Port calc help

[mikeyatx]

Greetings fellow bass heads, this is my first post. I work in the pro audioindustry primarlily building analog gear for recording but was recently asked to builf a couple of cabs each using one 12" Eninence Kappalite 3012lf.. My design includes two 4" Aero ports in each cab, due to the guy cutting the wood on the big saw a home depot I realized when I got home that my cab went from 2.7 to 2.52. The original design called for the port lenght to be just over 10" giving me a preferred 4" clearance from the back of the cabs (ports are front mounted). So I now have some 90 elbows and am turning them down toward the bottom of the cab....my problem is figuring thr length of the 90's. Aero Port says I need one lenght and Eminenc3 says another....trying to tune it to 44hz. SO I al also a bit oconfused about measuring the port length, di I measure from where the flare starts or end of flare to end of flare? Again the ports are Aero ports and I have to use the 90 degree elbow to turn the inside port down. Any help would be freatly appreciated and I am glad to be here. Thanks in advance! I'll try and post some pics of the progress asap.

[will33]

What's the interior depth of the cab? Ports should be about 11" no? 47hz tuning will bring them down to about 9-1/4". Bump too big for ya?

[mikeyatx]

Originally Posted by will33

What's the interior depth of the cab? Ports should be about 11" no? 47hz tuning will bring them down to about 9-1/4". Bump too big for ya?

Yeah evem at 11 they are to close to rear of cabinet then there is also a big flare on the aero port on the inside of the cab, thats why We are using a 90 degree elbow to turn them doen toward the bottom. I was just using Eminence's recommendation to tune them at 44hz. Straight pipe measureing is easy its the 90 elbow thats got be a bit confused. Thanks lot for the reply! Emiminence has modeled up these designs using their softwre but did not consider the new Aero Ports...supposed to add 3db of gain!

[will33]

Originally Posted by mikeyatx

Emiminence has modeled up these designs using their softwre but did not consider the new Aero Ports...supposed to add 3db of gain!

I don't know about all thatbut......

Have you modeled them in WinISD? I haven't loaded them in mine.

There's this too.

http://greenboy.us/fEARful/#earfuls

You are using a mid with the LF right? A one-way cab would use a 3012HO/deltaliteII/basslite, etc.

[will33]

I see the pic there. Is that a dedicated sub? Also guessing at a 16" +/- internal width, your ports are a lot bigger than 4", even considering the flare.

[mikeyatx]

Originally Posted by will33

I don't know about all thatbut......

Have you modeled them in WinISD? I haven't loaded them in mine.

There's this too.

fEARful enclosures for bass/drums/keys

You are using a mid with the LF right? A one-way cab would use a 3012HO/deltaliteII/basslite, etc.

I tried win isd jut it just frustrated me as there was no way to calculate the 90 dgree elbow. We are going straight 12" for now no mid or horn, the guy plays country rock and claims he'll be fine without it. I told hime we can a add a mid later and I can build the crossover but he issists he will like them with just the 12"s. I know the fad lately is to use the mid driver but he opted out. Emeinence's model shows it pretty much flat out to 1k with this design.

[mikeyatx]

The cab is built like a beast with all seams glued and screwed using coated 1.5" coated deck screws and all edges routed down. I tend to be a bit on the obsessive perfectionist side. As you can see in the pic the ports fit just by a hair, we made a special router template to cut all the holes. We countersunk all the screws and used wood filler to fill them then sanded them down for a smooth finish.

[will33]

Originally Posted by mikeyatx

I tried win isd jut it just frustrated me as there was no way to calculate the 90 dgree elbow. We are going straight 12" for now no mid or horn, the guy plays country rock and claims he'll be fine without it. I told hime we can a add a mid later and I can build the crossover but he issists he will like them with just the 12"s. I know the fad lately is to use the mid driver but he iopted out. Emeinence's model shows it pretty much flat out to 1k with this design.

Stuff that drops off at 2k (old vented dustcap 15's, etc.) can still sound pretty dark, kinda like you got flatwounds on even if you don't.

I'd try taking a length measurement around the bend at the inside of the elbow, then a length around the bend at the outside of the elbow and averaging the 2, consider that the "length of the elbow". May not be right-on but close enough for government work. Neither of you are going to be able to hear if it ended up at a dead-on 44 or 44.7, nobody else is either.

[will33]

Originally Posted by mikeyatx

The cab is built like a beast with all seams glued and screwed using coated 1.5" coated deck screws and all edges routed down. I tend to be a bit on the obsessive perfectionist side. As you can see in the pic the ports fit just by a hair, we made a special router template to cut all the holes. We countersunk all the screws and used wood filler to fill them then sanded them down for a smooth finish.

Add a couple dowels to tie the front and back panels together, between the speaker and the ports and I'd call it a good box. Remember bracing across the panels and tying panels together is what makes the box more resistant to flex in the panels, making a good speaker box. Extra meat in the corners isn't as important in this case.