ABC Math

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Mar 31, 2005 | 02:26 PM

maltesechicken

Thread Starter

2000 Watt CAFz'r

Joined: Jan 2001

Posts: 2,026

I know there have been a few posts on ABC boxes, but I want to clarify and see if I've got this right.

Hypothetical (for the sake of easy numbers):
I have a speaker that will work well in 1.5 cubic feet with a 3"D x 12"L round port.

To ABC the box, it is a 1/3 - 2/3 ratio correct?

So with my given scenario, the Speaker will be mounted in a 1 cubic foot chamber. This chamber will have 2 ports (both 3x12) one going outside the box, the other going into the next chamber. The next chamber will be .5 cubic feet, with a third port going outside the box. All 3 ports are of equal length.

Questions:
How will converting to ABC effect the Freq. response chart as I noticed in WinISD?

What are the benefits of ABC: Increased low end excursion? Higher SPL?

Just let me know if I'm getting this right. I've got a new sub coming and I think I want to play with this.

Ryan

Mar 31, 2005 | 02:48 PM

Paul Niwranski

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For the venting - you figure out the required length for a standard vented box with two vents.

So for your example if the sample box was 1.5cuft with two 3"x12" vents and you made an ABC with 3 3"x12" vents then yes you are correct. Remember to allow and adjust for displacements.

The ABC has an upper resonance approximately 2x the tuning frequency. It is similar to a vented bandpass in this way but obviously does not have the rolloff in the top end that the bandpass does.

Apr 2, 2005 | 05:35 PM

miked

50 Watt CAFz'r

Joined: Sep 2004

Posts: 61

dumb question but.. when making the box.. do u base the size of it off of sealed or ported?
like say the sub is 1ft sealed, 2 ported.
which one would you base your 2/3 part on?

Apr 2, 2005 | 10:20 PM

Paul Niwranski

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^ The largest vented box the woofer will work in.

ABCs are never small. The 1.5cuft one I have is for an 8 [img]graemlins/thumb.gif[/img]

Apr 4, 2005 | 07:56 PM

maltesechicken

Thread Starter

2000 Watt CAFz'r

Joined: Jan 2001

Posts: 2,026

Okay, going back to the benefits of ABC, I'm not sure what you mean by "The ABC has an upper resonance approximately 2x the tuning frequency. It is similar to a vented bandpass in this way but obviously does not have the rolloff in the top end that the bandpass does"

Upper resonance - does that mean there will be an increase SPL between the tuning freq and the upper resonance?

What do you classify as the "biggest" possible box? How much of a db spike at the tuning freq should there be to classify it as the biggest possible?

Thanks

Apr 4, 2005 | 08:04 PM

maltesechicken

Thread Starter

2000 Watt CAFz'r

Joined: Jan 2001

Posts: 2,026

If you're willing to work with what I have . . .
The speaker I want to try this with is an eD 9Kv.2

qts - .30
qms - 3.5
qes - .38
re - 7.4
vas - 45L
fs - 23
bl - 15.34
xmax- 14.1 mm

I think the biggest box would be 0.8 cubic feet tuned to 34 - 35 hz

Apr 5, 2005 | 01:05 PM

Paul Niwranski

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The 'biggest' box is the largest it will work in and not slap the magnet or lose control. "Minimum size" boxes do not work.

It is hard to make an ABC under 1.5cuft. The vents just get too long.

The box exhibits two tuning frequencies. For instance, a box tuned to 35hz will also have a resonance at 68hz. The response between the two is slightly saddle shaped but quite livable.