MrDBM

hi folks,

i've recently installed (what a PITA BTW) some new 6x9's in the scoob. For some reason I'm encountering some low level distortion / hum. Do you think this could be due to (or made worse by) the quality of mp3's..?

Sounds odd I know, but I have a selection ranging from 128 to 320 kbps on one CD, and it's starting to do my head in with the contant variety of hum. Thankfully the new fronts are fine, and it can only be heard at very low volume!

Opinions anyone??? (complete ICE novice obviously!!!)

GaryCat

I use variable bit rate between 128 & 320 and have no problems. Below 128 the vocal start to sound a bit nasal. Have you tried using original CD's to see if you still have the problem?

Hum/distortion is normally caused by bad earthing or bad connections if it isn't on the source music.

MrDBM

hi mate, cheers for the reply..! Tried a normal CD this morning and the distortion is still there, so I'm guessing that rules out low quality mp3.

I'll recheck all of the connections this weekend, that's the only thing I can think of..!

chiark

Can you describe your system a bit more? How are you powering the 6x9s - from an amp or through the head unit? What's the head unit?

Gary's absolutely right on the causes - earthing or connections are most common, but you can also get interferance through wire routing in some cases, with the most common cause being interferance in RCA leads.

What fronts have you got (this is largely irrelevant, but might help you get a better sound in the long run )

FWIW, I encode using Lame with the "--preset extreme" option, which is VBR up to 320kbps with an emphasis on quality.

MrDBM

Hi Chiark,

I have Boston Acoustics up front (can't remember models - exact fit using the existing mount - cool) and Alpine 6x9's in the rear. They are both running from a JVC khd501 (i think) head unit. I've set the F/R bias to around 60% front.

Interestingly, to my novice ears, the Alpines sound better than the Bostons, but I reckon my connections are at fault. Obviously the connections to the stock speakers were one-plug jobs, so I dismantled those and connected the wiring from the speakers kit, enabling me to just connect them up using the two small metal plugs. (if the makes any sense) No choice really as the wiring in the scoob already was a little short to reach the new connection points.

I've going to try and connect the wires properly this afternoon, with connectors or something, well, anything apart from just twisting them togther

Is it possible that I have the + and - the wrong way around, or would this just have blown the speaker - I was really careful to mark them up before taking off the orginal plug and connecting up.

Thanks again guys

dave

chiark

+ and - the wrong way around will just mean the speaker is out of phase - ie, it's pulling backwards when the other speakers are pushing forwards. It won't damage anything, and it doesn't cause hum.

I know what you mean with the plugs - you've plugged them into the stock connector. That isn't a problem, and again shouldn't cause hum.

About the only thing that could be causing hum is the head unit IMHO, or the passive x-overs for the fronts. If you've tucked them behind the kick panels, it is possible to pick up noise from the car's wiring loom...

Quite a weird one, this!

MrDBM

yup, driving me nuts

Slightly confused now, as I think the fronts are fine, the hum is definately confined to the rear.

How would I check the headunit? I just plugged in the ISO pretty much. For what it's worth, for a few weeks the headunit powered the stock rears and I had no low level hum. Assuming that would mean HU ok?

Hmmm, will try and get connections peach-perfect and see if that helps.

Considering the pain I went through to install the damn things, they ain't no way they're coming out again

MrDBM

well, still stuck...

tried redoing all of the connections with proper bullet connectors, no joy at all. I still have a very annoying low frequency buzz through the rears. It's also present on the radio, so I guess this rules out the CD or mp3..?

Stuck for options now - anyone any ideas?

rosqo

How about setting your bias to 100% front and testing and then 100% rear and testing and 50/50 to see if its a speaker or a head unit fault, also have the engine off at the time.

chiark

hmmm... I think I'd be running a new set of speaker cables to the rear now. also, try swapping fronts to rears if you can (I guess you can't as you're using an ISO block) and see if the distortion shifts...

MrDBM

morning chaps

well, I shifted the headunit settings to 100% front, then rear - hum still there at the back. Does this mean the headunit is ok?

chiark

So the hum was still there even with no signal playing through it?

MrDBM

sorry, my mistake. The hum dissappears when no sound is routed to the rears, 100% front produces nice clear sound. I assume therefore that HU is fine.

I could really do with a set of speakers to try in the rear, this would confirm wiring problem me thinks?