For quite a while I have wanted to try a weird experiment - what happens if I use an extra pair of speakers, digitally delay them, then point it at the wall to create "ambience"? The idea is similar to digital reverb ("concert hall effect" on AVR's) - but those don't work because the reverb is coming out from the same speakers which is producing the direct sound. Linkwitz said that we need "enveloping" sound, so the idea was to take the extra speakers and place them behind me in both corners of the room, pointing away from the listening position. But I did not have enough DAC channels to do it. That's when I found out that the answer has been under my nose all along - VB-Audio Matrix!
I downloaded it earlier today and got it to work.
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First step: grab my computer speakers (AudioEngine A2) and linearize them.
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Before linearization (red) and after linearization (green). Even before linearization it measured quite OK. There is not much <120Hz, but that's no problem - I don't need them to make bass. Look at that textbook step response!
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Because the AudioEngines are on a different interface, I suspected that the latency would be off, so I checked with Acourate. I came up with a method to sweep both the tweeter on my main system and the little AudioEngine at the same time. It involved:
- Create a 2 way XO for the Audioengine. I used a 50Hz corner frequency. Then I deleted XO1 and renamed XO2 to XO1.
- Copy a previously generated XO for my mains tweeter and renamed it XO2. So now I have XO1 = Audioengine high passed at 50Hz, and XO2 = tweeter reference from main speakers.
- Generate a Multiway WAV and logsweep both. Result as above.
I can see that the AudioEngine is 9010 samples (187.5ms) delayed with respect to the tweeters. I then time aligned both speakers.
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Then I assigned all my DAC's to ASIO channels and enabled the virtual ASIO I/O channel.
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Next step is to route all the channels appropriately. Look at that, I have 3 DAC's in the same ASIO channel! VB Matrix allows me to delay the AudioEngine, so I dialled in a 20ms delay.
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Then I set up Acourate Convolver to send channels 1-8 to the main speakers, and channels 9-10 to the "ambience" speakers.
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Then I had fun placing the "ambience" speakers in various positions in the room. My main speakers have a little gap at the back, perfect to hide a pair of small computer speakers, effectively converting it into an "almost" dipole. I am limited by cable length as to where I can place the speakers - the furthest I can place them apart is on either front corner of the room. Can't place them where I want just yet.
The effect is pretty remarkable - the 20ms delay was chosen because it lays outside the Haas fusion zone and early enough to be perceived as "ambience" but not so late that it is perceived as an "echo". It really
does add spaciousness, and the effect is far more convincing than "concert hall" reverb.