Maximum Optimization: Using REW and Minidsp's 2x4 HD

In a past article I shared my experience and life with a MiniDSP DDRC-88A with bass management. One of the things that kinda irritated me while using Dirac Live was what seemingly was a push towards REW not only from fellow Dirac Live users but in many instructionals. REW was so intimidating to me and the vast learning curve and mountain of information had me frustrated. I had no desire or time to learn REW back then but here I am now half a year or so later. On this day I have no idea as to why anyone might purchase Dirac Live for a 2.2 channel system if desiring to learn or already familiar with REW. If you're not familiar about REW the software may be downloaded here: Room EQ Wizard

Once I learned that house curves could be loaded into REW I decided there's no sense at all for me to use Dirac Live in a 2.2 channel system. I mean if learning REW then why Dirac Live? After all, doesn't one want to verify actual results rather than only accept Dirac Live's "projected" correction?

I was fortunate enough to find a used MiniDSP 2x4 HD for only 80 bucks. I made the mistake of deciding to upgrade the 2x4 HD to the DDRC Dirac Live model. After upgrading I decided why bother w/ Dirac Live at all if using REW? Save some money and learn from my mistake tisk tisk. So I downgraded the firmware back to the 2x4HD firmware. 

Please, if anyone has advice or wishes to chime in by all means feel free in the comment section!

Here're the instructional videos which I am following as these instructional videos are well worth the time to view. 

First video provides instruction on how to align multiple subwoofers into one virtual subwoofer. I can't emphasize enough how final alignment is important. In the REW video one can see individual subwoofer frequency output and how adding a second or more subwoofers w/out alignment can actually be worse than one subwoofer! 


Once "the" subwoofer is created by multiple subwoofers this next video provides instructions on how to use REW's time alignment tool to integrate "the" subwoofer into the mains:


I'm also including a parts list for everything I needed. All parts were purchased through Amazon. To note you may notice that the pricing on Amazon for the MiniDSP or UMIK-1 is more than the retail price direct from MiniDSP, but that's because custom charges are included in the Amazon price. 


 Parts List:

  1. MiniDSP 2x4 HD
  2. 2x: USB 32 ft Extension Cable with Repeater [Reason for such length is because I'll be using my home PC located in another room. This position is more appealing to me because I don't need a laptop or worry about affecting the measurement results if in the actual listening room. Two extension cables are needed 1 from Minidsp to PC and other Microphone to PC]
  3. Umik-1 Calibrated Microphone
  4. Microphone Stand
  5. 2x Unbalanced RCA cables - 1 meter [From DAC to MiniDSP]
  6. 2x Unbalanced RCA cables - 2 meters [From Minidsp to Main Amp]
  7. 2x Unbalanced RCA cables - 5 meters [From Minidsp to Active sub amps]

Harman Research house curves free for download. Note: the files will need be opened w/ a text editor and then converted/saved to a .txt file for REW. 

I'll be making connections to the outputs my Minidsp as follows:
Out 1: Left Main - Amplifier
Out 2: Right Main - Amplifier
Out 3: Left Subwoofer - Active Subs
Out 4: Right Subwoofer - Active Subs

 Bluesound Node 2i and SMSL M400 DAC send signals to the Minidsp. Note: I use a coaxial cable from the Bluesound Node 2i to the SMSL M400 DAC:


Two unbalanced RCA seen on Left to feed stereo L and R signals into the Minidsp. 4 Outputs on right side fed to amplifiers:


Parasound Halo A31 and AcInfinity cooler


Summation of audio chain before speakers:


Input from PC to Minidsp:

Connect the USB (Type B mini) port of the miniDSP 2x4 HD to a free USB 2.0 port on your computer using the supplied cable. The USB is used for:
  • Configuration and real-time control of the miniDSP 2x4 HD
  • Streaming audio from a computer or other device such as a music streamer, at up to 192 kHz
  • Streaming the processed audio (four output channels) from the miniDSP 2x4 HD to the computer.
Minidsp's computer or PC software isn't called an app but rather a "plugin". After making all connections to your Minidsp be sure to start the plugin and connect to the Minidsp. In the inputs you'll see a drop down menu. I'm going to generate a signal from my PC to the Minidsp through the USB. 

In the Minidsp plugin we can see the Routing information. The 2x4's input 1 and 2 as well as 4 outputs. As seen below we are going to take the stereo inputs 1 and create a mono signal to both outputs 3 and 4 which are subwoofers. We are also going to do the same for input 2 and sum both inputs to the subwoofers. This setup creates a mono signal from stereo inputs to both subwoofers which may be tuned individually thereby creating one aligned virtual subwoofer. Once this is done we call the time aligned multiple subwoofers "the" subwoofer as multiple subwoofers will be treated as one subwoofer.   


Positioning the microphone in MLP w/ blanket draped over the back of the couch to cut down on reflections around the mic:



I began in REW by generating test tones starting at 10hz to 300hz for subs and to 20,000hz for mains. Then applied the psychoacoustic smoothing to the following graphs. 

Here's both Tekton 4-10 subwoofers:


And here's the summation total of 2.2 channels after filters:


After only my first few hours ever working with REW I'm not sure if I'm doing this "optimally" but I measured each speaker [mains and subs] individually and applied created biquad filters to each channel's outputs. Then, I began measuring summed response and created a summed biquad filter and imported it into the 2x4 HD's inputs. 

Anyhoot, this is the final result of doing so mind you to reduce the low frequency spl/gain to this point I have the subwoofers gained down -10db! In the next days I'll try a lesser level low frequency curve by Harman Research. 

Update:




REW's alignment tool is very nice and easy to use to integrate subs into the mains. The second video in the OP makes the process easy. Just sweep the subs playing.  Then sweep both mains playing. In the config option choose alignment tool and place cursor at your subwoofer crossover point. Hit align slopes and phase and wallaa -  a delay will be kicked.

The delay is a minus number for the mains but ya can put that number for the subwoofer delay settings in the Minidsp as positive.

Here's a recap of the steps. Sweep both mains and then both subs:


In Controls select alignment tool. Move cursor to crossover point in graph and then select align phase and slopes to cursor. In my case my mains and subs were out of alignment by 3.42 milliseconds or 3 feet 10 inches @120hz:


A little explanation about the graph above. In the bottom portion the green as well as red lines are out of alignment. Delaying the red or subwoofer would result in time alignment of the subwoofer to mains. 

Input the delays in the Minidsp:



Stay tuned for my results as this article will be continued throughout the next week! 

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