Loudspeaker

Single Degree of Freedom Transducer Brace

This article documents the development a new loudspeaker bracing method to control extraneous resonance from transducer vibration. I have named my method SDOF brace (Single Degree of Freedom brace). SDOF concept is used by aerospace engineers and seismologists to perform mathematical calculations to better understand the effect of unwanted vibration.

SDOF application to loudspeaker

Cabinet resonance induced by a speaker unit's vibrations have negative consequences. The aim is to control vibrations emanating from the basket to the cabinet in a way that doesn't require the DIY builder to have access to CNC machinery for precision cutting.

The SDOF concept suggests that by adding mass to a brace it will resonate at a less disruptive frequency. By my interpretation of the science (making no mathematical calculation) I conclude that a brace of appropriate mass pressed against the transducer's magnet assembly will excite energy back to the baffle. The aim is to lessen the magnitude of the ripple and is not meant to replace orthodox cabinet bracing. Inspired by Negative Feedback I estimate that exciting the energy back to the baffle is appropriate.

Early mockups of brace

The photo galleries to the left show early wood cuts whilst developing the idea. The hole is drilled for an m8 Allen bolt (m5 or 6 might have been better for the 3-inch drivers). On 18 mm plywood a T-nut is sunk to facilitate gluing on second layer of plywood. To add mass to the brace I have 2.5mm lead strips which I'll secure with cable ties. 3mm dense rubber (not Sorbothane type) pads will sit between the brace and magnet assembly (method to secure in trial).

Dead mass demonstration

This is a video posted by someone on U-Tube demonstrating a dead mass applied to a loudspeaker. I believe my development of the SDOF brace is vastly more practical.

FAQ

SDOF is used by seismologists, aerospace and civil engineers so how could it relate to loudspeaker enclosures?

Using the analogy of earth tremors, replace an earthquake epicenter with a speaker driver and the sea or a land mass with the speaker's baffle. SDOF concept is used by seismologists and civil engineers to enable them in the development of earthquake-resistant engineering. The amplitude of the shock waves rippling through the ground is of interest to them. I believe the SDOF brace application, which I have a proposed as an addition to orthodox cabinet bracing methods, has place in cabinet design to control resonance to the listeners benefit.

What empirical evidence exists?
SDOF related peer reviewed empirical studies are plentiful but these are generally to be found in the deep web and viewable only for a fee or subscription. For loudspeakers application I don't know that exist.

Free to use for non-commercial use

Private use of descriptions above for SDOF brace application in loudspeaker cabinet design is permitted. Those wishing to implement this are welcome to try it for themselves. No technical support is being offered. If sharing your work online please attribute my work on this subject. For commercial use please contact me to obtain permission.