Vehicle microphone?

[murrayatuptown]

Hello:

I have not unplugged the overhead microphone inside my vehicle's headliner yet, to check, and I assume measuring for a bias voltage will assure me...

I want to experiment with an alternate microphone in my car due to terrible road noise...

I chose a cardioid electret lavalier mic with TA4F connector because cardioid's have served me well with camera & phone recordings of live music in noisy environments.

There will be no live music recordings in my car, just telephone conversation.

The schematic for the mic shows MIC+ and MIC- with the (-) connected to shield. I am hoping there is already bias voltage on MIC+...otherwise it is in a remote, less-than-ideal connector, maybe under one of the car seats... There is a + V elsewhere (I think in the 54-pin module connector.

The cardioid mic is compatible with Shure systems, so I have a pinout for what the mic's TA4F wiring is.

Does this sound reasonably thought out? Or am I potentially going to run into problems with an active noise-cancellation system that exists, but the performance is so bad I assumed there was only the mic properties and placement by design?

If there is no bias voltage in the mic cavity, then I guess it would not be an ECM. I suppose I could also use a CR2032 or two crammed inside the cavity, along with a DC blocking capacitor.

I made an awful lot of assumptions from one camera's service manual to connect a Linkwitz-modded ECM capsule to a point & shoot camera with only one resistor change needed (2nd guess success). My luck could run out...

Thank you

Murray

 

[Pariah Zero]

Hello:

I have not unplugged the overhead microphone inside my vehicle's headliner yet, to check, and I assume measuring for a bias voltage will assure me...

I want to experiment with an alternate microphone in my car due to terrible road noise...

I chose a cardioid electret lavalier mic with TA4F connector because cardioid's have served me well with camera & phone recordings of live music in noisy environments.

There will be no live music recordings in my car, just telephone conversation.

No carpool karaoke?

The schematic for the mic shows MIC+ and MIC- with the (-) connected to shield. I am hoping there is already bias voltage on MIC+...otherwise it is in a remote, less-than-ideal connector, maybe under one of the car seats... There is a + V elsewhere (I think in the 54-pin module connector.

It almost certainly doesn't go underneath the seat, but rather behind the center console in the dashboard to a box adjacent to the "Head Unit" (infotainment system). The pinout is going to be in car's the service manual.

The cardioid mic is compatible with Shure systems, so I have a pinout for what the mic's TA4F wiring is.

Does this sound reasonably thought out? Or am I potentially going to run into problems with an active noise-cancellation system that exists, but the performance is so bad I assumed there was only the mic properties and placement by design?

What kind of active noise cancellation are you implying? If you're thinking in terms of using the speakers to cancel noise, then no... There's a reason the only real active noise cancellation you can buy is headphones. Normal things would screw with it - like adjusting your seat, turning/tilting your head, even bobbing your head to the music. Even worse, it's frequency-dependent, which is disorienting and unpleasant. Disorientation is kinda bad while driving.

As far as noise cancellation from the microphone goes... well, Garbage in, Garbage out. Less noise is always good. It's far more likely that changing the mic would screw up the built-in EQ compensation and what the system expects the mic output level to be. EQ is likely no big deal for a telephone conversation, but not enough output (or clipping) is.

If there is no bias voltage in the mic cavity, then I guess it would not be an ECM. I suppose I could also use a CR2032 or two crammed inside the cavity, along with a DC blocking capacitor.

Or it could be the mic doesn't have a built-in IC, so it doesn't need a bias voltage. It'd be unusual, but the perversity of the universe trends to a maximum.

There's the off chance they used a MEMS microphone - which is really an ECM on an IC. (They also make analog MEMS mics).

I made an awful lot of assumptions from one camera's service manual to connect a Linkwitz-modded ECM capsule to a point & shoot camera with only one resistor change needed (2nd guess success). My luck could run out...

If your car's mics are ECM's, one question is if they have built-in IC's or not. I don't know much about lav mics, so I don't know if it's common for them to have IC's in the capsule, or if the circuitry is built-in to the other end of the wire.

In any event, I'd learn the most I could before I cut any wires - see if I could find the service manual, and find the mic connector, and measure the voltage across the mic's pins. I'd be unsurprised if the mic has its own connector.

 

[murrayatuptown]

I can find the Mic connector...I haven't gone further than freeing the cabling from whatever adhesive it was placed with. I keep finding other things to do.

That replacement original microphones are available made me think it is accessible directly via the snap-in housing, not requiring removal of the headliner, the front fender and the intake manifold (never know, they have designed some crazy things before).

I will take the disconnect opportunity as the time to see if I can get some of that butyl damping sheet in there as well. I better do it before the temperature gets below the suggested lower limit for application.

I'll be certain to make my substitution reversible in case I end up with a different type of garbage-out. I'll think of another repurpose.

When the snow flies, and I drive slower, tire (I know, it's spelled incorrectly) noise will be reduced.

Thank you

 

[Pariah Zero]

When the snow flies, and I drive slower, tire (I know, it's spelled incorrectly) noise will be reduced.

Tire/Tyre spelling depends on the continent, of course.

I'm somewhat fortunate in that my local weather is very, very warm for the time of year. It's plenty toasty to work with butyl CLD.


Just remember the stuff doesn't block sound - it only dampens vibration.

There's extensive stuff over at DIYMA (diy mobile audio) where they showed that you hit the point of little to no gains with butyl CLD sheets covering more than ~25% of the flexible sheet metal.

Putting it over holes just wastes the (expensive) material. (I've also learned that the expensive way... if it can't flex like a drum, butyl sheets won't help much - being strategic in placement can get the same result with a lot less material)

 

[murrayatuptown]

OK. Thank you!

 

[JohnRoberts]

many cheap GP microphones have a JFET built in to make audio output when terminated by a resistance fed from a DC voltage, I wouldn't expect the auto industry to make this more expensive than needed.

to improve S/N try to get the mic closer to the sound source.

JR

 

[Pariah Zero]

The other problem with a lot of vehicle-borne mics are the number - for the same cost reasons, they use only one. There's a reason good bluetooth headsets have 3-4 mics.

It's not simply a matter of getting a better signal - with multiple mics, "known" positions and mic patterns, DSP magic can be used to isolate individual sources very effectively - specifically, the speaker.

'ol man story: I had a university professor demonstrate with three recordings - all three were a cluttered/noisy cacophony, as the mics were all placed about a meter apart from one other in the center of his living room. None were particularly intelligible. There were three main sources of sound:

• His wife, reading a bedtime story to a child (softly)
• A TV blaring commercials
• A teenager practicing violin

Then he ran the (then in-development, research) algorithm (while playing one of the recordings). Like flipping a switch, the TV and violin dropped in volume almost entirely, leaving the mom reading the story (quietly) to the child. It was like magic in 2003...

He then explained that the trick was multiple microphones, and you needed at least one microphone per source for the algorithm to work. Give it a couple of decades and the technology is all over the place.

I've used my Plantronics Voyager 5200 to hold phone conversations while mowing the lawn, and the other end of the conversation could barely hear the mower...

 

[Ricardus]

Darn. I was hoping this thread was going to be about what mics were used on this recording session...