#### Re: Brass freight car noise

Richard Townsend

Here's something a little off the wall related to Schuyler's suggestion. Years ago I used to participate in a theater group that used portable stage risers. To reduce the resonance of the risers we put in internal baffles. The important thing was to create spaces having a dimensional ratio of 1:1.62. It usually meant there were some odd-sized spaces left over, but the 1:1.62 ratio worked. I know this ratio is important in art and architecture (it's often referred to as the golden ratio). So if the internal width of the brass car is one inch, you could put in baffles 1.62 inches from each end.  In between might be a space big enough for a third 1:1.62 baffle and some minor left-over space.

Disclaimer: I have no brass house cars and have never tried this.

Richard Townsend
Lincoln City, OR

-----Original Message-----
From: Schuyler Larrabee via groups.io <schuyler.larrabee@...>
To: main@RealSTMFC.groups.io
Sent: Thu, Aug 27, 2020 8:30 am
Subject: Re: [RealSTMFC] Brass freight car noise

As might a stick of styrene carefully wedged between the sides, perhaps glued in place.  CAREFULLY as you don’t want to inadvertently deform the car sides by pushing them outward so make the stick just long enough to stay in place but without using a lot of force.  By changing the length of the vibrating side, you interfere with whatever resonance is causing the noise.

Schuyler

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Dennis Storzek
Sent: Thursday, August 27, 2020 11:20 AM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Brass freight car noise

On Wed, Aug 26, 2020 at 07:38 PM, erieblt2 wrote:
Working with sound isolation for the Navy the noise-vibration-can be lessened by of of two (or both) methods: isolation or increase mass to change the vibration (Noise)wavelengths.
Indeed. The hollow brass body is acting as a sounding board, amplifying the vibrations caused by the wheels on the rails, the same as the hollow body of a stringed instrument amplifies the vibrations of the strings. What is needed is to change the resonance of the body. If the model could use a bit more weight, I bet a couple of those self stick tire weights that some use for weighting cars would help, IF they were stuck to the inside of the body shell rather than the floor.

Dennis Storzek

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