I'm finally back in-country and have a chance to test that inline amp (
https://www.amazon.com/gp/product/B00B5MUJ3U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1) to boost the i8's native exhaust sound.
1. I wired up the amp to my harness connector and started the car and pur her in "sport mode" to be sure the engine fired up. However, I could detect no change in the sound of the vehicle with the amp in place.
2. So, now I am concerned that maybe the signal level in the harness was "Line Level" and not "Speaker Level". It might be possible that the signal interception was between the source and the amp although I was expecting a speaker-level signal. I could re-wire that particular amp for line-level input, however if that was indeed appropriate, I would NOT want to feed the speaker-level output from the amp into another amp which was expecting a line level source. That could be disastrous!
So I needed to find some way to determine/confirm the signal level in the harness.
3. I made yet another custom connector which would let me easily tap into the harness from outside the trunk. I broke out my oscilloscope, and with my wife in the car, I sampled the native BMW signal in the harness. My wife started the car, kept her foot on the brake, shifted into drive, and moved the lever into sport mode. The signal I captured is shown below.
4. Note that the measured signal has an amplitude of only 32 millivolts. A "speaker-Level" output would be in multiple volts, and a line level output would be less than a volt (but not this low). So something was missing here...
5. What I failed to anticipate, was that the i8 does not provide any external audio augmentation when the car is idling. I was able to confirm this by opening and closing the harness circuit while the car was idling. I did not notice any change in the sound of the car at idle! So, apparently BMW does not produce any sound augmentation while the car is idling!
* If you want to have an augmented idle sound, it looks like you have no choice but to use an aftermarket sound booster (Maxhaust, Maserati, etc) as the BMW module doesn't provide any sound at idle!
6. However, the question still remains about what the exact signal type is. I was able to confirm that the signal level in the harness is indeed "Speaker Level" as expected by feeding in a speaker level source directly to the harness itself. I did this with the car turned off as I did not want to blow up any downstream amp if it should be powered up. But its kind of interesting to note that you CAN feed the BMW external speaker with music from a standard audio amp! (Although it obviously favors the lower frequencies)!
* The signal in the harness is indeed "Speaker Level"
7. So now the question becomes: When and how does BMW actually provide sound to the external speaker? Only above certain RPM's? Only at higher loads? Only at higher road speeds? More investigation is needed...
8. A major complication is that we can't simply RUN the engine in the i8 while in park or neutral - and we have no way to REV the engine while in park or neutral. (PLEASE correct me if you know otherwise!) Additional challenges arise from trying to discriminate between the sound generated internally vs externally while actually driving the car. IOW: Its hard to detect when the external sound is being generated with the internal sound being generated at the same time!
9. So, I've got another couple of items on order which should be arriving in the next few days to help get a handle on how/when the BMW amp generates external sound:
Line Out Converter (LOC):
https://www.amazon.com/gp/product/B001EAWS3W/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Bluetooth Transmitter (rechargeable):
https://www.amazon.com/gp/product/B01EHSX28M/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Bluetooth Speaker (rechargeable):
https://www.amazon.com/gp/product/B010OYASRG/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
- The Line Out Converter will allow me to reduce the Speaker Level output of the BMW Amp to a Line Level suitable for input to the Bluetooth Transmitter.
- The Bluetooth transmitter will transmit the BMW sound to the rechargeable wireless speaker (or bluetooth headphones) I can have INSIDE the car.
- This will allow me to easily hear when BMW generates the external sound for the i8.
More to follow!