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2015 Tahoe "Enhanced Sound"


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I was able to mix and match options on my 2015 Tahoe when I purchased in Mar of this year, so I have a special Nav package with an upgraded audio system (additional speakers and some other bell and whistle). I noticed when I scrolled through the XM channels and stopped on a station which emphasized bass in the music, the sound seem to be terribly enhanced in the cab of the vehicle. I would turn down the music but noticed it was still there, just not as enhanced. When I changed to a XM channel that does not use a lot of bass, the sound was not enhanced at all.

 

If you are in a plane and your ears will not pop, this is what I mean by enhanced. This effect does not work well with me, my last episode on a plane resulted in coughing-up blood associated with this “enhanced sound”.

 

Anon2015, an acoustician who frequents this forum and provides an informative, expert analysis on issues of sound, articulates what I believe to be the issue (“The Bose system in these vehicles, and more to the point those with AudioPilot, are very poor. The bass management is horrible and you can have just nasty overwhelming bass on certain tracks ... at levels not in the recording”). Although this issue is similar to the effect on the “2015 Yukon Noise In Cabin” thread, it's unlike that thread 'cause it can be mitigated, just change the channel. Not letting GM off the hook though, I spent too much money on this vehicle for this to be happening in the first place.

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Anon2015 – I understand the following paragraph, but this is in your lane, let me know if the words are technically accurate.

 

Here is a piece of my research how the Bose Audio Pilot (BAP) system works: BAP uses a microphone/s in the vehicle’s cabin to monitor ambient noise, and digital signal processing to adjust the music or other program material’s level and equalization in “real time.” Using information from cabin-mounted microphone/s and engine information from the vehicle’s data bus communication system, a Bose algorithm continuously monitors and measures noise, and sends acoustically opposite sound signals through the vehicle’s speakers to cancel targeted noise. The system is programmed specifically for each vehicle, responding only when needed. A strategically placed microphone in the vehicle cabin continuously monitors ambient noise conditions, while a sophisticated Bose algorithm analyzes the music signal and adjusts it to reduce the effect.

 

Based on my complete research, I am going to conduct a little R&D on my vehicle to test one part of a theory. If it works, the Enhanced Sound in my vehicle will be greatly reduced or eliminated. As a bonus, the folks on the Yukon Noise In Cabin thread may benefit. If it doesn’t work, there is the second part of the theory, but will require external support from Bose.

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Kinda of.

You need to view this as two separate systems... Noise Cancellation and volume compensation. On the Noise Cancellation front, there is an entirely separate low frequency driver (call it a subwoofer if you'd like) which is dedicated to the purpose of noise cancellation. From the physics perspective, noise cancellation is effective in the majority of seating locations only at low frequencies. Noise cancellation works when two sounds are 180 degrees out of phase and of the same energy (let's say loudness). Two make the picture somewhat clear, you need to equate phase with distance. So, if you want to cancel out sound in exactly one location, that is relatively easy. But, if you want to cancel for two statics locations (like left and right ear) it is still somewhat easy BUT only for frequencies lower than about 560Hz (consider the ears are between 6 and 8 inches apart). Now, you want to do that for 4 seating locations (8 ears on heads that move). The issue becomes much more complex and you're not likely to do an effective job for frequencies above, say 70Hz. This is exacerbated when you only have one speaker to create the out of phase signal and multiple seating locations and multiple source vectors. From the practical point of view, a GM Engineer (whose name I have conveniently forgotten) said the Active Noise Cancellation in these trucks is designed to only reduce engine rumble (noise) which occurs between two specific RPM points. In his words then, the engine set up has been designed to create an annoying noise between two specific low RPM points and the frequency and volume of the rumble is known. Thus, the Active Noise Cancellation is "off" outside that range. Now if active noise cancellation is always on, that could be a contributor or cause of the noise/pressure issue felt by many and among its symptoms would be different intensities in different seating locations and potentially vestibular disorientation. To test this, you do not want to be pulling circuit breakers ... locate the speaker used for noise cancellation in the rear area of the truck, remove the wire leads to the speaker (tape them off to prevent shorting) and see if that resolves the problem. (In my case, I placed a recording voltmeter on the speaker leads and discovered Active Noise Cancellation was not working. The dealer, of course, said it was working based upon what the computer said. None-the-less, it isn't and wasn't, and GM basically said stuff it....which was the same story with the racked body panels.)

 

Volume Compensation - The volume compensation feature uses multiple microphones in the truck to determine the frequency spectra and loudness (SPL) of the in cabin noise. Earlier implementations of volume compensation, simply raised the volume of the radio to overcome the background noise (note the problem here ... when the radio gets louder, the cabin is louder as a result and volume compensation wants to raise the volume even more)...so the implementation is a bit more complex than a microphone and automatic volume control. In the Bose AudioPilot system, the attempt is to only increase the volume of those frequencies which are masked by outside noise sources...this is where Digital Signal Processing and their algorithms come into play. What Bose will tell consumers to do to test the system, is to have the car stationary, in a quiet area, engine running and tune the radio to a talk station. Set the volume as low as you can and still hear and understand the dialog. You then drive the car and note how the volume of the speech increases so you can hear and understand "even with the windows open". That's a fail. It will not do that (at least as implemented in my Denali). In fairness to GM, GM never said it would do that...that representation comes from Bose who has liability for that misrepresentation.

 

Unlike the Harman, Meridian, Lexicon (Harman) and other up scale systems, the Bose does not do ambiance extraction and the quality of music from XM and radio sources is really pretty crummy. Multichannel music from BluRay or DVD is not too bad (for a car).

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Anon2015 - got it, tracking. For accountability, GM was the prime contractor, Bose was a subcontractor. The prime contractor is ultimately responsible. As long as BAP is driving the sound train, GM will not be able to mitigate this issue unless they consult Bose or have Bose technicians on staff.

 

Would you know if the BAP has it's own power source or directly connected to the battery?

 

If you decreased Volume Compensation (VC) capacity, would that impact Noise Cancellation (NC)?

 

What are the percentages of VC and NC in this truck?

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Volume compensation and Active Noise Cancellation are independent of each other.

 

According to GM, "These are independent systems." (direct quote).

 

Power source: I cannot confirm nor deny this...I suspect it does not have it's own power source but since this is very likely headed to litigation I cannot be tearing this apart to find out.

 

Bose may be the subcontractor; however, GM has made no claim with respect to the functionality of the Volume Compensation provided by Bose. The statement about its performance in GM Vehicles was made directly to me by a Bose engineer. Therefore, there is no claim against GM for the volume compensation functionality.

 

Bose AudioPilot to the best of my knowledge does not provide Active Noise Cancellation.

 

Of secondary interest: http://worldwide.bose.com/axa/en_au/web/suspension_system/page.html

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Anon2015 - got it.

 

What would totally eliminating VC do in this vehicle?

 

I know what Bose Rapid Mode Transition (RMT) does, explain how it works?

 

Would you know if RMT is employed in GM fullsize SUV line?

 

Is RMT something separate that can be purchased?

 

 

I visited your link a few weeks back, you didn't think I was that intelligent did you. BTW, did/do you work for Bose or a sound system competitor

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Bose will not sell RMT directly to an end user. Whether or not RMT, EHE, or other Bose technologies are, or are not, employed in GM's active noise cancellation offering is unknown to me at this time. Whether or not is not relevant to my various claims.

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NDA, totally got it. I’ll throttle back a bit, ‘cause my questions can lead us out of your lane and into mine. Appreciate all your professional feedback.

 

Doesn’t appear any other members are experiencing my issue so I need to be as smart and thorough as I can when making a complaint to GM and the NHTSA. There are a lot of vehicle dynamics involved for BAP to manage sound (most of which you probably already know), such as static vehicle volume (amount of open unoccupied space), driving with open windows, engine transition, radio on or off, amount of personnel in the vehicle, and on and on.

 

What’s your thought on this, here is my vehicle dynamic when the Enhanced Sound occurs; vehicle could be off or on, driving or stopped. But let’s talk the vehicle off, stopped position (in the driveway). One person in the vehicle, windows up, bench second row, sound distributed in the center, no bass or treble extremes, usually no more than a 10 mph external wind, and I believe 10 or 12 speakers. When I tune XM to a channel that emphasizes bass; amount of bearable pressure is equated to higher or lower radio volume. The higher end of the spectrum has to be what the folks are experiencing on the Yukon Cabin noise thread. But if the culprit channel is not tuned, there is “zero” pressure effect. But unlike the Yukon Cabin issue, bumps, V8 to V4 transition, driving with window open, doesn’t generate any pressure issue in my vehicle.

 

You are not experiencing either, did you rig additional acoustics, maybe.....?

 

What's your vehicle dynamics?

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I have experienced exactly what you have under various conditions. I have not pursued reviewing the raw data to see exactly what is going on; but, I suspect one, or both, of the following:

 

1. XM has decided their audience wants chest compressions and has run up the low frequency; and/or

2. BAP has increased LF SPL because BAP detects it falls outside the loudness curve they have set...HOWEVER, I'm not really not thinking that is really going on because there is no difference in the annoyance level engine running, not running, driving, stationary, etc.

 

No, zero modifications from stock on this truck. From the day I picked up this truck, I knew it and I would have a short relationship. It has just been a bit longer than I had been promised.

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Anon2015 - understand the NDA piece, what's your non-professional spin of what's going on.

 

Do you have this specific issue in litigation? If so, I need to send you a private message and get up to speed especially since we have this issue in common.

 

Are you in waiting for a buy-back of your truck?

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My issue is non-related to any of this. That being said, GM is demonstrating a general propensity to disregard, bury, ignore, and/or keep quiet issues which negatively reflect on quality and safety of the vehicle. That is a pattern which will work against them.

 

With respect to the buffeting...not certain as to the cause nor contributing factors (such as air tightness of truck). If I could get my hands on one for a couple of days, I might get closer to an answer.

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Anon2015 - It would be great that someone like you with the ability and capability could get closer to an answer, but I am somewhat confused about your last comment, "if you could get your hands on one for a couple of days". Does your "one" comment infer you don't have the availability of a truck. I believe I missed something.

 

Comparing my '01 and '08 GM fullsize SUV's to this current one, I would agree the '15 version is wrapped jelly-tight

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I do have a '15 Yukon Denali ... it does not have the buffeting/noise issue. In the absence of a truck with that problem, there's little experimentation I can do.

 

My issue with GM and the dealer reflects back to a failure of communication within GM, deliberate misrepresentation (aka lies) about the delivery and future availability of certain capabilities, misrepresenting their willingness to resolve the matter in a timely fashion, along with what is beginning to appear as an effort to deliberately further defer resolution. This has had an adverse impact on my business and my volunteer SAR and first responder activities. This is in addition to their refusal to address/repair the Active Noise Cancellation, the Bose AudioPilot, and the racked body panels.

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