VituixCAD For Newbies

[AllenB]

The funny thing about REW, it that it doesn't treat phase relative to the window reference,

HolmImpulse does this too and it's a necessary feature. If the window start coincided with the main impulse, information could be misrepresented.

Here you can see Holm feathers it's windows, which wouldn't be the case if it was meant to coincide directly with the impulse peak.

 

[Nordo]

The funny thing about REW, it that it doesn't treat phase relative to the window reference, but to t=0, so the delay between the acoustic reference and measured speaker is included, always. This is different from the way other software will process phase, where phase is represented relative to the window start time. In order to remove the excess delay in REW, either use a timing offset when measuring, or t=0 can be moved in the impulse response tab after measuring, but make sure same adjustment is made to all measurements so relative differences are maintained.

Alternative is to process measurements through VituixCAD IR -> FR tool. This can be done with REW, but some steps are required to export the impulse response from REW correctly. I've made a quick instruction on this, attached.
(Since you are using an acoustic timing reference, it will be important that the acoustic timing reference is closer to the mic than the speaker being measured for this instruction, since I am effectively deleting everything prior to t=0 in the export).

After I had completed my measurements using REW, and exported them into VituixCAD (on another computer), I noticed in Kimmo's REW instructions that he had added added a timing offset in REW for the distance from test speaker to mic.
Because I was using an acoustic reference speaker, I wasn't sure if I should have added that delay or not. 🤔

Also reading this post of yours, makes me concerned that I had my reference speaker around 1800mm from the mic, while the test speaker was at 1000mm.
I'm not sure how to position the reference speaker closer to the mic without running the chance of getting early reflections off it's cabinet (it's a medium sized bookshelf).

I'll have a good read of your attached instructions. But I'm still trying to get my head around when and where to add in delays or time offsets when using an acoustic timing reference, as I don't want to double up, or add a delay that's not necessary.
It's moments like this that I wish I had studied electronics and audio, instead of structural engineering.
Part of my structural course included electrical engineering, and it was the part I think I enjoyed the most.

 

[DcibeL]

HolmImpulse does this too and it's a necessary feature. If the window start coincided with the main impulse, information could be misrepresented.

Here you can see Holm feathers it's windows, which wouldn't be the case if it was meant to coincide directly with the impulse peak.

View attachment 1122427

No...window is "featured" due to the window function as non-rectangular. You haven't actually shown anything relating to phase. In Holm, t=0 and window start reference time are one and the same. Besides, Holm is a single channel measurement application using impulse peak detection for t=0 reference, it really shouldn't be on anyone's radar with VituixCAD in mind (this thread).

 

[DcibeL]

After I had completed my measurements using REW, and exported them into VituixCAD (on another computer), I noticed in Kimmo's REW instructions that he had added added a timing offset in REW for the distance from test speaker to mic.
Because I was using an acoustic reference speaker, I wasn't sure if I should have added that delay or not. 🤔

Yes, use timing offset, but not distance from speaker being measured to mic, but the difference in distance between acoustic timing reference and speaker being measured. You should find impulse near t=0 with this offset included.

Also reading this post of yours, makes me concerned that I had my reference speaker around 1800mm from the mic, while the test speaker was at 1000mm.
I'm not sure how to position the reference speaker closer to the mic without running the chance of getting early reflections off it's cabinet (it's a medium sized bookshelf).

You may find that one piddly little bookshelf speaker off to the side of your mic may have little effect on the resulting response. You can measure it for yourself without timing reference, just place the speaker somewhere, then take it away and repeat measurement. Or place far away like you have, the choice is yours. Just keep in mind that to follow my instruction above for IR export, you should apply t=0 offset to all measurements so that the impulse is in front of zero location.

I'll have a good read of your attached instructions. But I'm still trying to get my head around when and where to add in delays or time offsets when using an acoustic timing reference, as I don't want to double up, or add a delay that's not necessary.

If you can use a measuring tape, you should be able to figure out the relation of timing reference to measurement location. Hold down ctrl + right click on the impulse response chart to make physical distance measurements. Useful in overlay tab when viewing multiple measurements to measure distance between them.

With loopback timing reference, t=0 is the location of the speaker being measured, so distance from t=0 to impulse is "time of flight". With acoustic timing reference, t=0 is not the speaker being measured, but the secondary source with location chosen by you, so distance from t=0 to impulse is the difference in distance between the acoustic reference and the speaker being measured. You should see this clearly in your measurements.

 

[AllenB]

You haven't actually shown anything relating to phase.

Phase changes with the timing, not the window. I could show screenshots.

Besides, Holm is a single channel measurement application using impulse peak detection for t=0 reference,

HolmImpulse is an accurate system in regards to timing. It will lock timing between measurements and timing is as adjustable and selectable as it should be. It does the same as a dual channel system does, with one less channel. It is recommended for any speaker design including simulation.

 

[DcibeL]

Phase changes with the timing, not the window. I could show screenshots.

Already mentioned, window reference and t=0 are the same thing in Holm, window reference cannot be moved from t=0 like in other software, only the impulse can be shifted from t=0.

Not so. HolmImpulse is an accurate system in regards to timing. It will lock timing between measurements and timing is as adjustable and selectable as it should be. It does the same as a dual channel system does, with one less channel. It is recommended for any speaker design including simulation.

I tried it with a USB mic, it was a complete failure. Not going to be recommended from me, ever.

 

[AllenB]

HolmImpulse was around before USB mics were much of a thing, and I'm sure we all prefer proper mics.

HolmImpulse users were surprised to learn that REW required 2 channels to do the same thing. In any case it's written in Java and is portable, so....

window reference cannot be moved from t=0 like in other software

It can if you move both sides by the same amount

 

[DcibeL]

HolmImpulse was around before USB mics were much of a thing, and I'm sure we all prefer proper mics.

Then what's the point? I swear there is some DIY mentality of needing to prove that you to get by with a paperclip and a rubber band, when the correct tool is just an arms length away. Standard XLR mic, loopback cable, record both channels, it's not complicated.

With most single channel users attempting to do so with USB mics, really have to be clear on the reliability of "timing lock" in Holm.

Is this really that much trouble?

 

[AllenB]

a paperclip and a rubber band

HolmImpulse is in some ways a superior measurement system to REW, and has found favour with the likes of Dr Geddes.

 

[DcibeL]

Ok...

Perhaps you can write the measurement guide for Holm then. Until that happens, ARTA, REW, Clio, or SoundEasy are fine choices for VituixCAD, as all are capable of measurements with timing reference, and have measurement guides available in the help page. FWIW I prefer ARTA for use with VituixCAD, it has a nice 1 click and repeat process for sequenced spatial measurements with automatic file naming, and VituixCAD IR - FR tool I find to be the easiest method for measurement processing.

 

[Nordo]

Enough, already.
Merry Christmas guys.

 

[Nordo]

The funny thing about REW, it that it doesn't treat phase relative to the window reference, but to t=0, so the delay between the acoustic reference and measured speaker is included, always. This is different from the way other software will process phase, where phase is represented relative to the window start time. In order to remove the excess delay in REW, either use a timing offset when measuring, or t=0 can be moved in the impulse response tab after measuring, but make sure same adjustment is made to all measurements so relative differences are maintained.

Alternative is to process measurements through VituixCAD IR -> FR tool. This can be done with REW, but some steps are required to export the impulse response from REW correctly. I've made a quick instruction on this, attached.
(Since you are using an acoustic timing reference, it will be important that the acoustic timing reference is closer to the mic than the speaker being measured for this instruction, since I am effectively deleting everything prior to t=0 in the export).

After I had completed my measurements using REW, and exported them into VituixCAD (on another computer), I noticed in Kimmo's REW instructions that he had added added a timing offset in REW for the distance from test speaker to mic.
Because I was using an acoustic reference speaker, I wasn't sure if I should have added that delay or not. 🤔

Also reading this post of yours, makes me concerned that I had my reference speaker around 1800mm from the mic, while the test speaker was at 1000mm.
I'm not sure how to position the reference speaker closer to the mic without running the chance of getting early reflections off it's cabinet (it's a medium sized bookshelf).

I'll have a good read of your attached instructions. But I'm still trying to get my head around when and where to add in delays or time offsets when using an acoustic timing reference, as I don't want to double up, or add a delay that's not necessary.
It's moments like this that I wish I had studied electronics and audio, instead of structural engineering.
Part of my structural course included electrical engineering, and it was the part I think I enjoyed the most.

 

[DcibeL]

That's what you said yesterday.

 

[Nordo]

That's what you said yesterday.

Sorry - too much festive imbibing.
The forum page today was indicating that I hadn't sent my post, even though I thought I had.
So I just clicked on Post.

 

[kimmosto]

HolmImpulse is in some ways a superior measurement system to REW, and has found favour with the likes of Dr Geddes.

Discontinued product without off-axis measurement sequence is just worthless crap no matter how many Dr Einsteins like and use it.

 

[Lge62]

Rookie qustion here

If using the factory measurements and using seas drivers its stated on their webpage "All loudspeakers are measured at 0.5 m/2.83 V on axis in our anechoic chamber using the TRF-module from Klippel GmbH. The microphone is a B&K 4133." does this mean i only have to set the x and y in vituixcad and can set z to zero or have i misunderstod the whole thing ? I understand that measuring yourself is that you really should to but a dont have measuring gear and is only making a single pair of speakers for myself so dont want to invest in that. Since Seas measure their woofers in box i keep the with of the box the same as their measuring box.

 

[Nordo]

Rookie qustion here

If using the factory measurements and using seas drivers its stated on their webpage "All loudspeakers are measured at 0.5 m/2.83 V on axis in our anechoic chamber using the TRF-module from Klippel GmbH. The microphone is a B&K 4133." does this mean i only have to set the x and y in vituixcad and can set z to zero or have i misunderstod the whole thing ? I understand that measuring yourself is that you really should to but a dont have measuring gear and is only making a single pair of speakers for myself so dont want to invest in that. Since Seas measure their woofers in box i keep the with of the box the same as their measuring box.

In my opinion, the factory test data is only good for matching drivers for your DIY project, or for learning how to use programs such as VituixCAD.

You should :-
1. Select the type of enclosure (sealed, ported, transmission line, etc.).
2. Select a suitable woofer to match the enclosure type.
3. Select a tweeter to match the woofer.
4. Design and build the enclosure.
5. Measure the drivers in the enclosure - Far field and Near field. I used REW and a USB mic (UMIK-1). The USB mic make the job a bit of a fiddle, but it can be done. A must better mic is a calibrated measurement mic that requires phantom power. However, they are more expensive and with the added expense of something to provide the phantom power.
6. Follow Kimmo's instructions on measuring using REW and on transferring the data to VituixCAD.
7. Only now can you design a crossover that will produce the best crossover for your design.

The minidsp UMIK-1 microphone is relatively cheap, and is always handy for not only measuring your project prior to crossover design, but can be used to measuring the completed project.
If you think your listening room is ruining the "magic" sound your speakers are producing, you can again use the mic to find out what your room is doing to your sound, and what needs to be done to fix it (this was the original intention of REW).
BTW, I also bought a cheap boom mic stand to hold the mic.

 

[Nordo]

My Google Drive document collection has been updated with a new addition on the usefullness (or uselessness) of minimum phase. This document in combination with my other on single vs dual channel measurements should highlight the reason why dual channel measurements and using measured data including phase should be done where ever possible when designing with VituixCAD.
https://drive.google.com/file/d/1dq7mLeQMint8V95oJ1i6GXxyYRFfCgXG/view?usp=share_link

Complete set of documents is found here:
https://drive.google.com/drive/folders/1KDyECkAIVAuNEtKVobKmsfvtFczGqOQw?usp=share_link

I've read your article on "How To Export Impulse Response from REW for Processing in VituixCAD".
I've now started to use it to re-structure my IR data and export as Text to VituixCAD.
However, I can't make sense of the Export part of the instructions.
Your window with the export settings (I assume in REW) is different to mine.
My REW Export window is shown below.
There are several settings that can be adjusted, but not "normalise samples to peak value" and "Apply IR Window before Export".

 

[DcibeL]

Try selecting “export impulse”, not export measurement.

 

[Nordo]

Try selecting “export impulse”, not export measurement.

I assume that I now have to transfer the IR files to FR files using VituixCAD's "Convert IR to FR" tool?
Do you recommend any settings different from Kimmo's settings in his online Help?