Any suggestions of measurement hardware?

Are you asking about it for basic PA setup/tuning or is this for speaker development work?

For designing speakers, I like CLIO because all of the signal generation and capture hardware is integrated. It costs more, but it's plug and play and correct right out of the box, without any extra hardware/setup/Windows/sound card shenanigans. If you don't want to spend that much and are OK with more effort on the front end, there are several options. REW is one of the more common ones, so help is pretty easy to find.
 
It’s a bit of a dilemma. Clio is too expensive for incidental use (and still requires basic knowledge) and my suggestion requires training and remembering settings in apps like ARTA and REW. So you have to use them more than occasionally. But I prefer the ARTA/REW-route. It offers more (think of integration with VituixCAD, creating polars and performing room and speech acoustics measurements), is more versatile.
 
@SoZo, it all depends on what kind of measurements you want to do, and if you need this for a one-off project or if you want to invest into a more general setup for efficient day-to-day work on a long term basis.

The ECM8000 does give good SPL response curves, if you have a good calibration for it. However, the ECM8000 tends to go out of spec quite quickly, so you'd have to recalibrate it after a few months.
 
It all depends on what you want/need. The ECM8000 mics out there have a pretty variable response, especially at high frequencies. If that's important to you, calibration will be necessary from time to time. Or get a better microphone that comes with good calibration data and will not drift away from this.
 
In my opinion, making accurate, repeatable acoustic measurements is one of the more challenging aspects of designing and building speakers.

Acoustical measurements require a test microphone, which usually means a small capsule omnidirectional microphone with a calibration file. Entry level measurement microphones are about ~ $80. You can use a USB microphone which plugs directly into a laptop, or you can use an XLR-connection microphone. The USB option has the advantage of being simple, plug and play, and fewer opportunities to mess up the measurements. The XLR-connection mic will require a USB audio interface. The USB option can serve you well for a time, but eventually your skill and knowledge will progress to the point where you will want more data than it can supply. At that point you will have to switch to an XLR-mic and a 2 channel audio interface. Only you can assess your technical skill and knowledge and judge which type of mic you should start with.

I started with a Dayton Omnimic, which has its own measurement software. When I decided I wanted to do full polar measurements to support a more robust simulation, I bought a Berringer UMC202HD USB audio interface, and an Audix TM1 microphone.

I use ARTA for acoustical measurements. It is not free, but the liscensing fee is modest. Other people use REW, which as far as I know is free.

I am not an expert on impedance measurements. I know there are inexpensive ways to measure impedance that T/S parameters, but I use the Dayton DATS v3 for this.

j.
 
I am not an expert on impedance measurements. I know there are inexpensive ways to measure impedance that T/S parameters, but I use the Dayton DATS v3 for this.
The measurement of impedance is quite easy if one follows the instructions in the ARTA manual. It requires a power amp, a few resistors plus some protection zeners and some soldering. My ‘interface’ measures about 3x2x1”, has cost me some €10 and enables very accurate measurement with LIMP, included in the ARTA bundle.