On this episode of Ask The Expert, Otto explains what speaker cabinets do, describes an alternative construction method, and ultimately concludes that the cabinet is king.
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This is a very interesting topic – let's dive in!
First of all, we have to understand that a speaker driver not only plays sound forward, but also backwards – as much sound as it plays forward in fact. (see fig 1.)
If and when a speaker driver is free-standing, and depending on its diameter, its lower frequencies will cancel out the sound coming from the front, resulting in a lower output below a certain frequency.
This is obviously not what we want – we want the sound output to be the same across all frequencies. One method of achieving this without a cabinet would be to put speaker driver inside a baffle or a large plate, which would then block the sound at the back from reaching the front of the speaker, and thereby solve the issue. (see fig 2.)
The larger this plate is, the lower the frequencies you will blocking from the back to the front. If you were to make this plate large enough, then you wouldn't actually need the cabinet at all, you will have created what's called an open baffle speaker – a baffle so large that the sound from the back does not reach the front.
The problem with this is that it takes up a lot of space in your listening room, and this is why we typically wrap the "baffle" around the back of the speaker driver in order to create what we know and recognise to be a cabinet. (see fig 3.)
The cabinet is essentially a box of air that the driver pushes against when playing the music, and the volume of that box of air has a big impact on the sound of the driver. This in itself is the lovely conundrum that is speaker cabinet design, which we will have to address more fully in another episode of Ask The Expert, seeing that it is such a large topic.
In the meantime, however, please check out these other episodes where we discuss related topics such as bass ports and cabinet construction.
- Infinite baffle speaker - why don't we make one?
- Why are bass ports on the back of speakers?
- What kind of subwoofer should I choose? Sealed or ported?
- Should I plug my speaker's bass port?