Using REW with Focusrite Solo and Dayton EMM-6 for speaker design setup questions.

[David Eisan]

Hello,

For the last year I had been using REW with a UMIK-1 for measuring drivers to import into crossover design software to build speakers, but the timing info was not perfect and the phase between drivers was not always giving me the results in real life the crossover design software said I should be getting. I had been using gated measurements (3-4ms depending) and exporting minimum phase versions of the sweeps. Of course I was also doing nearfield measurements and splicing them to the gated measurements and using software to model/overlay bafflestep.

After reading a lot on the forums about what I thought I needed for better measurements I bought a Focusrite Solo and an EMM-6 to take better measurements and I have found a whole new learning curve. This isn't nearly as plug and play as a UMIK-1, but I am hoping it will yield more accurate results.

The Focusrite Scarlett Solo is installed, soundcard calibration is done and the mic is working. Loop back is from the right channel RCA out to the 1/4" jack in on the front. Output is from the left channel RCA out to my preamp/poweramp/speaker box I want to test. Microphone is obviously connected to the XLR on the front, phantom power is turned on.

With the loop back I am getting distance measurements between the mic and the drivers being tested.

A couple of questions.

It seems like I also need a separate dB meter to calibrate the dB readings in REW that I didn't need with the USB UMIK-1. I used a Dayton iMM-6 with my phone to set the dB by playing pink random and comparing what REW was hearing with what my phone was reading in the same position as the EMM-6 and making the correction.

Are there some base guidelines for settings on mic gain, loopback input gain and monitor out to preamp?

Once I set these, it would seem that they should be left alone and never touched, or calibrating the dB will have to be done again.

How do I set the mic and loopback headroom to be similar (do they need to be?), and just what should that headroom be?

Any hints on setup for measuring drivers with this setup?

Is there a simple guide for using REW with a non-usb mic for speaker builders?

I spent about 4 hours on this tonight learning and setting up, I hope I can do some useful measuring tomorrow!

Thank you,

David - London, Canada.

 

[John Mulcahy]

You could also use the UMIK for SPL calibration. Set the loopback input gain so the level on the loopback input is around -12 dBFS when you play your measurement signal (i.e. 12 dB headroom). It isn't very critical, anywhere from -30 to -6 dBFS should work fine. The input and loopback headrooms do not need to be the same, though you'll get better signal to noise from your mic if the gain is set so peak level during a measurement is around - 12 dBFS or thereabouts. Again, not very critical. If you change the mic gain after SPL calibration you would need to redo the SPL calibration, though that is quick to do.

 

[Bernard]

Hello,

Thank you gentlemen ! You bring me precious help.

I am looking for a usb audio interface to replace my IBF MPB-USB mic preamp and my Creative soundcard I used with ETF Acoustics ETF5.
(The site no longer exists and I wonder what has become of Mr. Doug Plumb.)

I have an IBF EMM-8 calibrated mic and wonder if I should use 48V phantom power without the microphone turning itself into a ghost !

The Isemcom data sheet gives the following information:
Sensitivity 6mV / Pa / 1kHz +- 4dB @bias 2.5V, 2.2 kOhm
Power requirements 1.5 - 10V / approx. 0.5 mA

The Dayton EMM-6 datasheet gives :
Sensitivity at 1kHz at 1K ohm: 10mV / Pa (-40dBV, re 0 dB = 1V / Pa)

Can the IBF micro suit ?

Best regards from France.
Bernard

 

[John Mulcahy]

Best checking with iSEMcon whether the EMM-8 can take 48V, the preamp IBF sold with that was powered from a 9V battery.

 

[musicguy]

What if you use the umm-6. With an audiobox 22vsl. I cant do the loop back to calibrate the audiobox. Or do i even need to do this sence its a usb from box to computer

 

[John Mulcahy]

No soundcard calibration when using a USB mic.

 

[musicguy]

Sorry its a emm-6. its a phantom powered mic. Into a presonus 22 vsl. Is considered a usb mic? The 22 vsl only has audio out and no audio inputs. To do the loop calibration. So should i just skip the loop calibration. The connection of the 22 vsl to my computer. Is a usb cable only

i really want to do things correct and learn rew.
Thank you for your help

 

[John Mulcahy]

No, "USB mic" in the context of REW means a mic that connects directly over USB, not an analog mic that connects through an audio interface. The 22 VSL has mic inputs, instrument inputs, analog outputs and a headphone output. It is an audio interface with all the connections needed to do a loopback calibration of its response.

 

[musicguy]

Thank you for clearing that up. I watch other videos on the loop back calibration. I just dont know how i would do it on a 22 vsl. Is there a post on how to loop soundcard calibration for the 22 vsl somewhere

musicgiy