USB Soundcard Recommendation

Hello, I'm setting up a new install of REW and would like to use an external sound card. Doesn't have to be the best but something nice. I will be using REW primarily for loudspeaker design, so both frequency and impedance measurements, Any recommendations?

The RME ADI-2 Pro is excellent for impedance measurements as it is DC coupled and its headphone outputs have high drive capability. It doesn't have mic preamps though. More general purpose interfaces with mic preamps include the Focusrite Scarlett 2i2 and the Steinberg UR22C.

Steinberg UR22C has a high level of input noise. It is better to consider Steinberg IXO 22 instead.

Most any USB interface with two matching inputs will be suitable, don't cheap out on an interface that has one mic input and one instrument input. I wouldn't recommend Focusrite due to driver issues under Windows, constant buffer under-runs regardless of settings.

For a low cost option there's Behringer UMC202HD, don't expect very high performance from it though for distortion/noise analysis, but for basic frequency response and impedance measurements it will be fine. I used to use a Steinberg UR22mkii which I would recommend as a solid mid-range unit, I can only imagine the newer UR22C is quite similar.

For a higher performance but still affordable option, Motu M2 or M4 are great. I use an M4 myself. Unlike the budget options like Behringer, Focusrite, Steinberg, Motu has a real balanced output, and both TRS and RCA connectors are available which is convenient for connection to most home audio equipment without needing a TRS to RCA adapter. The visual level indicators are handy, as a downside, the analog knobs for adjusting gain levels are digitized, they move in discrete steps despite the analog feel of the knob.

I use this jig in my setup:

For Motu M2/M4, I'd recommend using around 1k and 8k ohm resistors instead of the 47k/22k shown for the voltage dividers.

dcibel said:

For a low cost option there's Behringer UMC202HD, don't expect very high performance from it though for distortion/noise analysis, but for basic frequency response and impedance measurements it will be fine. I used to use a Steinberg UR22mkii which I would recommend as a solid mid-range unit, I can only imagine the newer UR22C is quite similar.

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The Jig looks great, I wil check out your recomandations

dcibel said:

For Motu M2/M4, I'd recommend using around 1k and 8k ohm resistors instead of the 47k/22k shown for the voltage dividers.

Click to expand...

The Moto looks great. So correct me if I am wrong but it appears that the amplifier is used for both impedance and SPL measurements. What voltage / wattage do you typically use for impedance measurements? Around 1V to 1.5V? Are better measurements achieved with higher than line level voltage or are the audio interfaces just not capable of driving a driver properly?

G

Yes, I use the amp for both impedance and SPL, it allows for flexibility of other measurements at higher output levels, for example you could characterize change in impedance at different output levels. I've placed the feeback loop after a speaker crossover to measure the transfer function of a passive filter. Lots of possibilities if you put your mind to it. It also avoids having to switch much cabling to change from electrical impedance measurement to acoustic measurement. All connections between interface and speaker can remain the same, just input the impedance probe, plug in the mic and you're done.

T/S parameters are low level by definition, so these measurements only need ~250mV, anywhere from 200-500mV is usually plenty.