DiyMobileAudio.com Car Stereo Forum banner

1 - 20 of 455 Posts

·
Registered
Joined
·
4,936 Posts
OK. I've had some requests how to measure your car audio system and how to work with RoomEQ as well as fine-tuning your system for optimal staging and tonality. Rather than explaining it all in private chats I might as well do a quick guide as more people can learn and members can refer to this thread if someone asks questions.

I've previously made threads about RoomEQ available here:

Measure T/A with RoomEQ

http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/145484-measure-time-delay-t-arta-roomeq.html

How to use the AutoEQ function in RoomEQ

http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/144455-quick-tip-using-auto-eq-roomeq-rew.html

But let's start with the basics...

What you need:


  • [*]Computer, preferably a laptop

    [*]RoomEQ/REW software, available here: RoomEQ BETA DOWNLOAD

    [*]Measurement microphone, preferably a calibrated microphone or a microphone that have a supplied calibration file. Both USB microphones and phantom powered microphones that require a preamp are common.

    [*]DSP, either built-in in the headunit or preferably a stand-alone unit. Left and Right side equalization is an absolute necessity!

    [*]AUX-in feature of the headunit. In a standalone DSP you can simply use the DSP inputs directly from the soundcard output.
BE IN A QUIET PLACE WHILE MEASURING!! ENGINE OFF, ALL WINDOWS, DOORS, TRUNK CLOSED

as an alternative you CAN use a CD with uncorrelated pink noise as a "trigger source" together with the RTA function in RoomEQ but I don't recommend this way of measuring since you will attain less data than sine sweeps and you won't be able to use the more advanced features in RoomEQ.

See pictures below how to setup the hardware. Use headunit AUX-in if possible.





Alright. When that's done it's time to configure RoomEQ. This is how RoomEQ looks when you enter the software, begin with clicking on "Preferences".



In preferences, you first setup your Audio input and output. If you got an USB mic, it will show up under input device. IF you got a mic together with a pre-amp you might wanna do a soundcard calibration by connecting the line-in to the headphone jack of the soundcard and hit that "Calibration" button. It's usually not that critical though.



The next tab in preferences that's important is "Mic/Meter". Here you import the calibration file of the microphone. Some microphones got a "general" calibration based on averages over many microphones, some got individual calibration files for each single microphone... and obviously that's more accurate. A calibration file for the microphone is generally more important than calibration the soundcard. Most microphones tend to get non-linear in the lows and the higher 2 octaves. A calibration file is highly recommended!



Under "House Curve" you can import a target response for usage with RoomEQ's autoEQ function. This step is optional.



NOW CLOSE PREFERENCES.

Now you can choose how you want to measure. If you don't have a stand-alone DSP or an AUX-in in your headunit you might need to use a CD with pink noise and use the RTA function highlighted in BLUE in the picture below.

For normal measurements, click "Measure".



This the "Measure" screen:

Start Freq: 20Hz
End Freq: 20000Hz
Length: 256k
Sweeps: Determines the amount of sweeps, these will be automatically averaged. Use 2, it's generally enough.
Level: Set an appropriate level here, don't let the sweep clip (i.e reach 0.0dB while sweeping).



Now, click "Start Measuring".

After the measurement is finished you should have a graph on your screen, it should look something like the picture below (it might not look so smooth before any EQ).



The graph shows level in the Y-axis and frequency in the X-axis, i.e SPL vs Frequency (Frequency Response).

Below is a zoomed in picture the menu-tab.

*Use "All SPL" to observe the Frequency Response, you can overlay several measurements under this tab as well.

*Set scaling of the graph in "Limits". Highlighted in RED.



--Scaling should be set so you see the graph in 5dB steps, between 20Hz and 20000Hz. You can set it to 20-400Hz if you looking at the subwoofer response for example). I had mine set for 0dB bottom, and 90dB top in the example.

--In "Controls" the most important feature is "Smoothing". Choose the amount you want and click "Apply to selected". Here's a rule of thumb...

For Subwoofer measurements, use 1/24dB.
For Midbass/Midrange measurements, use 1/12oct
For Tweeter measurements, use 1/6oct or even 1/3oct if you have done few "physical" averages,







I will continue the guide tomorrow, but you should get the basics "HOW TO MEASURE" now... I shall explain where the microphone should be placed, how to use autoEQ, parametric equalization and more in the next posts. Hope you enjoy this.
 

·
Registered
Joined
·
68 Posts
This is great! Thanks for posting such a detailed tutorial. I have been using REW now for a few weeks, read tons of threads and finally getting my system dialed in, such that I like it. I know this will help a lot of people that are just starting out.

Looking forward to more!
 

·
Premium Member
Joined
·
2,414 Posts
STICKY!


My UMIK-1 should be arriving any day now. Your timing with this thread was perfect!
 

·
Registered
Joined
·
4,936 Posts
Discussion Starter #11 (Edited)
Thanks guys! ;)

Here's the next part:

Managing measurements...

OK. When we measure our system we need to do several measurements to get a complete picture of what's going on. I highly recommend measuring each speaker in the entire system separate (all speakers muted but one). Doing lots of measurements takes some managing of all the graphs, otherwise you get lost in a mess of plots that makes your head spin ;)

So before going into the basics of equalization we going to continue working with the software to make ourself more familiar with the important features.

Here's a overview over some important functions:



*The list to the left is used to manage and select the current measurement.

*Change color of the graph if two plots end up having the same color which makes overlays hard to differentiate from each other.

*Name each measurement and use the comment section to manage each graph. An example how to use naming and comments; Name = Left Midrange // Comment = "Measured 2 inch in front of the left ear".

Now let's do a second measurement (right driver in the example below).



*The second measurement will end up directly below the first one in the list to the left. Name it appropriately. IMPORTANT! ( Avoid creating a mess... ;) )

*At the bottom of the graph, there's now two boxes which you can check and uncheck. This hides or shows the different measurements in the "All SPL" tab.

*Choose the appropriate smoothing for easier viewing. Smoothing a plot is not permanent and does not result in loss of data, you can "unsmooth" it at any time.

Now to another very important feature. "Averaging".

(Note how the graph got easier to view as I applied smoothing to the measurements.)



Facts: When you measure a speaker in the car, the frequency response will change as you move the microphone a little. The effect is minor in the lower frequencies, in the "modal range" but gets worse as the wavelengths get smaller, i.e higher frequencies. The higher frequency you measure, the more reason to do "physical averaging", i.e moving the mic and perform several measurements on the same speaker. We do not sit stationary in one exact spot, that's why we need to consider this.

*While overlaying graphs in the "All SPL" tab you can average them together inside the software. This is an important and very useful feature! I always do 8 sweeps (8 measurements) on EACH SPEAKER, between each measurement I move the microphone a little (I'll explain this more in detail later...) When I got 8 measurements, I do a spatial average inside the software by selecting ALL GRAPHS (bottom of the screen) and click "Average the Responses" in the bottom left corner. You will now get a new "measurement" in the list to the left called "Average 1", this one represent all those 8 measurements as it's an average of all.

[*]Important: The "Average measurement" does only contain Frequency Response data. Do NOT remove the other measurements as they contain the impulse response which is needed for the more advanced functions and time data inside RoomEQ.

[*]In the modal range, i.e low frequencies, let's say below ~200Hz averaging is not really required. The response will not change very much over small distances. Use 1/24oct smoothing in this range.

[*]Smoothing inside the software and "physical averaging" serve a similar purpose in a sense.

Finally... Save each SET of measurements, as a separate file. The RoomEQ files will have a *.mdat file extension. These files can be sent to others for analysis, this is a neat feature since we can share files and help each other using objective hard data. The mdat file contain the full impulse response and all advanced features can be accessed through it.

*Use the "Save all" button in top left or via the menu "File" / "Save all measurements".

I will get into microphone placement and some tips and tricks next time and then back to RoomEQ and common DSP software, how equalization work etc. Stay tuned.
 

·
Registered
Joined
·
6,213 Posts
STICKY!


My UMIK-1 should be arriving any day now. Your timing with this thread was perfect!
My UmiK-1 arrived a couple days ago...agreed..perfect timing.

I was planning on using the software supplied with my Helix, is there a reason why i cant use that and should use RoomEQ instead?
 

·
Registered
Joined
·
4,936 Posts
Discussion Starter #14
My UmiK-1 arrived a couple days ago...agreed..perfect timing.

I was planning on using the software supplied with my Helix, is there a reason why i cant use that and should use RoomEQ instead?
Yeah... several. The Helix software is just an RTA, you can't do any real troubleshooting or observe the time domain with an RTA. RoomEQ can perform autoEQ with both graphic and parametric filtering. It got a better overlay, average and graph managing ability. Quicker to work with (imo).

If you're just interested in the the overall FR, the Helix software works indeed. I'll present a few reasons why RoomEQ is better later on ;)
 

·
Registered
Joined
·
4,936 Posts
Discussion Starter #15
MUCH THANKS!!!

Any recomendations for a microphone?
ECM8000 is a good mic, I'm using it. It requires a preamp with phantom power.
UMIK-1 and Dayton OmniMic are also great, they are USB mics. The drawback is no ability to use loopback to measure delay etc. I've heard the USB mics can be noisy if you're doing precision measurements but idk really. No real experience with any of them, my ECM8000 has worked fine for the last 5 years ;)
 

·
Registered
Joined
·
4,936 Posts
Discussion Starter #16 (Edited)
Microphone measurement technique

If you look in a manual of an auto-tune DSP or ask 10 different 'experts' I'm sure you get different answers every time. I will present my technique here, in my experience, it has worked best in those systems I've installed. I've sort of 'back engineered' this technique via comprehensive listening tests...

So how do you place your microphone while measuring?

Good question! Sit in the car, hold the microphone as the pictures below describe. Run one sweep in RoomEQ for EACH POINT. 8 sweeps in total for each individual speaker. Hold the microphone still while running the sweep and make sure the microphone doesn't hit your head or anything.

FOR SUBWOOFER MEASUREMENTS, A SINGLE MICROPHONE PLACEMENT IS ENOUGH. PLACE IT IN THE MIDDLE OF THE HEADREST OR IN FRONT OF YOUR HEAD (you don't even need to be in the car for this one)

- As I said before, measure in a quiet area.
- Measure at moderate/"normal listening" volume ~90dB or so.
- Use hearing protection if you want, the sweep is annoying to listen to.







!! AVERAGE THE MEASUREMENTS FROM THESE POINTS AS DESCRIBED IN MY LAST POST !!

Why 5/3 ratio for the left side and 6/2 ratio for the right side?

I believe this is due more "hearing crosstalk" left side, the speaker is more in front of us and also closer to both ears. The listening tests confirm that this is the "best" way to average (IME).

Pro-tip: Use a battery charger while measuring / tuning. Your battery will thank you ;)
 

·
Premium Member
Joined
·
2,414 Posts

·
Registered
Joined
·
4,936 Posts
Discussion Starter #19

·
Wave Shepherd
Joined
·
2,374 Posts
Great work Hanatsu, I really look forward to seeing this develop further.

Do you plan to talk about connecting the 2nd channel in a "loopback" configuration? I find it is exceptionally useful for time alignment.
 
1 - 20 of 455 Posts
Top