Need electrical engineer/designer: project

[danyl]

I need help with an electrical project. Here's the overall picture:

New higher-end cars come with a speed adjusted volume control on their factory stereos. The driver sets the maximum volume at crusing speed, and the radio automatically lowers the volume as they slow down. Some systems even have a rate control setting.

There does not seem to be any such system offered for aftermarket stereos.

Having a convertible, I would love to have my stereo automatically ramp the volume up and down as wind noise increases and decreases.

There is a device called an L-Pad which is essentially an in-line potentiometer which can be used to adjust individual speaker volumes. Potentiometers are generally mechanical. I'd need either a stepper motor controlled L-pad(s) or a circuit which could increase inline resistance based upon an input.

My idea is this: A small microphone mounts somewhere in the car. The noise level is sensed by some form of circuit and then adjusts the L-Pads on the speaker outputs from my car stereo.

I've found a number of simple circuits that could do the trick, I need some help making them work together.

Anyone up for the challange?

[jazig.k]

brilliant!

i love the idea of this, and i know some other people who might too. Mobile Electronics Australia | Forums | Product Reviews | Custom Installations | Advice | Tips | Community

theres heaps of very smart fellas there, that no doubt would love to help out, if they dont already know of a aftermarket gadget that does it already.

keep updating us, sounds like an interesting project.
goodluck

[mrgibbysworth]

I bet it could be done, but suggest using the vehicle speed (taken from speedo). I think the speedo sensor is a generator whose voltage scales with speed. You could tap into that and drive an attenuator. Maybe use a pot to adjust the degree of the effect.

Using a mic could get complicated, as noise level can change more quickly than vehicle speed plus you have to cancel out the sound from the stereo speakers.

I'm not an EE, but I like this idea...

[BattleBug]

You oughta post your question in the Discover Circuits Forum.

[alfahaka]

Before you get to carried away with the circuit you need to define the problem you want it to solve. It sounds to me what you really want is something close to a constant signal (whatever you are playing on the stereo) to noise (be it wind induced, tyre roar or a noisy passenger ). There are relatively sophisticated ways (x-correlating a feed from the stereo with one from a mic that hears noise and subtracting out to get a measure of "just noise") and unsophisticated ones (stick the mic somewhere noisy away from speakers and hope it measures "just noise"). You can also decide if you want to measure "noise" directly or measure "noise factors" such as vehicle speed. Anyway, whatever you do you will almost certainly find it cheaper and simpler to run an amp and put your circuit between the head unit and amp (the circuit can then be all electronic - no horrible electromechanical attenuator). The "guts" of such a solution is a fairly generic DSP platform (potentially something off-the-shelf) that has at least 3 analog in (assuming stereo signal you want and 1 mic for measuring noise) and 2 analog out (audio to the amp). Of course, given such a setup, its just an algorithm issue how fancy you get - you could start not just adjusting volume, but actively canceling noise (another high-end feature).... Its a fun project if you have the time and the skills (or the desire to acquire them) but don't start it if the result is the destination and getting it right (the journey) is something to endure....

Personally, I'd just turn down the noise (stereo) and listen to the signal (engine), and enjoy the modulation via right foot....

[danyl]

It's wind noise I want to overwhelm. I can easily mount the mic away from the speakers and in the windstream. As that volume (wind) increases the circuit can remove resistance from my line level out that goes from the head unit to the amp.

The driver adjusts the volume in the noisiest environment, engauges the circuit, and then the circuit reduces the pre-amp output as wind noise decreases.