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Old 07-31-2005, 02:09 AM
el_duderino el_duderino is offline
Join Date: Jul 2005
Location: Portland OR
Posts: 499
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In-depth analysis of 2005 X5 "DSP" Nav audio system

Hi there. My name's Ken, and I own a car audio shop in Portland, Oregon (avincar auto sound, we're at ). A forum member just had us upgrade his X5 audio system. I'll let him tell you about the factory system and his experience of our upgrade to it (hopefully that's all positive, but I hope that if anything comes up, he tells you and us: )

This post is intended to tell you about how the OEM audio system works, and what's complicated about it, and how we worked with it. THIS IS NOT A DIY POST. One, I didn't do the wiring personally (our installation manager did) and can't tell you wire colors anyway. Two, I know there's a lot of variation from system type to system type, so I might not describe the car you're working with anyway. Three, I do this for a living, and while I don't mind helping as much as I can over the internet (I advise many people on an Acura forum about A/V questions), this is a very complicated process, and - no offense meant - I frankly don't want to take reponsibility for your results.

OEM system basics

So first off, this system is a Nav system with a changer and Sirius, and there is a menu line for "DSP". HOWEVER, there is no digital cable out of the changer. Apparently that means that it's some sort of "quasi" DSP system.

The signal that comes out of the HU to the OEM amp is two-channel, and fixed in level. That means that when we manipulate the Volume, Fader, and Balance controls, nothing changes on this signal. Apparently there are also data lines from the HU to the amp, and these control the tone controls inside the amp. (We did not test these preamp signal wires for frequency response, nor did we test to see if the seven-band EQ in the HU affected the signal on these wires. More on this later.)

The amplifier has either twelve or fourteen channels of output. That's right - fourteen.

Front tweets in the mirror sails (2). Front mids in the front top of the dash (2). Front mid-bass in the doors (2). Rear mids in the rear doors (2). Rear midbass in the rear doors (2). And two dual-voice coil "subs" in the right rear corner (2 or 4 - didn't take the amp apart to find out).

Frequency distribution and equalization

The front tweeters play from 5000 Hz and up. There is a slight amount of EQ "bump" at about 16K, but not a lot.

The front mids play from 5K down to 800 Hz. They have a slight EQ bump at about 1K.

The front midbass play from 800 Hz down to about 80 Hz. Lot of midbass EQ boost.

The rear midrange plays from 5K down to 800. The rear midbass plays from 400 to around 50 (it *seemed* to play lower than the front midbass according to our analyzer, an NT Instruments Acoustilyzer). There is a one-octave hole from 400 to 800, and since there are no rear tweeters, there is no significant output above 5K in the rear doors.

The subs play from 80 and down. While there doesn't seem to be much in the way of obvious subsonic filtering, there does seem to be an EQ "bump" around 65.

Design flaws

The audio system bears all the marks of having been designed by a committee of electrical engineers - in that it's a very complex and highly engineered train wreck : ) The speakers look expensively made (although in Hungary, not Germany) and the amp must have cost a small fortune. However, sound quality was horrid in both my opinion and the customer's.

The 6" midbass in the doors have a mechanical resonant frequency of 50 Hz. This allows them to play pretty low - in the front doors, lower than they are allowed to play.

The "subs, on the other hand, are not only trying to play through 3mm of ABS panel and 20mm of felt noise-padding (as has been pointed out here by many, many posters) - they also have a mechanical resonant frequency of 80 Hz! They mechanically start rolling off at 12dB/octave AT THE LOWPASS CROSSOVER FREQUENCY! (Translation - weak and thin bass.) The woofers look well made, but poorly designed for this application.

All the speaker voice coils are 8 Ohm impedance (nominal, measured with an impedance meter, not an ohmmeter). Why use 8 Ohm speakers in a 12V electrical system in this design is beyond me. It means you have 1/2 as many watts with the same electrical parts in the amplifier. If you upgraded the speakers to 4 ohm, you *should* get twice the power - IF you can figure out what speakers to use.

Upgrade issues

Well, the first issue is that VERY few manufacturers, if any, make speakers that correspond to the OEM speakers in size and function. 2" cone mids are almost unheard of (at least by me). If you wanted to bolt in new speakers and have them play off of the OEM amplifier, you would have a tough time covering all the frequencies. This is why some of the posters here have put in new tweeters and new midbass, but have continued to use the OEM midranges.

The second issue is that the signal to the rear doors is NOT full-range - it has two huge holes in it (400-800 Hz, and 5kHz and up).

The third is that the "preamp" balanced signal from the HU to the OEM amp does not change with volume - it's more like the output on the back of a home CD player than it is the output of an aftermarket car CD player. So you can't run this signal straight into an aftermarket amp.

Also, there ain't much room for amps.


Well, the first option I'm going to mention is a JL Audio Clean Sweep - tap it into the fixed line out from the HU to the OEM amp. This has pluses and minuses. A plus is simplicity (compared to what we did below). A minus is that your fader and your steering wheel volume controls are all useless afterwards, and I believe that your OEM 7-band EQ is as well (but I did not verify this). If you are working with a shop that's not too good with theory, this might not be a bad choice (if you can stand losing all that functionality) because the second option may kick their butts.

The second option is to take the various channels of output and run them into certain high-voltage Line Output Converters and then sum their outputs together to get a full-range response (as SIM did with janix). We did this. This approach has pluses and minuses too.

The pluses include retaining the OEM EQ and the steering wheel controls (but probably not the fader). The minuses include requiring some skilled troubleshooting of RPM-associated "alternator whine", addressing the resulting frequency response curve (which looks like the roller coaster at Coney Island, and NOT just because of the BMW equalization, no matter what anyone says), and probably purposely losing the OEM fader.

Why lose the fader? Because IF you go with rear speakers (some of us believe that rear speakers are a Commie plot, but many of you will ignore me on that one), then the OEM amp's output to the rear speakers is unsuitable - it has those two huge holes in it. Any speaker connected to those output signals would suffer from the same problem. Garbage in, garbage out.

So our approach to this car is to interface with the outputs of the OEM amp, re-combine the audio signals so that we can use midrange-tweeter components instead of the three-way setup that BMW uses, then address the frequency response issues with a parametric EQ, and THEN install new amps and speakers (and we take the front output and split it to both front and rear, and put a fader knob in the ashtray).

The OEM graphic EQ in the HU just doesn't give us enough flexibility to correct the response, which is screwed up when you "sum" the signals back together. In the stopbands of the outputs of the crossover, the signals are out of phase with each other to some degree, and the result is dips and peaks in the response around the crossover points that do not correspond to the predicted response from looking at individual response curves. We also use the EQ as a line driver because the LOC outputs aren't as strong as we'd like, and we don't want to gain up the amps in order to avoid noise (a bugaboo which we finally have eliminated with this car (knock on wood)).

So what we did was put silk-dome tweets with a low resonant frequency in the OEM midrange dash locations, kill the mirror-sail tweets, and install 6.5 mids in the midbass spots. Since the tweets play down to 2500 Hz with authority (and play more in the stopband of the passive crossover), the vocalist is firmly and solidly elevated into the windshield. With metal-dome or harder dome tweeters, which are crossed over an octave higher (usually 4500), this effect is lost. I want a good strong center-forward image over metal-dome tinkliness everytime. We then put a 10 in the back corner and some amps under the load floor (kept the spare, no visual mods).

Anyway, I hope this made sense - my apologies if it doesn't - and I hope that I can answer anybody's questions, which I also hope you feel free to ask. Use the e-mail feature - I probably won't check PM's too often.


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