Calculating slotted port size in 2x12?

[dayl]

Here are the plans for the TL806 Electrovoice 1x12 cab. I've seen and read of guys just doubling up the dimensions for a split 2x12 cab to great affect.
I'm no pro, just came across this looking for a reliable set of plans for a 1x12 and the Freq range appears to be in line with your average celestion. No reason why this wouldn't work as a 2x12.

https://robrobinette.com/images/Guitar/ ... _plans.pdf

[Bg]

My 2c worth. I think with mismatched speakers you're not going to get a port that suits both from the Theile values. I'd average them and take that as a starting point. If you're porting at the back, then its easy enough to tune by ear with different lengths etc.

[Reg18]

So after a couple of weeks of slowly putting it together this is where I have ended up. Tried it as a closed 2x12 but it had a slightly honky bass, ended up
Cutting a port in the front baffle which helped some, next I did some extra bracing in the cabinet itself. I could still
Hear the “ply” if that makes sense? Like if you knock the back panel and listen to the tone/note it sounds similar when you run an amp into it. I put some triangle shaped strips along the length of the back panel (inside) to strengthen the back panel and hopefully give some dispersion to the sound waves. It’s finally about where I wanted it but there has been many steps. Been jamming on it this arvo quite a bit with different guitars to see how it sounds and I think it might be in its final iteration. Next I’ll
Need to order some tolex for it.
[youtube]https://www.youtube.com/watch?v=1VophEW ... YXllcnM%3D[/youtube]

[sizzlingbadger]

That JCM sounds great through that cab mate !

[Anvil Amps Alan]

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?

For a rectangular port the length remains the same. Take the diameter of round port and calculate the area, then make the width and height of your rectangular port add up to the same area.
Ports mainly effect the low frequencies.
Reflected sound in the box can attenuate bass and mids.
The sound coming from the rear of the cones is obviously opposite to what you hear from the front of the speaker and when this bounces off the hard rear panel and back out through the cone these out of phase sound waves subtract from what you can hear.
Known as constructive and destructive interference
Easy to fix, just put sound absorbing material on the inside of the back panel.
Foam, Felt or just carpet will work.
Try this before you start with ports.
A square of sound absorbing material behind a car door mounted speaker makes a massive improvement for the same reason.

[Anvil Amps Alan]

Just thought I should mention The boundary effect.
The placement of speakers or open back combo Amps when setting up a stage can drastically improve loudness.
If a speaker is placed against a wall (pointing outwards of course),
Theoretically you will get a 3dB increase in SPL. (twice as loud)
Applies to open back or closed.
This works better for the audience if the speaker is raised above the ground, also you get better projection.
Similarly if your stage happens to have a corner and the speaker is placed in it facing out a 6dB increase in SPL can be expected.
I used these theories with a 22W Deluxe Reverb Amp when setting up for a gig and the Amp was loud enough
to perform with a full Drum Kit and a decent Bass Amp not drowning it out.
I learned all this stuff years ago when designing HiFi Systems and later running a Car Audio Shop.

[Reg18]

Just thought I should mention The boundary effect.
The placement of speakers or open back combo Amps when setting up a stage can drastically improve loudness.
If a speaker is placed against a wall (pointing outwards of course),
Theoretically you will get a 3dB increase in SPL. (twice as loud)
Applies to open back or closed.
This works better for the audience if the speaker is raised above the ground, also you get better projection.
Similarly if your stage happens to have a corner and the speaker is placed in it facing out a 6dB increase in SPL can be expected.
I used these theories with a 22W Deluxe Reverb Amp when setting up for a gig and the Amp was loud enough
to perform with a full Drum Kit and a decent Bass Amp not drowning it out.
I learned all this stuff years ago when designing HiFi Systems and later running a Car Audio Shop.

My gear room is essentially square but has desks and equipment etc, my amps sound noticeably worse on one side of the room, not louder but just not as good.
I figure the inside of a speaker cab must have similar principals, like can you put bass traps in the corners of a cab and it effect the sound?

On that note, is there a Device that can measure the db level of bass, mid, treble individually?

[Anvil Amps Alan]

in a sealed Cab you can reduce the internal volume (with a partition, or fit another sealed box inside to take up space?) to reduce bass response.
Bricks not a good idea Polystyrene Should work but I have not tried it.
Smaller Cab (Sealed) gives back pressure to the cone, damping excursion.
Strange, but if you absolutely stuff inside with Dacron Fibre you can realise 10% increase in Bass.
Use an Audio oscillator and measure dB at set frequency.
A Sound Proof Room is desirable here!
Or use a Spectrum analyser.