loop back

UMIK-1 or Phantom powered mic with external sound card withloop back ?

I am new in this forum, but have used REW for some time.
It seems like some users say, it is absolutely necessary to measure, using an external sound card with loop back to ensure time correct measures, while others is using the UMIK-1 without any issues.

I have the UMIK-1 but what is the advantage of using loop back when just designing a 2-way to 3-way speaker?
(I am aware of the trick to include a measurement with the drivers coupled I parallel)

If you will be making measurements far off axis a loopback would be more reliable than using the speaker to play the timing reference. With a UMIK in that situation it would be best to use a separate driver to play the timing reference and ensure it remained pointed at the mic.

Hello John,
Thank you for taking your time to answer my question. I really appreciate that.
Are there any more advantages for using loopback?
If you are only making on-axis measurements and do not care for nearfield measurements of bass reflex ports and extended bass response?
What I normally do, is just designing crossovers for two (or maybe three) drivers.

It would be better for someone who uses REW for similar purposes to comment on that, but if you already use the UMIK without encountering problems I don't know why you would need to make a change.

Thanks again.
I am working on a MacBook Pro M2 Max. running REW in MacOS.
For designing speaker crossovers, I started using XSim on Windows 11 via Parallels on the Mac. I found XSim had some issues "forgetting" the values of components and the program ended updating long ago.
For that reason, I started using VituixCAD 2, that is much more modern- and advanced.
The designer of the software (Kimmo Saunisto), do not recommend using USB microphones for speaker design.
This is the reason why I started this thread regarding USB mic vs analog mic connected to a seperat soundcard with loopback.
Are there any speaker builders that have experience with this topic?

I don't recommend usb mics either.

I did just review the J-Box III, a great all in one speaker measurement kit to get started with speaker design, with a loopback timing reference.

Hi dcibel,

Thank you for your input.
I already have a MOTU2 and am very happy with the quality, but because of that, I would not invest in the reviewed product.
Still interesting to know, that an integrated product like this exist.

What is your reason for not using a USB mic like UMIK-1?

I use a Motu M4 and Line Audio Omni1 for my measurements. If you already have a nice USB audio interface, why are you looking at USB mics?

For design a loudspeaker, it involves combining the response of multiple sources from multiple measurements, which requires accurate phase relationships between all measurements. The easiest way to accomplish this is to use a USB audio interface, so playback and record are from the same device, and utilize a loopback cable for a timing reference so all measurements are captured with the correct relative distance between DUT and mic.

With a USB mic you will need an external timing reference such as an acoustic reference. It's not as reliable and much more fussy to set up, the loopback cable is plug and play and easily repeatable when mic and speakers are moved around.

Recommendation for designing with VituixCAD is to use a standard mic with loopback timing reference, follow the measurement guide for REW to gather and process the measurement data.