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Hi everyone, brand new here. 
 

looking for some insight into the stock Bose system for my 2017 Sierra Denali. I’ve heard there are 2 types of Bose system a “standard” and a “luxury”. Heard that a few GM models (one being the Denali) has the “luxury”Bose system. I’ve seen that the luxury system is all controlled by the amp which has Crossovers and tuning programmed specifically for this sound system. 
 

Here’s what I’ve done that led me to this research. 
Added a 4 channel amplifier for the door speakers and a monoblock for my subwoofers. I integrated this with a “loop back harness” made by LLJ customs. Factory plug and play harness that takes signal from the Bose amp, send speaker inputs to an audiocontrol LC7i to give me 3 sets of rca outs (2 for 4 channel and 1 for mono) and also gives me speaker wires to hook up to the 4 channel spliced back into the factory plug in to door speakers. The harness also links the factory tweeters and subwoofer back in which are still feeding from the Bose factory amp. 
 

I’m not too pleased with the sound. I noticed that sitting in each seat around the truck sounds completely different. Front speakers seem full range with mids and highs while rear speakers sound almost like tweeters just more high range. After some tuning and testing I also checked the subwoofers out for sound. Sounds good however really low end drops out. Seems anything below roughly 32 hz does not play through the subwoofers. 
 

at this point I plugged the factory harness back in to sound check the factory. Funny thing is, just about the same thing. Different sound from every seat. 
 

my thought is that Bose somehow is factory tuned this way possibly in an attempt to optimize sound for the driver? Am I onto something with this in also thinking I can’t play very low frequencies because the Bose system has filtered it out in an attempt to protect the factory speakers or subwoofer? 
 

Looking for any information on how the Bose system works. If my hunch is right I think the only way to improve at this point would be to switch to an aftermarket head unit and cut the Bose amp out completely. 
 

Thanks in advance 

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Use the fronts(whatever speaker wires have full range) across the channels you need full range sound going into the lc7i. It should work just fine. The signal/ voltage is powerful enough with my non bose I'd assume its even better with your bose. Give it a shot and post the results. The rear channels suck as you've found just that way from the factory...

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You run the front wires into one input of the lc7i and jumper wire from there

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18 minutes ago, Snowcamo said:

Use the fronts(whatever speaker wires have full range) across the channels you need full range sound going into the lc7i. It should work just fine. The signal/ voltage is powerful enough with my non bose I'd assume its even better with your bose. Give it a shot and post the results. The rear channels suck as you've found just that way from the factory...

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17 minutes ago, Snowcamo said:

You run the front wires into one input of the lc7i and jumper wire from there

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That’s what this harness does. The LC7i has 3 sets of speaker signal inputs. Output 3 rcas to sub amp is supplied a signal from input 2 which is the front door speaker signal. Output 2 to 4 channel. Input 1 is from the rear speakers however there is a feature for “channel summing” on the lc7i which uses input 2 and merges it with input 1 and puts that merged signal out on output1. Essentially with the lc7i I’m able to use the front speaker input signals to produce all 3 output signals. I’m worried that the “full range” signal is not actually full range and filtering out the extreme lows. 
my other thought is that the factory tuning is the cause of the difference in sound from every speaker because it sounds roughly the same (just less powerful) when I take the harness out of the equation and plug back into stock. 

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That’s what this harness does. The LC7i has 3 sets of speaker signal inputs. Output 3 rcas to sub amp is supplied a signal from input 2 which is the front door speaker signal. Output 2 to 4 channel. Input 1 is from the rear speakers however there is a feature for “channel summing” on the lc7i which uses input 2 and merges it with input 1 and puts that merged signal out on output1. Essentially with the lc7i I’m able to use the front speaker input signals to produce all 3 output signals. I’m worried that the “full range” signal is not actually full range and filtering out the extreme lows. 
my other thought is that the factory tuning is the cause of the difference in sound from every speaker because it sounds roughly the same (just less powerful) when I take the harness out of the equation and plug back into stock. 
Ok so in short if you only use the front channels connected to ch2 and ch3 (not using the rear)all the speakers still sound the same? Makes me wonder if the amp is even bypassed. Are you using aftermarket speakers? Also you can open the lc7i and turn off all the dip switches btw. I do not have this issue with mine. Then again mine isn't bose.

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23 minutes ago, Snowcamo said:

Ok so in short if you only use the front channels connected to ch2 and ch3 (not using the rear)all the speakers still sound the same? Makes me wonder if the amp is even bypassed. Are you using aftermarket speakers? Also you can open the lc7i and turn off all the dip switches btw. I do not have this issue with mine. Then again mine isn't bose.

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Yes, that’s what I’m looking for more clarification on. The Bose amp is bypassed for only the front and rear door speakers. The factory tweets and factory subwoofer are still in tact and powered by the Bose amp. 
the Bose system is very different than stock setups and Bose/gm make the detailed info tough to find. This is why I’m reaching out, I’m hoping there may be a GM tech or someone heavy into audio that ya dealt with this before that may have info and or schematics on what’s going on behind the scenes with the Bose setup. 
 

 

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Gotcha. Makes zero sense if your using aftermarket speakers in the doors. There isn't an inline bass blocker or anything that would cause issues. Just doesn't add up weather its different or not what ever the front sends out the amp lc7i should put out to the amps then speakers.

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You might just endup running speaker wire from the amp to the doors

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4 minutes ago, Snowcamo said:

You might just endup running speaker wire from the amp to the doorsemoji848.png

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From my understanding the Bose is different in that the head unit is not sending the signal to the speakers. It sends signal to the Bose amp which has factory tuning/crossovers/filters. Being that the actual speaker signal comes from the amp, for this type of setup you have to use the Bose amp outputs to go into the lc7i there is no speaker level signal available before the Bose amp. Being that this is the only signal I can use I’m at the mercy of whatever the Bose amp is putting out for a signal. So whatever Bose has decided to filter and tune out is the signal I’m getting. 

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From my understanding the Bose is different in that the head unit is not sending the signal to the speakers. It sends signal to the Bose amp which has factory tuning/crossovers/filters. Being that the actual speaker signal comes from the amp, for this type of setup you have to use the Bose amp outputs to go into the lc7i there is no speaker level signal available before the Bose amp. Being that this is the only signal I can use I’m at the mercy of whatever the Bose amp is putting out for a signal. So whatever Bose has decided to filter and tune out is the signal I’m getting. 
Agreed, but if your bypassing as in not trying to send the sig back to the bose from your aftermarket amp (then speakers), the doors and sub should all receive the frequency range of the front doors. There lies my quarrel. I think we both agree something isn't the way it should be. Have you tried taking a speaker and checking directly from the aftermarket amp?

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10 minutes ago, Snowcamo said:

Agreed, but if your bypassing as in not trying to send the sig back to the bose from your aftermarket amp (then speakers), the doors and sub should all receive the frequency range of the front doors. There lies my quarrel. I think we both agree something isn't the way it should be. Have you tried taking a speaker and checking directly from the aftermarket amp?

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Correct that’s how the harness works. The wires from my 4 channel amp do not go back to the Bose amp they go directly to the speakers. The Bose amp is essentially the head unit in this case. Picture the Bose amp as the original source of output which in most cases is the head unit. Except this head unit (the Bose amp) is already programmed with crossovers and filters that are not adjustable. I am indeed taking a “full range” from the front speakers. I believe the issue is that the full range is limited by these internal settings. Bose idea of a full range seems to bottom out below 32ish hertz. Again I think this is a protection they build in as an attempt to protect the stock woofer. 

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Correct that’s how the harness works. The wires from my 4 channel amp do not go back to the Bose amp they go directly to the speakers. The Bose amp is essentially the head unit in this case. Picture the Bose amp as the original source of output which in most cases is the head unit. Except this head unit (the Bose amp) is already programmed with crossovers and filters that are not adjustable. I am indeed taking a “full range” from the front speakers. I believe the issue is that the full range is limited by these internal settings. Bose idea of a full range seems to bottom out below 32ish hertz. Again I think this is a protection they build in as an attempt to protect the stock woofer. 

Yeah i could see that. I mean most door speakers dont play that low and that tiny bose sub can't hang with the lows man... It'd sound like crap trying to hit 20hz. Lol

 

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Edit: word change

 

 

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Try keeping the volume under half of the max. The turn up the gain on the lc7i and amp. Does it still sound the same? Here's a thread on a diff forum post 18 is a bit informative.

https://www.corvetteforum.com/forums/c7-general-discussion/4329173-c7-stingray-bose-stereo-does-not-sound-good-2.html

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4 hours ago, Snowcamo said:

Try keeping the volume under half of the max. The turn up the gain on the lc7i and amp. Does it still sound the same? Here's a thread on a diff forum post 18 is a bit informative.

https://www.corvetteforum.com/forums/c7-general-discussion/4329173-c7-stingray-bose-stereo-does-not-sound-good-2.html

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Good info, thanks for the share. Unfortunately this further confirms my theory of the Bose system having its own tuning to optimize the setup, or as some say, "compensate for their crappy speakers". I'll have to test out low volume vs high volume. So far no matter the volume I haven't noticed any real differences and I've done a lot of playing around. Either way even if the sound or range is better at lower volumes, not sure there's much that can be done as a work around. To keep volume on the head unit below half, the gains would need to be cranked and that may dirty up the signal. 

 

Crappy situation, I was actually somewhat high on the bose stock system as in my last truck (2012 silverado ltz with bose) I had almost this same setup I've just installed except different subs and no lc7i. I had a more basic head unit that I opted to switch out to aftermarket since I wasn't losing much in features and integration. Completely took the bose amp and all the logic out and had rca outs off the aftermarket head unit. The speakers sounded great as did the overall system. Ran it this was for almost 7 years and loved it. Figured I'd be able to accomplish the same quality without going aftermarket on the head unit in this truck but was unaware of how the bose operates. I thought what you've been thinking. Front speakers will give me a full range signal without question. Just need a nice LOC to keep a clean signal to send to my amps and I'll be all set. Oh how wrong I was.

 

Not sure if I'm just being picky because I'm used to a better sounding aftermarket sound system or what to really expect. I'm sure most average people wouldn't even notice the extreme low end bass dropping out as these frequencies only come up in certain songs. I've been into car audio since around 2004 so I guess my ears may be a little pickier than someone who has stuck to stock and not gone aftermarket their entire (driving) life.

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Actually I have been screaming DSP as it was told to me by very knowledgeable forum members who are no more or just stopped posting. In short the signal does need to be boosted and cleaned up. On the base model you can get away with a LOC just barely and have a somewhat decent signal. For the guy on a budget(i.e. me lol) its a go. That being said 

You have every right to be particular to the sound you are after and I wouldn't take less. It really sucks these factory radios are crap. Because these trucks are the most sought after these days. You'd think they would of stepped up the game the base factory plays as low as it comes. 

The thing folks who no little about car audio dont realize is theres no way your gonna get a super clean/ powerful signal outta that little module thats smaller then a mans wallet. Just aint gonna happen. Not enough goin on inside that little turd to make music really sound decent. Anhoo. Theres a forum member named (NASTY) I havent seen him post here in a while. He will be the dude to talk to fore sure as he's tried every dang thing with these trucks. He is or was a member of Stevemadedesigns.com id pm him over there and get the real deal. You might have to (wait for it...) But he can help.

 

Theres other members here with bose. Maybe they will come out of hybernation/ lurking and say what they have and if it works for them. 

Im all for low bass. So more power to ya getting squared away👍

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