Lead Flashing?

[grantgoold]

Anybody consider using lead flashing as part of their generator sound box?

Pros vs. Cons?


Grant

[wvanative]

I know back in the 70's I went to look at some buses at Houseman in Des Plaines, IL. and the salesman told me guys were melting lead, and brushing it on the back, and floors to sound proof the coach from the engine. I thought that sounded like something I would not want to do for health reasons. but I don't know about the use you are looking at.

WVaNative

[rv_safetyman]

Grant, I used lead sheet sandwiched between two sheets of plywood for my generator box.  Seems to make it reasonably quiet.  You still have to work on airflow and exhaust.  Folks tell me that the intake should have a muffler as well. 

I also used the noise deadening material that Dick Wright sells on the inside of the box.

Mine is reasonably quiet and I did not go to extremes.

Jim

[Bob Belter]

Ahoy, BusFolk,

Yes, lead flashing works great.

In my case, for my genset box, I used the following soundproofing technique:

One layer of 1/2" birch plywood, two layers of 30# roofing felt, one layer of 2lb/sqft roofer's lead sheet, two layers of roofing felt, one layer of 1/2" plywood.

You also need in and out sound labyrinths, for cooling airflow, plus mufflers on both ends.

My genset is so quiet that if anyone around is running their's, you cannot hear mine.

As a matter of interest, the electric dynamo cranks out a LOT of heat.  I measured my Gillete dynamo 'out' temp at ~~ 225f, and was quite worried. 

I called Gillete, and was advised that the limit is 350f  !!!!  Plan for it ----

BTW, the Gillete dynamo is 'double wound', so that phase balance is far less important.  You can draw 80% of the rated load from just one phase.

Enjoy  /s/  Bob

[jjrbus]

 I used a foil covered vynil/foam for the walls and ceiling. I could not see how it would work under the genset so used some heavy lead sheeting on the floor. I do not know how well it worked as I have nothing to compare it to. But my genset is very quiet. Baffeling of the incomeing air is also important.

I could only buy the lead in full roll's where I was, so I stoped by the local scrapyard, they had piles of lead sheeting, I was able to buy just what I needed.

                                                                                HTH Jim

[JohnEd]

I see only some that go the full yard with the soundproofing.

As I understand it and auto makers build it the air intake is silenced with a VERY carefully crafted filter resonator cavity.  Mine even has chambers built on the side of the pipe feeding the engine that have no obvious utility but are intricate in design.  I suggest you get a inlet filter and box from a small displacement Honda or Toy and modify it for your genset motor.  That would also give you a cheap and effective air filter alternative.

The muffler is also an acoustical engineering item.  They are designed around the "frequency" of the exhaust that they want to silence.  Cars are a compromise but the more spendy the car the more silent the muffler so a 4 cylinder Accord would have a more silent muf than a Civic "maybe".  You can listen to them at the dealer's location.  Remember that you are only interested in the mufs perf at the rpm at which the gen operates.  I think you have a ton of choices from the Jap stuff and their mufs last the longest for some reason that you want to take advantage of.  They also all use a resonator and you could also put one downstream of the muffler.

Sound energy will travel thru the enclosure wall....no matter what you do but you can attenuate it greatly.  Rubber is good cause it doesn't like to move quick and it absorbs some of the energy in that manner.  Additionally, it is dense and difficult to get moving and that is a significant factor in its sound deadening performance.  The thicker the better but size and weight are a factor.

Lead is great stuff because it is heavier by dimension(density) than anything you can use.  I wouldn't pass up using lead as part of my design.  It is safe to live with lead as long as it isn't being converted to something that the body can absorb. 

Hard and light plywood is inferior as a sound block to soft plywood.  Think about the comparison between a drum skin and a piece of cardboard.  Scratch the drum head/skin with your finger nail and it almost seems to amplify the sound.  There is a particle board that is far denser than the usual stuff.  Pattern makers and others use it and it is commonly available and not expensive.  Any home depot type shop can point it out to you.  Even common particle board would be superior to plywood of any kind for soundproofing.  Look at your spendy speaker enclosures and just try to lift one.....200 pounds is not rare for woofers.

You can "spend" the sound energy by passing it thru a light material many times.  Acoustic tile operates on that principle.  Sound readily enter it as a medium and bounces of the underlying wall and travels back thru the tile.  The tile material absorbs the sound but not so much for the sound going thru the wall.  Still its attenuation is worth going after in the final design.  In "quiet rooms" they use a acoustic material that is built up into little cones.  I don't know where you could get that but that material would be optimum for application to the interior surface. Common acoustic tile would work pretty well to reduce the energy of the sound that reaches the wall.

You can dramaticall reduce the sound trans-missability of any wall by just gluing a weight to the center of the wall.  Your propane furnace can be significantly silenced by gluing heavy washers to the center of all the flat sheet metal.  Like wise the cabnet in which it is mounted can be improved by gluing 1 X 2s to the center of big walls. 

The coolant fan contributes greatly to the gen noise output.  You can eliminate almost all of that noise by plumbing you gen coolant into your engine radiator.  Many do this without a hitch.  With the engine off the rad has a thermo controlled electric fan to handle the gen and with the rad capacity even that would have a duty cycle.

Even without the gen rad load you still have to have cooling air flow for the generator windings and misc motor heat.  That flow must be thru carefully designed and sized baffles.  Point the air flow at the ground insted of out the side of the bus.

Lexus seems to be the only car I have ever encountered that can be driven away from me and I can hear absolutely no exhaust sound whatsoever.  You can't get there so yours will have "some" noise.  Even the quietest of exhaust will still be poison and objectionable to anyone immediately down wind.  To relieve that the Genny exhaust is run thru a pipe that is hung on the exterior wall of the bus to get the fumes 13 feet up in the air.  That works to eliminate a component of the noise.  PVC pipe will deaden more noise than rain spout metal tubing.  Plumb the exhaust into a larger diameter PVC/ABS pipe and the air flow caused by parasitic convection will keep the pipe cool enuf.

No box will isolate the low frequency hammering that is in the motor block if the gen is hard mounted to the wall/floor.  The gen must be mounted on rubber pillow isolators that are sized for the weight that will rest on each isolator.

I don't think roofing felt would contribute much to the sound absorbing performance of a wall.


Sooooo.....  From the outside:  1/4" particle board, 1/8" rubber sheet, 1/8 lead sheet, 1/8 rubber sheet and 1/4 " particle board layer of acoustic tile.  You can increase the various thicknesses to your application.  Air cooled gen sets will need more isolation and Chinese gens will require an 8 inch thick wall.
YMMV

My thoughts and I hope for some constructive crit.

HTH

John

[edroelle]

John,

You are right that particle board does an excellent job at reducing the low frequency noise.   I used that in my last installation.  But due to a small antifreeze leak, I would not recommend its use.  Rather, I would us a compromise of 3/4" Wolmanized plywood.  You could always "kick it up a notch" with lead.

Ed Roelle

[JohnEd]

Ed,

That is a good point.  You can compensate with the plywood , you just need to make the plywood thicker to get the same results.  That other stuff that I mentioned is waterproof....I think.

thanks,

John

[coachconverter]

One extra suggestion, although pricey, is to pickup a couple of "stall mats" from Tractor supply.  These are fatigue mats about 3x5 feet in size, about 7/8" thick and double sided with alternating corrugation.  Build your box with this material sandwiched in on all sides and you'll be amazed on the noise it eats.  But like others have said, you have to work on the intake noise almost as much as the exhaust.

HTH

Todd

[Sojourner]

Thank you grantgold for your post on the subject about reducing generator noises.

Thank you JohnEd for getting the point across about the how to contain the noise maker. You said it well...a good writer indeed.

I used to work in the General Motor Noise & Vibration for 3 years and learn of what Mr. JohnEd just posted. And yes to Ed Roelle about using thicker plywood an alternative to particle board due to the condition of the generator environment.

Base Wedge...This the best of all sound adsorbing material but it too thick (the deeper the better) and not for water & oil environment.

However, use something with the highest NRC (see below) that is most practical and reasonable such as the following example:
Anechoic studio foam (left click and all the blues)

Pyramid studio foam

Bass Wedge studio foam

Note: I have no connection with the above company and no knowledge of their business practices.

To know what to look for in regard for the NRC rating.
Noise Reduction Coefficient
The NRC of an acoustical material is the arithmetic average to the nearest multiple of 0.05 of its absorption coefficients at 4 one-third octave bands with center frequencies of 250, 500, 1000, 2000 Hertz. The NRC rating can be viewed as a percentage (example: .80 = 80%) of what soundwaves that come in contact with the acoustical material are absorbed by the material and NOT reflected back within the room.
From Glossary of Acoustical Terms

About air intake...is one of the most over look noise maker. Need to contain the pressure wave pulses. Similar as the exhaust muffler.  As per JohnEd mention...need a good designed air cleaner to contain the noise.

About exhaust muffler...need a thicker walled container with a heavy build baffles with a set of restrictor tubes. Restrictors even out the pressure pulses and to be design without restricting the total exhaust flow to a point.

About generator set mounts...always thrive for the best practical isolator.  Such as air bag mount that allows the weight of generator to float on air bearing with thinnest bag's wall without breaking in the long run. These are equips with limiting lateral & vertical movement bumper while traveling on highways and rough road.
Airmount™ Isolators

About exhaust plumbing...use small stain-steel woven wire (super-flex) Exhaust Flexible Pipe isolator connecting between gen-set to stationary exhaust system.
SS Exhaust Flexible Pipe Connector
Right off hand I don't have a link to a smaller diameter version to match your generator's exhaust size. Someone here can post their finding for the source.

FWIW

Sojourn for Christ, Gerald

[JohnEd]

Thanks Gerald....right back atcha.

John

[JackConrad]

When I did some research before building our compartment, I found that the reason to use a pyramid/egg crate type foam on the inside was that all those"bumps" create much more surface area for the sound waves to be absorbed.  Sound waves are energy and are either absorbed or reflected.  If absorbed they have to cause something to vibrate to dissapate the energy. At least that was my understanding, we will probably learn a whole lot about this from Ed at Bussin' 09.  Jack

[cody]

Another factor to concider is that sound waves travel in a straight line, by channeling the intake or exhaust thru several offset chambers you can dramaticaly reduce the levels, that used in conjunction with sound absorbant material would offer a cost effective alternative too.

[boogiethecat]

Impedance mismatch. That's the trick when building sould blocking walls.
IE a wall that's a sandwich of more than a few layers will be the most effective at not transmitting sound.  And the layers themselves should be of different materials.

Thus an amazing sound stopping wall might go something like: Plywood-vinyl-aluminum-fiberglass-foam-lead-more vinyl-plywood. That's a bit overkill but hopefully you get the point.
When sound goes thru a wall, the interface between mismatched-density layers kills some of the frequencies but not all. Different mismatches (ie different materials) get other frequencies.

Always sandwich 'softer" things with "harder" things; soft things layered directly together, or harder things layered directly together, don't do as good of a job as alternating soft and hard.

I've made many walls this way, some with lead some not.  If done properly with the right combinations, lead isn't all that important but it is better than many materials as in itself it's absorbant to more frequencies than most other materials, especially if it's thin sheet.

1/2" of Air can be considered a layer...

[JohnEd]

Boogie,

Thanks for a sorta tech explanation I could follow.  Had no idea about dissimmilar materials.

I know lead is excellent and I thought it was mostly due to mass and I guess I got that wrong. Tkanks!  Now I was told that rubber has a property whereby it resists "rapid" movement but will bend and form easily to slow.  Those silastic suspensions on nthe Eagle must have a self shock absorbing behavior that would improve ride.

My question is:  how does rubber stack up against lead?

Thanks Guy.  Always good to get one of your posts.

John