[lowrydr310]

Before anyone points me to the mega thread on e90 audio upgrades, I've read all through that and searched everywhere yet I still couldn't find any answers to my questions.

I have a 2006 325i with the HiFi system and CCC iDrive. I'm moving a subwoofer from my other car so I have all of the wiring I need, and I don't feel like spending $75+ on the Technic harness (despite the convenience/quality). I have a Rockford Fosgate P300-12, which is an all-in-one enclosure with built in amplifier. It's not high end but it provides some nice added bass which greatly improved my mediocre factory sound system in my other car (which sounds worse than the e90 HiFi system). It accepts high level inputs or RCA inputs.

It sounds like the preferred option is to tap off the subwoofer output (high level signals) of the HiFi amplifier, since the high frequency signals are already filtered out, and then connect that to a line output converter, then use RCAs to connect to my amplifier input. Is that correct?

Why is that preferred over splicing into the HiFi amplifier rear channel inputs (the low level outputs from the headunit) then converting to RCA connectors and plugging into the RCA inputs on my subwoofer amplifier?

I understand that those HiFi amp inputs are unfiltered, however my subwoofer amplifier has a crossover which currently does a fine job of filtering. Also, I read in a few places that despite my amplifier accepting high level inputs, it is preferable to use a standalone line output converter due to the relatively higher power levels coming out of the HiFi amplifier (not the typical lower power levels from a factory headunit).

[bluewater328]

Originally Posted by lowrydr310

Before anyone points me to the mega thread on e90 audio upgrades, I've read all through that and searched everywhere yet I still couldn't find any answers to my questions.

I have a 2006 325i with the HiFi system and CCC iDrive. I'm moving a subwoofer from my other car so I have all of the wiring I need, and I don't feel like spending $75+ on the Technic harness (despite the convenience/quality). I have a Rockford Fosgate P300-12, which is an all-in-one enclosure with built in amplifier. It's not high end but it provides some nice added bass which greatly improved my mediocre factory sound system in my other car (which sounds worse than the e90 HiFi system). It accepts high level inputs or RCA inputs.

It sounds like the preferred option is to tap off the subwoofer output (high level signals) of the HiFi amplifier, since the high frequency signals are already filtered out, and then connect that to a line output converter, then use RCAs to connect to my amplifier input. Is that correct?

Why is that preferred over splicing into the HiFi amplifier rear channel inputs (the low level outputs from the headunit) then converting to RCA connectors and plugging into the RCA inputs on my subwoofer amplifier?

I understand that those HiFi amp inputs are unfiltered, however my subwoofer amplifier has a crossover which currently does a fine job of filtering. Also, I read in a few places that despite my amplifier accepting high level inputs, it is preferable to use a standalone line output converter due to the relatively higher power levels coming out of the HiFi amplifier (not the typical lower power levels from a factory headunit).

You don't line-tap off the rear lines because they are already hi-passed. You will hear nothing if your sub is low-passed since your source doesn't have the information. That's why you tap off the amp from a full spectrum or low-passed source. Plus its closer to the trunk with your sub.

With a line-level converter, you could try to tap the line that goes out to the door speakers. This is basically mimicking some of the things the Technics harness does -- just not as clean as having a plug and play harness.

[lowrydr310]

Originally Posted by bluewater328

You don't line-tap off the rear lines because they are already hi-passed. You will hear nothing if your sub is low-passed since your source doesn't have the information. That's why you tap off the amp from a full spectrum or low-passed source. Plus its closer to the trunk with your sub.

I wasn't referring to the rear deck speakers, I was referring to the rear channel headunit output which feeds the HiFi amp, which is in the trunk.

From what I read and based on the wiring diagram I saw on the sticky "Start here" audio upgrade post, there are only four inputs to the HiFi amp, output from the headunit: Front L/R and Rear L/R. It is my understanding that the rear pair output from the headunit is unprocessed/unfiltered and is split/filtered at the HiFi amp into two additional channels with one pair of L/R powering the under seat woofers and one pair powering the rear deck speakers.

I was just wondering why it is preferred to use the high level HiFi amp outputs as a signal source instead of tapping off the low level HiFi amp inputs.

[6spdcoupe]

It's perfectly fine to use the preamp level if you amp accepts the balanced input.

[6spdcoupe]

Originally Posted by bluewater328

You don't line-tap off the rear lines because they are already hi-passed. You will hear nothing if your sub is low-passed since your source doesn't have the information. That's why you tap off the amp from a full spectrum or low-passed source. Plus its closer to the trunk with your sub.

With a line-level converter, you could try to tap the line that goes out to the door speakers. This is basically mimicking some of the things the Technics harness does -- just not as clean as having a plug and play harness.

None are 'closer' to the sub if you're getting the signal at the amplifier. Even if there was a difference in distance though it makes zero difference in performance. Rears are all highpassed after the amp.

[bluewater328]

Originally Posted by 6spdcoupe

None are 'closer' to the sub if you're getting the signal at the amplifier. Even if there was a difference in distance though it makes zero difference in performance. Rears are all highpassed after the amp.

I was talking about tapping the amp vs running cable to tap up front near the deck.

[6spdcoupe]

Originally Posted by bluewater328

I was talking about tapping the amp vs running cable to tap up front near the deck.

The cable up front at the deck is the same one that goes Into the amp so either way there's no reason to run anything up front.

[bluewater328]

Originally Posted by 6spdcoupe

The cable up front at the deck is the same one that goes Into the amp so either way there's no reason to run anything up front.

I think I got confused with my own (Base to HiFi) install with the Technics -- where I would have had to run a line. In my case passed through to allow the deck to power the rear speakers just for PDC beeps.

[6spdcoupe]

Originally Posted by bluewater328

I think I got confused with my own (Base to HiFi) install with the Technics -- where I would have had to run a line. In my case passed through to allow the deck to power the rear speakers just for PDC beeps.

Ahh yes, that makes perfect sense then since with Base you have to go up to the headunit itself.