# Science Project?

Objective. Determine which frequency loses most /least energy passing through a medium (Foam ice cooler)

Method, Using Audacity on two computers A & B,

1. generated different tones on computer A,
2. record tone on Computer B using microphone inside closed foam ice chest (medium)
3. analyse difference in ? (not sure what but think dBL

Problem.
We are unable to record the tone on computer B using microphone (with/without foam ice chest).
Have tested the microphone and it will record spoken voice but not tone coming from speakers (Computer A)

Part B

Not sure what/how to analyse difference assuming we get it to work. The hypothesis is that a high or lower frequency will more effectivley penetrate the medium and this will be detectable

A SIMPLE 8TH GRADE SCIENCE PROJECT!

Because none of your equipment is calibrated you will get only a rough indication at best.

What sort of microphone are you using?
Most microphones have a deliberately non-linear frequency response. If the microphone that you are using is designed for speech then it will probably pick up the 300Hz to 3kHz range well, but be very weak higher or lower than this.

When we originally did a quick dry run for this project we used a cheap microphone , the type you would use with a webcam but one that is separate from the camera. I am not sure which one it was but I think it was able to pick up and record the tone generated by Audacity. Unfortunately it has been misplaced and the microphones “Dynamic Microphone” By Kenwood and a microphone from a Logitech headset/micro combo do not seem to work. Can you suggest a recording device that might work.

The idea was to make, play and then record about 5-6 sound files in the range 500-3000 MHz and see if there was a detectible difference in the level of penetration through the medium.( Foam box). We theorized it would be noticeble as a differnce in volume. It is a middle school project and neither I nor my 8th grader has much of an understanding of sound and its properties so thought this “simple” experiment may teach us something. We did not expect it to be anything other than a rough measure.

Any suggestions would be appreciated

Thanks

It’s dBSPL. Sound Pressure Level.

You may have generated more of a sound class than you think. Your ear responds to sound in a very odd manner in order to hear both very loud and very soft sounds – all the better to keep from getting eaten.

In the modern world, what your microphone picks up and what you’re ear picks up can be really different. It’s not unusual for a microphone in front of a voice performer to pick up just fine, but lose him if he backs up ten feet or so, but doesn’t change anything else. He still sounds just fine to you, but the signal from the microphone went into the mud.

If you’re depending on the sound card as the only microphone amplifier, this may be a problem. PC sound card’s chief attribute is cheapness, and this tends to limit the volume you can expect. You run out way before you want to.

You might be able to partially compensate for a wimpy microphone by getting the sound source inside the cabinet much louder – like driven by somebody’s guitar amplifier.

You can also use the 32-bit floating setting in Audacity with a few tricks. Use the microphone just like it is – low – and Export As WAV. Then Effect > Amplify and see if that tool can dig a performance up enough to use. This only works really well in 32-bit floating in Audacity Preferences. 16-bit (Music CD standard) doesn’t have the range.

You also need a super quiet room to keep the MetroBus outside the building from getting into the act. Finding a quiet room may be the most difficult thing you do. That’s another class.

Koz

I think you probably mean 500Hz to 3000Hz (100’s MHz is the VHF/UHF radio frequency range - Audio frequencies are in the range 20Hz to 20kHz).

Dynamic microphones and headset microphones typically have low sensitivity because they are designed to be used with fairly loud sound sources (voice) in close proximity. The distance between the microphone and the sound source is critical - if you start with the sound source 2cm away from the microphone and record, then move the microphone to a distance of 10cm from the sound source, you will see an enormous drop in recording level.
A video camera microphone is quite a good choice as they are usually quite sensitive (designed for picking up sound at distance) and will usually have a reasonably broad frequency response (should be able to cope with 300 Hz to 10kHz with ease).

As Koz suggested, using a loud sound source will help a lot. You could perhaps make a test CD with a series of tones on it and play it loudly on a CD player right next to the ice cooler. If you use a guitar amplifier you will need to take care that the sound is “clean” - any distortion will produce harmonics at higher frequencies that will completely mess up your measurements.

Ordinary loudspeakers are not capable of producing high frequency sounds at high volume levels - you will need to take some care not to blow up your speakers.