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How to make quasi-anechoic speaker measurements/spinoramas with REW and VituixCAD

kimmosto

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One small note. VituixCAD supports dash styles since 2.0.70.0 and high contrast for years. Aspect ratio was discussed earlier elsewhere: it stays e.g. 25 dB/dec as long as you don't change SPL span or frequency range outside Options window, or return how they were in Options (where size in px is calculated with aspect ratio, freq. range and SPL span). So there's no reason to import traces back to REW. It's just extra work.
 

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Fonsecafsa

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Hey Napilopez, first of all, excelent work in all the guide.

I never could use the REW correctly, and I am interested in try it, but can you give me a little help in the calibration of mic?
I know that the ideal for REW is the UMIK-1, but in the cases where users like me only have others mics, can you help in the calibration to validate the results?
I am trying to use a denon audyssey mic BTW, but when I tested my speakers, the results look way too flat to be true (or I am interpretating wrong), check the pic pls. If you can suggest anything, I appreciate! Thanks
 

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fluid

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The scale of your graph covers more than 350dB. Anything will look flat at this scale. You need to change the zoom to have something like 5dB increments visible to get any kind of idea of the measured response.

There is no simple way to use a mic that does not come with it's own calibration file for making reliable measurements. You can calibrate it against another calibrated mic if you know anyone who has one.
 

Fonsecafsa

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The scale of your graph covers more than 350dB. Anything will look flat at this scale. You need to change the zoom to have something like 5dB increments visible to get any kind of idea of the measured response.

There is no simple way to use a mic that does not come with it's own calibration file for making reliable measurements. You can calibrate it against another calibrated mic if you know anyone who has one.

Oh, thanks for the answer.
About the mic, the calibration is necessary, right? Or should I just roll the test without calibration and the REW will do the thing?
I will tweak these things tomorrow and try to understand better how to use the software.
 

fluid

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Each model of Denon Receiver has the calibration curve built in for the mic it was supplied with. It is very hard to say what the differences might be. In general cheap electret mics are fairly flat up to 1k and then deviate quite a lot beyond that.

If you want to have any confidence in the measurements you take then you need a calibrated reference. If you want to look at room modes or stuff below 500Hz then it will work well enough to see where the problems are but beyond that I wouldn't want to rely on it.
 

Arash

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I hope this is not off-topic as I was reading the first post and a questions came to my mind. Actually I've been using gating for some measurements for years now and I already know for this kinda measurement we need to keep the speaker as far from the first reflecting walls as we need resolution according to lowest frequency. I was wondering if it would be possible to have high accuracy in gating down to bass frequencies like 20hz if we have an enough big space let's say a 20meters cube. I don't see a reason it couldn't be done and if so why would anybody bother to invest millions to build an anechoic chamber or even spend 100k on Klippel NFS. Any idea?
 

fluid

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I was wondering if it would be possible to have high accuracy in gating down to bass frequencies like 20hz if we have an enough big space let's say a 20meters cube. I don't see a reason it couldn't be done and if so why would anybody bother to invest millions to build an anechoic chamber or even spend 100k on Klippel NFS. Any idea?
Yes it can be done and is usually how how corrections to anechoic chamber calibrations are derived. To gate and get 20Hz you need a 50ms time window. Generally this means the speaker and microphone needs to be at least 10m off the ground.

Vituix shows this graphically in one of it's tools but only goes to 5m

Vituix Time Window.png



Your empty 20m building in all directions could do this. Usually it is done outdoors but then you are subject to wind, weather and environmental noise for good measurements. Getting the speaker and mic 10m off the ground is not that easy :) Most companies don't want their measurement location to be in a place where the environmental noise is low enough so they build anechoic chambers or use an NFS because they can.

JBL have used the roof of a building for big PA rigs that won't fit in a chamber, or ground plane in a large enough quiet enough parking lot.
 
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napilopez

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Hey Napilopez, first of all, excelent work in all the guide.

I never could use the REW correctly, and I am interested in try it, but can you give me a little help in the calibration of mic?
I know that the ideal for REW is the UMIK-1, but in the cases where users like me only have others mics, can you help in the calibration to validate the results?
I am trying to use a denon audyssey mic BTW, but when I tested my speakers, the results look way too flat to be true (or I am interpretating wrong), check the pic pls. If you can suggest anything, I appreciate! Thanks

Unfortunately, I basically second everything @fluid says. You need to know your microphone is reasonably flat for your measurements to really be valid.I mean, if you have a speaker that's been measured by a reliable source, you could see how your measurements compare, but really it's worth making the investment in a calibrated mic if you ccan.

As for your measurements being flat, set your SPL limits to a range of 50dB, or export images as noted in the guide. That will get you in the ballpark.

I hope this is not off-topic as I was reading the first post and a questions came to my mind. Actually I've been using gating for some measurements for years now and I already know for this kinda measurement we need to keep the speaker as far from the first reflecting walls as we need resolution according to lowest frequency. I was wondering if it would be possible to have high accuracy in gating down to bass frequencies like 20hz if we have an enough big space let's say a 20meters cube. I don't see a reason it couldn't be done and if so why would anybody bother to invest millions to build an anechoic chamber or even spend 100k on Klippel NFS. Any idea?

You are correct! But as @fluid notes, it's usually the raising the speaker off the ground is the hardest part. Doing regular measurements at that height isn't a lot of fun unless you have a fancy system for it.

But my understanding is that what you propose is exactly what Dynaudio does with it's Jupiter setup.

 

Fonsecafsa

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Anyone knows one microphone from Aliexpress that could be used, affordable and good?
I know that the reference mics are the ideal, but unfortunately it is very hard to import from US to here.
 

Ata

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Anyone knows one microphone from Aliexpress that could be used, affordable and good?
I know that the reference mics are the ideal, but unfortunately it is very hard to import from US to here.

Why not use the MiniDSP UMIK-1 shipping from Hong Kong? I guess depends what is affordable.
 

Ata

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This is a guide to taking simple quasi-anechoic measurements for the least hardware expense possible, using Room EQ Wizard (donate!) and VituixCAD (donate!). This way, I can also stop repeating myself every time someone asks me how I do it!

Warning: this guide will be wordy. My hope is that even a beginner can learn to do quasi-anechoic speaker measurements this way, so I apologize if I repeat myself or state some obvious things. I started measuring speakers with absolutely no engineering background and barely any knowledge of acoustics, and I wished there'd been a wordy guide for me starting out.

I'd like to start by acknowledging the late Jeff Bagby, whose white paper on quasi-anechoic measurements is basically how I got started; much of what's in this guide is essentially just a 'translation' for REW. Of course, Dr Toole's book was invaluable for the initial inspiration and teaching me how to interpret that data. To Amir for providing a platform to emphasize speaker measurements, as well as Stereophile, Soundstage Network, Erin/hardisj, and others who provide valuable sources of speaker measurements that I've often used to compare my data with.

This guide will be divided into 6 parts. How many you read depends on how thorough you want to be with your measurements:
  1. Introduction to quasi-anechoic measurements
  2. Setup and gear
  3. On-axis measurement (sans low bass)
  4. Nearfield bass measurements
  5. Off-axis measurements
  6. Create a full shebang spinorama
Each part will build on the previous ones, so you don't have to the full guide. If you're already familiar with the ideas behind quasi-anechoic measurements and just want to know how to do them in REW, you can skip the 'On-axis measurement' section.

Please give this a try! Even if you just perform a single on-axis measurement without bass, that's already a lot more useful than most of the speaker information available on the web.

Finally, please keep in mind this is just one way of doing things, lots of which I've learned through trial and error. I am open to feedback =]

Update 4/12/21: Fixed some typos, reworded some bits for clarity.
Update 5/11/21: Fixed some more typos, reworded more bits for clarity.
Update 5/20/21: Added reminder to make sure sample rates for input and output device match (should be 48 kHz with Umik-1)

1) Intro

The best thing you can do is send your speaker to Amir or Erin for testing with the Klippel NFS. But if you can't do that for whatever reason, creating quasi-anechoic measurements can help contribute to the pool of valuable speaker data. Even a single on-axis measurement can be extremely useful.

Quasi-anechoic measurements are basically a way to take a speaker measurement indoors or outdoors and ignore the influence of walls (including the ceiling and floor). The gist of it is to make a sine sweep in REW and truncate the impulse response such that REW only includes the data from right before the first major reflection 'hits' the microphone (it's much easier to do than it sounds!).

View attachment 120852
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This is called 'gating' or 'time-windowing' the impulse response. In doing so, you lose some resolution, which is most apparent at low frequencies, and the data becomes completely invalid for the bass (usually below 100-200 Hz). The wider the gate, the higher the resolution of your data. A 5ms gate, such as is used by Stereophile, will give you a resolution and lowest valid frequency of 200Hz. My measurements are typically done at 6.5ms, which gives me a resolution of 154Hz. The resolution calculation is 1/[window in seconds], so 1/0.0065, though REW will let you know too.

To make up for the lack of resolution at lower frequencies, we can take super-nearfield measurements of the speaker's bass components (woofers, ports, and passive radiators), and simulate the far-field bass response from it. (Another common, even more reliable method for bass measurements is the ground-plane method, but that requires an ample amount of space, so I've never really used it).

With a bit of care and trial-and-error, you can get results that greatly approximate those made in an anechoic chamber or with the Klippel NFS. For some validation of the method, and an idea of what you can expect, here are some examples of my own measurements compared to anechoic sources.

JBL HDI-1600 (vs Amir's NFS):

View attachment 120854
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View attachment 120855

D&D 8C (vs Erin/hardisj's NFS):

View attachment 120856

Focal Chora 806 vs Soundstage Network's at the NRC anechoic chamber:
View attachment 120857

The Spinorama/CTA-2034A standard says that a ±1.5dB measurement agreement for the same speaker is considered 'good'. You can see the above measurements are very close to that, despite measuring different test units.

Note that this does not mean the quasi-anechoic method is as accurate as an anechoic chamber or Klippel NFS. In particular, resolution in the low mids pales in comparison, which means narrow resonances may be obscured partially or entirely. But the data is still very useful for determining trends in tonality and can become effectively equivalent to anechoic ones by the upper mids.

2) Setup and gear

Here's what you'll need:
  • Room EQ Wizard. This guide was written with beta Version 5.20 RC6. As of writing this guide there are a several important features in the betas not available in the 'stable' release that is currently available on the REW website (V5.19). In my experience, the betas are extremely stable for the type of work we're doing
  • (If splicing nearfield bass) The Jeff Bagby Diffraction and Boundary Simulator, for adjusting nearfield bass measurements to match farfield results. This requires Excel; I've not tried it on Google Sheets or other spreadsheet software.
  • (If doing full spinoramas) VituixCAD (version 2.0.65.0 was used for this guide). It will automatically create a spinorama once provided with enough horizontal and vertical off axis measurements. It can also adjust nearfield bass measurements, but I prefer the simplicity of the Bagby spreadsheet.
  • A MiniDSP Umik-1 or other flat measurement microphone. If you don't already have one, I'd highly recommend getting a calibrated Umik-1 from Cross Spectrum Labs for extra accuracy. It only costs a few bucks more than ordering one directly from MiniDSP ($110+ shipping). It's not necessary, but increases accuracy in the upper treble and lower bass and adds peace of mind.
  • A microphone stand. It just needs to be thin so as to be minimally reflective. I use something like this, about 20 bucks.
  • A sturdy way to elevate speakers far off the ground, preferably 5+ feet, but as far from surfaces as you can manage. I've typically simply placed my speaker stand on top of a table. The sturdiness of the speaker stand is particularly important if you want to do vertical measurements. I'm currently using this.
  • (If doing off-axis measurements) You'll need some kind of turntable to place your stand on. I use this and label it with angles in 5 degree increments. For added security, especially for vertical measurements, I highly recommend getting a rachet or cam strap to secure the speaker while it's off-balance. I use one or two of these.
  • Open space. If measuring indoors at 1m — sufficient distance for most bookshelf speakers, in my experience — you'll want the closest wall (including the floor and ceiling) to be about 1.5+ m (5+ feet) to match the time window and resolution I've used in most of my measurements (6.5ms). You'll also want to move all furniture out of that 1.5 foot radius — or as far as possible — but small objects shouldn't cause much of a problem. If you have low ceilings and can't measure outdoors, you might have to settle for a smaller gate or measuring at less than 1m.
The open space is key. Again, the greater the time difference between when direct sound hits the microphone and the first big reflection hits the microphone, the more resolution your data will have, and the lower the frequency your measurement will be valid to.

When setting up your speaker on the stand, it should look something like this (taken from the CTA-2034A standard):
View attachment 120858

It is important to make the edge of the speaker stand as flush as possible with the speaker's baffle, as otherwise the setup can introduce minor reflections that might look like resonances. And again, I'm using a 1-meter distance, rather than the 2m the spinorama standard technically asks for, in order to increase the available time window.

Neither 1m nor 2m are magic numbers, by the way. For horizontal measurements of small speakers, simply being 2-3x the baffle width is usually enough. For a single on-axis measurement of a small speaker, you might get away with less than 2 feet. Experiment and see how the response changes at different distances, and find the best compromise for your space. Vertical polar measurements will be the most affected by short distances, so I would try to keep at least 1 meter for those for most speakers.

Don't sweat your setup too much. It doesn't need to be too fancy. This is what I used for the JBL HDI-1600 measurements above (set up for vertical measurements):

View attachment 120861
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The important thing is to simply minimize reflections enough to keep your data sufficiently clean to be useful, which you can readily assess from the resulting frequency and impulse response. If the impulse response looks messy or the frequency response looks unexpectedly 'squiggly', try to move stuff around to make it as clean as possible, then remeasure. It'll take some trial and error, but again, don't sweat it too much. Perfect is the enemy of good.

One more note: make sure that the sample rate for your input and output devices are the same (Thanks for the reminder @sweetchaos). The Umik-1 can only operate at 48kHz for example, so you'll want your audio output to be at 48kHz as well. Many devices will default to 44.1 kHz and using a different sample rate can have a slight effect on the highest frequencies in my experience. Using a higher sample rate won't improve accuracy, per REW documentation.

On Windows 10, you can do this by going to Sound Settings> Sound Control Panel, tapping on your playback device's properties, and then changing the sample rate in the 'advanced' tab.

View attachment 130931

You should also make sure any spatial audio effects and the like are turned off.

3) The On-Axis measurement (sans bass)

The most basic quasi-anechoic measurement you can do is a simple on-axis sweep.

It's way easier and faster to perform, say, a single on-axis quasi-anechoic measurement (or even a few horizontal off-axis angles), than to do a full vertical and horizontal spinorama with nearfield bass spliced in. In fact, if you can position the speaker fast enough, it only takes a few minutes to do.

As noted earlier, creating open space around the speaker is key and your setup will likely take the most time in this whole process. Before even making a quasi-anechoic measurement, simply moving your speaker away from walls and measuring from closer — thereby minimizing the 'loudness' of reflections — cleans up the data a lot.

To illustrate this effect, here is an old measurement of the Buchardt A500. This is an on-axis measurement taken as a single sweep from my listening position 3m (~10ft) away:

View attachment 120862
Q_A500_Single.png

This doesn't tell us much about the speaker's direct sound.

Now here is another measurement taken from just 1 meter, after repositioning the speaker such that it is 5+ feet from every wall, including the floor:

View attachment 120863
Q_A500_walls.png

The highs are much cleaner now, and we have a better idea of the speaker's sound, but this is still not terribly useful. Next, I'll show the exact same measurement file you see above, except with a gate or time window applied. Note that this was not a separate sweep, I am simply modifying how REW interprets the same file:

View attachment 120866
Q_A500_gated.png

That's more like it! Although we lost the bass response, we have now removed the 'noise' of the room and have something that tells us something much more useful about the "true" direct sound of the speaker.

Here's how you do it.

Again, position your speaker as far away from walls as possible. Make the speaker's baffle flush with the edge of its stand. Aim your microphone at the speaker's reference axis; check the manual, but if not stated, it's usually the tweeter or midway between the tweeter and woofer. If you're using a boom microphone, try to keep the arm extended such that the microphone is far from the 'stem' to minimize reflections near the microphone.

View attachment 120868

(Ideally, the boom would be in line with the microphone, but I couldn't get it high enough in this case).

Then just take a regular sweep measurement in REW. I assume most of you know how to do this, but it can be done from the 'Measure' button on the upper left (shortcut: Ctrl+M). These are my usual settings:

View attachment 120869
Untitled.png

(Ignore the output and input settings, as the microphone wasn't connected when I took this screenshot).

There is one important setting in the 'measure' window that you should keep in mind for doing off-axis measurements later. By default, REW sets t=0 at the IR peak, but this causes problems once you go more than 90 degrees off-axis (basically, the reflection off a wall might be louder/have a higher IR peak than the direct sound). So it's better to set it to t=0 at IR start. The resulting FR should be the same.

View attachment 120870

Now tap start (or press the spacebar), and once the sweep is complete you have all the data you need!

From here, we just need to change the way REW interprets the data to get our quasi-anechoic measurement.

Head over to 'Impulse' tab, and make sure you're in the percentage view on the upper left. The impulse response shows us the same FR data we just captured from a time perspective.

View attachment 120871

Snag_19f5787a.png
You should now see something like this:

View attachment 120872
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See that blip right before 7ms, and how the data is all messy after that? That is where the first reflection hits the mic (each subsequent 'blip is another reflection). Were going to remove those blips from our data. You may need to finagle a bit with the zoom controls on the upper left and bottom right corners to get a good view of the blips:

View attachment 120873
Snag_1a18cd76.png

If you're measuring outdoors, you might not see such pronounced reflections. That's fine; don't worry about it too much, as we can always adjust the gate later.

Now tap on 'IR Windows' at the top of the REW window. Set the 'right window' to a time just before your first reflection. In my case, I set it to 6.5ms. The left window is usually not very important, but if measuring outdoors, it may help to shorten it to about 2-5ms to prevent loud sounds from contaminating the data.

View attachment 120874
Untitled.png

If you're doing off-axis measurements, it's good to leave yourself a little 'slack' between your window and the first reflection, as sometimes distances change a little bit as you're rotating the speaker. Hence me using 6.5ms even though I could stretch the window a little higher.

As noted earlier, the longer you have before the first reflection hits the microphone, the more resolution you have in your data, and the lower the frequency your data is accurate to.

REW will tell you what the frequency resolution of your measurement is, which will also be the lowest frequency the data is useful to. As shown above, 6.5 ms gives a resolution of 154 Hz. If possible, try to get at least a 5ms gate (this is what Stereophile uses, for reference, although they measure from a further distance), which has a resolution of 200Hz. Still, even a smaller gate can be useful, just know you'll have lower resolution.

And that's basically it. Once you tap on 'Apply Windows' you should now see a cleaner frequency response. You can also get a live view of the changes caused by changing the time window by dragging the green 'R' marker at the top of the Impulse tab.

a5DhRzr.gif


Then return to the 'All SPL' tab and you should see your new gated measurement.

Some miscellaneous notes:
  • Make sure REW is set to a reasonable scaling to get a useful view of data. It's easy to obscure flaws in the frequency response with very tall scaling. If you tap on 'Limits' in the All SPL window, the SPL Top and Bottom should be a 50dB difference in most cases.
  • For a better way to ensure consistent scaling when sharing your frequency response, I recommend using REW's built-in 'Capture' button on the upper left. Under 'graph aspect ratio,' select 25 dB/decade. This is technically the aspect ratio defined by the spinorama/CTA-2034A standard too, although not even Harman uses it most of the time. The good thing about using this method is that even if you set different vertical limits than the usual 50dB, your frequency response will export at the same scaling.
  • 1/24 is my preferred smoothing.
  • You can make your frequency response dashed or dotted by tapping 'Controls' and then 'Trace Options.'
  • As we're not measuring sensitivity for this guide, SPL choice isn't terribly important. 85dB @1m is a reasonable SPL, but I used 75dB for a long time to not annoy neighbors. It matters most when using DSP speakers whose frequency response might change (compress) significantly with SPL level.
  • Sometimes there are objects that cause unexpected reflections. Others matter a lot less than you'd think (like your own body, sometimes!). You can usually tell if something is amiss by how 'messy' the impulse response looks, or if the frequency response looks unexpectedly wiggly. Again, trial and error. Mess around with positioning and settings until you find something that works consistently.
Phew. I know that was a lot, but you should see it's really not all that difficult. Hopefully, this will get you started!

Kudos for the detailed guide!

Can these simple quasi-anechoic measurements be used for reliable speaker correction with REW, as opposed to room correction? I assume doing this properly will require at least a few off-axis measurements, how many would you recommend?

My plan for Room EQ is to first get a set of convolution filters to compensate for the speaker response, then a separate set of filters for the room response.
 

Fonsecafsa

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Why not use the MiniDSP UMIK-1 shipping from Hong Kong? I guess depends what is affordable.
I bought the Behringer ECM8000, it was, with deliver included, and a phantom power unit, around (converted) $78 but because it is splitted, I will not be taxed by the $50+ importation tax otherwise the umik here would cost $79+ 60%of $79 + deliver plus 60% of deliver, so it would cost maybe double of the behringer plus its psu. I saw some posts, but unfortunately the umik is way too expensive here, so I hope the behringer will be good enough
 

abdo123

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@napilopez

How do you go about measuring a speaker with two tweeters? each one of them is pointed at slightly different angle.

1624918788657.png


Also, are there any members who are willing to tackle this beast with me in the Benelux area? :p
 

Fonsecafsa

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I tried the best that I could to adapt the techniques inside my apartment, but I have a terrible ressonance at 60, 120, 180, etc Hz, so I don't know if the results are right or if it can be used, still, I tried my 4 speakers. TBH the results are not what I expected, so if someone can guive me a little light if I did it right, I appreciate (4 ms gate, otherwise I get these huge reflections.
Just to add a note, I tested with two receivers, very similar responses, but with around 3 dbs of difference (I was curious if it would be really different)
 

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napilopez

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I tried the best that I could to adapt the techniques inside my apartment, but I have a terrible ressonance at 60, 120, 180, etc Hz, so I don't know if the results are right or if it can be used, still, I tried my 4 speakers. TBH the results are not what I expected, so if someone can guive me a little light if I did it right, I appreciate (4 ms gate, otherwise I get these huge reflections.
Just to add a note, I tested with two receivers, very similar responses, but with around 3 dbs of difference (I was curious if it would be really different)

I'm not sure what I'm seeing here... first of all though, tap on the 'Freq. Axis' button on the upper right of rew because you are using a linear X-axis as opposed to logarithmic. So naturally the results will look very weird. Half of the graph is just the stuff above 10kHz which barely matters =]

Second, you're using dBFS on the Y-axis, which shouldn't really affect the appearance, but normally SPL is what we use.

Third please use at least 1/12 scaling for quasi-anechoic measurements to be useful, preferably 1/24.

Forth, I'm not sure why you're even seeing resonances at 60/120/180Hz. With a 4 Ms gate, the lowest valid frequency is 250Hz, so REW should automatically cut off anything before that.

Start with these changes and we can proceed from there!

@napilopez

How do you go about measuring a speaker with two tweeters? each one of them is pointed at slightly different angle.

View attachment 137994

Also, are there any members who are willing to tackle this beast with me in the Benelux area? :p

The same as any other speaker! Just pick a reference axis and go with it (alternatively, measure a few vertical angles and find which one appears to be the best).
 

Fonsecafsa

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I'm not sure what I'm seeing here... first of all though, tap on the 'Freq. Axis' button on the upper right of rew because you are using a linear X-axis as opposed to logarithmic. So naturally the results will look very weird. Half of the graph is just the stuff above 10kHz which barely matters =]

Second, you're using dBFS on the Y-axis, which shouldn't really affect the appearance, but normally SPL is what we use.

Third please use at least 1/12 scaling for quasi-anechoic measurements to be useful, preferably 1/24.

Forth, I'm not sure why you're even seeing resonances at 60/120/180Hz. With a 4 Ms gate, the lowest valid frequency is 250Hz, so REW should automatically cut off anything before that.

Start with these changes and we can proceed from there!

Thanks for the answer, I corrected what you pointed and I am uploading a new pic.
My point about the reflection was a doubt if it is a room thing or some interference like the frequency matching the electrical power AC frequency, but it is not but it is not related to the post itself (I do think it is 59 hz instead 60, because at 118 hz tone the sound is super loud), it is just a side note.

Also, thanks again, I am learning a lot and I hope that I can contribute with this knowledge in the future.

Today I made another tests too, like running these same speakers in two different receivers, tell me if you want to see the data and please point if I can make another modification to make the data more visible.
 

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fjhuerta

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Absolutely spectacular post. I had looked for this information for ages. THANK YOU!
 

DaveFred

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When merging nearfield woofer and nearfield passive radiator, are you looking to match up the bottom ends of the tails like you would with a port merge?

The reason I ask, is I am taking both measurements 1/4" from the cone, but I am having to adjust the PR response up almost 4dB in order to get the tails to match.

First pic, nearfield of woofer and PR, a copy of the PR raised to match the tail of the woofer.

two tails.jpg


Second pic, summation with matching tails.

matching tails.jpg


Third pic, summation with no level matching.

not matching tails.jpg


I know I need to add mass to the PR, but before I start those trials, I would like to make sure I am summing them correctly.

This is to be merged with the farfield of the woofer for use in a two way crossover.

Drivers are,
Visaton W130X Woofer SD=94cm^2
SB Acoustics SB16PFCR-00 6" Passive Radiator SD=124cm^2
 

Fonsecafsa

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Jun 10, 2021
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Hey napilopez, just something that I though, how about a measurement pointing to the sky? The point would be avoid echoes. I know that the gavity factor ebters in the equation, but how much can it compare to the usual sound?
(Or pointing to the window of an apartment for example, the worst part would be set up the mic on the air)
 

fluid

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When merging nearfield woofer and nearfield passive radiator, are you looking to match up the bottom ends of the tails like you would with a port merge?
There is always something of a fudge factor with merging measurements.

There is some information in this Klippel Application note on how to make a measurement between the two radiators to find the minimum output point and to compare this against a modelled response. Thiele Small models based off measured parameters are very accurate below 100Hz and should point to how best to merge them. Alternatively a ground plane measurement would help.

https://www.klippel.de/fileadmin/kl...39_Merging_Near_and_Farfield_Measurements.pdf

Hey napilopez, just something that I though, how about a measurement pointing to the sky? The point would be avoid echoes. I know that the gavity factor ebters in the equation, but how much can it compare to the usual sound?
(Or pointing to the window of an apartment for example, the worst part would be set up the mic on the air)
There are techniques to get 2pi measurements by digging a hole in the ground and putting the mic above the speaker. This will not give the free field response. If you put the speaker on it's back on the floor and the mic above there will be reflection and diffraction from the baffle to floor distance which will contaminate the result. It can work for frequencies above the baffle step but no better than getting the speaker off the ground.
 
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