Nest Theater Part Thirteen - Damping The BLHs & New Room Equalization 06Aug20

In ongoing efforts to tame the shout from the DRC BLHs and smooth the frequency response of the system overall, I added 1" dampening foam in the cavity behind the drivers. It helped a little but driven raw (without EQ) they still shout a bit. The number of Infinite Impulse Response (IIR) filters needed to equalize the system were sharply reduced to just 5 from 15... so that's something, but my search continued.

REW's analyses to measure the system and derive IIR filters, and JRiver MC's capability to EQ the material using these filters directly in the PC are great... they are also insufficient for me for a couple reasons. First, I also listen to YouTube & Vimeo playing from a Roku, as well as other apps, and that material is not EQed at all as the optical (derived in the TV from HDMI from the Roku) PCM stream has been dropped directly into the DAC for audio reproduction. This audio chain frustratingly does not  sound as good on the system. I did try to run YouTube under JRiver MC (in order to get the EQ applied) but there is a browser incompatibility which I imagine will persist. Second, strict frequency magnitude filtering (IIR filters) employs feedback and does not really account for impulse response issues, but is cheaper to implement than Finite Impulse Response (FIR) filters. So... I have added more hardware, strictly in the digital domain, to measure the system, design appropriate FIR filters and apply that equalization to both the PC output on USB and the Roku output on optical. The scheme I chose for FIR filtering is a well known and respected one from Sweden called Dirac Live and I chose to have it implemented simply for my 2.1 channel system via a miniDSP product called DDRC-22D ($650). I also needed to get the USB out from the PC converted to optical/TosLink or COAX S/PDIF for input to the DDRC and chose to use a Topping D10s for that ($90). I now should have much greater control over equalization of my room & system and solved the issues I've had with the prior EQ scheme... WooHoo. Plus, it will sound great - though of course the 128Kbps AAC stream from YouTube ($16/mo premium gets one better fidelity, but still not HD) still can not compare to the 24bit/96KHz PCM or 64fs/128fs DSD coming from JRiver Media Center on the PC. These are complex issues and making digitally reproduced material sound organic in any room is challenging -  but I am really excited for the new "room correction" scheme coupled with the already great tri-amped speaker scheme and musical Denafrips DAC.

Update #1 - Topping 10S... I'm using the 10S just as a media changer but this little gem works great and is a steal for $90 IMO. It works as advertised and accepts high rate PCM and DSD no problem. It does down sample the DSD to 64 on output and (if input is higher) will downsample PCM to 24bit/198KHz on output - not a problem for me really. It's cool having a display of the current file's sample rate easily visible.

Update #2 - miniDSP DDRC 22D & Dirac Live... OMG! DHL finally got the miniDSP hardware to me from Hong Kong and I downloaded needed support code from Dirac in Sweden to analyze and create filters. Dirac has an interesting IP scheme - measurement and correction are local to my PC and the DDRC hardware but analysis to filter creation is in the cloud and very protected. After 9 measurements around my head (who else counts?) the room correction is completely amazing and worth my time in research, purchase and config. The DDRC 22D solved both needs mentioned: YouTube is EQed brilliantly now and of course so are FLAC, DSD and MP3 files from my PC AND the FIR EQ is brilliant and finer. The shout and all other aberrations are gone and while I would have liked to rid them acoustically, I am still thrilled with a super-system able to proximate my room curve vibrantly on all inputs. I'm done; I can't make the audio better; I've not heard better 'cept my COS reference headphones, but this is more fun and LOT louder at 6 watts. I measured the Dirac corrected response with REW raw in the image below (@ 1/6 curve smoothing). Perfection is not as elusive as a nearby hummingbird.

Allow me say unequivocally that the Chinese have arrived, neh - should now dominate digital audio reproduction, at least at the consumer level. This week's tweaks to NestT were professional adjustments packaged in consumer gear heretofore unaffordable to commoners - props to the Chinese, way ahead of NAmerica here - miniDSP and Denafrips rock. Too, I measure my source material now for dynamic range... unfortunately many modern tracks are "loud," as opposed to Dire Straits and others, but yea - be aware.

I'm sure audiophile purists will pooh-pooh my use of digital sources (vs an analog phono turntable) and especially my manipulation of source material with digital signal processing to compensate for aspects of my speakers and room, but the Nest Theater audio is now exactly where I need it to be and sounds GR8. There's no adulteration from the amp or speakers themselves and it's minimal actually from the DAC and the FIR filters applied for EQ

Update #3 - I rebalanced the sub with the full range BLHs in order to assure an optimal "crossover" from 20Hz-200Hz.  Of course I did this with all DSP and EQ stuff off. The process is one of setting overall volume of random pink sub (30-200Hz) noise at listening position to ~80dB and then taking n (I did 5) SPL measurements below desired crossover (20, 35, 50, 65 & 80Hz for me), which is 90Hz on my system, and n measurements above desired crossover to 200Hz (for me 100, 120, 140, 160 & 180). I'm able to make these measurements with a mic and a tone generator on my PC but a CD with such tones and a C-weighted SPL sound meter is fine. The balancing objective is to use sub's separate volume control (without altering main volume) to get the average of "below" to be equal to the average of "above" SPL measurements. Successively measure and fine tune sub volume till equal. Then it's all good. First, assure phase is correct of course and you have a good location for the sub. After I completed the rebalancing, I remeasured using Dirac Live to set up optimal filtering of the "new" balanced full range setup 16Hz to 21KHz. Awesome.