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In Reply to: RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics posted by Satie on March 02, 2017 at 11:42:08
I didn't try them further back because the woofers were in the way, but I did try another angle in an attempt to minimize sidewall reflections. It didn't work as well for reasons I don't know. I think the next step is to experiment nore systematically, beginning with MGbert's ray tracing diagram, but of course I'll have to figure out how to accommodate the woofer panels.
Extension of the board behind the MT panel -- I'm guessing the more the merrier because at lower frequencies you're going to get diffraction so the barrier will be effective only when it's large compared to the wavelength. I just had them extended sufficiently to completely block the reflection of the panels in the mirror, so a few inches beyond the actual driver.
Extension of the board in front of the panel -- if you look at the photo from the listening seat, you can see that they were extending in front for the RFZ experiment they didn't occlude the drivers at all. For that purpose, flush with the front would presumably be better because you wouldn't get diffraction at the proximate edge.
In the parallax barrier experiment, I had the boards positioned so that I could see the tweeter with the proximate eye but not the distal one. One of the reasons it may not have worked as well as MGBert's setup is that he was using MMG's, which have a lower XO to the tweeter -- my barriers were only effective from 3 kHz up. Interesting about the effect of the sidewalls. Mine are both irregular and reflective, not sure how to characterize them.
Why did you give up on your barrier? I still have some other options -- Fresnel reflector (which however is a major production), polycylindrical diffusors (but again, that's a major production since to preserve the window, I'd need to bend Plexiglas), and of course the QRD's. Or I could just move to somewhere with a bigger listening room. :-|
Follow Ups:
Hello,I am using Ambiophonics method for about 5 to 6 years. I just got to know about this forum and thread through Google alert.
I use Sound Lab ESL speakers. I first discovered Ambiophonics early 2000s and experimented with a mattress. I am currently using AmbiophonicsDSP with JRiver.
MGBert approach is rather unique. Reading MGBert's original post, I suspect he did not get the full effect of crosstalk cancellation with the barrier due to the speakers spread or angle.
It is very important that the speakers should be around 20 degrees for the Ambiophonics to be successful. Even at 30 degrees the effect would not be good enough.
In MGBert's method, what is the recommended speakers angle?
Thank you.
Edits: 03/04/17 03/05/17
I don't think he said but according to the dimension on the diagram, the adjacent should be roughly 68" and the opposite 35", so that would be about +/- 27 degrees or basically the standard Blumlein equilateral triangle.
I assume the reason you want them closer in an ambiophonic setup is the HRTF? This is a practical issue for me since I have a projector and can't put my speakers at the recommended angle.
Your system must sound pretty spectacular, what with the Sound Labs and ther controlled directivity! I tried some of the sample recordings on the ambiophonics site last night with the backwave barriers in place and was surprised that I got a lot of the effect since I was listening at +/- 30 degrees. Not a 180 degree spread, but definitely outside the speakers and the sense of three dimensionality that I've heard from ambiophonics in the past, with sounds vastly in the distance or right up to the speakers depending. It was rough -- occasional buzzing and a hole in the middle -- but it was impressive nonetheless, particularly since my earlier ambio experiments with Maggies have failed.
Sorry for the delay. I am still unsure how to navigate here.
If you are using a barrier than the ideal separation should be around 10 degrees. Like in the picture below. It must not be more than 30 degrees. Unfortunately this is not practical to most.
The ambiophonics prepossessed files in the website can be listened without the barrier. That's how it should be listened. If you add the barrier than the cancellation signals would not reach you other ears and that explains the lack of soundstage.
Try again without the barrier. Alternatively, you can use any stereo recording and use it with a barrier. It requires no preprocessing or DSP. If you are using the ambiophonics plugins than do not use the barrier.
My main speakers are about one foot apart. There are no barriers. I use AmbiophonicsDSP with JRiver. I also use additional speakers for convolution. Basically, total speakers in my system are 26 units. Except for the main speakers, the rest are low priced small/micro home theater speakers.
IMO, even with the standard 2 speakers they sound so much better than stereo.
Hi STC,
Sorry if I wasn't clear but I listened to the preprocessed files without the barrier -- I used the barrier to listen only to unprocessed files. The barrier worked brilliantly even though the speakers were at the standard 60 degree angle, but I couldn't get the preprocessed files to work very well even though I tried the panels at the recommended angles and tried listening at various distances. I did get a spread beyond the speakers when I was in the sweet range, but it was actually less of a spread than what I get with the speakers at 60 degrees and no crosstalk cancellation.
I have Tympani IVA's in split configuration so the woofer panels are separate, and timed differently. However, the crossover from woofer to mid-tweeter panels is 300 Hz third order and as I understand it in the RACE algorithm the bass below 400 Hz bypasses the crosstalk cancellation. The separate panels also didn't have a deleterious effect when I used the barrier.
Maybe I should try the panels even closer together? I thought I had them at about 20 degrees or less. As others have mentioned, though, the Maggies have side-by-side mids and tweeters whereas you're using the crossoverless Soundlabs and I'm thinking that the lateral displacement of the drivers may be interfering with the crosstalk cancellation since the acoustic centers are laterally displaced by about 5":
Also am I correct that the greatest effect of the XTC is at about 1 kHz? In which case maybe I should optimize the distance for the midrange units -- will try it again using that as a parameter. Meanwhile, I ordered a copy of AmbiophonicDSP to play with.
I'm impressed that you're doing convolution! I'd love to do that but I didn't see a way to make it practical. Don't the inexpensive home theater speakers reduce the quality of the sound? I assume you got the impulse responses from the source mentioned on the Ambiophonics site, but I'm curious about what you used for amplification and DA conversion and what you're using for the convolution -- will JRiver handle that many channels? Have you written this up somewhere? I'm intensely curious -- it's something I'd love to do.
> > Also am I correct that the greatest effect of the XTC is at about 1 kHz? In which case maybe I should optimize the distance for the midrange units -- will try it again using that as a parameter. Meanwhile, I ordered a copy of AmbiophonicDSP to play with.
I forgot to address this point earlier. The barriers will do the isolation from above 1000Hz. However, the separation gradually declines from 1000Hz to 400Hz. it was mentioned in the many AES papers that you will find on the website.
Just a word of caution here. Ideally, the main speakers should be line array type. So it is possible that you are right.
I hope you get your AmbiophonicsDSP working well. Please note that the values would change if the sampling rate of the source changes. Initially, it would be tter to experiment with big ensemble classical music and only then move to other genres. The "zentrum" should be set around 2 to 3dB. With convolution speakers, I set the "space" to zero. However, your mileage may vary and set them according to your taste for non convolution approach.
And lastly, here is the link which was made earlier with 8 convolution speakers.
It is difficult to evaluate the sample as my stereo and Ambio with 12 speakers were recorded with binaural microphone and meant to be heard with headphones. The original file is inserted between for you to compare all three versions.I could have done better with the stereo recordings but it wasn't easy to move the speakers. :)
"Just a word of caution here. Ideally, the main speakers should be line array type. So it is possible that you are right."
I think I may have made a mistake by using the central axis as a guideline. At 3 kHz, a wavelength is only about 4", so relative phase loses significance. There would still be an intensity difference that in theory needs crosstalk cancellation, but I don't think it can really be done effectively at that frequency since even a 2" head shift will change the effect from cancellation to reinforcement. So I plan to try again with the midrange as the baseline, and also with the software although I'm currently building a new HTPC so it will be a few days before I can try that.
Wow, huge difference in the sample! I'm just listening on cheap earbuds now, I'll head upstairs at some point tomorrow and find my Etymotics. But it's obvious even with the cheap earbuds. No wonder you're enthusiastic. How have you positioned the convolution speakers?
"How have you positioned the convolution speakers?"
It is recommended by Ralph that the rear half of the side wall to be given priority and followed by the rear and front half.The recommendation was based on numerous research.
Since I am limited to only one IR, I placed mine at 90 to 130 degrees, covering the rear half. I use St.Cecilia concert hall's IR for 45 degrees. With my current speakers arrangement this yields a better integration over the 60 degrees IR. Over this weekend, I will be trying 90 degrees IR and see if it improves further.
While the proper way is to use all 25 IR of St.Cecilia or any other IR by placing the speakers at the actual measured location, I opted to recreate my own "wall" due to space and lack of technical knowledge for pro sound implementation.
It is addictive as playing around with the convolution creates the very best listening experience. The method works for stereo setup too.
Thanks, I was reading up on inexpensive speakers. It looks like there are some decent ones though hard to know what would work. But man, once you add all those DAC racks and amplification it wouldn't be cheap! Also, I'm not sure how I'd feed the DAW with my usual source, JRiver -- haven't looked into it but I wonder whether you'd need to run two machines.
OTOH, no reason I can't do what you did and try a simpler setup. I have some Monsoon computer speakers and I could use the motherboard audio to experiment, with the impulse response in JRiver . . .
Josh,You need not spend a fortune on the small speakers. Mine are a mix of Yamaha, Panasonics and Sony. Speakers the size of a CD (see picture). The role of the convolution speakers is to act as sound bouncing off the wall and therefore the quality, in a small room, doesnt matter. Moreover, the I use JRiver's PEQ to cut all frequencies below 200Hz and above 4500Hz.
Basically, you only need one amplifier. I was driving 4 speakers with one amplifier. Now, I am driving all 22 speakers with just 3 amplifiers. You can drive all speakers with one 100Watt Amp or better still get a Behringer or Crown to drive all the speakers as the output volume is very low.
I am using the http://www.gearbest.com/speakers/pp_39924.html amp to drive the other 8 speakers. You would probably need less than 10 Watt for all the speakers. You can see the diagram in my profile page. My total budget for all the speakers and amplifiers is below US$200 as the HT speakers were bought used.
ST
Edits: 03/07/17
Wow, at that price, you can't afford not too!
I'm definitely going to try this once I get my new HTPC up -- I have the box built, but the monitor I was planning to get is backordered so right now I'm scrambling for a substitute.
You raised an interesting point. Will forward your query to Ambiophonics founder, Mr. Glasgal. You can also email him at glasgal at ambiophonics.org.
Meanwhile, about the my convolution setup, it was a simpler version with one IR only. I would do another two or three IR in the future but frankly, this is already very good considering my room size. You just need to be creative. I also think the convolution would work with stereo setup as well.
The small HT speakers output are low and ithey don't affect the SQ. I have the actual recording of 2L Magnificat where you can compare the original and Ambio with 12 speakers. I used Roland CS10EM binaural microphone. Unfortunately, I couldn't insert the SoundCloud link with my phone. The sample is also available in my profile page.
I will try to put in the link tomorrow. It is way past bed time ....:)
ST
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