Generac 7500 Noise

 

I want to build a "box" for my Generac 7500.  After researching this
newsgroup, here is a link of my plan with diagram and notes.  This is a
top view and I do plan a top with the same material as the sides.  The
generator will sit on concrete pavers and the box will rest on pressure
treated wood around the perimeter of the pavers.  The idea here is to
minimize sound transmission to the box through vibration.

http://mynet11.tripod.com/Genbox.htm

I am only concerned with the noise on three sides.  It is my hope that
this design will allow enough breathing for the machine so there will
be no need for a fan and the noise will only be significant on the open
side.

Your comments and suggestions would sure be appreciated.

Thanks.

IC

 

Major problem, IMO: The gypsum will reflect, not absorb, sound.
There will be some unintended  "megaphone" ports the way it is.
You want to use absorptive materials as the first layer.

 

Pop wrote:

The gypsum (and foam) is the inner material and one-half inch plywood
is on each side.  This is like a sandwich with plywood as the bread and
gypsum & foam as the meat :-).  The inside of the box will be lined
with sound absorbing egg crate foam.  Do you still see this as a
problem??  Also, do you have a suggestion for a material other than
gypsum?  What about acoustical ceiling tile material to replace the
gypsum?

What do you think about heat build-up?

Thanks.

IC

 



IMO your spending a lot of time for zilch.   There are materials that are
water resistant, that do the job. The rental generators we get use this
material.
I agree with the other poster, you going to make a directional megaphone.

http://yarchive.net/car/rv/generator_quiet.html

have you changed the muffler yet?

 


====>  Yes, I'd get rid of the gypsum.  The only place you
want -anything- rigid is the last, outermost layer.
   Ceiling tile might be OK, but the soft kind, not the kind with
a hard backboard.  You might just want to eliminate that whole
layer you called gypsum, actually.

As for heat, you'll just have to monitor it and see what happens.
Assuming North was toward the top of your pic, an east or west
wind might not be able to provide a lot of cooling, but ... I'm
no expert, I"m just visualizing on my own experience here.  If
the normal ambient temp (without the generator running) within
the box doesn't rise above the ambient stated for the machine to
be able to run in, then it's probably OK.

If you'd like a personal observation, you're trying to block
noise in too many directions.  Two directions, and using a more
open approach might be more effective.  Don't make 90 degree
corners meet; leave them open a little.  In fact, avoid 90
degrees if you can; 60 degrees might be just as effective.  And
allow more air flow.  And the sides don't need to be vertical; a
slight slant will help air flow AND blocking.  For air entry at
the bottoms, near the ground, a screened blanket of insulation
that lets air pass thru would kill any "port" design inherent,
plus allow more air in.  Say, a 6 inch space to the ground all
around the baffles.
   Just thinking out loud - no real experience here with genset
noise.
You have of course, looked into -compatible- mufflers, right?  Be
certain it's rated for YOUR engine if you do!
   I"ve seen noise abatement schemes for highways that are
nothing more than vertical, slanted, closely located, slats of
wood, so there are lots of wayt to think about the subject.
Unfortunately, I don't know of any good web references though.

   Start with some test baffles:  Look for the best
setting/directions/placement, and finesse it from there.


====>  See above, please.