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Old 05-15-2014   #26
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Old 05-15-2014   #27
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Default Re: First-timers guide to measuring your system

I have a Dayton umm-6 usb mic, which says its A weighted.

The options in REW is "C weighted" or "Mic or Z weighted", which one should be selected?

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Old 05-15-2014   #28
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Default Re: First-timers guide to measuring your system

Quote:
Originally Posted by crackinhedz View Post
I have a Dayton umm-6 usb mic, which says its A weighted.

The options in REW is "C weighted" or "Mic or Z weighted", which one should be selected?
That's kinda weird. If you load the calibration file the weighing will be disregarded inside the range of the cal file. Choose Z otherwise.

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Old 05-15-2014   #29
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Default Re: First-timers guide to measuring your system

Quote:
Originally Posted by Hanatsu View Post
That's kinda weird. If you load the calibration file the weighing will be disregarded inside the range of the cal file. Choose Z otherwise.
yes I have the calibration file loaded and "mic or Z weighted" selected. Thanks for this helpful guide as I just installed REW and was not sure where to begin! Thanks

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Old 05-15-2014   #30
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Default Re: First-timers guide to measuring your system

Setup your system, Pt1: Interpret your measurements

OK. We had three parts so far. You should be a little more familiar with the software and how to do the "actual measurements" now but we won't jump into the advanced features just yet. First we need to understand what the measurement actually describes, what we can do with it and why we need equalization in a car. I'll try to keep it as simple as possible.

Even if this is a measurement tutorial I think that knowing some of the basic theory how we interpret sound is a good thing. It allows you to understand what you're doing and WHY you are doing it.

So, first some quick facts how we humans interpret sound, how we localize sound and why it's important.

[*] At low frequencies we localize sound based on the time it takes for the sound to travel from one ear to the other. This is called the "inter-aural time difference (ITD)". ITD is the main contributor for sound localization below ~800Hz.

[*] At high frequencies we localize sound based on the intensity (volume/level) difference between the ears. This is called the "inter-aural intensity difference (IID)". IID is the main contributor to sound localization beyond ~1600Hz.

[*] Between 800-2000Hz there's "gray area" where both IID and ITD contributing to sound localization and in the area 1000-3000Hz it's harder to pin-point where sound originates from than usual. Good to know when tuning.

Why is this important? Because if we want a good soundstage, with the vocals centered and a stable focused stage we need to consider both the difference in physical distance between speakers and the intensity difference altered by the interior of the car.

*Some headunits and basically all DSPs got a feature called 'Time Alignment' which is used to delay the speakers closest to you and therefore electronically compensate for the distance difference between left and right side speakers. T/A (Time Alignment) mainly affects the 'ITD frequency range'.

*Few headunits and many DSPs got channel independent equalization (L/R EQ). EQ is basically a "frequency selective volume adjuster", that makes sense to you? To compensate for the intensity difference between the left and right side we need equalization on both channels. As you might guess, the L/R EQ function affects the 'IID frequency range' to a great extent, but it does also affect the 'ITD frequency range' in a way* (I'll discuss this and the 'modal range' later on).

Basically L/R EQ and T/A go hand in hand. You need both for correct tonality and staging. That's why a DSP is so important, all Car audio systems need processing of some kind to sound right.

See the picture below for an illustration:

rew18.jpg

OK. Let's return to RoomEQ again... If you have followed the previous instructions in measuring all individual speakers and several averaging points of each, you could end up with something like this:

rew19.jpg

This is just an illustration of the mess of trying to manage every graph at the same time (not smoothing the graphs add to the mess). If you want to avoid this, first deselect all graphs (see picture below) and then select the graphs you want to work with.

rew20.jpg

For this little example I selected the subwoofers (remember to set an appropriate graph frequency and level limit for easier viewing).

rew21.jpg

-------------------------------------------------

Various good-to-know facts before you get started.

## OK. I'm going to go through some various things before going into the fun stuff. First off:

There's a big misconception about crossovers!

[1.] So you enter your desired crossover points and slopes in the DSP and that's it, right...? Unfortunately, there's two "forms" of crossovers. One of the "forms" exist in the electrical domain and one in the acoustic domain. The ones you set in the DSP is the ELECTRICAL CROSSOVERS and they NOT the same as an acoustic crossover.

[2.] The ACOUSTIC CROSSOVER is the MEASURED crossover point and slope (as in 'measured with a microphone inside the Car - in listening position'). This is "real" crossover point, the electrical crossovers can be set in any way you want as long as you reach the "optimal" acoustic crossover point/slope.

[2a.] Tip: Use different crossover points and slopes, left and right side to fix some of the frequency response errors BEFORE EQing the system. (We'll discuss this in detail later).

[3.] The actual (acoustic) crossover point is dependent on the relative level/volume of two speakers. IMPORTANT! See pictures below:

"Normal levels"
rew22.jpg

Midwoofers levels are offset by +10dB and resulting crossover point changes as you can see.
rew23.jpg

This might be an eye-opener for some

So how bad can it be? Do we really need a DSP?

The picture below speak for itself. This is a typical door mounted Speaker frequency response (fullrange, no EQ, same input level between L/R speaker).

rew24.jpg

15dB difference! Right in the smack of the lower midrange (vocal fundamentals lies here). That can't be good... I promise, it isn't. We can do "some work" by being creative with levels and crossovers but we're still going to need equalization here to level out the difference. As you might understand by now, an ordinary EQ is not enough, you need a channel independent EQ to compensate for such issues as in this example...

That's it for now... I have few more things I want to add but soon we're going to discuss the fun stuff

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Old 05-21-2014   #31
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Default Re: First-timers guide to measuring your system

Question. Should the Time Alignment be measured and determined before performing these room measurements and EQ with REW?

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Old 05-21-2014   #32
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Default Re: First-timers guide to measuring your system

Doesn't matter. I do it before.

I'll will write up the next part soon, very busy at the moment.

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Old 05-21-2014   #33
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Default Re: First-timers guide to measuring your system

Quote:
Originally Posted by Hanatsu View Post
Doesn't matter. I do it before.

I'll will write up the next part soon, very busy at the moment.
Cool. I figured it best to do time alignment first.

I'm waiting for my Behrenger mic to arrive. Going to use my MacBook Pro with REW and an Allen & Heath Xone DB4.
It will be overkill on the soundcard, but should work. That way I don't need to buy something new.

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Old 05-23-2014   #34
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Default Re: First-timers guide to measuring your system

My microphone is being delivered today. Really excited to start working with REW.

Going to do time alignment first, and then check the response and work on my EQ.

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Old 05-23-2014   #35
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Default Re: First-timers guide to measuring your system

All right. Let's continue from my last post.

Setup your system, Pt2: Equalization theory

This is where I left off last time... If we look closely at the picture below we can see that there are peaks and dips in the response, it has a response deviation of 20dB from the highest peak to the lowest dip.

rew21.jpg
PICTURE 1 (Subwoofer Measurement, Sealed enclosure - Measured inside car)

A response deviation as large as 20dB is an issue, it WILL be audible and affect the tonal balance severely. As you may know, EQ is a feature to compensate for frequency response errors such as the graph shows, but can all response issues be 'fixed' with EQ and if not, why?

[*] As you boost with EQ, you will demand more more Power from the amplifier in the EQ'ed area. A 3dB boost equals twice as much Power and 6dB equals four times the power!

This goes both ways, if you cut with EQ you will demand less power from the amp.

[*] EQ will affect the speaker's performance in more ways than you might think. I won't go into detail of this but as you increase volume a speaker's (non-linear) distortion level will also increase. As EQ basically is a frequency selective volume control you will increase or decrease distortion if you boost or cut in a given area.

[*] Some areas can't be EQed, large dips in the response, especially those low in frequency 'in the modal range', should be left alone. They are related to the speakers locations, the listening position and the inner dimensions of the car. Problems around 60-80Hz and 120-160Hz are common in average sized cars (see "picture 1", the dip at ~65Hz is one of these issues). These areas can actually be viewed inside RoomEQ and this is an 'advanced feature' I will discuss later...

There can be cancellations in the response due to phase inconsistencies as well. Incorrect set time delay between speakers or incorrect polarity are common issues that can result in dips in the response. The response dip will not respond well to EQ in this case.


Before I describe how to use the autoEQ of RoomEQ/REW, you must understand the basics of equalization...

There are basically two types of EQ's available in most Car audio DSP's and headunits. They are called "Graphic Equalizer" or "GEQ" and "Parametric Equalizer" or "PEQ" in short. A graphic EQ is easier to use, but also less powerful than the parametric type. Since parametric equalization is so widely used nowadays I will put some focus on that.

Graphic, "Semi-Parametric" and "Full-Parametric" EQ

A graphic EQ is the "normal" type of equalizer most people probably have seen in both home audio and Car audio at some point. A GEQ has a varying number of EQ bands, which are centered around FIXED frequencies. The better units often got EQ bands with 1/3 octave spacing, i.e 200Hz, 250Hz, 315Hz, 400, 500Hz etc. Each of these frequency bands also got a FIXED BANDWIDTH, this means that if you choose to decrease 500Hz by 10dB, you won't simply lower just 500Hz, the frequencies around 500Hz will also be affected. That's why we call each EQ band "Center Frequency" . The area around the 'center frequency' is called "Bandwidth". The bandwidth is defined as "Q". A larger "Q"-value means a NARROW bandwidth (only the frequencies close to the center frequency are affected), a smaller Q-value have a WIDE bandwidth and will therefore affect a large amount of frequencies around the center frequencies.

parmet2.gif
EQ bandwidth (Q's)


*With a GEQ you will have FIXED center frequencies with a FIXED spacing and each center frequency will have a FIXED bandwidth (Q). This type of equalizer is easy to use but not as flexible as a parametric EQ.

*A parametric CAN be used in the same way as a graphic EQ. With a PEQ you gain the ability to CHANGE center frequency and bandwidth (Q). This type is more advanced to setup but is far more powerful if used correctly. A "full parametric EQ" will basically allow you choose whatever center frequency you want freely and a wide range of Q values. A "semi-parametric EQ" will allow you to change center frequency in a fixed octave spacing.


Example; You have an issue at 140Hz in the frequency response that needs EQing. With a good graphic EQ you should have EQ bands at 125Hz and 160Hz, unfortunately you won't be able to touch 140Hz without affecting the the frequencies around 125 and 160Hz as well. A parametric EQ allows you to choose a center EQ-band at 140Hz and the desired bandwidth (Q) to only attack the problem directly without touching the 125 and 160Hz bands.

How to EQ...

*Generally speaking, never use narrow band (high Q) EQ in the higher frequencies!

*Higher Q equalization/filters should only be used within the modal range (lower frequencies).

*Rather cut than boost. Remember the Speaker strain and power requirement when boosting. I generally recommend not to boost more than 3dB.

*If the the frequency response doesn't respond to boosting an area by equalization, DON'T USE EQ there. You will only increase distortion.

*Don't be afraid to use large amount of EQ in problem areas, it's the acoustic response that matters.

Make sure levels and crossovers are optimized before EQ. IMPORTANT!

The optimization of levels and crossovers will therefore be be first step in setting up your system and I will discuss this in detail in PART 3. So you who have been waiting for the practical tutorial in RoomEQ will be happy next time

Until next time ^^

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Old 05-23-2014   #36
 
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Default Re: First-timers guide to measuring your system

Hurry please
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Old 05-23-2014   #37
 
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Default Re: First-timers guide to measuring your system

Maybe a quick tip on level and crossover setup?
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Old 05-23-2014   #38
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Default Re: First-timers guide to measuring your system

Almost midnight here. Gotta sleep

You'll have a detailed post tomorrow.

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Old 05-23-2014   #39
 
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Default Re: First-timers guide to measuring your system

Lol. Nooo.
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Old 05-23-2014   #40
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Default Re: First-timers guide to measuring your system

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Old 05-24-2014   #41
 
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Default Re: First-timers guide to measuring your system

This is great, anxiously awaiting the next installment of "Newbees Tune Your Ride". I recently started using REW and this really helps clarify some of the things I need to do. Hope you got a good nights sleep!
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Old 05-24-2014   #42
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Default Re: First-timers guide to measuring your system

Tried to get started with the time alignment portion today, but can't get my soundcard inputs to display in the REW preferences properly. Only shows Left or Right, but my soundcard has 4 channels of L/R input/output.

Going to try on my PC laptop this time to see if it's just because it doesn't like the Mac CoreAudio drivers.

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Default Re: First-timers guide to measuring your system

Wish there was a better USB Mic method.
I use a usb Mic, so I'm doing the "invert one speaker, delay until most destructive interference at the crossover point" method
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Default Re: First-timers guide to measuring your system

Quote:
Originally Posted by calebkhill View Post
Wish there was a better USB Mic method.
I use a usb Mic, so I'm doing the "invert one speaker, delay until most destructive interference at the crossover point" method
Yeah, I have a UMIK-1 and a Behringer mic.

Was trying to get the Behringer to work so I could do the time alignment, but still can't get it working. I'm using a mixer for the mic preamp but no matter how high I turn up the gain and levels, it's still saying too low.

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Default Re: First-timers guide to measuring your system

Setup your system, Pt3: Adjust L/R Levels

"The following two parts will show how to set up levels and crossover points correctly, before EQ"

Alright, let's begin with setting up L/R levels properly. This step should be done before EQing your system. For this part I'm going to assume you have read my previous post about 'electrical vs acoustical crossover points' and 'how to measure' and so on. Time for the boring theory lesson to pay off. We will also begin discussing the subject of target responses, which is the main point in performing "response shaping".

*** Levels, Crossovers and EQ are tools to shape the response to a desired curve. Focus on what happens in the acoustic domain and less how the electrical filters look ***

Let's begin, step for step:

Step 1. Choose a desired target response. What works or doesn't is highly individual for each install and Car interior size. I will supply a 'generic' curve that we'll use in this example.

Here's a informative thread that discusses different target responses if you're interested...

Step 1a. Load this file into RoomEQ: generic target curve.txt

You load the file by going into "Preferences" / "House Curve" (Make sure 'Use Logarithmic Interpolation' is checked.)

Step 2. Set all drivers to fullrange, i.e bypass/disable all crossover filters in the DSP/HU or on the amplifiers. Exception!! Place a HIGHPASS FILTER (HPF) on all Tweeters and dome midranges, a fullrange signal might damage the drivers! A 24dB/oct HPF 1/2 octave (1,5 times the Fs value) above resonance (Fs) will be sufficient to protect the drivers and still get a proper "fullrange" signal out of them. Check the speaker's data sheet to find the resonance frequency (Fs), most manufacturers supply that kind of data.

Step 3. Measure all speakers individually. It doesn't matter if you don't have Speaker independent EQ or not. Do NOT touch the volume control, gains or any other settings during the measurements. Use 'normal' listening levels during the measurements. It should look something like the picture below after this is done. (Read the previous posts on 'Managing measurements' if you don't understand this.)

rew25-low res.jpg
"Picture 1. After individual measurements."

Step 4. Now we'll start with level matching the speakers to each other. We want as similar response from left and right side, with each set of drivers. This is the tricky part, you can level match with both levels and the crossover settings sort of. There's a few ways to do this step, there's no right or wrong. I'll present an option here but first we need to check the overall levels off all measurements to check that they are not too far off.

Step 4a. Set smoothing off all plots to 1/1oct. Now it should look like this:

rew26-low-res.jpg
""Picture 2. After 1/1 smoothing applied."

Step 4b. Select left/right side measurements for each set of drivers. For example, (left & right midbass) together and (left & right tweeters) together. See picture below. Repeat for each set of drivers.

rew27.jpg
""Picture 3. Zoomed in view. Average level difference, left/right side"

Step 4c. Make the the necessary changes in your DSP or HU. Lower the side with the loudest overall response by the appropriate amount, in the example above the average level was about 3-4dB too high on the the driver side, YMMV. All DSPs I've seen have a separate level control on each speaker, it's often located in the crossover section of the interface.

rew28.jpg
""Picture 4. Zoomed in view. Average level difference, left/right side - AFTER LEVEL ADJUSTING IN DSP"

The picture above shows how the drivers now are better level matched on an average basis.

--------------------------------------------------------------------

Step 4d. When you have done the level matching for each set of drivers it's time to check how they compare to each other, i.e how the levels between subwoofers --> mids --> tweeters look. IMPORTANT! Remember that the levels should NOT be the same here, they should match the target response we loaded (which isn't flat). I'll explain this in the next step.

Step 5. Select one of the measurements in the left row, for example the subwoofer measurement. This one will be used as a reference. See picture below:

rew29.jpg
""Picture 5. Zoomed in view. Select the "reference" driver and go into the EQ tab."

Step 6. When you inside the EQ menu, you need to make some adjustments. See picture below:

rew30.jpg
""Picture 6. EQ MENU"

Step 6a. Select the type of DSP you got, if it's not in the list. Choose "Generic".

Step 6b.

rew31.jpg

*Set "Speaker Type" to "Full Range".
*Set "LF Cutoff (Hz) to "0".
*Set LF Rise Slope (dB/octave) to "0".
*Set HF Fall Slope (dB/octave) to "0".

Step 6c.

Set "Target Level (dB) to match the measurement you loaded. See "picture 6". Set it so the level is close to the target response. It doesn't need to be 100%, we will EQ that later. IMPORTANT! The "Target Level" you choose will be the "REFERENCE Target Level". Make note of this number for later.

Next time we'll continue to setup crossovers and levels for each 'type' of drivers to match the target response by using autoEQ.

# In a time of universal deceit - telling the truth is a revolutionary act # (George Orwell)

- Build Thread 1, Mercedes-Benz E 320T (2000) -

- Build Thread 2, VW Passat 1.8T (2000) -

Last edited by Hanatsu; 05-26-2014 at 03:23 PM..
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Old 05-26-2014   #46
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Default Re: First-timers guide to measuring your system

I'll continue writing this tomorrow, I'll just continue where I left off (it's incomplete so far)

# In a time of universal deceit - telling the truth is a revolutionary act # (George Orwell)

- Build Thread 1, Mercedes-Benz E 320T (2000) -

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Old 05-26-2014   #47
 
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Default Re: First-timers guide to measuring your system

this is awesome man!.
i have just finished my first ever install and this site has been an excellent source of info.
i have read loads about REW and my UMIK-1 mic has just come from cross spectrum labs so this is excellent timing!
many many thanks hanatsu and to everyone else who's threads have been so much help.
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Old 05-26-2014   #48
 
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Default Re: First-timers guide to measuring your system

Awesome. This is epic.
Hopefully by the end of this, and hopefully it'll be ongoing , US noobs can refer here fur anything we need in rew.
Someone should take these posts and compile them into an organized "book" . That'd be serious.
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Old 05-26-2014   #49
 
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Default Re: First-timers guide to measuring your system

Couldn't agree more. We should make this thread a sticky so people just coming here can benefit without having to search too much. I have watched a bunch of videos and read so many threads on REW and similar products. I think this thread is the best so far. Looking forward to tomorrow's post! Now I just need to make some time to get back into my Car and continue tuning. Damn work keeps getting in the way!
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Old 05-26-2014   #50
 
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Thumbs up Re: First-timers guide to measuring your system

Sticky xxx!
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