07 acura tl type r woofer hum

Ok..this is about the weirdest thing I have seen in quite a while..and believe me..I get all the weird stuff.

The story is that a customer came into my shop after another shop added an amp and sub to the vehicle. He stated it had noise so I figured a simple ground loop problem...charge the guy 50 bucks and everyones happy. But not this time.....

This humm sound ONLY occurs when the vehicle is at idle.(900 rpm or so)..and at around 1000-1500 RPM. It completly goes away if the idle is 50RPM below idle and anything above 1500 or so. Keep in mind this is NOT alternator whine or any kind of engine noise...it is a hum...around 60 -70hz. Now the noise also completly goes away when you open any door. Close the door and it creeps back in.

Now I tried all the usual stuff...changing out the LOC.(tried several types and brands)...regrounding...running ground to the battery..running power outside the vehicle..tapping the LOC before and after the factory amp., soldering RCA;s off the preamp side..experimenting with resistors..inductors...shielding...ground lifts...ground adds..different amps (went through 3 different amps with no change)...different sub box (didn;t think that would help but wanted to eliminate all possibilities) no change. I even tried a sub-sonic filter and still no improvement although the tone/level would change slightly... which leads me into believing this "hum" is in the audio itself somehow through the head unit which has all kinds of lord knows what integrated into it with this cluster%^*k of  a vehicle.

The vehicle (a 2007 Acura TL type R six speed) has nav...reverse cam...voice recognition..blue tooth..basically loaded to the hilt with factory over enginnering. But I see no reason why an amp and sub should be such a problem..it's a glorified Honda for jeepers sake.

But heres the real clincher.....although I don't know what is actually causing this...I found a way to make it stop...at least until the vehicle is shut off..then re started. What happens is exactly this...I get in, close the door, start the car and wait until I hear the hum. Then I open the door, the hum stops..close the door...the hum starts again. I open the trunk and can see the subs moving and hear the hum. I hoover my arm around the sub enclosure (the amp is mounted on it as well) from the side and top of the enclosure back and forth and like magic...the hum completly goes away. Literally like magic..but it is not magic. It happens.

I have never seen anything like this before but there must be a logical explaination. For now I simply put a switch on the amp remote wire up front so the customer can turn off the hum (it goes away while driving and only returns at those specific RPM's) but this is just a band aid for now.

I requested he leave me the vehicle for some time to perhaps find a way to shield this noise out because somehow waving my arm in the rear area of the vehicle does cause it to go away..but I would hate to spend all day on this and not be able to solve it so....if anyone has ever experienced this issue before..or has any ideas what this is I would really appreciate it. The only other thing I ask is please don't ask me to check grounds and basic stuff like that..it's been done to death on this car.

Thanks

It almost seems like it is RF interference.  What happens if you take some aluminum foil and put it where your hand 'blocks' the hum?  It could be something as simple as the signal coming from the TPS (tire pressure sensors).  I would find this odd, but it could be.  Typically TPS transmit around 433mhz, which shouldn't cause any low frequency hum.  But, RF interference is the only thing I can think of that would be effected by your hand/arm/body.

Get an RPM switch and hook it up to the remote wire!   :)

Thats funny because I actually thought about adding a VSS sensor to shut the amp down..but realistcally that would be annoying.

As far as it being RF..yes it is possible but this hum is definatly below 70hz although I can hear upper octives as well..and perhaps some harmonics but hard to tell by ear.

I am considering trying foil but I can't really find the specific area that "blocks" the noise..I have to wave my arm in the visinity of the rear deck, left 1/4 panel area. Another strange phenomina is that once the hum stops after waving my arm...it stays away until the vehicle is shut off..then it returns once re-started. So my arm movement is not actually blocking this hum..it is shutting down whatever is causing it..at least until the vehicle is shut down and restarted.

One of the installers here has a brother that just bought the indentical car with the same options. We are installing an amp/sub into it soon. I am curious to see if it has the same issue. If so..we know it is an inherant "problem" ..if not, I am considering removing everything and having the head unit warrantied. But I have a feeling this my be an issue with all of them..it's just too odd of an issue.

I am hoping the customer is willing to let us try to figure it out as well but we will need to charge for the time..however if I can't fix it we will have a very unhappy customer.

I appreciate the suggestions and can only hope that someone else out there can find a resolution as this can really put a damper on the industry if this issue occurs in more new vehicles hampering our ability to add amps and subs..that would really suck as we would be stuck looking for ipod adaptors as the only add-on and we know how fun it is finding those.

Take care.

I don't normaly post replies or even register on any website to post replies. BUT. I was reading about your problem because one of the guys that I used to work with called me for a little tech support. I worked in the Car Audio business as a shop manager for 11 years untill this January. I manage a sign shop now (we build BIGGER stuff).  Sorry back to my point I read about the same problem that you were having and had to do a little research. Turns out that the new TL has a little thing called "Active noise controll". It uses the speakers to cancel road noise. It hears the road noise through 2 microphones. The primary one is located in the front overhead console near the dome light, and is also used for the Navi, Bluetooth, and Audio and HVAC controlls. Please don't mess with this one. The other one is located in the center of the rear headliner. Between the rear domelight and the rear window. All that you need to do is to unplug this little f*^#@*. Take out the rear dome light. you'll see a wire tie holding the wires in place, cut it and you'll be able to unplug it. Problem Solved!!!!

Without me (and my access to Acura's tech site) it would have been a long time before anyone figured this one out. And that is why I registered to my first forum to reply to your post. Enjoy!     ----- Charlie

Good information, I've never heard of that feature.

So, the rear mic is picking up the bass and trying to cancel it out?

Interesting.

13Charlie....I am going to call the customer to bring the Acura in and try out what you suggested...sounds like we have a winner. I knew it had to be something really odd like that and I wasn't hallucinating..lol....but like you stated..it would have been a real long shot to figure that on my own..if ever. You made my day.

So..you're doing signs now..cool. I good friend of mine is in that biz and I actually use him to help with some custom...like his 100,000 dollar router comes in handy when carving logos into plexi..also have had him make killer metal panels for me, I give him the templates, he bends and welds em up for me..I cover them.

I will post back the results. Thanks a million..I owe ya one.

Taken from: http://www.hondanews.com/categories/733/releases/3743

Active Noise Cancellation™

In order to provide a more hushed driving environment during highway cruising, the 2007 TL Type-S uses Active Noise Cancellation™ (ANC), which is designed to dramatically reduce low frequency exhaust booming noise in the interior. The system operates whenever the car is running, regardless of whether the audio system is on or off. There are two microphones in the headliner, one in the front passenger cabin, and another in the rear. The microphones capture low-end drivetrain frequencies entering the cabin, and send a signal to the Active Noise Cancellation unit hidden in the dash. The control unit then creates a precisely timed reverse phase audio signal that is sent to an amplifier, which powers the door speakers and the subwoofer positioned on the rear deck.

Since the system is designed to cancel low-frequency sound, it doesn't use any of the audio system's tweeters. The system dramatically reduces the booming sound of the exhaust, front and rear. In the rear seat, "boom" is reduced by a very impressive 17 db.

Sounds pretty cool! 

I guess it is pretty cool..but obviosly not aftermarket amp/sub friendly. It would seem to me this deals with resonance to cancel exhaust noise....explains the low frequency hum at specific RPM's. Apparently if you amplify this it is very loud through the aftermarket amp/sub.

I imagine the customer will not notice the increase in exhaust noise when the subs are booming away but if he really wants to use them he will have to sacrafice that feature when I unplug the rear mic.

Thanks for the info...major help in understanding what was happening..as well as future customers with this feature that are considering an amp/sub add on..