a ported sub, the cone is more free to move with the signal rather than having to fight with the air which is trying to do something else?

personally i cant see how a ported enclosere can distort more than a sealed one.
sorry aaron but i just cant make sence of what you are trying to say. it doesn't fir together.

if the driver is being pulled back hard and the signal tries to push it forward it will not happen

if a 50hz signal is played and then a 20hz signal is also played, it will mean the cone id moving in and out 10times a sec and while its moving in and out it will also be vibrating at 50hz. so effectively its an ossillation of the ossillating cone.
what you are saying by the cone being extened by a signal and then further extension pushing its past its linear response is just the speaker distorting. a ported box will do this aswell. a free air sub will also do this if its eing pushed past its x-max.
i think that answers that bit.

also as for a cone being harder to push and pull in a sealed box that will definately not introduce distotrsion. the air will be getting pressurised therefore reducing the cone's movement and also its flex.

pretty sure that answers it.

[phree]

I origionally brought up this topic in a convo with Garfa about Sealed Enclosures being more prone to distortion than Ported Enclosures. Google "Sealed vs Ported" and in every site it will tell you that Sealed is more prone to it.
Why is this? We have had rough stabs at it but cant seem to make any sense of it. Now we are just confused and curious...

Anybody?

Which sites say that? What type of "distortion"? More the other way round I think. Sealed enclosures are usually chosen when sound quality is paramount. Ported are louder but generally less accurate. This is not really distortion though, more "colouration".

Perhaps it's because the sealed enclosure requires more power to go as loud as the ported. Therefore a given amp is running closer to clipping levels.

[azzfox]

sorry i made a mistake, google "sealed vs ported distortion"
iv come up with this site which has alot of info=

http://diyaudiocorner.tripod.com/dilemma.htm
scroll down to second table for advantages/disavantages.

it also had this = "On the downside, a sealed driver reaches maximum excursion at resonance, which adds considerably to the distortion produced at high output levels."

[phree]

At normal levels it should be inaudible i think. There is some good reading here:

http://mobile.jlaudio.com/support_pages.php?page_id=147

[azzfox]

At normal levels it should be inaudible i think. There is some good reading here:

http://mobile.jlaudio.com/support_pages.php?page_id=147

i also found this on that link = "At moderate power levels all of these enclosure types exhibit pretty decent manners. The ported box and the bandpass designs produce less distortion than the sealed box, but the difference is marginal."

[garfa]

ok fantastic to quote sources, but i want to know why. dont care if some one tells me something unless i can see exactly how it works i will not beleive them.

[azzfox]

well hey, this thread was started for that exact reason.. "WHY"
im doin tha best i can for now. at least im making an effort.

[semi]

jsut throwing ideas out, maybe a sealed box could be more prone to clip, because it will move less 'freely' because its not influencing box presure as much.

Hmm, doenst make much sense, hard for me to describe what im thinking. Can we turn on the 12V-light??

[garfa]

semi unfortunately sealed boxes allow the sub to handle more power. and specically the smaller the box the more the sub can handle, because of the air restricting movement.
as for not making an effort, i dont really have time and cant be bothered. i was hoping for 12volt or stone or kal to come in and settle this.

[StoneX]

I'm not a box expert, but you can't generalise with "ported enclosures" as the tuning frequency makes a massive difference to have the driver reacts.

I don't know how to explain it but there is more pressure inside a ported box. Also, ported subwoofers have handle more power around the tuning frequency as the cone and port "react" to create the sound and the cone excursion is reduced to virtually nothing but the sub will be at it's loudest and highest power handling.

Ask on Termpro or CAA forums... There are alot of people who will KNOW the answer, but still a few who will be guessing and repeating crap they've read.

[Tasmaniak]

They are different types of distortion occuring....Stone is correct in saying that there is more resistance inside a sealed enclosure. It's pretty simple really. When the cone is moved back it pushes the air inside the back around. Now, that air has to go somewhere right? Wrong. It's an airtight enclosure remember? What the driver has to do is COMPRESS the air inside the box. It can do this...but it also makes it a lot harder for it to move back to where it's supposed to be. Thus causing an alteration in the repoduced signal. So, what about when the driver moves forward? Well, then the box effectively tries to create a vacumm! When that happens..you have the power driving the driver forwards but the vacumm effect pulling it back in. Once again, you alter the sound reproduction. So, with all that said, why use a sealed enclosure at all? Because when all is said and done the right size and SHAPE allows the driver to use that effect to it's advantage. Hence why sealed enclosures are known for their tightness. It's because of this factor that sealed systems generally handle more power then ported...theres more resistance keeping everything in check.

Now, onto the port side of things.

When that speakers is pulled back....it does try to compress the air. Instead, it forces it all the port tubing...then when it moves forward, it SUCKS the air back inside the box. So, for all intent purposes, the pressure on the inside of the box is equivalent to the pressure on the outside of the box.

But, because of this equal LOW pressure system in the front and back the driver is MUCH more inclined to start distortion and reaching it's Xmax long before it max power handling has been reached as there is nothing pushing out when it wants to go in and nothing sucking back when it wants to go out.... But because of this, there is less coloration added into the music signal being reproduced making for a more pleasant and smoth response curve. But, don't forget, that it can easily become unstable at higher power (not neccessarily higher volume)

did that make sense at all?

[semi]

yeh it did, thats what i was trying to say, but wasnt able to do it so eloquently (sp?)