Making a small speaker louder with no power at all
Braeburn Acoustics built machined aluminium cradles that made a phone louder without drawing a single milliamp. This archive keeps the engineering behind passive acoustic amplification: how a horn works, what sets its limit, and how the gain is measured rather than claimed.
- Gain stated
- up to 8 dB
- Power drawn
- none
- Geometry
- Auricle waveguide
- Body
- aluminium, unibody
- Process
- CNC milled
- Record
- 2012–2019
Why geometry alone makes a difference
A loudspeaker the size of a fingernail is poorly matched to the air in front of it. It moves a small amount of air a long way, while the room needs a large amount of air moved a short way. Almost all of the mechanical work the driver performs is reflected back at the diaphragm instead of radiating away as sound.
A horn fixes the mismatch instead of fighting it. By expanding from a throat that matches the driver to a mouth that matches the room, it lets the same cone excursion radiate far more acoustic power. Nothing is added. The energy was always there — a horn simply stops wasting it, which is why passive amplification needs no electricity at all.
Designing a horn, in the order the work actually goes
Each step constrains the next, and the order is not interchangeable — a mouth chosen before a throat is a mouth that will have to be cut again.
Measure what the source does
Before any geometry, the bare driver is measured at a fixed distance and level. Everything downstream is a comparison against this, and a gain figure without a stated reference is meaningless.
Fix the throat to the driver
The throat area follows the radiating area of the source. Too wide and the coupling is lost; too narrow and the air in the throat becomes a restriction of its own.
Choose the expansion
Conical, exponential or tractrix — the flare law sets how smoothly impedance changes along the axis. A discontinuity anywhere is a reflection back toward the throat.
Set the mouth from the lowest useful frequency
The mouth must be large enough for the longest wavelength it is expected to load. Below that point the horn stops behaving as a horn and the response falls away.
Cut it, then measure again
Aluminium is unforgiving and final. The measured curve, not the intended one, decides whether the geometry was right.
Three dimensions carry the result
Length and finish are easy to discuss and change little. These three decide what the device does.
Throat coupling
Sets how much of the driver's work enters the horn at all. Get this wrong and no amount of length or mouth area recovers it.
Flare continuity
Decides whether energy travels to the mouth or returns as a standing wave. Smoothness matters more than the particular curve chosen.
Mouth area
Fixes the low-frequency limit. This is the dimension that makes a desk-sized horn a mid-and-treble device, not a bass device.
How the archive is laid out
Five sections carry the engineering, in the order the work goes: the geometry, what it does, how it was cut, how it was finished, and how any of it is measured.
The Auricle waveguide
The named geometry of the original product: throat, flare and mouth, and what each dimension is answerable for.
Where the gain comes from
Impedance matching, directivity and the difference between real acoustic gain and simply aiming the sound at the listener.
Aluminium and the cut
Why a unibody billet was chosen over a moulding, and what CNC work contributes to an acoustic part.
Measuring the gain
How a figure such as 8 dB is established, the reference it needs, and the ways a measurement flatters a horn.
Anodising and powdercoat
Seven finishes shipped on the product line, and the acoustic consequence of a coating inside a horn.
What the hardware looked like
The cradles were built for devices of their time — an iPhone 5 and an iPad 3 were current when these were machined. The geometry outlasts the fittings, which is why the pages above describe the horn rather than the dock.
