Porting / SPL / volume vs shape of cabs…

[plumberstrummer]

hi everyone,

Making excellent progress with try cab, have the calculations from the speaker manufacturer, and they are helping with the porting calculations as well.

I just wanna confirm my thinking is correct; that the most important thing is that internal volume matches what the speaker needs for the response we are after, more so than the shape?

Additionally, I have seen ports inside of the speaker chamber, and I have seen them outside and next to the speaker chamber, allowing air in. I imagine that you want the port inside of the speaker chamber to let air in and not compromise the volume? Correct?

Also, does the port shape matter, and does it change the response where it releases into the cab?

I am sure there are other threads that have already gone over this many times… Feel free to point me in the right direction. Really appreciate all the deep knowledge you guys have here! (Way better than tgp, just sayin…)

 

[agedhorse]

Who ports outside the cabinet? Was that from AI?

 

[fdeck]

Could be talking about a slot port. Some of those extend beyond the baffle setback. But they also extend into the cab.

 

[agedhorse]

Could be talking about a slot port. Some of those extend beyond the baffle setback. But they also extend into the cab.

but it's still inside the cabinet, in my mind the edge of the cabinet is the limits, not the baffle.

 

[plumberstrummer]

Who ports outside the cabinet? Was that from AI?

Not outside the cabinet, it was just sitting on one of the walls venting in. I don’t recall exactly in what context I saw it - so, a port just needs to set inside of the enclosure of the speaker, as outlined by the volume requirements of the speaker? Porting inside volume?

 

[plumberstrummer]

but it's still inside the cabinet, in my mind the edge of the cabinet is the limits, not the baffle.

Thank you. Understood…

And how about the shape of the port? Does it matter?

 

[Redbrangus]

And how about the shape of the port? Does it matter?

The shape doesn't matter, within reason. The volume of air in the port does: cross-sectional area X length (depth).

 

[Wasnex]

In general ports are built inside of speaker cabinets. The volume taken up by ports, braces, drivers, etc, is subtracted from the total volume of the cab.

Example:

AFAIK V(total) is the volume of the box before the volume displaced by ports, braces, and drivers is subtracted. Vb is the effective volume for tuning purposes.

The graphic is from the first design in this document:
ref: https://www.parts-express.com/pedocs/more-info/290-593--eminence-deltalite-2512-cabinet-design.pdf

From Eminence 2512 spec sheet:

AFAIK this is how much space the 2512 takes up in a box.

In some cases, the shape of the box and ports can have an impact on tuning.

 

[ninjatanzen]

I know this wasn't where the intent went, but ports can be outside the cabinet right? I assume it's not done because of looks, durability, costs, etc. but it's not inherently wrong from an audio perspective right?

 

[Wasnex]

I know this wasn't where the intent went, but ports can be outside the cabinet right? I assume it's not done because of looks, durability, costs, etc. but it's not inherently wrong from an audio perspective right?

AFAIK yes.

 

[agedhorse]

The shape doesn't matter, within reason. The volume of air in the port does: cross-sectional area X length (depth).

Correct.

 

[agedhorse]

I know this wasn't where the intent went, but ports can be outside the cabinet right? I assume it's not done because of looks, durability, costs, etc. but it's not inherently wrong from an audio perspective right?

Yes, but it’s horribly impractical when you have to transport it…

In some cases, the shape of the box and ports can have an impact on tuning.

Not so much “within reason”.

 

[ninjatanzen]

Yes, but it’s horribly impractical when you have to transport it…

I can imagine so, it was more of a curiosity than plans to do so.

 

[plumberstrummer]

@agedhorse

does the overall size of the speaker enclosure matter as much as the volume of the space? In as much as, if I am aiming for 54 L does it matter if I am creating an enclosure that has a 24 inch with or a 15 inch width, in any significant way as long as I achieve 54 L,? I imagine it does, and those impacts can be hard to predict, but maybe I am wrong… Maybe those impacts are nominal, as long as the enclosure is airtight, pressure, tight, and has the correct volume and ports… am I totally off base?

 

[agedhorse]

It’s just the internal volume, but that works with the porting and driver parameters to define the performance.

 

[JamesGrant]

Idea for you, shape the cab like an old style power station, ports on the top - outside, like chimneys!
Am I serious? Even I don’t know - I wanna see it!

 

[fdeck]

Something I remember from long ago is a picture of homemade hi-fi speakers, where the ports were outside of the box, made of clay drain pipe, and doubled as the speaker stands. They were anything if not creative.

One thing that’s worth trying is to raise and lower the box volume by the volume of the port. If your design is fairly mainstream, a couple liters give or take won’t dramatically change the response curves. In fact I recommend what I call “poor mans tolerance analysis,” which is to vary each design parameter by a bit and see how the curves change. This will give you an idea of just how precise everything needs to be. Typically the tolerances are fairly loose because the conversion to dB (i.e. 20*log(whatever)) covers a lot of sins.

 

[joelb79]

Who ports outside the cabinet? Was that from AI?

The examples of this in the car audio realm are endless.

 

[agedhorse]

The examples of this in the car audio realm are endless.

I don’t have anything to do with the car audio industry.

 

[joelb79]

Thank gosh, because those are just kids being kids.. and a fire risk