Is it a real bass reflex cab ?

[ReidK]

Beware of the results of software

OK, everybody write that down.

Trust me, I'm a software developer.

 

[vinceom]

For me, a port is a helmholtz resonator and i can't understand how a port with a depth of 2 cm works …

 

[Guitalia]

For me, a port is a helmholtz resonator and i can't understand how a port with a depth of 2 cm works …

From this page:

A ported subwoofer functions as a type of Helmholtz resonator. The subwoofer cone compresses and decompresses air inside the box, exciting the air mass in the port.

(That company uses the word "port" rather than "vent" here, but as Aged Horse notes, "port" and "vent" mean the same.)

 

[6thplanet]

At what depth does a port become a vent?
What do the thoughts of a butterfly weight?
What's the square root of a bowl of oatmeal?
...so many questions...so little time.

For me, a port is a helmholtz resonator and i can't understand how a port with a depth of 2 cm works …

Because a hole 10cm x 2cm has mass, just less than 10cm x 8cm.

 

[agedhorse]

For me, a port is a helmholtz resonator and i can't understand how a port with a depth of 2 cm works …

There is still port volume with a thickness of 2cm, don't overthink it.

 

[darwin-bass]

I've made a number of ported enclosures by simply cutting a hole in the 3/4" plywood front panel. Cut the hole to the size that gives me the resonant frequency I needed. Easy, peasy.

And you can measure the resonant frequency with a frequency generator (phone app) and your amp. Find the frequency where woofer cone excursion dips which will (should) correspond with the most air puffing from the port and voila, you have your frequency.

And, yes, I realize what I just posted is not the same as true engineering.

 

[S-Bigbottom]

A hole is a hole regardless of depth.

 

[agedhorse]

A hole is a hole regardless of depth.

There's a hole in the bucket, dear Liza, dear Liza...

 

[ReidK]

Because a hole 10cm x 2cm has mass

A hole has mass?

Just kidding! This reminded me of the old riddle "How much dirt is there in a hole 2'x3'x4'?", except that there is air in the hole.

 

[6thplanet]

A hole has mass?

Just kidding! This reminded me of the old riddle "How much dirt is there in a hole 2'x3'x4'?", except that there is air in the hole.

I once created a port with so much mass it reached singularity. Once.

 

[ReidK]

I once created a port with so much mass it reached singularity. Once.

Black, I assume. Tort pickguard?

 

[6thplanet]

Black, I assume. Tort pickguard?

Yeah, scrapped the whole cab, couldn't get anything out of it.

 

[Bassdirty]

The port for a bass reflex enclosure doesn't necessarily need to have any more depth than the thickness of the baffle board. Your Behringer box IS a bass reflex cab -- that doesn't necessarily mean it's tuned appropriately for the replacement driver you've chosen.

Or that Behringer's chosen for that matter.


Ok, just kidding. I've owned plenty a Behringer Items over the years. But funny is funny.


T$

 

[LetItGrowTone]

I understand the original poster's concern that the air *in* the port just doesn't have much mass;
the air in the cab, with a hole in the baffle, seems not as well defined as a "mass and spring", as the mass seems diffuse,
so is there any truth to the idea that a longer tube, with a greater mass of air in the tube, can pump more powerfully, or something?

EDIT: If it's true that the hole-in-the-baffle is less effective, then I would have something positive to say about that, that compensates.

 

[agedhorse]

I understand the original poster's concern that the air *in* the port just doesn't have much mass;
the air in the cab, with a hole in the baffle, seems not as well defined as a "mass and spring", as the mass seems diffuse,
so is there any truth to the idea that a longer tube, with a greater mass of air in the tube, can pump more powerfully, or something?

EDIT: If it's true that the hole-in-the-baffle is less effective, then I would have something positive to say about that, that compensates.

It's exactly the same within the context of the equations that govern the speaker performance.

 

[LetItGrowTone]

Then I wonder why more cab designers don't just leave holes in the baffle instead of providing tubes.

 

[agedhorse]

Then I wonder why more cab designers don't just leave holes in the baffle instead of providing tubes.

Because at high power, it's usually difficult to achieve an acceptable tuning. Sometimes it works out ok.

 

[toughluck]

Educated in England - not sure if that makes a difference. I'd learned (perhaps incorrectly) - but happy to be wrong of course! Three terms to describe a nuance regarding the 'type' of opening.

Reflex - like a folded design

I think you are referring to either a transmission line which is a type of a vent, or to a folded horn.

Vented - like this post

One distinction I heard is that "vented" applies to any enclosure that's not sealed, passive radiator for open baffle. So regardless of whether it's a bass reflex port (of any shape), a transmission line or a folded horn, all are examples of vented enclosures.

Ported - like a tube (cylinder or other shape, generally no folds.

Ported=Reflex=Bass reflex. Regardless of shape (folded or not) or size. IIRC, there's a formula to determine if it's just a port or if it's a transmission line.

(And I'm not opening the Pandora's box of 4th, 6th and 8th order bandpass enclosures and other more exotic designs… Oops, seems I did.)

Edit: Forgot the most important thing: Even if somebody ever distinguished between vented/ported/reflex enclosures the way you described, it lost all its meaning and is irrelevant now.
But I think @agedhorse is right in that they always meant the same thing. It's just that somebody looked at a bass reflex enclosure and called it vented, another person called it a port, yet another called it bass reflex. Maaaaaaybe somebody called it ported to draw attention to the fact that it has a port, maaaaybe somebody called it bass reflex to describe the behavior of air inside a ported enclosure. But they all mean the same thing.