- #1

Albertgauss

Gold Member

- 294

- 37

Hello,

Many of you are familiar with the homework problem that goes like the below, and though straightforward to solve in most general physics homework sets, I need to help getting it to work, which is not so easy in real-life.

Consider two speakers separated by 2.0 meters. Find the points along the path from one of the speakers where destructive or constructive interference occurs. The frequency is 1000 Hertz.

The picture and calculations are attached in the jpeg “Slide 1 and 2" for Problem and Solution.

I reproduce here the N’s (Dest), M's (Cons) and X’s (position from first speaker on a line in meters) for which destructive interference should occur.

N X where Dest occurs M X where Cons occurs

two Pasco 60 Watt Speakers

Both speakers are driven by an AFG1022 Textronix Function Generator, with the intent to drive them at the same time

The microphone is USB, Fifine Company

The waveform software is “Audacity.” which is freely downloaded

Bascially, I move the microphone along the direction “X” in the photo “Setup.jpg”. I move it slowly so that is why the waveforms look stretched out. I move the microphone continuously and slowly, but only barely can I get discernible humps and valleys as maxes or mins. I did also try moving it quickly, but my results were no better (not shown). Lots of times, the points of destructive or constructive interference don’t match very well.When I move the microphone to the X values above, you can see the waveforms of what I get in the following jpegs. “desNeq1.jpg” shows that, when I moved the microphone to 1.9 meters, I got a hint of the destructive interference that I should. However, when I moved the microphone to 1.4 meters, I got a destructive interference I did not predict. These waveforms are not very clear however.

In the jpeg “ConsANDdest.jpg”, you can see that, for constructive interference predicted at 1.3 meters, I actually measure a MIN but not a MAX, as I was supposed to. When X = 1 meter or so, I got another unpredicted MAX. For X = 0.8, I do predict a MIN there, but what I measure is barely convincing.

How could I change my situation/setup so that I can find easily the points of constructive or destructive interference for this problem? I checked my math several times, and I am certain the calculations are right. Would the changes be a lot or a little, expensive or cheap in equipment? What is making my data so unclear? Could reflections in the room itself cause a problem and should this be done outside? I had assumed that since this homework problem appears so often in general, lower-division physics classes, it would be easy to reproduce. Certainly not the case and I’m looking for suggestions on how to improve this, if it can be.

Many of you are familiar with the homework problem that goes like the below, and though straightforward to solve in most general physics homework sets, I need to help getting it to work, which is not so easy in real-life.

Consider two speakers separated by 2.0 meters. Find the points along the path from one of the speakers where destructive or constructive interference occurs. The frequency is 1000 Hertz.

The picture and calculations are attached in the jpeg “Slide 1 and 2" for Problem and Solution.

I reproduce here the N’s (Dest), M's (Cons) and X’s (position from first speaker on a line in meters) for which destructive interference should occur.

N X where Dest occurs M X where Cons occurs

**n = 1 --> 1.9 meters = X m = 2 --> 1.3 meters = X**

n = 2 --> 0.88 meters = X m = 3 --> 0.6 meters = XThe jpeg “Setup” shows the equipment I use and I list the equipment below.n = 2 --> 0.88 meters = X m = 3 --> 0.6 meters = X

two Pasco 60 Watt Speakers

Both speakers are driven by an AFG1022 Textronix Function Generator, with the intent to drive them at the same time

The microphone is USB, Fifine Company

The waveform software is “Audacity.” which is freely downloaded

Bascially, I move the microphone along the direction “X” in the photo “Setup.jpg”. I move it slowly so that is why the waveforms look stretched out. I move the microphone continuously and slowly, but only barely can I get discernible humps and valleys as maxes or mins. I did also try moving it quickly, but my results were no better (not shown). Lots of times, the points of destructive or constructive interference don’t match very well.When I move the microphone to the X values above, you can see the waveforms of what I get in the following jpegs. “desNeq1.jpg” shows that, when I moved the microphone to 1.9 meters, I got a hint of the destructive interference that I should. However, when I moved the microphone to 1.4 meters, I got a destructive interference I did not predict. These waveforms are not very clear however.

In the jpeg “ConsANDdest.jpg”, you can see that, for constructive interference predicted at 1.3 meters, I actually measure a MIN but not a MAX, as I was supposed to. When X = 1 meter or so, I got another unpredicted MAX. For X = 0.8, I do predict a MIN there, but what I measure is barely convincing.

How could I change my situation/setup so that I can find easily the points of constructive or destructive interference for this problem? I checked my math several times, and I am certain the calculations are right. Would the changes be a lot or a little, expensive or cheap in equipment? What is making my data so unclear? Could reflections in the room itself cause a problem and should this be done outside? I had assumed that since this homework problem appears so often in general, lower-division physics classes, it would be easy to reproduce. Certainly not the case and I’m looking for suggestions on how to improve this, if it can be.