A BMW 3-Series gets a multichannel 2-seat upgrade

A few years back, I bought a BMW 335xi GT. I really like the car, but not the audio. The “harman/kardon” system in my BMW should have sounded awesome, but it didn’t. 

The amplifier can generate 100 watts per channel to each underseat 8” flat woofer. The other speakers receive 30 watts per channel. The positioning of the 4” midranges and 1” tweeters up front is excellent. The center channel and rear effects channels are derived by Harman’s Logic 7 upmixer (Harman ended up with Logic 7 when they bought Lexicon). 

However, while it was loud, it didn’t sound great – and I think there were a few reasons. 

  • The center speaker was harsh-sounding. The midrange lacked any low-pass crossover filter, and the tweeter had the standard series capacitor (which filters at the rudimentary 6dB/octave). So the sound from the most critical speaker in the car wasn’t that good.
  • The center channel wasn’t loud enough to create a true center, so each front-seat passenger got their own center image, biased toward their side of the car. This may have been the goal, or maybe Harman didn’t want to drive that center hard enough since it didn’t sound that great. 
  • The midbass was lacking. This was due to the unusual decision to ask the 4-inch midranges to play down to 80 Hz, where the underseat woofers come in. Previous BMW models didn’t do this, and subsequent BMW models didn’t do this – it seemed to be something they tried in the 3-Series, and gave up in the 4-Series. Regardless, the 80-160 Hz octave measured very weakly. 

When I bought the car, I was just beginning to learn about upmixer technology – but it was my first car with a center-speaker grille, and so I really wanted to try it out. So we installed a multichannel system into my car using a discontinued processor with Dolby Pro Logic II. For reasons which still escape me (and which are not mentioned in the manual for this product), the Dolby PLII would not turn on for any inputs other than the Toslink SPDIF input. In my car, this was an easy fix – I used a gateway which converted MOST 25 into Toslink. 

So, that Dolby system was pretty good, but it wasn’t great. It certainly wasn’t nearly as good-sounding as the best upmixer upgrade I’ve been involved with – a 2017 Range Rover with Meridian (those cars use Dolby Pro Logic II or DTS Neo upmixing, and that amplifier/processor did an amazing job). I think some of it was the implementation of the Dolby PL II function, some of it was the center speaker I used (a passive two-way coaxial), and some of it was the limited audio processing available in that older device. 

I eventually removed that system, so I could test other products in a traditional one-seat arrangement – but I always wanted to try again, so recently I designed a new system. I was working with Elettromedia on a training contract at the time (now I’m a Technical Product Marketing manager with the company), so I designed a system using Audison products. I planned on re-installing my h/k processor/amplifier, but I couldn’t find it anywhere. I finally bought a replacement online, and that wasn’t cheap – don’t misplace $1200 OEM amplifiers! (Fortunately I found one used for much less). 

My system used all 9 channels out of the h/k amplifier:

  • Center
  • Front Left and Right
  • Underseat Left and Right Woofers
  • Rear Doors Left and Right 
  • D-Pillar Surrounds Left and Right

We ran all of these into an Audison bit Virtuoso. The Virtuoso has 12 channels in, and it can handle voltages up to 32VAC, so we didn’t need any external attenuation of the bass channels. Then we split those input channels up like this:

  • Center High and Low (active 2-way components)
  • Front Door High and Low (active 2-way)
  • Rear Doors High
  • D-pillar Effects (passthrough)
  • Underseat Woofers Band-passed as midbass (with a higher crossover point)
  • Subwoofer Low

The cabin speakers were all Audison Prima BMW drivers. While these speakers are in the Prima line, they are higher in performance than many of the other Prima speakers. They have cast aluminum frames on the midranges, as well as neodymium magnets and waterproofed cones. There are 2” voice coils on the woofers with aluminum formers, and the tweeters have 29mm domes (this is the largest snap-in BMW tweeter on the market). The drivers themselves are really impressive, but because they were intended for OEM amplified use, the crossover is a basic 6dB design, and this limits their potential performance – you can get higher performance by going with a steeper crossover slope in a true two-way configuration. Since we went fully-active on the midrange/tweeter crossover handoff, we overcame this limitation – and I urge anyone who’s doing a high-performance BMW system to do the same!

We retained the OEM rear-effects speakers in the D-pillar – fidelity is not crucial with these speakers, and very little power is sent to them. 

The subwoofer is an APS10D dual-voice-coil driver in a sealed enclosure.

For amplification, we used three Audison SR amplifiers for a total of 13 channels:

  • Two SR 4.300 85×4 amps
  • One SR 5.600 75×4/550×1 amp

The amplifiers and the Virtuoso processor, along with a fused power distribution block from the Connection line, are in a rack based on the Musicar bolt-in amp rack for the F3x BMW platforms. The basic design was modified by Pierce Barrett, who also did the rest of the electronic installation (Patrick Rollins assisted with the speaker drivers).

The four 75-watt channels power the rear surrounds and the rear doors. The eight 85-watt channels power the front mids and tweeters (actively), the front center mid and tweeter (actively), and the underseat woofers. We used APS BMW-2 2-ohm underseat woofers, so the SR amps actually deliver 130 watts RMS to each woofer. The sub gets 550W from the SR 5.600. 

When I fired this system up, it took me a bit of time to get the levels sorted out, but once I did, I was really surprised at how good the system sounded with the h/k amp as the source. One improvement was the fully-active front end – my previous system had not been fully active, and this was a definite performance upgrade!

When tuning it, I used the new bit Virtuoso 3.0 feature set, including phase equalization on the outputs, to get the final results. I also used the Educar Test & Tune app, which has Left Center and Right Center test tones. These are essential when setting the level of a center channel – too loud and it becomes a black hole that eats all the instruments, but too quiet and you split the center image in two. 

One of the things I have learned is about cancellations. We get phase cancellations whenever one sound arrives at two different times from two different speakers. That can happen when front and rear speakers are different distances away. It can happen when left and right speakers are different distances away, and the recording places the sound in the center and routes that identical sound to both left and right. It can happen at a crossover point in the transition band, where both the high-passed speaker and the low-passed speaker are playing the same note. 

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We use delay to address all of these problems in an active one-seat system. Once we switch to an active upmixed system, we can’t use delay to address most of these issues without ruining the two-seat stereo effect we are trying to deliver. I used the phase equalization in the bit Virtuoso to address these issues, and that was another huge advantage this system had over the Dolby Pro Logic II system – I got better up-front bass, more cohesive midbass, and better imaging by using tools which most DSPs still don’t offer. 

More and more premium vehicles have 2-seat presentations – we can upgrade them more easily than we might think!

Takeaways:

– In upmixed systems, the center is the most important speaker. Use the best speaker you can, and go active whenever possible. 

– The Audison BMW speakers are capable of great performance in an active configuration.

– The BMW h/k amp is capable of passing great sound to your system (as long as you handle the bass channel voltage properly)!

– For best results with an upmixer, a powerful DSP is needed, with phase equalization as well as parametric equalization. 

– The Educar app helps set the levels of upmixed center speakers easily.