August 5, 2010

Basic measurement setup

Why measure?

Every system can potentially benefit from using measurements. If you are designing or modifying your own speakers, or setting up a subwoofer, measurements are essential. Even if you have a simple 2 channel system there is still some benefit. Measurements won't replace critical listening skills, but they will help you make better choices, including many that simply can't be made by ear. It is a learning process, where you take measurements as well as listen carefully. In this process, you learn what to look for in the measurements since better looking measurements don't always sound better. Expectations often need to change.

Isn't it better to everything by ear, since it is the ear that is the final judge?

Find the answer here:
Measurements vs doing it by ear >

The best $150 you've ever spent on audio?

It's affordable and not exceptionally difficult. In the past, the cost was much greater where a measurement setup would most likely cost more than $1k. Now low cost tools will do the job.

Behringer ECM8000 measurement mic >
Behringer XENYX 502 mixer >
Sound card which supports full duplex operation
Mic tripod (you can use a camera tripod but it's inconvenient)

Highly Recommended:

Cross spectrum calibrated mics >
(slightly more expensive than a stock ECM mic, but far more reliable results)
Boom mic stand

You'll find it much easier with a proper stand and if you plan to measure on a fairly regular basis, the extra expense is certainly worth it.

Why can't I just plug the mic into the PC?

The signal will be too low and you will not get a measurement at all.


Fortunately, this part is free.

For bass measurements, download the free program REW from the HT shack here >


For full range measurements, Holm Impulse is both free and very easy to use:
Download Holm Impulse here >

Do you need a calibrated mic?

This depends on what you will measure. For fullrange measurements - definitely. For bass optimisation, you be the judge. Here is a chart that shows a number of the Behringer Mic unit to unit variation:

Image courtesy of Cross Spectrum Labs who offer a calibration service, and supply calibrated mics (including the Behringer mic shown here) at a very attractive price.
View Cross Spectrum Labs website >

As you can see, you get about +/- 2db at 40 Hz, worse at 20 Hz but not as bad higher up. The most you are likely to see is 2db out above this point, but if you are lucky you may get 1db or less. In truth that is probably enough, but then when you consider that it doesn't cost much more to be sure I think most would simply pay the extra.

If you already have a mic, you are probably best to sell it and simply buy a new one direct from the lab that has already been calibrated:

Cross spectrum calibrated mics >

The cost shipped to Australia is little more than the stock ECM mic.

There is a thread on the HT shack about this service, with some very useful info:

More info on the service >

Cables and connections

You will need balanced mic cable to connect the mic to the mixer and it's a good idea to pick up a good length like 10m, with XLR connectors on each end. Connect to a PC with jacks on "main out." The simple way is to connect jack > RCA adaptors then just run an RCA cable to PC. You can get a cable with RCA on one end and mini jack on the other, or again use an adaptor.

What kind of results will I see?

The most common use will be to get the bass right in your room. The best bass can't be bought - it must be tuned to your room.

Here is an example of in-room bass measurements >

In that example you will see examples of the mains and subs, how they are combined and a final result with EQ applied.

In the most basic system, it will show you which sub and speaker placements work best. In a more sophisticated system, it will help with placing multiple subwoofers and with using EQ without killing headroom.

How do I measure?

There are various methods to measure covered here:

Measurement techniques - an introduction


  1. Thanks for the link to the Calibrated Behringer ECM8000 microphones.

  2. Hi Paul,

    A basic question; How does the 502 connect to the computer as I see no USB connection? I would like to run it into a MacBook if possible?

  3. Good question. What inputs do you have on your sound card? PC sound cards typically have mini jacks so it's a matter of either getting cables with the right connectors, or using adaptors. If you don't have any typical audio inputs then you might need to soure a special adaptor for Macs. Also keep in mind that you can have gain issues depending on whether you use mic or line inputs.

  4. Hi Paul, The input on a Mac is mini jack that also work as Toslink optical. No soundcard as such in a Mac...any suggestions? Hopefully the XENYX 502 will bring up the ECM8000 to a level that the Mac can work with?

  5. In that case it's the same as my setup. You just need to get from a stereo mini jack to two pro style jacks. There are many ways to do it, including soldering your own cable, buying cable with the desired connectors already on each end, or using adaptors. I prefer adaptors as they are handy to have anyway. You should not have a problem with gain, although I did find that out of the two available inputs (mic and line in), only one of them was suitable. If a pro mixer doesn't give you enough gain, I don't know what will. I've found that when using the right input, I can easily get the level high enough to cause clipping of the signal. Fortunately REW gives you a warning when this happens.

  6. Hi Paul,

    I am looking to get a setup to measure my speakers and my room.

    Why do we need the Behringer XENYX 502 mixer? Why can't we just connect a microphone to the line in port of a soundcard and use software to generate a frequency response chart? wouldnt that enable us to view the spikes and dips and fix that via placement, room treatment or equalisation?

  7. Hi Simon,

    Good question - I will update the blog when I get the chance. The problem is one of gain and being able to ensure that it's in the right range for measurement. Too much gain and the signal gets clipped. Not enough and you won't get an accurate measurement or in fact any measurement. You not only need the gain, but also gain adjustment so that you are above the noise floor without clipping the signal fed to the sound card.

  8. Can you please elaborate on the gain issue? Do you mean if i turn up the microphone in volume too high on the pc, then the frequency response graph will be clipped, but too low and it will be overcome with noise?

    how does the mic preamp help with that?

  9. Yes. If the gain is too high, you get clipping of the signal and the measurement isn't accurate. The gain needs to be in an acceptable range to get an accurate measurement.

  10. well i may as well buy the microphone first and see if i get a good result without the mixer, and if not then buy the mixer.

    it has a 3-pin XLR, would it work if i bought a 3-pin XLR to 2.5mm stereo adaptor for connecting to a soundcard?

  11. Without the mixer which provides gain control, you probably won't get any result. With the mixer, you plug in an XLR mic cable, then you can see at the top "main output" (just under "502") where you have two TRS jacks. I use Jack > RCA adaptors then connect that to PC via a cable with RCA on one end, mini jack on the other. This goes into mic input on the sound card. You of course also need an output from the sound card into the sound system so the program can send out a signal to measure.

  12. I am certainly no expert but I am pretty sure that the Behringer mics need "phantom power" whatever that is. PC and Mac inputs almost certainly don't have "Phantom Power" so therefore you need a semi-pro mixer or similar that has this feature.

  13. As you say, phantom power is required for the Behringer mic and it is provided by the mixer shown in the photo.


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