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So, I'm revisiting this. Given that I have a 10" sub in the rear compartment. should I apply filters to the 5.5" rear speakers as well? if so, does anyone have a recommendation?
The factory connectors for the "front" OEM Bose 3½" twiddlers are "spade" ones and they do follow Bose's standard, which is the opposite of what aftermarket manufacturers use.
To properly connect your new front speakers, you will need to cut the factory spade connectors and crimp new ones following the "normal" standard (reversed in relation to Bose), or create your own adapter harnesses if you don't want to cut and crimp the front OEM wires
Take a look at this Post for more details and tips on how to proceed.
Just bringing this thread back, as I found it in a search and just installed the JBL GX302s in the doors of my C5 Z06, including the above polarity reversal. They sound great - thanks for all the info!
Hello- struggling with the same issue. I wanted to confirm with aftermarket HU based on your diagram that the 3.5s and rears will no longer be going through the DSP? The signal is only passed down to the DSP to get the low frequencies, process, and share to the door subs?
I did see another post where someone said the 3.5"s are crossed over at 150-200hz, but it wasn't clear what device was providing that crossover.
I read on crutchfield the DSP was engineered to make everything sound good in the corvettes unique and tight cabin, and I wanted to preserve that as much as possible.
For ref. right now I have es9000 HU with open filters on fronts and rears, 79Hz on the subwoofer output, factory door woofers/speakers/DSP/AMP kit, factory rears, and then added an ARC X2650 amp and ARC low profile 12" sub in custom torch red box. I did not do the first install, so I cant testify which adapter/converter/harness/interface was put in when the factory HU was removed. Right now with the filters open on the fronts and rears, and the EQ fine tuned, and the sub filtered, its sounds really really above average. Its actually really good. Not like modern day Bose implementations. My tuner friend wanted to make sure the 3.5"s were getting filtered and DSP'd correctly following my HU upgrade.
THANKS
Originally Posted by GCG
@Budwise The original design is similar to a hometheater receiver driving 4 small satellite speakers, while complemented by 2 subwoofers. The audio signals from the OEM headunit are sent to the Bose DSP module (via connector C4), where a 2-way crossover filter is applied. The mids and highs receive additional conditioning and then are returned to the headunit (via connector C3). At the same time, the signal processor adds up the low frequency information from the 4 channels and sends it to the 2 subwoofer amps in the doors. In other words, the 4 twiddlers only handle mids and highs, while the 2 subwoofers take care of the lows.
The Axxess and PAC adapters tap the aftermarket headunit's 4 main channels speaker outputs to generate the line level signals that are passed to the Bose DSP module via connector C4. The 4 main channels need to run at full bandwidth, otherwise the DSP module would not be able to pass the low frequencies to the subwoofers, as you have discovered.
Moreover, the highpass-filtered signals that used to return to the headunit via connector C3 are NOT used anymore (connector C3 remains unplugged). Since they are generated from the speaker outputs, they are useless because the speakers are already receiving full bandwidth information anyways.
This is the reason the 3½" speakers could be a little overwhelmed, as a result of too much bass at too high levels.
This is a very good quality speaker, but after all, its woofer is just 3½" and there is only so much it can do with that small size in a less than ideal enclosure trying to reproduce full bandwidth audio at high levels... Physics laws have no mercy
The only way to make this work as before would be to find a new headunit with Pre-Amp outputs and Amp inputs for the 4 main channels, like the OEM has, and connect everything at line level.
Other than that, what you can do is place an in-line highpass filter just before the 3½" speakers to avoid distortion from overdriving them with more bass than they can handle.
Crutchfield has these 300Hz in-line highpass filters that you may want to try and they are not expensive (click here). This way you will be highpassing the 3½" for mids and highs, while attenuating the lows (both regions: Sub-Bass, 20Hz-60Hz, and Bass, 60Hz-250Hz).
This is not a brickwall filter. It has a gradual slope of 6db/octave. That means a 300Hz highpass filter will attenuate as follows:
6db @ 150Hz
12db @ 75Hz
18db @ 37.5Hz
The Bass region (60Hz-250Hz) can produce boominess and this filter might be enough to tame it.
On the other hand, if you want to play it even safer, it might not be a bad idea to order as well the 600Hz highpass filter (click here) and try them both, keep the one you like better and return the other one.
It's also a 6db/octave and this is how it will attenuate:
6db @ 300Hz
12db @ 150Hz
18db @ 75Hz
24db @ 37.5Hz
It will attenuate a little the Low Midrange region (250Hz-500Hz), which in excess could produce muddiness, while reducing even further the lows to make things easier for the little 3½" speakers.
The following diagram may help better understand this (it's the same for AXXESS or PAC):
As to your question-- the DSP is absolute ****. Most people that upgrade their head units/speakers bypass the dsp as step one.
The dsp is necessary because the bose speakers are such horrible crap the frequencies need to be tweaked to make them sound passable. It doesn't work well with after market speakers... don't waste your time trying to use it, you'll regret it.
As to your question-- the DSP is absolute ****. Most people that upgrade their head units/speakers bypass the dsp as step one.
The dsp is necessary because the bose speakers are such horrible crap the frequencies need to be tweaked to make them sound passable. It doesn't work well with after market speakers... don't waste your time trying to use it, you'll regret it.
When I purchased my red 99, it had a really nice double DIN Kenwood head unit in it. The previous owner left the Bose system intact. One of the worst sounding stereos I've heard. Upgraded to Infinity main speakers, JL Audio subwoofer, and JL Audio amplifiers. MUCH better now.
Filter recommendation for rears?
When I purchased my red 99, it had a really nice double DIN Kenwood head unit in it. The previous owner left the Bose system intact. One of the worst sounding stereos I've heard. Upgraded to Infinity main speakers, JL Audio subwoofer, and JL Audio amplifiers. MUCH better now. 
