Tablet as Car Stereo - no head unit
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I’m buying a used car soon and I saw a bunch of threads on reddit, XDA-devs and NASIOC about people installing Nexus 7 tablets in their dashboard. However all the installs simply had the Nexus 7 installed and running AUX out into their aftermarket car stereo head unit. I’m not an audiophile but I have a head unit in my current car and use the USB-in and it sounds great. But I connected my Nexus 7 to it over AUX and it suffers in sound quality. It’s not terrible quality like Bluetooth streaming or anything, but it’s not the greatest either.
 
So my question is would it be possible to wire my Nexus 7 directly to my car speakers and bypass the use of a head unit altogether? Would a headphone amp, DAC, or Line Out Converter make this possible or do I still need a head unit to interface with the car speakers? I am aware I'm probably better off asking at a car audio forum, but car audio is notoriously plagued by "professionals" that throw money at problems and just fire off name brands without any actual knowledge.
 
Thanks in advance
 
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  I’m buying a used car soon and I saw a bunch of threads on reddit, XDA-devs and NASIOC about people installing Nexus 7 tablets in their dashboard. However all the installs simply had the Nexus 7 installed and running AUX out into their aftermarket car stereo head unit. I’m not an audiophile but I have a head unit in my current car and use the USB-in and it sounds great. But I connected my Nexus 7 to it over AUX and it suffers in sound quality. It’s not terrible quality like Bluetooth streaming or anything, but it’s not the greatest either.
 
So my question is would it be possible to wire my Nexus 7 directly to my car speakers and bypass the use of a head unit altogether? Would a headphone amp, DAC, or Line Out Converter make this possible or do I still need a head unit to interface with the car speakers? I am aware I'm probably better off asking at a car audio forum, but car audio is notoriously plagued by "professionals" that throw money at problems and just fire off name brands without any actual knowledge.
 
Thanks in advance
 
The headphone amp of Nexus 7 is not powerful enough to drive the car speakers in full dynamic range. You would still need a preamp / amp. Probably, you can bypass the built in DAC and use much higher quality DAC as well.
 
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So if I bought a headphone amp / DAC combo, could I just splice RCA connectors to the speaker wires from the wiring harness? Or would that not work? 
 
Then it would be 
 
Nexus 7 --> amp/DAC ---> speakers
 
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Why would you get a headphone amp to drive speakers when you could just buy a car stereo amplifier instead?
 
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So if I bought a headphone amp / DAC combo, could I just splice RCA connectors to the speaker wires from the wiring harness? Or would that not work? 

Then it would be 

Nexus 7 --> amp/DAC ---> speakers

What you need is a DAC AND a speaker amp.

Just make sure your Nexus 7 is compatible with whatever DAC you use. Not all Android tablets (or phones) support USB audio out, and not all DACs work well with usb audio out either. Not sure about your Nexus 7.
 
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So if I bought a headphone amp / DAC combo, could I just splice RCA connectors to the speaker wires from the wiring harness? Or would that not work? 


 


Then it would be 


 


Nexus 7 --> amp/DAC ---> speakers
 


No. Headphone amps don't have that much power. To drive a 50W rated speaker, you would need 50-75W rated amp.
Generally, the output from the car headunits woould be 2v to 5v. I am not sure how much is the line out from Nexus 7. If it is too low, the SQ won't be that good. You migh need to add a preamp to compensate that. Using external DAC for Nexus 7 is not straight forward as using one in Samsung / Sony tablets. Venture into it after good amount of reading about it.

I would still say it is worth the effort and money spent on using a tablet as a HU. Hell a lot of customization options.

And of course...the easiest way is to buy a touch screen unit with 50W output and leave everything as stock.
 
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So basically my options are:
 
Nexus --> HU (only for AUX input and to drive speakers)
simple and effective, worst SQ but adequate, price $35-$150, may take some force to jam HU behind dashboard
 
Nexus --> DAC --> amp
must research DAC & amp, best SQ, most expensive option (amp $150+), wiring & mounting will be a huge PITA, heat may be an issue
 
Nexus --> DAC --> HU (only for AUX input and to drive speakers)
must research DAC, price $35+DAC, SQ in-between other 2 options
 
 
 
 
 
 
 
...okay fine I'll buy a damn head unit. BUT I DON'T WANT TO :frowning2:
 
 

 
now to find a good USB-powered DAC that works with N7 on Timur ROM :)
 
thanks for the help so far everyone, your input is greatly appreciated
 
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Class D car amplifiers do not put out a lot of heat and some of them are pretty small.

Just curious. What is it that you want the Nexus 7 for? You'll get better SQ putting your music files on a USB flash drive and using that with a good head unit over hooking up the Nexus 7 to an aux in on a HU.
 
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a multitude of reasons. head units are poorly engineered and even more poorly manufactured. UIs haven't changed in 10 years, they're buggy, never updated, and the firmware stacks do not follow official specs (eg bluetooth)
 
with the Nexus 7 I have solid hardware and software backed by Google and an entire forum of 3rd party developers. bluetooth stacks are written to spec, software updates are guaranteed for years, and apps are plenty. with apps i have flawless Spotify, Pandora and Netflix (when parked!) support, phone pairing that actually works, and ECU monitoring through OBD2/Torque Pro. 
 
i've been listening to my music on a USB flash drive through my head unit for about a year now, but only because i've been waiting to sell my car. before that i used my iPod which died from the heat.
 
however i must admit, the primary reason is that maintaining a music library on a hard drive and transferring it to your DAP/thumb drive is a time-consuming chore, and thanks to Spotify i've entirely given up on that (aka i'm lazy)
 
 
 
quick question though. if i understand this correctly, audio is processed by Nexus 7's internal DAC (which isn't that bad actually, better than my GS4) and then passed into the HU through AUX, then it gets processed by the HU's own DAC. So, then, is a USB DAC inherently redundant in this case - because it's being fed into another DAC anyway? or is it only redundant if the USB DAC is of lower quality than the HU's DAC? to analogize, is this like transcoding from MP3 to FLAC where quality cannot go up because it's already been compressed, FLAC to FLAC where quality cannot go down because it's lossless, or MP3 to MP3 where quality absolutely goes down because it's being compressed twice?
 
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You left out a step. The Nexus 7 DAC processes the digital to analog, and then it runs through a headphone amp of some kind, and you are sending that signal to the HU's aux input, not a typical line input signal. So it's getting amped unnecessarily (albeit a small amount).

And yes. Most likely your HU unit will convert everything back to digital to do whatever processing it needs to (tone controls, volume control, any crossovers for subs, etc.).

This is why Nexus 7-> DAC->amp can give you the best sound since you would be eliminating all the extra audio processing steps before it goes to the speaker amp. As well as the fact that you could buy a better DAC than is in the Nexus 7 and external speaker amps can sound better than HU amps.

This is all assuming that your Nexus 7 works well with USB audio out.
 
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Cant you just use a two or four channel amplifier like one you could find here?
http://www.crutchfield.com/m_100/Car-Amplifiers.html
 
Just get an amplifier that takes RCA preamp input and use an adapter to connect the Nexus 7 headphone out to it. Or you might be able to use a line out dock to bypass the headphone amp. As far as I know the amplifier should work completely in the analog domain, unless it uses digital crossover filters or something.
 
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You left out a step. The Nexus 7 DAC processes the digital to analog, and then it runs through a headphone amp of some kind, and you are sending that signal to the HU's aux input, not a typical line input signal. So it's getting amped unnecessarily (albeit a small amount).

And yes. Most likely your HU unit will convert everything back to digital to do whatever processing it needs to (tone controls, volume control, any crossovers for subs, etc.).

This is why Nexus 7-> DAC->amp can give you the best sound since you would be eliminating all the extra audio processing steps before it goes to the speaker amp. As well as the fact that you could buy a better DAC than is in the Nexus 7 and external speaker amps can sound better than HU amps.

This is all assuming that your Nexus 7 works well with USB audio out.

New here, and want to do the same in my van.
 
What I'm having a hard time understanding is which device I need between a tablet and the amp which has a master volume and maybe a cross over etc.  What would it be called? DAC ...  Or any hardware suggestions?
 
Thanks
 
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A tablet only has stereo output. What would you use a crossover for on the audio out? And if you want a crossover to integrate speakers and a sub, then buy a speaker car amp that has a high pass filter, and a sub amp that has a low pass filter. Use that to set it up :)
 
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  So my question is would it be possible to wire my Nexus 7 directly to my car speakers and bypass the use of a head unit altogether? Would a headphone amp, DAC, or Line Out Converter make this possible or do I still need a head unit to interface with the car speakers? I am aware I'm probably better off asking at a car audio forum, but car audio is notoriously plagued by "professionals" that throw money at problems and just fire off name brands without any actual knowledge.
 
First off, you're better asking in car audio forums for two reasons: safety and if this is also your goal, proper sound quality. I'm going to guess the second is a priority because you are not saying that this is purely for convenience and you're willing to go out and use a DAC and line out converter. I'll address the tablet later and deal with your use of quotation marks up there first - even if you don't want to go as far as I describe, at least you'd get why they are there and what you should be really wary about.
 
Now, here's the reason why there are professionals, or more accurately, pros (who run shops), non-pros* (competitors) : you can install a $10,000 DAC in a car and power it somehow along with equally eyeball-gouging amps and speakers, but in no way have you managed to even scratch the surface of what really matters in a car audio environment. In  sense, car audio is more like pro audio than home audio considering all the tweaking you have to do to minimize the negative effects of the car's cabin as your listening environment. If you have a speaker system at home, you can try this too. Place your speakers directly facing each other, then sit closer to the left or right speaker. Switch on another audio system in another room, like a TV, with its back a wall adjacent to that listening room. Now, replace the speakers, DACs/CDPs, amps. Did the sound get better? Nope, not really, because:
 
1. You're not sitting in a spot equidistant between the two speakers (and in a car your tweeters on the dash can be, what, at least 18inches away from the midwoofer low in the door)
2. You're sitting off-center, in a spot that is not equidistant to both speakers
3. Your speakers are directly firing at each other, with no sense of proper toe-in
 
Now ask yourself: does anyone actually listen that way at home? Have you ever seen a home set-up like that? No, not really, and this is where those "professionals" come in. They will install everything so that instead of throwing money at expensive gear without targeting the acoustic realities in a car cabin, they will allow you to split your money properly on gear and installation. Think of this as acoustic treatments in an audio room at home, except this time you're addressing noise as well as time alignment and phase issues. They will install, at minimum, the midwoofers so that they can be properly dampened and the front of the cone isolated from the rear of the cone inside the doors (and minimize the most basic type of cancellation) and tweeters at an angle to improve the center image and minimize glare for the seat nearer to each side tweeter. Past that, they might install the midwoofers outside the door panel, if not on the kickpanel, getting rid of cancellations caused by the soundwaves from the front of the cone bouncing around behind the interior door trim. The subwoofers also get installed in such a way as to minimize room modes depending on the car, as well as for aesthetics if you want or if you're a tweaker have the amps and processor if you have one installed in such a way that you can easily reach them.
 
Past the proper installation of your speakers, you could work on using a time alignment processor - this allows for a DSP to introduce custom delays for each tweeter, each midwoofer (or midrange and midbass, if you're using a 3-way system in front) relative to each other and  the subwoofer at the back. Installs and time alignment (and other processor settings) done correctly, you can have along the dash properly centered main vocals with every other instrument spread out relative to it as you would on near field monitors, with the subwoofer's output (with the lowest safe high-pass setting in front and lower low-pass for the sub, so all it does is provide the low freq reinforcement for the notes) seemingly coming from the front despite being 4ft in the luggage compartment behind you.
 
Basically, what I'm saying is that it actually is a bad idea to ask about car audio outside of a car audio forum (unless I'm going to intervene), because it is inherently more similar to pro audio or professionally-installed home audio/HT systems. Worse still is asking about car audio in a headphone forum, where many of the regulars with authoritative reputations from high post counts don't even deal with room modes (and some don't even know what that is) by nature of headphone listening, and attribute changes in sound to "burn in" than earpad wear, hence they'll tend to think of lossless and GIGO instead of actually dealing with the acoustics and safety issues. At minimum your processor needs to have some kind of auto-tune using a reference disc, but back then we were manually measuring the response, and then USB mics just made that a bit easier since we can have the real-time analyzer running on a laptop (and we're not even the "pros" who do this for a living, just some people who would rather get stuck in traffic on the ground than pack into a sardine can on the rails above or below). The usual GIGO principle for the signal chain and throwing money at DACs isn't going to address what a proper DSP can - no ESS9023 will perform in a car better than simply addressing the inherent issues. Processors nowadays even take the signal off a factory-installed system's amp (so as not to fess around with  the interface on the dash or lose GPS), using a high-level input with an auto-ranging volume control as in the Alpine processor with Audyssey that I just traded in an older HU+processor for. Even 320kbps through a time alignment DSP on a properly-installed system can sound better than expensive speakers just screwed in wherever they fit playing lossless/CDs.
 
This is the primary problem you are dealing with past the noise floor. Top view shows the different distance to each tweeter, midwoofer, and subwoofer (color coded); side view at bottom shows the height differential (color-coded) in midwoofer-tweeter height, plus the problem with how a sub in the trunk can be reinforced or reduced by cancellation depending on how many paths it takes into the cabin.
 

 
 
 
This is basically what the normal imaging in a car "looks" like: called a "rainbow image," as the driver you have the driver-side of the soundstage image with "bigger" and more up-front instruments vs the passenger side (and vice versa).

 
Using the balance control will only reverse that.
 

 
 
 
 
Here's an image just to illustrate why it got that name.

 
 
Now these are what you need those "professionals" for, unless you can DIY fiberglass.

 

 

 

 

 

 
Of course, yes there are things you have to look out for - not every professional installer is actually "professional" in conduct, nor transparent - they have to run their businesses and if it's a general car audio/electronics shop they are also dealers who have to push their own products. Car audio forums here divide and recombine and repeat thanks to heavy-handed marketing. For someone who doesn't fully understand all these, this is why car audio forums are also important - they will at least explain these acoustic issues better, and best of all, www.diyma.com. While that forum might sound like it's dedicated to  DIY-ers only, the thing is they are less susceptible to marketing since the forum doesn't even have huge ad banners diplaying BeWith, DLS, Hertz, etc. Learn there, and they might be able to point you in the right direction when you have work done on your car - basically, you need to find an installer who is likely to tell you what I already did: split your money between the gear and the installation properly, instead of pushing more expensive $h1t and then just sticking them in there.
 
Over here an Accord once won the "budget" category in an SQ competition using an old Alpine HU+processor, cheap $35 speakers and a $40 subwoofer (from what essentially is a factory that is a bit like Parts Express) along with a counterfeit $40 Alpine subwoofer amp (why they let these compete still escapes me). How did he do that? He basically spent nearly all the budget limit on the receiver+processor, which also had a high-current built-in "V-Drive" amp that needed its own connection to the battery. He then used the internal digital processor to apply crossover and time alignment settings, running the front speakers off the cleaner (and authentic) Alpine HU's amplifier and driving the sub with the counterfeit amp. He undercut the budget limit and still imaged a lot better than the cars one category up with expensive speakers and "Burr Brown DAC"-equipped DVD receivers (yeah TI/BB DACs were a thing in the past decade) sporting huge multichannel amplifiers.
 
 
*Meaning those who take their own cars to EMMA and IASCA events, even against the people who built their cars (and sometimes they actually win against them, and it's still a plus to the shop that did the work, since the shop gets credit for isntalling everything properly)
 
 
------------------------------------------------------
 
Now, as to your installation specifically, you're going to have to deal with two problems when you permanently install the tablet in your car (and again arguably this is one of the reasons why you need a "pro"): how do you charge it? You could use an OTG and USB hub, then an inverter, but then be aware how easily this can be dislodged. However I've heard of them being installed properly, so again look in DIYMA - there might be kits or at least some ways to manage those problems.

Second, about bypassing the HU - how do you control the volume? You either use something like a UDAC, so it'll have a potentiometer hence a pre-amp output, but then how do you mount that? Again, unless you know what you're doing vis a vis the electronics as well as fabrication, you'd be better off just leaving this alone. Audiophile systems in cars built around a tablet instead of an HU are configured in two ways: either they are just a remote interface for a miniPC installed elsewhere (Google "headless audio server") or they run into a USB DAC. Either way, in both cases they employ some kind of integration processor, which would have otherwise worked on their stock sound system (as I described above) - the only real gain being that the tablet or headless PC+tablet can play FLAC.
 
There are easier ways of going about all this. First, if for example your car has GPS, then just install an integration processor - some can use the stock volume control while others require that you install one that connects to the preamp on the processor (mine can do both, depending on the source - high level inputs can retain the use of the receiver's pot).
 
Second, if you have an older car (still has the DIN slots, or converter kits are cheap and don't really affect the other controls, aesthetically or functionally) but don't care about GPS nor that much for SQ, you can get a proper media receiver - Clarion has one that goes for around $60 on Crutchfield and can use portable storage devices and 320kbps music. This will still have basically proper DACs and output stages, without the hassles of how to charge a tablet or USB cables getting detached. You can still use the GPS on the tablet via the AUX input on the HU if the app has voice commands like in car GPS systems.
 
Third, if you have an older car (still has the DIN slots, or converter kits are cheap and don't really affect the other controls, aesthetically or functionally) but want SQ as well (and again, the option to hook up the tablet to the AUX input if you want to use its GPS), then get the Alpine media receiver (around $200 to $300) and the PXA-H100 processor (around $150; even cheaper on eBay). These work together seamlessly using Alpine's Ai-Net protocol, originally used to control and transmit digital audio from the CD changer. This time the signal goes the other way and not back: digital audio leaves the HU+storage device, goes into the DSP, gets split into the appropriate outputs, then goes into the amps and then the speakers. You also control the processor from the HU itself, unlike integration processors that have buttons on them (which is inconvenient, especially if you already installed it, like below one of the seats) or a laptop (in which case if it's already installed you still have to reach under and plug in the USB cable).
 
Basically, what I'm saying is that bypassing the HU is too much work with too many considerations, and despite what money you'll throw at the DAC, it's not bound to sound that much better, especially if you're still dealing with the problems inherent to sitting off-center in a small space where the tweeters, midwoofers, and subwoofer are far apart from each other mounted on flawed baffles as well as having a high noise floor.
 
 
 
 
 
 
 
 
 
 
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First off, you're better asking in car audio forums for two reasons: safety and if this is also your goal, proper sound quality. I'm going to guess the second is a priority because you are not saying that this is purely for convenience and you're willing to go out and use a DAC and line out converter. I'll address the tablet later and deal with your use of quotation marks up there first - even if you don't want to go as far as I describe, at least you'd get why they are there and what you should be really wary about.
 
Now, here's the reason why there are professionals, or more accurately, pros (who run shops), non-pros* (competitors) : you can install a $10,000 DAC in a car and power it somehow along with equally eyeball-gouging amps and speakers, but in no way have you managed to even scratch the surface of what really matters in a car audio environment. In  sense, car audio is more like pro audio than home audio considering all the tweaking you have to do to minimize the negative effects of the car's cabin as your listening environment. If you have a speaker system at home, you can try this too. Place your speakers directly facing each other, then sit closer to the left or right speaker. Switch on another audio system in another room, like a TV, with its back a wall adjacent to that listening room. Now, replace the speakers, DACs/CDPs, amps. Did the sound get better? Nope, not really, because:
 
1. You're not sitting in a spot equidistant between the two speakers (and in a car your tweeters on the dash can be, what, at least 18inches away from the midwoofer low in the door)
2. You're sitting off-center, in a spot that is not equidistant to both speakers
3. Your speakers are directly firing at each other, with no sense of proper toe-in
 
Now ask yourself: does anyone actually listen that way at home? Have you ever seen a home set-up like that? No, not really, and this is where those "professionals" come in. They will install everything so that instead of throwing money at expensive gear without targeting the acoustic realities in a car cabin, they will allow you to split your money properly on gear and installation. Think of this as acoustic treatments in an audio room at home, except this time you're addressing noise as well as time alignment and phase issues. They will install, at minimum, the midwoofers so that they can be properly dampened and the front of the cone isolated from the rear of the cone inside the doors (and minimize the most basic type of cancellation) and tweeters at an angle to improve the center image and minimize glare for the seat nearer to each side tweeter. Past that, they might install the midwoofers outside the door panel, if not on the kickpanel, getting rid of cancellations caused by the soundwaves from the front of the cone bouncing around behind the interior door trim. The subwoofers also get installed in such a way as to minimize room modes depending on the car, as well as for aesthetics if you want or if you're a tweaker have the amps and processor if you have one installed in such a way that you can easily reach them.
 
Past the proper installation of your speakers, you could work on using a time alignment processor - this allows for a DSP to introduce custom delays for each tweeter, each midwoofer (or midrange and midbass, if you're using a 3-way system in front) relative to each other and  the subwoofer at the back. Installs and time alignment (and other processor settings) done correctly, you can have along the dash properly centered main vocals with every other instrument spread out relative to it as you would on near field monitors, with the subwoofer's output (with the lowest safe high-pass setting in front and lower low-pass for the sub, so all it does is provide the low freq reinforcement for the notes) seemingly coming from the front despite being 4ft in the luggage compartment behind you.
 
Basically, what I'm saying is that it actually is a bad idea to ask about car audio outside of a car audio forum (unless I'm going to intervene), because it is inherently more similar to pro audio or professionally-installed home audio/HT systems. Worse still is asking about car audio in a headphone forum, where many of the regulars with authoritative reputations from high post counts don't even deal with room modes (and some don't even know what that is) by nature of headphone listening, and attribute changes in sound to "burn in" than earpad wear, hence they'll tend to think of lossless and GIGO instead of actually dealing with the acoustics and safety issues. At minimum your processor needs to have some kind of auto-tune using a reference disc, but back then we were manually measuring the response, and then USB mics just made that a bit easier since we can have the real-time analyzer running on a laptop (and we're not even the "pros" who do this for a living, just some people who would rather get stuck in traffic on the ground than pack into a sardine can on the rails above or below). The usual GIGO principle for the signal chain and throwing money at DACs isn't going to address what a proper DSP can - no ESS9023 will perform in a car better than simply addressing the inherent issues. Processors nowadays even take the signal off a factory-installed system's amp (so as not to fess around with  the interface on the dash or lose GPS), using a high-level input with an auto-ranging volume control as in the Alpine processor with Audyssey that I just traded in an older HU+processor for. Even 320kbps through a time alignment DSP on a properly-installed system can sound better than expensive speakers just screwed in wherever they fit playing lossless/CDs.
 
This is the primary problem you are dealing with past the noise floor. Top view shows the different distance to each tweeter, midwoofer, and subwoofer (color coded); side view at bottom shows the height differential (color-coded) in midwoofer-tweeter height, plus the problem with how a sub in the trunk can be reinforced or reduced by cancellation depending on how many paths it takes into the cabin.
 

 
 
 
This is basically what the normal imaging in a car "looks" like: called a "rainbow image," as the driver you have the driver-side of the soundstage image with "bigger" and more up-front instruments vs the passenger side (and vice versa).

 
Using the balance control will only reverse that.
 

 
 
 
 
Here's an image just to illustrate why it got that name.

 
 
Now these are what you need those "professionals" for, unless you can DIY fiberglass.

 

 

 

 

 

 
Of course, yes there are things you have to look out for - not every professional installer is actually "professional" in conduct, nor transparent - they have to run their businesses and if it's a general car audio/electronics shop they are also dealers who have to push their own products. Car audio forums here divide and recombine and repeat thanks to heavy-handed marketing. For someone who doesn't fully understand all these, this is why car audio forums are also important - they will at least explain these acoustic issues better, and best of all, www.diyma.com. While that forum might sound like it's dedicated to  DIY-ers only, the thing is they are less susceptible to marketing since the forum doesn't even have huge ad banners diplaying BeWith, DLS, Hertz, etc. Learn there, and they might be able to point you in the right direction when you have work done on your car - basically, you need to find an installer who is likely to tell you what I already did: split your money between the gear and the installation properly, instead of pushing more expensive $h1t and then just sticking them in there.
 
Over here an Accord once won the "budget" category in an SQ competition using an old Alpine HU+processor, cheap $35 speakers and a $40 subwoofer (from what essentially is a factory that is a bit like Parts Express) along with a counterfeit $40 Alpine subwoofer amp (why they let these compete still escapes me). How did he do that? He basically spent nearly all the budget limit on the receiver+processor, which also had a high-current built-in "V-Drive" amp that needed its own connection to the battery. He then used the internal digital processor to apply crossover and time alignment settings, running the front speakers off the cleaner (and authentic) Alpine HU's amplifier and driving the sub with the counterfeit amp. He undercut the budget limit and still imaged a lot better than the cars one category up with expensive speakers and "Burr Brown DAC"-equipped DVD receivers (yeah TI/BB DACs were a thing in the past decade) sporting huge multichannel amplifiers.
 
 
*Meaning those who take their own cars to EMMA and IASCA events, even against the people who built their cars (and sometimes they actually win against them, and it's still a plus to the shop that did the work, since the shop gets credit for isntalling everything properly)
 
 
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Now, as to your installation specifically, you're going to have to deal with two problems when you permanently install the tablet in your car (and again arguably this is one of the reasons why you need a "pro"): how do you charge it? You could use an OTG and USB hub, then an inverter, but then be aware how easily this can be dislodged. However I've heard of them being installed properly, so again look in DIYMA - there might be kits or at least some ways to manage those problems.

Second, about bypassing the HU - how do you control the volume? You either use something like a UDAC, so it'll have a potentiometer hence a pre-amp output, but then how do you mount that? Again, unless you know what you're doing vis a vis the electronics as well as fabrication, you'd be better off just leaving this alone. Audiophile systems in cars built around a tablet instead of an HU are configured in two ways: either they are just a remote interface for a miniPC installed elsewhere (Google "headless audio server") or they run into a USB DAC. Either way, in both cases they employ some kind of integration processor, which would have otherwise worked on their stock sound system (as I described above) - the only real gain being that the tablet or headless PC+tablet can play FLAC.
 
There are easier ways of going about all this. First, if for example your car has GPS, then just install an integration processor - some can use the stock volume control while others require that you install one that connects to the preamp on the processor (mine can do both, depending on the source - high level inputs can retain the use of the receiver's pot).
 
Second, if you have an older car (still has the DIN slots, or converter kits are cheap and don't really affect the other controls, aesthetically or functionally) but don't care about GPS nor that much for SQ, you can get a proper media receiver - Clarion has one that goes for around $60 on Crutchfield and can use portable storage devices and 320kbps music. This will still have basically proper DACs and output stages, without the hassles of how to charge a tablet or USB cables getting detached. You can still use the GPS on the tablet via the AUX input on the HU if the app has voice commands like in car GPS systems.
 
Third, if you have an older car (still has the DIN slots, or converter kits are cheap and don't really affect the other controls, aesthetically or functionally) but want SQ as well (and again, the option to hook up the tablet to the AUX input if you want to use its GPS), then get the Alpine media receiver (around $200 to $300) and the PXA-H100 processor (around $150; even cheaper on eBay). These work together seamlessly using Alpine's Ai-Net protocol, originally used to control and transmit digital audio from the CD changer. This time the signal goes the other way and not back: digital audio leaves the HU+storage device, goes into the DSP, gets split into the appropriate outputs, then goes into the amps and then the speakers. You also control the processor from the HU itself, unlike integration processors that have buttons on them (which is inconvenient, especially if you already installed it, like below one of the seats) or a laptop (in which case if it's already installed you still have to reach under and plug in the USB cable).
 
Basically, what I'm saying is that bypassing the HU is too much work with too many considerations, and despite what money you'll throw at the DAC, it's not bound to sound that much better, especially if you're still dealing with the problems inherent to sitting off-center in a small space where the tweeters, midwoofers, and subwoofer are far apart from each other mounted on flawed baffles as well as having a high noise floor.
 
 
 
 
 
 

Thanks for the detailed reply.  I apologize for asking my car stereo question here, as I came across this site searching for people who have used tablets as HU's 
 
  I'm looking at the Audison processors for a Tablet/ipod as HU application and Im convinced they would sound superior to anything not using Optical.
 
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