View Full Version : Weird slow mo sub action

05-03-2011, 09:55 PM
Put a tang band 8" in a little sealed truck box until i finish my ported truck box. The sub sounds surprisingly good but I couldn't help but notice the sub slowely (like 1hz slow) moving around when there is no music playing. it seems like when the head unit makes mechanical noises (like when switching songs, turning on, etc.). any idea what the deal is?

Deck is kenwood Excelon XXV-01d (pretty nice). amp is am mtx 4002 bridged at 8 ohms.

05-03-2011, 10:08 PM
could it be your RCA are getting a current from the 12v? Most of the time you install them apart from eachother. My friend had that issue that sounds like yours. Bestbuy installed his amp that way and every time he turned his car off it "Burped" for half a second.

05-04-2011, 12:20 AM
yeah i have my power/grnd installed on the side under the panels and the RCAs are running through the middle. pretty far apart and separated by layers of insulation and carpet.

05-04-2011, 12:17 PM

05-05-2011, 03:24 AM
Could just be the deck producing some weird subsonic interference. Does it do it all the time? If so, does it do it even with the RCAs disconnected from the amp?

05-05-2011, 03:27 AM
does it all the time and not when the RCA's are disconnected. this makes me believe its a head unit thing. but even when the sub is playing a frequency, it will still throw the motion in and out.. odd but for example.. if i was to play a 30hz tone.. the sub would sound fine and move as it is supposed to.. but even then you can see the motion phasing a couple millimeters one way, then a couple the other way. its weird...

05-06-2011, 06:31 PM

05-07-2011, 01:55 PM
If it only happens when the RCA's are connected to the head unit, then the noise has to be coming from the unit or traveling down the RCA's to the amp inputs.

One way to test is to attach a mp3 player, with an adapter cable, straight to the amp. If the problem goes away, then try using just the original RCA's with HU not attached. Check for weird movement. If there's no movement, then its definitely coming from the HU itself. :)

I've also seen this happen on old amps that have some type of power supply issues where it looks like the amp switching speed is off. On a steady test tone, the xmax of the sub is changing at a slow rate like the phase is going 180 and back to 0 again. ;) maybe check if it does that too....

05-07-2011, 02:10 PM
hmm, ill definately check that out man, thanks. I'll plug the mp3 player in to the inputs and test it, that would tell me if its the amp at least, then if not, ill test the cables themselves (which i'm sure are fine), then ill take the unit out and plug it up to make sure its not something weird with the connection or something to the head unit.