Loudspeaker

Single Degree of Freedom Transducer Brace

This article documents the development a new loudspeaker bracing method for reducing unwanted 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

Unwanted cabinet resonance induced by a speaker unit's vibrations have negative consequences to the sound of a loudspeaker. The aim is to damp the transducer to reduce vibration emanating from its basket to the cabinet. The SDOF concept suggests that by adding mass to the 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.

Early mockups of brace

The photo galleries to the left show early wood cuts and assembly. 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 rubber 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 what's its connection 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. While a speaker driver will likely operated for many years without trouble 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 benefit Hi-Fi.

What inspired this idea?
Some enclosure designs I found of interest for my self-build speaker project included an internal brace placed against the back of the diver's magnet assembly. My DIY skills aren't up to that sort of precise measuring and cutting so the SDOF brace is my answer to the problem I faced.

Why haven't you applied for a patent?
I patented something else I developed in the 90's. From that experience I learned that once an application is accepted it is put in the public domain and one needs deep pockets to defend the patent from violators once awarded. Patents are for multi-national corporations.

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 however I don't know that exists nor do I expect there to be in the future. Having worked the audio industry I know of nobody with knowledge of SDOF or the skill to blend the two engineering domains. Now that I'm a member of the silver-hair gentleman's club I'm too busy enjoying other retirement pursuits.

What experience of this subject have you?
Excluding hand assembling RadioMobile car stereos in the 70's and distributing RUARK loudspeakers in the 90's I have experience of proofreading or translation correcting seismology related research papers for institutes in Japan including Tokyo University, Ohsaki Research Institute and Hitachi Construction Machinery.

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 (https://www.terrysweb.link/sdof).
For commercial use please contact me to obtain permission.