924Board.org

Lorenzo Booker · Joined: 08 Jun 2004 Posts: 33

How can I add a speaker into the center dash with a deck that has a wiring harness for only 4 speakers. Can I make an extension off of any of the existing speaker wires?

Smoothie · Posted: Mon May 23, 2005 11:43 am Post subject:

You have to consider the combined impedance (ohms rating) of the wired-together speakers. If all 4 now are 8 ohm, the system is well balanced. Then if you take another 8 ohm and wire it directly to one of the existing 8 ohm speakers, the combined impedance of those 2 together will either double or halve depending on how they're wired - if wired in parallel the combined impedance would be 4 ohms. If wired in series, two 8 ohm speakers would combine as 16 ohms. Either way, the load on the amp would be out of balance. There are some tricks that can be done to match impedances - Porsche used 2 different arrangements to get 3 speakers working together in the 924. One used speakers of different impedance that when combined, presented a balanced load to each side of the stereo. The other arrangement used 3 speakers all rated at the same impedance in conjunction with impedance matching handled by another component - the fader control I believe.
What's the ohms rating of your present speakers?
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

chris24 · Posted: Mon May 23, 2005 5:46 pm Post subject:

Sorry to jump your thread...
I've only got two front speakers wired into the front ports at the back of the stereo. The rear speaker ports are obviously empty. I was thinking of putting a third speaker in the centre console.
How would any of you guys wire the one new centre speaker to the rear ports?
Just use one and accept that it won't be fully stereo balanced in the car now?
I can't connect one speaker to both the left & right rear ports can I..? That would be leading to trouble...
Any ideas? I don't fancy putting two speakers in the back by the rear seats as you need to remove the rear windows to do the trim properly I think.
Thanks
_________________
1983 - 924 (185K miles) - not mint
1985 - 924 (148K miles) - mint
1990 - 944S2 cab (52K miles)

Lorenzo Booker · Joined: 08 Jun 2004 Posts: 33

My ratings are 4 ohms all around.

chris24, here is a link that should assist you in installing your rear speakers without removing the window

http://www.924board.org/viewtopic.php?t=12286&highlight=speakers

chris24 · Posted: Wed May 25, 2005 5:13 am Post subject:

Maybe I will then...need to build up some courage as someone clearly tried to take the back panels off to put speakers into the rear of my broken 924 and made a proper mess. Those links are ideal, I had searched but had not found!
_________________
1983 - 924 (185K miles) - not mint
1985 - 924 (148K miles) - mint
1990 - 944S2 cab (52K miles)

Smoothie · Posted: Thu May 26, 2005 8:37 pm Post subject:

Lorenzo - Porche's solutions to the problem seem to be the best and between their 2 solutions, I think you'd prefer the one that uses speakers of all the same (4 ohm) impedance with the added fader control. They had the fader located forward-left of the shift lever, but it could be added anywhere - in the glove box for instance. Below is a link to it at Pelican. I'd try to find a used one..
http://www.pelicanparts.com/cgi-bin/ksearch/pel_search.cgi?command=DWsearch&description=477035465&I1.x=13&I1.y=11

To go without that fader, you'd have to swap one of your existing speakers with an 8 ohm, and move the 4 ohm to the front wired in series with the other existing front 4 ohm. Problems with that are that the existing 4 ohm won't necessarily fit in the front-center location and your impedance for each front channel would now be 8 ohms which would be mismatched with the rears that would still be 4 ohms.

Another possibility would be to add 2 very small drivers at the front-center location, one wired to one front channel and the other to the other. You'd also have the front-rear impedance mismatch with this arrangement though. Could add 8 ohm drivers wired in parallel with the 4 ohmers for combined impedances of 6 ohms - not significant, but still a mismatch.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox