3000W Chinese Gensets Info.

daytona7 wrote:
Just a little something for your mind. How would a Hearth Rug be if cemented or attached to the inside walls of the Pink Fiberfoam generator box. They are fire resistent, light weight and fairly cheap, $35 and up.:@

Well, IMHO I would not say it is needed - but it shows that you are doing some great brainstorming! Still, if you are willing to spend the extra money, it might provide some benefit and give designers yet another material to consider.

Looking back through my WORD document files I ran across a couple of articles that I honestly do not remember if I posted or not. You know, I forget a lot of things :S.

Anyway, at risk of repeating, you have two primary objectives that can be in conflict with each other. One is the maximum possible reduction is noise level, the other is to maximize air flow for cooling (heat extraction). A single design that does only one or the other is easy - a design that does both gets more complicated.

On the subject of sound abatement, the article quoted below might be beneficial when considering what materials to use and what type of sound we are trying to cancel.

excerpted from Mix, August 1997, “Room Acoustics wrote:

All materials have some sound absorbing properties. Incident sound energy which is not absorbed must be reflected, transmitted or dissipated. A material’s sound absorbing properties can be described as a sound absorption coefficient in a particular frequency range. The coefficient can be viewed as a percentage of sound being absorbed, where 1.00 is complete absorption (100%) and 0.01 is minimal (1%).
Incident sound striking a room surface yields sound energy comprising reflected sound, absorbed sound and transmitted sound. Most good sound reflectors prevent sound transmission by forming a solid, impervious barrier. Conversely, most good sound absorbers readily transmit sound. Sound reflectors tend to be impervious and massive, while sound absorbers are generally porous, lightweight material. It is for this reason that sound transmitted between rooms is little affected by adding sound absorption to the wall surface.
There are three basic categories of sound absorbers: porous materials commonly formed of matted or spun fibers; panel (membrane) absorbers having an impervious surface mounted over an airspace; and resonators created by holes or slots connected to an enclosed volume of trapped air. The absorptivity of each type of sound absorber is dramatically (in some cases) influenced by the mounting method employed.
1) Porous absorbers: Common porous absorbers include carpet, draperies, spray-applied cellulose, aerated plaster, fibrous mineral wool and glass fiber, open-cell foam, and felted or cast porous ceiling tile. Generally, all of these materials allow air to flow into a cellular structure where sound energy is converted to heat. Porous absorbers are the most commonly used sound absorbing materials. Thickness plays an important role in sound absorption by porous materials. Fabric applied directly to a hard, massive substrate such as plaster or gypsum board does not make an efficient sound absorber due to the very thin layer of fiber. Thicker materials generally provide more bass sound absorption or damping.
2) Panel Absorbers: Typically, panel absorbers are non-rigid, non-porous materials which are placed over an airspace that vibrates in a flexural mode in response to sound pressure exerted by adjacent air molecules. Common panel (membrane) absorbers include thin wood paneling over framing, lightweight impervious ceilings and floors, glazing and other large surfaces capable of resonating in response to sound. Panel absorbers are usually most efficient at absorbing low frequencies. This fact has been learned repeatedly on orchestra platforms where thin wood paneling traps most of the bass sound, robbing the room of “warmth.”
3) Resonators: Resonators typically act to absorb sound in a narrow frequency range. Resonators include some perforated materials and materials that have openings (holes and slots). The classic example of a resonator is the Helmholtz resonator, which has the shape of a bottle. The resonant frequency is governed by the size of the opening, the length of the neck and the volume of air trapped in the chamber. Typically, perforated materials only absorb the mid-frequency range unless special care is taken in designing the facing to be as acoustically transparent as possible. Slots usually have a similar acoustic response. Long narrow slots can be used to absorb low frequencies. For this reason, long narrow air distribution slots in rooms for acoustic music production should be viewed with suspicion since the slots may absorb valuable low-frequency energy.

OK - let me add to the above a piece of an article I wrote in 2006 that was, in part, drawn from the sound abatement research I had conducted.

Professor95 wrote:
I began to conduct some much needed research on the characteristics of sound waves along with their propagation and reproduction. Not surprisingly, the best source of information was found from elements of acoustical design. Buildings, auditoriums, speaker cabinets and even boom cars all draw from the same basic principles.

In designing a new enclosure, there were four basic principles that had to be considered; reflection, absorption, frequency and amplitude.

Through measurements made with a microphone, graphic equalizer and oscilloscope it was determined that the majority of sound energy was, as expected, under 5,000 Hz.

The amplitude had previously been established through measurements with a digital sound level meter and manufacturer’s data.

Since the sound frequencies were below 5,000 Hz, a small enclosure would do a better job of canceling the sound waves. Low frequencies have a longer wave length or period than high frequencies - the smaller the cabinet, the more attenuation of low frequency sound will occur. Audiophiles depend upon large diameter speakers, cabinets and tuned reflex ports for low frequency reproduction. Conversely, small diameter speakers and cabinets do a better job of reproducing high frequencies.

Anyone who has ever hooked up a set of speakers knows that they must be equally phased to reproduce sound properly. If one speaker is out of phase, or pulling the speaker cone in while the opposite speaker is pushing the cone out, the resultant sound waves will somewhat counter each other. Reflection of sound waves would be important in an enclosure to reduce sound pressure.

Absorption of sound waves turned out to be a considerably more complex than I originally believed. While it is true that materials with an open cellular structure can do an effective job of absorbing sound, caution must be exercised in selecting the material to assure there is sufficient density to cancel the effects of sound transmissions. Simply stated, when sound waves hit the surface of some materials the molecules in the material can also move or vibrate at the same rate as the sound pressure pushing against the material. Density, or thickness, of the material is a factor for consideration.

All of the experiments I considered were never completed. I had to choose one or two and run with the ball. The 2" foam board was available and met in part the sound reduction goals I sought while being lightweight and inexpensive. But, I emphasize that there are other materials that may be much better and more available. Considering the above may be beneficial in selecting a material. Additionally, it is not only the material but the path of the sound waves - which, by the way, are in the 5,000Hz range and DO NOT like to go around bends or corners. But, alas, turbulence can be introduced for cooling air flow by this type of design - so we go back to compromise 101 - which is where I left off......