When porting a cab, do you...?

[qts]

I still don't get the logic. What I understand from winisd is that this driver will do well in 1.48cft SBB4 alignment.
To keep the volume 1.48cft, I would make the cab bigger by adding the volume displacement of the driver,duct and bracing, in this case we can talk about the bruto volume of the cab

In my imagination winisd see driver and duct, mounted on the outside of the cab, so there will be nothing in the cab that will reduce the volume, and then Vb will stay 1,48cft
Now there's free space of volume(air) where the cone and the air in the duct can resonate without takenup the space in the cab

What I understand from you is that the volume winisd calculate, will become less than 1,48cft , if I have to substact driver and duct volume from the "netto" volume

Does it mean that I should build a cab with a internal volume less then 1,48cft for the 2510II ??
In this case the word "netto" has no meaning to me

 

[m.oreilly]

http://www.bcae1.com/spboxnew2.htm
i used the calculator in the ported section on this page to get an idea re what i'd be running into re speaker/duct displacement. this was before i was tipped about winisd. it's a neat app if you know what the driver manufacture recommends.

 

[bgavin]

Let's start at the top.

Start with a cube cabinet, internals are 13.67" inches.
This is 1.48 cubic feet.

The 2510-II displaces 0.026 cubic feet.

When you install the driver into the cabinet, the net volume is 1.48 - 0.026 = 1.454 cubic feet.

Next, install a big round ducted port.
7.622" inside diameter, wall thickness 0.3", total diameter = 8.22".
Make the duct 6.5" long.
The external volume displaced by the duct is 0.20 cubic feet.

This duct is inside the cabinet, so it reduces the net volume by 0.20 cubic feet.
The net volume is reduced a total of (0.026 + 0.20) cubic feet.

You have to make the box larger to get back to the desired 1.48 cubic feet net volume.
This is 1.48 + 0.026 + 0.20 = 1.706 cubic feet.

Doing the math again:
1.706 - 0.026 (driver) - 0.20 (duct) = 1.48 cubic feet net volume.

The words "bruto" and "netto" mean nothing to me.
I assume they are translations from Swedish to English.

 

[qts]

Exactly what I mean with "to add" instead of substract.
Now you convince me I allready thought; If I want to build a cab for example the 2510II in SBB4 alignment, I need to "add" the volume taken up by the driver and the duct (0.226cft)to the netto volume (1.48cft), so this will make the cab larger(1.706cft)

It makes me confused you said; "substract" the duct from the netto volume.
In my imagination the cab(volume) will become smaller when build.

Thanx

 

[m.oreilly]

it will, so you have to build it bigger to get the final original volume you wanted. the internal volume shrinks the more you put into it

 

[qts]

The aproximation of Bgavin and I makes the diverends, but end up the same

 

[bgavin]

The language issue does make me laugh.
Sorry about "Swedish", when I should have said "Dutch". Your English is much better than my Dutch will ever be...


If it helps, think of the internal box components as bricks.
When you add a brick for the driver and another brick for the duct, the amount of free space in the box is less.

The driver expects to work in a free space volume of 1.48 cubic feet, so you have to make the box bigger to compensate for those two added bricks.

 

[qts]

for some words I use the dictionary on the internet, and put them together with my gramma Your expanation of the bricks is the most easiest to understand.
Sometimes people with a lot of knowledge make simple things more complecated as needed

Thanx anyway

 

[fivestringgecko]

+1, the brick analogy is pretty good.

5sg.

 

[m.oreilly]

it's 'done', save for a grill and final tuning. i'll have to get to drum kit volume to really see what it does. the new baffle turned out neat (3/4" furniture ply/a bit of crinkle paint), along with the (rear) port. i'll post some pics once i can spend more time around it (the paint is still out gassing after 24 hours)

 

[m.oreilly]

i am impressed. with a final tuning at the eminence recommended 58Hz, i'm getting a very tight bass with clear mids and up. since this was intended for a more portable, low wattage rig, i tried out an old peavey classic series 60 tube power amp i have had laying around for years, and used my tone hammer as the front end...wow, just wow. a big a$$ed drum kit driving volume/full tone, little, cheap, modern-ish/'fliptop-ish' style rig.

 

[bgavin]

How did you measure the tuning?

The nearfield technique is quite accurate, more so than the impedance trough.
The notch is the null point in cone output (tuning frequency).

The link below shows the nearfield response of an 8" woofer tuned at 60".
This is not the system response, but the woofer with the mic 0.25" from the dome center.

Link Removed

 

[m.oreilly]

...with a tape measure. followed winisd/eminence, and cut the port to the recommended length. sounds great