Speaker Enclosure Size – Effect on Audio Quality

Question
Does a speaker’s enclosure size have any effect on audio quality? I’ve always assumed a larger enclosure size is better, but I never understood why that is the case.

– Tyrone B.
Winsford, Cheshire UK

Answer:
The short answer to your question is “Yes”, speaker enclosure size does affect the audio quality. That size, however, depends on a multitude of factors including the type of enclosure, properties of the driver, the enclosure material, the shape of the enclosure, quality of craftsmanship, etc. Speaker manufacturers spend endless hours calculating and measuring the effect of these changes to produce the flattest possible response over the widest frequency range. While a full primer on speaker enclosure design is well beyond the scope of this QA, there are many DIY websites that provide quite good information.

Given the enormous variety of speaker enclosure shapes and designs, there is clearly no one correct answer as to what produces the best sound. For example, the Bowers and Wilkins “Nautilus”.

One of the World’s most iconic speakers, looks very little like a speaker. The Nautilus’s enclosure is made of multiple, tapering tubes, the result is quite striking and does indeed resemble its’ nautical namesake. In utilizing this unique enclosure B&W has solved one of the many problems that speaker enclosures themselves can create, the problem of standing waves that result from parallel surfaces.

In the broadest sense, all else being equal, certain, larger dimension enclosures with certain HxWxD ratios can enhance specific low frequency characteristics. The primary mechanism for this is when a driver moves forward to produce a sound wave towards the listener, it must also return to neutral, thus producing a sound wave 1800 out of phase. If this wave were allowed to propagate around the room back to the listener it would result in distortion and phase cancellation. This is mostly a problem for lower frequencies, and may manifest as “gaps” or “smearing” of the bass. In order to prevent this, the out of phase wave is contained within the enclosure.

But all is not equal.

If bigger = better, how can Raidho ask $17k for their C 1.1 speakers and Magico charge $26.5k for the Q1, when neither is even 15” tall?

The answer is, of course, they couldn’t. Instead of concentrating on how the size of an enclosure affects the lower frequency spectrum, these companies have focused on creating a cabinet that does not add or subtract anything from the sound wave being produced. Not as easy as it sounds.

I will pose your question in a slightly different way: If an enclosure is required for high quality sound reproduction, then shouldn’t speakers with no enclosure sound sub-par?

If the answer was “They do,” companies such as Quad, Martin Logan and Magnepan would have been out of business a long time ago. By eliminating the enclosure entirely (they do have a frame, but nothing that “encloses” the drivers), they avoid the problems caused by the enclosure itself (and thus eliminate the R&D costs associated with trying to perfect the enclosure, see Raidho and Magico above).

These manufacturers produce what are collectively called “electrostatic” speakers. The basic principle is this: a VERY thin (12 microns) charged diaphragm is stretched between two large, perforated metal sheets called stators. The stators then have voltage applied across them from the amplifier, thus moving the diaphragm. This movement creates the sound wave. Because most electrostatic speakers are quite wide, the speaker itself acts as a physical barrier for the out of phase low frequency sound waves. While electrostatic speakers have their own set of problems, an enclosure is not one of them.

So now we have come full circle: while a speaker’s enclosure does have a profound effect the sound, a bigger enclosure is not necessarily better; some speakers don’t even have one. Bigger ? Better. Better = Better.