# setting up for REW measurements



## imprezap2 (May 13, 2010)

Hello

Today I spent some time playing with my new Tascam US-144mkII, took me a while to find out that I had to turn the mon-mix knob towards computer to get things going. (what a knob
Calibration screen shot looks good as far as I can tell (cannot attach a picture yet)

Now I have to wait till my mic gets delivered. (calibrated ECM-8000)

When the audio interface is being connected to my stereo, there is a humming noise coming through my speakers. Only when I remove the power supply to my laptop the humming stops.
I tried to fix it with a separate earth connection to the Tascam, but no result.
Is this normal, or can we only measure with the laptop on battery power ?


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## JohnM (Apr 11, 2006)

Not unusual for laptops.


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## imprezap2 (May 13, 2010)

Ok, I will wait for the microphone to arrive and measure on battery power


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## imprezap2 (May 13, 2010)

The SPL meter from Galaxy (CM-140) arrived today, time to start playing a bit. (ECM-8000 is on order)
At least I can learn a bit to read the results. (although the CM-140 specs say only up to 8000Hz)

*Equipment used:*
Amplifier: Accuphase E-560
Speakers: Focal Electra 1037be
Audio interface: Tascam US-144mkII
SPL meter: Galaxy CM 140 (Level was set around 72dB, used as microphone)
Laptop: Sony Vaio (battery powered only)
Room: 5,5mtr x 4mtr x 2,7mtr (LxWxH)

As I am new to this all comments are welcome, see attached the first readings.
It looks a bit strange between 30 and 60Hz.


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## JohnM (Apr 11, 2006)

Measurements look fine, but set the vertical range to span 45 .. 105dB - we try to stick to that for easier visual comparison between plots. Also not much worth seeing below 15Hz, so can set the left side frequency to 15. Both of those can be set up by clicking the Graph Axis Limits button (top right of the graph, next to the controls Cog icon).


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## imprezap2 (May 13, 2010)

Thanks John, see attached the same graph but with the limits changed.
It looks like a little boost on 30Hz and then a -12dB dip at 60 Hz. (reference level on CM-140 was 72dB)
Tomorrow I will try to do some measurements again.


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## imprezap2 (May 13, 2010)

The EMM-6 arrived yesterday and this morning I have made some measurements. (see attached pics)
The frequency curve worries me a bit, especially the way curve goes down at higher frequencies.
Any thoughts on why this happens ?

The RT60 graph shows long decay time for the lower frequencies, will it help here to install some bass traps ?

Till now I was quite happy with the performance of my set, but now I wonder if the room is holding it back.
(all between the ears I know)


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## laser188139 (Sep 19, 2009)

imprezap2 said:


> ... The frequency curve worries me a bit, especially the way curve goes down at higher frequencies.
> Any thoughts on why this happens ? ...


I can suggest a few possibilities:

1) If you have a receiver with Audyssey equalization, the Audyssey Reference curve has a slight deliberate fall-off above 10kHz to keep films from sounding too bright in a normal room environment. Most receivers also offer an Audyssey Flat choice if this works better for music in your environment. 

2) At these high frequencies, any obstruction at all between you and the tweeters can affect the measured performance. This could be a stack of magazines on a table high enough to block some of the direct sound, a blanket or cushion set on top of a chair -- anything at all close to the direct line between you and the tweeters. 

3) The off-angle dispersion of the tweeters may reduce as the frequency increases. So if the speakers are not toed-in and pointed at you, you could see this. 

4) This is above the level of human hearing; the tweeters themselves may be designed to be flat only to ~16kHz. 

5) Is the Tascam US-144 also the source of phantom power and the mic preamp? If not, when I introduced a Xenyx 802 for phantom power and mic preamp, I noticed it has a slight falloff at the high end when I built a soundcard calibration file that included the effect of the Xenyx even without going through the mic preamp stage. This would not explain the falloff, but it might reduce the measured levels by just a bit more. 

You could reduce the room effects by taking near field measurements 1-2 ft in front of each speaker, positioned well away from any wall, and see how the speakers themselves behave. 

Bill


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## imprezap2 (May 13, 2010)

Hi Bill,

I don't have audyssey in my system, it's stereo only, Accuphase E-560 amplifier and Focal Electra 1037be speakers. The Beryllium tweeter should be ok till 40KHz, although that is way out of my hearing range.
The room is dedicated for listening and there are no obstructions between the speakers and listening position.

In principle I am happy with the system, the staging is excellent, resolution is very good and I can listen to the system for hours without fatigue. (just the measurements make me think something is wrong)

I will try some measurements closer to the speaker.

Thx for your comments

Olaf


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