Calculating slotted port size in 2x12?

[Reg18]

Currently building a 2x12 cab roughly the size of a Marshall 1936 cab, 760x560x290
I like the idea of trying a slotted port to add some depth.
How do you calculate the size of a slotted port as one wall is technically the whole width of the cabinet? Or is it?
The simplest is to do the same as the Friedman 2x12 (pic attached) which is slot cut on the back panel near the bottom, I also wondered about the Z Best cab which is a big slot in the front (other pic)Obviously the size of each cabs port is vastly different so they must be emphasising different freq?
If I did the Friedman thing how would I calculate the freq?

[Reg18]

Turns out Hiwatt and soldano have done it with some 2x12s as well, the slots look like a different size again.

[NippleWrestler]

Having played (front) ported 2x12s I didn't notice a huge (if any) difference for guitar if the ports were covered/bunged or not.

But to answer your question have a look for Thiele/Small parameters and have your chosen speakers datasheet on hand as the cabs should be tuned for that specific speaker.

[Jay]

http://www.troelsgravesen.dk/BOX-PORT-CALC.htm

[Reg18]

Having played (front) ported 2x12s I didn't notice a huge (if any) difference for guitar if the ports were covered/bunged or not.

But to answer your question have a look for Thiele/Small parameters and have your chosen speakers datasheet on hand as the cabs should be tuned for that specific speaker.

When you say datasheet, which specs am I needing for my calculation? I’m using a G12H75 and a G12H55hz so being 2 different speakers can I even work out what I need?
From what I’ve been reading in relation to the Friedman, Hiwatt, Soldano cabs with the little port cut out at the back at the bottom it helps tune out any boominess and midrangey weirdness.

[Reg18]

http://www.troelsgravesen.dk/BOX-PORT-CALC.htm

Thanks for the link, read it through twice, bit over my head though. Still unsure how I would calculate the port length if it’s cut out of the bottom of the cab?

[codedog]

Turns out Hiwatt and soldano have done it with some 2x12s as well, the slots look like a different size again.

Geez... I always thought those are just to make lifting the back cover off easier!

[Optical]

The Z best cab has a lot of low end - more than a 4x12. Couldnt hurt to make the port size adjustable - there are lots of bass reflex cab design simulators around, the principle is extending the low frequency response using a port tuned to an optimised frequency

[Snarblinge]

buy some mdf and experiment. it's the only way to be happy.

or buy more ply and make some smaller boxes with the rejected parts, though this is a dangerous slope I am kinda sliding down at the moment..

[Reg18]

buy some mdf and experiment. it's the only way to be happy.

or buy more ply and make some smaller boxes with the rejected parts, though this is a dangerous slope I am kinda sliding down at the moment..

I’ve got a bunch of left over ply from some recent renovations, might make a couple of different back plate options.
I’ve built around 4 cabs over the years. I generally based them Closer to the Mesa 2x12 dimensions but I think there is something to be said for a bit of extra height in a 2x12 like the Bognor OS. Hence I’ve based it on roughly that size.
My 2 favourite cabs (of the ones I built) were a 2x12 with just one G12H75 in (the other 12” hole was empty waiting for another speaker) so it was technically a “detuned” oversized 1x12. It never sounded as good when I finally put the second 12” in. And a clone of a Ported Jackson 1x12. 2 ports on the sides which I guessed the length for but it sounded really good! Hence my desire to have a crack at porting/tuning my next 2x12

[jeremyb]

Isn't porting more suitable for bass cabs? 6 string guitars aren't well known for their low frequencies, I would have thought having the option to make it closed back with a panel to allow it to be semi-open would give you more of a contrast?

[Reg18]

Isn't porting more suitable for bass cabs? 6 string guitars aren't well known for their low frequencies, I would have thought having the option to make it closed back with a panel to allow it to be semi-open would give you more of a contrast?

It’s no so much bass level low end I’m looking for but tuning it to be tight and getting the mid range sounding right. In theory I could tune the cabinet to 100hz or 500hz depending on what size port I used. But using the same method as the Hiwatt,Soldano, Friedman cabs I still can’t figure out if the width of the cabinet would be considered one side of the port? The back panel on the bareface stuff looks interesting too, gets rave reviews also but that looks even more complicated to figure out!

[Reg18]

Another reason I’m very curious about tuning is I have a little Marshall 1922 2x12. Sounds small and boxy as a 2x12, it was converted to a 1x12 baffle. sounds slightly better as a 1x12 closed back. Sounds nice and open if you take off both side handles so it’s like an open back, sounds even better if you just have 1 handle on and the other off. Mid range sounds better. So that tells me there is a tuning factor to getting the right size port/opening.
One of the previous owners Steve said it sounded best to him with an open oval shaped back as a 1x12 and from
My experiments that sounds about right.

[H671]

Another reason I’m very curious about tuning is I have a little Marshall 1922 2x12. Sounds small and boxy as a 2x12, it was converted to a 1x12 baffle. sounds slightly better as a 1x12 closed back. Sounds nice and open if you take off both side handles so it’s like an open back, sounds even better if you just have 1 handle on and the other off. Mid range sounds better. So that tells me there is a tuning factor to getting the right size port/opening.
One of the previous owners Steve said it sounded best to him with an open oval shaped back as a 1x12 and from
My experiments that sounds about right.

You might be over thinking it - the secret is in how many baked bean tins that you use for ports.
This cab was originally made for an old Jansen Sessionman bass head, I then cut it down in size for my Joyo 5E3. With the Jansen I has 3 baked bean tins & with the Joyo only 2. Also the tins need to be covered with carpet.

IMG_20220529_130449_resized_20220529_010520708.jpg (877.02 KiB) Viewed 5441 times

[Reg18]

Another reason I’m very curious about tuning is I have a little Marshall 1922 2x12. Sounds small and boxy as a 2x12, it was converted to a 1x12 baffle. sounds slightly better as a 1x12 closed back. Sounds nice and open if you take off both side handles so it’s like an open back, sounds even better if you just have 1 handle on and the other off. Mid range sounds better. So that tells me there is a tuning factor to getting the right size port/opening.
One of the previous owners Steve said it sounded best to him with an open oval shaped back as a 1x12 and from
My experiments that sounds about right.

You might be over thinking it - the secret is in how many baked bean tins that you use for ports.
This cab was originally made for an old Jansen Sessionman bass head, I then cut it down in size for my Joyo 5E3. With the Jansen I has 3 baked bean tins & with the Joyo only 2. Also the tins need to be covered with carpet.

IMG_20220529_130449_resized_20220529_010520708.jpg

Might be overthinking it but I often do, when I’m making pedals I can spend hours getting the right sounding germanium transistors or components until I’m
Happy. Sometimes I just stick to the schematic but often find my ears telling me if i made some minor tweaks it would sound better. Same thing here, doubt I’ll be satisfied until I try a port to either rule it out or in. I was hoping there might be some people on here who could help me work out the calculations for hz tuning but it seems I may be on my own with this one.