Isobaric loading in double the size enclosure

[Bassick]

Does anybody have any experience in isobaric loading. I'm currently pondering my next trunk setup. I have 2 15" subs that will take 4 cubes each. I have the space for a 8 cubed enclosure, but it doesn't leave much room for amp, crossover install. Sure I can still install the 3 amps I'm using and the crossover, but it just wouldn't be attractive at all.

So, I'm thinking instead of a dual sub configuration (8^3feet), I'll opt for just 1 sub configuration (4^3feet). Which leaves me with 1 subwoofer unused. But, and there is always a BUT, I paid for two subs and I would like to use both of them. So, now I'm thinking ISOBARIC.

With isobaric loading, I get to use a 2^3feet box instead of a 4^3feet box. My question is this, can I make a 4^3 box and isobaric load tow subwoofers, that are rated for 4^3feet each.

Ok, here is my reasoning. Research (internet searches) tell me that manufacturers sometimes gives a recommended enclosure size thats sometimes half of what the sub can really handle. So, if one of my subs is recommended at 4 cubes, I'm thinking it will perform with a lower extension if placed in 8 cubes. Now, if I take the 8 cube thinking and apply isobaric loading, I get 4 cubes.

So can anyone give me insight on using isobaric loading in double the size enclosure?

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[bbeljefe]

You would have to model the specific subs in the enclosure you want to build in order to make an educated guess. And that stands to reason regardless of the alignment or subs you choose. That you're thinking of an isobaric alignment doesn't really make that a better or worse, easier or more difficult task. It's just one more way to build a loudspeaker.

 

[winkychevelle 10+ year member]

You would only need 2cubes but I would run 3cubes decent amount of port and tuned mildly.

since you have so much motor force it should dig low power handling will stay the same

 

[TaylorFade 10+ year member]

In order to make up for the efficiency loss, you have to run full power to both subs. You might run into overexcursion issues going that big. It'd be like doing one sub in 8 cubes. How do you think that would work?

I say try it. Shit on it. See what happens. Tune low though.

 

[Mass Car Audio 10+ year member]

Who do realize that when you isobaric load there is a loss of 3db by running them clammed and at the same time you have to double the power. I really don't think you gain anything from a isobaric configuration.

3dB represents a ratio of two to one or a doubling of power and when you isobaric load you will loose that 3db gain.

 

[akadj 10+ year member]

You will lose 3db, but gain 3db back if lowering impedance and doubling your output power from 1 sub to 2 subs. So in short.. If your woofer is rated at 90db @ 1 watt.. With two you will still be at 90db.. At least that what I've been told

Another thing that you will gain with compound isobaric set ups is they have a lot more SQ, faster or more accurate response and reduce odd order harmonics.

I tried this in my wall and didn't notice any change in SPL as it claims and because im just set up for burps I couldn't tell ya if the SQ myth was true either.

 

[cablguy184 10+ year member]

SPL driver will not make good Isoberic drivers ... Takes too much power to push the tough suspensions correctly ...

However, If you plan to use SQ drivers (you did not specify in your first post) ... Isoberic works great with low end definition.

And also, you only build your enclosure for one driver which saves space ...

 

[Mass Car Audio 10+ year member]

You will lose 3db, but gain 3db back if lowering impedance and doubling your output power from 1 sub to 2 subs. So in short.. If your woofer is rated at 90db @ 1 watt.. With two you will still be at 90db.. At least that what I've been told
Another thing that you will gain with compound isobaric set ups is they have a lot more SQ, faster or more accurate response and reduce odd order harmonics.

I tried this in my wall and didn't notice any change in SPL as it claims and because im just set up for burps I couldn't tell ya if the SQ myth was true either.

YA it's kinda useless to isobaric load, maybe if you had a bunch of power to use up and make your build look cool from having a bunch of woofers.

 

[Mass Car Audio 10+ year member]

SPL driver will not make good Isoberic drivers ... Takes too much power to push the tough suspensions correctly ... However, If you plan to use SQ drivers (you did not specify in your first post) ... Isoberic works great with low end definition.

And also, you only build your enclosure for one driver which saves space ...

Actually you need to build your enclosure for 1.5 subwoofers if you have two of them in a isobaric load configuration.

 

[bbeljefe]

Drivers in isobaric alignment will fire in half the space of one driver. That's the only benefit to isobaric loading... it saves space but maintains motor force.

 

[cablguy184 10+ year member]

Actually you need to build your enclosure for 1.5 subwoofers if you have two of them in a isobaric load configuration.

Not according to this ... Custom Car Audio Boxes

Isobaric Loading

Another enclosure design that you may hear of is isobaric. Isobaric is not actually an enclosure type but a woofer loading method. Isobaric loading can be used in conjunction with any of the enclosure types, except perhaps infinite baffle. Isobaric loading consists of two woofers coupled together by a short enclosure which is only long enough to prevent the two woofers from striking one another. The woofers may be mounted face to face, back to back or front to back. However it is important to have the woofers firing in phase with one another. In order to accomplish this with the woofers firing front to front or back to back one of the woofers speaker leads must be reversed with respect to the other woofer.

Isobaric loading is usually used when space is at a premium or a maximum number of woofers wish to be used in a certain volume of space. By isobarically loading the woofers, a box of only half the size of a one woofer box is needed. For example, if a 12" woofer requires a two cubic foot box, the same 12" woofer isobarically loaded only requires a one cubic foot box. The cost of this design, other than doubling the woofer cost, is a reduction in the subwoofer system efficiency by three decibels (if both woofers are given the same power as a single woofer), which is equivalent to halving the amplifier power. New, small box subwoofer designs have all but eliminated the need for isobaric loading in car audio and it has fallen out of popularity.

Advantages of this design are increased linearity in the speaker movement, lower space requirements, and increased power handling.

Disadvantages are increased cost, increased design and assembly complexity, and decreased efficiency.

I'm running a pair of Isoberic enclosures in my truck ...

 

[Mass Car Audio 10+ year member]

Really half the space of one driver for two in a isobaric load ? I've been told for many of years different.

 

[cablguy184 10+ year member]

Really half the space of one driver for two in a isobaric load ? I've been told for many of years different.

Yep ... I quoted that from a trusted site. Plus, I've ran Isoberic enclosures for many years ... I'm running 4 10s Isoberic now in my truck ...