By Ken Ward
“What’s an upmixer? It’s a piece of software implemented in a DSP that’s designed to turn a 2-channel stereo signal into a multichannel stereo signal. This has nothing to do with watching movies. It is designed to provide similar imaging in all of the listening positions in the car.
If you’re working on a car with an upmixer, you can save yourself a lot of hassle by retaining the factory amp and the original signal processing.”
–Andy Wehmeyer, Audiofrog, in his 2016 Dallas KnowledgeFest class
We at Musicar Northwest recently met a client with a 2017 Mazda 6 with Bose Centerpoint audio. The Bose system was pretty well conceived. Front midrange and tweeter speakers left and right in the top corners of the dash, sharing left and right amp channels, and there was a center speaker as well with its own amp channel, all fed by the Centerpoint upmixing processing. (Since a center speaker is required by upmixers, when we see one, we need to check for the presence of a factory upmixer).
Woofers were in the left and right doors, powered by their own amp channels. Rear door speakers and small rear effects speakers rounded out the speaker complement (the rear effects speakers were on a single shared channel).
The client wanted better detail and tonality, and was hoping that we could supply that with some speakers he already owned, which had come out of his previous vehicle. The sizes and types really didn’t match up with his new car, and I couldn’t guarantee that his speakers would sound better off of the heavily equalized Bose amplifier.
“So what would you do?” he asked. We proposed leaving the factory amp to serve as a pre-amp/upmixer and adding a multichannel amplifier/processor and retaining the 5.1 sound. The added amplifier would improve the per-speaker power while still using the processed, upmixed signal from the Bose factory amplifier/processor. The new MATCH amplifier’s built-in DSP equalization allows us to control each speaker’s response better. This is a technique which was the topic of a KnowledgeFest class presented by Andy Wehymeyer and Jay Oliphant in 2016, and we learned a lot about this approach at that class.
We selected Audiotex Fischer MATCH 86DSP, with 6 discrete channels in and 8 amplified channels out (it also has a 9th preamp channel, which we did not use in this application). Based on our measurements, we believe the Bose amp provides around 25 watts per channel, and around 40 watts to the woofers. This amplifier is providing 55 watts per channel, and 70 watts to the woofers, so we are confident that we delivered a tangible improvement in dynamics.
We ran the left and right dash, left and right bass, center, and rear effects signal from the Bose amplifier/processor into its 6 channels. This allowed us to keep the upmixed signals isolated, so the 5.1 effect is retained. We left the rear door speakers in place, controlled by the in-dash fader, for when the rear seats were occupied.
We didn’t have to use crossovers or time-delay settings in the amplifier. Tuning it was much easier than with most single-seat systems we install. We used the upmixer test tracks from Andy Wehmeyer’s class to set the level of the center, and we equalized the left speakers, the center speaker, and the right speakers using his recommended technique. We found that, counterintuitively, to get a true center image we needed to increase the level from the center by about 6dB. Doing that created some sounds we didn’t like at certain notes, and we used the EQ to control those.
There are 12 speakers in that car. We improved the sound from 10 of them significantly, and with a lot less shop time and vehicle disassembly than speaker installation requires. We also improved the sound of the multichannel upmixed system without defeating it.
We use this approach as what we call a “Premium DSP Upgrade.” We amplify and enhance stock premium-sound speakers without replacing them. We see this as being a material part of our business in the future, and it fits our model of continually improving our technical offerings to our clients.
We could have done this same upgrade in a more complex and traditional scenario, replacing the speakers and the amplification, while retaining the OEM processing. We have done this already in several vehicles, and we have also started adding it with aftermarket upmixer processors (unfortunately, at the moment there is only one aftermarket processor available in the US to my knowledge).
Wehmeyer’s detailed information on this topic, along with test tracks, are available to professionals through Educar’s online resources at no cost. Contact them at educartraining.com.
Ken Ward is the founder of Educar Training and Co-owner of Musicar NW, Portland, OR