I finally got around to measuring the Mark Levinson system in my 2023 IS350 with a calibrated UMIK-1 Microphone. I measured both the driver and passenger positions, then did a few more sweeps with the bass and treble settings changed just to see what the Lexus controls are actually doing. Figured i'd post it here as others might be curious.
Overall, I'm pretty impressed with it.
I wouldn't call the response from the stereo "flat" because it definitely isn't. There's already a pretty healthy bass shelf built into the factory tuning, but through most of the mids and treble the overall balance is surprisingly good for a factory car system.
For most people I think a really good starting point is:
Bass +1
Mid 0
Treble 0
The +1 bass setting is actually pretty mild. It's only adding a small amount down low, roughly a couple dB depending on the frequency, rather than completely changing the character of the system.
I think +1 bass makes the most sense if you normally listen at lower or moderate volumes. Because of the Fletcher-Munson/equal-loudness effect, our ears become less sensitive to bass as listening volume drops, so that little bit of extra bass can actually make things sound more balanced.
If you tend to listen fairly loud, I could honestly see leaving Bass at 0. The factory tuning already has plenty of low end, and as the volume comes up you don't really need as much extra compensation.
Treble +1 is also pretty subtle. I personally don't think the system needs it, but it could make sense if you like a little more top end or if your hearing has started to roll off at higher frequencies. High-frequency sensitivity generally decreases with age, so some older listeners may actually prefer +1 treble. Obviously everyone's hearing is different.
I wouldn't touch the mid control.
There are some pretty noticeable dips in the measurements, but a lot of them change depending on whether you're measuring the driver or passenger seat. That's a good indication that you're mostly looking at cabin cancellations rather than something you should be trying to fix with the Lexus EQ.
One interesting thing I noticed is that the passenger side gets a little less bass overall than the driver. It's not lower at every individual frequency because the cabin modes move things around, but overall the driver position has roughly a couple dB more low-frequency energy.
There's also some pretty impressive extension down low. There's still a lot of output happening around 20 Hz, which I wasn't really expecting from a completely stock system.
For comparison, I've actually used Spotify's EQ in some of my other vehicles because they had some pretty horrible dips or tonal issues that were obvious enough to bother me. With the ML system, I really don't feel the need to do that. There are still cabin-related peaks and nulls, obviously, but nothing about the overall tuning makes me want to start trying to correct it with a full EQ.
I also checked distortion and it was pretty decent overall. Through most of the range THD was under roughly 1–2% at the level I tested. There was one uglier area around 300 Hz, but I've heard some plastic trim buzz in that region before, so I suspect at least some of that is the car vibrating rather than the speakers themselves.
That's probably the biggest compliment I can give it. It doesn't measure perfectly, because no car is going to, but the underlying tuning seems really well thought out.
For me I'd basically say:
Lower/moderate volume: Bass +1 / Mid 0 / Treble 0
Higher volume: Bass 0 / Mid 0 / Treble 0
Optional: Treble +1 if you want or need a little more top end (or are older)
Beyond that, I honestly don't think it needs much messing with.
The blue Harman curve in the graphs is just there as a visual reference. I'm not suggesting the Lexus should perfectly follow it.
Unfortunately I don't have access to a non-ML car to see the differences.
