Car stereo volume control circuit to compensate for ambient cabin noise.  - Page 1
Forum section: electronics / beginners

author: btrom56
author_rank: Newbie
timestamp: August 16, 2015, 02:56:49 am
content: Is there a circuit design that can be added to a car stereo at the speaker outputs to control the volume to compensate for road noise in relation to vehicle speed. Thanks.

author: singapol
author_rank: Frequent Contributor
timestamp: August 16, 2015, 03:27:01 am
content: Just but a luxury class car.Think about it just a flick of the volume control or remote would solve it.No need to put sensor to read engine rpm.

author: Len
author_rank: Frequent Contributor
timestamp: August 16, 2015, 03:31:50 am
content: I've had two car stereos with this feature and neither one worked very well. I always have to adjust the volume manually anyway. So unless someone has a way of doing this that's better than what's on the market, I wouldn't bother trying.

author: singapol
author_rank: Frequent Contributor
timestamp: August 16, 2015, 03:51:28 am
content: Quote from: Len on August 16, 2015, 03:31:50 amI'll bet it uses a microphone to hear ambient noise...which is not as direct as sensing engine rpm or tapping the tachometer...just too much trouble and modification.Just does not warrant spending RnDmoney for such feature.

author: flynwill
author_rank: Regular Contributor
timestamp: August 16, 2015, 03:54:33 am
content: Also it's not just adjusting the volume. What's needed is a compressor who's ratio is varied depending on the level of the background noise.

author: peter.mitchell
author_rank: Super Contributor
timestamp: August 16, 2015, 04:04:49 am
content: to me, this sounds like a really bad idea/positive feedback situation

author: max666
author_rank: Frequent Contributor
timestamp: August 16, 2015, 07:43:00 am
content: Quote from: flynwill on August 16, 2015, 03:54:33 amWhy is that? Or better yet, what does a compressor do?

author: flynwill
author_rank: Regular Contributor
timestamp: August 16, 2015, 02:29:39 pm
content: A compressor dynamically adjusts the gain as a function of the amplitude of the input signal. Making the softer bits louder.Radio stations use them all of the time because they know the majority of their listeners are in noisy vehicles.

author: max666
author_rank: Frequent Contributor
timestamp: August 16, 2015, 05:03:36 pm
content: Ahh, got it. So you lift only those parts of the signal over the noise floor, that would otherwise disappear in it. Thanks

author: fubar.gr
author_rank: Unknown
timestamp: August 16, 2015, 06:03:50 pm
content: I own a car with this feature. The car is a Citroen C4 VTS and is factory equipped with a loud exhaust system. It's not as loud as aftermarket tuning exhausts, but is definitely louder than most cars.When the feature is enabled, the radio CD unit manages to keep the music volume always on top of the car noise, so I guess it works as advertised. However I always keep it disabled.Why? The car is quite noisy as is. When cruising at highway speeds the engine noise is barely tolerable. Imagine the radio automatically cranking the volume to 11 to cover the engine noise. Now you have engine noise plus a blaring radio.Another bad situation is on roads where the car speed can vary significantly, eg when driving fast on some winding back road. The radio volume will go up and down constantly and this can be extremely annoying.On the technical side, the car's radio cd unit is the Blaupunkt RD4:As strange as it might sound, this unit is connected via CAN bus and controls several functions, such as the parking sensors and the trip computer. So it already has access to various vehicle parameters, such as speed, engine RPM and my guess is that it uses these to control the volume.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2015, 06:08:50 pm
content: How about active noise cancellation? Rather than adjusting the volume, play the same noise from the engine but antiphase to cancel it out.

author: max666
author_rank: Frequent Contributor
timestamp: August 16, 2015, 07:12:16 pm
content: Actually repetitive noise, like from the engine, would be the best case scenario for active noise cancelling, but the standard placement of the speakers in cars is the worst they can be for that. If the placement of the speakers isn't right, you just create an interference pattern or standing waves, where you get cancellation in some places, but double the noise in others. Active noise cancellation is manageable in headphones, where you have a confined space with defined direction of where the noise is coming from, but can get insanely complicated in an, what I would even call an, open space like a car interior.

author: GreyWoolfe
author_rank: Unknown
timestamp: August 16, 2015, 07:40:29 pm
content: I would leave it alone. Years ago, I had a rental car that had this feature. Drove me crazy driving around town. I ended up leaving the radio off.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 16, 2015, 07:46:21 pm
content: Mercedes does this, and you do not even notice it.However, Mercedes is really silent to begin with. So it's an unfair comparison.

author: Chris C
author_rank: Frequent Contributor
timestamp: August 17, 2015, 12:05:54 am
content: I'm thinking of those sections of highway where the pavement is laterally grooved. Makes a lot of tire noise when driving over them. Enough that it's hard to appreciate music at a comfortable volume. I wouldn't want the volume automatically increasing in an attempt to compensate for that!But a compressor is a wonderful thing to have in a noisy environment.

author: David_AVD
author_rank: Super Contributor
timestamp: August 17, 2015, 03:13:34 am
content: I had a Holden Combo (Made by Opel) van a few years ago and the Blaupunkt audio system had that feature.It seems to be based on road speed and actually worked quite well.

author: dom0
author_rank: Super Contributor
timestamp: August 17, 2015, 07:52:55 am
content: Quote from: Len on August 16, 2015, 03:31:50 amIt worked very well with our old (and long gone) Opel Sintra. All cars since then didn't have that feature, I really miss it. And it feels like newer cars are getting louder (on the last Autobahn ride with the Yeti I packed ear plugs - AND I USED THEM - so loud is that car!)... probably the same story as with vacuum cleaners ("it's so loud, it MUST be powerful!")... [until you drive an A4 and fail to notice that you're already at 180 because it's just so silent!]So, for implementation.The analog way would be a compressor and a VCA (think LM13700, or any other more modern alternative). Best results are probably attained by multiple sensors, e.g. a tachometer "tap" and a microphone in the cabin.With a DSP it's basically the same story.

author: Rerouter
author_rank: Super Contributor
timestamp: August 17, 2015, 08:32:29 am
content: to make use of all the connections you already have, if your car has steering wheel controls, or the option for them, grab a tiny micro, either hook into an analog speed signal to the dash, or use something like an elm chip or a micro with built in can bus to read in the road speed off the can bus, pulse the volume up/down as required using the micro to scale correctly, done,That or for certain models of radios, if you dig a bit, you may find the feature can be turned on in the developer menus, some of these are documented online,

author: max666
author_rank: Frequent Contributor
timestamp: August 17, 2015, 07:45:45 pm
content: Quote from: Chris C on August 17, 2015, 12:05:54 am

author: btrom56
author_rank: Newbie
timestamp: August 18, 2015, 01:11:47 am
content: Taking all these factors in consideration and just wanting to experiment, any ideas on how the circuit would look?