Something to consider when choosing the microphone element...

While there are many microphones to choose from, and they vary greatly in their absolute sensitivity, they basically do not vary in their relative sensitivity. Using strange numbers that make this point easier to see... let's say mic A makes a 1 V signal when you are 6 inches away, and a 0.5 V signal when you are three meters away. If mic B has 1/10 the sensitivity and makes 0.1 V when you are 6 inches away, then it probably will make very close to 0.05 V when you are 1 m away. With a little extra gain for mic B, the two will be electrically very similar, sensitivity patterns and frequency response being equal.

ak

Your proportions for db/distance are way off, but the principle you espouse is true. For a single mic element, the only thing that matters in this context is the distance. For a matched pair of mics wired in opposition, the numbers change more with distance because of the intentional rejection of equal SPL.

In other words, if Bug wants good amplitude from 12 feet away, using two mics might be exactly the wrong thing to do. To test the results, build the dual mic circuit and short out the signal from one mic to test the difference in performance.

 

Something to consider when choosing the microphone element...

While there are many microphones to choose from, and they vary greatly in their absolute sensitivity, they basically do not vary in their relative sensitivity. Using strange numbers that make this point easier to see... let's say mic A makes a 1 V signal when you are 6 inches away, and a 0.5 V signal when you are three meters away. If mic B has 1/10 the sensitivity and makes 0.1 V when you are 6 inches away, then it probably will make very close to 0.05 V when you are 1 m away. With a little extra gain for mic B, the two will be electrically very similar, sensitivity patterns and frequency response being equal.

ak

Thats good to know, thanks!

 

Your proportions for db/distance are way off, but the principle you espouse is true. For a single mic element, the only thing that matters in this context is the distance. For a matched pair of mics wired in opposition, the numbers change more with distance because of the intentional rejection of equal SPL.

In other words, if Bug wants good amplitude from 12 feet away, using two mics might be exactly the wrong thing to do. To test the results, build the dual mic circuit and short out the signal from one mic to test the difference in performance.

So I don't need to build the dual then, but still, that's an interesting circuit, I would like to build one to play around with.

 

So I don't need to build the dual then,

It depends. Do you want people speaking to the mic from 12 feet away?

 

It depends. Do you want people speaking to the mic from 12 feet away?

not 12 feet, but that will be good.
I want the intercom to be able to pick up conversation at least 1 meter away (~3.2 feets)

 

Any microphone has a range of 1 m. Think about it. A human voice compresses air to a value of xxx dynes per square meter. That wave front travels a distance and the pressure decreases according to a modified version of the inverse square law. Then the pressure wave hits the microphone diaphragm. Notice that nothing in there has anything to do with mics or preamps or whatever. In the microphone housing you can use some physics tricks to reduce the sensitivity to waves coming in at an angle to the central axis. In the preamp you can use some electronic tricks to reduce the amplification of frequencies determined not to be required for intelligibility.

Two questions about having one microphone cover a large volume space - where is the mic located and how far off-axis do you want intelligible pickup? The off-axis thing is a big tradeoff, because the more you want to be able to hear someone 1 m away but 90 degrees off-axis, the less directionality the mic can have and that will increase room noise pickup.

ak

 

Hi Hypatia

Thanks for your replay. I have never used an analog switch. Will the on resistance a problem in my application?

Inasmuch as said parameter is generally < 200Ω, there should be no problem at input impedances typically encountered in AF amplification applications...

Note that for lowest R_on, the devices should be powered at design maximum VCC (nominally 15V)
Here is a link to specs for a typical device of the referenced type...

Best regards and good luck!
HP

I say HP's suggestion of cmos selector is best solution but plz don't use 4016 cuz it has high von and channel offset that can distort analog signal So if you use 4066 with good vdd it is perfect! That's how I did multi-loop (which are really mulifilter) PLL synthesizers to tune fast but not step on lf FMing when locked

 

Any microphone has a range of 1 m. Think about it. A human voice compresses air to a value of xxx dynes per square meter. That wave front travels a distance and the pressure decreases according to a modified version of the inverse square law. Then the pressure wave hits the microphone diaphragm. Notice that nothing in there has anything to do with mics or preamps or whatever. In the microphone housing you can use some physics tricks to reduce the sensitivity to waves coming in at an angle to the central axis. In the preamp you can use some electronic tricks to reduce the amplification of frequencies determined not to be required for intelligibility.

Two questions about having one microphone cover a large volume space - where is the mic located and how far off-axis do you want intelligible pickup? The off-axis thing is a big tradeoff, because the more you want to be able to hear someone 1 m away but 90 degrees off-axis, the less directionality the mic can have and that will increase room noise pickup.

ak

We have a few different type of mics for a conference room where we do some web-based meetings. After one speaker finished talking, the shotgun microphone pointed at the podium was accidentally turned away from the podium and all the remote attendees suddenly complained of a loud hiss. We realized that the shot-gun microphone was aimed at an HVAC vent and that flowing air sound overwhelmed everything else.

 

I say HP's suggestion of cmos selector is best solution but plz don't use 4016 cuz it has high von and channel offset that can distort analog signal

Um... Aleph? Kindly indicate where I suggested use of the CD4016? Would you deign to actually attend my post{s} you would see that I referred specifically to the CD4066 -- So there!

Best regards
HP

 

Um... Aleph? Kindly indicate where I suggested use of the CD4016? Would you deign to actually attend my post{s} you would see that I referred specifically to the CD4066 -- So there!

HP you need to get over it cuz I didn't say you suggested 4016! I was only saying that all cmos bls aren't created the same!

 

HP you need to get over it

Shall we declare this 'horse' officially dead --- and both 'get over it'?