# REW for testing a full range speaker.



## aceinc (Oct 24, 2006)

I have used REW (v 4.11) for tuning my subwoofers with good success. Today I am trying to use it to test some full range speakers.

The story;

I picked up 6 KEF 101/2 speakers, one is dead but five seem to function. They sound pretty light in the bass, and a little loud in the midrange. So I thought, why not try using REW in a close mic arrangement to see if I could see the issues.

The setup;

Toshiba notebook -> NAD 2200PE power amplifier -> KEF 101/2 -> RS SPL Meter (about 4" from center of drivers) -> Toshiba Notebook.

The REW settings;

RS Calibration file, 80 db target, 50hz-20khz sweep.

The problem;

The graphs, I tried two different speakers, on multiple sweeps, are nastier than I would have expected. I find it difficult to believe that the speakers are really this bad, and am wondering if I am doing something wrong. A sample of a graph is below.

Can REW be used for this purpose?

What information do you need from me to determine whether I have things setup optimally?

Paul


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## aceinc (Oct 24, 2006)

BTW, the specs for the 101/2 are supposed to be "Frequency response: 50-20,0001-1z (-6dB at 38Hz)."

They are meant to be installed against a wall which would add 3 DB to the low end.

Thanks for your help.

Paul


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## laser188139 (Sep 19, 2009)

If you are running two front speakers simultaneously, some of what you are seeing may be comb filtering. 

More importantly, there can be a lot of variation among RS meters above about 3kHz-4kHz. So most of what you see above that, you should probably ignore. If you want to make full range measurements, you should really buy a microphone with its own individual calibration file. The generic files for the ECM8000 or the EMM-6 work well up to ~10kHz, but above there the variation between mics becomes significant; you can see this in the graphs in the generic mic calibration file download page. 

Bill


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## Wayne A. Pflughaupt (Apr 13, 2006)

Hi Paul,

Four inches is not a good distance for taking a full-range measurement. The manufacturers’ specs you typically see are generally taken at a distance of about 3 ft. For the rest of us, our main concern is how the speakers sound at our listening position, so that’s the best place to take a measurement.

By the way, the RS meter is not going to be accurate above ~3 kHz. If you’re interested in accurate full-range measurements you really should look at getting a calibrated mic and appropriate USB interface, especially if you intend to do some equalizing.

Regards,
Wayne


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## fusseli (May 1, 2007)

I'd been wondering the same thing about doing full range measurements with a radioshack meter. Good to know.

Is it safe to say that the radioshack meter IS reliable from 10-3000 Hz, then?


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## Wayne A. Pflughaupt (Apr 13, 2006)

Yeah, it’s fine for an “FYI” measurement up to 3 kHz or so – i.e. to give you an idea of what you have.

Regards,
Wayne


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## aceinc (Oct 24, 2006)

I am testing one speaker at a time.

The KEF 101/2 speaker is a uniQ style speaker, effectively coaxial with the tweeter in the center of the woofer. I was using the mic close so as to limit reflective interference. My reasoning is that at 1 meter, I need to increase the volume such that it will cause reflections from walls etc, since I do not have an anechoic chamber.

OK, so the RS meter is bad above 3khz, what about the drop off below 350hz?

I do have a Behringer mic, and phantom power source, but it is more difficult to setup, would that be better than the RS SPL Meter?

Paul


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## Wayne A. Pflughaupt (Apr 13, 2006)

> My reasoning is that at 1 meter, I need to increase the volume such that it will cause reflections from walls etc, since I do not have an anechoic chamber.


My reasoning is, why would you want to duplicate an anechoic-chamber measurement if your listening room isn’t one?




> OK, so the RS meter is bad above 3khz, what about the drop off below 350hz?


Not to worry, there’ s no reason to take stock in any measurement taken from 4 inches. It’s not valid and bears absolutely no resemblance to what you’re going to be hearing at the listening position.




> I do have a Behringer mic, and phantom power source, but it is more difficult to setup, would that be better than the RS SPL Meter?


Depends: Do you want to see what the response above 3 kHz is? 

Regards,
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

Just remembered, REW can take a gated measurement that can simulate an anechoic chamber. Basically what it does is shut down the mic before reflections have a chance to arrive. However, it won’t work for the low frequencies.

Regards,
Wayne


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## aceinc (Oct 24, 2006)

The reason for anechoic measurements is to determine what is speaker, and what is environment. For the sake of these tests, I really do not care what I will hear at a listening position. What I care about it is what does the speaker do when the room is taken out of the equation.

I take it that you suggest that the Behringer microphone is worth the effort.

Are gated measurments on by default? 

If not how do you turn them on? 

In reference to gated measurements, at what frequency do they become unavailable or ineffective?

Paul


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## laser188139 (Sep 19, 2009)

After you take a measurement, you can adjust the gating used to analyze the impulse by clicking on the IR Windows icon at the top. The Can someone explain GATING in response measurements? thread may help you with it might be used. As you go to shorter and shorter windows, it should be clear where the low end information disappears or becomes less meaningful.

Bill


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## laser188139 (Sep 19, 2009)

aceinc said:


> ... OK, so the RS meter is bad above 3khz, what about the drop off below 350hz? ...


The drop off below 350Hz is not an effect of the RS meter. One sees variation below 20Hz among RS meters, such that you would want to use the Behringer mic at very low frequencies, but not at 350Hz. 

That falloff below 350Hz is very consistent, 6dB/octave. So it is surely not a room effect, especially measuring near field. And it cannot be an effect of filtering in your computer, as you would have seen this when you built the soundcard calibration file, unless you changed the soundcard options after building the calibration file and introduced a filter at the low end. 



aceinc said:


> ... They are meant to be installed against a wall which would add 3 DB to the low end. ...


My guess is you are seeing the designed response of the speakers. You indicate they are intended for corner placement. This rolloff may be designed with the expectation that reinforcement from the corner will restore the response back to approximately flat. 

Bill


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## Joppnl (Nov 2, 2010)

What I did to get a graph of the speakers themselves in stead of the room:

- put the RSmeter on a stand, 'bout 3 feet (1meter) from the speaker, height in between the lowest and highest speakerunit

- take a feather bed (or eiderdown (mm. I don't know if this is correct English, looked it up at the dictionary) or heavy blankets and make a kind of a cage around the mic and speaker.

Be sure that the blanket or f.bed is not in between the mic and the speakerunit.

The thicker the blanket is the more room reflections will not come through.

For me it became clear that the speakers I use are ok but the room is the problem.

Hope it helps for you


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## Mika75 (Feb 5, 2009)

*****DanTheMan's blog*****

Dan's a member here, his blog contains very informative information regarding the measurement of loudspeakers using REW. 

Highly recommended reading :T


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