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Discussion Starter · #1 ·
I want to use the EQ wizard to check my room frequencies and I do this with just my radioshack meter and a condenser neuman microphone
 

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You’ll also need a duplex sound card, but once you have that the Radio Shack SPL meter is suitable for measuring subwoofers, and response above that out to about 3 kHz or so. If you want to do full range measurements, that’ll require a calibrated mic. You would have to have access to a calibration file, or you can create one if you have a factory frequency response graph of the mic.

Recommended reading:
REW Cabling and Connection Basics
REW Help Files

Regards,
Wayne
 

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Discussion Starter · #3 · (Edited)
You’ll also need a duplex sound card, but once you have that the Radio Shack SPL meter is suitable for measuring subwoofers, and response above that out to about 3 kHz or so. If you want to do full range measurements, that’ll require a calibrated mic. You would have to have access to a calibration file, or you can create one if you have a factory frequency response graph of the mic.

Recommended reading:
REW Cabling and Connection Basics
REW Help Files

Regards,
Wayne
My setup is as follows.
2 KRK VXT6 monitors.
1 KRK sub woofer
Two cables from the output on the RMe fireface 800 feed the subwoofer and then the nearfield monitors are connected to the sub woofer.
How is the setup done for this as the diagram in the setup seems to be for a Hardware EQ setup.
Is it possible to do a room check using this device.If that is not possible I will get a usb soundblaster external card which is the same as in the help files but i would also need an eq drvice to connect my sub and monitors to.
How do you create a calibration file f you have a factory frequency response graph of the mic?

I also have a mackie vlz 1200 mixer I presume I could use that.
 

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I believe that's a firewire interface, so if you're using a MAC you might run into issues with REW. Otherwise, you can ignore the hardware EQ in the setup, connect the output of your RME directly to the sub's input, and the RME input to the RS meter to make measurements (after calibration). I'm making the assumption here that the RME is capable of duplex operation (being able to send output from the computer to the sub while taking input from the meter to the computer, and keeping the two separate).
As for cal files, we have generic ones that work with RS meters available for download here
http://www.hometheatershack.com/forums/downloads-area/19-downloads-page.html
If you have specific cal data that will be more accurate for your particular meter, you can enter it into notepad and save as a *.cal file, the format is
FREQ1[tab]DEVIATION
FREQ2[tab]DEVIATION
 

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Discussion Starter · #5 ·
I'm using a pc and you are correct, its a firewire connection.
I will need to check with rme about duplex part?
 

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Or find someone who knows more than I... :bigsmile:
If you already have the device, hook it up, if it works with believable results, it's probably good to go.
 

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Is it possible to do a room check using this device [RME Fireface 800].
It looks like you may be able to, unless the Mac causes some issues. A line in and line out is required in order for REW to generate a calibration file for the sound card (or interface in your case). This is necessary in order compensate for any deviation from flat response that the interface might have. It looks like the RME has the connections capability to accomplish that. If not, you can probably skip the calibration – I expect a $1600 interface should have flat response. :)

The only possible issue I can see, I’m not sure if the REW program can “talk to” the RME interface via a firewire connection. If it has a USB output as well, you might try using that for the purposes of running this program.


How is the setup done for this as the diagram in the setup seems to be for a Hardware EQ setup.
It’s no different from what you have, really. Since we’re typically dealing with home theater systems, our diagrams show a signal being sent from the sound card to the A/V amplifier, or powered subwoofer. That’s really no different than your situation, sending the signal from the interface to powered monitors.


but i would also need an eq drvice to connect my sub and monitors to.
Only if you intend to equalize your sound system via external means.


How do you create a calibration file if you have a factory frequency response graph of the mic?
As noted, you must first have a frequency response graph of the mic to work with, typically supplied by the manufacturer. Open a Notepad file, and enter the deviations from response as they appear on the frequency response chart. The first figure on each line is the frequency, followed by a “space”, “tab” or “comma,” and then the deviation value. Using the graph below as an example, it would look something like this:

500 -1
1000 0
3000 +1
5500 +5
9000 +1
9800 0
10000 -1




REW will "fill in the blanks" between any two values, so if you have a long, straight line at some point in response, no need to enter a bunch of values between where it starts and stops. Naturally, the file would have to account for all the up-and-down ripples in the graph above 10 kHz, and I did not enter any values below 500 Hz, but hopefully you get the idea. As noted, save the file with a *.CAL extension.

Here’s what a file looks like from a mic that’s been professionally calibrated.

Hope this helps.

Regards,
Wayne
 

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Discussion Starter · #9 ·
I had an email back from RME and they said full duplex will work. I have some very expensive microphone sadly none have calibration files I will read that last message you posted how to create one in more detail to night and see if I can get my head around it.
Kind Regards
 

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You can go ahead and create a file from their chart. Just be aware, there are sometimes variations between different serial numbers of the mics, and it's not the same as having a chart custom created for your particular serial number.
On the mics more commonly used by our members, we have data from a bunch of mics that are all what we consider to be "close enough" for "home user-enthusiast" purposes. So at the moment, we really don't know just how accurate the chart you've found will be for your particular mic.
If it was me, I'd give it a try and see if the results are believable. If you don't mind being off by a few db here and there, it's probably "good enough," depending on your goals.
 

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Discussion Starter · #13 · (Edited)
I also have a set of akg stereo mics and I couldn't believe my eyes behind the foam was two frequency charts for the two mics. I now see what you mean by a slight difference. Each one is signed by hand by whoever tested them. They are akg C451
The frequency is hovering on the O line from 25 to 4K it has slight upwards movement at the 4k about +1 reaching +5 at 10k and dropping back to +3 at 20K.
Thats a rough guide as its impossible to be 100% accurate from the grid supplied.
http://www.akg.com/picture.php?txt=...nbank2/pspic/hires//95/c451b4055c348bb371.jpg
Mine is almost identical except my line is straight up to the 4k
 

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Understood. You need only be as accurate as your own purposes dictate.:bigsmile:
 
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