Why the enclosure of a speaker is important

22nd October 2014

I recently purchased an S10 blue-tooth speaker to improve the sound-quality of my phone.

S10 speaker
size of a small apple

On receiving it I found it had terrible sound-quality and decided to rebuild it by making it a new enclosure. This project inspired me to write about why speaker enclosures are important.

Firstly let's imagine a speaker with no enclosure, perhaps we have our transducer standing on a stalk.

transducer on stalk
an imaginary speaker system

You can easily build a speaker like this if you want to see what it sounds like. Sound comes out of both the back and front of the transducer. As these sound waves mix together all around the transducer some will re-enforce and some cancel out. This makes it sound terrible.

So, the purpose of an enclosure is to "disappear" the sounds out of the back of the transducer so that you don't get any such effects.

transducer in box

Now the biggest problem with enclosures is that, unless they are extremely large, you get pressure build-up behind the transducer for low frequencies (bass). This weakens the movement of the transducer cone resulting in weak bass.

There are a lot of clever techniques to alleviate this problem that involve either using a special transducer or adding some sort of hole to the box to help strengthen the bass. Any speaker on the market smaller than a microwave that has any bass almost certainly uses some such technique. I can't write about such systems because I don't understand them well-enough but I know that their design is very mathematical and can't be done without knowing what you are doing.

But I do know that for simple sealed enclosures, the bigger the enclosure is relative to the size of the transducer, the less the enclosure will interfere with the natural performance of the transducer.

If you want to know more then www.loudspeakerdesign.co.uk has some in-depth articles on speaker design.