In Reply to: ok well.... posted by stereo man on December 09, 2001 at 20:07:25:
As putting a aa bat to a speaker may damage older speakers. It may damage the voice coil in it. This is an ok test for a newer speaker, but in say a 88 car with factory speakers it could damage the speakers. The best way to test a speaker is to use an ohm meter to test it. If you get 0 impedance then the speaker is good. (give or take a few due to the different setup of speakers. Also you may not want to use your factory fader either. The bmw faders are known for failing with a new head unit. My sugestion is to just wire around the fader thus allowing your new head unit to do the job. I just thought I'd give in my input as I don't want to see you hurt your existing speakers.
There should be no problem with using the HU amp to power the factory speakers by bypassing the factory amp, even though the ohm load is different for the front speakers than the rear speakers. The difference is the sound level will be different front to rear, which can be adjusted using the fader. Is this correct?
That's correct. May be different depending on the efficiency of the speakers front to back. Will not cause a problem with the HU. Use a AA battery to buzz out the speakers making sure you don't have common ground. Each speaker should have two separate wires going to it. You must have "four" wires going to say the rear; not "three" wires. Three wires going to two speakers is called common ground since they have to share one of the wires. Thus that wire is common to both speakers. Your HU will not like that situation. If that situation exist you have to run new speaker wires or one wire to make it "four" two to each speaker. BTW buzz mean holding one of the pair of speaker wire to the bottom of the AA battery and using the other to touch the top of the battery a bussing sound will be emitted from that speaker. This tell you that good connection exist to that speaker. Do this to all four and you will be in good shape.
There is absolutely no problem using a AA battery to buss the speaker. I should have added INTERMITTENTLY. What do you think your ohm meter is. Well for your information on "RX1" it is applying 1.5V. If the woofer cannot handle 1.5V get rid of it. BTW you can apply 1.5 volts across a woofer even old all day without damage. Current is really what damage a voice coil and a AA battery will not damage it. A tweeter would be more prone to damage but is protected by the blocking capacitor in the cross over net work.
With due respect to you Stereo Man you are correct a speaker can be damaged with DC current and only with DC current unless over driven by AC current. Speakers with very narrow voice coil gap will fall prey to smaller amount of DC current. These kind of speakers are high efficiency speakers and not employed in Mobil audio. You may wonder why a majority of speakers in Mobil audio applications are of the 4 ohm verity. One of the reasons are that a 4 ohm speaker have a very robust voice coil and can handle large amount of current required to produce the higher volume and deep bass required to over come the high ambient noises level of the automobile. I stand corrected I should have emphasize "intermittently" touching the battery since this action simulate an AC signal and will cause no harm to the speaker voice coil.