Head unit mystery/deficiency

**waterdog** · 06-20-2011, 09:02 PM

I finished installing DB651S speakers in all four doors this weekend. Coming home from work tonight, I was enjoying the new sound at about 25 or so on the sound scale for about 15 minutes on a 75 degree evening

, when suddenly the sound was gone

. The head unit was still powered, everything else still worked, and there were no fuses blown. I stopped in to a store for about 10 minutes, and when I came out everything was back to normal.

I am guessing that the head unit overheated and a thermal fuse tripped - though I am interested to know if any of you have other theories.

Assuming that is what happened, I am pretty disappointed in the head unit. This was just a simple upgrade of the OEM speakers with some pretty common reasonably efficient coaxials (sensitivity 92 db). If this keeps happening, I may break down an add an amp, but I was hoping to get a reasonable sound upgrade without that hassle. I don't feel the need for a sub, and didn't think I would need an amp unless I added a sub.

When they are running, the new speakers do sound good - a significant upgrade from the OEM speakers. I also added some dynamat to the doors - not complete coverage, as some have done, but even the partial dynamat coverage provides very noticeable noise reduction.

Cobb · 06-20-2011, 11:56 PM

Are you using the stock head unit? Does this have nav or just the USB thing?

I use to leave it at 40 and never had any problems with it cutting out with the stock speakers. I upgraded the speakers with radio, so I cant say. The increased load could cause a thermal issue. Typically audio equipment starts to clip the signal before it cuts out.

**waterdog** · 06-21-2011, 08:54 AM

I am using the stock head unit with Nav. As far as I can till, it just stopped suddenly. If it started clipping first, I didn't notice.

I never had a problem with the stock speakers, though also never played them very loud because I didn't think they sounded good loud.

Cobb · 06-21-2011, 10:14 AM

You can not hear them at low volume and they do not sound good at a higher one

?

Well, one reason I replaced mines. I didnt need as much volume afterwards. Most nav units put out less power than non nav head units. You may still be right.

Basically when it starts to clip it starts to remove the lows and highs. Then finally all audio cuts out.

**waterdog** · 06-22-2011, 12:22 AM

Quote:

Originally Posted by Cobb

You can not hear them at low volume and they do not sound good at a higher one

?

I thought the OEM speakers started to sound distorted and muddy at high volumes - not sure what your point is about not being able to hear them at low volumes.

Regardless, on my way in to work today I kept the volume at 30 and the sound cut out after about 15 minutes. On the way home I kept the volume at 20 and made it all the way home with music (about 30 minutes)

Darbraun · 06-22-2011, 04:15 PM

Those speakers are 4 ohms, does the impedance match with the Navi Unit?
i.e - an 8ohm source pushing a 4ohm load, or vice-versa.

**waterdog** · 06-22-2011, 09:57 PM

Quote:

Originally Posted by Darbraun

Those speakers are 4 ohms, does the impedance match with the Navi Unit?
i.e - an 8ohm source pushing a 4ohm load, or vice-versa.

The stock OEM speakers are supposed to be 4 ohm (according to my shop manual). I may take my doors apart this weekend and measure the impedance in the new speakers to see if any of them are defective.

The behavior is getting crazier. This morning I made it all the way to work (about a half hour) at volume 20 with no problem. On the way home, the speakers cut out after about 5 minutes at the same volume. They also cut out about 30 seconds after I took a call through the bluetooth connection. I couldn't tell if the two events were related, or if it was just coincidence that the speakers cut out so soon after the call.

In the meantime, I found a very compact amp that should fit under the front seat, a Rockford Fosgate PBR300X4. Does anyone know anything about this amp? It is new, not even shipping yet.

**waterdog** · 06-27-2011, 07:19 PM

I took everything apart and checked each speaker. They all read at 3 ohms on my 1.5 volt multi-meter. When taking one of the speakers out, however, I noticed that the terminals seemed pretty close to the door sheet metal where the metal curves in to create the slots for the speaker brackets. I couldn't tell for certain if there was any contact, but wanting to make certain, I rotated all the speakers so that contacts were pointing to the side, where the cutout in the sheet metal forms a full circle.

So far everything is working fine at any volume for any length of time.

I speculate that I was getting occasional ground faults, maybe due to slight flexing of the panel, maybe combined with a bit of speaker heating. The prior speaker behavior, sudden cut-outs rather than clipping of highs and lows, is more consistent with a fault than with overdriving the head unit.

Cobb · 07-06-2011, 01:05 AM

Good find. I would have never suspected that. I wanted to upgade my speakers to louder ones an amp and use those osund deadening cups behind the speaker.

**waterdog** · 07-06-2011, 08:56 AM

I use the sound deadening cups, but with a big port cut out of the bottom because I thought they muffled the sound too much when they were intact - so they were missing in the locations that might have provided protection from electrical contact with the car body when the speakers were in the original orientation.

Audio system is still working great. Have not had any problems at any volume since I made the change described above.

I may still add an amp someday just to further improve the sound, but at least I don't need to add an amp just to drive the speakers.