Mac setup for dummies?

[Jazzman53]

Hello all,
This is my first post here and I'm completely new to REW. Also, being a computer illiterate old guy, learning to use REW is for me a daunting proposition. I'm wanting to use it to tune a DIY hybrid electrostatic speaker I just finished. I think I over-tensioned the diaphragms a bit because I hear a nasty resonance which I will need to identify and mitigate with a notch filter.

I have a Macbook Pro, a Behringer ECM-8000 microphone, Behringer PS400 phantom power supply and an XLR to USB cable to connect the MacBook to the mic. I also have a Behringer DCX2496 and DEQ2496.

I have a couple of initial questions about the connections for REW:
1. The PS400 isn't a preamp, just a phantom power supply.. can I run the measurement sweeps from the Mac's earphone out?
2. I've read that REW setup requires doing a feedback loop and initial sweep to establish a time reference. The PS 400 has only mic in and mic thru connections -- no other ins/outs that could be used for a feedback loop. What are my options for the timing reference?

 

[John Mulcahy]

Yes, the headphone out can be used.

REW setup does not require a loopback, and it isn't essential to perform soundcard calibration - one of the main purposes of that is to make sure there isn't any monitoring enabled. If you need a timing reference for your measurements the Acoustic Timing Reference option could be used.

 

[Jazzman53]

Thanks John for answering that question.

Now I have another:

I've been doing some more reading in the REW setup guide and I think it says therein that the Behringer ECM8000 mic requires a phantom power supply with a preamp. It also says that a USB mic can be plugged directly into a MacBook and this would negate having to calibrate an external sound card.

I have a Behringer ECM8000 mic, a PS400 phantom power supply (does not include a preamp) for the mic, and an XLR-to-USB adapter cable to connect between the PS400 mic thru and a USB port on the Mac. Why would this combination NOT be equivalent to a USB mic? Can I use it?

 

[John Mulcahy]

You can certainly use it, but it doesn't make it quite the same as the USB mics referred to. Those are supplied with a calibration file by the manufacturer which compensates for the mic's frequency response and includes a sensitivity figure that allows REW to convert the mic readings to SPL, taking account of the volume setting. With the ECM8000 you will have to manually calibrate the SPL reading (straightforward) and accept that it's response will have a low end roll-off and some higher frequency bumps and wiggles that are unknown, so you'll need to allow for that. You could get the mic calibrated at http://www.cross-spectrum.com/ if required, but you may find you can do what you need without that.

 

[Ronin0]

Hello all! This is my first post, so please be gentle.
I am wondering why a mic such as the ECM8000, with a supposedly linear frequency response from 20 Hz - 20 kHz would require a calibration file.
Why would we expect it to have a LF roll-off and some HF "bumps and wiggles". I get that a calibration file is ideal, but surely the 'non-calibrated' response would be within plus or minus 3dB of the published response from mic to mic, or is that too imprecise for REW?
Am I missing something here?

Thanks in advance for any clarification.

 

[John Mulcahy]

The variation can be larger than one might expect, but an uncalibrated mic is fine for deciding on speaker positioning and seeing what improvement treatments bring, for example, just don't pay too much attention to what it shows above a few kHz.

 

[Ronin0]

Thanks John. That's precisely what I intend to use REW for, placement and checking acoustic treatment.
I have since read in the guide that there is a procedure for calibrating the mic sensitivity with an SPL meter, so I will do that and skip loading a profile.
I have either been blessed or cursed with vaulted parallel walls starting about 3 feet up and reaching an apex with rounded seams and a foot wide celing strip. I previously had great sounding acoustics in this room for recording and Hi-Fi listening, plus my monitors have built-in room correction that I will calibrate eventually. In the meantime, they sound great set to flat and positioned close to the vaulted front wall ~8", in order to minimize SBIR while still allowing space for a panel behind them.