so, in dead of night when outside has low ambient noise, from inside i can hear a low level (faint) hum, in the range of 250Hz. any ideas to build a simple directional detector that 1) can detect the frequency, and 2) allow me to get an idea as to the direction the sound is emanating from. i suspect the sound is coming from a nearby pool pump, but would be neat to build a detector that can help solve the mystery (and stop annoying me).

since i am working another project that may use piezo element, how about mounting a bare piezo element to a 1/2" thick vertical AL plate or wood with heavy base, couple that to a high gain opamp? just not sure if 250Hz would couple well to a piezo element, might get ran over by noise in the gain. i guess one side of piezo should be on heavy mass while the other side couple to a "fork" that has resonance down low near 250Hz?

your thoughts?

 

Use two microphones back-to-back (one on each side of a 3/4" piece of plywood (to block/deaden sound). Then connect to differential amplifier. You will need to zero the signals with a pot on one of the microphones to zero the delta in a silent room. Then rotate and find the biggest response to the + input on your op amp or instrumentation amp.

Have fun.

 

Get a stethoscope and you will find your noise

 

Remember the old conical megaphones? Make one out of cardboard, press it against your ear and go hunting.

 

Remember the old conical megaphones? Make one out of cardboard, press it against your ear and go hunting.

the diameter around 1.5ft ?

 

the diameter around 1.5ft ?

Sounds Good

 

(one on each side of a 3/4" piece of plywood

Styrofoam works, too.

ps, 250 Hz isn't consider, "Low" in some frames of reference, like power line frequency or musical instruments. 250 Hz is near the fifth string on a guitar.

 

Styrofoam works, too.

I have a piece of plywood in the garage - if I would have had Styrofoam, I would have suggested that.

 

if I would have had Styrofoam, I would have suggested that.

I have a piece of styrofoam in the laundry room...left over packing from a garbage disposer. That's why I thought of it. Besides that, styrofoam heads are used for testing headphones, so styrofoam probably works in the audio range.