M3S: Calibration

In Part 7 – DSP we used a miniDSP to tune our subwoofers specifically for the Model 3. In that post I mentioned a mysterious “desired target curve”, but I didn’t explain how I came up with that curve or why you might want to create one of your own.

Should you read on?

This post is both advanced and optional, which is why I left it till the end. Every Premium Sound Model 3 will have the same starting curve, so the config file I shared in the previous post should help anyone starting with that system. But here are some reasons you might want to continue reading this post:

• You have a Model 3 SR or SR+ without premium sound. If you’re in this group, creating a custom config may yield better results. If you create one please share it with me so that I can share it with others.
• You have a very different subwoofer setup. I did all of my calibration with two JL Audio 10w6v2’s in a ported enclosure tuned to 32 Hz. If your subs or enclosure are vastly different from mine, you will end up with a very different target curve.
• You have a different vehicle. The config file in the previous post is tailored for a Model 3 with the OEM 50 Hz bump. If you have a different vehicle, your starting point will be significantly different and therefore so will your target curve.
• You just want to learn. Why fix something when it ain’t broke? Because you can learn from it and maybe make it better, right? I respect that.

What you will need

Sticking around? Awesome! Just one last thing though. If you actually want to measure and create your own custom calibration, you will need:

I know it’s hard to justify spending $91 bucks on a microphone when the DSP itself was $104. But I promise that having the right microphone is critical to this process. If you already have access to another calibrated mic that works with REW, feel free to use it. Just please don’t try to use a standard “off the shelf” microphone because results will be terrible. Any truly calibrated microphone will have a data file specific to that individually produced mic. If your mic doesn’t have a data file, it’s not a calibrated mic.

Process overview

Room EQ Wizard (REW) has been around for quite some time. It’s an incredibly powerful piece of software that’s integrated tightly with a number of DSPs. The overall calibration process goes like this:

1. Install REW on a laptop.
2. Carry the laptop out to the car.
3. Get sound from the laptop to play through the car speakers.
   1. On the Model 3 this requires Bluetooth pairing.
   2. On other vehicles you may use an AUX jack.
4. Start REW
5. Connect the calibrated mic to the laptop’s USB port
6. Configure REW for your specific individually produced microphone using the data file that came with the mic. (In this step use the 90 degree file.)
7. Make sure REW is set to play sounds through your car and set volume levels accordingly.
8. Take measurements throughout the car.
9. Average the measurements together.
10. Load a House Curve that defines your ideal sound (more on this soon).
11. Have REW generate a Parametric EQ, which tries to adjust your speakers as close to the House Curve as possible.
12. Save the Parametric EQ file from REW, then load it into the DSP

Video guide

Throughout this series I’ve tried hard not to recreate the wheel. Any time there’s already a clear and concise guide, I prefer to link you there instead. The same is true for this process, and an amazing guide already exists. However, there are some important modifications to that guide that need to be noted.

Julian Krause produced an amazing video on using REW to calibrate speakers. In all my searching, his guide is by far the easiest to understand. I will include that video below, but here are some important differences to be aware of:

• Instead of calibrating subwoofers, Julian is calibrating desktop speakers. This is important in two ways:
  • When Julian takes measurements, his microphone is pointed horizontally toward the speaker he’s measuring. Since we will be measuring subwoofers, our microphone will be pointed up toward the ceiling.
  • When Julian loads his microphone calibration file he loads the default (zero degree) version. This is because horizontal measurements are the default. When we load our mic calibration file we need to load the “90 degree” version since our microphone will be pointed vertical.
• Instead of a hardware DSP, Julian is using a software-based DSP called Equalizer APO. This is also important for two reasons:
  • When Julian opens the EQ window (around 9:23) he sets the equalizer to Generic. Instead, ours should be set to minDSP.
  • After Julian exports the EQ file file (around 13:00) he imports the file into Equalizer APO. We can skip the rest of his video at that point since we’ll switch back to the miniDSP software for import.

I’ll insert the video now, but as you watch it keep an eye on the timestamped notes below the video. This is where I’ll call out these differences again, as well as tell you what to do after the video is over.

01:04 – Umik-1 Configuration
In this step be sure to load the 90 degree file instead of the default one. Again, this is because our microphone will be pointed up.

01:29 – Audio Device Configuration
Here be sure to pick your car as the output device. For the Model 3, you should see something about a Tesla Bluetooth audio device.

02:42 – Setting up the Microphone
Remember that our microphone should be pointed straight up and positioned at ear-level. I found it helpful to use a microphone stand like this one, standing on the floorboard in the back seat. From here, the arm could easily be swiveled around to various positions in the front seat area.

03:04 – Setting Audio Levels
If you have to leave the vehicle and come back for any reason, do your best to get the same SPL number every time. If you do not get the same SPL number here, new measurements will appear louder or softer than previous ones.

04:21 – First Measurement
This is the first measurement of several. At a bare minimum I recommend measuring the drivers seat, the front passenger seat, and halfway between the two.

05:38 – Displaying and Smoothing a Measurement

06:58 – Average Measurements

07:58 – What is a House Curve
Watch this segment up to 8:57, then pause the video and read this call-out box before moving on.

House Curves

I created a collection of the most popular House Curves and made them available as a single archive. You can download the archive below, but note that the files must be extracted from the archive before they can be imported into REW.

House Curves

1 file(s) 2.21 KB

Download

08:58 – Setting a House Curve
Download the archive above and extract it to a folder on your machine. Julian used the Harman curve, but for car audio I recommend starting with the JBL curve. Ultimately this is a matter of taste, and you’ll want to try a few to find the one you like best.

09:12 – Calculating EQ
This is where Julian sets it to Generic but ours should be set to miniDSP.
You’ll also want to set the speaker type to None and I’ll explain why below.

10:19 – Crossover
Rule of thumb: 12db for sealed, 24db for ported

10:31 – Cutoff (Hz)
Controls the roll-off at the low or high end of the speaker type. The blue target line should match the roll-off of the average curve.

10:50 – Target Level
Set this too high and nothing gets EQ’d. Set it too low and everything will be clamped (meaning the amplifier has to work harder). Clicking the ‘Set target level’ hyperlink will set it to a recommended position somewhere in the middle.

11:36 – Configuring the EQ
I’ll explain why below, but instead of the values Julian provides in the video, use these:

Range: 20 – 20,000
Individual Max Boost: 3
Overall Max Boost: 6
Flatness Target: 3

12:36 – Calculating the EQ

12:58 – At this point, stop the video and proceed to the next section.

Importing the EQ File

Now that we have an EQ file we can import it into the DSP. For this I’ll link you to the official Subwoofer Equalization Guide from miniDSP. You’ll see that we’ve already completed most of these steps by following the video above. You’ll also see the numbers I suggested you use instead of the values Julian supplied.

IMPORTANT: One thing you’ll want to skip in the minDSP guide is Step 4 – Add a room curve. That’s because “room curve” is just another name for House Curve, which we already took care of in the REW software.

Final thoughts

With a total custom calibration in place, we come to the end of Part 8 and (sadly) the project as a whole.

As I mentioned in the beginning, Model 3 Sound was a project of love for me. If you learned something cool or have any thoughts, please leave them in the comments below or look me up on the forums. My forum information can be found on the project overview page, so see you online!