Sound attenuating enclosure? 1

[nocam1334]

I am working on a design for a portable sound enclosure to cover a diesel engine. I don't know much about sound attenuation, but initially am thinking about a sheet metal type enclosure with sound attenuating material or baffling on the inside.

The requirements I have is that the enclosure be portable (able to be removed and put together by 1 or 2 people) and relatively cheap. I don't expect (or require) that the sound reduction be so much that you could stand next to it and barely notice it. But maybe down into the 70-85 dB range.

Mainly what I need advice on is sound attenuating material and/or baffling configuration. Would appreciate any advice or input.

 

[spongebob007]

I think the first thing you need to consider is the frequency or frequency range you need to attenuate. If the noise is broadband you might take one enclousure design approach. If it is a single known frequency, you might take a different apporach. Even for a single frequency, high frequency attenuation will be different than low frequency attenuation.

Since you probably have a deadline that does not allow you to become an acoustics expert, my advice would be to figure out the noise source frequency and contact a vendor that makes enclosures/isloation materials. Their engineers will be expeerts in this area and should be able to suggest an enclosure configuration.

 

[Tmoose]

The necessity of providing openings for ventilation and many cfm of air for combustion makes enclosure design difficult.

B and K used to have a small brown handbook that covered many useful principles.

 

[MotorVib]

The best thing you can do is to take a look at some of the portable gen set if your set is small under 300 Kw there are a lot of sets out there like the one that you are talking about. This will give you are good idea of what works, because cost is a big thing in small sets they try to cut cost were they can. Most need only need 2 people to assembl.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[carnage1]

I suggest looking at an industrial supply catalog. They usually have good explanations about the different types of sound reduction and the basics behind how they work.
(mcmaster and msc were the two I used to use most often)

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[VibeAC]

How big is the generator? Openings for exhaust, radiator relief and intake air govern the noise control options.

If this is a large generator, then a sound attenuating enclosure and critical-grade muffler designed by the manufacturer should be looked into. If this is a small system, an acoustical barrier system may work, but depends highly on where the noise sensitive receiver is, and how much noise reduction you need. Noise from generators is broad-band and can be well over 100dBA when measured 10-20 feet from the source.

In general a well designed barrier system can give you approximately 10dB of noise reduction at most frequency bands from 63Hz to 8kHz.

Andrew Gorton, MSc
Noise & Vibration Consultant

http://www.PapadimosGroup.com

 

[Rob45]

Depending on how large your diesel engine is, the requirement for portability might be tough to meet:
In order for an enclosure to be effective, the walls must be effective barriers, and that will require a surface weight on the order of 2 lbs/sq.ft. - this is the primary factor is determining transmission loss, the barrier effectiveness. Greater weight might be needed, but you need to pay attention to effective sealing before trying this.
Then you want the enclosure to be lined with an absorber, typically a lightweight open-cell "acoustic" foam of at least a couple inches thickness. Or use glass-fibre absorber if temperatures are higher than a foam can stand. A cover over the absorber may be needed to prevent contamination with oil; you do NOT want a fire to start with oil-soaked insulation!
Next you want good sealing of the pass-throughs for coolant, fuel, intake and exhaust, AND you want those isolated so vibration is not transferred to the enclosure surface.
Finally, you need to have good mufflers on both the intake and exhaust, these must be decoupled from the engine, and they may even require enclosures of their own to prevent shell noise radiation.
Or of course you could place the intake and exhaust silencers inside your engine enclosure, but this somewhat worsens the heat problems with which you'll be faced.