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I'm looking for some ideas on how to set up a science fair project for my son that explores the differences in construction materials for attentuating sound. I've built a good many home made sound panels for my room but here's what I'm thinking:
Build a small box about 2' x 2' x 2'. Mount a speaker on sone side firing in. DRive with a signal generator. Install a SPL meter inside the box and line the box with different materials like plain sheetrock, wood, FG, foam, carpet, etc. etc. Record spls at varying frequencies w/varying materials and graph.
Any better ideas or improvements would be greatly appreciated. I need to keep it simple enough and not to big but make meaningful at a basic level.
Regards,
Jim D.
You've got to be able to see the SPL meter, unless you're using a mic connected to a computer outside the box and equipped with sound analysis software, so you may wish to consider a glass side, preferably a double glazed glass side.
What you're describing will illustrate absorption, ie the reduction of sound within the "room" since the meter is inside the box, but it won't illustrate how well different materials block transmission of sound from one room to another.
What you want is 2 meters, one inside the box and one outside . Make the box with the speaker in one end wall and the opposite end wall open but able to be closed by panels of your test materials. The first control measurements are taken with the end of the box opposite the speaker open, then further measurements with the box sealed with various materials. These could include a standard plasterboard wall section one of your materials, then similar wall section panels with various materials in the space between the 2 plasterboard sides of the section.
If you're using computer software you can even show frequency spectrums for the sound being measured by the 2 meters, showing the different absorption and transmission spectrums and illustrating how it is much easier to absorb and/or to block high frequency sound than it is to do the same with low frequency sound.
If some of your panels to close the box are materials like fibreglass boards with known absorption/transmission properties, you can show how your measurements confirm or differ from the material's published specifications. You won't get similar measurements to the specifications because your test chamber is very different to the standard test chamber but there should be some broad correlation between what you measure and the published specs.
David Aiken
David,
Thank you for the followup. I have a couple questions.
I thought about doing what you say.....measuring the relative efficiency of materials for blocking sound transmission rather than absorption. In the design you describe, are you saying that all 6 sides of the enclosure would have be switched out every time or using a "soundproof" box that only uses one changeable side. Wouldn't sound leak out and give bad data if only doing one side? Another variation on what you describe may be to build a two-compartment enclosure, thereby isolating the 2 meters from each other better.
And yes, I was going to construct one transparent side or at least have a small window to see the inside meter.
It might just be easier to measure absorbtion in this case, but what you describe is more practical to understand for the average person.
Regards,
Jim D.
No, not all 6 sides, just the one opposite the speaker. I'd try and make the other sides as non-transmissive as possible. Sound will leak but if you've got a "reference reading" made with the switchable side open, you can compare that reading to readings with that sized closed by various materials/constructions and you can then see the effect that each switchable side has had in blocking transmission.
I thought about the 2 compartment enclosure, actually my first draft had that in it, but in the end I figured that it would make the box quite large and that could be a problem. The smaller box is easier to display and a lot easier to build and carry.
Measuring absorption within the box can be done but I wonder how useful the results will be in an extremely small box. They're not going to be accurate and they won't match the published data though you would expect to see somewhat similar curves for absorption at different frequencies. The small enclosure volume and small area of material being measured are going to have an effect on the results and it's going to be hard to do the standard mountings with spacings 4" away from a surface and have reasonable space for the mic or meter in a small box. The high frequency reflectivity of glass and its low frequency "leakiness" will also have an effect on the results if you're using a side with a window of some kind.
David Aiken
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