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Good day all, after starting and reading posts on the topic of speakers and audio I think I am ready to take specific actions (baby steps) towards audio system improvement. The intent of this thread is rear speaker replacement. I have a 2015 2LT vert and I am referring to the speaker in the back of the trunk in the 10 speaker system. I know some think the audio is fine as is and others say replacing just a speaker or three won't provide any improvement. But I'd like to try nonetheless.
I am looking for advice on how to 1) remove the rear speaker and a 2) recommendation on an aftermarket replacement.
It appears as though the rear speaker can be remove from the rear trim panel. So my questions are as follows:
How do I remove that speaker?
What would be a good speaker replacement to try? I've read conflicting information on its size, I've seen both 7.5" and 8". Also I read that the speaker should be 2 ohm impedance.
Your help would be greatly appreciated.
Last edited by shakinrock; 12-11-2018 at 08:27 AM.
Somebody on the forum did this, but it is hit-or-miss as to whether it will sound any better, as the characteristics of enclosure (volume, and port tuning frequency) are designed to work with the specific electro-acoustic properties of the Bose speaker/driver installed. Although you can easily find another driver that physically fits into the enclosure, the electro-acoustic properties are not likely a match to the Bose original.
I can’t confirm the speakers’ size, but they are 2 ohms...
That is the key, Bose uses a very low resistance (or reactance) and their amp does not do well with other "better" speakers. Getting a signal from their system for another amp to power another speaker is also not simple! They have matched that rear subwoofer box volume to their speaker. It is usually size dependent but in Bose case even the same size "better speaker" may not work as designed. Just cautions for the OP, have fun.
If you don't replace the amp you are honestly wasting your time due to the processing Bose applies. Gone are the days of just swapping components for a quick and easy audio fix as everything is integrated. This is especially true as the Bose has all kinds of specialized EQ parameters programmed into the amplifer. I've tested it with a calibrated microphone and system automatically lowers bass levels as you turn the volume up. This roll-off is a common trick Bose applies in many GM vehicles to keep their speakers from sounding distorted.
Based on my research (have not physically confirmed) you would want a 2 ohm dual voice coil sub. While the box is ported I have no idea at which frequency (likely too high), so personally I would seal it completely and replace the factory sub with a Kicker CompRT 8" subwoofer (shallow mount). The factory box is 14 liters which is .49 cu ft. so you need a speaker that performs in that sized enclosure. Keep in mind the factory amp is very weak / under-powered thus its ability to drive an aftermarket sub to decent levels is doubtful.
If you want to keep the other speakers and have an upgrade path I would use a PAC AP4-GM61 to interface with the factory system plus give you a clean unmolested low frequency signal. Take that output and feed it to an aftermarket mono block amp driving your chosen sub in the factory enclosure. If you want to avoid the factory box and just add a sub Vette Nuts sells a box (for a 10" JL Audio sub) that drops into the rear cubby that looks decent but I've never heard it to comment any further.
^^^
Frankly, having looked at many posts since I got my 2014 Z51 in October 2013 the only ones that have reported a significant sound reduction used the Crazy Cowboy Extreme kit. That is two layers of sound deadening on every surface, particularly the aluminum panels behind the seats and on the torque tube sides. It's not easy and a number have had Crazy Cowboy do it. It requires removing the seats and all carpet. Some have also removed the door panels and put sound deadening there.
IMO it's a waste to "improve" the components unless that is done. The tire and road noise is worse than my C6 Coupe. But that is my opinion. I use a method that doesn't fit most folks. I have the sound system playing a bit past half volume as soon a I start the car and it's seldom off! I have it playing over1000 songs in shuffle mode. The only thing I find is my basic balance and settings work fine but for 10% of the songs the bass is too boomy. Joss Stone singing "Tear Drops" is a good example. I have used a system that a poster described and I implemented. I have three presets saved with different bass levels. Just push a button when a song has excess bass and issue solved! This is a step by step of how to set accomplish this for any balance, bias etc desired: http://netwelding.com/Boomy_Bass.pdf
Works for me but I seldom have anyone in the car and my iPhone is set to not receive calls when moving!
If you are going to change the speakers you need to do it all. I replaced my whole system in my C5 Z06 and sound deadening. Unbelievable sound from the Audio system and the nice noise reduction. If I have my C7 Z06 done I will be doing the same thing. The only thing I will try and work around is not changing the headunit.
^^^
Frankly, having looked at many posts since I got my 2014 Z51 in October 2013 the only ones that have reported a significant sound reduction used the Crazy Cowboy Extreme kit. That is two layers of sound deadening on every surface, particularly the aluminum panels behind the seats and on the torque tube sides.
Did you know that the point of diminishing returns on Dynamat type sound deadening is somewhere around 30% coverage?
Above that, there are improvements in the sound deadening, but the purpose of that material is to reduce the vibrations of the panels and at some point, you are adding weight without a significant reduction in noise.
Sounding deadening will certainly improved sound quality.
Overall I agree - whatever sound deading you do WILL help... but only so much. Honestly for me the C7 isn't that bad, my previous car (a Nissan 350Z) was MUCH worse! So like most things audio related this is very subjective.
Originally Posted by ZO6 cracker
If you are going to change the speakers you need to do it all.
I think you can piecemeal it. But YOU must bypass the Bose amplifier as you go. Will the replacements speakers sound "better"? Maybe... but the Bose equalization curves will still be applied (YUK!) and since the Bose system KILLS the bass response as volume increases (see below) anyone interested in adding a subwoofer or attempting a low frequency bass fix in this car MUST remove the Bose amplifier from the signal chain.
Here are the results of my calibrated microphone test with pink noise (equal energy) on the C7 Bose system with subwoofer at two different volume levels:
Blue is low volume, red is high volume. Results have been normalized to reflect the nearly identical mid to upper frequency response so you can see what is actually happening to the lower bass frequencies. The bass is artificially boosted at low volumes but then massive reduced as volume increase. This was immediately noticeable to me as I have an Alpine Imprint DSP aftermarket audio system in my other vehicle.
Can you compensate for this mess with the factory EQ? Somewhat, but its just a band-aid and requires constant tweaking as you change the volume. JerryU's solution posted above is a neat trick to use as a workaround.
and adding tweeters to the rear also helps balance out the sound around you.
And thus ruin your sound stage if you had true surround sound material (like in the movies) then rear speakers are needed, but music sources are 2 channel stereo. In fact if your staging is good you don't even need the center channel speeaker. Basically you should run your fader forward enough that you can no longer hear the rear speakers for optimal imagining.
Yeah I agree you can piece meal it. Bose really makes it challenging. I think guys were having better luck with bypassing the Bose system in the C5’s. And keeping the Bose headunit. My friend owns a audio store and they do a lot of installs plus do a lot of the audio competitions shows. I will need to talk with him and see what’s possible to do without costing a fortune.
Here's a longish blurb on my understanding of the sound system in the C7. Others will chime in I'm sure.
The C7 comes with a Bose system integrated into the head unit. As others have posted, the Bose system dynamically adjusts frequency response based on the volume settings and it also adjusts based on the ambient noise levels. This is a engineered system. The speakers are specific to the C7 and the Bose system. The system is designed to give "acceptable" sound based on the vehicle acoustics and budget allowed by GM. As it is an engineered system everything is designed to work together. Replacing just a part of the system will not give good results. To get better sound that stock you'll need to engineer a system that is better than stock.
Ambient noise levels are high - the C7 has a lot of tire noise. The majority of it comes from the wheel wells, the bulkhead behind the seats, and the center of the coupe floor. The convertible is somewhat quieter as the wheel wells and rear floor aren't as open to the cab. Reduction of this noise can be done using various levels of sound control. 1st is CLD - Constrained Layer Damping. Products like Dynamat are CLD. They control resonances in panels and can give a reduction in noise. Only 25 -30% of a panel needs to have the CLD adhered, assuming it is evenly distributed over the panel. 25% in one corner is not the same as 25% spread out over the entire panel. CLD adds weight, typically about 0.7lb per square foot (depends on product thickness). The next layer is a sound block. This blocks sound and usually MLV (mass loaded vinyl) is used, though another product is also available (metal foil between 2 layers of foam). These weigh about 1lb/sqft. Unlike CLD, this needs to be installed to cover as much surface as possible to give maximum benefit. The C7 requires ~50sqft for a full install (coupe, convertible is less). The CLD and MLV work together and both are needed if you want maximum sound reduction. Reducing noise will improve what you hear from the Bose system as it isn't fighting as hard against ambient noise. What improvements can you make? My wife has a Lexus RC350. My C7 is quieter than her Lexus. That is with ~80lbs of sound control. Not something you want to do if you track your C7. Mine is aimed to be a tourer where an additional 80lbs isn't a concern.
Noise control takes you part ways, but what about the Bose system? Many are happy with their Bose system and that's fine. If everyone had the same tastes the C7 would only come in one configuration and one color. If you're one that wants more than the stock system there is equipment to take you further. To truly get better sound you'll need a DSP (Digital Signal processor). The DSP adjusts the frequency response and time delay (and more) that optimizes the sound to the C7's interior. To properly adjust a DSP requires experience. It is something you can do, though most will have an experienced tuner make these adjustments to get optimum sound. This is what the Bose system does, however these aftermarket systems are more flexible and capable than the build in Bose. What about all the adjustments the Bose system is doing though? Won't that cause a problem feeding into our DSP? You bet it will. DSPs can undo the Bose adjustments but only at one volume. To truly get a "pure" output to feed a DSP to get top level sound you'll need a device that taps the signal from the head unit without the Bose adjustments. There are 2-4 different manufacturers that offer these devices. They output a clean signal for the DSP. The DSP then feeds the results to an amplifier(s) and on to the speakers. The stock speakers aren't of what many would describe as high quality. Regardless, they're designed to be used with the Bose adjustments and would have to be replaced. The C7 (coupe) comes with 2 speakers in each door, 3 speakers in the dash (2 "tweeters" and a center channel), and 2 rears. If you have a 2LT/3LT you'll also have a subwoofer. All of these would need to be replaced. So as you're probably starting to realize, a special interface device to get a clean signal, DSP, amplifiers, and all those speakers can get expensive. How expensive really depends on the equipment you buy and the sky's the limit.
Ambient noise levels are high - the C7 has a lot of tire noise. The majority of it comes from the wheel wells, the bulkhead behind the seats, and the center of the coupe floor. The convertible is somewhat quieter as the wheel wells and rear floor aren't as open to the cab. Reduction of this noise can be done using various levels of sound control. 1st is CLD - Constrained Layer Damping. Products like Dynamat are CLD. They control resonances in panels and can give a reduction in noise. Only 25 -30% of a panel needs to have the CLD adhered, assuming it is evenly distributed over the panel. 25% in one corner is not the same as 25% spread out over the entire panel. CLD adds weight, typically about 0.7lb per square foot (depends on product thickness). The next layer is a sound block. This blocks sound and usually MLV (mass loaded vinyl) is used, though another product is also available (metal foil between 2 layers of foam).These weigh about 1lb/sqft. Unlike CLD, this needs to be installed to cover as much surface as possible to give maximum benefit. The C7 requires ~50sqft for a full install (coupe, convertible is less). The CLD and MLV work together and both are needed if you want maximum sound reduction. …. That is with ~80lbs of sound control.
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Great summary. From what I have read from Posters who tried various "sound deadening" products, the Crazy Cowboy Extreme kit (which has the two layers you describe) is the only one where I have seen significant quantified sound reduction, perhaps sufficient to invest in "improving" components that come with the 2 and 3LT Bose. From my experience with my C6, which did not have one, the added C7 rear subwoofer is a help in covering up the very noisy coupe interior.
My solution is playing the sound system 99% of the time at a level a bit above half way which drowns out the tire and road noise for me, Then I seldom have anyone in the Corvette and have NPP set at Track and a low restriction air intake that at WOT has a great "sucking sound" that helps mask the objectionable noise.
For what I am doing the OEM Bose with added subwoofer and using presets with three bass levels (see my post #9, this Thread) to match the songs is just fine for me.
12-11-2018, 08:10 AM
Rear Speaker Replacement
That is the key, Bose uses a very low resistance (or reactance) and their amp does not do well with other "better" speakers. Getting a signal from their system for another amp to power another speaker is also not simple! They have matched that rear subwoofer box volume to their speaker. It is usually size dependent but in Bose case even the same size "better speaker" may not work as designed. Just cautions for the OP, have fun.
if you had true surround sound material (like in the movies) then rear speakers are needed, but music sources are 2 channel stereo. In fact if your staging is good you don't even need the center channel speeaker. Basically you should run your fader forward enough that you can no longer hear the rear speakers for optimal imagining.
