Sub / Resistance Question - PeachParts Mercedes-Benz Forum

jbhebert · #1 12-16-2004, 09:17 AM

I have done several audio installs, but most involved only 4 speakers, and more specifically one speaker per channel. I have a question for those far more knowledgable in car audio than I. Would this scenario work:

Head unit: Alpine CDA-9835
Front Dash Speakers: Rainbow (4 ohm?)
Read Deck Speakers: Rainbow (4 ohm?)
Door Speakers: Some form of dual voice coil dedicated sub (4 ohm/coil)

Front left and right outputs go to the front dash speakers and one voice coil on each door sub via a passive crossover, effectively giving me a 2 ohm load on the front channels. Rear left and right outputs go to the rear deck speakers and the other voice coil on each door sub via another passive crossover, also giving me a 2 ohm load on the front channels.

I guess my main questions are:

1) What does a passive crossover do to resistance? Double it (i.e., running in series), half it (i.e., running in parallel), or does it stay the same? I want to say it effectively acts like running the speakers in parallel, but I'm not sure.

2) Is the V-Drive amp in the higher-end Alpines stable to 2 ohms?

3) Do the voice coils in a dual voice coil sub act as seperate "virtual" speakers, and can they be seperated onto two different channels as outlined above?

If the answer to the first question is what I am thinking, and the answer to the latter 2 is "yes", then I think this will work without the need for an external amp. If not, do I need an amp for the subs, or are there other solutions?

Thanks.

donbryce · #2 12-17-2004, 01:29 PM

Quote:

I have a question for those far more knowledgable in car audio than I.

My knowledge level is perhaps average, so I hope you don't mind some opinions that may be subject to correction, but this post idea is interesting and I couldn't resist.

Quote:

1) What does a passive crossover do to resistance?

IMO, nothing. It filters the frequency of the audio signal, so a sub gets low frequencies and a tweeter gets highs, with a 3-way crossover passing/filtering some part of the middle frequenciy to a mid-range speaker.

Quote:

2) Is the V-Drive amp in the higher-end Alpines stable to 2 ohms?

I doubt it very, very much. The only audio amps I've ever heard of that are stable down to 2 ohms are 'D' (?) class mono sub amps.

Quote:

3) Do the voice coils in a dual voice coil sub act as seperate "virtual" speakers, and can they be seperated onto two different channels as outlined above?

Yes, they are effectively 2 speakers from the perspective of the incoming signals from the amp, but a dual VC should never be 'fed' from separate channels.

Quote:

Front left and right outputs go to the front dash speakers and one voice coil on each door sub via a passive crossover, effectively giving me a 2 ohm load on the front channels.

I presume you are thinking of a crossover that sends the low frequencies to one coil of the door subs, and the mid-highs to the front dash speakers? OK, I guess, until you connect the low frequency output from the rear channel to the other coil, effectively driving the dual sub coils from separate channels (bad).

This wouldn't change the impedance of the speaker connection to the amp's channel(s) either. Connecting 2 4ohm speakers, or the coils of a dual VC speaker, in series equals 8 ohms. Connecting 2 4ohm coils in parallel equals 2 ohms.

Lastly, there may be some out there, but most dual voice coil subs tend to be 10" and up, and are very deep, much too big for a door installation I would think.

I may be off, and don't mean to rain on your parade, but I'm afraid your set-up wouldn't be very practical, would probably fry several of the components, including the amp, and would probably sound awful even if you could get everything to work together (I'm thinking here of the concept of the sound-stage)....Here's a link to a very good site that presents all of this in easily understood form http://www.bcae1.com/

jbhebert · #3 12-21-2004, 04:28 PM

Your points are well taken, and coincide with feadback I have gotten elsewhere. I have decided to take a different path and will be installing a dedicated 5 channel amp to drive the speakers. This will give me a lot more options, and sound much better.

I am in the process of collecting the equipment right now. Hopefully I'll be able to at least start the installation over the Christmas/New Years holiday.

I'll keep everyone posted.

Thansk.

Ramblin · #4 12-22-2004, 05:59 AM

3) Do the voice coils in a dual voice coil sub act as seperate "virtual" speakers, and can they be seperated onto two different channels as outlined above?

The only thing I would say is that in 2 cars that I own I have dual voice coil subs and both are fed with bridged 4 channel amps and they sound great. As long as the impedence is matched with the amplifier and the amp is not below its rated impedence I really don't think there would be a problem.