Cotinental Head Units

[bmwman91]

Yeah, I do plan on running an amplifier. However, this head unit does not have pre-amp outputs, so I'd have to get a converter or an amp with one built in. I've read that there is not that big of a difference in sound quality. I'm not really an audiophile, so I don't know that I could tell.

The sound quality difference between converting speaker level outputs and pre-amp outputs is going to be negligible in most cases. Sure, if you hooked them both up to a distortion analyzer, the pre-amp outputs would (probably) be cleaner. But, the final signal-to-noise ratio that reaches your ears is going to be dominated by engine and road noise. That extra 10dB (or however many) of noise in the speaker level outputs is going to be swamped by 60dB or more of noise from the fact that you are in a moving car. It's not worth going nuts on hi-fi gear unless you plan to really go nuts with sound deadening first. Even then, outside of a parking lot with the engine off, you are unlikely to hear a difference between the two outputs.

If you do use speaker level outputs, obviously use a level converter or find an amp with built-in conversion (I vote for the latter, it's one less piece of hardware that way). Run the signals with some twisted pair cat5/6 cable, with each channel occupying a twisted pair (so front left + and front left - on one twisted pair, front right + and front right - on another, etc). It is a pseudo-differential signal, and the twisted pairs help a lot with ensuring that all the EMI the lines pick up is common-mode which will then be rejected at the other endpoint.

At this point, I would go with whatever option looks the most OEM, because sound quality on basically all head units is going to be about the same. I have taken apart a ton of them, and they all use the same components (not terrible, not great, just OK for the application). Literally everything you read in the specs for head units is marketing BS and just ignore any and all numbers you see because they are either lies or just don't matter. Also consider sound deadening the entire cabin (floor, doors, rear quarters, sunroof, rear bulkhead, etc). That is going to do more for your signal-to-noise ratio than anything. I recommend Damplifier by Second Skin, followed by a covering of 1/8" thick closed cell foam. That's what I did before my build and it was a solid choice.

Here are some bad ideas for you to noodle on lol.
Original build:

http://www.r3vlimited.com/board/showthread.php?t=170725

Updates to build:

http://www.r3vlimited.com/board/showthread.php?t=339298

(it may be possible to retrofit one of my pre-amp boards to the Continental HU, but I'd need to see the internals first, if you are interested)

[scabzzzz]

Jesus dude, that might be the best audio related post I've ever read on here. Using CAT5/6 is super interesting to me as a network engineer. Cheers

[earthwormjim]

Jesus dude, that might be the best audio related post I've ever read on here. Using CAT5/6 is super interesting to me as a network engineer. Cheers

CAT5 doesn't work quite as well in most audio applications for noise cancellation, it's not better than properly shielded cable, but I would say it is better than a lot of the twisted audio cabling you might regularly buy. Copper construction, lots of twists, each pair is properly impedance matched, high strand counts so good use of the conductors.

In networking, the whole system is perfectly balanced, so each twisted pair carries an exactly opposite signal of exactly the same magnitude, and each pair has the exact same line impedance, and the amplifiers used to send the signals are identical. Which yields excellent noise rejection. You really have two identical opposing signals.

Car stereos are usually not balanced, you never have equal opposing signals, so the noise rejection isn't that great. But it's typically good enough, especially in a car, with its relatively short wire runs. If you are using differential signaling or balanced audio, then even better, Cat5/6 is great since its designed for balanced signaling. Ultimately it's a bunch of twisted copper wires, what else could you ask for (besides a shield)?

[george graves]

Also consider sound deadening the entire cabin (floor, doors, rear quarters, sunroof, rear bulkhead, etc).

Also, but quality stuff. I read great reviews of "E-dead" from Elemental Designs. The stuff out-gasses so much, that I have a greasy constant film on my windows. It's so annoying. In bright sun, it's super annoying, but even worse, in the winter, it attracts waters! So hello constant foggy windows!

I'm going to pull it all out, and not even replace it. Wasn't worth it.

[bmwman91]

Jesus dude, that might be the best audio related post I've ever read on here. Using CAT5/6 is super interesting to me as a network engineer. Cheers

Haha, the nomination is appreciated but I have definitely seen cleaner installs on here by Luke and others. I might be the only one that drew out pretty looking block diagrams though lol.

CAT5 doesn't work quite as well in most audio applications for noise cancellation, it's not better than properly shielded cable, but I would say it is better than a lot of the twisted audio cabling you might regularly buy. Copper construction, lots of twists, each pair is properly impedance matched, high strand counts so good use of the conductors.

In networking, the whole system is perfectly balanced, so each twisted pair carries an exactly opposite signal of exactly the same magnitude, and each pair has the exact same line impedance, and the amplifiers used to send the signals are identical. Which yields excellent noise rejection. You really have two identical opposing signals.

Car stereos are usually not balanced, you never have equal opposing signals, so the noise rejection isn't that great. But it's typically good enough, especially in a car, with its relatively short wire runs. If you are using differential signaling or balanced audio, then even better, Cat5/6 is great since its designed for balanced signaling. Ultimately it's a bunch of twisted copper wires, what else could you ask for (besides a shield)?

I agree that properly shielded wire is likely to be better than twisted, even with a single-ended signal. The problem is the "properly" part.

I have bought and disassembled numerous RCA type cables found online and in stores, cheap and relatively expensive, and it is ALL shit. It is either shielded with aluminum foil plus a scrawny bare conductor inside of it, or just a cheapo wrapping of copper strands with big voids and gaps. I ended up building my own cables from some Canare stage-grade mic cable since it actually has specs available and the copper braided shield is guaranteed to have >95% optical coverage with a maximum gap diameter of 100 microns (IIRC) which is perfectly capable of blocking the RFI in a car. Best of all, it is under a dollar per foot, and the burly Canare 1/8" & RCA connectors are super tough...I built multiple runs of cables for my car for like $30 and they will last forever.

Strictly speaking, the speaker-level outputs from HU's are bridge tied loads, rather than true differential signals, as you note. There is some small DC offset between the channels, and the gains are not perfectly matched so amplitudes differ between sides of the pair. But it is more than close enough to a differential pair to work well if you are sending the signal pairs to a device with differential inputs inputs and high CMRR.

Also, but quality stuff. I read great reviews of "E-dead" from Elemental Designs. The stuff out-gasses so much, that I have a greasy constant film on my windows. It's so annoying. In bright sun, it's super annoying, but even worse, in the winter, it attracts waters! So hello constant foggy windows!

I'm going to pull it all out, and not even replace it. Wasn't worth it.

Crap, that sucks. I went with Damplifier by Second Skin Audio. It had a little bit of a funky smell for a month or so, but I did not have crap getting deposited on windows or anything. Yikes! It is a butyl rubber base with thick aluminum foil facing. I covered it all with some 1/8" closed cell foam after installing.

[4tDX]

The sound quality difference between converting speaker level outputs and pre-amp outputs is going to be negligible in most cases. Sure, if you hooked them both up to a distortion analyzer, the pre-amp outputs would (probably) be cleaner. But, the final signal-to-noise ratio that reaches your ears is going to be dominated by engine and road noise. That extra 10dB (or however many) of noise in the speaker level outputs is going to be swamped by 60dB or more of noise from the fact that you are in a moving car. It's not worth going nuts on hi-fi gear unless you plan to really go nuts with sound deadening first. Even then, outside of a parking lot with the engine off, you are unlikely to hear a difference between the two outputs.

If you do use speaker level outputs, obviously use a level converter or find an amp with built-in conversion (I vote for the latter, it's one less piece of hardware that way). Run the signals with some twisted pair cat5/6 cable, with each channel occupying a twisted pair (so front left + and front left - on one twisted pair, front right + and front right - on another, etc). It is a pseudo-differential signal, and the twisted pairs help a lot with ensuring that all the EMI the lines pick up is common-mode which will then be rejected at the other endpoint.

At this point, I would go with whatever option looks the most OEM, because sound quality on basically all head units is going to be about the same. I have taken apart a ton of them, and they all use the same components (not terrible, not great, just OK for the application). Literally everything you read in the specs for head units is marketing BS and just ignore any and all numbers you see because they are either lies or just don't matter. Also consider sound deadening the entire cabin (floor, doors, rear quarters, sunroof, rear bulkhead, etc). That is going to do more for your signal-to-noise ratio than anything. I recommend Damplifier by Second Skin, followed by a covering of 1/8" thick closed cell foam. That's what I did before my build and it was a solid choice.

Here are some bad ideas for you to noodle on lol.
Original build:

http://www.r3vlimited.com/board/showthread.php?t=170725

Updates to build:

http://www.r3vlimited.com/board/showthread.php?t=339298

(it may be possible to retrofit one of my pre-amp boards to the Continental HU, but I'd need to see the internals first, if you are interested)

I've spent some more time reading through all this goodness and I think I'm ready to ask semi-intelligent questions...

In your build you went with a external converter (external to the amp) so that you could run the lines through a crossover? Is this because you were driving the tweeters directly from the amplifier? Typically these would just pull the mid-range/woofers speakers lines such as how it is wired stock in the E30 would they not?

I'm guessing the channels are set to 60W for the woofers, what did you set them at for the tweeters? I see that the amp can run 60W or 120W, but the specs on the tweeters recommend 90W w/ a peak of 150W.

I'd still like to stay away from a sub as I currently daily my E30 and make full use of the trunk. If I ran a similar setup without the sub, would that be a big hit to sound quality?

Again, if I were to run this setup what would be your thoughts (or others) on continuing the drive the rear speakers as well?

On the follow up thread, the pre-amp basically just provides additional noise reduction?

Lastly, you seem like the kind of person to measure this ;), did you measure the in cabin noise before and after installing the sound proofing? Its been some years since I researched this, but I thought I recall minimal results from people's attempts to sound proof the cabin.

Thanks again for all the input.

[george graves]

I went with Damplifier by Second Skin Audio. It had a little bit of a funky smell for a month or so, but I did not have crap getting deposited on windows or anything. Yikes! It is a butyl rubber base with thick aluminum foil facing.

Yep - the eDead was the exact same looking thing - complete with AL foil backing and fancy printing. But apparently the cheap stuff(this wasn't that cheap) isn't butyl, as much as it is a knock-off petroleum product.

PS - Don't ask me the difference, I was working 40 hours a week when I took college chemistry - it was my only nap time :yawn:

[4tDX]

Here another NA supplier with about the same cost as the German suppliers. They also have the VDO option which is blue lit instead of orange.

http://www.egauges.com/ProductDetail...de=TR7412UB-OR

[bmwman91]

I've spent some more time reading through all this goodness and I think I'm ready to ask semi-intelligent questions...

In your build you went with a external converter (external to the amp) so that you could run the lines through a crossover? Is this because you were driving the tweeters directly from the amplifier? Typically these would just pull the mid-range/woofers speakers lines such as how it is wired stock in the E30 would they not?

I'm guessing the channels are set to 60W for the woofers, what did you set them at for the tweeters? I see that the amp can run 60W or 120W, but the specs on the tweeters recommend 90W w/ a peak of 150W.

I'd still like to stay away from a sub as I currently daily my E30 and make full use of the trunk. If I ran a similar setup without the sub, would that be a big hit to sound quality?

Again, if I were to run this setup what would be your thoughts (or others) on continuing the drive the rear speakers as well?

On the follow up thread, the pre-amp basically just provides additional noise reduction?

Lastly, you seem like the kind of person to measure this ;), did you measure the in cabin noise before and after installing the sound proofing? Its been some years since I researched this, but I thought I recall minimal results from people's attempts to sound proof the cabin.

Thanks again for all the input.

The 6XS active crossover cannot handle a bridge tied load (BTL) input as it does not have a differential input stage. Hence it can only accept a single-ended input. So the LC6i line level converter is there to take the CD43's speaker level BTL outputs into its differential input stage and provide a clean single ended output for the 6XS. Note that this was somewhat unnecessary. I could have just used one of the signals from each speaker level pair and made a nice RCA cable with good shielding and run it back to the 6XS, and it is most likely that there would not have been any EMI/noise issues with that. But, I wanted to run the BTL "differential" pairs instead. Because OCD.

Why the 6XS? This gets into system fundamentals. There are two main routes that you can go: active or passive crossovers. Each has pros and cons.

Passive crossovers are the original / oldest way to filter low / mid / high frequency signals for a multi-driver system. If designed well, they will sound great.
Pros:
- In general, less expensive than active crossovers
- Less TOTAL space occupied than active crossovers (but they do impose space issues, described in cons)
- Often sold with mid+tweeter kits, so no tuning/design is needed since they were designed for those drivers
Cons:
- The crossovers themselves are bulky and usually need to be close to the drivers...not gonna fit into E30 kick wells!
- No tuning flexibility
- Crossovers built with quality components (poly or wax caps, air core inductors) are huge and expensive.
- Higher amplifier power requirements per channel
- Greatly reduce the damping factor of the amplifier's output (less cone control / increased distortion, mostly at low frequencies)

Active crossovers are by no means new, but they did not really cone into their own until integrated circuit technology was on the scene. If designed and tuned well, they will sound great.
Pros:
- No bulky crossover modules to stuff into kick wells
- Flexible tuning, so you can pick crossover frequencies and pre-amp gains
- No additional impedance added to amplifier outputs since they are in the signal chain before the power amp
Cons:
- You are going to need a larger amp (more channels) or an additional amp. A left + right, mid + high system (called bi-amp'ed) will need amplifier 4 channels. Sub(s) will mean 5 or 6 channels (left + right, low + mid + high, called tri-amp'ed).
- Probably more expensive than passive since you need the active crossover and more power amp stages.

I opted for the active system because I think that it has technical advantages and it allows me more tuning flexibility. You cannot change the crossover frequencies on a passive crossover (well, you can, it is called building a completely new one).

All of the drivers in my system are ~4 Ohms, so the amp can deliver up to 60W to the mids & tweeters. The stated power specs on drivers are not what they require, just what they can handle. The power specs are useful for determining the maximum sound pressure ("volume") that can be created. Say a driver has a sensitivity rating of 90dB SPL (deciBels Sound Pressure Level) @ 1W. How much juice do you need to hit 111dB? That's only a 21dB increase, right? Well, it is going to take 128W of power! Power increases in an exponential fashion as you increase deciBels (which are a logarithmic term, the inverse of an exponential). I won't get into the math, but what you need to remember is that every 3dB increase in SPL requires double the power. So for our driver, 93dB takes 2W, 96dB takes 4W, 99dB takes 8W, 102dB takes 16W, etc. The other big item to remember is that we are talking about RMS (root mean square) power here, not peak power. Think of RMS power as steady-state or continuous power output, and it is going to be the most important figure rather than peak power. Always make sure to be clear on whether a manufacturer is stating RMS or peak power output specs (they often give a peak number without labeling it because it looks more impressive, but the equipment can only do it for very brief amounts of time).

You want a subwoofer. Yeah it eats trunk space, but you need it if you care about sound quality. It is not about shaking the mirrors off of the car. It is about sound quality, and bass is absolutely an important part of it. There are 3 frequency bands of importance in audio...lows, mids, and highs. They span 3 decades (factors of 10) of frequency. 20-200Hz, 200-2000Hz and 2000-20000Hz. As far as human hearing goes, and convention in the audio world, low, mid and high ranges are more commonly thought of a being 20-100Hz, 100-1500Hz and 1500-20000Hz. Whatever the case, the low frequencies may seem insignificant since they only span like 80Hz, right? Hell, shouldn't the tweeters be the real power hogs since they need to produce like 93% of the stuff we hear (18500Hz out of the total 20000Hz)?!?! Nope, not the case. The bass, by far, demands the most power. More than the mids and highs combined, actually. The amount of air that you need to move to produce a frequency gets larger really fast as your frequencies get low. It is related to the ratio of wavelength of the frequency and the driver diameter, and wavelength gets longer really fast as you get down into lower and lower frequencies (hence, driver diameter goes up really fast). On top of that, big drivers like subs are typically less power efficient than mids and tweeters, meaning even more power is needed to keep up.

Ultimately, you want all of the drivers (lows, mids and highs) to produce the same SPL when operating together so that you have a flat frequency response. Say your sub is rated at 84dB @ 1W and the tweeters are rated at 93dB @ 1W. You will want to reduce the gain on the tweeter channels by 9dB, or increase the gain on the sub channel by 9dB, or some combination thereof (+4dB to sub, -5dB to tweeters). Either way, the net effect is that you will be delivering 8X more power to the sub (9dB / 3dB = 3 => 1W * 2 * 2 * 2 = 8W). This is stuff to consider when selecting components since you will need to adjust this, and it is almost always going to be easier to reduce gain than to increase it since increasing it means you will run into power limitations sooner.

On the updated build, I developed the pre-amp board because it should have less noise than the output from the speaker level amp. So yes, you are correct there.

I did not measure the noise SPL in the cabin as a result of the sound deadening install. However, I would guesstimate that the noise SPL on the highway went from 70dB to 60dB, which to the human ear is about half of the loudness (a 10dB SPL change is perceived as a doubling or halving in loudness). The sound deadening does not do all that much about lower frequency noise in the cabin, but it made one hell of a difference in the mid and high frequency noise. Similar to power requirements of speakers, sound deadening/absorption requires more and more mass as the frequency gets lower.

Lastly, keep in mind that SPL refers to sound PRESSURE, not sound power. They are related, but different. Most things are in terms of sound pressure, which is just as well since what we experience as sound is pressure waves in air. Sound power is a specific term that is a function of sound power squared through a virtual, enclosed volume of space. There are all sorts of other rules and definitions for calculating sound pressure at a distance from a source, interactions in multi-source systems (which a car system is), effects of the physical objects adjacent to drivers and other nitty gritty things. Most of that stuff is completely beyond control in the car environment, so don't worry about it.

Phew. That was a hell of a post. Hopefully it answered more questions than it created! I am sort of sunburned from yard work all weekend and full of beer now, so forgive spelling + grammar errors lol.

If you want to learn, read everything in the Beginner's Luck section:

http://sound.whsites.net/articles.htm

It taught me a lot of what I know when I was first starting out. The fundamentals and more are all there! I started out knowing jack about any of this, but years of reading on the web (the diyaudio forums are also a good resource) slowly got me up to speed on stuff. You'll get there.