Speaker Enclosures - Part 2

In Part 1, we saw how all rectangular solids resonate at frequencies determined by their physical dimensions (dimensional resonances). And we saw how online calculators help determine where these resonances occur in your speakers and if these dimensional resonances occur (group together) around notes on the musical scale. We also saw how to correct for these dimensional resonances by building new rectangular boxes of different dimensions but with the same internal volume and then stuffing it with the existing hardware. In part 2, we will explore alternative physical shapes and learn why such shapes can be even better than that (have fewer clustered resonances) of evan a well-designed solid rectangle.

Before I begin, I understand that most of you do not want to redesign your speaker cabinets and nor do I recommend you do so. However, armed with knowledge of the compromises designers make in creating a production loudspeaker, you will better understand why choices are made and what these choices can sound like. If you see a cabinet of one design, you can listen for the resonances that always occur as a compromise of choosing that design. Remember, with knowledge comes wisdom.

Everything in the world is a compromise of some sort to gain something else and anyone who tells you different is not being honest with you. Saying it another way, to get this you have to give up that. When someone makes rational excuses for a compromise they are, as the old saying goes, “trying to sell you something.” (I find it interesting that “sales” is generally perceived as being a dishonest profession, one tolerated and even encouraged behavior from which the root of many of this world’s problems arise.) The joke “How can you tell when a salesperson (or politician, or...) is lying? When his/her lips are moving.” simplistically sums up the impression people have about honesty in general. OK, I’m off the soap box now and let’s get on with the show and get honest and talk about desired gains and resulting compromises.

The first alternative shape is the triangular solid or "wedge" enclosure. Here, there are only two parallel walls (gain: one major "side-to-side" resonance and several minor resonances) and such a cabinet is exactly half the volume of an equivalent-dimension solid rectangle (compromise: a box that is literally twice the physical size to maintain the equivalent internal volume). Wedges are relatively simple to build and you can place the drivers on one of the right-angle faces with the slope at the back preserving the current solid-rectangle appeal. Waste is also kept to a minimum with such a design.

A Wedge-Shaped Enclosure

Wedges are therefore a really good choice as an alternative-shape enclosure. Drivers can be placed on any of the three non-parallel surfaces so its unconventional looks can be somewhat disguised. It does, however, cost a little more to build this style enclosure. You can use an online calculator such as the one found for "Wedge 1" at http://www.the12volt.com/caraudio/boxcalcs.asp#wed to determine the equivalent volume of a wedge cabinet for your specific needs.

All speaker cabinets resonate in three "modes" just as rooms do: axial (simple back-and-forth from two walls), tangential (simple bounce off of all three or four walls), and oblique (complex bounce off of all five or six walls). Making a wedge-shaped cabinet uses fewer parallel surfaces (and fewer surfaces) and minimizes the number of resonant axial modes. Wedge cabinets do little to reduce the number of tangential or oblique modes. In the next part of this series, we will see if there are other ways to deal with the remaining resonant modes. Until then, listen to your stereo with your ears and not your eyes.

But there is more about basic cabinet design and you can read about it in Part 3.

Related ArticlesSee all entries about speaker enclosures in Part 1, Part 2, Part 3, and Part 4. Also, a related article on the effects of crossover network components on driver performance.

Yours for higher fidelity,

Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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