sound transfer

[c0rd0bes]

Hi all, my appologies if this is not the correct place for this.

Can anyone help here.

in regards bushing for a roller what would give the lowest sound transfer. Delrin or Brass with a concave profile running on 2 steel screws with a convex profile.

Loading etc is not required here sound transfer is.

thanks

c0rd0bes (mechanical)

 

[patprimmer]

I have not got your physical description of the part clearly in my head, but typically in bush or bearing applications, plastics run a lot quieter than metals. Tap a piece of brass then tap a piece of acetal (Delrin is but one trade name) or nylon or polyethylene with a hammer and see which one rings.

Another hint. They don't make bells out of plastic.

Regards
Pat
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[c0rd0bes]

Thanks pat, appreciated

here is my drawing, my apologies I cant get to Autocad at the minute.

--> >O< <--

--> side view of a steel screw with concave end (haha)
> insert to the roller with the convex profile (delrin or brass)
O side view of the roller


Yeah i appreciate that delrin is a dupont brand name for an acetal homopolymer, I guess I was looking for assurance before I buy the parts as there seems to be a transatlantic message mixup.

its actaully for a JL Fisher Boom arm the rollers are near the front 3 off them. This hold the microphone at the end , used throughout the cinema and tv industry. (basically a glorified extendible fishing rod on a hydro pneumatic base)

 

[patprimmer]

OK

While actual sound waves may be less with acetal, electrical noise may become an issue.

Acetal will be a good choice in that environment, especially if it is protected from UV light by being encased in metal or being indoors away from high intensity lights that are high in UV.

Nylon will run a tad quieter as it's a bit softer, but the fit will vary with moisture uptake if a precision fit is required.

Various types of polyethylene are likely to be quieter still as they are a lot softer.

Regards
Pat
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[c0rd0bes]

yeah the rollers are encapsulated in the metal housing near the end, 3 off finely set, as they will stop the carbon fibre pole from turning about its centre as it is wound in and out, and if you set them too heavy you can hear them running from the microphone.

When you say electrical noise what do you mean - how would that affect me in the setup?

The microphone is mounted on a "noise free" *cough* cradle at the front and a cable runs down the side and around the rollers (that allows it to extend as you wind the arm in and out). The cable is a cloth covered microphone spec cable to help minimise mechanical friction noises, and is side mounted on some form of plastic at various points along the way.

I would say if you put brass in there there is more chance to hear the running noise from that than delrin (albeit the sound boys are by nature very particular in that department - great guys though)

 

[patprimmer]

I mean static discharge creating electrical spikes that might be seen as an electrical signal in the mike or the wires attached to it.

Regards
Pat
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[c0rd0bes]

Pat I appreciate your input here its been most valuable.

Thanks again
c0rd0bes

 

[patprimmer]

Remember plastics are insulators and can build up static.

Regards
Pat
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