Noise insulation, Engineer types opinions needed Options

[nivekdodge]

Just a thought

There's another thread today discussing using perlon for the back pad and if it was quieter or not. Something I've notice is Some GM hood have their inner surface looking like a golf ball. There are 3" round divots and when asked about it I was told it reflects the sound back to the motor and that kills the sound.Anyone know if there is truth to this?

This would of course be in the engine compartment.

Kevin

[Rusty]

Not sure how much value this will add, but here goes.

I spent 3 weekends ripping out the interior and soundproofing my brand new F150. I researched beforehand and learned a lot during the job.

Noise comes from a variety of sources... and the materials you choose for soundproofing should be selected for what noise you're trying to defeat. Stuff I used included:

Constrained layer dampening (CLD). Think dynamat or the factory soundproofing on the floors. It works by reducing resonance in a panel.

Mass Loaded Vinyl (MLV). Think a sheet of heavy rubber that floats on the floorboard between the car and the carpet. It absorbs the energy of noise from below. Imagine throwing a football at a bedsheet hung on a laundry line. A flimsy, free-floating bedsheet can absorb the energy from the football and not transfer it to anything else - resulting in a much quieter passenger compartment.

Insulation. Think EZ Cool (closed cell foam) or 3M Thinsulate SM600 (batting). These materials will absorb ambient noise as well. They can also function as thermal insulation. Van-dwellers use the EZ Cool stuff to help make their abodes more pleasant.

I think our 914s would benefit from strategic placement of these materials, depending on what noise you're trying to diminish. The factory engine compartment pad was probably an attempt to do CLD & insulation in one package. It was probably the best solution they had 50 years ago, but we have better options today.

Of course, none of these will protect a pedestrian's head during an impact. (IMG:style_emoticons/default/laugh.gif)

best,
Rusty

[Superhawk996]

Not sure how much value this will add, but here goes.

I spent 3 weekends ripping out the interior and soundproofing my brand new F150. I researched beforehand and learned a lot during the job.

Noise comes from a variety of sources... and the materials you choose for soundproofing should be selected for what noise you're trying to defeat. Stuff I used included:

Constrained layer dampening (CLD). Think dynamat or the factory soundproofing on the floors. It works by reducing resonance in a panel.

Mass Loaded Vinyl (MLV). Think a sheet of heavy rubber that floats on the floorboard between the car and the carpet. It absorbs the energy of noise from below. Imagine throwing a football at a bedsheet hung on a laundry line. A flimsy, free-floating bedsheet can absorb the energy from the football and not transfer it to anything else - resulting in a much quieter passenger compartment.

Insulation. Think EZ Cool (closed cell foam) or 3M Thinsulate SM600 (batting). These materials will absorb ambient noise as well. They can also function as thermal insulation. Van-dwellers use the EZ Cool stuff to help make their abodes more pleasant.

I think our 914s would benefit from strategic placement of these materials, depending on what noise you're trying to diminish. The factory engine compartment pad was probably an attempt to do CLD & insulation in one package. It was probably the best solution they had 50 years ago, but we have better options today.

Of course, none of these will protect a pedestrian's head during an impact. (IMG:style_emoticons/default/laugh.gif)

best,
Rusty

Really good summary (IMG:style_emoticons/default/aktion035.gif)

The only other thing I’ll add is that treatments are also specific to the frequency.

Low frequency noises (<100 hz) usually respond better to mass damping and constrained layer damping.

High frequency (>100 hz) usually respond better to blockage and absorption. Good old fashioned cotton shoddy pad is still highly effective.

One of the most import aspects of reducing noise is to make sure you don’t have pass-through holes that allow noise to enter the cabin unimpeded. Talking about things like DAPO holes drilled for stereos, wiring, a/c installs, oil cooler lines, etc.

OEMs do a pretty good job of optimizing NVH but they have to do that against cost constraints, manufacturing constraints, and weight constraints that affect fuel economy. You can always do more when those constraints are removed. However as previously stated, the further you go, the more you’re chasing diminishing returns.