S10 mini speaker bass-boost technology

25th October 2014

size of a small apple

Most small speakers have some sort of technology to "boost" their bass. When I disassembled the S10 blue-tooth mini speaker I found it had a very interesting bass boost design. But before I explain it, I will show some simplified diagrams of how a standard sealed speaker system works.

The transducer contains a ring magnet and a coil. When current passes through the coil it magnetises it and causes it to move. This in turn moves the cone to create the vibrations (sound). The surround is just a rubber or foam ring that suspends the cone.

The problem with a speaker system like this is, (as I explained in a previous post) you get pressure build-up behind the transducer for low frequencies (bass). This weakens the movement of the cone resulting in weak bass.

How the S10 mini speaker works

In the S10, the transducer is not mounted directly onto the enclosure but onto an extra surround! Now, with low frequencies, this means you get a kind recoil effect due to pressure build-up where the entire transducer moves back when it's cone moves forwards, and visa versa. So the transducer cone and the transducer as a whole can both vibrate independently to some degree.

The recoil effect allows the cone to move more easily at low frequencies. However, the cone's ultimate (environment-relative) movement is reduced by however much the transducer as a whole recoils.

My theory as to why this system boosts bass:

The cone, being small, light and stiffly suspended (because of the spider which I didn't draw) has a high resonant frequency. The transducer as a whole has a low resonant frequency because it's heavy and loosely suspended. Therefore you get resonance at both high and low frequencies.

Does it work?

Yes. The S10 speaker has a surprisingly loud bass response and plenty of treble too.

Do I think it is a good system?

No. Because the proof of the pudding is in the tasting and to my ears the S10 speaker has horrible sound quality. I think it sounds no better than my phone's built-in speaker (although it can go louder of course). I expect that if I had measured the frequency response curve of the S10 I would have found that it had a large dip in the mid-range frequencies, which would explain the bad sound. The mid-range are the most important frequencies!

Other thoughts

Another interesting thing about the S10 is that the enclosure is surrounded by an iron cylinder. Yes I'm not kidding, iron, and IIRC ≥ 2mm thick. The weight of this iron cylinder is 128 grams. For comparison the entire transducer only weighs 25 grams. The reason for the iron cylinder is obvious after a bit of thought. The transducer contains a magnet, and a vibrating magnet obviously gives off electromagnetic radiation, which could cause interference to other electronic equipment. Now iron atoms align themselves to magnetic fields, and it takes energy to change this alignment. So the electromagnetic radiation is converted to heat and dissipated by the iron enclosure. Anyway, the cylinder is so strong that it withstood two strong blows with a hammer without even bending. I'll ask Demolition Ranch to test if it's bulletproof.

It's a shame I didn't get any pictures of the insides of this speaker or measure it's frequency response curve before I disassembled it. I'm almost tempted to buy another one just to study it. I will make a post in the near-future explaining what happened to the parts of the disassembled S10. My readers will be astonished and amazed :).