Why Use an Accelerometer for DIY Speaker Testing?
Traditional DIY speaker testing leans heavily on microphones and software, which reveal what you hear in the air but not how a cone or cabinet actually moves. An accelerometer-based system closes that gap by measuring the physical acceleration of a driver or panel directly at the surface. The classic audioXpress ACH-01 project proved that enthusiasts can achieve lab-style speaker driver measurement without exotic equipment. Over nearly 15 years, the community refined the companion amplifier into the AP-805, an accelerometer amplifier and analog signal processor that delivers dedicated outputs for acceleration, velocity, and excursion. This lets you examine mechanical behavior such as breakup modes, panel resonances, and enclosure vibration more precisely than with acoustic measurements alone. The result is a compact, repeatable DIY speaker testing rig that helps you optimize drivers, crossovers, and cabinets with data, not guesswork.
Meet the 805M1 Sensor and AP-805 Accelerometer Amplifier
The heart of this DIY speaker testing setup is the pairing of TE Connectivity’s 805M1 accelerometer with the AP-805 amplifier. The 805M1-200 version is a small, single-axis sensor in a TO-5 metal can that outputs an analog voltage proportional to acceleration, with a sensitivity of 10 mV/g and a typical nonlinearity of ±1% of full scale. Its flat response from roughly sub-Hz to several kilohertz makes it suitable for loudspeaker cones and cabinet walls. Because the original ACH-01 sensor became hard to source, the amplifier was adapted and renamed AP-805, requiring only modest circuit changes such as reducing the sensor supply to below 5.5 V and tweaking the input and gain stages. The rest of the analog signal processor — including selectable gain, high-pass and low-pass filters, mains hum notch, and separate motion outputs — remains essentially the same, giving you a flexible, purpose-built accelerometer amplifier for loudspeaker work.
Building a Robust Accelerometer Cable and Connector
A reliable cable is critical for consistent speaker driver measurement, because any flex near the accelerometer can inject noise and errors. Instead of ultra-fine individual wires, you can follow the refined approach used in later versions of the project: a miniature balanced microphone cable such as the Mogami W2901. This cable offers two small conductors plus a shield in a compact, flexible jacket, providing the needed mechanical strength for frequent repositioning on different drivers and enclosures. Start by carefully stripping and tinning the conductors, then solder them to the accelerometer pins with minimal heat and dwell time. Next, prepare a small connector at the amplifier end so you can easily swap or extend sensors. Once soldering is complete, encapsulate the pins and cable transition with silicone RTV to relieve stress and protect against fatigue. The result is a durable, low-noise link between the accelerometer and AP-805 amplifier that will survive repeated test sessions.
Mounting the Accelerometer on Cones and Cabinets
Mounting technique largely determines how accurate your accelerometer readings will be. For permanent installations, the manufacturer recommends a smooth, clean surface and a thin layer of cyanoacrylate adhesive to ensure rigid coupling and good high-frequency performance. However, DIY speaker testing often demands frequent repositioning between cabinet walls, bracing, and various drivers. In that case, a thin, high-quality double-sided tape offers a practical compromise: it holds the sensor firmly while allowing careful removal with reduced risk of damaging delicate paper or composite cones. Whichever method you choose, keep in mind that the sensor’s metal housing is tied to circuit ground, so introduce an insulating adhesive layer if you need ground isolation from the test surface. Finally, immobilize the first few centimeters of cable with paper tape on the same surface as the sensor. Preventing cable motion near the accelerometer dramatically reduces spurious low-frequency signals.
Putting the AP-805 System to Work in Your Home Lab
Once your 805M1 sensor and AP-805 accelerometer amplifier are built and wired, you have a compact measurement front end ready to integrate with your audio interface or oscilloscope. Connect the acceleration, velocity, and excursion outputs to separate channels so you can observe how a driver behaves under sweeps and bursts, or how an enclosure panel responds to different bracing schemes. Adjust the AP-805’s gain settings to match your interface input range, engage the high-pass and low-pass filters to focus on relevant bandwidths, and use the notch filter to tame 50/60 Hz mains interference that easily couples into high-impedance sensor wiring. Over years of iterative updates, the audioXpress community has honed this analog signal processor into a robust DIY tool. For hobbyists and loudspeaker builders, it offers a practical, affordable path to deeper insight into driver motion and cabinet vibration without relying solely on microphone-based measurements.
