Is it audible? Probably not.

When it comes to Isobarik designs, there is really one big plus gained by trading off two costly minuses:

The BIG plus (The Good):
A really small box that produces a whole lotta sound!

Costly Minus #1 (The Bad):
Two drivers cost twice as much as one and you must double your amplifier power to achieve the same loudness level compared to a non-isobarik design. But, since the box can handle twice the power, you're right back where you started, only twice as poor.

Minus #2 (The Ugly):
Since the drivers are arranged in a "clamshell", the frame of one of the drivers can be seen extruding from the outside of the box which, quite frankly, is as ugly as sin. However, if you have the money, and enclosure SIZE is your main concern, then this design is indeed for you! Also keep in mind that building an additional box for the mid-bass WILL be necessary! LITTLE or NO mid-bass will be produced from the clamshell design! The question is, are you willing to sacrifice the money (and ugly) to achieve big time sound from a relatively tiny enclosure (the parallel here being an expensive and cosmetically challenged companion who can do quite a number with a golf ball in a garden hose).

However, we can treat The Ugly:

How? By installing the two drivers like this: (in a “tube" facing the same direction)

Now, the speaker is MUCH more aesthetically pleasing! In fact, no one can even tell that there's two drivers in the box! And, you won't have to build an additional box for the midbass! Unfortunately, that's about it for the good news...

As you probably suspect, there simply must be a trade-off here somewhere... And, you're right. Let us now venture into a little number-less math.

First of all, let's explore the theory behind all this Isobarik gibberish. Essentially, when you load two identical drivers Isobarikally, in effect what you're doing is making one "monster" driver by combining the two. What I mean by this is that since the two drivers are always "helping" each other (they are physically "coupled" in an airtight chamber and are wired in parallel so that they always move in unison to the electrical signal applied to them) as they work, then the math says that the two drivers can be (and are) considered as ONE driver acting alone, only with half the Vas rating. That also amounts to half (-3dB) the SPL, and twice the Power rating as compared to ONE of the drivers acting alone.

Ok, so, where does this help us and, more importantly, where does it hurt us? Well, the Vas being cut in half is definitely a plus (that's why the box size is cut in half as compared to a single driver), but the SPL being chopped by 3dB (effectively in half) sucks, but that can be made up for by the power handling capability being doubled (of course, you gotta fork out more bucks for a more powerful amp). So, essentially, you can "buy your way out" of this drawback.


This brings us to The Ugly. By using the "pretty" Isobarik design, we win on pretty. But, we lose a little on box volume and "high" (or more accurately put..."extended") power performance.

The "loss" on box volume is this...instead of having half the sized box, we have half the sized box plus the extra space needed by the frame of the front woofer. Unless you're dealing with a woofer which already "defaults" to a really small box (already has a really low Vas), however, this "loss" may not be so bad. Depending on the size of the woofer that you're dealing with, this added volume could be anywhere from 0.25 to 1.5 cubic feet, so you must decide whether or not "pretty" is worth it.

The other loss we must deal with is the loss in overall speaker performance over extended high power demands. Here's the scoop... When you're really cranking out the sound from your favorite CD, the woofers are working hard, and are therefore generating alot of heat. This is natural. So, ask yourself, "where does a woofer generate heat?". Well, it generates heat in the voice coil (which is inside the big round magnet). And, when any object heats up, its physical characteristics inevitably change. Look again at the diagram of the "pretty" isobarik design:

Now, doesn't it seem logical that the voice coil (magnet area) of the front woofer has less "natural" cooling opportunity than that of the rear woofer? The answer, of course, is yes. And, since we're on the logic bandwagon, doesn't it stand to reason that if the voice coil of the front woofer is alot hotter than that of the rear woofer, that the characteristics of the two woofers would be different? You guessed it, yes again.

Ah, but here come the "so what?" 'ers. Well, when you consider that the whole idea behind Isobarik is based upon two identical woofers "working as one", but now one of them is alot hotter (and is therefore responding differently to the electrical signal being given to it) than its counterpart, then it's not hard to imagine that your "benefits" of Isobarik design are quickly going down the tubes.

Given these facts, any competition audio professional would tell you not to design an Isobarik box in such a fashion. However, if you're just trying to get good, deep bass out of a small box, and this small box is to be in view of your friends and family, then this design is quite ok! Remember, it's only after extended periods of high power demands that you begin to see the deterioration effects of this phenomenon.

If you are an average Joe who wants a good sounding box, but who doesn't intend on cranking it up for extended periods everyday (while being monitored by a competition judge and his sound equipment), then you can beat The Ugly, no problem.. Like Clint says, "A man's GOT to know his limitations." Personally, I've used this design for many years with no problems, but I had to include this information to satisfy the "purists"...

As touched on above, this "pretty" configuration also has the added benefit (over the clamshell design) of being able to produce more mid-bass/midrange frequencies, since the front (voice coil) of one of the driver cones is able to radiate that acoustic energy from the box, and therefore you will probably be able to get away without having to build an additional mid-bass box.

Likewise, if you go with the clamshell design, keep in mind that building an additional mid-bass box is an absolute necessity. There will be little or no mid-bass produced by this design. This clamshell design along with an separate mid-bass box will most certainly out perform the "pretty" design by itself, but now you have to build more boxes. Again, it all comes down to pluses and minuses...the name of the game is "trade-off". If there were a perfect speaker design everyone would use it, and you wouldn't be reading this...