For each of the readings, I used the ‘Sound Meter’ app as before
BHPian adithya.m.bhat recently shared this with other enthusiasts:
Thanks to Kelly66 for igniting my curiosity. Cabin insulation was something I totally missed evaluating earlier, and his comment made me realize that I had overlooked a rather important aspect. Initially, I thought I’d just record the values one morning and share them. But then it hit me — why stop there? There was a chance to make this more detailed, more intricate, and of course, more technical! How could I miss out on such an opportunity?
Theory:
I began thinking through how to approach this in a structured way. As some of you rightly mentioned earlier in this thread, cabin insulation isn’t only due to the acoustic glass used in the windows, but a combination of materials and design choices that insulate the entire cabin. So it became clear that I wasn’t evaluating just a component — I was looking at the whole vehicle. I still wasn’t sure how best to go about it, so I decided to narrow it down to parts I could easily control: the windows. Rolling them up and down gave me a straightforward way to introduce variation. It also meant I could collect data for different insulation states: one with all windows rolled down, another with all but the driver’s rolled up, and finally, with everything fully sealed.
Next challenge — I needed a consistent and reliable source of external sound. This part wasn’t easy. I initially considered recording noise in a busy traffic area, but the unpredictability and lack of control ruled that out quickly. I thought about asking a friend to idle or rev an ICE vehicle next to mine — but again, it needed coordination and time. That’s when my wife pitched in with an idea: “Why don’t we play some white noise outside using our phones and amplify it using the Bluetooth speaker?” That was promising — our little 10W Xiaomi speaker could work — but I wasn’t sure of its decibel output.
And then, a lightbulb moment: SonicSuite! The car already had the perfect setup for this. (For those unfamiliar, SonicSuite is a setting in the BE6 that uses exterior and/or interior speakers to simulate engine noise. It mimics engine rumble based on the accelerator pedal input, and the best part is — it works even when the car is parked.) Noise source sorted!
Methodology:
I moved on to the test plan. I needed two phones — one to act as the microphone using the ‘Sound Meter’ app, and the other to take notes. I was planning to convince my wife to lend me her phone for a bit. But after all the back-and-forth we had while brainstorming, she was already too invested in the idea — especially with SonicSuite involved (its her favourite feature in the car!). In fact, before I could even ask, she offered to join in herself. There was no way she was going to miss out on the fun.
So we made our way down to the basement parking. For context, the car is parked at Level -1, and our apartment is about 200 meters from the main road. Hardly any traffic noise filters in.
Occasionally, there’s some water flow from the pipelines overhead, or a car or bike passing through. We made sure to take our readings when no vehicles were entering or leaving to reduce unwanted spikes. I didn’t want these minor background variations to derail the test, so I decided to take three readings at each data point and use the average as the final value.
The first set of noise level readings was taken right outside the vehicle — this served as the baseline reference for the ambient noise in the surroundings. The next set was recorded near the boot of the car, since that’s where the exterior speakers for the SonicSuite feature are positioned, roughly below the rear bumper area. These readings were captured twice: once with SonicSuite turned on in ‘V8 Tribute’ mode but without any accelerator input (to simulate an idling engine), and again with the accelerator fully pressed — mimicking the engine redlining. All three scenarios — SonicSuite off, on with idle, and on with full throttle — were then repeated inside the cabin under three different window configurations: first with all windows rolled down, then with only the driver’s window down and the remaining three up, and finally with all windows rolled up. This approach gave me a clearer picture of the noise insulation offered specifically by the window glass, and how much of a difference each configuration makes.
For each of the readings, I used the ‘Sound Meter’ app as before. The min, max, and average values were reset for every recording, and I waited for the average to settle a bit before noting it down — typically, stabilization took around 20–25 seconds. For the readings inside the car, my wife hopped in enthusiastically and placed the phone on the convenient flat gear lever. All other sound-generating features were switched off — including the AC, ventilated seats, and music — to ensure a clean measurement. After each reading, she would call out the average value, and I’d note it down while standing outside the car. The idea of keeping just one person inside was intentional — it helps maintain consistency in the testing procedure, especially if any fellow BHPians want to try replicating the setup themselves.
Observations: Here’s how the data shaped up:
(I am evaluating Google Sheets this time; Like it so far!)
Results:
Below are the charts showing the average sound level recorded across the three different scenarios — with SonicSuite off, SonicSuite mimicking engine idling, and SonicSuite mimicking engine redlining. These charts help illustrate the effect of insulation from two angles:
The body of the car itself (when all windows are down)
The contribution of the windows (as is progressively rolled up)
To get a clearer sense of overall insulation, here’s a chart comparing outside sound levels versus inside levels (with all windows rolled up).
What stands out immediately is that the drop in sound level isn’t constant — it increases with the external noise level. In other words, the louder it is outside, the more effective the cabin insulation appears in terms of absolute dB reduction. Take the Engine Redlining scenario, for instance — the drop is dramatic: from 76.5 dB outside to 48.47 dB inside (with windows up). That’s a 28 dB reduction, and it genuinely felt impressive in person. To better understand how each part of the cabin contributes to insulation, I created a few additional plots that show the step-by-step reduction in sound levels — starting from all windows down, then moving to only the driver’s window down (with the other three up), and finally to all four windows rolled up.
Takeaway Points:
- The cabin body does the heavy lifting — even with windows down, there’s a solid reduction in noise, thanks to the structure and materials used.
- In low-noise conditions, partially rolling up windows (just 2–3 of them) can still lead to a noticeable reduction in sound — something you can actually feel.
- In high-noise conditions, like engine redlining simulations, closing all windows becomes essential. The last window alone gave a massive 11.66 dB drop inside the cabin — a significant reduction in perceived loudness.
Conclusions:
This little experiment turned out to be far more insightful than I initially imagined. While I always appreciated a quiet cabin, quantifying just how much insulation the car offers was both surprising and satisfying. The data clearly shows that the cabin body itself does most of the heavy liftingwith the windows adding meaningful reinforcement, especially under high external noise conditions. What stood out most was how dramatic the drop in noise was when moving from all windows down to all windows up—particularly when the SonicSuite simulated a redlining engine. That final window, which might often be left open out of habit or convenience, made a whopping 11.66 dB difference! Another interesting takeaway was how even partially rolled-up windows can offer noticeable insulation, especially in quieter environments. This gives a lot of perspective on how cabin refinement isn’t just about high-end materials, but how everything works together to cocoon the occupants from the world outside.
On a personal note, it was also a fun reminder of how features like SonicSuite—designed primarily for engagement—can double up as a handy test tool! And of course, none of this would’ve been half as fun without my partner-in-crime who was just as eager to explore the acoustics of our ride.
A special thanks to the BHPians in this thread who sparked the idea—particularly Kelly66, whose comment nudged me to think and explore insulation more analytically. Cheers to many more nerdy deep-dives like this!
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