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While servicing my clutch of Hornby 0-6-0PT's, I noticed that they ran much quieter with the body off. Contacted Hornby looking for a possible 'paint the body interior' solution. Hornby went into denial mode saying that nobody else had complained and their boffins could find no noise problems, yet all those I have shown the comparison (with and without), agreed that there was a noticeable difference. I'm not looking to apportion blame here, just trying to find a solution. Have also noticed the problem with other makes, though not as much as Hornby. Seems to me the body acts as a magnifier, a sort of 'megaphone' effect. Anyone else have any thoughts on the matter, or more importantly, can anyone suggest a solution. A 'paint-on' liquid rubber perhaps?
 

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My guess is that you need to stop something vibratiing. If it's the body then some kind of "mastic" painted on might deaden it in much the same way that car manufacturers used to try in times gone by. If it's the air volume inside the body, then baffles might stop that. Apart from that, you're probably in for a tough time. Controlling Noise Vibration and Harshness is a specialism all of its own.

David
 

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There's an article in this months model rail about someone using double sided adhesive pads to cure the noise problem in their farish locomotives.
 

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I think it is the body vibrating from noise generated by the motor, the gears or the like - it's acting as a sort of speaker diaphragm and thus amplifying noises which are there but are too quiet to hear with the unaided ear when the body's off. You need to dampen the body by adding something to the inside - mastic, lead weights or something.

Regards,
John Webb
 

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I suppose like anything else we all have differing levels of tolerance when it comes to noise. Some for example like track laid on the baseboard while other like to use sound deadening underlay. It does sound like a tricky one though.
 

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It is true that some bodies and empty tenders do resonate. They act like speaker boxes with the sound.

On a few of my models, I have filled up the voids with cotton wool. Especially important to do this with tenders on steam locos, filling the space under the coal load. I did this on the Bachmann 9F and it completely changed the sound of the model. Much better.
 

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QUOTE (woody2shoes @ 19 Sep 2007, 06:04) <{POST_SNAPBACK}>While servicing my clutch of Hornby 0-6-0PT's, I noticed that they ran much quieter with the body off. Contacted Hornby looking for a possible 'paint the body interior' solution. Hornby went into denial mode saying that nobody else had complained and their boffins could find no noise problems, yet all those I have shown the comparison (with and without), agreed that there was a noticeable difference. I'm not looking to apportion blame here, just trying to find a solution. Have also noticed the problem with other makes, though not as much as Hornby. Seems to me the body acts as a magnifier, a sort of 'megaphone' effect. Anyone else have any thoughts on the matter, or more importantly, can anyone suggest a solution. A 'paint-on' liquid rubber perhaps?

***Most of the answers are spot on: The issue is "sympathetic resonance" and the body is acting like a speaker and vibrating at a frequency created by the mechanism. The adding of mass is often the answer, as "soft" fillings are actually only useful at high frequencies, and then only when a LOT of the material is used, and this isn't practical when talking about a tank loco.

Mastic and the like are good solutions, but messy. I'd suggest that plastiscene or blu-tack will do a lot, with extreme cases fixed by adding small bits of lead sheet randomly to the cavity (tank) walls as the best answer. (use a flexible type glue).

Neat work doesn't always rule here.... Random "stressing" of any surface will usually stop it resonating better than neat symmetrical additions.

This effect is usually worse when there is a clipped on (as in tender body) or body fixed very firmly to the chassis by two screws / one front and rear. It can be made better by having one screw plus a lip or similar holding the body, with the area round the "lip" having a pad of foam tape or similar as a "damper"
 

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I work for a company that makes electric motors from 90 watts to 250 kW. We have found that very slight changes to very small things have a large effect on emitted noise. For instance placing a slot behind the bolt holding the fan cowl in place is enough to reduce the noise levels by 3 dBa. Doesn't sound a lot but bear in mind it's a logarithmic scale so that's half the noise level. The moral of the story is ....... unless you have a noise camera (yes such things exist) you just need to experiment until you get the right results.

QUOTE (Richard Johnson @ 10 Dec 2007, 01:52) <{POST_SNAPBACK}>***Most of the answers are spot on: The issue is "sympathetic resonance" and the body is acting like a speaker and vibrating at a frequency created by the mechanism. The adding of mass is often the answer, as "soft" fillings are actually only useful at high frequencies, and then only when a LOT of the material is used, and this isn't practical when talking about a tank loco.

Mastic and the like are good solutions, but messy. I'd suggest that plastiscene or blu-tack will do a lot, with extreme cases fixed by adding small bits of lead sheet randomly to the cavity (tank) walls as the best answer. (use a flexible type glue).

Neat work doesn't always rule here.... Random "stressing" of any surface will usually stop it resonating better than neat symmetrical additions.

This effect is usually worse when there is a clipped on (as in tender body) or body fixed very firmly to the chassis by two screws / one front and rear. It can be made better by having one screw plus a lip or similar holding the body, with the area round the "lip" having a pad of foam tape or similar as a "damper"
 
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