wasted911

iTrader: (2)

Alright, I'm trying to figure out how to design an ABC enclosure, but I'm not sure on a few things... the tutorial I found says to take regular ported box specs and split the box so you have two thirds for the side with the driver, and one third for the other enclosure. But in this example I found, they dont say how to seperately change the tuned frequencies. Do all three port lengths have to be identical? What happens when you make the second chamber larger or smaller than 1/3rd?

I wont post the website where the example is, due to forum rules.

BigRedGuy

iTrader: (11)

(1) All three ports must be the same length.

(2) The box size ratio must be kept at 2/3 and 1/3 or it will sound like ***.

The purpose of the split is to create a second peak one octave apart from the original frequency. Altering the ratio or having ports of different lengths will move the frequencies in undesirable ways. This also means that driver and port displacement must be very carefully calculated.

He may slap me around for saying this..... , but Dukk is the resident expert on ABCs. With any luck he may have the text he wrote out from a famous ABC post from another forum years ago on his computer and can re-post it here.

HTH

Dukk

^ BRG has the two most important rules to remember right there.

And I have the link to that post in my favourites at work. I'll find it when I get back in the office on Wednesday. Really it just confirms the same thing.

wasted911

iTrader: (2)

so basicly what you guys are saying is pick one frequency, and the second frequency is whatever you get, and I'm screwed with it?

BigRedGuy

iTrader: (11)

That's an interesting interpretation of what I wrote.....

The whole point is to get more sound out of the one driver.....the second peak created by the interaction of the 2 chambers 1 octave above the fundamental gives you that extra thud for free.

For example....if your original box design was tuned for 30hz, making the ABC gives an extra punch at 60hz....if you have the sub LPF'd at 80hz, virtually all of your bass gets that extra punch.

Still trying to figure out how you're getting screwed by this.....

wasted911

iTrader: (2)

haha, sorry.. I never meant it like that... My original interpretation of the ABC was that I could choose the frequencies. But this is just as nice. Sorry about my choice of words.

BigRedGuy

iTrader: (11)

N.P....

You still get to choose the original tuning frequency.....the ABC does the rest for you, and when it's done right the results can be surprising.

Good luck with it if you decide to do it.....I'm sure a few people here would appreciate pics of the construction process along the way.....

wasted911

iTrader: (2)

I probably will go with it.. But I'm deciding on using slot ports, dishing out the cash for flaired, or making my own...

wasted911

iTrader: (2)

damn I never knew this would be such a bitch.

more questions. The source I've been using to help me thorugh this is here:
The Subwoofer DIY Page - Dual-chamber ported systems
(sorry Rick)
but anyways, they use two 3" ports. Now, is that one port per chamber (divide the port into two for the chambers) or 2 ports per chamber, and 2 connecting the chambers?

Do I have to compensate for the connecting ports when I split the box up into the 1/3-2/3 ratio?

BigRedGuy

iTrader: (11)

ABCs are a pain to do....compensating for all those extra parts is the cause....

They use 2 3" ports in the original box design. One gets used to vent each side of the ABC, and the 3rd passes air between the 2 chambers. The air volumes in each chamber must be calculated very carefully.....but I think I already mentioned that....

I am curious about the frequencies given in the example tho.....I have always believed they will be 1 octave apart, but not in that post.....hmmm....

HTH