sealed vs. port cabs

[billfitzmaurice]

To save me some typing, all the following quoted is wrong:



Alex

+100.

I see a trend toward rear porting with some Ashdown cabs and the Aguilar DB810 for instance. Is that just marketing in your opinion or in some cases does it work?

The location of the port has no bearing on response, assuming you don't push the cab so tight to the wall that the port is blocked, and the rear of the cone is not visible through the port. The rear ported Ashdowns are smaller than the front ported versions loaded with the same drivers, make of that what you will.

Are you including Bag End cabs in this generalization? I realize that you qualified it with "often".

You always need to qualify, as for every rule there's always the exception. There are reasons for rear porting other than there not being enough room on the front, and not all rear ported cabs are too small. But those factors are commonly seen.

 

[rpsands]

Generally, sealed cabinets are made by unicorns and ported cabinets by leprechauns. I hope that helps.

 

[Eublet]

and the rear of the cone is not visible through the port.

Can you elaborate further on this? Do you mean the paper cone, or the rear-center of the magnet/frame? Should it not be visible at all, regardless of viewing angle, or only if viewing from directly in front of the port at a distance?

 

[fdeck]

Can you elaborate further on this? Do you mean the paper cone, or the rear-center of the magnet/frame? Should it not be visible at all, regardless of viewing angle, or only if viewing from directly in front of the port at a distance?

The cone. What you don't want is a direct pathway for midrange to radiate from the cone out the port. This is achieved by saying that the cone is not visible at all through the port.

 

[Eublet]

The cone. What you don't want is a direct pathway for midrange to radiate from the cone out the port. This is achieved by saying that the cone is not visible at all through the port.

Why wouldn't you want that, or what are the consequences? I'm thinking of several rear-ported cabinets where the cones are visible and they sound/perform great.

 

[Rezdog]

Greetings from the North,

+1 rpsands.

Rezdog

 

[fdeck]

Why wouldn't you want that, or what are the consequences? I'm thinking of several rear-ported cabinets where the cones are visible and they sound/perform great.

I suspect the extent to which the leakage is noticeable depends on a lot of factors, such as whether there is a reflecting or absorbing surface behind the speaker. If one already owns such a cab, I would advise simply listening and deciding if it's a problem. But at least from a DIY standpoint, it is not too difficult to avoid a line of sight to the cone.

 

[billfitzmaurice]

Why wouldn't you want that, or what are the consequences? I'm thinking of several rear-ported cabinets where the cones are visible and they sound/perform great.

They may seem OK, but if the cone is visible through the port then frequencies above the bass frequencies that are supposed to come through the port will also go through it. That can lead to all sorts of problems when those frequencies reflect off walls or other objects in back of the cab. It is a design defect.

 

[Eublet]

They may seem OK, but if the cone is visible through the port then frequencies above the bass frequencies that are supposed to come through the port will also go through it. That can lead to all sorts of problems when those frequencies reflect off walls or other objects in back of the cab. It is a design defect.

There are so many cabs that fit into this category, many made by very reputable builders. I've used some of them, even when placed close to a wall. I can't say I've noticed such issues with the cabs I'm thinking of. In fact I have two such cabinets right now made by TC Electronic that seem much more than OK. They don't seem to have any more problems than my front ported cabinets do. I guess to get the kind of side effect you are referring to would really depend on the amount of visibility from the port to the cone. Most of the cabs I've seen with rear ports have fairly long tubes that extend into the cabinet, and you really have to put your eyeball in the hole to see much of anything.

 

[billfitzmaurice]

Most of the cabs I've seen with rear ports have fairly long tubes that extend into the cabinet, and you really have to put your eyeball in the hole to see much of anything.

Ideally the duct extends far enough into the cab that, in concert with the port location, there's minimal to no leakage of above port bandwidth sound through the port. But if the port is directly behind the driver no good will come of it, or out of it.

 

[otis_thick]

Does anyone remember the port plugs that came with Trace Elliot's...you could either have sealed or ported...I have a custom 410 that uses rubber surrounds from Eminence and with ports plugged it literally danced across the floor B4 I installed internal bracing...miking and studio is were IMO sealed cabs shine although less efficient the lows are rounder and rubbery

 

[Frankie Fender]

Ideally the duct extends far enough into the cab that, in concert with the port location, there's minimal to no leakage of above port bandwidth sound through the port. But if the port is directly behind the driver no good will come of it, or out of it.

Well I guess by that definition you are saying that the Bag End bass cabs are poorly designed and should sound like crap, but I for one happen to think that that sit really well in a mix unlike many other boomy font ported cabs I have played.

I understand there is a physics behind that reasoning, but I've also heard that a bumblebee should not be able to fly if it were up to the laws of physics too.

 

[mophead]

I picked up an Ampeg 810 classic about 2 months ago,I gotta say I liked it better than any cab I've ever played through. I could hear everything my amp put out, I could boost the mids without being nasaly,the top end was just right(no tweeters!). So I'm getting a custom 610 made voiced just like,or close to,the ampeg 810. Got nothing against ported cabs,you just gotta see what works best with your gear,and what your ears prefer.

Your custom 610 is already available. NV610 Bergantino.

 

[alexclaber]

Well I guess by that definition you are saying that the Bag End bass cabs are poorly designed and should sound like crap, but I for one happen to think that that sit really well in a mix unlike many other boomy font ported cabs I have played.

The Bag End S-15D is a great cab but there have been quite a few comments on here about how placement fussy it is, which is a result of having its port directly behind the driver so midrange energy escapes.

I understand there is a physics behind that reasoning, but I've also heard that a bumblebee should not be able to fly if it were up to the laws of physics too.

More recent and correct analysis of this has shown that a bumblebee definitely can fly.

Lots of cabs with less than ideal porting will sound just fine but that doesn't mean that with better designed porting they wouldn't sound better!

Alex

 

[Eublet]

That can lead to all sorts of problems when those frequencies reflect off walls or other objects in back of the cab. It is a design defect.

So how much effectiveness would be achieved by placing some acoustic foam against the wall directly behind the cab?

 

[rpsands]

Your custom 610 is already available. NV610 Bergantino.

Yeah, 'cept the one he's getting is half the price of an NV610 and 2/3rds of the weight The NV is definitely an awesome sounding beast but price and weight are rough.

 

[billfitzmaurice]

So how much effectiveness would be achieved by placing some acoustic foam against the wall directly behind the cab?

Having to do so at every gig seems a tad inconvenient. If the cab is within a few inches of the wall it's not much of a problem, it's when the cab is maybe a foot or more away where midrange out the port can reflect off the wall to cause midrange response peaks and valleys. Preventing that would take a rather large and thick pad, at least the size of the cab and at least two inches thick.

 

[Eublet]

Having to do so at every gig seems a tad inconvenient. If the cab is within a few inches of the wall it's not much of a problem, it's when the cab is maybe a foot or more away where midrange out the port can reflect off the wall to cause midrange response peaks and valleys. Preventing that would take a rather large and thick pad, at least the size of the cab and at least two inches thick.

I guess I'm just trying to learn more about how all this stuff works. What frequency range are we talking about here that would escape the cab port?

 

[billfitzmaurice]

I guess I'm just trying to learn more about how all this stuff works. What frequency range are we talking about here that would escape the cab port?

With a port in back of the driver, everything; up to about 100 Hz is what it would be with the port properly located.

 

[Eublet]

With a port in back of the driver, everything; up to about 100 Hz is what it would be with the port properly located.

I'm not sure I understand you. So 100hz and lower would escape through an improperly placed rear port or vice versa? I'm not sure how foam or even the cabinet walls itself would block such low frequencies.

Also, why would you need a large piece of foam? If the foam covered all areas that had line of sight through the rear to the cone, wouldn't that suffice?