High Back-EMF

High Back-EMF

Sunfire’s High Back-EMF Technology allows the production of massive amounts of deep bass from a cabinet that is not much larger than the actual woofer itself. The challenge is, it’s not possible to build a small box subwoofer with large amounts of bass output and extension with a conventional driver. So Sunfire had to first greatly increase the input power... by a factor of 10 or more. Two hundred watts becomes 2,000 watts (enter the Sunfire Tracking Downconverter amplifier).

To handle that type of power, custom drivers had to be designed with oversized magnets and voice coils that would allow for a huge amount of Xmax (the measurement of the distance that a speaker can move linearly in one direction from rest).

The accumulation of all of these factors yields Sunfire’s High Back-EMF Design. The absolute most amount of bass from the smallest subwoofers imaginable.

At this point, we should mention Hoffman’s Iron Law, which says in speaker design you can have two of the following three attributes, but NOT all three:

1. Efficiency

2. Small Enclosure

3. Bass Extension

Big Box Solution

In a big box solution, you have lots of air inside the cabinet so it doesn’t take much force to compress it. 

  • Without much force, it doesn’t take much amplifier current, so the voice coil remains cool.
  • This is a Low-back-EMF, low-current, low Bℓ  subwoofer system that’s been around for years.
  • Requires a BIG BOX.

Hoffman Scorecard:

Check Efficiency X Small Boxcheck Bass


Small Box with Big Box Fundamentals

Sunfire is about small boxes, but you can’t approach a small box with the same force and driver as in a big box design.

  • Yes, the voice coil remains cool, but…
  • Since the air is hard to compress, you end up with:

Hoffman Scorecard:

check Efficiency check Small Boxx Bass


Small Box Done Wrong

So just add force, right? Wrong. Boosting the current – and nothing else – causes the voice coil in a conventional driver to overheat.

  • It works great… but only for a few seconds!
  • That’s not a well-designed product by any definition.
  • So how do we do it?

Hoffman Scorecard:

x Efficiency check Small Boxcheck Bass


Sunfire High Back-EMF

To achieve high Bℓ, we changed the geometry of the woofer.

  • Custom Long Throw Woofer (increased stroke)
  • Custom Designed Voice Coil (increased “ℓ”)
  • Custom Chosen Large Magnet (high “B”)
  • And, we add High Power (but not destructively high current) with our Tracking Downconverter amplifier. The result is LOW current but HIGH Bℓ

Hoffman Scorecard:

check Efficiency check Small Boxcheck Bass

And the result is? Sunfire’s subwoofers are Little, Low and Loud, delivering big BIG bass from enclosures not much bigger than the woofers themselves.

check LITTLE - Easily hidden – High aesthetic acceptance factor

check LOW - Superior low frequency reproduction for movies and music

check LOUD - Increased dynamic range