Post by ansat on Jan 1, 2015 18:04:47 GMT -5
Do I need a minidsp for multiple subs and how to use one for such
how to use the USB input to measure other speakers
Interpreting your dirac results
Dirac / XMC-1 F.A.Q.
I have been meaning to write up some very basic tools that can be used with REW and had a few parts that got in the way. A measurement microphone and a common audio interface with the pre/pro. Now that the Xmc is out and contains a calibrated microphone. This solves one of the major issues with coming up with something easy to set up. In my other Beginners REW tutorial for determining if you need outboard EQ for multiple subwoofers. The method of using the USB input can be used in many different ways to get started with REW. So a lot of the steps will seem similar to my other beginners tutorials (cause I copied and pasted them )
This write up is to assist with subwoofer placement in your room. While there are many interpretations and some will focus on different tools in REW. This will be a pretty basic get the most output and avoiding locations with high amounts of cancelation. I will not be addressing decay, which is another important factor in placement, but does not fit the level of a beginners REW course.
You will need:
1. a measurement microphone (the emotiva emm-1 will work great)
2. REW link
3. a long usb connection to the XMC
Step 1 - plug sub(s) the XMC left subwoofer out.
Step 2 - Configure the XMC as the following (you will need to have speaker preset 2 clear of any PEQ or distances) In preset 2, configure your mains as small speakers and set the xover to 200hz (do not set this any lower) and configure the sub(s) to mono.
Step 3 - Plug in the usb connection to the back of the xmc and to your computer (drivers should start installing)
Step 4 - Plug in the XMC microphone to the computer
Step 5 - Open REW and click on preferences. Your "Output Device and Output" will be Speakers (#-usb2.0..) set the default output to SPEAKER. set the "Input Device and Input" to microphone (#-C-Media). Check the "Control output mixer/volume" and set the "output volume" to 1.0
Step 6 - either turn off or disconnect your main speakers at the amplifier. (your subs need to remain powered on)
Step 7 - change the input on the xmc to USB stream and set the speaker set to Preset 2 and surround mode to Direct.
Ok, So what I had you do was set a crazy high crossover point for your subwoofers as the usb will only support 2 channels. By turning off the main speakers when we use rew, only the subs will play as REW is going to try and take a measurement of your left speaker and the XMC bass management will send all frequencies below 200 to the subwoofer. I did this as this is the only way that will be universal for 99% of the XMC users out there.
It is also important that you find a good location to place your computer and yourself. We are measuring direct and reflective energy, and while we do not need to have accurate SPL or adequately remove background noises, a walking bass trap (such as yourself) can create or hide problems in the measurements. I usually sit right behind my main listening position on a stool or step. Avoid the corners of the room and all first reflection points.
1. If you have multiple subwoofers - Unplug all but one sub
2. On the xmc - set the volume to 40 (you can go higher or lower - just use caution)
3. On REW - click on the Generator and the RTA
4. Configure the Generator to use Pink Noise and select Sub Cal (you can use the custom if you are sure that your subs can handle it.) Now click on the green play button.
5. Configure the RTA - Click the red start on the upper right then click the control icon (looks like a gear) Set the Mode to RTA 1/6 octave. (0r you can go lower if you want to see finer detail), set the averaging to 16, and update interval to 1.
6. From here you can place your sub in different locations and see their effects on your listening position. (Or you can place your sub in the main listening position and move the microphone to potential sub locations (but this has never worked out well for me and damaged one of my seats)) your aiming for max SPL and as few dips as possible in the frequency response - One large hump is normal for some subwoofers. Once you have identified your ideal location, its time to take a measurement.
7. On REW - Close the RTA and stop the signal generator - Click Measure (if you get a calibration warning - ignore it)
8. On the popup screen set the start Freq to 20hz (or lower if your subs can handle it) the end frequency to 20000 and the length to 256k
9. Click start measuring (if you get a calibration warning - ignore it)
10. Once finished, on the middle top of the screen click the all spl button. On the right side click controls and where it says No Smoothing, select 1/6 and click apply to selected.
If everything still looks good, you can optionally measure your other listening positions to make sure that they are acceptable and make fine adjustments to your subwoofers location. (repeating the measurement after each placement change) This is also the time to use any built in DSP in the subwoofer to make fine adjustments to the response.
If you have multiple subs, this gets a little trickier . if you have external dsp, such as a minidsp - click here If you have another type of manual outboard DSP that link will still work for your setup but you will need to configure your equipment with its interface.
If you have a phase knob on your subwoofer (not the 0,180 switch - a variable knob), then unplug the subwoofer that you just found the optimal position for and repeat the process with each additional sub. After the ideal locations are found, you will phase align the subwoofers. To do so, use the RTA and the signal generator with both subs playing and adjust the phase (there is a 16 second time delay as we set the RTA to average 16 samples) You will see some wild swings with the phase. Your trying to get the highest SPL with the sum of the subs. Once satisfied, use the measurement tool and make smaller adjustments to get the best response. (Perfect would be +6db higher then just one sub. You will normally not get perfect over the whole frequency) If you have more then 2 subs add one sub at a time to the sum.
No phase control, no outboard EQ.
This one is a little more straight forward, but placement limitations will be the issues. So repeat the same steps that you did with first sub, but this time you will leave the first sub connected.
Make sure you label all measurements and save them.
Let me know if I missed something critical. I have used REW daily for a month solid and I could have missed something important. Also, as always, questions are always welcome.